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The paper presents the validation of two multiaxial fatigue criteria with the implemented concept of life dependent material parameters. The recent research exhibits that an application of damage parameter defined by multiaxial fatigue criterion to lifetime calculation requires substituting material constants with the fatigue characteristic. The damage parameter is compared with the stress amplitude of given fatigue characteristic and in the result, the fatigue life is calculated. Since the introduced fatigue characteristics are also the function of a number of cycles to failure the calculation process of the final lifetime becomes complex. This life depended material parameter concept was successfully implemented into a few well-known fatigue criteria. The main aim of the paper is the validation of two multiaxial fatigue criteria under high cycle fatigue regime with the application of the life dependent material parameters.

In the present work, two-component ductile fracture criteria with high estimation accuracy were established. They were formulated by using a weighted superposition of the existing ductile fracture criteria as basic components, which possessed the same form but different parameters. The flexibility of new criteria was greatly enhanced because of increased material constants. The micro-mechanism-inspired DF2012 criterion and its improved form of DF2014 criterion were chosen as the basic components, respectively. Based on the established criteria, the fracture surfaces of aluminum alloys 2024-T351 in various stress and strain spaces were constructed and compared with those constructed by the single-component criteria. The results showed that the two-component criteria have better prediction accuracy than the single-component counterparts, especially for the tests at high stress triaxiality region. Due to the shear-linking assumption, fracture strains constructed by the single-component DF2012 and DF2014 criteria at high stress triaxiality region inevitably carried large errors. However, these errors were largely reduced by the established two-component criteria. It indicates that the two-component criteria can overcome some inherent shortcomings of the single-component criteria, which is an effective solution to promote the fracture estimation accuracy.

For engine components under complex loadings, multiaxial fatigue life prediction is critical for ensuring their structural integrity and reliability. Combining the critical plane method with the virtual strain energy concept, a new multiaxial fatigue damage parameter is proposed to characterize the influence of both shear/normal mean stress and non-proportional hardening on fatigue life. Particularly, no extra material constants are needed for model application. Experimental data of TC4 and GH4169 alloys under various loading paths are utilized to evaluate and validate the proposed damage parameter as well as four other models. Results show that the proposed damage parameter yields a higher accuracy on multiaxial fatigue life prediction than others.

Time-Domain Terahertz Spectroscopy (TDTS) is a rapidly developing measurement technique constantly finding new applications in various areas of materials science such as measurements of material constants of solids [1]. Terahertz frequencies i.e. frequencies from tens of GHz to few THz, lay between the operation ranges of classical microwave and infrared spectroscopy and thus cannot be effectively covered by any of these techniques. TDTS fills this gap enabling the study of materials properties in the part of the electromagnetic spectrum that is of a particular interest for the materials science [2, 4]. TDTS is the only applicable far-infrared spectroscopic technique. Far infrared imaging based on TDTS is currently an extremely promising way of non-destructive method for testing samples from substances. In the proposed article there are presented the results of measurements we have made upon some pharmaceuticals and pesticides, using our own experimental setup for TDTS.

Compared to ordinary Portland cement-based concrete (OPC), geopolymer concrete (GPC) is an environmental-friendly construction material because it is mixed by replacing Portland cement with industry wastes such as fly ash. Despite intensive researches in the last two decades, application of geopolymer concrete in construction is still rather limited. One of the reasons is the quasi-static and dynamic material properties of geopolymer concrete, which are different from those of ordinary Portland-cement concrete, are not well defined yet, and the available design guides for geopolymer concrete structures are very limited. The existing design guides and dynamic constitutive models for OPC cannot be directly employed in design analysis and numerical modelling of GPC structures subjected to blast and impact loads. This paper first summaries the available dynamic material testing data on GPC, compares them with the widely used dynamic constitutive models for OPC, and discusses the suitability of those models for modelling GPC structures. Then, based on the available GPC material testing data, new material constants for strength model, equation of state and dynamic increase factors are derived for GPC. Finally numerical modellings are carried out using these material models with modifications for GPC material to examine their accuracies in simulating the dynamic responses and damages of structural components made of GPC subjected to blast and impact loads.

The article presents the characteristics of 1.3964 steel and the results of firing a 7.62 mm projectile with a steel core. A simplified Johnson&ndash, Cook material model for steel and projectile was used. Then, a FEM (finite element method) simulation was prepared to calibrate the material constants and boundary conditions necessary to be used in simulations of the entire hull model. It was checked how projectile modeling affects the FEM calculation results. After obtaining the simulation results consistent with the experimental results, using the model of a modern minehunter, the resistance of the ship&rsquo, s hull to penetration by a small-caliber projectile was tested.

