Similar Mechanical Response Research Articles

Transfer learning-based Gaussian process classification for lattice structure damage detection

This study presents a novel approach for real-time vision-based structural health monitoring, focusing on evaluating the deformation state of lattice structures. The structures are renowned for their remarkable recovery capabilities and exhibit similar mechanical responses under compressive loads. Despite these characteristics, quickly assessing the health status of the applied structure using knowledge from another related lattice structure is usually time-consuming and impractical. To address this, we propose to combine Gaussian process classification with transfer learning, termed TL-GPC, to detect damage states under compressive loads while also achieving uncertainty quantification. By employing structural deformations captured via the optical flow algorithm as inputs, the internal transfer kernel factor in TL-GPC is tailored to model knowledge transfer between source and target domain inputs. Experimental results show that the proposed TL-GPC model can deliver higher damage detection accuracy while ensuring stable uncertainty quantification in scenarios with limited and unbalanced experimental data.

Effect of Press-Fit Size on Insertion Mechanics and Cartilage Viability in Human and Ovine Osteochondral Grafts.

The osteochondral allograft procedure uses grafts constructed larger than the recipient site to stabilize the graft, in what is known as the press-fit technique. This research aims to characterize the relationships between press-fit size, insertion forces, and cell viability in ovine and human osteochondral tissue. Human (4 donors) and ovine (5 animals) articular joints were used to harvest osteochondral grafts (4.55 mm diameter, N = 33 Human, N = 35 Ovine) and create recipient sites with grafts constructed to achieve varying degrees of press fit (0.025-0.240 mm). Donor grafts were inserted into recipient sites while insertion forces were measured followed by quantification of chondrocyte viability and histological staining to evaluate the extracellular matrix. Both human and ovine tissues exhibited similar mechanical and cellular responses to changes in press-fit. Insertion forces (Human: 3-169 MPa, Ovine: 36-314 MPa) and cell viability (Human: 16%-89% live, Ovine: 2%-76% live) were correlated to press-fit size for both human (force: r = 0.539, viability: r = -0.729) and ovine (force: r = 0.655, viability: r = -0.714) tissues. In both species, a press-fit above 0.14 mm resulted in reduced cell viability below a level acceptable for transplantation, increased insertion forces, and reduced linear correlation to press-fit size compared to samples with a press-fit below 0.14 mm. Increasing press-fit size required increased insertion forces and resulted in reduced cell viability. Ovine and human osteochondral tissues responded similarly to impact insertion and varying press-fit size, providing evidence for the use of the ovine model in allograft-related research.

Microstructural and mechanical characterization of additively manufactured parts of maraging 18Ni300M steel with water and gas atomized powders feedstock

The demand for manufacturing components with complex geometries, good mechanical properties, and material efficiency has surged across various industries, encompassing aerospace, military, nuclear, and naval sectors. Laser powder bed fusion (LPBF), as an additive manufacturing (AM) process, has emerged as a promising method for producing ultra-high mechanical strength alloys, like maraging 300 steel (18Ni300M). However, in numerous studies in the literature concerning the effects of processing parameters on the properties of 18Ni300M steel parts fabricated through LPBF, limited attention has been given to the influence that powder atomization methods may exert on the final properties of these parts. This article investigated the effect of gas atomization (GA) and water atomization (WA) processes on the microstructure of 18Ni300M steel powders and the mechanical properties, microstructure, and chemical composition of LPBF-produced parts. The results revealed significant distinctions in the morphology, aggregation degree, and particle size distribution between the GA and WA powders, which directly influenced the microstructure and affected the amount of defects in LPBF-produced parts. Despite the similar mechanical response found in the WA and GA specimens in the elastic region, the samples produced with the WA batch presented a brittle behavior with a ductility of only 4.06%, whereas the GA parts had an elastoplastic behavior with an elongation of 11.52%. The bulks from the WA batch produced in the LPBF process were compromised due to powder contamination with oxygen, which increased gas porosity and effected fragile oxide particles visible on the fracture surface.

Does flash sintering alter the deformation mechanisms of tungsten carbide?

