Strain History Research Articles

Biomechanical characterization of cadaveric brachial plexus regions using uniaxial tensile tests

IntroductionThe proximal regions of the brachial plexus (roots, trunks) are more susceptible to permanent damage due to stretch injuries than the distal regions (cords, terminal branches). A better description of brachial plexus mechanical behavior is necessary to better understand deformation mechanisms in stretch injury.The purpose of this study was to model the biomechanical behavior of each portion of the brachial plexus (roots, trunks, cords, peripheral nerves) in a cadaveric model and report differences in elastic modulus, maximum stress and maximum strain. MethodsEight cadaveric plexi, divided into 47 segments according to regions of interest, underwent cyclical uniaxial tensile tests, using a BOSE® Electroforce® 3330 and INSTRON® 5969 material testing machines, to obtain the stress and strain histories of each specimen.Maximum stress, maximum strain and elastic modulus were extracted from the load–displacement and stress–strain curves.Statistical analyses used 1-way ANOVA with post-hoc Tukey HSD (Honestly Significant Difference) and Mann-Whitney tests. ResultsMean elastic modulus was 8.65 MPa for roots, 8.82 MPa for trunks, 22.44 MPa for cords, and 26.43 MPa for peripheral nerves. Differences in elastic modulus and in maximum stress were statistically significant (p < 0.001) between proximal (roots, trunks) and distal (cords, peripheral nerves) specimens. ConclusionsProximal structures demonstrated significantly smaller elastic modulus and maximum stress than distal structures. These data confirm the greater fragility of proximal regions of the brachial plexus.

Vibration-based FE-model updating for strain history estimation of a 3MW offshore wind turbine tower

Vibration-based FE-model updating for strain history estimation of a 3MW offshore wind turbine tower

Using crack width for shear, stiffness, and stirrup strain history predictions for reinforced concrete beams

Shear failures in reinforced concrete structures occur with little or no warning. Reinforced concrete members with shear cracks should be evaluated to ensure safety. Existing evaluation methods have large variability, require time-consuming modeling or expert opinion. This study uses machine learning to investigate correlations of crack width with shear loading, stiffness, and stirrup strain histories. Experimental literature enables the assembly of a database of rectangular reinforced concrete slender beams with crack width measurements for beams with shear reinforcement amounts smaller and larger than the minimum required by ACI 318-19. Measured data include crack widths from 122 beams, load–displacement relationship from 100 beams, and stirrup strains from 46 beams. Gaussian Process Regression is used to correlate crack width and geometric, material and design properties to shear loading, stiffness, and stirrup strain histories. Ten-fold cross validation training shows mean absolute percent errors of 18, 33 and 77% for shear, stiffness, and stirrup strain history predictions. The proposed algorithms can be used to accelerate the evaluation of in-service structures and can be updated upon availability of additional data.

Influence of lateral variations in décollement strength on the structure of fold-and-thrust belts: Insights from viscous wedge models

Fold-and-thrust belts (FTBs) evolve over a mechanically weak basal décollement that separates the overlying intensely deformed rocks from the underlying less deformed ones. Although deformation structures in FTBs commonly show lateral continuity, a closer inspection reveals distinctive variations in structural style (e.g., fold style) along and across mountain belts. This study uses laboratory-scale viscous models to investigate the influence of lateral décollement strength variations on the spatio-temporal evolution of strain patterns in FTBs. These experiments, simulating crustal-scale deformation, show notable changes in the mode of tectonic wedge growth, including the topographic evolution and ductile strain pattern distribution. For example, the deformation front propagates faster over weakly coupled décollement than the laterally adjacent strongly coupled segment, leading to along-strike variations of the topographic slope and curved outline of the deformation front. Constrictional strain, characteristic of regions of weak coupling, is transient and replaced by flattening strain beyond ∼20 % bulk shortening. The latter prevails in regions over strong décollement, whereas complex strain histories mark the transition zone between weak and strong décollements. Based on our modelling results, we propose that variations in décollement strength may cause the segmentation of deformation processes and the development of transverse faults in FTBs.

New metal-epoxy-matrix carbon-fibre hybrids to tackle stress concentration

The paper explores the feasibility of improving the performance of composite structures with stress concentrators by local infusion of metals. The resulting material architecture presents Multi-Matrix Continuously-Reinforced Composites (MMCRC) – with shared domains of both the thermoset polymer and metal matrices with fibre-bridged interfaces between the domains. The study explores the manufacturing routes to creating such composites and assesses the resulting performance using the open-hole tensile test. It has been demonstrated that the presence of a rigid multi-matrix patch around the open hole, exhibiting minimal thickness variation, leads to a 15.0% improvement in failure load and a 16.6% improvement in failure strain for quasi-isotropic carbon fibre composite laminates. The strain history analysis of the MMCRC samples indicates the occurrence of plastic yielding within the metal matrix and strain redistribution mechanisms, leading to load sharing over the hybrid matrix area.

