Constant Compressive Stress Research Articles

Experimental analysis of the cyclic behavior of rammed earth walls reinforced with arundo donax natural fiber

This experimental study analyzes the seismic behavior of rammed earth walls with Arundo donax natural fiber inclusions, also called "caña brava” (REWC), and without inclusions (REW). The experimental program consists of two stages: physical and mechanical characterization of materials, where properties such as particle size, density, Atterberg limits, and compressive and flexural strength were determined; and dynamic tests, which included compressive and cyclic load tests on REW and REWC walls. The walls were subjected to cyclic loading with derivatives between 0.2 % and 1.4 % in-plane combined with a constant vertical compressive stress of 13 kPa to simulate seismic forces in the presence of gravity loads. The results regarding loading, hysteretic response, energy dissipation, stiffness degradation, and failure mode are compared. In addition, the envelope curves of the load-displacement hysteretic responses are analyzed using a capacity spectrum approach. It is observed that the inclusion of Arundo donax natural fiber negatively affects the mechanical properties of the walls and their hysteretic response. It is also observed that the energy dissipation is affected by the inclusion of Arundo donax natural fiber. However, the stiffness behavior is similar in all the walls. Rigid body failure modes are identified in all the walls, but the walls, including Arundo donax natural fiber, form failure planes that divide the wall into two bodies.

Stress–diffusion coupling. Application to interstitial diffusion

A numerical study of the stress–diffusion coupling theory based on the Cahn–Larché method is presented in the case of interstitial diffusion. Indeed, the interaction between diffusion and stress fields has been widely studied in the past. Most of the studies focused on the effect of chemical stress due to mass transport on diffusion. The majority of the studies have been focusing on the coupling between external mechanical and chemical stresses with diffusion. In this study, the effect of stress/strain on mobility and stress gradient mobility and driving forces are presented, based on the model of Voorhees and Larché. The analytical solutions are detailed, from general equations (interstitial diffusion, elastic material) to a macroscopic model (interstitial diffusion, isotropic elastic material, infinite dilute solution, 2D axisymmetric). Numerical simulations for different samples thickness and β parameter helped to better understand and then experimentally identify the prevailing effect of stress on mobility or diffusion driving forces. These studies demonstrated the impact of constant compressive and tensile stress on diffusion kinetics through the mobility term of the equation, as well as the effects of negative and positive stress gradients via the Nernstian term. The results show that constant compressive stress and negative stress gradient hinder the diffusion. On the contrary, tensile stress and positive stress gradient promote the diffusion. This work also demonstrates the importance of coupling between mobility and Nernstian effect on the diffusion promotion.

Quantitative in-situ investigation of dislocation loop motion in Fe9Cr1.5W ferritic/martensitic steel under the coupling effects of constant stress and irradiation

Dislocation loop motion plays an important role in irradiation creep but their dynamic evolution is hardly investigated. In this work, the one-dimensional motion of loops was investigated by in-situ TEM in Fe9Cr1.5W ferritic/martensitic steel under the combination of irradiation and constant compression stress and compared with the case of irradiation only to highlight the synergistic effect. Loops preferred to glide along one side that was close to the compression direction and the other side was retarded.. The proportion of large mobile loops was also increased. Jump frequency was doubled after the addition of compression, indicating the high sensitivity to stress.

Effect of temperature on ferroelastic and creep behavior of LaCoO3

The study investigates the time-dependent deformation of LaCoO3 under constant uniaxial compressive stresses at various temperatures ranging from room temperature to 880 °C. Through the acquisition of stress-strain curves at different temperatures, it has been observed that LaCoO3 exhibits non-linear ferroelastic behavior. The stiffness of LaCoO3 increases with temperature, up to 600 °C, after which it starts to decrease at higher temperatures. Furthermore, negative creep occurs at lower temperatures, whereas positive creep is observed at temperatures exceeding 600 °C. This can be attributed to transitioning from a ferroelastic creep at low temperatures to a combination of ferroelastic and high-temperature conventional creep at temperatures above 600 °C. The magnitude of both negative and positive creep is proportional to the temperature. The structural stability of LaCoO3 under creep loading at all temperatures has been assessed by comparing pre-test and post-test X-ray diffraction analyses, which showed the texture formation after testing.

Biomimetic Gradient Hydrogels with High Toughness and Antibacterial Properties.

