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In a material under stress, grain boundaries may give rise to stress discontinuities. The stress state at grain boundaries strongly affects microscopic processes, such as diffusion and segregation, as well as failure initiation, such as fatigue, creep, and corrosion. Here the general condition of incompatibility stress at grain boundaries is studied with a bicrystal model for linear elastic materials. In materials with cubic crystal structures, it is proven that hydrostatic stress does not lead to a stress discontinuity at grain boundaries. For bicrystals with inclined grain boundaries under uniaxial stress, the extreme values of the incompatibility stress as a function of the inclination angle are obtained by a simulated annealing method. A simple criterion is proposed to classify cubic materials into three groups. For cubic crystals with at most moderate anisotropy, the highest incompatibility stress occurs when the grain boundary plane is perpendicular to the uniaxial stress. For highly anisotropic materials, such as alkali metals and polymorphic high-temperature phases, the highest incompatibility stress occurs on grain boundaries with an inclination of about 47o., Team Marcel Sluiter

The design of bolt and nut thread comes in many variations, typically the designs are specified in standards like the metric ISO thread. The thread design is important for the connection strength, and bolted connections are used for many applications. In the present paper focus is on the strength of prestressed bolts, that is, where the preload is typically more than 75% of the proof strength. The objective is in the present work to reduce the stress concentration in the thread. The stress is found numerically using a full 3D finite element model, and a simplified 2D axisymmetric model. It is shown that the 2D model is sufficient for evaluating the maximum stress. Applying a symmetric design it is shown that a reduction in the maximum stress in the thread of 14% can be achieved. Allowing for an unsymmetrical thread design the maximum stress is reduced by 33%. With the unsymmetrical design some of the stress reduction is due to a more evenly load distribution along the thread. geometrically, all optimized designs are such that they can be manufactured by the same methods as a standard ISO thread.

Key connections in shaft hub assemblies are typically used due to the price of production but also the possibility for using it as an overload protection and safety device is important. The design of keyways and keys is specified in standards, different designs are available but typically the contact area is flat. The connection fatigue strength is improved if the stress concentration is reduced; important here is both the key shape and also the tolerances between key and keyway. The present designs described in standards are to some extend the result of previous possibilities for production. Today larger variations are possible without increasing the production price significantly. New designs with improved strength are presented and the design evaluation is done using both 2D and 3D finite element models including contact modeling. The design is primarily described by the super elliptical shape, that is, the design parameterization is simple. Improvement in the stress level found is significant, a maximum reduction of 78% is found, indicating that the fatigue strength can be significantly increased.

In this study, an efficient fatigue life estimation approach is proposed based on an equivalent solid model, along with two stress concentration factors, instead of a lattice model to simplify simulations for the strain-life method. One of the stress concentration factors accounts for the stress concentrations at the strut joints in lattice structures without any manufacturing effect, while the other accounts for the stress concentrations due to surface defects on the struts introduced by the additive manufacturing process. A simple solid cell, for which the dimensions are the same as those of the lattice cell, is first used to estimate the fatigue life of the bulk material used in the additive manufacturing process using the Brown-Miller strain-life method. Combinations of two stress concentration factors were then utilized to predict the fatigue life of the lattice structure from the equivalent solid model. Using this approach, computationally expensive lattice structure simulations were eliminated, and the fatigue life of the lattice structure was predicted directly from the bulk material fatigue life estimation. The proposed approach was applied to different lattice types made of Ti-6Al-4V alloy using the laser-powder bed fusion additive manufacturing process. The fatigue life results estimated using the proposed approach were in good agreement with the experimental fatigue life results reported in the literature.

This work employed a novel corrosion-based fatigue model to determine the fatigue life of offshore welded structures to enable the fatigue assessment of welds under corrosive conditions. In addition to the material's ultimate strength, endurance limit, and stress ratio (mean stress effect), the model includes a corrosion factor concept to account for the impact of corrosion pits on the fatigue performance of welded S355 steel, which is the novel contribution in this paper. X-ray computed tomography scans of corroded S355 specimens in a salt spray chamber were characterized. Surface texture characterization was employed to obtain surface roughness, size, and aspect ratio of corrosion pits. The corrosion factor was determined based on notch and surface fatigue theories using the characterized pit size, aspect ratio, and surface roughness. Fatigue S-N curves were then predicted for critical pits and compared against the fatigue code DNVGL-RP-C203 and experimental data from the literature. The novel approach combining corrosion characterization method with corrosion-based fatigue model for the prediction of fatigue S-N curves provided a minor deviation of only 2.8% between predicted and measured data. This approach can potentially be integrated into predictive frameworks for the remaining life assessment of offshore structures.

In this study, an efficient fatigue life estimation approach is proposed based on an equivalent solid model, along with two stress concentration factors, instead of a lattice model to simplify simulations for the strain-life method. One of the stress concentration factors accounts for the stress concentrations at the strut joints in lattice structures without any manufacturing effect, while the other accounts for the stress concentrations due to surface defects on the struts introduced by the additive manufacturing process. A simple solid cell, for which the dimensions are the same as those of the lattice cell, is first used to estimate the fatigue life of the bulk material used in the additive manufacturing process using the Brown-Miller strain-life method. Combinations of two stress concentration factors were then utilized to predict the fatigue life of the lattice structure from the equivalent solid model. Using this approach, computationally expensive lattice structure simulations were eliminated, and the fatigue life of the lattice structure was predicted directly from the bulk material fatigue life estimation. The proposed approach was applied to different lattice types made of Ti-6Al-4V alloy using the laser-powder bed fusion additive manufacturing process. The fatigue life results estimated using the proposed approach were in good agreement with the experimental fatigue life results reported in the literature.

