Abstract In this study, dynamic mechanical analysis (DMA) is employed to explore the dynamic performance of brick-shaped pure AM polymers at different frequencies. Brick-shaped specimens of AM nylon polymer manufactured using fused deposition modelling were investigated. DMA was carried out under 3-point bending for a frequency range of 1 – 51 Hz at 5 Hz intervals. The storage modulus was found to be almost an order of magnitude higher than the loss modulus for corresponding frequencies, yielding a low value of tan delta. The overall tan delta decreased with increasing frequency, with the highest value of 0.148 at 1 Hz and the lowest of 0.102 at 51 Hz. Similar behaviour was observed when comparing with existing studies on AM polymer-matrix composites. The experimental results were used to determine parameters of the Prony series in the frequency domain, useful for numerical studies.

Cast irons are the material of choice in cylinder heads and cylinder blocks of heavy-duty diesel engines with their operating temperatures in the range of 400 °C to 500 °C. Exposure to high thermal and mechanical loads and long-term operation at high temperatures make these products susceptible to creep-related failure mechanisms, resulting in performance degradation and premature failure. The focus of this paper is to demonstrate a methodology for development of micromechanical models for cast iron, incorporating a creep mechanism. Results are presented for a representative volume element. The effect of stress concentration on the material’s creep response is highlighted along with the plans for further improvements in the micromechanical models. The methodology and approach developed in this research is applicable to cast irons as well as other heterogeneous materials such as metal matrix composites.

Cast irons are extensively used in high-temperature applications such as cylinder heads of heavy-duty diesel engines, where sustained exposure to high stresses and temperatures can initiate creep-related failure mechanisms, impacting their long-term durability and efficiency. Our previous experimental research demonstrated significant differences in creep mechanisms and behaviour of compacted graphite iron (CGI) under tensile and compressive loading. In situ analysis of the microstructural effects defining these differences during long-term high-temperature experiments is hardly possible. An alternative way to study these effects is to develop advanced micromechanical models using a finite-element method. The aim of this paper is to study the local responses at microscale (considering local distributions of stresses and strains) to macroscale long-term loading at high temperature employing direct introduction of microstructural features into numerical models. The models consider elasto-visco-plastic behaviour of the CGI material under tensile and compressive loading regimes. The novel results presented in this paper are applicable to cast irons as well as other heterogeneous materials such as metal matrix composites and the models presented can be used as a tool in the development of materials with microstructures customised for high-temperature applications.

Longitudinal HR-pQCT scans can identify mineralised-tissue gains and losses after image registration, but whether baseline trabecular architecture can rank the locations of subsequent image-derived transitions remains unclear. This study tested whether surface-conditioned local trabecular support can rank subsequent formation-labelled transitions directly from baseline images and whether a longitudinal axial-prolate neighbourhood provides additional information beyond the isotropic local support. Baseline and 6-month distal-tibia HR-pQCT scans of nine postmenopausal women are analysed, giving 18 side-level image pairs. The analysis is restricted to baseline surface-marrow voxels, defined as marrow voxels sharing a face with baseline bone. A spherical support count provides an isotropic local-BV/TV-equivalent baseline. The proposed axial-prolate operator counts baseline bone voxels within an ellipsoidal neighbourhood, with its long axis aligned with the scanner's z-axis. Ranking performance is evaluated using leave-one-subject-out ROC-AUC. The obtained results indicate that the spherical local support ranks subsequent formation-labelled transitions above chance, showing that an isotropic local bone amount already contains prospective surface-conditioned information. The axial-prolate operator further improves this process. Matched-volume comparisons show that both anisotropy and longitudinal orientation contribute to this gain, while local-BV/TV-stratified analyses indicate that the directional signal is not fully reducible to the isotropic local bone amount. These findings establish an image-derived framework for ranking trabecular formation-labelled transitions from the baseline architecture alone. The distal-tibia application indicates that site-informed directional kernels can refine the general local-support framework. External validation is required to determine whether the kernel scale and alignment should be recalibrated for other anatomical sites and populations.