The study aims at unravelling the effect of fast and ultrafast electric current-assisted sintering on the plasticity of ultrahard binderless tungsten carbide. The small-scale deformation of polycrystalline micropillars obtained from samples consolidated by Spark Plasma Sintering (SPS) and Electrical Resistance Flash Sintering (ERFS) processes was studied. Micropillars, 3 µm in diameter, were prepared by focused ion beam and compressed ex and in-situ at room and high temperatures (700 °C). Electron-transparent lamellas were milled out from the pillars plastically deformed at different strain levels to carry out Transmission Kikuchi diffraction (TKD) and HRTEM analyses. At room temperature, the micropillars show similar mechanical responses under compression, reaching outstanding yield strengths (8–11 GPa) with plastic strain not exceeding 3–5% because of a dislocation-assisted toughening mechanism. At 700 °C, the pillar's yield strength drops to around 1.5–2 GPa accompanied by the relevant temperature-activated plasticity. However, only the pillars prepared from flash-sintered material can be homogeneously deformed up to ≈50%; conversely, those derived from SPS ceramics fail macroscopically at strains of ≈20–25% strain upon the localisation of plastic strain at shear bands.

The heterogeneous microstructure in laser powder bed fabricated Inconel 718 pillar and its influence on mechanical properties

The dimensions of small components have a strong influence on the microstructure and properties of structural material fabricated by the laser-based manufacturing approach. In this study, we analyzed the microstructure characteristics of Inconel 718 tiny pillars fabricated using laser powder bed fusion. We identified microscale heterogeneous microstructure with varying substructure sizes, arrangements of precipitates, dislocation structures, and segregation of solute atoms from the pillar center to the edge. The pillar center and edge owe very low-density dislocations, while the transition zone indicates high-density dislocation tangles on the substructure boundaries. For the first time, it is found the pillar center presents polygonal substructure with straight sub-boundaries in the absence of precipitates, which is entirely different from the typical microstructure in bulk Inconel 718 alloys manufactured using the same method. To evaluate the influence of the heterogeneous microstructure on the mechanical properties, nanoindentation and micropillar compression tests are conducted. The transition zone exhibits higher hardness and yield stress than the center and edge of the pillar. By contrast, the edge and the center region show similar mechanical responses.

Effect of Ethylene Comonomer Content on the Foam Processing Window of Long-Chain Branched Polypropylene

The non-optimized foam processing window (FPW) can create processing challenges and limit the possible materials with which a polymer of interest can be processed in emerging foaming technologies. To address this drawback, we aim to investigate the effect of ethylene comonomer content on the foaming behavior of polypropylene (PP), particularly the FPW. Two PP resins containing 0.75 and 1.5 wt % of ethylene comonomers were studied, while using a PP homopolymer as a control. High-pressure differential scanning calorimetry confirmed the decrease in the onset crystallization (Tc-onset) and end melting (Tm-end) temperatures with increasing ethylene comonomer content as a result of the defects the ethylene units induce in the crystalline structure of PP. Rheological measurements suggest that the addition of ethylene comonomer content resulted in negligible changes in the extensional and shear rheological responses of the PP-based resins. In addition, the foam expansion results and the observed morphologies reveal no significant change in the resins’ foamability, characterized by the shape of their expansion profiles with respect to the foaming temperature. Interestingly, the FPW was found to be the sole affected parameter, as 1.5 wt % of ethylene comonomers resulted in a 10 °C shift in the FPW toward lower temperatures, compared to the PP homopolymer. The resins with 0 and 1.5 wt % of ethylene comonomer content showed similar mechanical responses under compression tests for their optimally expanded samples. These findings reveal a potentially effective approach for tuning the FPW of processed PP resins without compromising their foaming and mechanical performances. Consequently, foam processing techniques are further enhanced, resulting in a wider span of potential applications.

