Strain State Research Articles

Analytical considerations of the load‐deflection behavior in fibers during a filament winding process

AbstractFilament winding is a manufacturing process used in the construction of fiber composite structures, where a thermoset resin impregnated bunch of fibers is deposited on a rotating mandrel. The evolving stress and strain states due to thermal and mechanical loads during the manufacturing process are of particular interest to avoid subsequent failure of the parts. In this first approach, the mechanical load within the fiber, mainly driven by the pre‐stressed fiber tension, is investigated. Thus, the development of the fiber tension and the pressure on the mandrel as a function of the number of windings is examined. Therefore, models based on the theory of large and small deformations are derived under certain assumptions, resulting in a boundary value problem. In case of large deformations, the boundary value problem using a three‐dimensional formulation based on incompressible, isotropic hyperelasticity does not yield a simple solution. Using a small deformation formulation on the basis of a one‐dimensional consideration an analytical solution can be found. The problems are described in curvilinear coordinates. From the derived models, the required quantities including the fiber tension, the pressure on the mandrel, also as a function of the number of windings, and the fiber elongation can be calculated.

Insights into strain dependent lattice thermal conductivity of α - and κ -Ga2O3

α- and κ-Ga2O3 are promising candidates for high-performance devices such as high-power electronics, but the low thermal conductivity (TC) severely hinders its application. Strain inevitably exists in practical Ga2O3-based devices due to the mismatch of lattice structure and thermal expansion brought by heteroepitaxial growth, and it significantly influences the thermal properties of α- and κ-Ga2O3. By employing first-principles calculations and the phonon Boltzmann transport equation, we have studied the TC at the induced strain and optimized strain axis in free states and 16 different strain states. The TC at the induced strain and optimized strain axis generally decreases with increasing strain. Under −4% XZ-axes biaxial compressive strain, the kzz of α-Ga2O3 can increase to ∼1.7 times its original value, while under −2% XY-axes biaxial compressive strain, the kxx of κ-Ga2O3 can increase to 2.8 times its original value. The improvement of thermal transport properties is attributed to the increase in phonon group velocity and relaxation time caused by the phonon hardening and decrease in three-phonon scattering channels, respectively. However, we observed an exception: under +4% X-axis tensile strain, kyy of α-Ga2O3 increased by 1.1 times. Moreover, atomic bond analysis revealed that under XY-direction strain, the ICOHP values for α-Ga2O3 are −3.94 eV (at −4% strain), −3.76 eV (unstrained state), and −3.63 eV (+4% strain). This discovery elucidates the origin of phonon hardening under compressive strain, indicating that strengthened bonds enhance phonon transport. This study provides essential insights into the mechanisms of α- and κ-Ga2O3 TC under different strains.

A deformation-diffusion interactive model to study crack-tip behaviour and predict crack growth rate under fatigue and hydrogen-embrittlement conditions

Hydrogen is accepted as a cleaner and more sustainable energy source, since it carries abundant energy and does not produce any effluent gas from burning when compared to fossil fuels. However, long-term degradation in mechanical properties, attributed to hydrogen embrittlement, is reported for metallic materials exposed to gaseous hydrogen, leading to accelerated crack growth behaviour under fatigue. In this paper, a visco-plastic deformation-diffusion interactive model is developed to study fatigue crack growth behaviour in a nickel-based superalloy under hydrogen-embrittlement condition. In the model, cyclic deformation is described by visco-plasticity constitutive model, while hydrogen diffusion is simulated by a modified form of Fick’s first law of diffusion which can address hydrogen diffusion driven by the hydrostatic stress gradient. In particular, trapped hydrogen, expressed as dependent on both diffusible hydrogen concentration and inelastic strain, is considered in the modelling of hydrogen diffusion. The model also describes the effects of hydrogen concentration on mechanical deformation by considering its influence on the evolution of isotropic hardening as well as on the strain state. Interaction between cyclic deformation and hydrogen diffusion is therefore studied for a crack tip in a compact tension specimen subjected to fatigue and hydrogen attack, showing a strong dependency on both loading frequency and stress intensity factor range. Subsequently, a two-parameter criterion is proposed for fatigue crack growth prediction, which accounts for the contributions of both cyclic deformation and hydrogen diffusion. The predictions show a good agreement with experimental data in terms of crack growth rate under fatigue and hydrogen-embrittlement conditions.

