Stress-strain Profiles Research Articles

Mechanical Characterization of Flax and Hemp Fibers Cultivated in Romania.

This study examines the mechanical properties, specifically strength and stiffness, of technical hemp and flax fibers grown in Romania. Tensile testing was employed to determine stress-strain curves and the Young's modulus and to assess the failure strength of both fiber types. Although samples of various lengths were tested, no significant length-dependent variations were observed. However, a strong dependence on fiber diameter was noted, with the smallest diameters approaching the documented strength of elementary fibers. Due to the considerable variability in the experimental results pertaining to the characteristics of the reinforced fibers, a statistical analysis using a two-parameter Weibull distribution was employed. The analysis revealed three distinct stress-strain curve profiles, i.e., linear, bi-linear, and tri-linear patterns, with the average ultimate stress ranging from 412 to 566 MPa for hemp and 502 to 598 MPa for flax.

Understanding the dynamics of in-situ micro-rolling in directed energy deposition using thermo-mechanical finite-element analyses

Rolling in Directed Energy Deposition (DED) has shown promising improvements in build quality by providing compressive deformations. The rolling dynamics and associated boundary conditions are crucial for how these deformations impact the stress–strain profiles on the deposited part and substrate. This study investigates these impacts by developing a fully coupled dynamic-thermo-mechanical finite-element model in Abaqus for in-situ micro-rolling in DED. Single bead analyses have been done with a 2D heat flux moving ahead of the roller at a fixed offset. Two rolling boundary condition cases with varying friction at the roller-bead interface have been examined: (i) only translation defined with rotation calculated from roller-bead interaction and (ii) translation with a defined rotation corresponding to a no-slip condition. In the first case, analyses have shown that the surface stress–strain conditions and rolling load variation are susceptible to interfacial friction. With increasing friction, the surface conditions deteriorate and variations in rolling load increase. However, beyond the surface, the overall stress–strain profiles remain similar. The surface stress–strain profile and rolling load variation have been smoothened in the second case because of the defined rotation. Further, a comparison has been made between the results of dynamic-explicit analyses and static-implicit analyses to quantify the roller’s inertia effects. The stress–strain profiles predicted by both analyses have marginal differences but with 16 % over-prediction in rolling load by dynamic-explicit analyses. These results imply that the roller’s inertia marginally affects the deposited part’s stress–strain evolution but has a notable role in rolling load. Also, providing an external drive to the roller corresponding to the second case can effectively minimise the deteriorating effects of roller-bead interfacial friction.

The mechanism for the superior isotropic mechanical properties attained in a cross rolling TiNb alloy

In the present study, the Ti–41Nb (wt.%) alloy featuring a microstructure composed of β and α″ phases have been prepared through the application of the Cross Rolling (CSR) technique to achieve a near-isotropic superior mechanical behavior. The experimental findings revealed that the CSR sample exhibits a uniform β matrix, randomly dispersed α″ martensite and a high density of dislocations and grain boundaries. Subsequent experiments unveiled that the CSR sample displays an almost isotropic mechanical response across three typical directions, Rolling Direction (RD), a 45° deviation from RD, and Transverse Direction (TD), evidenced by comparable stress-strain curve profiles and ultimate tensile strength (UTS) values. Due to the randomly distributed textures and high density of dislocations and grain boundaries, the stress-induced martensitic (SIM) transformation exhibits a similar characteristic in three typical directions, that is, the SIM transformation took place homogeneously and continuously. Consequently, the CSR sample can achieve a near-isotropic and outstanding mechanical performance due to the similar characteristics of martensitic phase transformation and the strengthening effect brought by the high density of dislocations and grain boundaries.

