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Both the mean contact force difference and the standard deviation of the contact force were minimised in the presented optimised design of a pantograph–catenary system for the purposes of improving of the current collection quality and the reduction of the contact wear. The non-dominated sorting genetic algorithm-II (NSGA-II) was applied to optimise the pantograph–catenary interaction system. The adopted NSGA-II algorithm was improved by avoiding repetition of FEM simulations with the duplicated input parameters and retaining only one of the duplicated results for the next generation selection. Either the catenary or the pantograph can be optimised individually by using the proposed versatile approach. In this research, the design optimisation of the catenary system was conducted first. After that, the pantograph was further optimised based on the optimised design of the catenary system. A case study indicated that the standard deviation of the contact force was reduced by 33.4% in the optimised catenary design and 39% in the optimised pantograph design, and the contact force differences were reduced by 98.3% and 99.9% in the optimised catenary design and the optimised pantograph design, respectively. Highlights Both the standard deviation of the contact force and the difference between the actual mean contact force and the ideal mean contact force are minimised in the optimisation design of a pantograph–catenary system. Either the catenary or the pantograph can be optimised separately by using the proposed versatile approach. Non-dominated Sorting Genetic Algorithm-II (NSGA-II) was improved by avoiding repetition of finite element method simulations with the same input parameter combinations and retaining only one of the same results for the next generation selection. A case study indicates that the standard deviation of the contact force can be reduced by 33.4% in the optimised catenary design and 39% in the optimised pantograph design, and the contact force difference can be reduced by 98.3% and 99.9% in the optimised catenary design and the optimised pantograph design, respectively. [ABSTRACT FROM AUTHOR]

The fatigue crack growth behavior of friction stir welded joints of AZ31 Mg alloy is investigated for three different notch locations. The extended finite element method based simulation is developed to capture the effect of stir zone on fatigue crack growth behavior. The notch locations with asymmetric material domain experience an asymmetric stress field, which leads to crack path deviation from the orthogonal direction to the applied force. This leads to a longer crack path. The near-tip stress field from the simulation enhances the understanding of unusual crack path. The experimental results including crack path trajectories from experiments compare well against the numerical predictions. [ABSTRACT FROM AUTHOR]

Designing roller cavity surfaces for rolling blades is a nontrivial task. This paper presents a new method to design cavity surfaces for rolling compressor blades with considering the springback and forward slip compensation. Firstly, a springback compensation model was proposed to modify the shape of section curves, and a forward slip model was proposed to determine the location of section curves to compensate the springback and forward slip in rolling process. Secondly, an algorithm was proposed to transform the updated section curves to the cavity section curves around the roller axis. The cavities were reconstructed through the transformed section curves. Finally, the designed roller cavities for a variable cross-section compressor blade were validated by the finite element method and experiment. The results revealed that the designed cavities meet the net shape precision at pressure and suction surfaces of the blade. The compensated design of cavities for blade rolling can save both time and costs while keeping excellent design quality. [ABSTRACT FROM PUBLISHER]

This study investigates topology optimization of energy absorbing structures in which material damage is accounted for in the optimization process. The optimization objective is to design the lightest structures that are able to absorb the required mechanical energy. A structural continuity constraint check is introduced that is able to detect when no feasible load path remains in the finite element model, usually as a result of large scale fracture. This assures that designs do not fail when loaded under the conditions prescribed in the design requirements. This continuity constraint check is automated and requires no intervention from the analyst once the optimization process is initiated. Consequently, the optimization algorithm proceeds towards evolving an energy absorbing structure with the minimum structural mass that is not susceptible to global structural failure. A method is also introduced to determine when the optimization process should halt. The method identifies when the optimization method has plateaued and is no longer likely to provide improved designs if continued for further iterations. This provides the designer with a rational method to determine the necessary time to run the optimization and avoid wasting computational resources on unnecessary iterations. A case study is presented to demonstrate the use of this method. [ABSTRACT FROM AUTHOR]