Due to the complex nature of woven fabrics, biaxial testing forms an integral part of designing lightweight fabric structures. By mimicking the multi-axial stress states the material experiences during its lifetime as a structure, the observed stress-strain relations and derived material parameters are much more representative than uniaxial results. Until recently however, no real standard regarding biaxial testing of fabric materials existed, leading to a significant variation in test and interpretation methods. The publication of EN 17117-1 in 2018 aimed to provide a modern reference which could serve as a framework for the biaxial testing of coated textiles. However, given the historical development within the field of testing fabrics, the code refrains from providing clear rules and rather opts to formulate guidelines and possibilities for various steps of the testing process. As a result, different test contexts and parameter derivation methods can still exist next to one another making inter-laboratory comparison of derived parameters still somewhat of a challenge. During this research a type II polyester-PVC fabric (Sioen T2103) was tested using a number of different test methods. Afterwards linear elastic orthotropic material constants were derived using a number of established mathematical methodologies and assumptions. By comparing the resulting material constants, the influence of the imposed alterations was assessed. This paper describes the testing and derivation procedures, compares the resulting material parameters and proceeds to formulate conclusions based on the observed differences, or lack thereof. These findings not only allow for a more founded comparison of test results between different facilities, but also aids to better understand the impact certain choices in test or derivation methodology can have on the test outcomes. The conducted tests did not only reveal that the variability of the derived material parameters in function of the verified parameters varied in function of the applied load profile, but also allowed for the identification of some relations between alterations in the test/derivation methodology and the resulting material parameters. Observing the effective variability that exists on the derived material parameters shows that the characterisation of coated textiles is still a valuable subject for further research and development. Through this study, and the identified relations between the boundary conditions and the resulting material parameters, we can now assess to a reasonable degree what variation to expect from biaxial tests conducted using various approaches and methodologies. The results presented in this paper not only further highlight the importance of a harmonised methodology for testing fabric materials and derive non-project-oriented material parameters, but also illustrate the need for a broader approach when interpreting these generalised material parameters and applying them in (preliminary) numerical models.

Spiral slot based flexural bearings are widely used in sterling engine in cryogenic application. This paper deals with parametric analysis of three spiral arm, double stage spiral slot flexural bearing of constant inner and outer diameter. The parameter analysis was conducted on ANSYS. In the parameter analysis; spiral angle, thickness of the flexural plate, spiral slot thickness were varied at different levels to study the axial displacement, axial and radial stiffness of the system and stresses developed. Among various geometrical attributes spiral angle, slot thickness and pitch of the spiral are the outcomes of the design for desired axial displacement for considered flexural plate thickness. The results obtained are generalized for the purpose of developing the design methodology. Further these results are presented in graphical way for design simplification leading to determination of geometrical parameters of flexural bearing based on predetermined geometrical and material constants.

This paper deals with the reflection and transmission of SH waves at a very rough interface separating two dissimilar isotropic elastic solids. The interface oscillates between two straight lines. By means of homogenization, the domain containing the very rough interface is replaced by an effective material layer whose elastic constants depend on the thickness variable. The reflection and transmission of SH waves at the very rough interface is then reduced to the ones at a FGM layer. The exact analytical formulas for the reflection and transmission coefficients have been derived. Based on them, the dependence of the reflection and transmission coefficients on the incident angle, the wave frequency, the material constants and the geometry of the rough interface are examined. Remarkably, it has been shown that a very rough interface of comb-type with the comb-tooth width varying periodically can produce band-gaps to SH waves. With this fact, many potential applications can be expected coming from very rough interfaces of comb-type with periodic comb-tooth width. It is also shown that the width and the location of band-gaps depend strongly on the contrast of rigidities of two half-spaces, the amplitude of the variation of the comb-tooth width, the incident angle of SH waves and the number of periods of comb-tooth.

The paper presents three engineer-oriented models based on the high-cycle accumulation (HCA) model of Niemunis et al. (2005), dedicated to the prediction of long-term deformations of offshore wind power plant (OWPP) foundations caused by wind and wave action. A sublayering model for shallow foundations under vertical cyclic loading and two different approaches (a sublayering model and a stiffness-degradation model) for monopile foundations subjected to horizontal cyclic loading are presented. The results of these models are compared to the solution from 2-D or 3-D finite element simulations with the original HCA model. Furthermore, the prediction is confronted with the prognosis of other engineer-oriented models proposed for OWPP foundations in the literature. Finally, a simplified procedure for the determination of the HCA material constants is briefly explained.

Life prediction based on the damage mechanics of aero-engine turbine blades is crucial for performing their strength design and ensuring the operational reliability under combined high and low cycle fatigue (CCF) loadings. In view of this, a simple and efficient life prediction method is developed to consider the interaction of high cycle fatigue (HCF) and low cycle fatigue (LCF) without any additional material constants, and as a basis of that a new nonlinear damage accumulation model is proposed by introducing threshold damage of the component related to material type and current HCF damage. In order to validate the presented methodology, model predictions were compared with the experimental data sets of turbine blades and its alloy materials. The predicted results indicate that the simple life prediction model is capable of estimating the fatigue life quickly with an acceptable accuracy in contrast to other four existing ones. Moreover, the threshold damage-based method provides the higher prediction accuracy than others due to improved HCF damage determined by the damage threshold.