Tailorable Energy Absorbing Cellular Materials via Sintering of Dry Powder Printed Hollow Glass Microspheres

This article examines amorphous glass-based foams as lightweight core materials for crash-resistant structures that offer tailorable energy absorption capabilities. Hollow glass microspheres (HGMs) of different densities are layered using dry powder print- ing (DPP), an additive manufacturing process, and subsequently sintered to consolidate these microspheres into a cellular foam structure. The tuning of energy absorption is achieved in these foams by layering hollow microspheres with different densities and different thickness ratios of the layers. The mechanical response to quasi-static uniax- ial compression of the bilayer foams is also investigated. Bilayer samples a distinctive two-step stress-strain profile that includes first and second plateau stress, as opposed to a single constant density which does not. The strain at which the second plateau occurs can be tuned by adjusting the thickness ratio of the two layers. The resulting tailorable stress-strain profile demonstrates tailorable energy absorption. Tailorability is found to be more significant if the density values of each layer differ greatly. For comparison, bilayer samples are fabricated using epoxy at the interface instead of the co-sintering process. Epoxy-bonded samples show a different mechanical response from the co-sintered sample with a different stress-strain profile. Designing the bilayer foams enables tailoring of the stress-strain profile, so that energy-absorption requirements can be met for a specific impact condition. The implementation of these materials for energy absorption, crashworthiness, and buoyancy applications will be discussed.

Modeling and Analysis of Coupled Thermal and Mechanical Capacity Degradation in Silicon-Based Lithium-Ion Batteries

Large-format cells are gaining popularity for battery electric vehicles (BEVs) to maximize volumetric and gravimetric energy densities but are associated with challenges in ensuring adequate thermal management. Spatial current density and temperature variations negatively affect overall cell utilization and lifetime.In addition, the mechanical stresses generated within the silicon-based battery electrodes also cause aging and resultant capacity loss. The coupled effects of the thermal and mechanical factors could thus particularly exacerbate cell capacity degradation. Rigorous mechano-thermo-electrochemical models for battery degradation can be a powerful complementary tool to understand these phenomena better. Simulating performance scenarios can significantly improve cell design and experimentation while reducing time and cost commitments. Model-based design approaches thus have the potential to yield substantial economic benefits.This work shall serve as an extension to the previously developed thermal degradation model for non-uniform aging in lithium-ion batteries by coupling with mechanical models predicting the effects of volume change within the batteries over cycling. The observed capacity fade trend for a given battery is ultimately the result of an interplay between multiple degradation mechanisms, which depend on a range of design and operating parameters. The errors between the model predictions and experimental data can provide information on the suitability of a given model and the relative prevalence of a given degradation mechanism, with functional and practical benefits, as there exists significant variation in the parameters, mechanisms, and predictive capability of models in the literature. In addition, a rigorous model of volume changes increases the accuracy of predictions of dynamic stress-strain profiles, which in turn helps improve predictions of associated mechanical degradation phenomena. As a first step towards including mechanical effects, the current model builds on the previously reported studies for modeling volume change in porous electrodes due to intercalation (deintercalation) during lithiation (delithiation). This volume change leads to dimensional and porosity changes in the porous electrodes. Furthermore, these mechanical models will help predict generated stresses and strain profiles within the battery and will be related to models of resultant degradation, especially in the case of silicon/graphite electrodes characterized by substantial volume changes.

Synthesis and characterization of waterborne bio-based hybrid isocyanate-free poly (hydroxy urethane)-poly(methacrylate) latexes with vitrimeric properties

Non-isocyanate poly(urethane)s (NIPU)s have emerged as an environmentally friendly alternative for conventional polyurethanes, but several challenges remain towards their wide-scale adoption (e.g., attainment of high molecular weights for sufficiently effective mechanical properties and ease of application). Adopting NIPUs as hybrid polymer-polymer particles with methacrylic monomers is one route towards obtaining higher overall molecular weight, improving properties, and introducing advantages of methacrylate functionality. First, NIPU latex was synthesized using dicarbonate terminated poly (propylene glycol) and the commercial vegetable oil-based diamine Priamine 1075 via step miniemulsion polymerization yielding stable particles with sizes <220 nm. Then, the NIPU latex was used as the seed for the synthesis of hybrid NIPU-poly(methacrylate) particles via conventional radical emulsion statistical copolymerization of a long side chain (13 alkyl groups) alkyl methacrylate (C13MA) and isobornyl methacrylate (IBOMA). Two polymeric phases were observed in cryo-microtomed TEM of the dried latexes at ambient temperature, indicating core-shell phase-separated morphologies. Moreover, 2-acetoacetoxyethyl methacrylate (AAEMA) was introduced in the formulation containing the methacrylate phase to impart dynamic covalent crosslinking into the hybrid via ketone-amine vinylogous urethane formation, resulting in materials with stress relaxation up to 90% at 130 °C and one-time recycled films with similar stress-strain profiles as the original films.

