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Inertia and damping influence the values of the stress intensity factors (SIFs) at high-frequency loading and they must be included in computations. In the present study, different dynamic simulation procedures were carried out for two types of specimen geometries and the achieved SIF values were compared. Fast computation procedures such as harmonic modal analysis and direct steady-state analysis were compared to the computationally expensive transient dynamic analysis. Two different methods for calculating the SIF, the J-integral and the crack tip opening displacement (CTOD) methods, were applied and compared and the results showed a near perfect agreement in calculation of the mode I SIF. The Rayleigh damping model was introduced into the dynamic computation to investigate its effect and the results revealed a clear effect on the SIF at 20 kHz frequency. The fast direct steady-state analysis showed good agreement to both harmonic modal and transient analysis with the different damping values used and is, after this study, the recommended procedure., Downloads before file update (240708): 211

This is the first volume of the concurring series of Reports in Applied Mechanics, which is based on the outcome of the advanced project course TMPM07 in Applied Mechanics at Link¨oping University during the autumn of 2022. The course lay-up is based on several industrial related projects within the field of Solid Mechanics, concerning fatigue, topology optimisation, structural dimensioning, contacts etc, and Fluid Mechanics, concerning fluid dynamics, flow, aerodynamics, heat transfer etc. The students tackle industry relevant projects in close collaboration with industry from near and neighbouring regions and work in project groups to solve the given tasks within the time limit of the course. Close collaboration with the industry is necessary to define planning, update and feedback for further evaluation at the industry. Three projects were performed during the course of 2022, two within Solid Mechanics and one in Fluid Mechanics. The projects were all performed in tight collaboration with industry partners, and had a close application to real industrial problems. A good opportunity for the students to show-off all their gained knowledge and apply in the best possible way to make innovative solutions in the respective projects. Something they all managed to do with success!, Collection of student reports.

A traumatic brain injury is usually caused by a direct impact to the head and is a common cause of disability and death all around the world. The most effective method to predict brain injury today, is to use a finite element head model. In this investigation, the three injury predictors strain, strain rate, and the product of strain and strain rate were investigated using a rat brain finite element model. The main goal was to find which injury predictor most effectively would predict injury. To find the injury predictor with the highest area under curve value, comparisons between experimental results obtained from simulations and results from previously performed experiments on rats were made. To better understand how different factors can affect the severity of symptoms from a traumatic brain injury, a parametric study with a focus on rotational direction and rotational duration was conducted. Simulations were run on a rat brain finite element model for three rotational directions and three rotational durations. The statistical analysis was completed for six experiments and nine brain regions. The three injury predictors were extracted from 26 simulations completed on a rat brain finite element model, and the maximum values of the 95th percentile for each brain region were extracted. The results showed that the product of the strain and the strain rate was the most effective injury predictor for four out of six experiments (unconscious time, EPM arm change, EPM open duration, and MWM session 3). The parametric study investigated rotation in the axial, coronal, and sagittal plane against the three rotational durations 1.5 ms, 3 ms, and 6 ms. The parametric study revealed that both the direction and duration of rotation importantly influence the extent of damage in traumatic brain injuries. The results showed that rotation in the axial plane and a 3 ms duration caused the most brain damage. It was also concluded that the results need to undergo additional verificat, En traumatisk hjärnskada orsakas vanligtvis av våld mot huvudet och är en vanlig orsak till både funktionsnedsättningar och dödsfall världen över. Den effektivastemetoden för att kunna förutsäga en hjärnskada idag är att använda en finit elementmetodmodell av en hjärna. I denna undersökning har de tre skadeprediktorerna belastning, belastningshastighet och produkten av belastningen och belastningshastigheten undersöktes med hjälp av simuleringar genomförda på en modell av en råtthjärna, byggd med hjälp av finita elementmetoden. Målet var att ta reda på vilken skadeprediktor som mest effektivt kunde förutsäga hjärnskada. För att hitta skadeprediktorn med högst area under curve-värde gjordes jämförelser mellan experimentella resultat från simuleringar mot resultat från tidigare utförda experiment på råttor. För att få en djupare förståelse för vilka parametrar som kan påverka graden av symptom från en traumatisk hjärnskada genomfördes en parametrisk studie med fokus på rotationsriktning och rotationstid. Nya simuleringar genomfördes på en finit elementmodell av en råtthjärna i tre rotationsriktningar och under tre rotationstider. Den statistiska analysen utfördes på sex experiment och för nio regioner i hjärnan. Belastningen, belastningshastigheten samt produkten av belastningen och belastningshastigheten extraherades från 26 simulerade finita element råtthjärnor och maximumvärdet från den 95.e percentilen sparades. Resultatet av den statistiska analysen visade att produkten av belastningen och belastningshastigheten var den skadeprediktorn med bäst skadeförutsägelse för fyra av sex experiment(medvetslös tid, EPM arm förflyttning, EPM varaktighet i öppet utrymme och MWM session 3). Under den parametriska studien undersöktes axial, koronal och sagittal rotationsriktning mot de tre rotationstiderna 1.5 ms, 3 ms och 6 ms. Resultatet av den parametriska studien visade att både rotationsriktning och rotationstid spelar viktiga roller när det kommer till omfattningen av s

We investigate how well a physics-based simulator can replicate a real wheel loader performing bucket filling in a pile of soil. The comparison is made using field-test time series of the vehicle motion and actuation forces, loaded mass, and total work. The vehicle was modeled as a rigid multibody system with frictional contacts, driveline, and linear actuators. For the soil, we tested discrete-element models of different resolutions, with and without multiscale acceleration. The spatiotemporal resolution ranged between 50–400 mm and 2–500 ms, and the computational speed was between 1/10,000 to 5 times faster than real time. The simulation-to-reality gap was found to be around 10% and exhibited a weak dependence on the level of fidelity, e.g., compatible with real-time simulation. Furthermore, the sensitivity of an optimized force-feedback controller under transfer between different simulation domains was investigated. The domain bias was observed to cause a performance reduction of 5% despite the domain gap being about 15%.

This paper investigates different actuator sector model implementation alternatives and how they compare to actuator line results. The velocity sampling method, tip/smearing correction, and time step are considered. A good agreement is seen between the line and sector model in the rotor plane and the wake flow. Using the sector model, it was possible to reduce the computational time by 75 % compared to the actuator line model as it is possible to run the simulations with a larger time step without compromising the accuracy considerably. The results suggest that the proposed velocity sampling method produces the closest results to the line model with different tip speed ratios. Moreover, the vortex-based smearing correction applied to the sector model results in the lowest error values, among the considered methods, to correct the radial load distributions. Also, it is seen that reducing the time step compared to the one used for the actuator disc/sector does not provide an advantage considering the increased computational time.

Bolted joints are a common fastening technique in the automotive industry. Through their connecting of different parts of a vehicle, their behavior can affect the deformation of the structure in the event of a crash. The aim of this thesis is to identify methods to evaluate the bolt models used for crash simulations at Scania against physical tests and suggest improvements for future use of the models. A pendulum impact test was used to determine the amount of energy needed to break a bolted joint in shear load. The difference between placing the shear plane in the shank or threaded region of the bolt was examined. A finite element model of the test setup was created in LS-Dyna to simulate the test. The test rig model was validated against test data before introducing the bolt models. The bolt models differed in element formulation and material model. The different bolt models were compared, and the model most used by the crash simulation team was chosen to investigate its failure and damage models. The results showed that there is a difference in behavior between fracture in the shank or threaded region, not only due to the difference in load bearing area. This is recommended to take into account when choosing an appropriate model for future simulations., Skruvförband är en vanlig fästteknik inom fordonsindustrin. Eftersom de kopplar samman olika delar av ett fordon kan deras beteende påverka deformationen av strukturen vid en kollision. Syftet med detta examensarbete är att identifiera metoder för att utvärdera skruvmodeller som används för krocksimuleringar på Scania genom att jämföra med fysiska tester, samt föreslå förbättringar för framtida användning av modellerna. Ett slagprov med pendel användes för att bestämma mängden energi som behövs för att bryta ett skruvförband i skjuvbelastning. Skillnaden mellan att placera skjuvplanet i skaftet eller den gängade delen av skruven undersöktes. En modell av testuppställningen ställdes upp och löstes med finita elementmetoden i LS-Dyna för att simulera testet. Modellen för testriggen validerades mot testdata innan skruvmodellerna introducerades. Skruvmodellerna skilde sig åt i elementformulering och materialmodell. De olika skruvmodellerna jämfördes, och den modell som används mest av krocksimuleringsgruppen valdes ut för att undersöka dess brottkriterier och skademodell närmare. Resultaten visade att det finns skillnader i beteende mellan brott i skaftet eller den gängade delen, inte bara på grund av skillnaden i lastbärande area. Detta rekommenderas att beakta vid val av lämplig modell för framtida simuleringar.