When curved glulam beams are subjected to bending, tension perpendicular to grain is introduced. In this work, Monte-Carlo analysis is conducted to study the influence of the annual-ring orientation of individual board on stress concentration in the radial direction. A virtual cutting program is developed which simulates the sawing processes of boards and yields a database of sawn boards, each with a characterized material direction with respect to the pith location. Lamellas are randomly selected from the database to construct curved glulam beams in FE models for Monte-Carlo simulation. Parameters including lumber diameter distribution, taper function, orthotropic elastic properties are considered for four common wood genera in Europe: spruce, pine, larch, and beech. Statistical analysis shows that when the annual-ring effect is considered, the average radial stress in the middle height area of the glulam beams can reach up 1.56 times (even higher on the middle width and height area) compared to the common practice, where wood is usually simplified as transverse isotropic material. Such stress concentration, which can trigger early damage of the structure, indicates an underestimation of stress perpendicular to grain in common practice. Moreover, parameter studies show that the stress redistribution depends not only on the mechanical properties of wood species but also on the width of the board layer., Green Open Access added to TU Delft Institutional Repository ‘You share, we take care!’ – Taverne project https://www.openaccess.nl/en/you-share-we-take-care Otherwise as indicated in the copyright section: the publisher is the copyright holder of this work and the author uses the Dutch legislation to make this work public., Bio-based Structures & Materials

After several decades of constant exploitation of the horizontal bulb turbine, which is an integral part of the hydroelectric power unit, empirically, the formation of a crack occurs in the turbine shaft due to the influence of corrosion, erosion and cavitation. Through experimental tests and calculations it has been determined that values of bending stresses of the turbine, which occur due to the action of fatigue and corrosion, as well as stress concentration, are bigger than 25 MPa for flanges exposed to water, and in other case bigger than 40 MPa for flanges exposed to `corrosive water` and can cause the occurrence of surface cracks on the transition radius between the cylindrical part of the shaft and the flange. It has been determined that stress values in the zone under the influence of bending stresses were bigger than allowable values, which led to the occurrence of many cracks due to fatigue corrosion. One of those cracks caused the failure of the shaft and of the whole turbine.

Designing, constructing and putting into operation a hydroelectric power plant includes complex tasks. Stresses of turbine and hydromechanical equipment of hydro power plants arise during the production of parts and assembly of equipment (residual stresses), in the process of performing functional requirements in exploitation and in the disturbed process of exploitation. After several decades of constant exploitation of the horizontal bulb turbine, which is an integral part of the hydroelectric power unit, empirically, the formation of a crack occurs in the turbine shaft due to the influence of corrosion, erosion and cavitation. Through experimental tests and calculations it has been determined that values of bending stresses of the turbine, which occur due to the action of fatigue and corrosion, as well as stress concentration, are bigger than 25 MPa for flanges exposed to water, and in other case bigger than 40 MPa for flanges exposed to `corrosive water` and can cause the occurrence of surface cracks on the transition radius between the cylindrical part of the shaft and the flange. It has been determined that stress values in the zone under the influence of bending stresses were bigger than allowable values, which led to the occurrence of many cracks due to fatigue corrosion. One of those cracks caused the failure of the shaft and of the whole turbine.

The potential for developing more efficient offshore wind support structures becomes increasingly critical as the offshore wind sector is faced with challenges such as rising commodity prices and shrinking profit margins. These challenges not only impact the industry’s capacity to meet growing global demand but also hinder efforts to address the imperative challenge of decarbonization. As the offshore wind industry expands, the roles of cost-effectiveness and ongoing research will be pivotal in driving the advancement of offshore wind energy on a global scale. The support structure is responsible for supporting the turbine, transferring loads to the ground, and allowing access for inspection and maintenance purposes. The environmental loads acting on an offshore wind support structure (OWSS) result from a combination of waves, wind speed, turbulence intensity acting on the shape of the turbine components. These loads can be grouped in a scatter diagrams that depict the probability of occurrence of a given wind wave combined condition which is also known as a "sea state". Different sea states lead to significant vibrations and stresses on the foundation, which can cause fatigue and failure over time. The perforated monopile consists of a monopile with holes around the splash zone to reduce frontal area, which reduces hydrodynamic loads on the foundation. Assesing the potential of perforated monopiles in deep waters was based on a comparative study of the loads acting on the monopile by developing a model that considers the structural response of the system to different sea states. FEM studies are essential in identifying potential stress concentrations and their effects on the overall integrity and safety of the structure. Thus, analysis focused on assessing the performance of both a reference monopile and a perforated monopile structural models under both parked and power production conditions, including sea states with 50-year and 1-year return pe, Offshore and Dredging Engineering

In all power transmitting machines the shaft-hub connection has a large impact on the overall machine size, if the strength can be increased we can reduce the size. The connection between shaft and hub is a machine element with many possible designs available and described in standards. The connection can be either permanent or changeable, the goal is in all cases to have as high a strength for the connection as possible. Focus is in the present paper on the connections with easy assembly and disassembly, that is, on positive connections (geometrically locked). The designs specified in standards are traditionally made with straight lines and circular arches. Alternatively the involute spline can be used. For this case the cutting tool shape is made with straight lines and circular arches. Present standard designs are not made with minimum stress concentrations as the main objective, other features as for example, easy manufacturing has the primary importance. In the present paper we show how the involute spline design can be significantly improved in relation to strength maximization by reducing the maximum stress. The maximum stress can in many cases be reduced by more than 54% relative to standard design.

Slotted waveguides embedded in aircraft skin panels may not support a buckling load without failure in the copper waveguide due to stress concentrations created by the corners of the slots. To create designs strong enough to avoid compressive failure before buckling instability, an initial offset in the copper waveguide may be added so that the supporting skin cover and backplane take additional load to prevent failure at the waveguide slot corners. A structural model is developed to include a gap in the eigenvalue analysis through a prestress term, and subsequently to account for the gap in an optimization procedure. Additionally, a curve fit is used to account for local buckling modes that reduce the plate buckling mode of the final panel design. These factors combine to allow for a low-fidelity model to account for the gap and local buckling without the need for a high-fidelity model using plate or contact modeling. This low-fidelity model is then run through an optimizer, producing designs that are stronger and/or lighter for a fraction of the computational cost of prior high-fidelity models.