Analysis of Changes in the Stress–Strain State and Permeability of a Terrigenous Reservoir Based on a Numerical Model of the Near-Well Zone with Casing and Perforation Channels

A finite element model, which includes reservoir rock, cement stone, casing, and perforation channels, was developed. The purpose of the study is to create a geomechanical model of the zone around the well, which includes support elements and perforation channels. This model will help predict changes in the productivity coefficient of a terrigenous reservoir and determine the most efficient mode of operation of a producing well. In order to exclude the stress concentration within the casing–cement stone and cement stone–rock, the numerical model applies contact elements. As a result, structural elements slip, while the stresses are redistributed accurately. The numerical simulation of a stress state in the near-well zone was carried out by using the developed model with differential pressure drawdown on the terrigenous reservoir, one of the oil fields in the Perm region. It is shown that the safety factor of the casing reaches roughly 3–4 units. The only exceptions are the upper and lower parts of the perforations, where this parameter is close to one unit. The safety factor of cement stone accounts for 2–3 units. However, parts with its lowest value (1.35) are also concentrated near the perforation channels. In order to analyze the change in permeability, the dependence of the safety factor on effective stresses was taken into account. Therefore, it was found that, in the upper and lower parts of perforations, the stresses decreased, while permeability rose by up to 20% of the initial value. An increase in differential pressure drawdown, on the contrary, can lead to a permeability reduction of 25%, especially in the lateral parts of the perforations. Areas of rock destruction under tensile and compressive forces were identified by using the Mohr–Coulomb criterion. It is estimated that with an increase in pressure drawdown, the areas of rock destruction under tensile force disappear, while the areas of rock destruction under compression increase. After further analysis, it was found that, with the maximum pressure drawdown of 12 MPa, the well productivity index can decrease by 15% due to the reservoir rock compaction.

Exploring the relationship between occupational stress, physical activity and sedentary behavior using the Job-Demand-Control Model

ObjectivesTo study the relationship between the occupational stress model, specifically the Job Demand-Control Model of Karasek, physical activity level and sedentary behavior.MethodThis is a cross-sectional, observational, descriptive study. A self-administered questionnaire was distributed to 100 volunteers working at Clermont Auvergne University. The questionnaire included the Karasek questionnaire and the International Physical Activity Questionnaire.ResultsThe results reveal that occupational characteristics play a significant role, with individuals exhibiting high job control showing reduced sitting time and increased physical activity compared to those with low job control. Job strain was associated with increased sitting time and decreased physical activity. Further analysis revealed that being in a state of job strain significantly predicted sitting for more than 7 h per day. Similarly, job strain and isostrain were explanatory factors for having a low to moderate physical activity level. Logistic regression quantified the risks, indicating that sitting for more than 7 h per day increased the risk of job strain by 4.80 times, while high physical activity levels and being male reduced the risk by 79 and 84%, respectively. Job strain also increased the risk of prolonged sitting by 5.06 times and low to moderate physical activity levels by 5.15 times. Additionally, mediation analysis revealed that a substantial portion of the association between sitting time and job strain was mediated by physical activity, and vice versa, emphasizing the interconnected nature of sedentary behavior and physical activity in influencing occupational stress.ConclusionThe study highlights the impact of sedentary behavior on occupational stress, assessed using Karasek’s Job-Demand-Control Model. Despite being less studied, sedentary behavior appears to be a relevant contributor to occupational stress. Furthermore, the results emphasize the significant role of physical activity levels, suggesting that it plays a substantial part in the relationship between sedentary behavior and occupational stress.

Epitaxial Thin Film Growth on Recycled SrTiO3 Substrates Toward Sustainable Processing of Complex Oxides.