A micro-statistical model is proposed for investigating the effective properties of a micro-damaged interface between a piezoelectric layer and a piezoelectric half-space under inplane electroelastostatic deformations. The interface is modeled as damaged by periodic arrays of micro-cracks. The lengths and the positions of the micro-cracks on a period interval of the interface are randomly generated. The conditions on the interfacial micro-cracks are formulated in terms of hypersingular integro-differential equations with the displacement and electrical potential jumps across the interface being unknown functions to be determined. To gain new useful physical insights into the behaviors of the imperfect interface, the influences of the material constants, the width of the layer and the crack densities of the interface on the effective properties of the interface are examined in details.

Based on the pseudo-strain method, a computational modeling technique coupling with Armstrong-Frederick type nonlinear kinematic hardening rule (Jiang-Sehitoglu model) is developed to calculate the multiaxial stress-strain responses of notched components. The pseudo-strain-true notch stress curve is determined using Neuber’s rule. The material constants in Jiang-Sehitoglu model are calculated using the Ramberg-Osgood curve. The presented method is applied to simulate the notch-tip deformations of circumferentially notched 1070 steel and S460N steel shafts subjected to various loadings, including box, circle, V-shape, zigzag-shape, and butterfly-shape loading paths. The calculated strain loops are in accord with experimental data and show reasonable accuracy.

QinetiQ has a major and long standing interest in the dynamic deformation and fracture response of materials and has been very active in developing constitutive and fracture models. These models have been validated across a number of different tests, triaxial stress states and strain rates [1] . The models have also been used on a range of Defence and commercial applications where the material characterisation has been controlled by QinetiQ. However, they have not been exercised extensively on industrial applications using available data in the literature. The constitutive models are based on interrupted tensile testing to separate the strain hardening, strain rate and thermal softening and for body centred cubic (BCC) steels give rise to the modified Armstrong-Zerilli model [1] . The ductile fracture model is based on a path dependent approach linking the damage to the stress-state resulting in the Goldthorpe Path Dependent Fracture (PDF) model [2] . Essentially the Goldthorpe PDF model gives a single value of critical damage (Void Fracture Number – VFN) applicable to all stress states and strain rates. This paper describes the application of the QinetiQ constitutive and fracture models in the simulation of an industrial application and assesses their ability to capture the main deformation and fracture mechanisms. The application was an anchor dropping onto a pipe both dynamically and statically to determine whether the pipe is fractured [3] . The DYNA3D hydrocode was used to simulate the dynamic impact and the subsequent deformation and fracture of the pipe. The material constants for the model were estimated for the actual materials by using the testing published in the literature [3] and comparing them with ‘similar’ materials within the QinetiQ materials database. Given there is some subjectivity in this process, the likeliness of failure was investigated, particularly regarding the VFN relating to the fracture process. The results are discussed with respect to the degree of deformation and fracture within the pipe and the sensitivity of these features to the input conditions. The results are also discussed in the context of whether the predictive accuracy of the simulations is such that they could ultimately be used to design a pipe that is more resistant to the impact loading, for example by increasing the yield strength through processing.

This paper presents the results of the research conducted on pine wood that was surface modified with polymerized polymethylmethacrylate (PMMA). The method of surface modification of wood was developed and patented by Jayne (1972). This method opens up new possibilities of wood application in the construction of yachts, fishing boats, lifeboats, building main decks and cargo holds, hydraulic constructions equipment, fenders beams, quays and elements of docks equipment. The principal goal of this work was to establish quantitative evaluation of this effect. Samples with varying content of the polymer were subjected to stretching in order to determine material constants of single layers. To determine the influence of polymer content in the wood-polymer composite (W-P C) on its strength, the sample was subjected to the cylindrical bending. These experiments showed that the surface modification of wood resulted in uniform distribution of the stresses in the beam cross section. Numerical calculations of plates made of natural wood whose surface was modified and was subjected to bending, confirmed the results of laboratory tests.

Purpose The purpose of this paper is to deal with an analytical investigation of delamination fracture in the mixed-mode bending (MMB) multilayer beam configurations taking into account the material non-linearity. Design/methodology/approach The J-integral approach was applied in fracture analysis. The beam layers non-linear mechanical response was described by using a power-law stress-strain relation with four material constants. Analytical solutions of the J-integral were derived by using the technical beam theory. The fracture analysis developed is valid for MMB beams whose layers may have different thicknesses. Also, the values of material constants in the non-linear stress-strain equation may be different for each layer. Findings The effect of material constants, crack location and layer thicknesses on the non-linear fracture was evaluated. The analytical solutions obtained are very suitable for parametric studies of non-linear fracture behaviour. The approach developed here can be used for optimization of multilayered beam structures with respect to the delamination fracture performance. The present study can also be useful for the understanding of fracture in multilayered beams exhibiting material non-linearity. Originality/value For the first time, an analytical study was performed of the delamination fracture behaviour of the MMB multilayered beam configuration taking into account the material non-linearity.