A novel strategy to enhance the interfacial bonding quality of CoCrFeMnNi high-entropy alloy joints produced by vacuum hot-compression bonding

The strain history of strain rate transient changes was introduced into the vacuum hot-compression bonding (VHCB) process of CoCrFeMnNi high-entropy alloy, which rapidly improved the interfacial bonding quality of the joint. The results of interfacial microstructure characterization indicated that the high-density dislocations generated in the interfacial region during the initial high strain rate stage not only promoted the nucleation of the interfacial recrystallized grains but also induced the transformation of the sub-boundaries and the interfacial grain boundaries (IGBs) to the high mobility twin boundaries (TBs). The accelerated discontinuous dynamic recrystallization process, the growth of TB-type continuous dynamic recrystallization grains, and the interfacial TB migration during the transient VHCB dramatically enhance the IGB migration level of the joints. This study provides an effective strategy for the interfacial regulation of high-quality VHCB joints.

Investigations on the Johnson-Cook Constitutive and Damage-Fracture Model Parameters of a Q345C Steel

Due to the rapid development of high-speed trains, the service safety of vehicle body materials and structures has become a focal point in transport and impact engineering. Numerical simulations on the collision resistance of vehicle materials and structures are crucial for the safety assessment and optimal structural design of high-speed trains but have not been fully investigated due to the lack of damage model parameters. This study focuses on the Johnson-Cook (J-C) constitutive and damage-fracture models of a typical vehicle material, Q345C steel. A series of mechanical tests are conducted on the Q345C steel, including the quasi-static and dynamic compression/tension tests, quasi-static tension tests at different temperatures, and fracture tests along different stress paths, using the material test system and the split Hopkinson pressure/tension bar. Then, the parameters of the Johnson-Cook constitutive and damage-fracture models are calibrated based on the experimental results. In terms of the damage parameters related to stress paths, a new method of combining experiments and simulations is proposed to obtain the real, local fracture strains of the Q345C steel samples. This method allows the measurements of equivalent plastic strain and stress triaxiality histories under nonlinear stress paths, which are hardly accessible from individual experiments, and facilitates the accurate calibration of stress-path-related damage parameters. In addition, a high-speed plate penetration test is used to validate the J-C parameters, which can be directly implemented in the commercial finite element software Abaqus. The projectile trajectories from the simulation and experiment agree well with each other, demonstrating the reliability of the model parameters for impact scenarios and the efficiency of the experimental procedures utilized for calibration.

Characteristics of nurses with musculoskeletal disorders from Dr Soedarso Regional Hospital, Pontianak, Indonesia

Musculoskeletal disorders (MSDs) can have a significant negative impact on quality of life, resulting in reduced ability to work, absenteeism, and possibly switching occupations. The purpose of this study was to investigate the relationship between the prevalence and severity of MSDs and the nurse characteristics (NCs) of nurses working in the Dr Soedarso Regional Hospital (DSRH) inpatient department. An analytical and descriptive cross-sectional methodology was used to examine 134 nurses from Inpatient Wards A and B. Total sampling was used to select the respondents. The level of exposure to the conditions investigated by the quick exposure check (QEC), namely, static and dynamic movements in the back, shoulders/arms, neck, and work-related stress, was significantly correlated with gender and neck (0.050), a history of education-related physical strain, such as back mobility (0.021), years of work-related strain on the neck (0.040), and work-related stress (0.033). There were no significant correlations found between age and static and dynamic movements of the back, shoulders/arms, and neck. Gender, education level, and employment duration all have a strong correlation with MSDs among DSRH inpatient nurses.