A shear-lag model with a cohesive fibre–matrix interface has been developed for the analysis of stress transfer between the fibre and the matrix in fibre-reinforced composites in this paper. A bilinear cohesive damage evolution law is used to describe the fibre–matrix interface behaviour. The governing equations for the interfacial shear stress and the axial stress in the fibre are derived. Accurate analytical solutions are obtained when the fibre–matrix interface is in the initial linear elastic deformation regime. When debonding occurs, interfacial damage and softening are modelled by superposing two elastic stress systems and satisfying the damage evolution law at both ends of the damage process zone, and approximate analytical solutions are obtained. The stress distribution and evolution during the fibre pull-out, the maximum pull-out force and the pull-out curve have been analysed using a shear strength-based debonding criterion. Analytical expressions for the maximum fibre pull-out force and its limit as the embedded fibre length approaches infinity are obtained. In addition, the new function proposed for describing the radial distribution of the shear stress in the matrix fixes the problem of zero shear-lag parameter when b / a approaches infinity, enabling the shear-lag analysis to deal with low fibre volume fractions. Generally, the analytical solutions compare satisfactorily well to the cohesive finite element calculations and experimental data in the literature. [ABSTRACT FROM AUTHOR]

Understanding the heterogeneity of biological structures, particularly at the micro/nano scale can offer insights valuable for multidisciplinary research in tissue engineering and biomimicry designs. Here we propose to combine nanocharacterisation tools, particularly Focused Ion Beam (FIB) and Atomic Force Microscopy (AFM) for three dimensional mapping of mechanical modulus and chemical signatures. The prototype platform is applied to image and investigate the fundamental mechanics of the rat face whiskers, a high-acuity sensor used to gain detailed information about the world. Grazing angle FIB milling was first applied to expose the interior cross section of the rat whisker sample, followed by a “lift-out” method to retrieve and position the target sample for further analyses. AFM force spectroscopy measurements revealed a non-uniform pattern of elastic modulus across the cross section, with a range from 0.8 GPa to 13.5 GPa. The highest elastic modulus was found at the outer cuticle region of the whisker, and values gradually decreased towards the interior cortex and medulla regions. Elemental mapping with EDS confirmed that the interior of the rat whisker is dominated by C, O, N, S, Cl and K, with a significant change of elemental distribution close to the exterior cuticle region. Based on these data, a novel comprehensive three dimensional (3D) elastic modulus model was constructed, and stress distributions under realistic conditions were investigated with Finite Element Analysis (FEA). The simulations could well account for the passive whisker deflections, with calculated resonant frequency as well as force–deflection for the whiskers being in good agreement with reported experimental data. Limitations and further applications are discussed for the proposed FIB/AFM approach, which holds good promise as a unique platform to gain insights on various heterogeneous biomaterials and biomechanical systems. [ABSTRACT FROM AUTHOR]

The finite element method was used to simulate indentation tests on a particle embedded in a matrix, to investigate the influence of the properties of the particle and the matrix, and the indentation depth on the measured hardness. The particle’s work-hardening exponent and the mismatch in particle and matrix yield strength have a significant influence on the measured hardness. A particle-dominated indentation depth was identified, within which the measured nanoindentation hardness agrees very well with the true hardness of the particle material. Numerical results from the simulations of a wide range of material properties determined that the measured hardness is within 5% difference of the particle’s true hardness when the indentation depth is less than 13.5% of the particle’s radius. The results can be used in practice as a guideline to measure the hardness of a particle embedded in a matrix and provides the theoretical basis to develop a particle-embedded method to measure the hardness of individual particles. [ABSTRACT FROM PUBLISHER]

An experimental study on the indentation hardness of NiTi shape memory alloys (SMAs) by using a spherical indenter tip and a finite element investigation to understand the experimental results are presented in this paper. It is shown that the spherical indentation hardness of NiTi SMAs increases with the indentation depth. The finding is contrary to the recent study on the hardness of NiTi SMAs using a sharp Berkovich indenter tip, where the interfacial energy plays a dominant role at small indentation depths. Our numerical investigation indicates that the influence of the interfacial energy is not significant on the spherical indentation hardness of SMAs. Furthermore, the depth dependency of SMA hardness under a spherical indenter is explained by the elastic spherical contact theory incorporating the deformation effect of phase transformation of SMAs. Hertz theory for purely elastic contact shows that the spherical hardness increases with the square root of the indentation depth. The phase transformation beneath the spherical tip weakens the depth effect of a purely elastic spherical hardness. This study enriches our knowledge on the basic concept of hardness for SMAs under spherical indentation at micro- and nanoscales. [ABSTRACT FROM AUTHOR]