Structural elements of ships are subjected to a high number of cyclic loads, which are critical to fatigue life. Especially for ultra-large container ships the cutting of thick steel plates with high finishing quality and good fatigue life is important, e.g. located at openings in walls and decks of ships. This study presents a series of fatigue tests with 50 mm thick S355 specimens that are thermally gas cut on different shipyards. The obtained stress-life (S-N) curve contains significant horizontal scatter which often occurs for specimens that spend a high number of cycles on crack initiation. However, it is found that both the local stress concentrations and the origin of failure affect the number of load cycles significantly. Accounting for local stress concentrations provides an explanation for the initially encountered scatter in the S-N curves and indicates possible limitations of the nominal stress approach for thermal cut edges., QC 20221125

type:PROCEEDINGS PAPER, Many fatigue damages are occurred in the welded built-up structures designed by the hot spot stress methodology, especially near a boxing fillet weld toe. These fatigue cracks usually initiate from the toe and propagate to the plate thickness direction. / Although fatigue life is affected by the stress gradient working over crack propagation path, the effect of stress gradient in cross section is not considered in the hot spot stress methodology. Then, many attempts based on fracture mechanics for the improvement of fatigue life estimation are proposed. Whereas stress distributions along the fatigue crack path must be given in order to apply the methods based on fracture mechanics for the precise fatigue life prediction, no stress distribution along the path considering the stress concentration caused by weld toe shape is obtained in practical structural design stages because the shell elements are used in finite element analyses in the design stages. / A simple estimation method of the stress distribution normal to cross section at weld toe in non-load carrying welded joints is proposed in this paper. Calculation results of finite element analysis with shell elements and geometrical conditions (radius and flank angle of fillet weld toe and plate thickness) are used as input data for the estimation. The validity of this method is confirmed by comparing estimation results with ones by finite element analysis with solid elements.

This study aims at evaluating the corrosion rate at the first stage of stress corrosion cracking by a numerical simulation. The stress corrosion cracking starts with a pitting corrosion which appears from a damaged portion of passive film induced by plastic deformation. From micromechanical standpoint, the stress and strain are concentrated around the grain boundaries due to the heterogeneity of micro-structures; therefore, the plastic slip occurs mainly around the grain boundaries and generates a fresh surface without passive film. This produces a microcell and affects the macroscopic polarization curve. We obtained this polarization curve of stainless steel from the open-circuit tensile tests associated with the microscopic electrostatic simulations. Moreover, this paper shows the two-dimensional formulation for coupling analysis of elastic stress and electrolytic potential. Both fields are solved by the boundary element method with the discontinuous quadratic element. The strain-dependent polarization curve is used as a nonlinear boundary condition of the potential problem. First, the elastic problem is solved to obtain the surface strain which governs the polarization curve on the surface. Next, the potential prob- lem is solved to obtain the current density on the surface which determines the corrosion rate. Since each node has two corrosion rates in different directions coming from the neighbouring elements, we average these two rates and directions, so as to conserve the volumetric reduction rate unchanged. After moving the nodes as a result of corrosion during the time step, we return to the stress analysis and iterate this procedure during the interested period of time. We demonstrate a corrosion pit growth from a small hemi-elliptic surface defect and show the availability of the proposed method., source:https://www.witpress.com/elibrary/cmem-volumes/9/1/2750

This study aims at evaluating the corrosion rate at the first stage of stress corrosion cracking by a numerical simulation. The stress corrosion cracking starts with a pitting corrosion which appears from a damaged portion of passive film induced by plastic deformation. From micromechanical standpoint, the stress and strain are concentrated around the grain boundaries due to the heterogeneity of micro-structures; therefore, the plastic slip occurs mainly around the grain boundaries and generates a fresh surface without passive film. This produces a microcell and affects the macroscopic polarization curve. We obtained this polarization curve of stainless steel from the open-circuit tensile tests associated with the microscopic electrostatic simulations. Moreover, this paper shows the two-dimensional formulation for coupling analysis of elastic stress and electrolytic potential. Both fields are solved by the boundary element method with the discontinuous quadratic element. The strain-dependent polarization curve is used as a nonlinear boundary condition of the potential problem. First, the elastic problem is solved to obtain the surface strain which governs the polarization curve on the surface. Next, the potential prob- lem is solved to obtain the current density on the surface which determines the corrosion rate. Since each node has two corrosion rates in different directions coming from the neighbouring elements, we average these two rates and directions, so as to conserve the volumetric reduction rate unchanged. After moving the nodes as a result of corrosion during the time step, we return to the stress analysis and iterate this procedure during the interested period of time. We demonstrate a corrosion pit growth from a small hemi-elliptic surface defect and show the availability of the proposed method., source:https://www.witpress.com/elibrary/cmem-volumes/9/1/2750

The use of threaded inserts embedded in plastic parts is very common in variety of industries including electronics, automotive, aerospace, medical, transportation, defense etc., particullary where frequent assembly and disassembly are required. Performed technique of placement the inserts in specimens is heat staking - pressing the heated insert into the mounting hole to melt the material surrounding the insert. Specimens were made of PLA and obtained using a commercial Creality Ender-6 3D printer. The square-shaped samples have dimensions of 20 x 20 x 4 [mm] with a 4.6 [mm] diameter central hole for placing brass inserts with M3 thread.

The use of threaded inserts embedded in plastic parts is very common in variety of industries including electronics, automotive, aerospace, medical, transportation, defense etc., particularly where frequent assembly and disassembly are required. Performed technique of placement the inserts in specimens is heat staking - pressing the heated insert into the mounting hole to melt the material surrounding the insert. Specimens were made of PLA and obtained using a commercial Creality Ender-6 3D printer. The square-shaped samples have dimensions of 20 x 20 x 4 [mm] with a 4.6 [mm] diameter central hole for placing brass inserts with M3 thread.