The reliability of screw joints found in tissue machines are crucial for ensuring smooth production. Screw joints are a fundamental machine element used in the tissue machines to join different parts, creating a solid joint. The screw joints play a vital role in maintaining the structural integrity of the machinery, and is important in maintenance operations. However, the reliability of the screw joints can be compromised, by factors such as improper clamping loads and tightening techniques. Such issues, could potentially lead to joint failure, which in turn can result in expensive repairs and production downtime. Because of this, understanding the fundamentals of screw joint behaviour is of high importance when dimensioning the joints. In this thesis, the objectives are to study the behaviour of the screw joints with spacer block design, optimize their design and determine a recommended tightening torque. The study aims to provide an analysis of the screw joints mechanical properties, by using finite element modeling and experimental testing. To address these problems, a combination of experimental testing and simulation methods was used. \ac{FEA} was used to model the various parts in the screw joint under different loading conditions and with varying designs to evaluate their performance. Additionally, the research include methods used to experimentally determine the coefficients of friction acting within the screw joint and their respective performance. The results of this thesis demonstrate improvements in the design of the screw joint with spacer block design found in tissue machines, together with findings, which reveal unexpected limitations in the screw tightening torque. The results prove, that appropriate material selection, a precise tightening process and optimized flange geometry can enhance the performance of the screw joint. These insights contribute to valuable guidelines for future designs of the screw joint with spacer block configuration., Tillförlitligheten hos skruvförband som finns i mjukpappersmaskiner är avgörande för att säkerställa smidig produktion. Skruvförband är ett grundläggande maskinelement som används i pappersmaskinerna för att sammanfoga olika delar. Skruvförbanden spelar en viktig roll för att upprätthålla maskinens strukturella integritet, men möjliggör också underhåll. Tillförlitligheten hos skruvförbanden kan dock äventyras, av faktorer som felaktiga klämbelastningar och åtdragningstekniker. Sådana problem kan potentiellt leda till fogfel, vilket i sin tur kan resultera i dyra reparationer och produktionsstopp. På grund av detta är den grundläggande förståelsen för skruvförbandsbeteende av stor vikt vid dimensionering av fogarna. I detta examensarbete är målen att studera beteendet hos skruvförbanden med distansblocksdesign, optimera deras design och bestämma ett rekommenderat åtdragningsmoment. Studien syftar till att ge en analys av skruvförbandens mekaniska egenskaper genom att använda finita elementmodellering och experimentell testning. För att lösa dessa problem användes en kombination av experimentell testning och simuleringsmetoder. FEA användes för att modellera de olika delarna i skruvförbandet under olika belastningsförhållanden och med varierande design för att utvärdera deras prestanda. Dessutom omfattar forskningen metoder som används för att experimentellt bestämma friktionskoefficienterna som verkar inom skruvförbandet och deras respektive prestanda. Resultaten av denna avhandling visar förbättringar i designen av skruvförbandet med distansblocksdesign som finns i mjukpappersmaskiner, tillsammans med fynd som avslöjar oväntade begränsningar i skruvdragningsmomentet. Resultaten visar att lämpligt materialval, en exakt åtdragningsprocess och optimerad flänsgeometri kan förbättra skruvförbandets prestanda. Dessa insikter bidrar till värdefulla riktlinjer för framtida konstruktioner av skruvförbandet med distansblockskonfiguration.

Vimek AB tillverkar skogsmaskiner i kompaktklassen som används för beståndsgående gallring, där högkvalitativt arbete med minimal miljöpåverkan står högt i fokus. Syftet med detta arbete var att kartlägga och analysera den teknikinformation som för närvarande produceras på Vimek samt hur denna information distribueras. Teknikinformationen som Vimek producerar innefattar bland annat maskinpärmar, prislistor och reservdelar och distribueras genom bland annat E-mail, vimeks hemsida och telefon. Arbetet inkluderar även en kartläggning av marknadens förväntningar genom intervjuer med några av Vimeks distributörer och medarbetare, i syfte att identifiera potentiella brister och möjliga lösningar. Genom att analysera den insamlade datan presenteras eventuella förbättringsförslag, och en bedömning gjordes för att prioritera vilka delar som bör åtgärdas först. Arbetet avgränsas till att endast föreslå förbättringar utan att genomföra dem. Under projektets gång har det identifierats huvudsakliga problemområden såsom dokumenthanteringen och prislistorna, där förbättringar i mappstrukturen och tillgång via SharePoint föreslås. Implementeringen av dessa förbättringar skulle eliminera behovet av en separat reservdelswebb och underlätta för kunder, återförsäljare och medarbetare att snabbt hitta relevant information. Vidare föreslås en återförsäljarportal för att förenkla åtkomsten till aktuella prislistor och beställningsprocesser. Dessa åtgärder kommer att förbättra effektiviteten, minska arbetsbelastningen för medarbetare och höja kvaliteten på Vimeks teknikinformation, vilket i sin tur stödjer företagets tillväxtmål och marknadsexpansion., Vimek AB manufactures compact-class forestry machines used for forest-weeding, where high-quality work with minimal environmental impact is a primary focus. The purpose of this study was to map and analyze the technical information currently produced at Vimek and how this information is distributed. The technical information produced by Vimek includes, among other things, machine binders, price lists, and spare parts, and is distributed via, among other methods, email, Vimek's website, and telephone. The work also includes mapping market expectations through interviews with some of Vimek's distributors and employees to identify potential inadequacies and possible solutions. By analyzing the collected data, potential improvement suggestions are presented, and an assessment is made to prioritize which areas should be addressed first. The scope of the work is limited to proposing improvements without implementing them. The main problem areas identified during the project include document management and price lists, where improvements in the folder structure and access via SharePoint are proposed. Implementing these improvements would eliminate the need for a separate spare parts website and facilitate quicker access to relevant information for customers, distributors, and employees. Additionally, a dealer portal is proposed to simplify access to current price lists and the ordering process. These measures will enhance efficiency, reduce the workload for employees, and improve the quality of Vimek's technical information, thereby supporting the company's growth objectives and market expansion.