Traditional hydrogels, as wound dressings, usually exhibit poor mechanical strength and slow drug release performance in clinical biomedical applications. Although various strategies have been investigated to address the above issues, it remains a challenge to develop a simple method for preparing hydrogels with both toughness and controlled drug release performance. In this study, a tannic acid-reinforced poly (sulfobetaine methacrylate) (TAPS) hydrogel was fabricated via free radical polymerization, and the TAPS hydrogel was subjected to a simple electrophoresis process to obtain the hydrogels with a gradient distribution of copper ions. These gradient hydrogels showed tunable mechanical properties by changing the electrophoresis time. When the electrophoresis time reached 15 min, the hydrogel had a tensile strength of 368.14 kPa, a tensile modulus of 16.17 kPa, and a compressive strength of 42.77 MPa. It could be loaded at 50% compressive strain and then unloaded for up to 70 cycles and maintained a constant compressive stress of 1.50 MPa. The controlled release of copper from different sides of the gradient hydrogels was observed. After 6 h of incubation, the hydrogel exhibited a strong bactericidal effect on Gram-positive Staphylococcus aureus and Gram-negative Escherichia coli, with low toxicity to NIH/3T3 fibroblasts. The high toughness, controlled release of copper, and enhanced antimicrobial properties of the gradient hydrogels make them excellent candidates for wound dressings in biomedical applications.

Numerical simulation of mechanical behavior of rock samples under uniaxial and triaxial compression testsy

Purpose. The research aims to investigate how the load influences the ultimate compressive strength of rocks at failure. It uses both a uniaxial compression test, which involves incremental displacements, and a triaxial compression test, which applies varying confining stresses while maintaining a constant axial compression stress and incrementally increasing the displacement. Methods. To conduct the investigation, the researchers used RS2D, a rock-soil software, to examine the impact of different incremental displacements and confining stresses on the strength properties of various rock samples. The numerical analysis includes Fayum argillaceous sand, Sinai coal, Aswan granite, Assiut limestone, and Red-Sea phosphate. Findings. The research findings indicate that the ultimate compressive strength of rocks at failure is achieved with minor incremental displacements. Conversely, an increase in the confining stress leads to higher ultimate tensile strength, deviatoric stresses, and volumetric strain. However, the stress factor decreases in relation to the axial strain percentage. Originality. The simulator adopts Mohr-Coulomb failure criterion, presents and discusses the results in terms of stress-strain (σ-ε) curves, stress ratio (σ1/σ3), deviatoric stresses (σ1-σ3) and volumetric strain with respect to the percentage of axial strain. Practical implications. Using numerical modeling analysis, it becomes possible to reproduce the rock failure mechanisms observed in uniaxial and triaxial compression tests. This methodology has the potential to reduce the need for extensive experimental testing when assessing the tensile strength of rocks under different loads. As a result, both time and costs can be minimized.

Buckling resistance of stiffened panels subjected to constant transverse compression stresses

AbstractIn a box girder cross‐section with inclined web panel, transverse compression may be introduced into the bottom panel from both sides in addition to constant longitudinal compressive stresses. In EN 1993‐1‐5, the only analytical method for determining the resistance of panels to biaxial compression is the Reduced Stress Method (RSM). However, the current rules were mainly derived for longitudinal stresses. Due to missing rules, in practice the longitudinal stiffeners need being verified according to flexural member buckling considering the transverse updrift forces.Therefore, in order to assess the real behaviour, a large parametric study of stiffened panels with closed longitudinal stiffeners under transverse compressive stresses was carried out using a verified numerical model. LBA and GMNIA are performed for each case. To apply the RSM, all critical buckling stresses were determined considering the torsional stiffness of stiffeners. According to EN 1993‐1‐5, the support of the edges of the panels parallel to the load direction should be set free when determining the critical stress for column‐like behaviour. In the case of a longitudinally stiffened panel under transverse stresses, it is not clear whether the support of the plate and the stiffeners or only the plate should be released. In this paper, these interpretations are discussed and results are compared. Finally, a simplified procedure to determine the global reduction factor of plate buckling for transverse stresses in a single step is proposed.

