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The aim of this study is to examine displacements, strains and stresses of a railway composite cord-rubber air brake tube undergoing uniaxial tension by microscale modelling. The micromodel is based on the macromodels (by matching the boundary conditions of the micromodels with displacements of the macromodels) created previously by authors of this article. The reinforcing yarns are described by an orthotropic, elastic material model, whereas the matrix has been described by a 2 parameter Mooney-Rivlin model, which all have been validated before by a uniaxial tensile test and a three-point bending test. Force-displacement curves of the micromodel and experimental results show a considerably good agreement. Failure of the reinforcement layers does not occur in case of the uniaxial tension of the composite tube sample, there was no failure event observed during the experiment of the tube sample. Load transfer mechanism has been demonstrated and characterized numerically by strain and stress results inside and between reinforcement layers (implying shear plays a dominant role in the load-transfer mechanism). The microscale nature of the FE model ensures that the strain and stress results are representative for the reinforcement layers.

The aim of this study is to examine displacements, strains and stresses as well as to predict possible failure mechanisms arising at the yarn-matrix level of a test specimen of a railway composite cord-rubber air brake tube undergoing uniaxial tension by microscale modelling.Furthermore, this paper also aims to verify the material properties of the micromodel of the test specimen.The micromodel is based on macromodels (by matching the boundary conditions of the micromodels with displacements of the macromodels) created previously by authors of this article. The reinforcing yarns are described by an orthotropic, elastic material model, whereas the matrix has been described by a 2 parameter Mooney-Rivlin model, which all have been validated before by a uniaxial tensile test and a three-point bending test.Force-displacement curves of the micromodel and experimental results show a considerably good agreement.Yarns have a less dominant role in the load transfer mechanism of the reinforcement layers, because of the short-yarn reinforced nature of the specimen. Shear strains are high at free yarn ends marking the possible locations of failure initiation in debonding in the shear mechanism of the reinforcement layers. High shear strain values imply that the dominant mode of load transfer is shear in the matrix in the reinforcement layers.

OBJECTIVES This study aims to compare mechanical stability of osteosynthesis (plate and screw fixation) alone versus the same method supplemented with hip arthroplasty (hybrid solution) for double column fractures in elderly. PATIENTS AND METHODS Mechanical investigations were performed on an advanced finite element pelvis model developed for double column fractures. The following simulated implant combinations were analyzed: modular acetabular basket with a ring with polyaxial screws and U-plate; plates with polyaxial screws placed on the medial-horizontal (linea terminalis) and quadrilateral bone surfaces; modular acetabular cup with U-plates; and polyaxial screws in sizes optimized based on a finite element model (FEM). Using the models, the possible shifts in peak load positions arising in different movement patterns caused by load and tension and implant deformation were measured. RESULTS Hybrid systems resulted in minimal deformation of the implants already available on the market. We observed less possible shifts and greater stability in the acetabular fracture zones, compared to conventional osteosynthesis alone. Optimization with available and compatible implant sizes led to a further significant increase in stability. CONCLUSION Hybrid method combining osteosynthesis and prosthesis implantation provide more stability in biomechanical models in the treatment of double column fractures in elderly.

In certain cases, rolling stocks and railway vehicle components, i.e. brake tubes need to operate under extreme conditions such as at sub-zero temperature (e.g. -40°C) and on a reverse curve track, when displacements of the suspension points of the tubes cause large deformations in tubes. In this paper, displacements of the suspension points of the tubes are determined by a kinematic model validated by a draw and buffing gear test [1]. Afterwards, FE simulation has been carried out at minimum and maximum suspension point distance based on these displacements for the investigation of stress, strain states and possible failure considering the case of internal pressure and no internal pressure. Equivalent strain, stress and Tsai-Hill failure indices are much below the criterial values, so failure is not probable. The straight section between the curves of opposite curvatures reduces deformation in tubes in the critical positions leading to lower strain, stress and failure index values.

OBJECTIVES This study aims to investigate if the stabilization of iliac wing fractures influences the stability of the acetabular osteosynthesis, if surgical fixation is the choice of treatment, and which technique to be used. MATERIALS AND METHODS In the study, measurements were performed with an improved finite element model. Tension and displacement values were measured in bicolumnar acetabular fractures in the following cases: combination of cranial and medial plate fixation through the linea terminalis, or combination of cranial plate and quadrilateral surface plates. The iliac wing fracture was either not fixed, or fixed with screws or with a plate. RESULTS In cases where osteosynthesis was performed through the linea terminalis, 0.01 mm fracture gap displacement was observed with the use of a combination of cranial and quadrilateral surface plate fixations. In the combination of cranial and medial positioned plates, the displacement in the fracture gap was 0.088 mm. The fixation of the iliac wing fracture did not improve the stability of the osteosynthesis of the linea terminalis. Plate fixation of the iliac wing fracture was more stable than screw fixation alone. CONCLUSION In double column fractures, if the reduction does not require an anterior approach, it is not necessary to fix the iliac wing fracture only to improve the stability of the fixation. If the reduction does require an anterior approach, it is worth fixing the iliac wing fracture with the technically less demanding screw fixation.