Morphological coupling of the distal organ in the Peruvian walking stick (Oreophoetes peruana): Structural and functional aspects

AbstractIn insects, the detection of mechanical stimuli from body movements, airborne sound, substrate vibration, medium flow, or gravity by mechanosensory organs plays an important role. These mechanosenory organs can have complex morphologies with numerous sensilla, and the functional morphology with specific attachments of the sensory neurons to surrounding tissues and structures determines the stimulation. In stick insects, the subgenual organ complex in the tibia of all legs is an elaborate system of two chordotonal organs, which respond to substrate vibrations, and associated tibial campaniform sensilla, which respond to cuticular strain. One chordotonal organ, the distal organ, is characterized by a linear set of sensilla. This distal organ has not been studied for its physiological characteristics in detail, but the attachment or mechanical coupling is functionally important. Here we characterize two aspects of attachment or mechanical coupling of the distal organ: At the dorsal side, the organ is connected to the inner side of the dorsal cuticle by connective tissue, which is shown to also contain the axons of campaniform sensilla. At the proximal end, a fine membrane runs to the adjacent chordotonal organ, the subgenual organ. This membrane spans the tibia in transverse direction. It does not contain neuronal elements, but as a connection between the subgenual and the distal organ, it may influence the mechanosensory activity of these organs. Such a connection is not present in other insects such as locusts or cockroaches and could affect the sensory function in stick insects (e.g., in vibration detection by the subgenual organ) or even couple the two organs, resulting in similar mechanical responses.

Mechanical response of a cemented soil over a wide range of porosities and cement contents

The adjusted porosity/cement index η/(Civ)a has proved its effectiveness in modelling the strength and stiffness of a variety of artificially cemented soils. In this regard, by establishing a specific η/(Civ)a value, either by increasing the cement content and decreasing the density (or the opposite), a similar mechanical response is expected. Nonetheless, the role of this sort of dosage changing has not yet been verified for triaxial testing and, particularly, the effect of different dosages assembled at the same η/(Civ)a value has not yet been evaluated considering the effective peak stress parameters. As a reason, present research fulfills this gap by conducting a series of CID triaxial tests on a cemented clayey sand and, as well, small strain stiffness tests and the unconfined compressive strength tests. The last two being part of a preliminary assessment which comprehended the study of, at least, three dosages assembled at five different η/(Civ)a values. The test data have revealed that both the stiffness and the strength outcomes could be properly correlated to the η/(Civ)a, regardless of the dosage type. Yet, the effective peak stress parameters (ϕ′peak and c′peak) could not be related to the η/(Civ)a index owing to the dosage-dependence of the strength mobilization mechanisms.

Durability response of a cemented clayey sand over a wide range of porosities and cement contents

The adjusted porosity/cement index η/(Civ)a has proven to be a powerful tool related to the dosage of soil–cement mixtures as it encompasses into a unique parameter the effect of either the cement content and the compactness on the mechanical response (e.g. strength, stiffness and durability) of such materials. Theoretically, by setting a specific η/(Civ)a value, a very similar mechanical response should be obtained by the use of distinct dosages assembled through the combinations of a variety of porosities and amounts of cement. In this regard, the most environmental attractive dosage can be chosen considering a specific construction case. Yet, such possibility has not yet been evaluated, specifically, for the durability tests. Thus, present study aspires to address this lacuna by carrying out these tests via wetting–drying-brushing cycles on different dosages established within five η/(Civ)0.28 values (i.e., 45, 30, 35, 25, and 20). Two different mix designs were assembled within each η/(Civ)0.28 for compacted clayey sand-cement blends, being the results statistically evaluated aiming to check for the equivalence of the attained results. In addition, the accumulated loss of mass data was successfully correlated to the η/(Civ)0.28 index through power-type relationships.