Complex oxide thin films cover a range of physical properties and multifunctionalities that are critical for logic, memory, and optical devices. Typically, the high-quality epitaxial growth of these complex oxide thin films requires single crystalline oxide substrates such as SrTiO3 (STO), MgO, LaAlO3, a-Al2O3, and many others. Recent successes in transferring these complex oxides as free-standing films not only offer great opportunities in integrating complex oxides on other devices, but also present enormous opportunities in recycling the deposited substrates after transfer for cost-effective and sustainable processing of complex oxide thin films. In this work, the surface modification effects introduced on the recycled STO are investigated, and their impacts on the microstructure and properties of subsequently grown epitaxial oxide thin films are assessed and compared with those grown on the pristine substrates. Detailed analyses using high-resolution scanning transmission electron microscopy and geometric phase analysis demonstrate distinct strain states on the surfaces of the recycled STO versus the pristine substrates, suggesting a pre-strain state in the recycled STO substrates due to the previous deposition layer. These findings offer opportunities in growing highly mismatched oxide films on the recycled STO substrates with enhanced physical properties. Specifically, yttrium iron garnet (Y3Fe5O12) films grown on recycled STO present different ferromagnetic responses compared to that on the pristine substrates, underscoring the effects of surface modification. The study demonstrates the feasibility of reuse and redeposition using recycled substrates. Via careful handling and preparation, high-quality epitaxial thin films can be grown on recycled substrates with comparable or even better structural and physical properties toward sustainable process of complex oxide devices.

Stress and Strain Analysis for a Topological Optimized Beam

This paper presents a study of a beam manufactured using fused deposition modeling (FDM) which was topologically optimized and subjected to 3-point bending. In this paper polylactic acid (PLA) was used as a material in order to obtain the beams. Topology optimization is a method widely used in the additive manufacturing (AM) field, that uses algorithmic models to optimize the material layout within some parametric restrictions, like conditions, constraints, or sets of loads and it maximizes the performance and capability of the design by extracting material from different zones that are insignificant in terms of carrying loads to reduce the weight of the model. In the first step, the stress and strain state of the simple beam was numerically and analytically calculated, likewise, the experimental test of the beam subjected to 3-point bending was achieved. After the calculus for the simple beam, the next phase aims at the topological optimization process of the beam subjected to 3-point bending. For all the numerical investigations a calibrated material determined experimentally was used. Following calculations and experimental tests, a final version of the beam topologically optimized was reached, with a minimization of the cost regarding the mass of the beam and the material required for its reproduction.

Test-and-FE-based method for obtaining complete stress-strain curves of structural steels including fracture

Ductile fracture is a common limit state of frameworks of steel structures and can be predicted by incorporating models for fracture initiation and propagation in finite element (FE) analyses. However, accurate prediction of fracture relies on unique fracture parameters for a given material, requiring precise predictions of fracture strain and stress states obtained through coupon tests and accompanying FE data analysis. In recent decades, various methods have been proposed to predict ductile fracture initiation, including various design geometries of coupons, test setups and FE analyses, which may lead to inconsistent fracture strains and stress states. Hence, there is a need for proposing a standard procedure for the design, test and accompanying FE-based calibration of fracture parameters, as pursued in this paper. Given that ductile fracture initiates under significant plastic strain, a constitutive model for the full strain range is required, as also proposed in this paper. Moreover, to reduce the experimental and data analytical efforts, an empirical method is proposed that uses only a small number of coupon tests to calibrate the fracture parameters. The method encompasses three levels wherein one, two, or three coupon tests are required. All in all, the paper presents a methodology for determining the full-range true stress-strain curve and the initiation of fracture, including a new post-necking constitutive model and methods for determining the free parameters of the post-necking and fracture initiation models. While applied to steel in this paper, the proposed methodology is potentially also applicable to other metals.

Research of Asymmetric and Symmetric Cold Rolling Influence on Microstructure, Mechanical Properties and Stress–Strain State of Steel Strips

Research of Asymmetric and Symmetric Cold Rolling Influence on Microstructure, Mechanical Properties and Stress–Strain State of Steel Strips

Breadth-first search algorithm on the finite element simulation of the electrical resistivity of the carbon black elastomeric pressurized sensor

Resistivity and piezoresistive sensitivity of Carbon Black (CB) elastomeric nanocomposites are studied using a finite element method with a conductive network model. CB spheres are placed into Representative Volume Elements (RVEs) in random positions to perform simulations and obtain the strained state and new position of particles. Numerical results are implemented into a breadth-first search algorithm tailored to find percolation pathways from one end of the RVE to another based on the shortest distance between CBs in the strained regime. Percolation pathways are used by the conductive network model to determine the critical distance for resistivity. Resistivity diminishes as the critical distance increases attributed to a greater number of electrons penetrating the barriers. Critical distance at which tunneling can occur expands with an increase in barrier potential. Smaller CBs that can more efficiently occupy the gaps lead to a reduction in the critical distance range necessary for percolation to happen.