In this paper the behavior of an O-ring made of NBR rubber was investigated under extreme conditions. The effect of the extreme initial compression, operating pressure and extreme temperature conditions were examined. The rubber material was tested in simple tension, pure shear and equibiaxial tension modes complemented with a Dynamic Mechanical Thermal Analysis (DMTA) to capture the viscoelastic behavior of the material. For the investigation, a large-strain viscoelastic material model was developed by the authors, to take into account the large deformations caused by extreme conditions. Insufficient space during installation causes extreme initial compression consequently leading the material to crack on the contacting outer surfaces. It was found that the excessive strain and friction induced shear stress contributes primarily to this phenomenon. Extreme operating pressure causes the seal to penetrate into the gap between the shaft and the housing. This behavior damages the material and cracks appear on the seal. High strain areas were found in the proximity of the gap in the material. The analysis of the extreme operating temperature showed that during cooling the O-ring can completely loose its ability to seal at -70°C. There are three contributing factors: the speed of cooling, the temperature and the coefficient of thermal expansion.

The aim of this paper is to present finite element model of a filament-wound composite tube subjected to three-point bending and bending in accordance with standard EN 15807:2011 (railway applications-pneumatic half couplings) along with its experimental verification. In the finite element model, composite reinforcement plies have been characterized by linear orthotropic material model, while rubber liners have been described by a two-parameter MooneyRivlin model. Force-displacement curves of three-point bending show fairly good agreement between simulation results and experimental data. Reaction forces of FE simulation and experiment of standard bending test are in good agreement.

The aim of this paper is to model the steady-state condition of a rotary shaft seal (RSS) system. For this, an iterative thermal-mechanical algorithm was developed based on incremental finite element analyzes. The behavior of the seal’s rubber material was taken into account by a large-strain viscoelastic, so called generalized Maxwell model, based on Dynamic Mechanical Thermal Analyses (DMTA) and tensile measurements. The pre-loaded garter spring was modelled with a bilinear material model and the shaft was assumed to be linear elastic. The density, coefficient of thermal expansion and the thermal conductance of the materials were taken into consideration during simulation. The friction between the rotary shaft seal and the shaft was simplified and modelled as a constant parameter. The iterative algorithm was evaluated at two different times, right after assembly and 1 h after assembly, so that rubber material’s stress relaxation effects are also incorporated. The results show good correlation with the literature data, which state that the permissible temperature for NBR70 (nitrile butadiene rubber) material contacting with ~80 mm shaft diameter, rotating at 2600/min is 100°C. The results show 107°C and 104°C for the two iterations. The effect of friction induced temperature, changes the width of the contact area between the seal and the shaft, and significantly reduces the contact pressure.

With the analysis example of a cast iron component a Finite Element Analysis (FEA) based modelling and post-processing methodology is proposed for the multiaxial high-cycle fatigue assessment of surface defects. Methods are proposed for the measurement and mechanical description of surface defects using an ellipsoid simplification and the well-known size parameter from Murakami (2002). Different methods are compared for the stress-computation near surface defects: elastic FEA, elastic-plastic FEA with nonlinear kinematic hardening material model, and analytical calculations with the Equivalent Inclusion Method from Eshelby (1957). The Defect Stress Gradient (DSG) approach from Vincent et al. (2014) is applied to predict crack initiation, whereby a new method is proposed for the estimation of the stress gradient, which allows the presentation of the DSG utilisation factor results field.

The aim of this paper is to demonstrate the mechanical behaviour of a filament-wound composite tube subjected to uniaxial tension by finite element analysis. Uniaxial tensile test experiments have been carried out on standard specimen and hose piece in order to verify finite element models and material properties and also to assess failure mode of composite plies. Composite reinforcement plies are modeled as linear orthotropic, while elastomer liners are described by hyperelastic material model. Results of finite element models and experiments show good agreement in the initial phase of uniaxial tension, which justifies utilized material models in the operating range. Results of finite element models show that transverse tension and shear load are dominant under tension. It is determined that principal failure mode of reinforcement plies is intra-ply yarn-matrix debonding caused by intensive shear of rubber matrix.