This report, conducted at the School of Engineering in Jönköping within mechanical engineering: product development and design, focuses on the development of an exoskeleton for hedge trimmer operators. The project is aimed to create a mechanical solution to reduce the strain on hedge trimmer operator’s shoulders and upper bodies during long workdays. Tasks involving hedge trimmers cause significant stress on the shoulder area, which can lead to long-term injuries. Exoskeletons have the potential to support users by redistributing the load to stronger parts of the body. The goal of the project was to design an exoskeleton specifically for hedge trimmer operators to reduce the risk of work-related injuries and improve the work environment. The project began with a preliminary study that included market analysis, interviews with professional users, and testing of existing exoskeletons. A specification of requirements was formulated based on the collected data, and several concepts were generated through brainstorming. The final concept was selected using Pugh's matrix, where different options were compared against a reference product from Hilti. The chosen design for the exoskeleton includes a spring-loaded mechanism placed on the user's back. The springs provide support at the right angle and reduce shoulder strain by transferring the load to the back and hips. The prototype was based on Husqvarna's existing harness, which contributed to reduced production costs and adaptability. The prototype meets most of the requirements in the specification, such as providing mechanical support to the shoulders and the ability to adjust the force. However, further tests and adjustments are needed to optimize the design and ensure user-friendliness. Future research should include field tests with actual users and the implementation of adjustment options for the spring force. This study lays the foundation for the future development of exoskeletons for hedge trimmer operators and po

Inter-project knowledge transfer is by scholars widely considered to be a crucial source of competitiveness for project-based organizations. Effective knowledge transfer not only brings economic benefits but also enhances firms’ environmental and social sustainability performance. However, to date, limited research has focused on ascertaining the prerequisites for effective knowledge transfer within the SME context. Correspondingly, through single-case study, this study aims to understand how interrelated organizational factors impact inter-project knowledge transfer in project-based SMEs. Aspects that were found to impact knowledge transfer could be grouped into three dimensions of organizational factors; project characteristics, organizational structure, and organizational culture. More specifically, project similarities, project complexity, horizontal differentiation, and strong interpersonal relationships were found to facilitate knowledge transfer. On the other hand, urgency, absence of formal project managers, low degree of formalization, centralization, low degree of vertical differentiation, and sense of ownership of knowledge were factors identified to hinder knowledge transfer. Furthermore, the present study discovered how the dimensions of organizational factors are interrelated in their impact on inter-project knowledge transfer. Based on the findings, academic and practical implications, and future research avenues are proposed.

Foam materials are used in many structural applications, especially where impact loads are expected. A common application is to absorb energy and reduce the forces that would otherwise be transferred to vehicle occupants in the event of a collision. A structure or material that does this effectively is said to have a high crashworthiness. Foam materials with high crashworthiness are essential for protecting infants and young children in child safety seats, also known as Child Restraint Systems (CRS). Physical testing is time-consuming and costly, and accurate modeling is required to evaluate safety performance. High-fidelity models and advanced methods in computational dynamics to predict acceleration-time response are crucial for evaluating human safety. This thesis investigates the constitutive behavior of foams within LS-DYNA for advanced material modeling and uses a deductive methodology to explore this. More specifically, the work focuses on constitutive modeling, finite elements, and parameter- fitting using optimization. The work contributes to the field of computational dynamics and solid mechanics. The thesis aims to improve the modeling of foams by providing an accurate, efficient, and robust framework. The results consist of best practices for how foams should generally be modeled for FEM applications. This includes the choice of constitutive material models, finite elements, mesh-free methods, optimization for parameter-fitting, contact formulations in contact robustness and stability, and the necessary experiments for defining material parameters for constitutive extrapolation of strain rates. Two constitutive relations, Jeong's and Nagy's, are proposed for modeling strain rate effects used in dynamic impact tests. Besides that, we propose two extrapolation schemes to artificially extend the densification range for numerical stability based on the proposal of Paul Du Bois. Python code is also presented for automatic input compatible with LS-DYNA when se

This thesis focuses on data-driven methods, specifically artificial neural networks, to identify material model parameters in high density polyethylene (HDPE) for finite element (FE) simulations. The study thoroughly examines the anisotropy in HDPE by testing different material orientations with digital image correlation (DIC) during uniaxial tensile tests. DIC enabled precise measurement of strain distribution,unveiling both diffuse and local necking strain. Two hardening models,the Swift-Hockett-Sherby (S/HS) and a custom model, were explored to characterize HDPE’s plastic behaviour in FE simulations. In consistencies between predicted outcomes using the SHS model and experimental results prompt the consideration of custom equations forenhanced accuracy. The Hill48 yield model was introduced for the FE model to cover the anisotropic properties of the material. Large datasets were generated from these simulations to cover a wide range of different material configurations. The datasets were used to train neural networks so that a wide range of different HDPE grades can later be fed to the network to determine the associated material parameters. An Abaqus-Isight model was developed to automate parameter variation, simulation, and data extraction, thus streamlining the process and saving time. Data extracted from simulations, including force displacement and strain, are leveraged for neural network training. The study evaluated two types of neural networks: feed forward neural networks (FFNN) and long short-term memory neural networks(LSTM). It was found that FFNN performed better than LSTM for this task. Therefore, the research focused more on refining the FFNN approach. Overall, the implementation of the custom hardening modelin combination with the Hill48 yield model was successful, but showed weaknesses in CD orientation

Traumatic brain injury (TBI) is a worldwide public health problem. It is often caused by impacts to the head, which can cause translational and rotational motions. During impacts to the head, the neck serves as one of the boundary conditions for determining its kinematic response. In today’s helmet assessment standards, the dynamics of the neck are not included, and in most standards only translational accelerations are examined within a short time interval around 20- 30 ms. However, to understand the risk of brain injury, it is also important to account for the rotational motions and the influence of the neck on head kinematics. In this thesis the influence of the neck on head kinematics was investigated by comparing 5 different finite element (FE) models of the human. By using finite element analysis, simulations of four different accident scenarios were conducted. Most models are produced for the automotive industry and are not validated in vertical impacts with forces acting on the head. The accident scenarios included vertical and horizontal impacts to the head with different striking objects. The models included two anthropomorphic test devices (ATD) and three human body models (HBM). Furthermore, an isolated head was also used. The models were equipped with an industrial safety helmet, with and without a low friction layer (LFL). Additionally, the helmet versions were used to investigate how the various FE models predict the difference in rotational kinematics. The head kinematics showed considerable disparities between the ATDs and the HBMs. The ATDs mostly showed a stiffer, spring-like behavior with higher translational accelerations and lesser rotational motions. Furthermore, the HBMs showed responses that were assumed to have been in better proximity to biofidelic responses. The incorporation of the LFL led to a reduction in peak resultant rotational velocity (PRV) in most models and accident scenarios. Furthermore, the results were highly influenced by, Traumatiska hjärnskador är ett globalt folkhälsoproblem. Traumatiska hjärnskador orsakas ofta av slag mot huvudet, vilket kan orsaka både translations- och rotationsrörelser av hjärnan. Vid slag mot huvudet verkar halsen som ett av randvillkoren som styr kinematiken av huvudet. I dagens hjälmstandarder är halsens dynamik inte inkluderad och i majoriteten av standarder är det endast translationsaccelerationer som undersöks samt inom en kort tidsram, runt 20-30 ms. För att förstå risken för hjärnskador behöver man även beakta rotationsrörelser och då blir halsens inflytande på huvudets kinematik av vikt, liksom att utvärdera kinematiken under en längre tid. I detta examensarbete studeras halsens inverkan på huvudets kinematik genom att jämföra fem olika finita element (FE) modeller av människan. Genom att använda finita elementmetoden, genomfördes simuleringar av 4 olika olycksscenarior. Olycksscenariorna inkluderade vertikala och horisontella islag med olika objekt. De modeller som användes var två krockdockor och tre humanmodeller samt ett isolerat huvud. De flesta modeller är framtagna för bilindustrin vilket påverkar dess användningsområde genom begränsade valideringar av vertikala slag med krafter som verkar direkt på huvudet. Alla modeller var utrustade med en industrihjälmsmodell, med respektive utan ett lågfriktionslager. Dessutom användes hjälmmodellerna till att undersöka hur de olika FE modellerna förutspådde skillnader i rotationskinematik. Kinematiken av huvudet visade på signifikanta skillnader mellan krockdockorna och humanmodellerna. Krockdockorna hade generellt ett stelare, fjäderliknande beteende med högre translationsacceleration och mindre rotationsrörelse. Vidare hade humanmodellerna ett beteende som var mer likt den förväntade mänskliga responsen. Användandet av lågfriktionslagret ledde till reduktion i resulterande peak rotationshastighet bland de flesta modeller och olycksscenarior. Result

This thesis regards the design process of a test rig for a new type of clutch. To save excessive fuel losses in heavy vehicles, a dog clutch has been designed with elastic engagement to lower peak torque. Currently, there is no way of testing this clutch. The purpose of this thesis is therefore to design a test rig that allows physical testing of this newly developed clutch. The thesis describes how suitable tests/measurements are found to indicate clutch functionality. By following a design process, these tests/measurements are incorporated in a test rig design. Initially, requirements were set. With these requirements, concepts have been generated. After some reviewing and improving, one final concept has been chosen. This concept has been designed using separate subsystems. When integrating these subsystems, a final design is realised. The final design measures the axial positions of components inside the clutch. It also measures torque and speed of the input and output. This all while having a variable input speed, engagement force, output braking torque, and output rotational inertia. The test rig is suitable for long-term testing to test wear of the different clutch components. Advice on future works has been given to the company based on the achieved results.