The Effects of Loading Angles on the Failure of Cross-Ply Notched Bio-Basalt Composites

A cross-ply basalt V-notched butterfly specimens were subjected to pure tension, combined tension-shear, and shear stress-strain state using a modified Arcan test fixture with loading angles from 0° to 90° with 15° increment. Multiaxial stress and strain states were studied using the principal stress and strain ratio, from which the principal angle was determined and used to represent principal states in the gauge section. The quasi-elastic to non-linear transition stresses were determined for each loading angle. In biaxial stress-strain states and pure shear, the deformation and consequently the shear-induced damage start to accumulate significantly. Also, in biaxial stress-strain states between 15°-75°, the shift from tension-shear to pure shear was observed after the transition to the non-linear part of the stress-strain curve. The digital image correlation (DIC) images and microscopic evaluation show that a large extent of damage is the consequence of the shear deformation after the rotation of 0° clamped fibres, while the 90° fibres maintained their original straight form. In off-axis tests, the principal strain axis rotates towards the weakest material axis even at small off-axis angles. This causes a transition from a tension-shear biaxial state in the linear loading part to shear in the non-linear part, leading to irreversible damage beyond the transition point.

Influence of different wrought processes on the microstructure and texture evolution in AZ31 magnesium alloy

AZ31 magnesium alloys were deformed by five wrought processes (forging, rolling, extrusion, equal-channel-angular-extrusion (ECAE), and caliber rolling) under the condition of an introduced equivalent plastic strain of approximately 1.5 at 573 K. The strain components induced by these wrought processes were computed using the finite element method (FEM). By combining the calculation results with the microstructure observations, the texture and microstructure evolution were discussed from the viewpoint of the strain state. The FEM showed that approximately the same equivalent strain was induced at the center of the alloys where observations were performed. Therefore, as the values of the equivalent plastic strain were fixed in all wrought processes, the effect of the strain component could be compared. The forged and rolled alloys had an intensive basal texture perpendicular to the compression and normal directions, respectively. In the others, a basal fiber texture parallel to the material flow direction was observed. These basal textures were oriented perpendicular to the compressive strain, and their intensities strengthened with an increase in the strain component. The microstructure became more refined and homogenized as the magnitude of the minimum principal strain decreased. This decrease corresponds to the transition of the deformation mode from the uniaxial compression mode to the multidirectional deformation mode as long as the same equivalent strain is induced. This result demonstrates that the microstructure obtained through dynamic recrystallization depends on the deformation mode, separately from the effect of the conventionally reported equivalent plastic strain.

Experimental Study on Damage Constitutive Model of Rock under Thermo-Confining Pressure Coupling

Underground engineering frequently encounters the challenges of high temperatures and high confining pressures. The combined effects of temperature and confining pressure can significantly alter the mechanical properties of rock. Evaluating the impact of these factors on rock is a crucial aspect of engineering. This study investigates the mechanical properties of rocks under various temperature and stress conditions, focusing on the deformation and failure characteristics of four typical rock types: granite, red sandstone, gray sandstone, and shale under temperature-confining pressure coupling. The results indicate that high temperatures cause internal structural damage and crack propagation in rocks, leading to a reduction in compressive strength and elastic modulus. Conversely, high confining pressures can inhibit crack propagation and enhance rock deformation capacity. Additionally, significant differences were observed in the mechanical responses of different rocks; red sandstone and shale predominantly exhibited shear failure under the coupled effects of temperature and confining pressure, whereas granite and gray sandstone exhibited bulging failure. Based on the experimental results, an elastic modulus fitting model considering the temperature-confining pressure coupling effect was proposed, and the parameters of the Drucker–Prager criterion were modified. A constitutive model was constructed to accurately reflect the stress–strain state of rocks under the coupled effects of temperature and confining pressure. The constitutive model results show good agreement with the experimental findings.