International audience; The impact of surface defects on the fatigue properties of cast iron material cannot be neglected in the fatigue design process. Allowable defect size maps are a practical tool for the quality control of surface defects on castings. These results present a compliance between the detrimental effect of surface inhomogeneities and the primary requirement of structural integrity during service life. The Defect Stress Gradient approach from Vincent et al. (2014) has been further improved by a general ellipsoidal geometry model for surface defects, and has been utilized for the fatigue assessment of defective nodular cast iron. After the study of defect size, shape and orientation effects calculations are compared with experimental results for high-strength ferritic nodular cast iron and 1045 steel. Two methods are proposed for an allowable defect size map based surface defect assessment using ellipsoidal description of the defect. The ellipsoidal description of the defect size, shape and orientation offers a more precise representation of real defects leading to more accurate results than the established hemispherical notch or surface crack methods.

A bone plate is required to restore the load-bearing capacity of the mandible following a segmental resection. A good understanding of the underlying principles is crucial for developing a reliable reconstruction. A finite element analysis (FEA) technique has been developed to study the biomechanics of the clinical scenarios managed after surgical resection of a tumour or severe trauma to assist in choosing the optimal hardware elements. A computer aided design (CAD) model of an edentulous human mandible was created. Then 4 common segmental defects were simulated. A single reconstruction plate was designed to span the defects. The hardware variations studied were: monocortical or bicortical screw fixation and non-locking or locking plate design. A standardized load was applied to mimic the human bite. The von Mises stress and strain, spatial changes at the screw-bone interfaces were analysed. In general, the locking plate and monocortical screw fixation systems were most effective. Non-locking plating systems produced larger screw "pull-out" displacements, especially at the hemimandible (up to 5% strain). Three screws on either side of the defect were adequate for all scenarios except extensive unilateral defects when additional screws and an increased screw diameter are recommended. The simplification of screw geometry may underestimate stress levels and factors such as poor adaptation of the plate or reduced bone quality are likely to be indications for bicortical locking screw fixation. The current model provides a good basis for understanding the complex biomechanics and developing future refinements in plate or scaffold design.

Objective This study aimed to explore whether cone beam computed tomography (CBCT) and multislice computed tomography (MSCT) can be used to quantify tissue density and to determine if the Hounsfield unit scale is applicable. Study Design A clinical MSCT scanner and effective energy adjusted photon beam attenuation references were used to compare the gray scale of CBCT images of the mandible region. A phantom was scanned using axial cadaver slices and 4 different homogeneous reference objects. The consistency of the references' gray values and 12 linear profile lines from both scanner data sets were compared. Results The gray values of the 2 scans showed strong correlation with quantified position-dependent differences as an outcome of the validation process. Conclusions The introduced internal, in-scan validation is able to estimate and has a potential to compensate for the differences between MSCT and CBCT protocols. This validation serves as a guide in situations where the users can expect deviations.

Objectives In this study, we aimed to create a realistic model which is suitable for computerized simulation of any kind of fractures and provides reliable results. Patients and methods We used a plastic pelvic model to construct advanced specimens. The data were retrieved from the computed tomography scans of a healthy pelvis. A geometrically exact model by the means of three-dimensional scanning of the plastic pelvis was obtained. The material properties of the bony parts based on the data retrieved from the computed tomography scans were modified. The pelvis was divided into distinct segments and the proportion of the cortical and cancellous bone substance in each segment were determined to make the material properties accurate. In the validation of the pelvic model, a type C pelvic injury was simulated and the fracture of the sacrum and the symphyseolysis were stabilized with plates. These data were compared with those of previously performed cadaver experiments. Results Based on the simulation performed on the new model, the shift values between the fragments of the broken sacrum approximated the reported values of our cadaver experiments and also arising strains remained in the tolerable interval. Conclusion Our new finite element pelvic model represents the pelvis more accurately than the former one. As the validation of the model was successful, it is suitable for computerized simulation of any kind of fractures offering reliable results.

For up-to-date bolted joints, first of all in vehicles, high strength bolts of 10.9 or even 12.9 are used, which are preloaded up to 90% or even 100% of the yield strength. The primary aim of this high degree utilization is the weight reduction. For the analytic dimensioning of bolted joints, the VDI 2230 Richtlinien German standard [1] provides support. However, the analytic model can mostly consider the true structural characteristics only in a limited way. The analytic modeling is especially uncertain in case of multiple bolted joints when the load distribution among the bolts depends reasonably upon the elastic deformation of the participating elements in the joints over the geometry of the bolted joint. The first part of this paper deals with the problems of numerical modeling and stress analysis, respectively specifying the analytic dimensioning procedure by applying elastic or rather elastic-plastic material law. The error magnitude in bolted joint calculation was examined in case of omitting the existing threaded connection—between the bolt and the nut—in order to simplify the model. The second part of the paper deals with the dimensioning of stands and cantilevers’ multi-bolt fixing problems, first of all, with the load distribution among the bolts keeping in view the analysis of the local slipping relations. For demonstrating the above technique, an elaborated numeric procedure is presented for a four-bolted cantilever, having bolted joints pre-tightened to the yield strength.