Abstract: The application of the indentation method to measure the elastic modulus of particles embedded in a composite is theoretically investigated in this paper by finite element simulation. The Oliver–Pharr method, which is widely used in commercial nanoindentation instruments, is used to probe the elastic modulus of the particle from the simulated indentation curve. The predicted elastic modulus is then compared with the inputted value. Two cases are studied, that of a stiff particle embedded in a soft matrix and a soft particle embedded in a stiff matrix. In both of these cases, there exists a particle-dominated depth. If the indentation depth lies within this particle-dominated depth, the Oliver–Pharr method is able to be applied to measure the particle’s elastic modulus with sufficient accuracy if the real contact area is used. This could lead to an experimentally-convenient method of determining the primary properties of individual particle, providing they can be well dispersed in the polymeric matrix. [Copyright &y& Elsevier]

A recently published finite element (FE) head model is modified to consider the viscoelasticity of the meninges, the spongy and compact bone in the skull. The cerebrospinal fluid (CSF) is simulated explicitly as a hydrostatic fluid by using a surface-based fluid modelling method, which allows fluid and structure interaction. It is found that the modified model yields smoother pressure responses in a head impact simulation. The baseline model underestimated the peak von Mises stress in the brain by 15% and the peak principal stress in the skull by 33%. The increase in the maximum principal stress in the skull is mainly caused by the updation of the material's viscoelasticity, and the change in the maximum von Mises stress in the brain is mainly caused by the improvement of the CSF simulation. The study shows that the viscoelasticity of the head tissue should be considered, and that the CSF should be modelled as a fluid, when using FE analysis to study head injury due to impact. [ABSTRACT FROM AUTHOR]

Abstract: Metallic foams are a new class of functional materials. They have found their applications as sandwich cores in lightweight structures and as implant materials in bioengineering. To characterize the mechanical properties of these materials becomes an interesting and relevant research topic. In the mean time, indentation method has been well accepted as a simple and effective way to measure the mechanical properties of solid materials. We believe that it is possible to study the averaged mechanical properties of a metallic foam from a spherical indentation test. In this paper, theoretical investigation to understand the spherical indentation responses of metallic foams is presented. Based on the dimensional analysis, several scaling relationships in the indentation of metallic foams with a spherical indenter are obtained. Numerical results from the finite element simulations are used to examine the dependence of the indentation response on the basic material parameters, such as the porosity, the work hardening exponent and the shape factor, which characterizes the plastic deformation of metallic foams due to hydrostatic loading. Our numerical results show that the maximum indentation force has a linear relationship with the indentation depth for different shape factor values. It is therefore proposed to calibrate the shape factor value from the slope of the maximum indentation force versus the indentation depth from a spherical indentation test, instead of a complicated hydrostatic loading test. We also find that the spherical indentation hardness varies about 11% within the examined indentation depths. The range of the ratio of the hardness to the yield strength of metallic foams is from 2.17 to 2.95, which is different from that of solid materials. Our study provides the basis for applying a simple spherical indentation test to investigate the mechanical properties of metallic foams. [Copyright &y& Elsevier]

Abstract: This paper directly examines the contact sliding distance experienced during a typical sheet metal stamping process—an area that has largely been neglected in the literature. A method to numerically quantify the sliding distance is proposed. The sliding distance predicted from this method, and the contact pressure obtained from numerical simulation, allow the recently identified time-dependent contact conditions on the die and blank surfaces to be completely characterized. Consequently, a new insight into the wear/galling that occurs at the die radius in sheet metal stamping is gained. The results show that the region close to zero degrees on the die radius is likely to experience the most wear, with the identified transient stage contributing to a large proportion of the total wear. Additionally, the region on the blank surface often observed to be heavily burnished – the die impact line – is estimated to experience the highest wear severity due to the transient contact conditions. The proposed method to numerically quantify the sliding contact conditions can be applied as a general approach to study any other two-body sliding contact situations. [Copyright &y& Elsevier]

The article presents a study which examines the dynamic response of irregular fibers that are under axial tension. The study utilizes finite element method in simulations, and examined the maximum first principal stress brought by dynamic pulling. Results indicate that the maximum first principal stress was too sensitive to the irregular amplitude changes.