Damage Analysis of Rolling Stock Automatic Coupler under Cyclic Loads

To ensure the operational safety of the automatic couplers of a rolling stock subjected to cyclic loading, reliability and residual service life must be determined. This paper involved the prediction of the durability of the automatic coupler SA3 by analytical summation of cyclic damage. During the investigation, the cyclic characteristics and damage modes of the automatic coupler material that influence the accumulation of damage are determined. The stress and strain state assessment model was developed using a 3D finite element method for the automatic coupler housing as a geometrically complex component. A methodology was used to assess damage per load cycle that is applicable to any sequence of automatic coupler load cycles. For this purpose, the authors used low-cycle stationary load dependencies that account for quasi-static and low-cycle fatigue damage. The investigation showed that a coupler may develop a crack due to accumulated quasi-static and fatigue damage. For damage summation, the dependences of low-cycle stationary stress-controlled load accounting for low-cycle, quasi-static fatigue damage are proposed in view of the variation of the load on the automatic coupler during operation depending on the weight of the rolling stock, velocity, and railway relief. The proposed methodology is applicable to the calculation of other housings under similar loading conditions.

Interfacial Stress Transfer and Fracture in van der Waals Heterostructures.

Artificially stacking 2D materials (2DMs) into vdW heterostructures creates materials with properties not present in nature that offer great potential for various applications such as flexible electronics. Properties of such stacked structures are controlled largely by the interfacial interactions and the structural integrity of the 2DMs. In spite of their crucial roles, interfacial stress transfer and the failure mechanisms of the vdW heterostructures, particularly during deformation, have not been well addressed so far. In this work, the interfacial stress transfer and failure mechanisms of a MoS2/graphene vdW heterostructure are studied, through the strain distributions both laterally in individual 2DMs and vertically across different 2DMs revealed in-situ. The fracture of the MoS2 and the associated states of stress and strain are monitored experimentally. This enables various interfacial properties, such as the interfacial shear strength and interfacial fracture energy, to be estimated. Based only on the measured strength and interfacial properties of a single vdW heterostructure, a failure criterion is proposed to predict the failure mechanisms of similar vdW heterostructures with any lateral dimensions. This work provides an insight to the deformation micromechanics of vdW heterostructures that are of great value for their miniaturization and applications, especially in flexible electronics.

Dynamic digital image correlation method for rolling convective contact

Digital image correlation (DIC) is an increasingly popular and effective non-contact method for measuring full-field displacements and strains of deformable bodies under load. Current DIC methods applied to bodies undergoing large displacements and rotations require a large measurement area for both the reference (i.e., undeformed) image and the deformed images. This can limit the resulting resolution of the displacement and strain fields. To address this issue, we propose a two-stage dynamic DIC method capable of measuring displacements and strains under material convection with high resolution. During the first stage, the reference image is assembled from smaller, high-resolution images of the undeformed object obtained using a spatially-fixed or moving frame. Following capture, each sub-image is rigidly translated and rotated into its appropriate place, thereby producing a full, high-resolution image of the reference body. In stage two, images of the loaded and deformed body, again obtained using a small camera frame with high resolution, are aligned with matching regions of the undeformed composite image using BRISK feature detection before performing DIC. We demonstrate the method on a contact problem whereby an elastomeric roller travels along a rigid surface. In doing so, we obtain fine-resolution measurements of the state of strain of the region of the roller sidewall in contact with the substrate, even as new material convects through the region of interest. We present these measurements as a series of images and videos capturing strain evolution as the roller transitions from static loads to a fully dynamic steady-state, documenting the effectiveness of the method.

Investigations on the effect of arsenic and phosphorus atomic exchange on the origin of crystal potential fluctuations in InAsP/InP epilayers

The study investigates the anion exchange mechanism between the ad-atoms of arsenic and phosphorus followed by their inter-diffusion processes, in InAsP/InP hetero-structures grown by metal organic vapor phase epitaxy technique. The energetics and kinetics of the ad-atoms like arsenic and phosphorus are governed by the growth conditions. It has been found that the percolation of arsenic and phosphorus in the epilayer depends on various factors, such as gas-phase diffusion coefficients, surface reaction rates, misfit strain energy, bond energy, segregations, and the presence of defects and dislocations. Effects of anion exchange mechanisms on generating local crystal potential states that originated due to the local crystal bonding environment are further investigated. The magnitude of these local potential states strongly depends on the strain states associated with the layer thickness. If the difference between the potential minima is small (< 25 meV), it leads to distinct “S” shaped temperature-dependent luminescence/absorption spectra. In contrast, a large difference gives rise to two distinctive luminescence/absorption peaks. Thus, by controlling the strain states associated with the energetics and kinetics of ad-atoms like arsenic/phosphorus and layer thickness, such “S” shaped behavior can be controlled.