A UMAP-based clustering method for multi-scale damage analysis of laminates

In this study, a novel multi-scale damage model based on the parametric finite-volume direct averaging micromechanics theory (parametric FVDAM), extended finite element method (XFEM), and a clustering algorithm, is built, to describe the progressive damage evolution of laminates, where a uniform manifold approximation and projection (UMAP)-based clustering method is specially designed and incorporated with the FVDAM and XFEM for the first time. The subvolumes in the unit cell generated by FVDAM with similar mechanical responses were included in the same cluster using the UMAP-based clustering method. The semi-analytical framework of FVDAM allows the efficient generation of unit cells. The built-in advantage in the visualization of the proposed UMAP-based clustering method allows researchers in the field of mechanics to have a clear and intuitive understanding of the clustering results. The clustered unit cell is then conjugated to the XFEM, which allows the damage information to be transmitted between different scales. Three damage mechanisms of laminates under a three-dimensional (3D) stress state are considered, which include matrix damage, fiber breakage, and delamination. Furthermore, a shear nonlinear matrix Ds for a 3D element is derived and introduced in the model, which enables the description of the unique elastic nonlinear behavior of laminates. The model is implemented using UDMGINI and USDFLD subroutines in ABAQUS, which not only allows the calculation of the load–displacement curve, but also the simulation of clear and smooth crack propagation paths. To verify the effectiveness of the model, the experiments of [±60]2s and [90]8 notched glass-fiber/epoxy laminates under tension were performed by digital image correlation (DIC) monitoring, and the results compared were in good agreement with the simulations, thus proving the effectiveness of the proposed model. The code of the UMAP-based clustering method developed in this study can be downloaded from https://github.com/Danhui-Yang/MicroMechanicsUmapClustering.

Foaming Performance of Linear Polypropylene Ionomers

Linear polypropylene (PP) exhibits poor foamability because of its inherently low melt strength. Incorporation of long-chain branches is a common approach to increase melt strength; however, it is a costly process. To bridge this gap, we set out to study the effect of ionic content on the foaming behavior of linear PP ionomers using a PP homopolymer as a control and a commercial high melt strength long-chain branched PP as a benchmark. Small-angle X-ray scattering confirms the presence of ion clusters in the ionomers, which act as physical cross-linking points as was recently shown, providing enhancement to the dynamic moduli, complex viscosity, and strain hardening behavior, even at ion contents below 0.1 mol %. We found that, upon foaming, the PP ionomer with a higher ionic content exhibited higher foam uniformity, higher cell density (∼108 cells/cm3), and smaller cell size (as small as 37 μm) compared to those of its linear counterpart. Furthermore, the linear ionomer resin and the commercial branched PP showed similar foam morphologies and mechanical responses under cyclic indentations over the temperature range 155–175 °C. These findings reveal a new, and potentially cost-effective, route to produce high performance foams using linear PPs that are compliant to industrial standards.

Microgels as globular protein model systems

Understanding globular protein adsorption to fluid interfaces, their interfacial assembly, and structural reorganization is not only important in the food industry, but also in medicine and biology. However, due to their intrinsic structural complexity, a unifying description of these phenomena remains elusive. Herein, we propose N-isopropylacrylamide microgels as a promising model system to isolate different aspects of adsorption, dilatational rheology, and interfacial structure at fluid interfaces with a wide range of interfacial tensions, and compare the results with the ones of globular proteins. In particular, the steady-state spontaneously-adsorbed interfacial pressure of microgels correlates closely to that of globular proteins, following the same power-law behavior as a function of the initial surface tension. However, the dilatational rheology of spontaneously-adsorbed microgel layers is dominated by the presence of a loosely packed polymer corona spread at the interface, and it thus exhibits a similar mechanical response as flexible, unstructured proteins, which are significantly weaker than globular ones. Finally, structurally, microgels reveal a similar spreading and flattening upon adsorption as globular proteins do. In conclusion, microgels offer interesting opportunities to act as powerful model systems to unravel the complex behavior of proteins at fluid interfaces.

Experimental study of gas diffusion layers nonlinear orthotropic behavior

One of the most important components of PEMFC is the gas diffusion layer (GDL), owing to its key role in the reactant diffusion, water management, thermal and electron conductivity. Therefore, the GDL must have an optimal stiffness to ensure these transport functions during numerous hydrothermal cycles. The understanding of its behavior is still a remaining issue. Its orthotropic mechanical behavior requires a series of mechanical characterizations in the plane of the fibers and out of plane. In addition, there are different manufacturing processes for GDL in sheet or roll form to optimize its functional properties. A macro porous layer (MPL) or different PTFE contents might be added by different manufacturers to optimize its performance. In this study, we have performed several mechanical tests differentiating between in plane and out of plane properties in order to characterize different GDLs available on the market. All of the experimental work has been done in the machine (MD) and cross machine direction (CD) according to the fiber orientation. The different GDL types were then classified into categories presenting similar mechanical response.