Offshore or drydock inspection performed by trained surveyors is required within the integrity management of an in-service marine structure to ensure safety and fitness for purpose. However, these physical inspection activities can lead to a considerable increase in lifecycle cost and significant downtime, and they can impose hazards for the surveyors. To this end, the use of a structural health monitoring (SHM) system could be an effective resolution. One of the key performance indicators of an SHM system is its ability to predict the structural response of unmonitored locations by using monitored data, i.e., an inverse prediction problem. This is highly relevant in practical engineering, since monitoring can only be performed at limited and discrete locations, and it is likely that structurally critical areas are inaccessible for the installation of sensors. An accurate inverse prediction can be achieved, ideally, via a dense sensor network such that more data can be provided. However, this is usually economically unfeasible due to budget limits. Hence, to improve the monitoring performance of an SHM system, an optimal sensor placement should be developed. This paper introduces a framework for optimising the sensor placement scheme to support SHM. The framework is demonstrated with an illustrative example to optimise the sensor placement of a cantilever steel plate. The inverse prediction problem is addressed by using a radial basis function approach, and the optimisation is carried out by means of an evolutionary algorithm. The results obtained from the demonstration support the proposal., Ship Design, Production and Operations

Low dimensional sp3 carbon nanostructures have attracted increasing attention recently, due to their unique properties and appealing applications. Based on in silico studies, this work exploits the impacts from functional groups on the tensile properties of carbon nanothreads (NTH) – a new sp3 carbon nanostructure. It is found that functional groups will alter the local bond configuration and induce initial stress concentration, which significantly reduces the fracture strain/strength of NTH. Different functional types lead to different local bond re-configurations, and introduce different impacts on NTH. Further studies reveal that the tensile properties decreases generally when the content of functional groups increases. However, some NTHs with higher content of functional groups exhibit higher fracture strain/strength than their counterparts with lower percentage. Such observations are attributed to the synergetic effects from the sample length, self-oscillation, and distribution of functional groups. Simulations show that the tensile behaviour of NTH with the same functional percentage differs when the distribution pattern varies. Overall, ethyl groups are found to induce larger degradation on the tensile properties of NTH than methyl and phenyl groups. This study provides a comprehensive understanding of the influence from functional groups, which should be beneficial to the engineering applications of NTH.

A parking garage of Eindhoven airport partially collapsed in 2017. It was caused by failure of the longitudinal joint (long-side) of the composite plank floor or breedplaatvloer on the roof level. Experimental and numerical research showed that the joint suffered high positive bending moment in its transverse direction. However, from the investigation results, there was not enough resistance at the concrete-to-concrete interface around the joint to transfer the tensile force from the precast to the cast-in-situ section, which led to delamination of the two layers of concrete and resulting in failure when the delamination crack reaches the end of the coupling reinforcements. As happened in that case, the concrete-to-concrete interface usually is the weakest link and has a critical role on behaviour of a composite concrete system, especially the one which has unreinforced interface (no stirrup near joint). Further studies have been conducted to understand the influence of various details around the joint on the interface behaviour. In this thesis, details in spacing between lap splices (coupling reinforcements in cast-in-situ layer and bottom reinforcements in precast layer), spacing between connecting reinforcements (stirrups crossing the interface near the joint), the role of connecting reinforcement, and the sensitivity of interface parameters were studied numerically using DIANA finite element analysis software. Since the spacings are in direction of the specimen’s width, interface behaviour was analysed in both longitudinal and transverse directions. An additional study about compressive membrane action or arching was also conducted to understand the influence of lateral restraint, which usually occurs in composite plank floor systems used in buildings, including the one used in Eindhoven parking garage, to the capacity of the structure. This action was suspected of providing additional strength to the existing composite plank floor Two composite SHCC-c, Civil Engineering | Structural Engineering

Current standards related to welded joint defects (EN ISO 5817) only consider individual cases (i.e., single defect in a welded joint). The question remains about the behaviour of a welded joint in the simultaneous presence of several different types of defects, so-called multiple defects, which is the topic of this research. The main focus is on defects most commonly encountered in practice, such as linear misalignments, undercuts, incomplete root penetration, and excess weld metal. The welding procedure used in this case was metal active gas welding, a common technique when it comes to welding low-alloy low-carbon steels, including those used for pressure equipment. Different combinations of these defects were deliberately made in welded plates and tested in a standard way on a tensile machine, along with numerical simulations using the finite element method (FEM), based on real geometries. The goal was to predict the behaviour in terms of stress concentrations caused by geometry and affected by multiple defects and material heterogeneity. Numerical and experimental results were in good agreement, but only after some modifications of numerical models. The obtained stress values in the models ranged from noticeably lower than the yield stress of the used materials to slightly higher than it, suggesting that some defect combinations resulted in plastic strain, whereas other models remained in the elastic area. The stress-strain diagram obtained for the first group (misalignment, undercut, and excess root penetration) shows significantly less plasticity. Its yield stress is very close to its ultimate tensile strength, which in turn is noticeably lower compared with the other three groups. This suggests that welded joints with misalignment and incomplete root penetration are indeed the weakest of the four groups either due to the combination of the present defects or perhaps because of an additional unseen internal defect. From the other three diagrams, it can be conc

A parking garage of Eindhoven airport partially collapsed in 2017. It was caused by failure of the longitudinal joint (long-side) of the composite plank floor or breedplaatvloer on the roof level. Experimental and numerical research showed that the joint suffered high positive bending moment in its transverse direction. However, from the investigation results, there was not enough resistance at the concrete-to-concrete interface around the joint to transfer the tensile force from the precast to the cast-in-situ section, which led to delamination of the two layers of concrete and resulting in failure when the delamination crack reaches the end of the coupling reinforcements. As happened in that case, the concrete-to-concrete interface usually is the weakest link and has a critical role on behaviour of a composite concrete system, especially the one which has unreinforced interface (no stirrup near joint). Further studies have been conducted to understand the influence of various details around the joint on the interface behaviour. In this thesis, details in spacing between lap splices (coupling reinforcements in cast-in-situ layer and bottom reinforcements in precast layer), spacing between connecting reinforcements (stirrups crossing the interface near the joint), the role of connecting reinforcement, and the sensitivity of interface parameters were studied numerically using DIANA finite element analysis software. Since the spacings are in direction of the specimen’s width, interface behaviour was analysed in both longitudinal and transverse directions. An additional study about compressive membrane action or arching was also conducted to understand the influence of lateral restraint, which usually occurs in composite plank floor systems used in buildings, including the one used in Eindhoven parking garage, to the capacity of the structure. This action was suspected of providing additional strength to the existing composite plank floor Two composite SHCC-c, Civil Engineering | Structural Engineering

In machine elements many different methods for connecting shaft and hub are specified in different standards. A not so common shaft–hub connection is the polygon profile as specified in DIN 32711 (P3G) and DIN 32712 (P4C). This type of connection is an alternative to key or spline connections. The practical point of the connection is the easy assembly and disassembly, but as for all shaft–hub connections the drawback is the high stress leading to a limited strength of these connections. The polygon connection design is to some extent due to an old production method, i.e. it is not design/ optimized for reducing the maximum stress. In the present paper it is shown how the connection strength can be improved significantly by the use of shape optimization. The focus here is both on the highest contact stress (compression) but also on the largest tensile stress. Overall reduction in the stress in the order of 20% to 40% is found relative to standard design.