Thermoelastoplastic hydrodynamic lubrication contact analysis of three dimensional rough tooth surface considering micro-scale effect and thermal effect

The contact properties of gear rough surfaces during meshing are influenced by various factors. The analysis of rough surface thermoelastoplastic hydrodynamic lubrication (TPEHL) considering micro-scale effect and thermal effect has not been addressed in the literature. This study establishes a new TEPHL model with multi-factor coupling of thermal field, fluid lubrication, stress-strain, and geometric profile. Based on strain gradient theory (SG), a new thermoelastoplastic material constitutive considering micro-scale effect is developed. Subsequently, the three-dimensional rough surface TPEHL-SG analysis of gear is conducted. The paper investigates the impact of thermal and micro-scale effects on various parameters during the meshing of gear in the full oil film lubrication condition, including surface pressure, oil film thickness, surface temperature, surface deformation, and friction coefficient.

On the calibration of a shear stress criterion for rock joints to represent the full stress-strain profile

Conventional numerical solutions developed to describe the geomechanical behavior of rock interfaces subjected to differential load emphasize peak and residual shear strengths. The detailed analysis of pre- and post-peak shear stress-displacement behavior is central to various time-dependent and dynamic rock mechanic problems such as rockbursts and structural instabilities in highly stressed conditions. The complete stress-displacement surface (CSDS) model was developed to describe analytically the pre- and post-peak behavior of rock interfaces under differential loads. Original formulations of the CSDS model required extensive curve-fitting iterations which limited its practical applicability and transparent integration into engineering tools. The present work proposes modifications to the CSDS model aimed at developing a comprehensive and modern calibration protocol to describe the complete shear stress-displacement behavior of rock interfaces under differential loads. The proposed update to the CSDS model incorporates the concept of mobilized shear strength to enhance the post-peak formulations. Barton's concepts of joint roughness coefficient (JRC) and joint compressive strength (JCS) are incorporated to facilitate empirical estimations for peak shear stress and normal closure relations. Triaxial/uniaxial compression test and direct shear test results are used to validate the updated model and exemplify the proposed calibration method. The results illustrate that the revised model successfully predicts the post-peak and complete axial stress–strain and shear stress–displacement curves for rock joints.

Experimental-based statistical models for the tensile characterization of synthetic fiber ropes: a machine learning approach

This study investigated the tensile behavior of some prevalent synthetic fiber ropes made of polyester, polypropylene, and nylon polymeric fibers. The aim was to generate well-documented experimental statistics and develop simplified stress–strain constitutive laws that can describe the ropes' tensile response. The methodology involved analyzing the thermal history of the fibers using the DSC technique, tensile testing of fibers and yarn components of the rope, and conducting 196 rope tensile tests with optimum testing conditions. Based on the test results, an experimental database of the ropes' tensile characteristics was established, containing different parameters of material properties, rope construction, fiber processing, fiber tensile properties, and rope tensile responses. Subsequently, ANN models were developed and optimized using MATLAB based on the generated dataset's inputs and outputs to predict the studied ropes' tri-linear stress–strain profiles. The results showed that the ANN models accurately predicted the stress–strain properties of ropes represented by the tri-linear approximation with an error of about 5% for the failure strength and strain. The study provides insight into the process-structure–property relationship of synthetic fiber ropes and contributes to minimizing the cost and effort in designing and predicting their tensile properties while contributing to the practical industry.

Molecular dynamics simulation study of thermomechanical properties and hydrogen bonding structures of two‐component polyurethanes

AbstractWe investigated the thermomechanical properties and hydrogen bonding (HB) structures of two‐component hexamethylenediisocyanate (HDI)‐poly(tetramethylene oxide) (PTMO) and 4,4′‐methylenediphenyldiisocyanate (MDI)‐PTMO polyurethanes with atomistic molecular dynamics simulations. We used different temperature‐scanning and sampling protocols to estimate the glass transition temperature (Tg) of these two polyurethanes. Our simulation results consistently predicted higher Tg values for MDI‐PTMO than those for HDI‐PTMO, in qualitative agreement with the same trend observed in experiments. We also studied two different types of HB interactions in these polyurethanes. At ambient temperature, more HB contacts between amide‐hydrogens and carbonyl‐oxygens of the carbamate groups along with longer lifetimes were noted in HDI‐PTMO than in MDI‐PTMO, while the latter revealed more HB contacts between amide‐hydrogens and ether‐oxygens of PTMO. MDI‐PTMO, encompassing more rigid chain structures, displayed higher stress values in stress–strain profiles from high strain‐rate tensile deformations at ambient temperature than HDI‐PTMO, which is consistent with a higher Tg value of MDI‐PTMO.