This master's thesis is focused on the structural response due to blast loading, where the geometry used was arbitrary but heavily inspired by Siemens Energy. The aim of the thesis is to gain a better understanding on how to model the blast load and how it affects the structure, as well as to study the modeling of bolts with both pre-tension and a damage criteria in an explicit analysis. Lastly, the importance of strain rate dependent material models was studied. Other aspects such as mass scaling and Rayleigh damping were also investigated. The software used to solve these tasks were Hypermesh, Abaqus and Python. To conclude, the conclusions drawn from this thesis was that bolts should be modeled using connector elements, and including pre-tension is more conservative than not using it for the case studied. However, for the material modeling it gives more conservative results when using a strain rate independent material model compared to the strain rate dependent model, and is advised to be used in the future.

Thermomechanical processes such as hot rolling have been used in the industry for a long time to process and shape metals to a desired form with specific properties. However it can be difficult to make changes to the different process parameters. That's where it is beneficial to use a hot deformation simulator such as the Gleeble 3800-GTC. It can be used to test metals in a controlled environment where the deformation, temperature and other parameters are easily changed. When the machine uses a Hydrawedge module, it is able to simulate hot rolling using uniaxial compression at high temperatures. Swerim AB has one such machine and has requested to investigate what occurs inside a specimen during testing in the Gleeble, specifically inside two low-alloyed steels with a hardness between 400 and 500 HV. Such tests were replicated using LS-DYNA, an FE software. The goal was to acquire true stress-strain graphs that showed similar behaviour to the data from the Gleeble and plots of the effective plastic strain which could be correlated to the grain structure pattern inside the deformed cylinders. An FE-model was created which replicates the procedure. The model was verified through numerous steps. An initial mesh verification was done where the simulation time took at least 5 hours and at most 86 hours. Using a technique called mass scaling, the elements inside the model were manipulated using additional mass to increase their time step and reduce the computational time. A verification of the mass scaling was done where the computational time was weighed off against accuracy. Afterwards the friction had to be verified where it was found that the Gleeble test specimens were deformed more than necessary which was taken into account and the models were adjusted for friction verification. After all was said and done, the model had a reasonable friction coefficient with an optimal mesh and mass scaling configuration. The resulting model simulated a test of 0.5 seconds in 15 mi

Forklifts are commonly perceived as simple machines that are not representative of modern technology. However, a deeper analysis uncovers their inherent complexity and sophistication. This project aims to develop a tire model for indoor forklifts with sufficient accuracy that it can replace the need for physical tests and significant calibration, thereby shortening development time and decreasing costs. This report is part of a Master's thesis work on modeling shocks generated when driving over obstacles with a forklift. The project is conducted in collaboration with Linköping University and Toyota Material Handling Manufacturing Sweden. Various methods for modeling tire behavior, along with different contact types, have been explored and tested, primarily focusing on the Fiala tire model. Developing a tire model that accurately captures all aspects of driving over obstacles is a challenging endeavor. Despite several challenges, the findings presented in this report suggest that, with additional time, it is possible to develop a model that effectively simulates shocks across various speeds and obstacle heights.

Detta examensarbete för en kandidatexamen i teknisk fysik gick ut på att i uppdrag av företaget Andritz AB, vars svenska koncern fokuserar framför allt på att ta fram maskiner och lösningar för industrin inom papper- och pappersmassa, hjälpa till att uppdatera och utveckla en beräkningsrutin som används för att beräkna hållfastheten på en axeltapp tillhörande utrustning med roterande delar. Beräkningsrutinen togs fram under 90-talet och var i behov av att uppdateras för att följa dagens standard och utvecklas för att kunna appliceras och få ett bredare användningsområde i deras arbete. En stor del av arbetet gick ut på att validera de befintliga funktioner och formler som använts för möjligheten att återanvända så mycket av det gamla programmet som möjligt. Det innebar att både uppdatera de delar som blivit utdaterade och eventuellt förbättra de formler med förbättringsmöjligheter. Förutom uppdatering av programmet lades även en stor del av arbetet på att ta fram nya funktioner till programmet för att bli mer användbart såsom att den kunde appliceras på fler typer av uppställningar av axeltappar, mer än en typ av ansats, möjligheten att approximera utmattningsvärden för material och ge uppskatta hållfastheten på svetsbehandlade axlar. Parallellt genomfördes ett arbete med gränssnittet för att göra programmet mer lättanvänt och minska risken för att programmet kunde kontamineras och förstöras genom att låsa celler som inte borde röras, införa listor för val och överföring av materialdata för att minska den mänskliga faktorn vid inmatning av data. Trots att flera förbättringsmöjligheter kvarstod efter avslutat arbete blev resultatet ett program som med dessa nya funktioner fick ett bredare användningsområde och en tryggare arbetsyta med mer pålitlighet av företagets användare., This bachelor's thesis in engineering physics was done one behalf of the company Andritz AB with their Swedish group primarily focused on developing machinery and solutions for the paper and pulp industry, to help update and develop a calculation routine used to determine the strength of a shaft extention used in their wash presses. The original program was developed in the 1990s and needed updating to meet current standards and to be expanded for broader application in their work. Much of the work involved validating the old functions and formulas used to maximize the reuse of the old program. This included both updating outdated parts and improving areas where improvement could be needed. In addition to updating the program, a significant portion of the work was devoted to developing new features to enhance its usability, such as applicability to a wider range of shaft pin configurations, more than one type of shoulder, the ability to approximate fatigue values for materials, and estimating the strength of welded shafts. Simultaneously, work with the interface was conducted to make the program more user-friendly and reduce the risk of contamination and destruction by locking cells that should not be accessed, introducing lists for selection and transferring of material data to reduce the human factor in data input. Although several improvement opportunities remained after the completion of the work, the result was a program with these new features that expanded its scope of application and provided a safer working environment with increased reliability for the company's users.