This paper presents fatigue property of CFRP-strengthened cracked steel plate. Firstly, the finite element model of CFRP-strengthened cracked steel plate is established by using the cohesive zone model. With the finite element model, stress intensity factor of the crack-tipis calculated. Then, it gives the fatigue tests of cracked steel plate. According to the experimental data, the material constants C and n value sare obtained. The prediction fatigue life is calculated by the finite element model and Paris function and verified by the experimental data. The results show that the prediction fatigue life, calculated by the finite element model and the Paris formula, is consistent with the experimental fatigue life, which verifies the accuracy of our prediction model with finite element model and the Paris function.

Failure mechanism criterion is proposed based on comprehensive analysis of experimental phenomenon and micro/ meso -mechanism of concrete failure. The failure mechanism criterion can successfully predict the multiaxial strength of normal-strength concrete (NSC) and high-strength concrete (HSC) in other studies. The newly proposed failure mechanism criterion is further developed to include temperature dependences and a cubic function is adopted to describe the relationship between material constants and temperature in the failure mechanism criterion. Then, the temperature dependent failure mechanism criterion is applied to predict the multiaxial strength of NSC and HSC after exposure to normal and high temperatures (NHTs). Good agreement is observed between the predicted values and experiment results from other studies. For the purpose of comparison, the mean error of the failure mechanism criterion is calculated and compared with that predicted by Seow–Swaddiwudhipong criterion, Songs criterion and He–Song criterion. The calculation indicates that the mean errors of the failure mechanism criterion, Seow–Swaddiwudhipong criterion, Songs criterion and He–Song criterion are 4.18%, 7.65%, 12.66% and 16.32%, respectively. This suggests that the failure mechanism criterion can give a more reliable prediction for engineering applications.

The present paper examines the effective macroscopic behavior of a microscopically damaged interface between an infinitely long piezoelectric layer and a piezoelectric half-space under antiplane deformation. The interface is modeled as containing a periodic array of micro-cracks. The lengths and the positions of the micro-cracks on a period interval of the interface are randomly generated. The micro-statistical model is formulated in terms of hypersingular integral equations and used to investigate in detail the influences of the material constants of the piezoelectric layer and the half-space and the width of the layer on the effective properties of the interface.

Based on the Stroh formalism of one-dimensional quasicrystals with piezoelectric effect, the problems of an infinite plane composed of two different quasicrystal half-planes are taken into account. The solutions of the internal and interfacial Green's functions of quasicrystal bi-material are obtained. Moreover, numerical examples are analyzed for a quasicrystal bi-material subjected to line forces or line dislocations, showing the contour maps of the coupled fields. The impacts of changing material constants on the coupled field components are investigated.

The thermo-mechanical fatigue (TMF) of power plant components is caused by the cyclic operation of power plant. A time-dependent plasticity model can be used to simulate the component response under cyclic thermo-mechanical loading. This paper is concerned with the modelling of thermo-mechanical behaviour of power plant steel under various loading conditions. Fully-reversed, strain-controlled tests were conducted on a parent material of P91 steel at high temperatures in order to determine material constants. A unified, Chaboche viscoplasticity model, was used to model the TMF behaviour of the steel. The multiaxial form of the Chaboche constitutive equations have been implemented in the finite element software and validated by comparing to experimental data. Simulation results have been compared with the results of anisothermal cyclic testing in order to validate the performance of the model in cyclic temperature conditions. The model’s performance under multiaxial stress conditions was investigated by testing and simulating the notched bar specimen under load-controlled conditions.

A plate under cyclic loading, containing two coplanar surface flaws with both identical and dissimilar sizes, is considered in the present study. By conducting detailed step-by-step finite element analyses, the conservatism contained in different combination rules for multiple coplanar flaws provided by fitness-for-service codes (ASME, BS7910, API579 and GB/T19624) have been quantitatively assessed for the fatigue failure mode. The findings show that the re-characterization guideline provided by ASME and BS7910 may cause non-conservative estimations when two crack sizes are similar, whereas API579 and GB/T19624 lead to excessively pessimistic predictions for almost all the cases. Based on the fatigue crack growth life, we suggest a new combination rule and conclude that it always yields a reasonable estimation with necessary conservatism, for various initial crack depths, material constants and relative sizes of two cracks.

Determination of material constants describing its behavior during superplastic gas forming is the main subject of this study. The main feature of free bulging tests is the stress-strain conditions which are very similar to ones occurring in the most of gas forming processes. On the other hand, the interpretation of the results of such tests is a complicated procedure. The paper presents a simple technique for the characterization of materials superplasticity by free bulging tests, which is based on inverse analysis. The main idea of this technique is a semianalytical solution of the direct problem instead of finite element simulation which allows one to reduce the calculation time significantly. At the same time the results this simplified solution are accurate enough to obtain realistic material constants.