Our investigation aimed to analyse the contact pressure distribution, the contact area and the sliding procedure in a railway wheel-rail contact by using finite element method. The analysis were created with linear elastic material model. The elaborated model provides opportunity to analyse the initial sticking zone within the contact zone that disappears and transforms into full sliding contact due to the tangential displacement of the contact zone. In that state we examined the equivalent stress distribution under the surface in full sliding condition as well.

For up-to-date bolted joints, first of all in vehicles, high strength bolts of 10.9 or even 12.9 are used, which are pre-tightened up to 90% or even 100% of the yield strength. The primary aim of this high degree utilization is the weight reduction. For the analytic dimensioning of bolted joints, the VDI 2230 Richtlinien German standard provides support. However, the analytic model can mostly consider the true structural characteristics only in a limited way. The analytic modeling is especially uncertain in case of multiple bolted joints when the load distribution among the bolts depends reasonably upon the elastic deformation of the participating elements in the joints over the geometry of the bolted joint. The first part of this paper deals with the problems of numerical modeling and stress analysis, respectively specifying the analytic dimensioning procedure by applying elastic or rather elastic-plastic material law. The error magnitude in bolted joint calculation was examined in case of omitting the existing threaded connection—between the bolt and the nut—in order to simplify the model. The second part of the paper deals with the dimensioning of stands and cantilevers’ multi-bolt fixing problems, first of all, with the load distribution among the bolts keeping in view the analysis of the local slipping relations. For demonstrating the above technique, an elaborated numeric procedure is presented for a four-bolted cantilever, having bolted joints pre-tightened to the yield strength.

a b s t r a c t Introduction: The strengthening effect of prophylactic internal fixation (PIF) with a bone plate at the radial osteocutaneous flap donor site has previously been demonstrated using the sheep tibia model of the human radius. This study investigated whether a finite element (FE) model could accurately represent this biomechanical model and whether stress or strain based failure criteria are most appropriate. Methods: An FE model of an osteotomised sheep tibia bone was strengthened using 4 types of plates with unilocking or bicortical screw fixation. Torsion and 4-point bending simulations were performed. The maximum von Mises stresses and strain failure criteria were studied. Results: The strengthening effects when applying stress failure criteria (factor 1.76-4.57 bending and 1.33-1.80 torsion) were comparable to the sheep biomechanical model (factor 1.73-2.43 bending and 1.54-2.63 torsion). The strongest construct was the straight 3.5 mm stainless steel unilocking plate. Applying strain criteria the strongest construct was the straight 3.5 mm stainless DCP plate with bicortical screw fixation. Conclusions: The FE model was validated by comparison with the sheep tibia model. The complex biome- chanics at the bone-screw interface require further investigation. This FE modelling technique may be applied to a model of the human radius and other sites.

The goal of the research is to examine the different reconstruction solutions, which are used for the often-occurring jaw cancer resection and finding those areas that show higher potential risks of implant fracture. Within the research some finite element analysis based on data provided by Computer tomography have been concluded. The model in practice is built up with the most frequently used reconstruction plates and monocortical screws. Both lock and non-lock system solutions were examined. The results supporting the practice showed that indeed the maximal stress would rise in the implants closer to the resection in case of screws and in case of plates this will occur in the closer areas of resection within the thinner cross-sections.

In type C pelvic ring injuries, the operative stabilization of the posterior ring is absolutely indicated. There exist four different types of operative methods: iliosacral screw fixation, transsacral plate synthesis, ventral plate fixation (primarily for sacroiliac luxations), and local plate synthesis performed on the dorsal cortex of the sacrum. In our current article, we analyzed the stability of fixation methods used together with bilateral iliolumbar techniques. We analyzed a finite element pelvic model attached to lumbar 4–5 vertebrae. By imitating a standing position on two feet, we measured the differences in tension and displacement in T1 and T2 thoracic vertebrae fractures with and without iliolumbar fusion in cases of iliosacral screw fixation, transsacral plate synthesis and KFI-H (small fragment-H) plate synthesis. The osteosynthesises reinforced via Galveston technique were rather stable; the amount of displacement measured in the fracture gap was significantly less than in the cases without iliolumbar fusion. The tension in the implants were below the allowed values, therefore they were capable of withstanding the imposed loads without permanent deformation. In unilateral pelvis injuries, if a non-weight bearing status cannot be achieved on the injured side, unilateral iliolumbar fusion reinforcement is justified, since the contralateral lower limb must also be non-weight bearing due to the pelvis injury itself. In the case of the most unstable sacrum fracture—“jumper’s fracture”, bilateral iliolumbar fusion is necessary, in which case the patient will be able to bear weight during the early postoperative period.