Performance Evaluation of Nonlinear Viscoelastic Materials using Finite Element Method

This research paper applies the finite element method as a methodology to evaluate the structural performance of nonlinear viscoelastic solids. A finite element algorithm was built and developed to simulate the mathematical nonlinear viscoelastic material behavior based on incremental constitutive equations. The derived Equation of the incremental constitutive included the complete strain and stress histories. The Schapery’s nonlinear viscoelastic material model was integrated within the displacement-based finite element environment to perform the analysis. A modified Newton-Raphson technique was used to solve the nonlinear part in the resultant equations. In this work, the deviatoric and volumetric strain–stress relations were decoupled, and the hereditary strains were updated at the end of each time increment. It is worth mentioning that the developed algorithm can be effectively employed for all the permissible values of Poisson’s ratio by using a selective integration procedure. The algorithm was tested for a number of applications, and the results were compared with some previously published experimental results. A small percentage error of (1%) was observed comparing the published experimental results. The developed algorithm can be considered a promising numerical tool that overcomes convergence issues, enhancing equilibrium with high-accuracy results.

Hardness Prediction of the Heat-Affected Zone in Multilayer Welded SUS316 Stainless Steel Based on Dislocation Density Change Behavior

The effects of strain hardening and recovery/recrystallization on the hardness of the heat-affected zone (HAZ) in multilayer welded austenitic stainless steel SUS316 were investigated in this study. The results revealed that strain hardening due to welding strain and softening due to recovery/recrystallization were the dominant factors affecting the hardness change in the HAZ during multilayer welding process. Furthermore, the relationship between the strain and dislocation density and that between the recovery/recrystallization and dislocation density were quantitatively investigated using positron annihilation lifetime spectroscopy. Based on these results, a new hardness prediction method based on the change in dislocation density in the HAZ during multilayer welding was proposed. The hardness values in the HAZ after the multilayer welding were predicted based on the simulated strain and thermal history, and the calculated hardness values agreed well with the measured results. This indicates that the newly proposed hardness prediction method based on the dislocation density change behavior in the HAZ during multilayer welding is valuable and effective for selecting the appropriate welding conditions before actual welding.

Mechanical Self-Organization of Particle Networks during Uniaxial Compression Yielding

Colloidal gels, sparse particle networks with large voids, are fundamental model systems of disordered porous materials. Unlike dense amorphous solids, they exhibit significant volumetric deformation while expelling solvents when subjected to external compression. Despite their importance in both natural and industrial settings, the relationship between their network microstructure and compressive yielding behavior has remained elusive. To address this problem, we employ confocal microscopy and a specially designed sample cell to observe the gravity-induced collapsing of colloidal gels at a single-particle level. The experimental insight gained is complemented by simulation results for gravitational collapse and homogeneous uniaxial compression. We find that, during compression, the microstructure of gels is uniquely determined solely by the local volume fraction. This relationship remains independent of the deformation strain history but is subtly influenced by the preparation history of the initial state. In contrast, compressive stress evolves as a unique function of local volume fraction, unaffected by both preparation and strain history, as long as the interparticle interaction remains identical. Moreover, we unveil that local yielding occurs in highly strained, narrow network domains, while highly stressed particles form chainlike structures to support the external stress. These findings suggest that colloidal gels undergoing compressive plastic deformation mechanically self-organize into a unique history-independent state to satisfy mechanical balance in a quasistatic condition, providing crucial microscopic insights into the compressive yielding behavior of particle network materials. Published by the American Physical Society 2024

Cracking performance in the hogging moment region of HSS-UHPC continuous composite girder bridges

To elucidate the cracking performance of concrete slabs at the negative bending moment region of high strength steel (HSS)-ultra high performance concrete (UHPC) continuous composite girder bridges, eight scale-reduced steel-concrete composite beams, constructed using HSS and UHPC that varying parameters of UHPC slab thickness and width and shear connection degree at the steel-concrete interface were prepared and tested. The composite beams' cracking pattern, bending stiffness, load-deflection curve, steel-concrete interfacial slippage, and strain history were presented and discussed. The test results show that the HSS-UHPC composite beams subjected to negative bending moments exhibited favorable cracking performance. With the UHPC slab width increasing from 450 mm to 550 mm, the composite beams' initial cracking moment, bending stiffness, and flexural ductility increased by 33.4%, 20.5%, and 39.8%, respectively. The utilization of a thick UHPC slab benefited the performance of the composite beams under negative bending moments. Replacing the 80 mm-thick slab with a 110 mm-thick slab improved the structure’s cracking moment and bending stiffness by 15.0% and 21.4%, respectively. Additionally, as the shear connection degree increases from 0.64 to 1.02, the initial cracking and ultimate failure moments of the composite beam were improved by 7.2% and 1.6%, respectively. In contrast, the bending stiffness of the beams with a shear connection degree of 1.02 was 12.4% smaller than those of 0.64. A comprehensive comparison between the formula-predicted cracking performance and current experimental results was performed to examine the capability of existing design approaches in calculating the HSS-UHPC composite beams. The flexural resistance algorithm proffered by Xu exhibits favorable alignment with test results, thereby providing a compelling methodology for designing HSS-UHPC continuous composite girder bridges.