Mining seismicity induced by coal fractures can cause strong seismic motions in roadway and result in serious seismic hazards to mining personnel and equipment. In order to assess the seismic hazards induced by coal fractures, a deterministic methodology was proposed based on a coal fracture source model and further developed into a numerical program called Mining-induced Seismic Hazard Assessment software (MSHA). The program accepts user-input material constants of in-situ coal seam and calculates the resultant seismic motions in the roadway; the seismic motions were fully verified by a comparison between the numerical and in situ results. The methodology was further applied to assess the seismic hazards in the panel 92201 of the Sanhejian Coal Mine, the seismic hazards were characterized by the peak particle velocity (PPV) and octahedral shear stress (OSS). The results indicate that the tensile strength of coal constitutes the most significant parameter of the coal fracture source model. Moreover, a general and practical conclusion was obtained that the intensity and scope of seismic hazards in roadway are positively related to the tensile strength of coal, and the left and right sides of the roadway might encounter significant seismic damage under impact of coal fracture. The conclusion is useful for mining engineers to identify the potential seismic hazard in the roadway, and therefore make targeted strategies in mining support system.

The ground penetrating radar (GPR) method has increasingly been applied in the non-destructive testing of reinforced concrete structures. The most common approach to the modelling of radar waves is to consider concrete as a homogeneous material. This paper proposes a novel, heterogeneous, numerical model of concrete for exhaustive interpretation of GPR data. An algorithm for determining the substitute values of the material constants of concrete is developed, based on the modified complex refractive index method. Experimental surveys and numerical simulations are conducted on a concrete laboratory sample with a controlled degree of saturation, and on a real concrete slab with two different degrees of saturation. The results indicate that the proposed model is fully capable of realistic finite-difference time-domain modelling of concrete for ground penetrating radar diagnostics of civil engineering structures with changing water content.

In this work a novel modification of the well-known Whitney-Nuismer criteria is proposed with the aim of having a simple and yet accurate fracture criterion for the important problem of estimating the strength of composite laminates with circular open-holes. The novelty is the use of a critical path curve that makes the proposed criteria quite general and provides very good correlation with experimental data for a wide range of laminates and hole sizes even when the characteristic lengths are assumed as material constants. This assumption dramatically reduces the amount of required experimental testing making these criteria very suitable for preliminary design.

The paper compares the numerical models of and experiments with a beam. The purpose is to evaluate the nonlinear material model of a steel structure. The steel is modelled as an ideal elastic-plastic material. The FEM and eight-node isoparametric finite elements are considered in the analysis. The 3D calculations use different material constants and several approaches are being tested in order to create the computational models. The calculations are performed in the software application developed by our university.

Damage caused by low velocity impact is so dangerous in composites because although in most cases it is not visible to the eye, it can greatly reduce the strength of the composite material. In this paper, damage development in U-section glass/polyester pultruded beams subjected to low velocity impact was considered. Different failure criteria such as Maximum stress, Maximum strain, Hou, Hashin and the combination of Maximum strain criteria for fiber failure and Hou criteria for matrix failure were programmed and implemented in ABAQUS software via a user subroutine VUMAT. A suitable degradation model was also considered for reducing material constants due to damage. Experimental tests, which performed to validate numerical results, showed that Hashin and Hou failure criteria have better accuracy in predicting force-time history than the other three criteria. However, maximum stress and Hashin failure criteria had the best prediction for damage area, in comparison with the other three criteria. Finally in order to compare numerical model with the experimental results in terms of extent of damage, bending test was performed after impact and the behavior of the beam was considered.

In this paper, we designed and fabricated the EM wave absorber consisted of Sendust for suppressing EM wave noise PCB in ISM (Industrial, Scientific and Medical) band of 2.4 GHz. We fabricated several samples with different composition ratios of some kinds of Sendust to CPE (Chlorinated Ploy-ethylene) as a binder, and it was confirmed that the optimum composition ratio of absorbing materials was Flaked Sendust : CPE = 72.5 : 27.5 wt.%.. The absorbing abilities were simulated by changing the thickness and the measured material constants of EM wave absorber. The measured absorption abilities were analyzed and compared with the simulated ones. As a result, the simulated results agree well with the measured ones, and the developed EM wave absorber with extremely thin thickness of 0.6 mm has absorption ability of 5.4 dB at 2.4 GHz is excellent one. The thin type EM wave absorber can be applied for suppressing and absorbing electromagnetic noises from information and communication equipments.

In present paper, 3D finite element (FE) method is used to determine plastic limit load solutions for pipe bends under combined bending and torsion moment. With a detailed analysis and comparison, a common awareness for loading effect is showing which will raise researchers concern. By the way, past solutions are not appropriate to estimate FE results. In this respect of finite element analysis, overall yielding considering the spread process of yield region from crown to the straight pipe shows these promising finite element results. A wide range of non-dimensional parameters for pipe bends are considered and plastic limit load solutions are suggested. The results show that r/t is the main factor affecting the limit loads. Plastic limit load is independent on the loading path and material constants by normalizing. Results show that the circular interaction rule is a great approximation for pipe bends under combined bending and torsion moment. A series of approaches are confirmed in order to validate our finite element method on plastic limit analysis. Based on the finite element results, approximate plastic limit load solutions are proposed. Present work will further improve the limit load solution for pipe bends under complex loading conditions.