Biomechanics, Energetics, and Structural Basis of Rupture of Fibrin Networks.

Fibrin provides the main structural integrity and mechanical strength to blood clots. Failure of fibrin clots can result in life-threating complications, such as stroke or pulmonary embolism. The dependence of rupture resistance of fibrin networks (uncracked and cracked) on fibrin(ogen) concentrations in the (patho)physiological 1-5gL-1 range is explored by performing the ultrastructural studies and theoretical analysis of the experimental stress-strain profiles available from mechanical tensile loading assays. Fibrin fibers in the uncracked network stretched evenly, whereas, in the cracked network, fibers around the crack tip showed greater deformation. Unlike fibrin fibers in cracked networks formed at the lower 1-2.7gL-1 fibrinogen concentrations, fibers formed at the higher 2.7-5gL-1 concentrations align and stretch simultaneously. Cracked fibrin networks formed in higher fibrinogen solutions are tougher yet less extensible. Statistical modeling revealed that the characteristic strain for fiber alignment, crack size, and fracture toughness of fibrin networks control their rupture resistance. The results obtained provide a structural and biomechanical basis to quantitatively understand the material properties of blood plasma clots and to illuminate the mechanisms of their rupture.

Investigation of tensile and flexural properties of habesha moringa‐bamboo fiber reinforced epoxy hybrid composite

AbstractIn the present investigation, moringa oleifera and bamboo fibers extracted from Ethiopia are studied to understand their mechanical properties. Three types of woven composites namely moringa/epoxy, bamboo/epoxy and moringa/bamboo/epoxy (hybrid) are fabricated by maintaining 60 vol% fiber content. Additionally, neat epoxy samples are prepared for comparison. Tensile and flexural properties are investigated in terms of strength and modulus. Tensile test results depict brittle failure for all composites and infer increase in fracture strain of woven composites as compared with neat epoxy. Tensile modulus and strength of woven composites increase in the range of 19%–39% and 18%–281%, respectively as compared with neat ones. Flexural stress–strain profiles of neat epoxy, moringa/epoxy and moringa/bamboo/epoxy composites linear curves until failure indicating brittle mode while bamboo/epoxy composites shows non‐linear stress–strain profiles revealing non‐brittle mode of failure. Flexural properties exhibited by bamboo/epoxy and moringa/bamboo/epoxy reveal comparable properties to each other yet superior than moringa/epoxy and neat epoxy composites mainly attributed to the good bonding of constituents and compatibility. All the woven composites reveal an increase in flexural modulus and strength and are in the range of 31%–96% and 5.79%–51.12%, higher than the neat epoxy. Finally, fractured surfaces of specimens are analyzed using scanning electron microscope to understand the structure property correlations.

Characterizing Tensile Strength of Building Sandstone via Uniaxial Tensile, Compressive, and Flexural Bending Tests.

Sandstone is widely used a construction and building material. However, its uniaxial tensile strength (UTS) is not adequately understood. To characterize the uniaxial tensile strength of natural sandstone, three groups of specimens were fabricated for four-point bending, uniaxial compressive, and tensile tests. To characterize the evolution of the stress-strain profiles obtained via these tests, representative expressions were developed in terms of normalized strain and strength. The magnitude of the uniaxial tensile strength exceeded that of the four-point bending strength, indicating that the uniaxial tensile strength cannot be represented by the four-point bending strength. The experimental ratio of uniaxial tensile and compression strength (33-41) was underestimated by the empirical expressions reported in the literature. The suggested correction coefficient for the FBS is 0.25. The compressive modulus (Ec) was generally identical to the experimental results published in the literature, whereas the tensile modulus (Et) was overestimated. The experimental modular ratio, Et/Ec, ranged from 0.12 to 0.14; it was not sensitive to Poisson's ratio, but it increased slightly with the compressive modulus. This work can serve as a reference for computing the load-bearing capacity of sandstone components under tension.