Evolution of crosslinking structure in vulcanized natural rubber during thermal aging in the presence of a constant compressive stress

The evolution process of the crosslinking structure in sulfur-cured natural rubber (NR) under the combined effect of compressive stress and temperature was investigated using a homemade constant-stress device. The aged NR samples were characterized by infrared spectroscopy, chemical probe method, differential scanning calorimetry, and mechanical analysis. The results revealed that compressive stress promoted the breakage of sulfur bonds (mainly low-energy ones) between NR chains, leading to a decline in crosslink density and an increase in mesh size. According to the Arrhenius equation, a compressive stress of 1.78 MPa reduced the apparent activation energy for the breakage of polysulfide bonds from 56.3 kJ/mol to 48.2 kJ/mol, resulting in a 14.4% decrease. The sulfur-containing side groups formed after the breakage of polysulfide bonds not only participated in post-crosslinking reactions after stress release but also increased the hysteresis loss of NR under large deformation.

Mixtures of colliery spoils and fluidized bed bottom ash: strength and swelling behavior under compressive stress in isolated conditions

The amount and variety of waste materials used in civil engineering are steadily increasing due to the depletion of natural resources and the implementation of environmental policies. A new mixture of colliery spoils and fluidized bed bottom ash was recently developed in Poland, which proved to be prone to excessive, long-term swelling, potentially damaging structures such as road embankments. Numerous papers discuss the heaving mechanisms in spoils or fluidized bed ash. However, no reports analyzing the expansion of their mixture seem to be available. The purpose of this paper is to fill this void. The experiment involved measurements of linear swelling of mixture samples stored inside CBR test molds and isolated from moisture loss/gain. Material expansion is caused by the reactivity of the fluidized bed ash; its content in the mix correlates positively with the final swelling strain. At the same time, colliery spoils provide an environment particularly conducive to the phenomenon’s occurrence. A linear swelling strain of 0.3–3.2% was observed after 6 months (disregarding the first 24 h of rapid volume growth). The expansion of mixtures was also measured under constant compressive stress of 0–100 kPa to better represent their actual working conditions. Based on the results, it is proposed to adapt a mathematical model developed for anhydrite-rich rock to describe the load-swelling relationship in mixtures of colliery spoils with fluidized bed bottom ash. Such a model can be potentially used, e.g., in numerical analyses, to assess the impact of the material’s expansion on embankments.

Creep of Foam Concrete from the Position of the Hereditary Theory of Aging

The technique and results of experimental studies of creep deformations of compressed elements made of foam concrete at constant compressive stresses in the 0.15-0.75 range of Rb are presented. The nature of the relationship between stresses and the corresponding deformations, the degree of reversibility of creep deformations during unloading of samples and the tendency of concrete to aging have been established. From the standpoint of the hereditary theory of aging, analytical expressions have been selected to approximate the curves of specific creep deformations depending on the average density of foam concrete and the magnitude of compression stresses. The largest deviations of the specific creep deformations of foam concrete between theoretical and experimental values are 11.4%, and the standard deviations for the entire observation period are 2.0%

Predictions of electromotive force of magnetic shape memory alloy (MSMA) using constitutive model and generalized regression neural network

Ferromagnetic shape memory alloys (MSMAs), such as Ni-Mn-Ga single crystals, can exhibit the shape memory effect due to an applied magnetic field at room temperature. Under a variable magnetic field and a constant bias stress loading, MSMAs have been used for actuation applications. Under variable stress and a constant bias field, MSMAs can be used in power harvesting or sensing devices, e.g. in structural health monitoring applications. This behavior is primarily a result of the approximately tetragonal unit cell whose magnetic easy axis is approximately aligned with the short axis of the unit cell within the Ni-Mn-Ga single crystals. Under an applied field, the magnetic easy axis tends to align with the external field. Similarly, under an applied compressive force, the short side of the unit cell tends to align with the direction of the force. This work introduced a new feature to the existing macro-scale magneto-mechanical model for Ni-Mn-Ga single crystal. This model includes the fact that the magnetic easy axis in the two variants is not exactly perpendicular as observed by D’silva et al (2020 Shape Mem. Superelasticity 6 67–88). This offset helps explain some of the power harvesting capabilities of MSMAs. Model predictions are compared to experimental data collected on a Ni-Mn-Ga single crystal. The experiments include both stress-controlled loading with constant bias magnetic field load (which mimics power harvesting or sensing) and field-controlled loading with constant bias compressive stress (which mimics actuation). Each type of test was performed at several different load levels, and the applied field was measured without the MSMA specimen present so that demagnetization does not affect the experimentally measured field as suggested by Eberle et al (2019 Smart Mater. Struct. 28 025022). Results show decent agreement between model predictions and experimental data. Although the model predicts experimental results decently, it does not capture all the features of the experimental data. In order to capture all the experimental features, finally, a generalized regression neural network (GRNN) was trained using the experimental data (stress, strain, magnetic field, & emf) so that it can make a reasonably better prediction.