Numerical analysis of selected type of the polyurethane rail pad is presented in the paper. A shaped pad with cylindrical-shaped elements in its working section was selected as a representative for the computational simulation. Analysis reflected the experimental test according to the valid standard. The test included loading of the vertical force perpendicular to the foot of the rail. Such test allows determining the static stiffness of the pad. The Mooney – Rivlin material model was selected in the current study. Necessary experimental tests including a uniaxial compression and tension were conducted to provide material constants for the hyperelastic material model applied for the FE model. Simplified FE models of the considered rail pad and the rail were developed. Rounded corners and edges of the cylindrical-shaped elements were omitted, since their modelling required a significant density of the FE mesh. Vertical force perpendicular to the foot of the rail was declared as nodal force distributed evenly along the edges of the selected finite element models Non-linear static analysis was performed using MSC.Marc software with large displacements and deformations taken into consideration. The obtained results allowed estimating deformations and the state of stress in a highly deformed rail pad. The static stiffness of the pad was defined as secant stiffness based on the vertical force – deflection curve.

This paper presents a numerical procedure for the analysis of complex laminate structures. The procedure is based on the application of reduced stiffness of complex laminate. Introduction of reduced stiffness of composite facilitates both linear and nonlinear numerical integration, i.e. the tangential stiffness matrix is translated in the classical plate theory problem. The formulated numerical procedure was implemented in the program system KOMIPS. Special subroutine REDKRUT that calculates reduced stiffness of the laminate was written, and its application in numerical verification of experiments conducted on chairs was presented in (Nestorovic, 2010). At the end of this work, for 3D stress and strain analysis of veneer composites, recommendations were given for experimental determination of all nine independent material constants E-x, E-y, E-z, v(xy), v(xz), G(xy), G(xz), G(yz), five of which were determined in the previous paper of the author (Nestorovic, 2010).

The present investigation provides the assessment of stationary points and uniform film thickness for the thin film flow of Sisko fluid model on a vertically upwards moving belt. The conditions for the stationary points, uniform film thickness and net upwards flow are specified. It is observed that the locations of stationary points are shifted towards the belt with an increase in the fluid behaviour index, Sisko fluid parameter and Stokes number. The behaviour of uniform film thickness is investigated by giving certain realistic values to the fluid behaviour index and material constants. Furthermore as special cases, locations of the stationary points and uniform film thickness for the Newtonian fluid film are discussed.

[EN] Nowadays, the rehabilitation of buildings takes more importance due to sustainability reasons. This involves working with existing building structures and the precise calculus of the building to guarantee the adequate strength and safety, from structures with change of use to deteriorated or damaged structures. Concrete is the most common material in building structures, but it is a heterogeneous and non-linear material. The concrete constitutive law, relation between strains and stresses in different directions, is very complex, and different in tension and compression. In the case of new construction project, the linear relationship between stress and strain has been proved safe enough, but it is unable to simulate the behaviour of used and damaged structures, where it is necessary to study the entire load range. In this work, the most widely used constitutive laws of concrete are compared, parameterizing the necessary constants for their professional application in advanced simulation structures software. Some of the evaluated constants are the Young's modulus, Poisson's ratio, stress cracking and crushing, failure energy or the law of damage evolution. Linear-multilinear behaviour, Willam-Warnke crushing and cracking criteria, continuum damage and microplane options are the assessed constitutive laws, showing the differences between the behaviour models and the tightest values of these material constants along the entire load range.

The pelvic floor muscles (PFM) consist of pubococcygeus, ileococcygeuys, coccygeus and puborectalis muscles. The pubococcygeus and puborectalis muscles have been collectively called as the pubovisceralis muscle, due to the difficulty to differentiate these muscles [1]. Pelvic floor dysfunctions — such as urinary incontinence (UI) and pelvic organ prolapse (POP) — can be associated with different risk factors. The most common risk factors responsible for these changes are vaginal delivery, hormonal changes, obesity, aging, among other, affecting the biomechanical behavior of the PFM [2]. In this sense, the mechanical characteristics of the female pelvic floor are relevant to understand the pelvic dysfunctions. The aim of the present work is to present distinct values of the material constants of the Yeoh hyperelastic constitutive model applied to pubovisceralis muscle of two women — one with POP and other without pathology. For this purpose, we used an optimization scheme, involving an inverse finite element analysis (FEA) and Powell's algorithm, using input information non-invasively (Magnetic Resonance Imaging (MRI)).

This paper has presented a life prediction model in the field of multiaxial low-cycle fatigue. The proposed model is generally applied for constant amplitude multiaxial proportional and non-proportional loading. Depending upon applied strain path the equivalent strain varies within a cycle. Equivalent average strain amplitude is considered as fatigue damage parameter in the proposed model. The model has requirement of only two material constants and no other tuning parameters. The model is examined by the proportional and non-proportional low-cycle fatigue life experimental data for eight different types of materials. The model is successfully correlated with multiaxial fatigue lives of eight different materials.