Evaluations and enhancements of fatigue crack initiation criteria for steels subjected to large shear deformations

While large accumulated plastic deformations occur in the rail surface layer where rolling contact fatigue cracks initiate, many available Low Cycle Fatigue (LCF) crack initiation criteria focus on small plastic strains. Accordingly, this paper evaluates available fatigue crack initiation criteria for highly shear-deformed R260 steels, reflecting the conditions in the surface layer of rails. Furthermore, modified crack initiation criteria are suggested. The evaluation is based on three different experiments: Large shear strain increments under varying axial loading (predeformation), strain-controlled LCF tests after some predeformation, and axial High Cycle Fatigue (HCF) experiments. For the predeformation, Finite Element (FE) simulations, with a large-strain plasticity model for cyclic and distortional hardening, provide predictions of the local stress and strain histories. A cross-validation procedure is used to assess the accuracy and reliability of both established and modified fatigue crack initiation criteria. The proposed modifications to one of the criteria show an improved fit to the experimental data. However, there is a tendency to overfitting, which can be improved by including more experimental data.

Realistic long-term stress levels in a deep segmented tunnel lining, from hereditary mechanics-informed evaluation of strain measurements

Realistic estimation of stresses in segmented tunnel linings is a challenge tackled herein by means of a hybrid, i.e. computational-experimental, approach. Thermistor-equipped vibrating wire strain gauges were installed (i) into concrete samples undergoing one year-long uniaxial creep tests under the environmental conditions of the tunnel site, and (ii) into the tubbings making up the tunnel lining of the Koralm tunnel. The data obtained from the creep tests allow for calibration and validation of an integro-differential thermo-viscoelastic model. The creep function combines a power-law for short-term creep with a logarithmic law for long-term creep. The corresponding relaxation function is determined by means of Laplace-Carson transformation, inversion, and back-transformation. This is the basis for translating the circumferential strain histories measured in the tubbings of Ring 2013 in Koralm tunnel KAT3 into circumferential and longitudinal stress evolutions. They are mainly due to mechanical ground-shell interactions. The corresponding degree of utilization increases during the first four months after ring installation, and remains virtually constant thereafter. Stress fluctuations due to seasonal temperature variations play only a minor role. With regards to a long-term prognosis, it is very interesting to note that the strain measurements recorded in the tubbings, when plotted as function of the logarithm of time, follow bi-linear trends. These trends can be extrapolated to 150 years, the targeted service life of newly built tunnels in Austria. Throughout this period, the viscoelasticity-based estimates of the stresses in the vicinity of the strain sensors stay temporally constant, at some 40% of the strength of concrete.

Experimental study and constitutive modelling of wire arc additively manufactured steel under cyclic loading

Wire arc additive manufacturing (WAAM) is an efficient and cost-effective method of metal 3D printing that is well suited to structural engineering applications. Fundamental test data on the mechanical properties of WAAM materials, especially under cyclic loading, are however lacking. To address this, an experimental study into the cyclic behaviour of WAAM steel plates has been undertaken and is reported herein. Following geometric and quasi-static mechanical characterisation, a total of 40 as-built and machined coupons were tested under different cyclic loading protocols. Key results from the tests, including the full hysteresis curves, are presented and discussed. A cyclic constitutive model allowing for a yield plateau and the degradation of elastic modulus is proposed and validated against the test data. It is shown that the examined WAAM steel exhibited cyclic hardening behaviour dependent on the strain amplitude and strain history. The elastic modulus of the WAAM material was found to decrease in the first few cycles and then remain stable with increasing accumulated plastic strain. Good energy dissipation performance was also observed, indicating the potential of WAAM steels for seismic applications.

Formula omitted]-TFA based multiscale analysis of failure in elasto-plastic composites

This paper describes a novel homogenization methodology for analyzing the failure of elastoplastic composite materials based on elastic and eigen influence tensors-driven transformation field analysis (E2-TFA). The proposed technique considers the microscopic eigenstrain field accounting for intra-phase damage and inelastic strains. This results in realistic computations by alleviating the post-damage stiffness response, which is a drawback of TFA-based methods. We attain computational efficiency by identifying the preprocessing data solely from the elastic and eigen transformation functions and adopting a reduced order modeling technique with a piecewise constant eigenstrain field throughout the subdomains. The performance of the model is assessed by simulating the response for (a) the representative volume element (RVE) as a homogenized continuum and (b) the various composites under complex load histories with intricate macroscale morphologies. Furthermore, the nonlinear shear stress–strain response of a glass fiber composite is calculated and compared to experimentally measured fracture initiation parameters, failure plane orientation, and strain histories. Finally, we show that E2-TFA can accurately and efficiently capture damage and inelastic deformations in order to estimate the mechanical response of composite materials in a better way.