The article presents specialized software methods for reducing stress concentration. Objects of study are cylindrical test specimens subjected to axial loading. Notching with different shapes and sizes on the specimens were formed to reduce the stresses in the endangered areas. The geometric parameters of notches identified through the specialized built-in modules to the ANSYS software. An analysis performed were to show the influence of stresses acting on the fatigue limit during different cycles. The results of the study were present in a graphical form.

Steel corrosion is a predominant factor leading to age-related structural degradation. To understand the different effects of pitting corrosion on the mechanical performances of deformed carbon and stainless steel reinforcing bars, an artificially accelerated method was conducted to corrode the steel bars. Using a 3D laser scanner, the three-dimensional models of corroded steel bars were reconstructed. The corrosion characterization was identified based on these 3D profiles. The results indicate that the number and the depth of corrosion pits of both types of steel increase with the increase of corrosion rate, however the pitting corrosion of stainless steel is much more obvious than the carbon steel. Axial tensile tests of corroded carbon and stainless steel bars were carried out. The tensile test results show that both the yield and ultimate loads linearly decreased with an increase of corrosion loss while the ductility decreased correspondingly. With the increase of corrosion loss, brittle fracture gradually occurred in the corroded carbon steel bars at the location of critical cross-sectional area. However, the degradation ratio of elongation of stainless steel is less than that of the carbon steel.

Numerical simulations of blood flow through a partially-blocked axisymmetric artery are performed to investigate the stress distributions in the plaque. We show that the combined effect of stenosis severity and the stiffness of the lipid core can drastically change the axial stress distribution, strongly affecting the potential sites of plaque rupture. The core stiffness is also an important factor when assessing plaque vulnerability, where a mild stenosis with a lipid-filled core presents higher stress levels than a severe stenosis with a calcified plaque. A shorter lipid core gives rise to an increase in the stress levels. However, the fibrous cap stiffness does not influence the stress distributions for the range of values considered in this work. Based on these mechanical analyses, we identify potential sites of rupture in the axial direction for each case: the midpoints of the upstream and downstream regions of the stenosis (for severe, lipid-filled plaques), the ends of the lipid core (for short cores), and the middle of the stenosis (for mild stenoses with positive remodelling of the arterial wall)., QC 20200427

This subject mainly uses Aluminum sheet metal material as the research object which is used in Volvo XC90 door, the elastic plasticity deformation within the different material angles and notch shape investigated with MTS tensile test equipment under uniaxial tension. The local strain curve studied by using DIC method to obtain the conventional physical quantity. Combining ABAQUS to analyze the distribution of stress in elastic and plastic regions, also use MATLAB to combine various parameters, and finally analyze the desired experimental results to find a relatively stable notch shape based on the yield curve and stress concentration factor.

As the transmission capacity of gas insulated transmission line (GIL) increases, the synergistic improvement in dielectric and mechanical strengths of GIL insulators is urgently needed for the development of advanced power systems. Mechanical defects in power equipment are prone to induce discharges during high voltage operations, which need to be mitigated. In this paper, the strains on the GIL insulator surface are measured by fiber Bragg grating (FBG) strain sensors during hydrostatic tests. An abnormal change of strain is detected near the interface between center conductor and the spacer. The numerical results of stress distributions of GIL insulator during manufacturing and high-voltage operation are calculated by the finite element method. The results indicate that the mechanical stresses are concentrated at the interface, which lead to the development of conductor-spacer interface separation. In addition, based on the hydrostatic test and the FEM calculations, the dielectric interfacial strength, including the electric field distribution, and flashover are investigated by a combination of numerical and experimental studies. The results indicate that the air gaps generated by the separated interface distort the electric field at the tip of the gap, which is likely to cause discharges and reduce the gas-solid interfacial flashover strength of the insulator, placing concerns of insulation failure and even operating failures of GIL. This work sheds light on the importance of interfacial structure of power equipment and will guide the design and the manufacture of GIL insulator.

This paper presents an analytical model to predict the stress redistribution around broken fibres in hybrid polymer composites. The model is used under the framework of a progressive failure approach to study the load redistribution around breaks in hybrid composites. The outcomes of the model are validated by comparing it with a spring element model. Moreover, the approach is further used to study the tensile behaviour of different hybrid composites. The results obtained show that the load redistribution around breaks depends on the stiffness ratio between both fibres as well as the matrix behaviour considered and the hybrid volume fraction. Furthermore, the different material parameters have a large effect on the tensile behaviour, with an increase of ductility achieved if the failure process of the two fibres is gradual., Postprint (published version)

This subject mainly uses Aluminum sheet metal material as the research object which is used in Volvo XC90 door, the elastic plasticity deformation within the different material angles and notch shape investigated with MTS tensile test equipment under uniaxial tension. The local strain curve studied by using DIC method to obtain the conventional physical quantity. Combining ABAQUS to analyze the distribution of stress in elastic and plastic regions, also use MATLAB to combine various parameters, and finally analyze the desired experimental results to find a relatively stable notch shape based on the yield curve and stress concentration factor.