This report investigates how the company Vätternkök AB can streamline its assembly and installation of kitchen frames. Vätternkök AB is a newly established company based in Jönköping, delivering kitchens, wardrobes, and bathroom furnishings in flat packs directly to construction sites. The kitchens are assembled and installed on-site by employees or hired carpenters.The project group conducted the thesis work over 18 weeks during the spring of 2024. Throughout the project, the group conducted literature reviews on how the assembly and installation of kitchen frames can be streamlined, performed analysis on both the construction and the carpenter's work onsite during a field study in Hultsfred, and developed proposals for improvements to the construction. What the group discovered during the field study was that the construction site was significantly behind schedule, making it difficult for the carpenter to carry out their work. This was the second installation the company conducted, and the same problem occurred as with the first installation.The group also conducted timing measurements to identify tasks that take up an unnecessarily long time and transitions between tasks. Through these timing measurements, the group identified several tasks that unnecessarily take a long time and could be changed or eliminated. The first is that the feet mounted on the kitchen frame require four holes each, which must be measured and drilled, where all kitchen frames have two or four legs. The second is the back panel of the kitchen frame, which is situated in a slot extending the height of the frame and then being stapled or nailed with a nail gun to keep it in place.With all the information from the literature study and analysis, the project group proposed changes to the existing construction. The first proposal is to pre-drill the holes for the feet of the frame, thus eliminating the steps of measuring and drilling the holes and saving time. The second proposal is to extend th

Detta projekt var ett samarbete mellan Luleå tekniska universtiet och CranabSlagkraft och har behandlat ett förbättringsprojekt av befintliga inner- och yttergripklor med namnet E36 tillhörande skogsgrip CE360. Produkten hade en dåvarande konstruktionslösning som företaget länge inte har varit nöjd med. Klorna hade plåtar som svetsades fast på sidan av gripklorna för att skapa stabilitet. Utan dem skulle gripen inte ha tillräcklig hållfasthet då klorna skulle böjas och deformeras omgående vid användning. Sedan hade gripen även problem med stora nötningsproblem. Denna grip ville företaget förbättra då den var både ekonomisk kostsam och tidskrävande att bygga. Produkten var inte heller ekonomisk gynnsam för slutanvändarna då produkten hade så kort teknisk livslängd. Detta projekt har bearbetat dessa problem noggrant med grundlig analys på ett ingenjörsmässigt sätt som resulterat i en slutgiltig lösning med ett ritningsunderlag som har presenterats godkänts och byggdes till en prototyp under 2012., This project was a collaboration between Luleå University of Technology and CranabSlagkraft and has addressed an improvement project of existing inner and outer gripc laws named E36 belonging to the forestry grip CE360. The product had a previous design solution that the company had long been dissatisfied with. The claws had plates welded to the sides of the grip claws to create stability. Without them, the grip would not have sufficient strength as the claws would bend and deform immediately during use. Furthermore, the grip also had significant wear issues. The company wanted to improve this grip as it was both economically costly and time-consuming to build. The product was also not economically beneficial for end-users as it had such a short technical lifespan. This project has meticulously addressed these problems with thorough analysis in an engineering manner, resulting in a final solution with a drawing basis that has been presented, approved, and built into a prototype in 2012.

High strain -rate testing of high -density polyethylene is the focus of the present work. This testing is accomplished by two types of experimental testing: uniaxial tensile testing using standard testing technique, and impact testing of a 3D structure with non -trivial geometry. Both the uniaxial tests and the impact tests were evaluated using a material model suited for rate -dependent inelasticity of polymers that has been developed. In the uniaxial tensile tests, a maximum strain -rate of about 28/s was attained. In the impact tests, strain -rates of the order of 100/s and beyond were predicted in the analyses. The impact tests were simulated and analysed by use of finite element simulations. Coupled Eulerian-Lagrangian (CEL) analyses were employed for some of the tests where there was an interaction between the compressed structure and air trapped inside it. Overall, the simulations were able to reproduce the outcome from the experiments well. In particular, the deformation scenarios in the impact tests for different loading situations could be reproduced.

This study addresses the critical need for a constitutive model to analyze the cyclic plasticity of additively manufactured 316L stainless steel. The anisotropic behavior at both room temperature and 300 degrees C is investigated experimentally based on cyclic hysteresis loops performed in different orientations with respect to the build direction. A comprehensive constitutive model is proposed, that integrates the Armstrong-Frederick nonlinear kinematic hardening, Voce nonlinear isotropic hardening and Hill's anisotropic yield criterion within a 3D return mapping algorithm. The model was calibrated to specimens in the 0 degrees and 90 degrees orientations and validated with specimens in the 45 degrees orientation. A single set of hardening parameters successfully represented the elastoplastic response for all orientations at room temperature. The algorithm effectively captured the full cyclic hysteresis loops, including historical effects observed in experimental tests. A consistent trend of reduced hardening was observed at elevated temperature, while the 45 degrees specimen orientation consistently exhibited the highest degree of strain hardening. The applicability of the model was demonstrated by computing energy dissipation for stabilized hysteresis loops, which was combined with fatigue tests to propose an energy-based fatigue life prediction model.

In the Värmland region, Sweden, an innovative sandwich structural element has been designed by the cooperation of pulp and paper companies for possible use in indoor products, such as tables, shelves, doors, and furniture in general [1]. The element, lightweight and strong, has facesheets of laminated paperboards made of recycled and/or virgin wood fibres. The core, made of paper pulp, has a unique shape like a cup box with staggered positions between the cups, see [1]). At the Department of Engineering and Chemical Science at Karlstad University, the mechanical performance and properties of the elements have been investigated via experimental tests and finite element (FE) models for different applications. Recently, four-point bending tests have been conducted in sandwich beams from the element, see Fig. 1(a). The facesheets of the beams were made of virgin and/or hybrid (virgin + recycled fibres) paper materials. Results from quasistatic experimental tests were evaluated by means of digital image correlation technique for accurate measurements of the beam deflection. In this presentation, we will address aspects of flexural and shear rigidities of the tested samples [2, 3], as well as main observations of failures, which occurred at the top facesheets (c.f. Fig 1(b)). A parametric FE model will also be presented along with its calibration, capability of predicting the failure (c.f. Fig 1(c)), and possibilities for structural optimization. References [1] Ecopals AB, Hållbar möblekonstruktion till en bråkdel av vikten/Durable furniture construction at a fraction of the weight. Retrieved March 03, 2024, https://ecopals.se/ [2] Howard, G.A., Analysis and design of structural sandwich panels, Pergamon, (1969) [3] Lorna, J.G., Michael, F.A., The design of sandwich panels with foam cores. In: Cellular Solids: Structure and Properties. Cambridge University Press, 345-386, (1997)

The reaction of a radial flexible ring with flanges in the supports of machine rotors to radial displacement has been studied. Two models of deformation and contact interaction of an elastic element with two rigid bodies positioned inside and outside of the ring have been developed. These models are based on variational statements with respect to the unknown forces and displacements. The options of gap and offset on both sides of the contact between the ring and the rigid bodies have been considered. A substantially nonlinear static reaction of the ring to radial displacement has been established. Radial reaction curves have been obtained across a wide range of design parameters, enabling a well-justified choice of an elastic damper with the desired stiffness properties.

Variable-frequency air injection and extraction is critical for salt cavern compressed air energy storage (CAES) power plants to smoothly integrate electricity into the power grid, and the magnitude of its effect on the mechanical properties and damage progression of the salt cavern surrounding rock determines the operation scheme of CAES power plants. To examine the impact of variable frequency, a series of monotonic loading tests with different rates and variable-frequency fatigue (VFF) tests with different upper limit stresses were carried out. Dilatancy stresses have a positive power function relationship with loading rate and frequency, but the fatigue loading process weakens this nonlinear tendency. The rate of change (CR) or the exponent of the fitted function can express it. From the initial stage to the steady stage, the CR of dilatancy stress increases about three times, and the CR of residual volumetric strain decreases about five to eight times. Increased upper-limit stress weakens this trend of change. Both high speed and high-frequency loading shift the damage acceleration point forward (e.g., b value accelerates earlier). The damage rate correlation is significant in the later stages of the VFF tests, the rate correlation of damage is significant. Both the upper stress and the extension of the main fracture zone enhance the rate dependence of fracture types. Moreover, the effect of rate on crystal penetrating cracks is more pronounced in the high-stress interval. The number of fractures significantly affects the dilatancy, rather than the type of fracture. This study serves as a guide for the design of variable frequency programs in different CAES salt cavern operation stages, as well as subsequent research., Funder: National Natural Science Fund of China (No. 52274073, 51834003); China Postdoctoral Science Foundation (No. 2023M730427); Chongqing Postdoctoral Research Project (No. 2023CQBSHTB3139);Fulltext license: CC BY