A microstructural thermo‐elastoplastic analysis of the mushy zone during laser beam welding

AbstractAs a modern method of contact free fusion, laser beam welding has gained importance in recent years. This is due to both the possibiliy of a high advance speed of the laser and low thermal distortion of the components compared to other welding processes, see Dal and Fabbro. These beneficial process properties follow from a focused laser, which thus results in a precise energy input. In addition, laser beam welding processes can be automated which makes the process attractive for a wide range of applications, cf. Dilthey. Nevertheless, various influences, like the temperature gradient, the chemical composition or process parameters, may have an effect on the occurrence of so‐called solidification cracks. Solidification cracks arise during solidification and occur in the area of the mushy zone, which is located behind the melt pool. The material behavior in the mushy zone is governed by a dendritic morphology. Due to this, liquid phase inclusions may occur in some parts of the mushy zone, see Hills et al.. When these trapped areas solidify, no further liquid phase can follow and a negative pressure is created. The resulting stresses can then lead to solidification cracks. In further studies, the geometry of the dendritic morphology will be generated on the basis of previous phase field simulations. These describe the dendrite growth controlled by the chemical concentration. The resulting geometry will then be simulated using the possibilities of a thermo‐elastoplastic material model, which will enable temperature‐driven imitation of growth. This contribution addresses the evolving state of the dendritic microstructure in a simplified manner. Therefore, for the first study, a simplified morphology is used, that is, no secondary arms and an elliptical geometry of the dendrites is assumed. Thermal as well as elastoplastic effects are already taken into account, in order to represent the inherent stress and strain states in the microstructure. These may be related to critical states leading to failure in the future.

The impact of mechanical strain on magnetic and structural properties of 2D materials: A Monte Carlo study.

The inherent flexibility of two-dimensional (2D) materials allows for efficient manipulation of their physical properties through strain application, which is essential for the development of advanced nanoscale devices. This study aimed to understand the impact of mechanical strain on the magnetic properties of two-dimensional (2D) materials using Monte Carlo simulations. The effects of several strain states on the magnetic properties were investigated using the Lennard-Jones potential and bond length-dependent exchange interactions. The key parameters analyzed include the Lindemann coefficient, radial distribution function, and magnetization in relation to temperature and magnetic field. The results indicate that applying biaxial tensile strain generally reduces the critical temperature (Tc). In contrast, the biaxial compressive strain increased Tc within the elastic range, but decreased at higher strain levels. Both compressive and tensile strains significantly influence the ferromagnetic properties and structural ordering, as evidenced by magnetization hysteresis. Notably, pure shear strain did not induce disorder, leaving the magnetization unaffected. In addition, our findings suggest the potential of domain-formation mechanisms. This study provides comprehensive insights into the influence of mechanical strain on the magnetic behavior and structural integrity of 2D materials, offering valuable guidance for future research and advanced material design applications.

A new approach on constitutive modeling for quasi-brittle materials under multiaxial loading

Abstract This work introduces a new method for expanding unidimensional models to predict material behavior under multiaxial loading. The concept of six-dimensional mechanical space is adopted, and in each basis direction of the space, there is one fiber-bundle model (FBM), so these six FBMs are independent amongst one another but follow the same damage evolution rule. Under triaxial loading, these FBMs have different stress and strain states, so six corresponding damage variables have different values. The anisotropic damage is thus represented by the six damage variables. When it is under uniaxial loading, the six-dimensional space reduces to one-dimensional space, so the proposed model can be calibrated using uniaxial loading test data, and the calibrated model can predict the material behavior under multiaxial loading conditions. Biaxial loading and triaxial loading test data are used to verify the proposed model, and parametric analyses are performed to analyze model predictions under different loading conditions. It shows that model predictions agree well with the test data and are consistent with experimental observations.