Abstract: For a given sheet metal forming process, an accurate determination of the contact pressure distribution is an essential step towards the estimation of tool life. This investigation utilizes finite element (FE) analysis to model and explain the evolution and distribution of contact pressure over the die radius, throughout the duration of a channel forming process. It was found that a typical two-peak steady-state contact pressure response exists for the majority of the process. However, this was preceded by an initial transient response, characterized by extremely large and localized contact pressures, which were more than double the magnitude of the steady-state peak pressure. The validity of the predicted contact pressure behavior was assessed via detailed numerical analysis and by examining the wear response of an experimental stamping operation. The experimental results revealed that the high contact pressure zones of the transient response corresponded to a severe galling wear mechanism. Therefore, the transient response may be of primary significance to the tool wear response; thus questioning the applicability of traditional bending-under-tension wear tests for sheet metal stamping processes. Finally, a parametric study was conducted, examining the influence of the major process parameters on the steady-state and peak transient contact pressures, using the developed FE model. It was found that the bend ratio and the blank material ultimate tensile strength had the most influence on the peak contact pressures. The main process-related parameters, friction coefficient and blank holder force, were found to have only a minor influence. [Copyright &y& Elsevier]

Abstract: Dimensional analysis and the finite element method are applied in this paper to study spherical indentation of superelastic shape memory alloys. The scaling relationships derived from dimensional analysis bridge the indentation response and the mechanical properties of a superelastic shape memory alloy. Several key variables of a superelastic indentation curve are revealed and examined. We prove that the bifurcation force in a superelastic indentation curve only relies on the forward transformation stress and the elastic properties of the initial austenite; and the return force in a superelastic indentation curve only relies on the reverse transformation stress and the elastic properties of the initial austenite. Furthermore, the dimensionless functions to determine the bifurcation force and the return force are proved to be identical. These results not only enhance our understanding of spherical indentation of superelastic shape memory alloys, but also provide the theoretical basis for developing a practicable method to calibrate the mechanical properties of a superelastic material from the spherical indentation test. [Copyright &y& Elsevier]

Abstract: Using dimensional analysis and the finite element method, the spherical indentation hardness of shape memory alloys (SMAs) is investigated. The scaling relationship between the hardness and the mechanical properties of a SMA, such as the forward transformation stress, the maximum transformation strain magnitude, has been derived. Numerical results demonstrated that the hardness increases with the indentation depth but there is no three-fold relationship between the hardness and the forward transformation stress. Increasing the maximum transformation strain magnitude would reduce the hardness of the material. These research results enhance our understanding of the hardness from the spherical indentation of SMAs. [Copyright &y& Elsevier]

A finite element (FE) model is developed to investigate mode I delamination toughness of z-pin reinforced composite laminates. The z-pin pullout process is simulated by the deformation of a set of non-linear springs. A critical crack opening displacement (COD) criterion is used to simulate crack growth in a double-cantilever-beam (DCB) made of z-pinned laminates. The toughness of the structure is quantified by the energy release rate, which is calculated using the contour integral method. The FE model is verified for both unpinned and z-pinned laminates. Predicted loading forces from FE analysis are compared to available test data. Good agreement is achieved. Our numerical results indicate that z-pins can greatly increase the mode I delamination toughness of the composite laminates. The influence of design parameters on the toughness enhancement of z-pinned laminates is also investigated, which provides important information to optimise and improve the z-pinning technique. [Copyright &y& Elsevier]

Abstract: Carbon nanotube (CNT)–hybridized carbon fibre (CF) composite is a new generation composite, where CNTs grow radially on carbon fibres to form a hybrid reinforcing phase. To evaluate the bridging effect of this new reinforcing phase, a numerical method is proposed to theoretically investigate the pullout of a hybrid fibre. There are two finite element models developed in this method, which are applied to simulate a single CNT pullout from the matrix at microscale and the pullout of the hybrid fibre at macroscale. The bridging effect of the CNTs during the hybrid fibre pullout is simulated by spring elements in the macroscale finite element model, where the properties of spring elements are obtained from the microscale finite element simulation. The numerical results indicate that the apparent interfacial shear strength of the hybrid fibre and the specific pullout energy can be significantly increased due to the additional bonding of the CNT–matrix interface. A parametric study indicates that the bridging effect of the hybrid fibre can be further enhanced by improving the interfacial bonding between CNT and matrix and increasing the size or length of CNTs. This study provides a new numerical method to simulate the multiscale CNT/CF hybrid fibre pullout. [Copyright &y& Elsevier]