We investigated the role of phosphorus (P) impurities on the fracture toughness and underlying failure mechanisms by means of classical atomistic modeling for a set of < 110 > symmetric tilt tungsten grain boundaries (GBs). This entailed the utilization of a quasi-static mode I displacement-controlled setup with cohesive zone volume elements (CZVEs) to study failure mechanisms and evaluate the fracture toughness of the GB cracks. The fracture toughness was estimated using three approaches: computing (i) the individual and (ii) the average energy release rate of CZVEs along the fractured surfaces and using them as inputs for the Griffith model, and (iii) relating the fracture toughness to crack propagation initiation. The cracks in all the pristine GBs evolved in a brittle fashion, occasionally forming facetted cleavage planes. Upon introduction of impurities, other mechanisms such as void formation and crack-tip transformation were also observed. Depending on the GB proximity of the occupied segregation sites, local strengthening was seen occasionally for individual CZVEs and at the crack-tip, which was triggered by local impurity-induced crack deflection onto planes with higher cohesion. But when the fracture toughness from the averaged energy release rate was considered, an overall reduction with increasing impurity segregation was found, although to a varying degree for different GBs. This indicates an overall increased degree of embrittlement with increasing P-segregation at the GBs, which concurs with most experimental results reported in the literature.

At least three probabilistic definitions of hidden Markov models (HMMs) have been used frequently in the literature. Unfortunately, one of these definitions shows fatal flaws, however nowadays a lot of literature still uses this definition. The aim of this paper is on one hand to specifically point out one such fatal flaw (in terms of deriving the well-known forward-backward algorithm), and on the other hand to list key properties of HMMs under the other two plausible (and equivalent) probabilistic definitions for further developments. As applications, we rigorously layout forward-backward algorithms for inhomogeneous HMMs and hidden reciprocal models, and fully present connections between HMMs and undirected graphical models which are not mentioned anywhere in the literature, to the best of our knowledge., Funding Agencies|Swedish International Development Cooperation Agency (SIDA)

The kinematics of polydisperse granular materials comprised of overlapping spheres is carefully analysed. A single-particle strain estimate is developed that summaries the deformation experienced by each particle in terms of a mean deformation gradient. This strain estimate accounts for material displaced at interparticle contacts as well as a compensatory motion of the free particle surface. Forces that are work-conjugate to the mean deformation gradient are determined; they constitute the many-body forces required for a correct mechanical behaviour in the zero-porosity limit. Notwithstanding this, pairwise interparticle forces are needed for two main reasons; they dominate the particle interactions at small overlaps and stabilise the formulation in the continuum limit. Numerical simulations are performed to demonstrate the properties of the single-particle strain estimate and to test certain aspects of the formulation. In particular, it is demonstrated that the formulation can accommodate large rotations and provides a mechanical response consistent with that of a solid material in the zero-porosity limit. It is concluded that this work forms the basis for future developments aiming at formulation of realistic contact models for plastic particles and macroscopically consistent discrete methods for granular materials.

The shear cutting process, which is the most common cutting technique in the sheet forming industry, is known for introducing damage to the cut edges of high strength metal. This damage may impair the forming- or fatigue properties of the material and can cause edge-cracking during forming or in-service part failure. The edge formability of a sheared edge is strongly linked with the appearance of large notches arising due to unfavorable process parameters. By numerical modelling of the shear cutting process with the possibility to vary important process parameters, the sheared edge damage can be detected and avoided in the manufacturing process. This work present numerical modelling of shear cutting in Advanced High Strength Steel using a novel Particle Finite Element Method approach. Numerical modelling of shear cutting processes over a large range of cutting clearances were conducted and validated against laboratory experiment results. The results showed that the PFEM modelling could detect the cut edge damages with the largest negative impact on formability, thus narrowing the feasible cutting clearance range., Full text license: CC BY;ISBN for host publication: 9781644903131

Rotor-to-stator rubbing in rotating machinery, resulting from tight clearances, introduces complex dynamics that can potentially lead to high vibrations and machine failure. Historically, the rubbing models were addressed using cylinder-to-cylinder contacts; however, recent attention has shifted towards examining blade-tip contact in turbines, which affects the systems dynamics and efficiency. This study investigates the impact of the variations in blade number on bladed rotor systems, emphasizing on the types of motion that occur as function of the operational speed in the sub-critical range. A simplified bladed rotor model has been developed, using a Jeffcott rotor with blades represented as damped elastic pendulums. The equations of motion are derived and numerical simulations are performed to explore the system’s behaviour with varying blade numbers (3, 5, 7, and 10) in order to analyse displacements, contact forces and bifurcation diagrams as function of the rotating speed. Results reveal distinct regions: periodic motion (I and III) and chaotic motion (II and IV) appear alternatively in the bifurcation diagram, with the chaotic regions occurring at specific fractions of the natural frequency and the number of blades. The study concludes that chaotic motions are associated with larger displacements and higher contact forces, and the vibrational behaviour becomes less hazardous as the number of blades increases. In addition, the appearance of periodic and chaotic motions occur in the same regions by scaling the rotating speed with the number of blades and natural frequency of the system. From an operational perspective, this dynamic investigation offers valuable insights into the severity of blade rubbing in industrial systems. It can guide the implementation of mitigation solutions to prevent worst-case failure scenarios and help to perform adjustments to either operational or design parameters., Full text license: CC BY

For battery pack assemblies, it is crucial that the laser welded cell-to-busbar joints demonstrate both high mechanical strength and minimal electrical resistance. The present study investigates the effect of different laser welding parameters, on the mechanical strength, electrical resistance, porosity formation and joint microstructure, for dissimilar material cell-to-busbar joints. Laser welding experiments are performed, on thin nickel-plated copper and steel plates. The plates are joined in an overlap configuration, using laser beam wobbling and power modulation. Both circular and sinusoidal laser beam wobbling are used as selected strategies to increase the interface width of the joints, where also a comparison is made between the two methods. The joint quality is evaluated using joint geometry analysis, shear strength tests, computed tomography scanning and electrical resistance measurements. The results show that circular laser beam wobbling gives a larger joint shear strength compared with sinusoidal laser beam wobbling. In addition, it is observed that both the total pore volume and material mixing are significantly increased with increasing laser power and wobbling frequency for circular laser beam wobbling. However, for the sinusoidal laser beam wobbling the wobbling frequency does not show a significant impact on the total pore volume., CC BY 4.0 DEEDCorresponding author: andreas.andersson.lassila@his.se (A.A. Lassila)This work was supported financially by Vinnova, Sweden through the Produktion 2030 project QWELD (dnr: 2021-03693)., QWELD

Presented test results on transverse cracking in cross-ply laminates upon tension–tension cyclic loading show that the increase of crack density depends not only on the maximum transverse stress in the cycle but also on the local cyclic stress ratio RTloc in the analyzed layer. To include the effect of the RTloc in the model with statistical failure stress distribution for crack initiation (based on Weibull distribution) adapted for fatigue, an equivalent stress is introduced in a similar manner as the equivalent strain energy release rate has been used for delamination crack propagation. The equivalent stress in the layer is defined as a power function of the maximum stress and the stress ratio in the layer. It was found, testing laminates with two different fiber contents that higher the local stress ratio in 90-layer, higher the transverse cracking resistance. Transverse crack density simulation using the developed equivalent stress model has been validated against test results., Validerad;2024;Nivå 2;2024-07-31 (signyg);Funder: Swedish Aeronautical Research Program NFFP 7 (2019-02777); Swedish Aeronautical Research Program NFFP 8 (2023-01199); GKN Aerospace, Sweden;Full text license: CC BY

Within the automotive industry, there is an increasing demand for a paradigmshift in terms of which materials are used for the manufacturing of the automotive body. Globalclimate goals are forcing a rapid adaption of new, advanced, sustainable material grades suchas the fossil free steels and materials containing higher scrap content. With the introduction ofthese new and untested materials, methods for accounting for variation in material propertiesare needed directly in the press lines.The following study will focus on creating an initial virtual shadow of the manufacturing of aVolvo XC90 inner door panel through the application of Artificial Neural Networks (ANN). Thevirtual shadow differs from the concept of the digital twin by only being a virtual representationof the production line, with training data generated exclusively by numerical simulations, andhaving no automated communication with the physical press line control system. The virtualshadow can be used as an assistance to the press line operators to see how different press linesettings and material parameter variations will impact the quality of the stamped component.The study aims to validate the virtual shadow through accurate predictions of the materialdraw-in measured in the physical press line.