A CONSTANT VOLUMETRIC-FAILURE-STRAIN EROSION FOR DETERMINING THE EFFECT OF INERTIA AND STRAIN RATE ON THE CRUSHING STRENGTH OF A CELLULAR CONCRETE

The effect of inertia and strain rate on the failure of a cellular autoclaved aerated concrete (600 kg m-3 ) was investigated using MAT_096 material model together with a constant volumetric-failure-strain erosion criterion in the LSDYNA. A rate insensitive, constant compressive yield stress, and a rate sensitive, variable compressive yield stress, model were implemented and the results of models were compared with those of experimental compression tests conducted at similar strain rates, between 2x10-3 s -1 and ~4150 s-1 . Results have shown an “s-type” compressive strength relation with strain rate, broadly composing of three distinct regions: a lower-velocity-dependentstrength region at the quasi-static velocities, a higher-velocity-dependent-strength region at intermediate velocities and again a lower-velocity-dependent-strength region above ~1150 s-1 . In experimentally tested samples, a shock fracture strength was presumed to be reached in the higher velocity-dependent strength region, resulting in a cut-off DIF value (2.78), while in numerically tested samples, the compressive strength increased with increasing strain rate in the third region. One dimensional state of strain condition above a critical velocity was also shown numerically. The stress triaxiality increased to 0.66 between 1 and 30 m s-1 , reaching a fully constraint 1D state of strain condition above 30 m s-1 . In accord with this, the numerical failure mode, as with that of experiments, switched from an axial- to a radial-dominated cracking after ~20 m s-1 . Finally, the strain rate dependent compressive strength was numerically shown as partly arising due to the change of deformation state from a 1D state of stress to a 1D state of strain and partly due to the intrinsic rate sensitivity of cellular concrete.

Stress evolution and thickness change of a lithium-ion pouch cell under various cycling conditions

To design large-sized lithium-ion battery modules for the application of electric vehicles and grid-level energy storage, it is of important significance to understand how stress and dimension of a single pouch cell fluctuate during charge/discharge cycles. In this study, stress evolution under the constant-thickness condition and thickness change under the constant-stress condition are measured for in-house fabricated pouch cells, respectively. The results of stress measurements show that the stress increase percentage generally decreases when the charge/discharge current increases, regardless of the value of the initial compressive stress. With the same current density, the stress increase percentage generally increases when the upper cutoff voltage increases. With the same current density and upper cutoff voltage, the stress increase percentage decreases when the initial compressive stress increases. The results of thickness measurements show that the volume expansion percentage generally increases when the current density increases, regardless of the value of the constant compressive stress. With the same current density, the volume expansion percentage generally increases when the upper cutoff voltage increases. With the same current density and upper cutoff voltage, the volume expansion decreases when the constant compressive stress increases. The results provide important insights into the design principles of battery packs.

Room Temperature Ferroelastic Creep Behavior of Porous (La0.6Sr0.4)0.95Co0.2Fe0.8O3-δ

The time-dependent deformation of porous (La0.6Sr0.4)0.95Co0.2Fe0.8O3-δ (LSCF) under constant uniaxial compressive stress at room temperature has been studied. Both axial and lateral stress–strain deformation curves clearly show the non-linear ferroelastic behavior of LSCF perovskite during compression. The ferroelastic characteristics of deformation curves such as coercive stress and apparent loading moduli decrease when the porosity of the samples increases. Ferroelastic creep deformations at applied stresses of 25 and 50 MPa demonstrate that stress and porosity are influencing factors on creep deformation, which increases with increasing stress and porosity. A negative creep or axial expansion and lateral contraction were observed in the sample with 35% porosity under 50-MPa constant compression stress.

Effect of constant compressive stress induced by imitating Tuina stimulation with various durations on the cell cycle, cellular secretion, apoptosis, and expression of myogenic differentiation and myogenic factor 5 of rat skeletal muscle cells in vitro.