Comparison of Isokinetic Strength Parameters of Quadriceps in Athletes and Non-Athletes

OBJECTIVE: To compare the quadriceps isokinetic strength parameters of athletes and non-athletes. METHODOLOGY: The cross-sectional study was conducted from July to December 2019 at the Pakistan Sports Board, Islamabad. The sample size was 81, selected through a non-probability convenience sampling technique and calculated by the Rao Soft tool. The 41 participants were in the athletes' group, and 40 were in the non-athletes' group. Individuals with a history of sprain, strain, or fracture in the lower limbs within the last six months were excluded. The self-structured questionnaire includes demographic data, waist-to-hip ratio, thigh circumference, peak torque values and agility t-test score. The isokinetic strength of the right lower limb (RLL) was measured via Biodex system Pro 3. Data was analyzed through SPSS 22, and an independent t-test was applied for analysis between groups. Pearson test was used for the correlation coefficient. RESULTS: Athletes had significantly higher quadriceps muscle strength than non-athletes (p&lt;0.001), indicating the positive impact of regular sports participation and physical training. Quadriceps peak torque positively correlated with thigh circumference (r=0.60, p&lt;0.001), consistent with previous studies. Surprisingly, athletes exhibited a weak to moderate negative correlation between quadriceps peak torque and agility (r=-0.35, p&lt;0.05), suggesting a potential trade-off between muscle mass and agility performance. Increased muscle bulk may compromise speed and flexibility. CONCLUSION: Athletes demonstrated superior quadriceps muscle strength, emphasizing the positive influence of sports involvement and physical training; thigh circumference positively correlated with Quadriceps peak torque, and Agility negatively correlated with quadriceps peak torque. KEYWORDS: Athletes and Non-athletes, Correlation, Isokinetic, Peak torque

Investigating dynamic compressive strength of concrete by using high-rate hydraulic universal testing machine

This study proposes using a new high-rate hydraulic universal testing machine (HR-UTM) to measure the compressive strength of concrete at high strain rates. The HR-UTM eliminated the necessity of friction between the specimen and support. Furthermore, the strain history could be directly measured using strain gauges attached to the specimen. The compressive stress versus strain response of concrete was successfully measured at high strain rates until 19.3 s−1. The proper aspect ratio of the cylinder specimen (D75 ×L150 mm) 2.0 and amounts of lubricants more than 11.3 mg/cm2 could minimize the effects of end friction on the concrete compressive strength.

An enhanced stress resultant plasticity model for shell structures with application in sheet metal roll forming

AbstractThe proposed Kirchhoff-Love shell stress resultant plasticity model extends a previously reported model for plates by complementing the constitutive law of elastoplasticity with membrane effects. This enhanced model is designed for bending dominant settings with small to moderate membrane forces. It is thus implemented in a purpose-built nonlinear mixed Eulerian–Lagrangian finite element scheme for the simulation of sheet metal roll forming. Numerical experiments by imposing artificial strain histories on a through-the-thickness element are conducted to test the model against previously reported stress resultant plasticity models and to validate it against the traditional continuum plasticity approach that features an integration of relations of elastoplasticity in a set of grid points distributed over the thickness. Results of actual roll forming simulations demonstrate the practicality in comparison to the computationally more expensive continuum plasticity approach.

Machine learning enabled identification of sheet metal localization

The Forming Limit Curve (FLC), which describes the maximum applicable strain before localization, depends on the particular material, but also on the applied load and history of the load. Recent investigations have shown that the non-proportional loading effect on the FLC can be predicted with data-driven or machine-learning-based methods. Here we compare different ML methods to their applicability in predicting localization points under multi-segmented non-proportional loading. Therefore, an FE-based metamodel is developed that allows imposing an arbitrary loading history on sheet metal to predict the point of localization. A series of virtual experiments are conducted with this metamodel to generate a database of bi-linear loading paths that are used for training. Different ML-based methods were used to predict the localization point based on the strain history data. The 1D-Convolutional Neural Network (1D-CNN), with the ability to learn dependency between input features, has the best accuracy in predicting the localization point.