Pressure-sinkage tests for determining vehicle sinkage on soft soils can be done using a bevameter. In this study, pressure-sinkage tests were performed on snow, which, like soil, is a granular material. However, unlike soil, snow layers are inhomogeneous with varying properties. For tracked vehicles, the shape of the track print is rectangular, which is why rectangular plates are often used for pressure-sinkage tests. The aim of this study was to see if smaller circular plate or smaller rectangular plates can be used instead of larger rectangular plates, and to understand the possible limitations of using small plates. Radius for the circular plate was chosen to be equal to the width of the rectangular plate. Three measuring sessions were performed at different locations during different snow conditions using circular pressure plates and rectangular pressure plates of different aspect ratios. The results show that smaller rectangular plates can be used if the width of the plates remains the same, or circular plates can be used if the radius of the circular plate is equal to the width of the rectangular plate. Limitation comes with increasing pressure, which occurs more quickly with larger-area plates, as larger plates sense solid ground more rapidly than smaller plates. To avoid this, snowpack thickness should be a minimum of five times thicker than maximum sinkage., Validerad;2024;Nivå 2;2024-04-11 (signyg);Full text license: CC BY

In this study, we present a novel nodal integration-based particle finite element method (N-PFEM) designed for the dynamic analysis of saturated soils. Our approach incorporates the nodal integration technique into a generalised Hellinger-Reissner (HR) variational principle, creating an implicit PFEM formulation. To mitigate the volumetric locking issue in low-order elements, we employ a node-based strain smoothing technique. By discretising field variables at the centre of smoothing cells, we achieve nodal integration over cells, eliminating the need for sophisticated mapping operations after re-meshing in the PFEM. We express the discretised governing equations as a min-max optimisation problem, which is further reformulated as a standard second-order cone programming (SOCP) problem. Stresses, pore water pressure, and displacements are simultaneously determined using the advanced primal-dual interior point method. Consequently, our numerical model offers improved accuracy for stresses and pore water pressure compared to the displacement-based PFEM formulation. Numerical experiments demonstrate that the N-PFEM efficiently captures both transient and long-term hydro-mechanical behaviour of saturated soils with high accuracy, obviating the need for stabilisation or regularisation techniques commonly employed in other nodal integration-based PFEM approaches. This work holds significant implications for the development of robust and accurate numerical tools for studying saturated soil dynamics., Validerad;2024;Nivå 2;2024-06-26 (joosat);Funder: Swiss National Science Foundation (189882); National Natural Science Foundation of China (41961134032); UK Engineering and Physical Sciences Research Council (EP/V012169/1);Full text: CC BY License

Hydropower generators withstand multiple forces from diverse sources during operation. To ensure their stability and safe performance, numerical tools are developed to characterize their dynamic properties. Traditionally, generators are assumed to be rigid in rotordynamic analyses. However, the measurements in power stations challenge this assumption. This article proposes a novel approach to modeling hydropower generators with floating rotor rims using a three-dimensional (3-D) Finite Element Method, aiming to study their dynamic performance and properties, including natural frequencies, the modes of vibrations, and expansion due to centrifugal and electromagnetic forces, with the goal of improving the reliability of modern designs. Both this approach and employing a two-dimensional (2-D) model using curved beams result in similar in-plane natural frequencies and the expansion of the rotor rim due to centrifugal forces. However, the 3-D model can be used to calculate the out-of-plane natural frequencies and modes, to model the dynamics of complex geometries, and to perform stress evaluation and fatigue analysis., Validerad;2024;Nivå 2;2024-06-26 (joosat);Full text: CC BY License, Swedish Hydropower Centre-SVC

There has been a huge interest in recent years in using phase -field theories for numerical analyses of fracture phenomena. However, in phase -field fracture theories, a critical aspect often involves a decomposition of the strain energy density to select physically trustworthy crack paths and to prevent interpenetration of crack surfaces. This aspect becomes even more critical in the case of mixed -mode loading under compression. To overcome these challenges, a hydrostatic-spectral-deviatoric decomposition, enhanced by separate critical energy release rates for different fracture modes, is employed in this study. In order to evaluate the enhanced decomposition strategy, a set of biaxially loaded crack experiments in global compression is designed. Samples of different geometries contain multiple flaws and holes. The experiments are numerically simulated using a unified set of material parameters and three different strain energy decomposition methods (i.e., hydrostaticspectral-deviatoric, spectral and hydrostatic-deviatoric). Simulations using the hydrostatic-spectral-deviatoric decomposition scheme capture both intricate crack paths and critical loads in the experiments. The enhanced decomposition strategy seems capable of simulating the experiments with reasonable precision, in sharp contrast to the two commonly used decomposition strategies (spectral and hydrostatic-deviatoric).

Mechanical degradation mechanisms are one of the leading causes of charge capacity loss in lithium-ion batteries. This study further develops a discrete element method (DEM) simulation framework, which investigates how the local contact behaviour affect the global mechanical properties of the active layer. The local microstructure consists of active particles held together by a binder domain, making up a granular medium. This study investigates the impact of the layer's global properties from the type of particle contact model. Experiments were also performed to measure size distribution and the material properties of the active material. The time dependency of the active layer, stemming from the viscoelastic binder domain, was studied in relaxation simulations, which were based on experimental measurements., Validerad;2024;Nivå 2;2024-06-11 (hanlid);Full text license: CC BY

Flow field measurements around cross-country skiers (xc skiers) are lacking in the literature to date. The aim was therefore to investigate the possibility of using particle tracking velocimetry for visualization and measurement of the flow field around xc skiers roller skiing on a treadmill in a wind tunnel. The airflow was seeded with neutrally buoyant helium-filled soap bubbles as tracer particles, following the flow without affecting it. As illumination, two different approaches were tested: first, a laser in the cameras’ line of sight (sagittal plane), then an LED unit directed vertically in a narrow slice, clearly limiting the depth of the measurement volume in the cameras’ line of sight. The flow field was studied at various speeds (3-7 m/s) around a single skier as well as around two skiers in line with the streaming airflow. It was found that the experimental approach has the potential to provide detailed insights, both qualitatively and quantitatively, into the flow field dynamics. The main challenges regarding setup, illumination, seeding, and cameras were identified, and possible improvements to streamline the experimental methodology were discussed., Validerad;2024;Nivå 1;2024-05-16 (hanlid);Full text license: CC BY-NC

Shear cutting processes have a detrimental effect on fatigue of high strength metal components. The effect tends to increase with material grade, counteracting the task of reducing weight in chassis components using higher strength materials. Base material fatigue data are often available, but assessment of components with cut edges often require additional costly and time-consuming testing. This paper provides a methodology for estimation of fatigue life reduction by using residual stresses obtained from process simulations, and measured surface roughness in the cut edge. A stress relaxation criterion is applied to handle reduction of the initial local residual stresses. Two complex phase steels and one aluminum alloy are studied for validating the approach. Polished fatigue data is reduced to estimate S–N curves of trimmed and punched specimens at different load ratios. Good agreement between the model and test results are found for all cases. The needed data for the predictions are only a high cycle S–N relationship for polished material, uniaxial tensile properties, and the cut edge fracture surface residual stress and roughness without any parameter fitting, making it a convenient tool for estimating the reduction in fatigue life and for parameter studies., Validerad;2024;Nivå 2;2024-05-27 (joosat);Full text: CC BY license;This article has previously appeared as a manuscript in a thesis.