The hysteretic part of the friction coefficient for rubber sliding on an ideal rigid, rough surface has been investigated by FE technique. The FE models were created by using two different FE softwares, ABAQUS and MSC.MARC. The surface roughness has been considered by using two different sine waves having a wavelength of 100 μm and 11.11 μm, as well as their superposition. Parameters of the viscoelastic material models of the rubber were gained, firstly from a fit to the measured storage modulus, secondly from a fit to the measured loss factor master curve of the rubber. The effect of viscoelastic material models, comparing 10-term and 40-term generalized Maxwell models was also considered together with the temperature effect between −50 and150°C. According to the results, both postprocessing methods, namely, the reaction force and the energy-based approach, show very similar coefficients of friction. The 40-term Maxwell model fitted to both the storage modulus and loss factor curve provided the most realistic results. The tendency of the FE results has been explained by semianalytical theory.

This study involves the finite element (FE) thermal modeling of a dry running ceramic clutch disk to be applied in passenger cars and a comparison with experimental measurement results. The problem can be handled by two independent FE models linked by heat partition changing in time and space. A distributed heat source was applied for modeling heat generation; furthermore, changes in time and space of the heat convection coefficient were also taken into consideration.

This paper has investigated theoretically the influence of sliding speed and temperature on the hysteretic friction in case of a smooth, reciprocating steel ball sliding on smooth rubber plate by finite element method (FEM). Generalized Maxwell-models combined with Mooney-Rivlin model have been used to describe the material behaviour of the ethylene- propylene-diene-monomer (EPDM) rubber studied. Additionally, the effect of the technique applied at the parameter iden- tification of the material model and the number of Maxwell elements on the coefficient of friction (COF) was also investigated. Finally, the open parameter of the Greenwood-Tabor analytical model has been determined from a fit to the FE results. By fitting, as usual, the Maxwell-model to the storage modulus master curve the predicted COF, in a broad fre- quency range, will be underestimated even in case of 40-term Maxwell-model. To obtain more accurate numerical predic- tion or to provide an upper limit for the hysteretic friction, in the interesting frequency range, the Maxwell parameters should be determined, as proposed, from a fit to the measured loss factor master curve. This conclusion can be generalized for all the FE simulations where the hysteresis plays an important role.

An algorithm has been developed for the analysis of asperities of various types of machined surfaces, in order to characterize wear processes in the course of dry friction. Wear experiments and surface roughness measurements were performed to study the microtopographies of worn surfaces. Investigations extended to wear in the case of the non-lubricated ceramic-steel clutch and lubricated camshaft and bushing. A statistical analysis of asperities and scratches was completed with distribution curves to display the results. The peak angle, the rate of the major and minor axis and orientation were analyzed to characterize the shape of asperities and the overall characteristics of the surface.

The viscoelastic properties of an ethylene/propylene/diene rubber (EPDM) containing 30 parts per hundred parts rubber [phr] carbon black (CB) were determined by dynamic mechanical thermal analysis (DMTA) measurements. A 15term Maxwell-model was created to describe the time-dependent material behavior of this rubber. The frictional behavior under dry rolling conditions was studied on a home-built rolling ball (steel)-on-plate (rubber) (RBOP) test rig. Both normal and tangential forces were detected during the measurements. The rolling test was simulated with the MSC.Marc finite element (FE) software using the evaluated viscoelastic material properties. Results of the experimental tests and of the simulation were compared and a good agreement was found between them.

The abrasive sliding friction and wear behaviours of silicon carbide (SiC) filled vinylester (VE) composites were investigated. The average grain size of the incorporated SiC particles was varied, holding the volume content of them in every case at 16 vol%. Mechanical properties (hardness, compression modulus, yield stress) of the filled and neat VE were determined. The tribological properties were investigated in block (composite) - on - ring (steel) test configuration. The steel counter bodies were covered with abrasive papers of different graining. Coefficient of friction (COF) and specific wear rate of the VE + SiC composites were determined. It was observed that the wear resistance increases with increasing average filler grain size and with decreasing abrasiveness of the counter surface. The COF of the VE + SiC composites is independent of the size of the incorporated particles, but it is strongly influenced by the abrasiveness of the counter body. The worn surfaces of the VE + SiC systems were analysed in scanning electron microscope (SEM) to deduce the typical wear mechanisms. The size effect of the SiC filler particles onto the abrasive wear characteristics was investigated by assuming that the roughness peaks of the abrasive paper and the indenter of the microhardness test cause similar micro scaled contact deformations in the composites. Therefore FE method was used to simulate the micro scaled deformation process in the VE + SiC systems during microindentation tests. The FE results provided valuable information on how to explain the size effect of the incorporated SiC filler.