Technicians have been going through trial-and-error processes to solve very small or micro deformation on automobile hood during the painting process. In order to establish a systematic improvement procedure which can replace the time-consuming trial-and-error method to reduce defects, an accurate analysis of how micro deformation occurs during the painting process is needed. We have utilized a stiffness scanning method in automobile hood and reverse engineering to build up a reliable and accurate structural analysis and measurement procedures. We measured the load-stroke data at critical locations on automobile hood through stiffness scanning to determine material constants closest to the measurement by assuming several critical hood parts, such as sealer inside the hood, hemming part, spot weld part, and other uncertain joints, as virtual elastic materials. After setting the difference between analytical and measured load-stroke data as an objective function, we computed and minimized it by using the response surface method and partial differentiation of the object function. As a result, by obtaining the reliability was over 91%, which showed a strong correlation between analysis and measured results. By comparing the actual strain measured in real painting lines with calculated strain, we confirmed the validity of our structural analysis method. It was concluded that the proper analysis tool could be utilized in determination of optimal locations of supports during the painting process.

A new approximate model for predicting the crack growth rate is proposed, which can condense the stable crack propagation stage curves for non-zero stress ratios to that for R = 0 in a narrow band. By using the new approximate model, the obtained material constants corresponding to R = 0 can be further widely used for different loading amplitude ratios. Many available experimental data taken from literature are analyzed using the proposed model for prediction of the crack growth rate. The results indicate that the new approximate model is accurate and effective to consider the R -ratio effect on the crack growth rate.

In cold region, the seasonal effects like changes in freeze-thaw should be investigated with respect to their influence on permanent settlement of foundation under long-term low-level repeated cyclic loading. Thereby, the influence of freeze-thaw processes on the accumulative axial strain of clays under long-term low-level repeated cyclic loading was investigated by conducting cyclic tri-axial tests and a numerical model for calculating the accumulative axial strain was proposed based on the experience observation in this paper. The normalized accumulative axial strain of clays increases significantly subjected to one freeze-thaw cycle, then decreases and tends up to be stable with the subsequent freeze-thaw cycles. The normalized accumulative axial strain increases with the increasing repeated cyclic stress amplitude, moisture content of samples and the number of loading cycles, but decreases with the increasing confining pressure. The modification parameters eta(FT) and functions f(ampl), f(C), f(W) and f(N) were proposed to consider the effects of the influence factors and were implemented into the accumulative strain model. In this model, all of the calculating procedures were explicit and all material constants of clays were presented. Therefore, the accumulative strain model can be used to predict the settlement of foundation under long-term low-level repeated cyclic loading in cold region. (C) 2013 Published by Elsevier B.V.

QFA (quench factor analysis) method is widely used to predict the mechanical properties such as hardness and strength according to temperature of quenched material that has to be determined by experimental heat treatment. But, QFA coupled with CFD (computational fluid dynamics) analysis of this study can predict the mechanical properties without the experiment of heat treatment except the experiment to determine the material constants of QFA. First of all, Jominy test and FPS (flexible polyhedron search) are performed to determine the material constants of QFA. The CFD analysis is applied to predict the cooling temperature of Al6061 cylinder cooled by water of 25°C during quenching of solid solution heat treatment. Hardnesses of T6 heat treated Al6061 cylinder is predicted by the QFA coupled with CFD analysis without experiment of heat treatment and then the predicted hardnesses are compared with experimentally measured hardnesses according to positions of cylinder. The predicted hardnesses of cylinder are in good agreement with the measured ones within a maximum error of 8.45%.

Failure prediction of adhesively bonded single-lap laminates joints with spew fillets in the overlap ends under uniaxial tensile loading is performed by progressive failure analysis method. A modified form of Hashins failure criterion by Shokrieh and maximum stress criterion are used to detect the laminate failure and adhesive failure, respectively, where a sudden degradation model is proposed to reduce engineering material constants. Five kinds of failure modes are considered. The numerical analysis of composites adhesive joints is implemented in ANSYS Parametric Design Language (APDL) with commercial finite element codes ANSYS. The error of simulation and experimental failure loads is 6.9% and the model has been validated by comparing numerical results with experimental results.

A recently formulated triaxiality dependent cohesive model for plane strain is implemented and its versatility is tested in simulation of ductile fracture of mild steel at different states of stress. The triaxiality dependent model was implemented as linear displacement formulation based elements whose constitutive behaviour was dependent on the stress-state of the neighbouring continuum element. By comparing the experimental data and predictions of corresponding plane strain simulations, the model parameters are estimated. The model is shown to be effective in reproducing characteristic features of the macroscopic response of both pre-cracked as well as geometries without a preexisting nominal defect. Since the model parameters are held constant for simulations at different stress-states, they are effectively material constants.

The langasite crystal has the capability of no phase change at temperatures exceeding 600°C for high temperature applications. Since the material properties of langasite were measured usually at 25 0C as the reference temperature they are no longer accurate at high temperature environments. We employ a Lagrangian formulation to investigate the temperature behavior of thickness vibrations of langasite in a wide temperature range from 25°C to 600°C. The analysis only requires the elastic constants and their effective temperature derivatives of elastic constants and thermal expansion coefficients to predict the material constants at any given temperature. Based on the new values of the elastic constants and thermal expansion coefficients, the zero-valued temperature coefficients of frequency are investigated. The presently identified temperature compensated crystal cuts of the thickness-shear modes of langasite at different temperatures were compared with those at reference temperature and also with some cuts found in the literature.