Tensile and Compressive Mechanical Behaviour of Human Blood Clot Analogues

Endovascular thrombectomy procedures are significantly influenced by the mechanical response of thrombi to the multi-axial loading imposed during retrieval. Compression tests are commonly used to determine compressive ex vivo thrombus and clot analogue stiffness. However, there is a shortage of data in tension. This study compares the tensile and compressive response of clot analogues made from the blood of healthy human donors in a range of compositions. Citrated whole blood was collected from six healthy human donors. Contracted and non-contracted fibrin clots, whole blood clots and clots reconstructed with a range of red blood cell (RBC) volumetric concentrations (5–80%) were prepared under static conditions. Both uniaxial tension and unconfined compression tests were performed using custom-built setups. Approximately linear nominal stress–strain profiles were found under tension, while strong strain-stiffening profiles were observed under compression. Low- and high-strain stiffness values were acquired by applying a linear fit to the initial and final 10% of the nominal stress–strain curves. Tensile stiffness values were approximately 15 times higher than low-strain compressive stiffness and 40 times lower than high-strain compressive stiffness values. Tensile stiffness decreased with an increasing RBC volume in the blood mixture. In contrast, high-strain compressive stiffness values increased from 0 to 10%, followed by a decrease from 20 to 80% RBC volumes. Furthermore, inter-donor differences were observed with up to 50% variation in the stiffness of whole blood clot analogues prepared in the same manner between healthy human donors.

Digitized design and mechanical property reprogrammability of multistable origami metamaterials

Origami-based multistable metamaterials have been recognized as a promising platform for diverse applications due to their exceptional mechanical properties. However, the current state of the art in designing origami metamaterials is mostly ad-hoc and narrowly focused on a particular mechanical property. In other words, there is a lack of basic research on deriving generic and systematic methodologies for the design, configuration tuning, and property programming of origami metamaterials, to explore their achievable ranges of mechanical properties comprehensively from the perspective of mechanics. In this work, a mathematically rigorous strategy for synthesizing and reconfiguring multistable origami metamaterials based on two basic modules is put forward, and a systematic approach to analyze and program the material properties is proposed. More specifically, by programming the binary design array of module arrangement and by mathematically expressing the connection constraints, a number of multistable origami cells with exceptional shape reconfigurability are generated. Building upon this, the fundamental mechanics properties, including the multistability, global stress-strain profiles, and tangent elastic moduli, are thoroughly investigated via examining the unit cell, i.e., the “infinitesimal element,” of the metamaterial. Considering the extreme cases of the unit cell architecture, boundaries of the material properties of the synthesized metamaterials at the stress-free configuration are derived, which are of vital importance for material selections and topological optimization. Moreover, due to the topologically different configurations, six categories of metamaterials with qualitatively different material densities and moduli programmability are revealed. In addition to the reprogrammable density and Young's modulus of conventional Miura origami metamaterial, more intriguing properties, such as reprogrammable shearing modulus, locking effect, and inner reconfiguration without modulus change, are discovered for the first time. A prototype made of dual-material 3D printing is created to experimentally evaluate and verify the effectiveness of the analysis method and the characterized material properties. Overall, this work provides a rigorous tool for designing multistable origami metamaterials and an effective strategy for characterizing their fundamental mechanical properties, which will greatly enhance the systematization of creating origami metamaterials.

Tunable Energy Absorbing Property of Bilayer Amorphous Glass Foam via Dry Powder Printing.

The research in this paper entails the design of material systems with tunable energy-absorbing properties. Hollow glass microspheres of different densities are layered using dry powder printing and subsequently sintered to form a cellular structure. The tunability of the bilayer foams is investigated using various combinations of hollow microspheres with different densities and different thickness ratios of the layers. The mechanical responses to quasi-static uniaxial compression of the bilayer foams are also investigated. These bilayer samples show different mechanical responses from uniform samples with a distinctive two-step stress-strain profile that includes a first and second plateau stress. The strain where the second plateau starts can be tuned by adjusting the thickness ratio of the two layers. The resulting tunable stress-strain profile demonstrates tunable energy absorption. The tunability is found to be more significant if the density values of each layer differ largely. For comparison, bilayer samples are fabricated using epoxy at the interface instead of a sintering process and a different mechanical response is shown from a sintered sample with the different stress-strain profile. Designing the layered foams allows tuning of the stress-strain profile, enabling desired energy-absorbing properties which are critical in diverse impact conditions.