In the present study, finite element transient contact and thermal sliding simulation and temperature measurement of dry sliding friction were performed in order to analyse the real contact area and temperature developed in the contact region. Real 3D surface worn topographies were taken into consideration, at macro and intermediate stages. The calculated real contact area has been changing in time and space in the course of sliding. The sliding components were high purity alumina ceramic palettes and 100Cr6 steel with constant accelerated motion. The calculated temperature results are in good agreement with the temperature data measured. Heat partition was changing in time during sliding. The developed algorithm based on incremental FE technique can characterize real processes.

Rollers of three different material structures were examined: rollers consisting of pure EP resin; homogeneous EP/SiC composite rollers containing 5 vol.% SiC; and EP/SiC composite rollers with functionally gradient (FG) material structure. Wear tests were performed on the rollers. The wear tests showed that rollers of gradient structure are the most wear-resistant of all. Microhardness measurements were performed on the materials of the three different rollers. SEM images were made of the surface of wear traces. In order to get to know better the effect of SiC reinforcement particles on the wear mechanism, microhardness measurements were simulated by 3D FE micro-models. The SEM images and the FE models were used to explain the excellent wear behavior of the tread of rollers with gradient material distribution.

OBJECTIVES This study aims to investigate whether positioning of the plate fixation plays a role in the stability of the osteosynthesis. MATERIALS AND METHODS We used finite element modelling to model an anterior pillar fracture and a T-type fracture of the acetabulum. Fracture fixation was carried out in three different variations: cranially positioned plate, medially positioned plate, and a combination of the two methods. In all cases, 3-3 screws were inserted on both ends of the plate to fix the fracture. RESULTS In both fractures, nearly the same amount of displacement was detected in the fracture gap using a cranially positioned or medially positioned plate, and the amount of displacement was not less when using both plates simultaneously. CONCLUSION The position of the plate fixation does not affect the stability of the osteosynthesis and in cases of simple fracture patterns, fixation using two plates does not provide more stability than one plate alone.

Functionally graded rings based on an epoxy matrix and SiC fillers were prepared and subjected to a compression test. For comparison, rings with homogeneous filler concentration and neat epoxy were also tested. The homogeneous and the graded rings showed the tendency to break at different locations. In order to have accurate information about the material properties, tension and compression tests were performed on isotropic specimens having various SiC volume fractions. The FE simulations of the compressed rings verified the experimental data, as the stress/strain components in the representing locations were able to predict the failure.

A debonding simulation technique, based on a series of nonlinear FE evaluations, has been developed to study the contact behavior and the debonding process of unidirectional fiber-reinforced polymer composites subjected to a sliding diamond indentor. In Part I, the normal fiber orientation was studied, while in Part II, the parallel and anti-parallel fiber orientations relative to the sliding direction are analyzed. The technique developed can consider both the shear and the tension type debonding events, and also the effect of friction causing limited debonding. The results show a dominant limited shear type debonding under compression for both fiber orientations.

To study the contact and debonding behaviors between a CF–PEEK fiber-reinforced polymer composite specimen and a sliding diamond indentor, finite element macro- and micro-models have been developed. Around each fiber, interface elements were introduced in order to detect the tension-type and also the shear-type debondings for different cases. If initial or final debonding has occurred, a “control algorithm” checked the limit strain conditions for the interface elements and changed the material properties according to the actual debonding condition. As a final result, it can be concluded, that the dominant debonding under compression is due to the shear loading conditions.

FE contact and thermal macro/micro-models have been developed to study the real contact and thermal behaviour of a fibre/matrix micro-structure under sliding motion against a steel asperity. The composite material studied consisted of carbon fibres, at different fibre orientations, and a polyether-etherketone (PEEK) matrix. At first, the contact parameters were evaluated using an approximate contact technique, followed by a transient thermal FE evaluation. The latter considers the heat partition between the steel asperity and the real fibre/matrix micro-environment of the composite material. To study the effect of the compacted wear debris layer, additional FE elements on top of the model, with the properties of the PEEK matrix material, were introduced. The temperature results obtained were compared with those representing a macroscopic approach.

Surface discontinuities are unavoidable properties of production castings, and have fundamental effect on in-service reliability. In the current study a multiaxial probabilistic fatigue analysis model has been developed for the description of local (e.g.: notches or surface defects) and structural gradient (e.g: bending) effects on crack initiation life. Identification of the model parameters and the validation has been done on the ferrite-pearlitic NCI grade EN GJS 500-7. The survival probability type simulation results are proven to be highly accurate with 5% average, and 11% maximum prediction error. In theory, the model might be able to assess the effect of arbitrarily complex defects on the fatigue strength, which is to be investigated in the future.