This study aims to develop a closed-form methodology for estimating the resultant forces in a finite composite plate, weakened by the presence of elliptical cutouts, under membrane loads. Following an innovative approach, the developed methodology can deal, in the presence of cutouts, with a non-uniform lay-up distribution in the plate. To this end, different laminate features, including the stacking sequence, thickness, and even local reinforcements, will be considered as variable inputs. The main motivation behind this research is to increase the range of applicability of the closed-form methodologies devoted to the structural analysis of composite plates with cutouts, with the purpose of using the present methodology in the first phases of component design

22nd European Conference on Fracture, ECF (2018: Metropol Palace Belgrade, Serbia), Unidirectional composites are very popular structural materials used in aerospace, marine, energy and automotive industries, thanks to their superior material properties. However, the mechanical behavior of composite materials is more complicated than isotropic materials because of their anisotropic nature. Also, stress concentration presence on the structure, like a hole, makes the problem further complicated. Therefore, enormous numbers of tests are required in understanding the mechanical behavior and strength of composites which contain stress concentration. Accurate finite element analysis and analytical models enable us to understand mechanical behavior and predict the strength of composites without enormous number of tests which cost serious time and money. In this study, unidirectional Carbon/Epoxy composite specimens with central circular holes were investigated in terms of stress concentration factor and strength prediction. The composite specimens which had different specimen width (W) to hole diameter (D) ratio were tested to investigate the effect of hole size on the stress concentration and strength. Also, specimens which had same specimen width to hole diameter ratio, but different sizes were tested to investigate the size effect. Finite element analysis were performed to determine the stress concentration factor for all specimen configurations. Also, Point stress criteria (PSC) was used to predict strength of the specimens. For quasi-isotropic laminate, it was found that the stress concentration factor at the hole tip increases approximately %15 as W/D ratio decreased from 6 to 3. Also, it is observed that as W/D ratio quadrupled with constant specimen width the failure strength increases by %62.4. For the specimens which had same width to hole diameter ratio but different (scaled) dimensions, the stress concentration factor at the hole tip was seen to be identical as expected. For these specimens, as W/D ratio doubled the specimen failure strength r, This study is funded by Defense Industry Undersecretariat (SSM) under Researcher Training Program for Defense Industry (SAYP)

22nd European Conference on Fracture, ECF (2018: Metropol Palace Belgrade, Serbia), Unidirectional composites are very popular structural materials used in aerospace, marine, energy and automotive industries, thanks to their superior material properties. However, the mechanical behavior of composite materials is more complicated than isotropic materials because of their anisotropic nature. Also, stress concentration presence on the structure, like a hole, makes the problem further complicated. Therefore, enormous numbers of tests are required in understanding the mechanical behavior and strength of composites which contain stress concentration. Accurate finite element analysis and analytical models enable us to understand mechanical behavior and predict the strength of composites without enormous number of tests which cost serious time and money. In this study, unidirectional Carbon/Epoxy composite specimens with central circular holes were investigated in terms of stress concentration factor and strength prediction. The composite specimens which had different specimen width (W) to hole diameter (D) ratio were tested to investigate the effect of hole size on the stress concentration and strength. Also, specimens which had same specimen width to hole diameter ratio, but different sizes were tested to investigate the size effect. Finite element analysis were performed to determine the stress concentration factor for all specimen configurations. Also, Point stress criteria (PSC) was used to predict strength of the specimens. For quasi-isotropic laminate, it was found that the stress concentration factor at the hole tip increases approximately %15 as W/D ratio decreased from 6 to 3. Also, it is observed that as W/D ratio quadrupled with constant specimen width the failure strength increases by %62.4. For the specimens which had same width to hole diameter ratio but different (scaled) dimensions, the stress concentration factor at the hole tip was seen to be identical as expected. For these specimens, as W/D ratio doubled the specimen failure strength r, This study is funded by Defense Industry Undersecretariat (SSM) under Researcher Training Program for Defense Industry (SAYP)

This study aims to develop a closed-form methodology for estimating the resultant forces in a finite composite plate, weakened by the presence of elliptical cutouts, under membrane loads. Following an innovative approach, the developed methodology can deal, in the presence of cutouts, with a non-uniform lay-up distribution in the plate. To this end, different laminate features, including the stacking sequence, thickness, and even local reinforcements, will be considered as variable inputs. The main motivation behind this research is to increase the range of applicability of the closed-form methodologies devoted to the structural analysis of composite plates with cutouts, with the purpose of using the present methodology in the first phases of component design

The present paper describes numerical and experimental methodology for the analysis of stress and deformation state in structural elements with geometrical discontinuities. The research is based on structural elements of the connecting lug type. The stress and deformation state was determined as the contact area size between the axle and the connecting lug was changing. Numerical analysis was conducted by applying the finite element method in a ''KOMIPS'' software package. Experiments were performed at the Laboratory for stress and deformation measurements, Faculty of Mechanical Engineering, University of Belgrade, using ''GOM'' equipment and ''ARAMIS'' software application (DIC). This paper demonstrates how it is possible to anticipate the results by applying FEM. A short review of current research in the field of structural elements with geometrical discontinuities is given within the framework of the paper.

This subject mainly uses Aluminum sheet metal material as the research object which is used in Volvo XC90 door, the elastic plasticity deformation within the different material angles and notch shape investigated with MTS tensile test equipment under uniaxial tension. The local strain curve studied by using DIC method to obtain the conventional physical quantity. Combining ABAQUS to analyze the distribution of stress in elastic and plastic regions, also use MATLAB to combine various parameters, and finally analyze the desired experimental results to find a relatively stable notch shape based on the yield curve and stress concentration factor.

This subject mainly uses Aluminum sheet metal material as the research object which is used in Volvo XC90 door, the elastic plasticity deformation within the different material angles and notch shape investigated with MTS tensile test equipment under uniaxial tension. The local strain curve studied by using DIC method to obtain the conventional physical quantity. Combining ABAQUS to analyze the distribution of stress in elastic and plastic regions, also use MATLAB to combine various parameters, and finally analyze the desired experimental results to find a relatively stable notch shape based on the yield curve and stress concentration factor.

This subject mainly uses Aluminum sheet metal material as the research object which is used in Volvo XC90 door, the elastic plasticity deformation within the different material angles and notch shape investigated with MTS tensile test equipment under uniaxial tension. The local strain curve studied by using DIC method to obtain the conventional physical quantity. Combining ABAQUS to analyze the distribution of stress in elastic and plastic regions, also use MATLAB to combine various parameters, and finally analyze the desired experimental results to find a relatively stable notch shape based on the yield curve and stress concentration factor.