Mechanical performance of fractal-like cementitious lightweight cellular structures: Numerical investigations

Cellular structures with tunable mechanical properties are promising lightweight structures for prefabricated construction. In this study, a 3D fractal structure named Menger-Sponge (MS) cube is analysed. Besides, six other alternative fractal-like structures are designed with respect to different shapes of their associated hollow sections. Finite element method (FEM) is employed to predict the structure's mechanical behaviours under a uniaxial compression load. The numerical model is validated by experimental results obtained from author's previous publication. Comparisons are made between triply periodic minimal surface (TPMS-Primitive) and the second-order MS cementitious structure, and also among other fractal structures with different hierarchies. Results indicate that the MS and Primitive blocks have similar mechanical responses. The fractal-square (FS) structures exhibit better structural performances, especially for the first and second fractal orders. Overall, this numerical investigation shows the effect of the shaped holes and thinnest cross-section area on the hierarchically porous structure.

Functionally Graded Scaffolds with Programmable Pore Size Distribution Based on Triply Periodic Minimal Surface Fabricated by Selective Laser Melting.

Functional graded materials are gaining increasing attention in tissue engineering (TE) due to their superior mechanical properties and high biocompatibility. Triply periodic minimal surface (TPMS) has the capability to produce smooth surfaces and interconnectivity, which are very essential for bone scaffolds. To further enhance the versatility of TPMS, a parametric design method for functionally graded scaffold (FGS) with programmable pore size distribution is proposed in this study. Combining the relative density and unit cell size, the effect of design parameters on the pore size was also considered to effectively govern the distribution of pores in generating FGS. We made use of Gyroid to generate different types of FGS, which were then fabricated using selective laser melting (SLM), followed by investigation and comparison of their structural characteristics and mechanical properties. Their morphological features could be effectively controlled, indicating that TPMS was an effective way to achieve functional gradients which had bone-mimicking architectures. In terms of mechanical performance, the proposed FGS could achieve similar mechanical response under compression tests compared to the reference FGS with the same range of density gradient. The proposed method with control over pore size allows for effectively generating porous scaffolds with tailored properties which are potentially adopted in various fields.

The Dynamic Evolution of Permeability in Compacting Carbonates: Phase Transition and Critical Points

Mechanical damage and resultant permeability evolution during compaction of highly porous reservoir rocks have strong implications on the extraction of mineral and energy resources. Laboratory Experiments can be performed to quantify this effect; however, the effect of size on these processes and the information they provide need to be evaluated before any conclusion can be drawn. As part of this study, conventional triaxial compression tests under different confining pressures were carried out on large samples (30 mm diameter and 60 mm length). These experiments were compared to the same setup for small samples with 12.7 mm diameter and 25.4 mm length which allowed monitoring of the pore structure changes through the use of an X-ray transparent triaxial cell at constant confining pressure. Both scales showed a similar mechanical response. The large-scale experiments were used to investigate the transition from brittle to ductile deformation, and the small-scale experiments allowed detailed investigation of the microstructural changes affecting the permeability evolution. The permeabilities of the specimens were continually measured during the triaxial loading at both scales. At defined increasing axial strain levels, the small sample was imaged using X-ray computed tomography (XRCT) and internal structural changes were mapped. A series of digital rock analysis techniques and Pore Network Modelling allowed accurate analysis of the evolution of the microstructure and its effect on permeability evolution using Pore Network Models. An XRCT-based, microstructurally enriched, continuum model successfully describes the permeability evolution measured during triaxial testing. Self-organized criticality of the propagating front of compaction was also shown by R2 values > 0.95 for a double Pareto fractal scaling law. Both approaches, as well as the macroscale experiments, confirmed a phase change in permeability at ~ 5% axial strain which provided a solid basis for microstructurally enriched assessment of the dynamic permeability.