Finite element (FE) micro-models have been developed in order to determine contact, stress and strain conditions produced by a steel asperity sliding on the surface of a fibre-reinforced polymer composite. Two cases were studied, i.e. a parallel and an anti-parallel fibre orientation relative to the sliding direction. In order to get more realistic simulation results relating to the failure conditions in the composite structure, FE contact macro/micro-models were used, contrary to the so far widely applied anisotropic analytical or numerical macro-models. To model a “micro-environment” as part of a “macro-environment”, the displacement coupling technique was introduced. The contact analysis operates on both the macro- and the micro-level, applying node-to-node contact elements. The contact results, especially the contact pressure distribution, can characterize the real fibre/matrix micro-system. Displacement and strain results lead to explanations of fibre related phenomena, matrix shear effects, and fibre/matrix debonding events. On the basis of the stress results, conclusions were drawn on the possible wear mechanisms of the fibre-reinforced polymer composite. For parallel fibre orientation, fibre/matrix debonding as a result of shear stresses at the interface, matrix shear type failure and fibre thinning are the dominant sliding wear mechanisms. If an anti-parallel fibre orientation is considered, matrix shear, tension/compression type fibre/matrix debonding and fibre thinning, associated with fibre cracking events, are the most dominant wear mechanisms. To study the wear mechanisms experimentally, diamond tip scratch tests were carried out, showing that the predicted failure events occur also in reality.

The number of patients diagnosed with cancer is reaching a scarily high number worldwide. This is no different in the area of mandible cancer. Unfortunately Hungary is quite high up in the ladder. The registered known number of patients with mandible cancer and the associated number of death occurrences are also showing signifi cant data in the country. However it is easy to diagnose, alcohol consumption and smoking or just bad oral hygiene really pushes the statistics. Inside the oral cavity, in case of mandible cancer and late diagnosis the only viable solution is the bone resection. To determine the extent of the cancer and to carefully plan the surgery procedure or in case of models which were created for biomechanical examinations, the medical science more and more often uses the image based processes and tools. Next to the realistically built models a more punctual mechanical parameter simulation becomes possible. It is highly important that the necessary information is extracted from the patients with the least stress. With the shortest time and smallest radiation the image must be made in a way that the scan can be well evaluated and it is usable. Within the current examination in the medical fi eld of imaging methods a gold standard MSCT and a specifi cally in the head-neck region used CBCT methods will be compared specifi cally from biomechanical modelling point of view. During the comparison the gray value was examined by the use of a cadaver head. The results show that the gray values provided by CBCT differs slightly from the MSCT values that is considered as reference. The more extent absolute error occurs with less frequency. Based on these facts the CBCT can be used for the density based material comparison for biomechanical models with less radiation dose. DOI: 10.17489/biohun/2014/2/04

Objectives This study aims to investigate whether surgical treatment of pubic rami fractures increases the stability of the posterior pelvis. Patients and methods A finite element pelvic model with improved geometric and material characteristics was analyzed. By imitating a standing position, a type I Denis sacrum fracture and a unilateral pubis fracture, we measured the differences in tension and displacement. The posterior injury was treated with a direct plate synthesis or transsacral plate synthesis, while the pubis fracture was left without fixation or fixed with either a retrograde pubic screw or plate synthesis. Results The operative fixation of pubic rami fractures decreased the movement in the fracture gap not only at the site of the pubis fracture, but also at the site of the fixed sacrum fracture. The plate synthesis provided greater stability of the anterior fracture than the retrograde screw. The tensions in the implants were below the allowed values. Conclusion We concluded that surgically fixation of pubic fracture increases the stability of the operated posterior pelvis.

Our investigations aimed to model the thermal stress development between wheel and rail, caused by heat generation during braking, by coupled transient thermal and elastic-plastic FE simulations. Stresses are generated due to thermal expansion caused by local temperature rise and changes in temperature in case of one revolution of the wheel. Our investigations resulted in the fact that thermal expansion caused by heat generation and heat conduction induced considerable local stresses along the thread of the wheel ∼0.1–0.5 mm underneath the surface.

An anisotropic numerical contact algorithm has been developed for real composite-steel surfaces in sliding contact. The results were based on measured surface roughness data, under conditions of different fibre orientations relative to the sliding direction. The location of the real contact area at certain positions of sliding contact could be predicted. These results can be considered as input data for contact temperature calculations and wear predictions. An experimental evaluation of the real contact area was carried out by testing a composite pin under static compressive load against a gold-covered glass surface, resulting in an asperity-type contact condition. In another experiment, the composite pin was slid over the glass surface, which resulted in the removal of the gold layer along a certain path, characterising the nature of the real contact area interaction between the two surfaces. The results showed that the densities of contact spots are similar obtained by both the contact algorithm and the experimental techniques.