Exercise is widely recommended to maintain lumbar bone mineral density (BMD), the tissue-level mechanical environment generated within the lumbar spine during different exercises remains difficult to assess in vivo. This study integrated individualized musculoskeletal modelling, finite element analysis, and longitudinal quantitative computed tomography (QCT) to characterise exercise-specific lumbar loading patterns and interpret them alongside regional BMD adaptation. Ten postmenopausal women with low BMD who completed a 6-month combined exercise intervention were included (ChiCTR2400081574). QCT scans were acquired at baseline and follow-up to quantify BMD changes in the vertebral body (VB) and posterior region (PR). Individualized musculoskeletal models of walking, heel drops, jumping, and resistance exercise were developed to estimate joint reaction forces and muscle forces. These loads were transferred to individualized lumbar finite element models using a MATLAB–Python workflow to calculate segmental and regional von Mises stresses. Longitudinal QCT revealed that BMD was preserved or increased in the VB, whereas BMD declined in the PR, particularly at L1–L3. Jumping produced the highest peak joint reaction forces and von Mises stresses in the superior lumbar segments, whereas resistance exercise generated the greatest loading at L4–L5. Across all tasks and vertebral levels, von Mises stresses were consistently higher in the VB than in the PR. Distinct exercise modalities generated different segmental and regional loading environments within the lumbar spine. These mechanical patterns were broadly consistent with the observed regional BMD changes, providing a mechanically informed interpretation of lumbar bone adaptation during exercise. Chinese Clinical Trial Registry, ChiCTR2400081574 (retrospectively registered 5 March 2024).

Abstract A novel, simple and effective finite element formulation is introduced for the analysis of functionally graded Timoshenko curved tapered beams. This formulation relies on a complementary variational approach based on a set of approximations that satisfy in a strong form all equilibrium conditions of the boundary-value problem. As a result, this formulation is naturally free from both shear and membrane locking phenomena. The effectiveness of the formulation is numerically demonstrated through its application to benchmark problems, with the obtained results analysed and discussed.

Abstract Skin is the largest organ of the human body and is susceptible to tears, abrasions and lacerations, some of which require extensive long-term care. These are more prevalent in prosthetic users due to prolonged contact between the skin and prosthetic socket and the different forces that are exhibited. This research focusses on the skin tissue, using silicone rubber as a synthetic skin substitute, to determine the mechanical properties of the material. Uniaxial tensile tests were performed on silicone rubber samples of various cross-sectional areas to reflect the different thicknesses of skin throughout the body. The results were validated using Digital Image Correlation (DIC) with GOM Correlate Software. The experimental results, alongside inverse modelling methods, were used to develop a finite-element numerical model with ABAQUS software which can be used to predict the results under more complex loading states. Understanding the mechanical properties of soft tissues under different forces is the first step in reducing discomfort on the skin within the prosthetic socket.

Mechanical properties of additively manufactured short-fiber-reinforced polymer composites depend on both the process parameters and the microstructural morphology of composites. Typically, reinforced thermoplastic polymer filaments are produced without control of the distribution of fibers, which may result in underestimation of the mechanical performance of 3D-printed parts. This study numerically investigates the impact of changes in microstructural parameters on the effective mechanical properties of acrylonitrile-butadiene-styrene (ABS) reinforced with carbon, glass, and basalt short fibers, using computational tools of mathematical morphology and finite-element (FE) modeling. The data on the internal arrangement of short fibers in the polymer are obtained with micro-computed tomography of the filament samples and presented as statistical distributions of fiber lengths and orientation angles. Three-dimensional representative volume elements are created in FE software with both original and modified distributions of the morphological parameters of reinforcement. The elastic properties of composites are assessed for cases when parameters of short-fiber distribution deviate from their original values. The results indicate that control of the microstructural arrangement of short fibers during filament manufacturing can increase the elastic modulus of reinforced ABS.

Corners are among the most common yet least understood features in material extrusion additive manufacturing (MEAM). They exist in almost all toolpaths, especially lattices and infills, impacting structural integrity and shear flow, especially for fibre composites. However, corners have been rarely quantified as microstructure-governing mechanical entities. This is the first microstructure-mechanics study for 3D‑printed corners, revealing how corner geometries dynamically dictated crack growth and direction, stress concentration, cyclic degradation, and fibre kinematics.Multi-layer single-filament corners with varied angles were 3D printed and tested. For monotonic tensile, highly similarly force-displacement responses of pure and short-fibre-reinforced polymers confirmed material-independent structure-dominated corner mechanics: force reduction and brittle-to-flexible transition with turn angles. For short fibre composites, corner microstructural evolution was identified with dynamic crack and fibre behaviours. Displacement-controlled cyclic tensile showed displacement dependency on self-stiffening and degradation of force, energy dissipation and increase of stiffness. The displacement-control cyclic tensile also revealed several competing mechanisms for fibre reinforced composites (fibre re-orientation and strain-hardening versus damage accumulation). Force-controlled cyclic tensile showed decreased with increasing turn angles, and transition from rupture of small turn angles to delayed rupture for greater angles with hinge-opening. Next, compared to angular corners, rounded corners showed that curvature effectively suppressed stress concentration and improved strength (>7-fold for normalised force), supported by a case study of zigzag lattices with rounded corners (>48% and >87% increase in strength and stiffness).This study highlights corners in MEAM from incidental geometry into primary microstructural features that govern performance, revealing how corner‑induced microstructures could govern load transfer, deformation modes, failure evolution, and fatigue. These provide an insight of corner‑aware toolpath strategies that enhance structural integrity and mitigate mechanical weakness or stress concentration in MEAM.