The goal of the research program implemented by the authors was to develop methodology to be used for determination of constants for Johnson-Cook material model using Charpy impact test. This model is used in programs for modeling by the FEM method in order to account for the influence of strain rate on the strength properties. The method we propose involves selection of the material constants by comparing behavior of a specimen during Charpy test with results of simulation using the FEM method, in LS-DYNA program. Measurement of strain on the specimen surface involved recording Charpy test by means of a fast video camera and time –lapse measurement of changes in the distance of markers.

In a lattice spring model (LSM), the material is discretised into particles linked by springs. However, LSMs always adopt linear springs, which results in a stiff approximation of the corresponding elastic solution. In this work, a high order LSM is proposed to overcome this limitation by introducing additional degrees of freedoms (DOFs) to the particles. Based on the energy minimisation principle and the local strain technique, equations for the stiffness matrices of high order LSM are derived. Relationships between micro spring parameters and macro material constants are derived from the Cauchy-born rules and the hyperelastic theory. Numerical examples show that the high order LSM can provide a better solution than that of the linear LSM and that the LSM is more suitable for modelling singularity and fracture problems.

Single frame structures with notches were fractured by applying drop impact loadings at room temperature and low temperature. Johnson-Cook shear failure model has been employed to simulate the fractured single frame structures. Through several numerical analyses, material constants for Johnson-Cook shear failure model have been found producing the cracks resulted from experiments. Fracture strain-stress triaxiality curves at both room temperature and low temperature are presented based on the extracted material constants. It is expected that the fracture strain-stress triaxiality curves can offer objective fracture criteria for the assessment of structural fractures of polar class vessel structures fabricated from DH36 steels. The fracture experiments of single frame structures revealed that the structure on low temperature condition fractures at much lower strain than that on room temperature condition despite the same stress states at both temperatures. In conclusion, the material properties on low temperature condition are essential to estimate the fracture characteristics of steel structures operated in the Northern Sea Route.

This report gives a discussion of a new wave characteristic as a material parameter for a composite with the magnetoelectric effect. The new parameter depends on the material constants of a piezoelectromagnetic composite. It can be implemented on: (A) mechanically free, electrically and magnetically open surface and (B) mechanically free, electrically and magnetically closed surface. These theoretical investigations are useful for researchers in the fields of acousto-optics, photonics and opto-acousto-electronics. Some sample calculations are carried out for BaTiO3–CoFe2O4 and PZT-5H–Terfenol-D composites of class 6 mm. Also, the first and second derivatives of the new parameter with respect to the electromagnetic constant α are graphically shown.

The paper contains a proposal for the classification of some selected constructional materials starting from the material properties as assumed according to the models based on the Manson–Coffin–Basquin (MCB) and Ramberg–Osgood (RO) laws. These laws are commonly used for strain-based fatigue life assessments. Three methods for determination of fatigue material constants occurring in the MCB and RO models, namely, the conventional, numerical and 3D methods, were used. The compatibility between the parameters derived from the aforementioned models was checked by evaluating the fatigue results for five groups of selected constructional materials.

An analytic survey of experimental data and theoretical approaches characterizing the long-term strength of metals in complex stress state is given. In Sections 2 and 3, the results of plane stress tests (with opposite and equal signs of the nonzero principal stresses, respectively) are analyzed. In Section 4, the results of inhomogeneous stress tests (thick-walled tubes under the action of internal pressures and tensile forces) are considered. All known experimental data (35 test series) are analyzed by a criterion approach. An equivalent stress σe is introduced as a characteristic of the stress state. Attention is mainly paid to the dependence of σe on the principal stresses. Statistical methods are used to obtain an expression for σe, which can be used to study various types of the complex stress state. It is shown that for the long-term strength criterion one can use the power or power-fractional dependence of the time to rupture on the equivalent stress. The methods proposed to describe the test results give a good correspondence between the experimental and theoretical values of the time to rupture. In Section 5, the possibilities of complicating the expressions for σe by using additional material constants are considered.

The paper deals with uniaxial ratcheting phenomenon of cyclic plasticity behavior of the materials SA333 carbon Manganese steel. A mechanistic model for the ratcheting phenomenon has been proposed. It is observed that von Mises yield criterion together with Chaboche’s kinematic hardening rules are not sufficient to model ratcheting phenomenon. Other associated phenomena like plastic strain memory surface, back stress memory points and over all the extra hardening behavior have to be incorporated to get a complete material model for ratcheting. The proposed model assembled all these ideas together with von Mises yield criterion and Chabache’s kinematic hardening rule. Low cycle fatigue tests and uniaxial ratcheting tests have been conducted for the materials. The material constants are identified and derived from experimental results. The ratcheting coefficients have been properly calibrated with these material constants. The material model, as mentioned above, for the ratcheting phenomenon has been implemented in an elastic plastic finite element code. The ratcheting results for different stress controlled ratcheting loads have been computed. The good feature of this model is that it reduces to symmetric low cycle fatigue model when loop closes.