Finite element (FE) contact and thermal macro/micro models have been developed to study the real thermal behavior of a fiber/matrix microstructure under sliding motion of a steel asperity. At first the contact parameters were evaluated using an approximate contact technique, followed by a transient thermal FE evaluation. The latter considers the heat partition between the steel asperity and the real fiber/matrix microenvironment of a normally oriented carbon fiber/polyether ether ketone composite. The temperature results obtained were compared with those representing a macroscopic approach.

FE micro-models have been developed in order to determine contact, stress and strain conditions produced by a steel asperity sliding on the surface of a fibre-reinforced polymer composite. Three cases were studied, i.e. a normal, a parallel and an anti-parallel fibre orientation relative to the sliding direction. In order to get more realistic simulation results about the failure conditions in the composite structure, FE contact macro/micro-models were used, contrary to the so far widely applied anisotropic analytical or numerical macro-models. To model a “micro-environment” as part of a “macro-environment”, the displacement coupling technique was introduced. On the basis of the stress results, conclusions were drawn on the possible wear mechanisms of the fibre-reinforced polymer composites. For each fibre orientation, surface failure of the matrix material occurs due to high shear stresses. The other characteristic source of failure is fibre/matrix debonding, eventually followed by fibre cracking events.

Several engineering components transfer load under sliding contact. Between two sliding bodies there are contacts over only small areas of the nominal contact area due to the surface roughness and surface waviness. The nominal contact pressure is therefore much smaller than the real contact pressure acting over the real contact areas inside the contour contact areas. To evaluate the contact parameters (location of the real contact area and contact pressure distribution) different numerical methods have been used in the past decades. The latest ones can consider the real surfaces based on measured surface roughness data. The present study focuses on the characteristic features of the asperities using hemispherical, ellipsoidal and parabolic surfaces as substituting surfaces. In each case the location of the real contact area and contact pressure distribution are evaluated and compared with the results representing the original measured surfaces. The best agreement was obtained if paraboloides were used for substituting asperities. This technique can provide statistical type results characterising the contact behaviour, if the substituting asperities are considered.

Finite-element (FE) thermal models have been developed in order to study the temperature distribution in a sliding pair comprising a poly(ether ether ketone) (PEEK) pin and a steel disc in a pin-on-disc configuration. First, a moving heat source model for the disc was created. An alternative distributed heat source model was also produced in order to reduce computing time for the evaluation of the moving heat source model by some orders of magnitude. This latter model gave the same results as the moving heat source model, except for a small region just below the moving heat source. On the basis of the distributed heat source approach, a complete axisymmetric FE model for the disc side (taking the effect of thermal resistance between the assembled components into consideration) and a steady-state quarter model for the pin were developed. Water cooling and air cooling of the steel shaft were also compared. It was found that air cooling allowed a higher temperature in the contact region of the two sliding partners. The experimental results obtained with thermocouples and a thermal camera showed good agreement with the model predictions.

For composite-steel surfaces in sliding contact an anisotropic numerical contact algorithm has been developed to study the ‘layer type’ problems. An FE contact analysis was applied to evaluate the contact parameters (real contact area, contact pressure distribution and normal approach). The contact temperature rise was determined by using both a numerical thermal algorithm for stationary and a FE transient thermal technique for ‘fast sliding’ problems. The effect of a continuous transfer film layer (TFL), that had built up during wear of the PEEK matrix material on the steel counterpart, was considered. Its thickness was assumed to be t=1 μm, and its material properties were that of PEEK at room temperature or, in the case of frictional heating, at a temperature of 150°C (i.e. above the glass transition temperature of the polymer matrix). Results are presented for a spherical steel asperity, with/without TFL, sliding over composite surfaces of different fibre orientation, and in addition, for real composite-steel surfaces (based on measured surface roughness data) in sliding contact. The TFL has an effect on the contact parameters especially at higher operating temperatures (i.e. 150°C); it results in the production of a larger contact area and a lower contact pressure distribution. The contact temperature rise is clearly higher if a TFL is present. Due to the low thermal conductivity of PEEK, the TFL is close to the melting state or it even gets molten within a small vicinity of the contact area.

Numerical techniques have been developed and used to evaluate the contact temperature distribution between real composite-steel surfaces in sliding contact. To characterise the contact temperature problem of composite materials, new definitions for composite Peclet numbers have been introduced. In the case of `slow sliding' problems, a stationary numerical technique was applied, whereas for `intermediate and fast sliding' problems, transient finite element (FE) solutions were preferred. Contact temperature results were presented for real composite-steel sliding surfaces; the latter will help to provide information about the actual stress conditions, which are necessary to model the wear process of this pair of materials in future works. Asperity type contact was also detected by an experimental evaluation of the real contact area; the latter was performed by compressing a composite pin onto a glass surface. To study the sliding contact of a composite pin, a micro-sliding test was also produced by a pulling unit.