Osteoporosis often leads to a site-specific vertebral fracture due to the regional heterogeneity of mechanical competence. High-impact combined with resistance exercise showed promise in improvement of volumetric bone mineral density (vBMD) at global spine-segment level. However, localized effects of such exercise on bone mineral density and mechanical strength remain under-explored. Thirty healthy postmenopausal women with low bone mass were recruited in randomized clinical trial of 6 months of high-impact and resistance exercises (ChiCTR2400081574). A voxel-based 3D registration method was designed to extract the identical seven anatomical sub-regions from QCT images scanned before and after this exercise. Seven finite-element models of each sub-region were developed to analyze the regional change of ultimate compressive strength (UCS) for the first time. Regionally, significantly lower changes of BMD were observed in the exercise group (EG) than the control group (CG) in the inferior articular process, transverse process, and anterior vertebral body (p < 0.05), although the BMD losses were found in both groups. While significant increases of UCS (up to 4.58

Cast irons are extensively used in high-temperature applications such as cylinder heads of heavy-duty diesel engines, where sustained exposure to high stresses and temperatures can initiate creep-related failure mechanisms, causing detrimental effects on the long-term durability and efficiency. Our previous paper [1] demonstrated significant differences in creep mechanisms and behaviour of compacted graphite iron (CGI) under tensile and compressive loading. In situ analysis of the microstructural effects driving these differences during long-term high-temperature experiments is hardly possible. An alternative way to study the microstructural effects is to develop advanced micromechanical models of the material using numerical modelling. The aim of this paper is to present a methodology for development of such micromechanical finite-element models for cast iron incorporating creep and plasticity effects. Computational results obtained for a representative volume element are presented to elucidate the effects of graphite morphology on spatial micro-scale elasto-viscoplastic behaviour of CGI. The effects of shape, aspect ratio and orientation of graphite inclusions are discussed highlighting significant effects of graphite morphology on the stress distribution as well as creep and plasticity in the material. These novel results along with the detailed methodology and analysis approach are applicable to cast irons as well as other heterogeneous materials such as metal matrix composites.

Trabecular bone is a living material that adapts its spatial organisation and mechanical properties when subjected to loading. There were efforts to describe adaptation in trabecular bone with mathematical models regulating resorption and formation activities as a function of mechanical stimuli. In this paper, an approach to optimise parameters of a bone-adaptation model is proposed and investigated, and the simulation results of trabecular-bone adaptation are quantitatively compared with high-resolution peripheral quantitative computed tomography (HR-pQCT) scans of a distal tibia in a participant following six months of physiological loading. For this purpose, finite-element models were developed from baseline scans of the participant's trabecular bone and used as an initial domain to run simulations regulated by the bone-adaptation model implemented in a Fortran subroutine. The simulated results were element-by-element compared with the corresponding models from follow-up HR-pQCT scans. Mechanostat parameters of the bone-adaptation model were optimised to improve correspondence between the simulated and follow-up HR-pQCT-based models. The developed approach captured the main trends in changes of bone volume fraction, trabecular thickness and separation and achieved 84 - 93 % of the element-by-element correspondence with the experimental models when utilising the optimised values of bone-adaptation parameters. These optimised values were different across the bone's cross-section. In the boundary conditions representing physiological loading, they predicted higher bone resorption rate in the inner regions of distal tibia than in the outer regions, intensified bone resorption in the anterior-inner, medial-inner and medial-outer regions, higher bone formation rate in the outer regions of distal tibia than in the inner regions, and intensified bone formation in the lateral-outer region.