Mechanical properties of 3D printed ceramic cellular materials with triply periodic minimal surface architectures

In this study, four types of triply periodic minimal surface (TPMS) were implemented to create cellular ceramics via digital light processing (DLP) technology, namely p-cell, gyroid, IWP and s14. The mechanical properties of these TPMS structures were investigated experimentally. Results showed that compressive strength of TPMS structures increases with relative density. IWP and s14 structures exhibit similar mechanical response under stress. In general, all TPMS structures can sustain >2% strain without failure and the compressive strength followed the order of s14 > IWP > gyroid > p-cell. The s14 structure can reach a high compressive strength of 105 MPa at a structural density of 30.5 % while gyroid structure can provide a compressive strength of 5.6 MPa at a very low structural density of 6.7 %. The porosity dependence of Young’s modulus of sintered zirconia TPMS demonstrated that the Pabst-Gregorova exponential relation can provide a better prediction than the classical Gibson-Ashby model.

The Hofmeister effect on protein hydrogels with stranded and particulate microstructures

The infiltration of ions into hydrogel matrix could significantly affect the microstructure and macroscopic mechanics of the gels. Here, the Hofmeister effect of various salts on the whey protein isolate hydrogels with fine-stranded and particulate microstructures is investigated by soaking the preformed hydrogels in the sodium salts of different anions. The infiltration of kosmotropic anions yield stiffer hydrogels, whereas the chaotropic anions soften the hydrogels. The hydrogels with fine-stranded microstructures are more sensitive to the salts comparing to the particulate ones due to the microscopic phase transitions and enhanced hydrophobic interactions between polymer chains occurred in fine-stranded hydrogels. Besides, despite the significant difference in water binding ability of different salts, the water holding capacity of the salt-treated hydrogels was mainly determined by the gel stiffness instead of the salt types. Similar mechanical responses of BSA and egg white protein hydrogels to the Hofmeister series was also demonstrated, suggesting that the results shown here could potentially be generalized for other globular protein hydrogels.

Thermodynamic equivalence of cyclic shear and deep cooling in glass formers

The extreme slowing down associated with glass formation in experiments and in simulations results in serious difficulties to prepare deeply quenched, well annealed, glassy material. Recently, methods to achieve such deep quenching were proposed, including vapor deposition on the experimental side and "swap Monte Carlo" and oscillatory shearing on the simulation side. The relation between the resulting glasses under different protocols remains unclear. Here we show that oscillatory shear and swap Monte Carlo result in thermodynamically equivalent glasses sharing the same statistical mechanics and similar mechanical responses under external strain.

The Influence of Soccer Playing Surface on the Loading Response to Ankle (P)Rehabilitation Exercises.

Contemporary synthetic playing surfaces have been associated with an increased risk of ankle injury in the various types of football. Triaxial accelerometers facilitate in vivo assessment of planar mechanical loading on the player. To quantify the influence of playing surface on the PlayerLoad elicited during footwork and plyometric drills focused on the mechanism of ankle injury. Repeated-measures, field-based design. Regulation soccer pitches. A total of 15 amateur soccer players (22.1 [2.4]y), injury free with ≥6 years competitive experience. Each player completed a test battery comprising 3 footwork drills (anterior, lateral, and diagonal) and 4 plyometric drills (anterior hop, inversion hop, eversion hop, and diagonal hop) on natural turf (NT), third-generation artificial turf (3G), and AstroTurf. Global positioning system sensors were located at C7 and the mid-tibia of each leg to measure triaxial acceleration (100Hz). PlayerLoad in each axial plane was calculated for each drill on each surface and at each global positioning system location. Analysis of variance revealed a significant main effect for sensor location in all drills, with PlayerLoad higher at mid-tibia than at C7 in all movement planes. AstroTurf elicited significantly higher PlayerLoad in the mediolateral and anteroposterior planes, with typically no difference between NT and 3G. In isolated inversion and eversion hopping trials, the 3G surface also elicited lower PlayerLoad than NT. PlayerLoad magnitude was sensitive to unit placement, advocating measurement with greater anatomical relevance when using microelectromechanical systems technology to monitor training or rehabilitation load. AstroTurf elicited higher PlayerLoad across all planes and drills and should be avoided for rehabilitative purposes, whereas 3G elicited a similar mechanical response to NT.