Approximate residual stress and plastic strain profiles for laser-peened alloy 600 surfaces

This paper presents approximate in-depth residual stress and plastic strain profiles for laser-peened alloy 600 surface via FE analysis. In approximations, effects of the initial welding residual stress and the number of shots are quantified. Based on FE analysis results, residual stress profiles are quantified by two variables; the maximum difference in stress before and after LSP, and the depth up to which the compressive residual stress exists. Plastic strain profiles are quantified by one variable, the maximum equivalent plastic strain at the surface. The proposed profiles are validated by comparing with published LSP experimental results for welded plates. Effects of the initial welding residual stress and the number of shots on these variables are discussed. The proposed profile can be directly applied to predict the mitigation effect of LSP on PWSCC and to efficiently perform structural integrity assessment of laser peened nuclear components.

Assessment of Textural Properties of Puffed Corn Cakes during Storage at Different Relative Humidity.

Moisture adsorption is considered a critical factor during production and shelf-life of puffed corn cakes (PCC). This study aims to develop and validate an instrumental method and a mathematical model for the characterization of the textural modifications caused by the moisture adsorption in PCC. For that purpose, PCC were stored at different relative humidities to achieve a wide range of water activities (from 0.1 to 0.8 at 22 ± 1 °C). A flexion–compression test was successfully validated in order to characterize the average textural properties of a PCC batch. A mathematical model considering consecutive elastic and plastic zones satisfactorily fitted (average VAR 99.65% and MRE 3.29%) the average stress–strain profiles of PCC and reported useful textural parameters, such as the deformability modulus (E), critical strain (εc), and n curvature parameter. The structural modifications caused by moisture adsorption led to the reduction in E and n and the increase in εc. Even minor changes on the PCC moisture content involve remarkable modifications of the textural properties, which has to be considered for industry and retail distribution.

Exploiting Nonlinear Fiber Patterning to Control Tubular Scaffold Mechanical Behavior

AbstractMelt electrowriting is an additive manufacturing technique capable of fabricating highly biomimetic polymer scaffolds with high‐resolution microarchitecture for a range of tissue engineering applications. The use of a rotating mandrel to fabricate tubular scaffolds using this technique is increasing in popularity; however, the translation of many novel scaffold designs that have been explored on flat collectors has yet to be realized using mandrels. This study reports novel tools to automatically generate scaffold gcode for several new tubular scaffold designs, investigating a range of auxetic pore geometries and open unit cell designs. Through optimization of printing parameters, the novel scaffold designs are successfully printed and mechanically tested to assess tensile properties. Open unit cells significantly reduce the tensile stiffness of scaffolds manufactured with closed pores. Auxetic scaffolds could also be widely tuned using the novel gcode generator tool to exhibit similar stress–strain profiles to typical crosshatch scaffolds but could be made to expand to desired radial dimensions. Finally, heterogeneous auxetic constructs are also fabricated with regions of various radial compliances. This study presents several, mechanically validated novel scaffold designs that are of interest for future applications in targeted tissue engineering product development as well as in soft robotic actuation.

A new direct compression mechanism of structural transition in Poria cocos extract composite particles

The structural transition to generate amorphous translucent grains in Poria cocos dry extract (PCE) composite particles was found and studied as a new direct compression mechanism. The pressure and displacement sensing techniques were used to obtained stress–strain profiles during compression. The Exponential function, Kawakita model, Shapiro model and Heckel model were used to analysis mechanical properties of powders. 12 parameters derived from compression models and powder physical properties were applied to partial least squares method (PLS) for analyzing powder compression mechanism. It was found that only the oven-dried PCE composite particles undergoes the structural transition and generate translucent grains scattered and embedded in tablet, and these tablets have excellent mechanical stability. The structural transition in plant dry extract as the PCE composite particles could be exploited to improve powder compression and tabletability.