Although concussions can result in persistent neurological post-concussion symptoms, they are typically invisible on routine magnetic resonance imaging (MRI) scans. Our study aimed to investigate the use of ultra-high-field diffusion tensor imaging (UHF-DTI) in discerning severity-dependent microstructural changes in the mouse brain following a concussion. Twenty-three C57BL/6 mice were randomly allocated into three groups: the low concussive (LC, n = 9) injury group, the high concussive (HC, n = 6) injury group, and the sham control (SC, n = 7) group. Mice were perfused on day 2 post-injury, and the brains were scanned on a 16.4T MRI scanner with UHF-DTI and neurite orientation dispersion imaging (NODDI). Finite element analysis (FEA) was performed to determine the pattern and extent of the physical impact on the brain tissue. MRI findings were correlated with histopathological analysis in a subset of mice. In the LC group, increased fractional anisotropy (FA) and decreased orientation dispersion index (ODI) but limited neurite density index (NDI) changes were found in the gray matter, and minimal changes to white matter (WM) were observed. The HC group presented increased mean diffusivity (MD), decreased NDI, and decreased ODI in the WM and gray matter (GM); decreased FA was also found in a small area of the WM. WM changes were associated with WM degeneration and neuroinflammation. FEA showed varying region-dependent degrees of stress, in line with the different imaging findings. This study provides evidence that UHF-DTI combined with NODDI can detect concussions of variable intensities. This has significant implications for the diagnosis of concussion in humans. [ABSTRACT FROM AUTHOR]

Mass discharging rate (MDR) is a critical aspect of hopper's performance in bulk solids handling. A shape optimization method is established in this study to increase the MDR of cohesionless granular materials from hoppers. This method is based on a continuum model of granular matter and the Eulerian Finite Element Method (FEM) which can efficiently simulate the discharging process and predict the MDR. In this work with the focus on conical hoppers, the widths of silo and hopper outlet as well as the vertical height of hopper are fixed. The meridian of the hopper, however, evolves from a straight line to some optimal curve, guided by a combined genetic algorithm (GA) and gradient descent method (GDM). Cubic spline function is employed to parametrize the hopper shape. The effectiveness of the shape optimization is examined by comparing the MDRs of the optimal hopper and conventional conical hopper, obtained by both FEM and discrete element method (DEM) respectively. It is shown that this shape optimization method can automatically search the optimal shape of the hopper in a given range of constraints, and increase the MDR substantially. In a typical hopper with an initial half angle of 45°, the MDR is increased by over 130% after the shape optimization. Notably, the optimal shape depends mainly on the geometrical factors, i.e. the allowed width and height for the hopper, whilst insensitive to the material properties, which favors its general use for different particles. Such curved hoppers are particularly useful for increasing the discharge rate of hoppers ranging from 30° to 50°, which, facilitated with advanced manufacturing technology, will find wide potential applications in bulk solids handling. Unlabelled Image • Shape optimization based on FEA was performed on conical hoppers to maximize the MDR. • An optimal concave hopper shape was obtained, which can increase the MDR by over 130% in a case study. • The optimal hopper shape depends on the initial hopper half-angle and the height of hoppers. • The optimal hopper shape is insensitive to granular material properties. [ABSTRACT FROM AUTHOR]