Steel corrosion is a predominant factor leading to age-related structural degradation. To understand the different effects of pitting corrosion on the mechanical performances of deformed carbon and stainless steel reinforcing bars, an artificially accelerated method was conducted to corrode the steel bars. Using a 3D laser scanner, the three-dimensional models of corroded steel bars were reconstructed. The corrosion characterization was identified based on these 3D profiles. The results indicate that the number and the depth of corrosion pits of both types of steel increase with the increase of corrosion rate, however the pitting corrosion of stainless steel is much more obvious than the carbon steel. Axial tensile tests of corroded carbon and stainless steel bars were carried out. The tensile test results show that both the yield and ultimate loads linearly decreased with an increase of corrosion loss while the ductility decreased correspondingly. With the increase of corrosion loss, brittle fracture gradually occurred in the corroded carbon steel bars at the location of critical cross-sectional area. However, the degradation ratio of elongation of stainless steel is less than that of the carbon steel.

This subject mainly uses Aluminum sheet metal material as the research object which is used in Volvo XC90 door, the elastic plasticity deformation within the different material angles and notch shape investigated with MTS tensile test equipment under uniaxial tension. The local strain curve studied by using DIC method to obtain the conventional physical quantity. Combining ABAQUS to analyze the distribution of stress in elastic and plastic regions, also use MATLAB to combine various parameters, and finally analyze the desired experimental results to find a relatively stable notch shape based on the yield curve and stress concentration factor.

A pinned connection or lug joint is a common connection type used both in civil engineering and mechanical engineering. In civil engineering, this connection is used for assembling truss members, and in mechanical engineering, this connection type is widely used in machine elements. The standard design is with a circular pin. The stress concentration factor size depends on the tolerances between pin and assembled parts and also by the three-dimensional design. Relatively different maximum stress values are seen depending on the modelling being done in two dimension (with assumptions) or in full three dimension. The focus in the present article is on the two-dimensional design and minimizing the maximum stress. It is shown that not only the contact geometry is important for reducing the stress, the external design is equally important. By finite element analysis including contact modelling, it is shown that reduction in the stress concentration factor of up to 18% is possible.

Energy absorption is a critical consideration in the design of porous structures design. This work studied the energy absorption mechanism of three porous structures (i.e. cubic, topology optimised and rhombic dodecahedron) at the early stage of deformation. Stress distribution results, obtained by finite element modelling, coupled with the investigation of the slip bands generated have been used to reveal the plasticity mechanism and local stress concentrations for each structure. The topology optimised structure exhibits the best balance of bending and buckling stress with a high elastic energy absorption, a low Young's modulus (~2.3 GPa) and a high compressive strength (~58 MPa).

Актуальність теми. Хрестові зварні з'єднання з конструктивною особливістю складання «в зуб» є елементом секцій захисних екранів для броньованих машин. Секції захисних екранів являють собою плоскі решітчасті зварні конструкції, які складаються зі сталевої полоси, товщина та ширина якої, а також відстані між її вертикальними і горизонтальними ребрами, обираються з умов забезпечення необхідної стійкості під час ударної взаємодії з протитанковою гранатою та належної руйнівної дії по її бойовій частині. Полоси з’єднуються між собою «в зуб» електродуговим зварюванням плавким електродом у захисному газі за допомогою кутових швів. Встановлено, що ефективний захист броньованої військової техніки від пробиття сучасними гранатами можливий лише у разі часткового або повного руйнування бойової частини гранати при її взаємодії із елементами екрану і, таким чином, попередження формування кумулятивного струменю та спрацювання протитанкового засобу у штатному режимі. При цьому деформаційно-ріжуча дія робочого елементу захисного екрану на бойову частину засобу ураження залежить від твердості та міцності застосованого матеріалу, стійкості та жорсткості зварної конструкції екрану. Застосування високоміцних сталей для виготовлення зварних протикумулятивних екранів зумовлює високий рівень залишкових напружень у зварному виробі, які можуть сприяти утворенню і розвитку тріщин, а також спричинити руйнування виробу з необхідністю його подальшого ремонту. Таким чином, актуальність даної роботи полягає у обґрунтуванні можливості використання низьковуглецевих сталей, замість високоміцних легованих сталей на основі порівняльного аналізу параметрів залишкових напружено-деформованих станів, визначених методом скінченних елементів для зварних вузлів решітчастої конструкції, виготовлених зі сталей трьох різних марок: низьковуглецевих ко нструкційних сталей звичайної якості Ст3пс і 09Г2С з границею міцності 490 МПа і 590 МПа та високоміцної низьколегованої сталі 30ХГСА у термообробленому стані з гран, Topic Relevance. Cruciform welded joints with the design feature of «in tooth" assembly are an integral part of the anti-shape effect shields for armored vehicles. Sections of the anti-shape effect shields are flat gridded weld structure, which consist of the steel band, the width and thickness of witch, and distance between vertical and horizontal edges are chosen according to required stability during the hit impact from the high explosive anti-tank projectiles and appropriate destruction action over its warhead. Bands are joined together “in tooth” by the electro-arc welding with the consumable electrode in shielded gas with the use of the fillet welds. It has been established that effective protection of armored military vehicles against penetration of the modern grenade is possible only in case of partial or complete destruction of grenade warhead when it interacts with the elements of the anti-shape effect shields and, thus, preventing the formation of shape charge focused jet and triggering of the explosive anti-tank projectiles in regular mode. Wherein, the deformation-cutting action of the working element of the anti-shape effect shields on the combat part of the warhead depends on the hardness and strength of the applied material, the stabil ity and rigidity of the welded anti-shape effect shields structure. The usage of high-strength steels for manufacturing of the welded anti-shape effect shields leads to a high level of residual stresses in the welded structures, which may contribute to the formation and development of cracks, as well as to cause the destruction of the product with the need of its subseque nt repair. Therefore, the relevance of this work is in substantiation of the possibility of using low-carbon steels instead of high-strength alloy steels based on a comparative analysis of the residual stress-strain states parameters determined by the finite element method for weld joints of the gridded type weld structure manufactured from steels of