This research endeavors to investigate the geometrically nonlinear dynamic characteristics of Carbon Nanotubes (CNTs) while incorporating size effects based on the Second Strain Gradient (SSG) elasticity theory. To this end, the nonlinear governing equations and its corresponding boundary conditions are deduced in alignment with the Green-Lagrange strain tensor and Hamilton's principle. Concurrently, the weak form is expounded through the utilization of the C3 continuum Hermite interpolation functions, which ensure the continuity and smoothness of higher -order strain and displacement fields. Subsequently, a perturbation methodology is introduced, incorporating nonlinear phenomena into the context of linear wave propagation within the framework of periodic structures theory. The wave propagation characteristics manifest a pronounced disparity between the models based on linear SSG theory and those through nonlinear SSG theory with stiffness hardening phenomenon. In contrast to the zigzag CNTs, armchair CNTs evince an elevated aptitude for wave control. The application of nonlinear SSG theory in combination with the wave finite element method is significant for comprehending the wave propagation characteristics of complex CNTs.

In 2015, a 45 MW vertical hydropower machine exhibited excessive vibration after refurbishment. Measurements revealed a substantial bearing clearance at the lower generator guide bearing. Consequently, the bearing was unable to generate sufficient opposing force to drive the rotor toward the bearing center, resulting in more pronounced overall system vibration. Addressing this challenge required a cost-effective and feasible solution for mitigating the vibration problem. To this end, a design modification was implemented wherein the lower generator guide bearing (originally a sleeve bearing) was modified to a four-lobe bearing by offsetting the two halves of the bearing twice in two axes. Numerical simulations and experimentations were conducted, and the dynamics of the machine before and after the design modification were investigated. Both the simulation and experimental results showed that the machine with the four-lobe bearing improved the system stability and reduced the vibration amplitudes. The numerical simulation result demonstrated that, due to the design modification, the first and second critical speeds were effectively eliminated for a speed range of up to three times the nominal speed. Furthermore, for nominal operation with unbalanced magnetic pull, the four-lobe bearing provided a stability advantage in terms of the modal parameters relative to the original sleeve bearing., Validerad;2024;Nivå 2;2024-04-08 (hanlid);Full text license: CC BY 4.0, Swedish Hydropower Centre-SVC

The exploration of graphene has attracted extensive interest owing to its significant structural and mechanical properties. In this research, we numerically investigate wave propagation in defect -free single -layer graphene, considering its geometrically nonlinear behavior through second -strain gradient elasticity. To capture the geometric nonlinearity, firstly, the nonlinear strain-displacement relations are introduced. The governing equation and associated boundary conditions are derived using Hamilton's principle. Then, the weak form, including the element matrices, is established. The eigenvalue problem is solved for 2D wave propagation through periodic structures theory. Finally, the dynamical properties such as band structures, mode shapes, energy flow, and wave beaming effects are analyzed. The numerical results reveal that the geometric nonlinearity through the second strain gradient influences the wave propagation characteristics in graphene. The findings are significant and contribute to the understanding of graphene's dynamic response, with implications for the engineering applications of graphene-based nanostructures.

Hydrogen-induced fracture of X65 pipeline steel under in -situ electrochemical charging is investigated by using slow strain-rate tensile (SSRT) test, hydrogen diffusion test, fractography analysis, and finite element simulation. Smooth and notched tensile specimens with varying notch radii are utilized to ascertain the impact of stress triaxiality on hydrogen embrittlement (HE) susceptibility. A fully coupled model, H-CGM+, capable of simulating the synergy between hydrogen-enhanced plasticity and decohesion, is employed. The simulation proficiently replicates both the global stress-strain trajectories and the local failure initiation sites of the in -situ SSRT tests. The findings indicate a predominance of dislocation trapping hydrogen mechanism in HE, with crack inception at the notch surface where local plastic strain peaks, subsequently advancing towards the center of the specimen. Notably, an inverse relationship is observed between HE susceptibility and stress triaxiality. A hydrogen-induced failure criterion, defined as a critical combination of local hydrogen concentration and plastic strain, is derived. The failure criterion is found to be independent of stress triaxiality, which serves as a good reference for safety assessment of hydrogen pipelines.

Exploring the wave propagation in nano-waveguides enables the development of on -chip nano -resonators, leading innovative capabilities that enhance acoustics and micro -mechanics. This paper conducts a numerical investigation into the dynamic properties of periodic nano-waveguides. The Second Strain Gradient (SSG) elasticity, which captures the size effects, is used in the determination of the constitutive relations. The weak form including the element matrices is deduced by the Hamilton's principle. Furthermore, a finite element method, based on the periodic structure theory, is introduced to explore the free wave propagation by solving the eigenvalue problems. The stiffness hardening phenomenon manifested in the dispersion curves, band structures, and energy flow vector fields is discussed. The sensitivity of higher order parameters existing in the SSG theory is analyzed. The numerical investigation for wave propagation in the periodic nano-waveguides through the SSG theory is an innovative work, highlighting the significance of the proposed methodology in explaining the special dynamic characteristics of complex nano-waveguides.

A non-local extension of the shear-modified Gurson model for porous plasticity is proposed, which is capable of preventing spurious strain localization and suitable for predicting crack initiation and growth under general loading conditions. In the extended model, the progression of shear failure is separated from flat dimple rupture by the assumption that these failure mechanisms are characterized by a deviatoric and a dilatational material length parameter, respectively. The two length parameters are introduced through a delocalization process based on the non-local integral approach evaluated on the current configuration. A comprehensive numerical investigation is conducted to disclose the influence of these length parameters. For this purpose, five different specimen geometries are considered covering a wide range of stress triaxiality including pure shear. It is observed that separation of the length parameters is essential for predicting crack branching driven by shear localization, e.g., the flat dimple-to-shear failure transition of a crack that approaches and penetrates a free surface., QC 20240926

A static-dynamic topology-sizing optimisation method is presented. The solution is based on a sequential Mixed-Integer Linear Programming solution and aims to minimise the mass of a structure subjected to concurrent constraints on static and dynamic response. It is shown that the classical problem of the dynamics of lightweight sandwich structures may be mitigated through core topology and face sheet thickness combinations, retaining the static load carrying capacity while presenting stringent dynamic properties at a low mass penalty. A numerical example, in the form of a load carrying sandwich beam which is excited at different frequencies, is used to demonstrate the method., QC 20240906

Implant designs highly influence their biomechanical performances when fixed with load-bearing long bone fractures. In this research work, the topology optimisation technique was used to obtain different shapes and designs of the bone plates according to three different loadings, e.g. lateral bending (LB), axial compression (AC), and physiological loads (PL), and solid volume fractions Vf of 30% and 70%. Bi-phasic mechano-regulation algorithm was used to investigate the callus healing for a given bone plate design, and stresses in screws and bone plates were monitored. To further validate the bone plate designs, fatigue analyses using Fe-safe and three-point bending tests were performed using additively manufactured plates. Topology-optimised bone plate PL with Vf 70% showed the maximum bending stiffness (peak load of 138 N and bending stiffness of 29 N/mm) among the optimised bone plates, with the best callus healing normalised stiffness of 0.6 and 0.7 in iterations 21 and 42, respectively. Thus, the bone plates produced using actual loading conditions (PL) outperformed other loading conditions during the biomechanical evaluation of fractured bones., QC 20240906