Flange tip lift crossings are widely utilized in modern tramlines to replace traditional crossings to enhance commuters' comfort and prevent crossing nose failures. However, due to altered contact conditions between wheel flanges and ramps of crossings, the use of flange tip lift crossing has led to the critical issue of ramp wear. To resolve this issue, this paper investigated the dynamic contact response of a ramp during in-service loading, as well as the resultant wear of the ramp. With a dynamic finite element model, the local contact pressure and local sliding distance were computed and subsequently applied in a local contact-based wear model to evaluate the nominal wear of the ramp. Our findings indicate that under typical in-service loading conditions, the ramp exhibited up to 120 times more wear than the rail head, owing to increased contact pressure and reduced contact area during the ramp contact. To mitigate this issue, a design change of a gentler ramp inclination from the default 1:100 ramp to a 1:150 ramp could provide approximately 10% wear reduction. In addition, increasing the flange radius by 1 mm could reduce the wear by up to 13%. Conversely, increasing the speed to 45 km/h from the recommended 15 km/h speed may cause up to 5 times more wear. Furthermore, an empty tram showed 56% less wear on the ramp when compared to the condition of the maximum allowable axle load. These results offer an insight into the detrimental wear of ramps used in flange tip lift crossings of tramlines and can assist in the development of new designs and operating guidelines to mitigate ramp wear. • Ramp wear of a tram crossing was investigated using dynamic finite element simulation and a local contact-based wear model. • The wear of the ramp was found to be up to 120 times greater than that on the rail head of tram rails. • Gentler ramp inclination, increased flange radius, reduced vehicle speed and lower axle load can reduce the wear of the ramp. [ABSTRACT FROM AUTHOR]

• The FaStrip algorithm is modified to estimate elastic-plastic traction distribution. • Softened zones of rail welds experience the highest ratcheting strain rate. • Ratcheting strain rates in the sampled 2000 m radius curved track are higher than those in the sampled tangent track. • The RCF initiation location is highly dependent on the magnitude and pattern of traction distribution. Ratcheting at the rail heads due to cyclic rolling contact stresses is often observed in heavy haul railways, especially when there are large steering forces developed in low-radius curves. Additionally, ratcheting behaviour can be exacerbated when associated with material strength loss in the heat affected zones of rail welds. However, the numerical evaluation of this failure mode requires a sophisticated representation of elastic–plastic contact pressures and traction distributions, which, to the best of the authors' knowledge, cannot be directly measured by any existing tools. In this paper, in order to accurately evaluate the ratcheting performance at rail welds in curved tracks, attempts were conducted to modify the FaStrip algorithm to analytically estimate the traction distributions based on contact pressures and creepages obtained from static finite element analysis and multi-body dynamic simulations, respectively. Cyclic rolling contact was then simulated by repeatedly applying contact pressure and traction on the rail surface consisting of both the rail weld and the parent rail regions. The weld region was divided into 23 sub-zones in the rolling direction to represent the material inhomogeneity within the heat affected zones. Cases on a 2000 m radius curved track and a tangent track were studied for comparison. It was found that the ratcheting strain rate in curved tracks can be significantly elevated due to the higher magnitude of traction, and the location of the elements with the highest ratcheting strain rate was dependent on the traction distribution patterns. The proposed method provides a general tool for predicting rolling contact fatigue initiation life and location, which will benefit the maintenance efficiency of heavy haul rail welds in curved track. [ABSTRACT FROM AUTHOR]

This paper details the theory and implementation of a composite damage model, addressing damage within a ply (intralaminar) and delamination (interlaminar), for the simulation of crushing of laminated composite structures. It includes a more accurate determination of the characteristic length to achieve mesh objectivity in capturing intralaminar damage consisting of matrix cracking and fibre failure, a load-history dependent material response, an isotropic hardening nonlinear matrix response, as well as a more physically-based interactive matrix-dominated damage mechanism. The developed damage model requires a set of material parameters obtained from a combination of standard and non-standard material characterisation tests. The fidelity of the model mitigates the need to manipulate, or “calibrate”, the input data to achieve good agreement with experimental results. The intralaminar damage model was implemented as a VUMAT subroutine, and used in conjunction with an existing interlaminar damage model, in Abaqus/Explicit. This approach was validated through the simulation of the crushing of a cross-ply composite tube with a tulip-shaped trigger, loaded in uniaxial compression. Despite the complexity of the chosen geometry, excellent correlation was achieved with experimental results. [ABSTRACT FROM AUTHOR]