Researchers in the field of fracture mechanics, predominantly developing appropriate solution algorithms for problems of solid bodies with cracks. Problems in mechanics generally, related with fracture and fatigue for solid bodies with various geometries of sharp notches, are studied to a much lesser extent. This situation can be explained by analytical difficulties arising in solving problems of elasticity theory for bodies with rounded notches. To solve problems of such class, starting from data on stress concentration in the rounded notch tip with a significant radius of curvature, simplified solutions with are therefore of great importance. Recent years, due to constant rise of computing power and development of numerical methods, re-evaluation of stress concentration factors from a viewpoint of theory of elasticity is present. This is mainly as a feedback from industry, which have requirements toward mega and nanostructures. Corrosion represents an important limitation to the safe and reliable use of many alloys in various industries. Pitting corrosion is a form of serious damage on metals surface such as high-strength aluminum alloys and stainless steel, which are susceptible to pitting when exposed to a corrosive attack in aggressive environments. This is particularly valid for dynamic loaded structures. The basic idea behind this paper is finding links between different scientific and engineering disciplines, which will enable useful level of applicability of existing knowledge. The subject of this paper is application of new method of determine length scale parameter for estimating the mechanistic aspect of corrosion pit under uniaxial/multiaxial high-cycle fatigue loading….

A crack occurred on gusset plate of pylon vertical truss of bucket wheel excavator (BWE) SchRs630. Numerical calculation model of pylons, slewing platform and undercarriage was formed. Calculations are done using finite element method (FEM) for different load cases. It was determined that the inertial forces caused by bucket wheel boom and counterweight boom masses while breaking slew drive cause the stress concentration in this spot. To complete the whole picture of the structure behaviour dynamic analysis was performed. Based on calculation and distribution of potential and kinetic energy on oscillation modes, using the reanalysis method, redesign of this part of the structure was proposed. The stress was reduced by over 20 % by the proposed redesign solution.

Researchers in the field of fracture mechanics, predominantly developing appropriate solution algorithms for problems of solid bodies with cracks. Problems in mechanics generally, related with fracture and fatigue for solid bodies with various geometries of sharp notches, are studied to a much lesser extent. This situation can be explained by analytical difficulties arising in solving problems of elasticity theory for bodies with rounded notches. To solve problems of such class, starting from data on stress concentration in the rounded notch tip with a significant radius of curvature, simplified solutions with are therefore of great importance. Recent years, due to constant rise of computing power and development of numerical methods, re-evaluation of stress concentration factors from a viewpoint of theory of elasticity is present. This is mainly as a feedback from industry, which have requirements toward mega and nanostructures. Corrosion represents an important limitation to the safe and reliable use of many alloys in various industries. Pitting corrosion is a form of serious damage on metals surface such as high-strength aluminum alloys and stainless steel, which are susceptible to pitting when exposed to a corrosive attack in aggressive environments. This is particularly valid for dynamic loaded structures. The basic idea behind this paper is finding links between different scientific and engineering disciplines, which will enable useful level of applicability of existing knowledge. The subject of this paper is application of new method of determine length scale parameter for estimating the mechanistic aspect of corrosion pit under uniaxial/multiaxial high-cycle fatigue loading….

Recent X-ray diffraction (XRD) measurements have revealed that plastic deformation and a residual elastic strain field can be present around the graphite particles in ductile cast iron after manufacturing, probably due to some local mismatch in thermal contraction. However, as only one component of the elastic strain tensor could be obtained from the XRD data, the shape and magnitude of the associated residual stress field have remained unknown. To compensate for this and to provide theoretical insight into this unexplored topic, a combined experimental-numerical approach is presented in this paper. First, a material equivalent to the ductile cast iron matrix is manufactured and subjected to dilatometric and high-temperature tensile tests. Subsequently, a two-scale hierarchical top-down model is devised, calibrated on the basis of the collected data and used to simulate the interaction between the graphite particles and the matrix during manufacturing of the industrial part considered in the XRD study. The model indicates that, besides the viscoplastic deformation of the matrix, the effect of the inelastic deformation of the graphite has to be considered to explain the magnitude of the XRD strain. Moreover, the model shows that the large elastic strain perturbations recorded with XRD close to the graphite–matrix interface are not artifacts due to e.g. sharp gradients in chemical composition, but correspond to residual stress concentrations induced by the conical sectors forming the internal structure of the graphite particles. In contrast to common belief, these results thus suggest that ductile cast iron parts cannot be considered, in general, as stress-free at the microstructural scale.

Although in scientific literature there are studies regarding the inclusion of relief grooves in order to diminish the amount of stress concentration in stepped shafts, the incorporation of optimization algorithms capable of parametrically determining their geometry remains unexplored. In this paper, an approach to the problem of size optimization of shoulder filleted shafts with relief grooves and subject to axial loads is presented. The objective of the optimization is to minimize the maximum value of stress at both, the root of the shoulder fillet, and the root of the groove, thus minimizing stress concentration and improving fatigue life of such elements. Under this methodology, different percentages of reduction of stress are achieved for the shafts with relief grooves, in comparison with the shafts without relief grooves. The novelty of this approach lies in the incorporation of an algorithm for the determination of the optimum geometry of the grooves., Aun cuando en la literatura científica se puede hallar artículos sobre la inclusión de ranuras de alivio para disminuir el nivel de concentración de esfuerzo en flechas escalonadas, la incorporación de algoritmos de optimización capaces de determinar su geometría de manera paramétrica permanece sin explorarse. En este artículo se presenta un enfoque al problema de optimización de tamaño de flechas escalonadas con ranuras de alivio, sujetas a cargas axiales. El objetivo de la optimización es minimizar el valor máximo del esfuerzo, tanto en la raíz del escalón como en la raíz de la ranura, disminuyendo la concentración de esfuerzo y mejorando la vida a la fatiga de tales elementos mecánicos. Bajo esta metodología, se alcanzan diversos porcentajes de reducción del esfuerzo al comparar las flechas ranuradas con las flechas no ranuradas. El enfoque aporta la incorporación de un algoritmo para la determinación de la geometría óptima de las ranuras de alivio.