A comprehensive study was carried out to numerically evaluate the ratcheting performance of three high strength pearlitic rail steels under different wheel–rail cyclic rolling contact conditions, i.e. free rolling, partial slip, and full slip conditions, different friction coefficients and different axle loads. The wheel–rail cyclic rolling contact was simulated by repeatedly passing a distributed contact pressure and a distributed tangential traction on the rail surface. This study combined the non-Hertzian contact pressure from finite element analysis with the longitudinal tangential traction from Carter’s theory to simulate the wheel–rail cyclic rolling contact problems. A cyclic plasticity material model considering the non-proportionally loading effect developed recently by the authors was applied to simulate the ratcheting behaviour of rail steels. The ratcheting performance of the rail steels was evaluated by the crack initiation life which was determined from the stabilized ratcheting strain rate and the ductility limit of the rail materials. The numerical results indicate that the crack initiation life decreases with the increase of the normalized tangential traction, the friction coefficient and the axle load for all three rail steels. Among the three rail steels, the hypereutectoid rail steel grade with a lower carbon content provides the best ratcheting performance under higher axle loads such as those used railway transport of mineral products in Australia. Furthermore, the numerical results obtained in this study are in reasonable agreement with the in-service performance of the three rail steels. This indicates that the developed approach has the capacity to evaluate the ratcheting performance of other rail steels under service loading conditions. The outcomes can provide useful information to the development and application of rail steels and the development of effective rail maintenance strategies in order to mitigate rail degradation. [ABSTRACT FROM AUTHOR]

• A shape optimization method was developed to improve the flow pattern in silo/hopper discharging. • The optimized curved design can increase the fraction of mass flow zone over 90%. • The extent of segregation can be reduced by 70% in the optimized curved design. • The same optimized curved design works well for different granular materials. A shape optimization method is presented in this paper to re-design hopper shapes for improving the flow patterns in silos. This method combines a continuum model of granular matter based on the Eulerian Finite Element Method, the optimization algorithms of genetic algorithm and the gradient descent method. Starting from a classic conical shape, the optimization method searches for the optimal shape of the hopper under given geometrical constraints. An optimized curve design can increase the mass flow zone in the hopper by more than 90%. The sensitivity of this method suggests that the shape optimization is of particular significance for initially funnel flow hoppers and granular materials with high internal friction. The optimized design was further characterized by using the Discrete Element Method. The DEM results demonstrate that the optimized hopper can also dramatically reduce particle segregation by around 70% during hopper discharge. [ABSTRACT FROM AUTHOR]

Abstract: A robust multiscale scheme referred to as micro–macro method has been developed for the prediction of localized damage in fiber reinforced composites and implemented in a finite element framework. The micro–macro method is based on the idea of partial homogenization of a structure. In this method, the microstructural details are included in a small region of interest in the structure and the rest is modeled as a homogeneous continuum. The solution to the microstructural fields is then obtained on solving the two different domains, simultaneously. This method accurately predicts local stress fields in stress concentration regions and is computationally efficient as compared with the solution of a full scale microstructural model. This scheme has been applied to obtain localized damage at high and low stress zones of a V-notched rail shear specimen. The prominent damage mechanisms under shear loading, namely, matrix cracking and interfacial debonding, have been modeled using Mohr–Coulomb plasticity and traction separation law, respectively. The average stress at the notch has been found to be 44% higher than the average stresses away from the notch for a 90N shear load. This stress rise is a direct outcome of the geometry of the notch. [Copyright &y& Elsevier]

Abstract: An experimental study was conducted to characterize the heat affected zone produced when laser heating a Ti6Al4V alloy plate workpiece. The emissivity and absorptivity of the Ti6Al4V alloy were determined experimentally. A 3D transient finite element method for a moving Gaussian laser heat source was developed to predict the depth and width of the heat affected zone on the Ti6Al4V alloy workpiece. There was a close correlation between the experimental data and the simulation results. It was found that the depth and width of the heat affected zone were strongly dependent on the laser parameters (laser power, laser scan speed, the angle of incidence and the diameter of the laser spot) and material properties (thermal conductivity, specific heat and density). Parametric studies showed that the depth and width of the heat affected zone increased with an increase in the laser power and decreased with an increase of the laser spot size and the laser scan speed. The thermal model can be used to determine the laser parameters for a given cut geometry that will yield no residual heat affected zone in the material after cutting. This provides the basis to optimize and improve laser assisted machining technique. [ABSTRACT FROM AUTHOR]