To investigate the effect of constant compressive stress induced by imitating Tuina stimulation with various durations on the cell cycle, cellular secretion, apoptosis, and expression of myogenic regulatory factors (MRFs), myogenic factor 5(Myf5) and myogenic differentiation (MyoD) of rat skeletal muscle cells (RSkMCs) in vitro. Third passage RSkMCs were subjected to constant compressive stresses with various durations at 2000 strain for 15, 30, 60, 90, and 120 min via a four-point bending system. The control group (CG) was cultured in the absence of mechanical loading. Alterations of the cell cycle and apoptosis rate were detected by flow cytometry (FCM). The concentrations of interleukin 6 (IL-6) / prostaglandin E2 (PGE2) and nitric oxide (NO) in supernatants were determined by enzyme-linked immunosorbent assays and the nitrate reductase method, respectively. Expression of Myf5 and MyoD was detected by immunohistochemistry. Compared with the CG, a significant alteration was observed in the synthesis phase fraction (SPF) (P < 0.01). The SPF and proliferation index (PI) were reduced from 15 to 90 min, but reached levels similar to those at 120 min. Apoptosis was increased significantly at 30 min (P < 0.05) and especially at 90 and 120 min (P < 0.01). Expression of MyoD and Myf5 was increased significantly at 15, 30, and 90 min (P < 0.01). Compared with 15 and 30 min, MyoD and Myf5 expression at 60 and 120 min was decreased significantly (P < 0.01). Compared with 60 min, MyoD expression at 90 min was increased significantly (P < 0.05), whereas MyoD and Myf5 expression at 120 min was significantly lower (P < 0.05). The IL-6 concentration was increased at 60 min compared with the CG and 15 min (P < 0.05), whereas the concentrations of PGE2 and NO were the highest at 15 and 30 min, respectively, compared with the CG and other time points (P < 0.05). The cell cycle, secretion, apoptosis, and Myf5 and MyoD expression of RSkMCs were regulated by compressive stress in a time-dependent manner. SPF and PI were inhibited at short durations (< 90 min), but NO and PGE2 secretion was the highest at shorter durations (< 30 min). With the prolongation of stimulation time, SPF, PI, and apoptosis were increased, but Myf5 and MyoD expression was decreased gradually at 15-30 min.

Modified-SST for Uniaxial Characterization of Electrical Steel Sheets Under Controlled Induced Voltage and Constant Stress

This article details the development of a uniaxial magnetomechanical bench that allows measuring the effect of constant tensile and compressive stress on the magnetic properties of electrical steel sheets. Following international standards for magnetic measurements, this work proposes reasonable modifications of a single-sheet-tester set up to provide a reliable magnetomechanical characterization of the material. The magnetic circuit and the excitation and control techniques employed are described. Specifications concerning magnetic measurements are also offered, alongside mechanical considerations regarding the antibuckling fixture developed to allow the application of compressive stress. Finally, results obtained for various stress levels and frequencies are validated and analyzed. Among other results, the proposed bench allows observing the negative impact of compressive stress on magnetic properties of nonoriented steel, as well as the positive effect of mild tensile stress.

Mechanical Response of Carbon Nanotube Bundle to Lateral Compression

Structure evolution and mechanical response of the carbon nanotube (CNT) bundle under lateral biaxial compression is investigated in plane strain conditions using the chain model. In this model, tensile and bending rigidity of CTN walls, and the van der Waals interactions between them are taken into account. Initially the bundle in cross section is a triangular lattice of circular zigzag CNTs. Under increasing strain control compression, several structure transformations are observed. Firstly, the second-order phase transition leads to the crystalline structure with doubled translational cell. Then the first-order phase transition takes place with the appearance of collapsed CNTs. Further compression results in increase of the fraction of collapsed CNTs at nearly constant compressive stress and eventually all CNTs collapse. It is found that the potential energy of the CNT bundle during deformation changes mainly due to bending of CNT walls, while the contribution from the walls tension-compression and from the van der Waals energies is considerably smaller.

Cross Hardening of a Shape Memory Alloy during Compression

Abstract—The influence of the preliminary direct martensitic transformation in titanium nickelide under a constant compressive stress on the diagrams of subsequent loading under martensitic inelasticity at a monotonically increasing compressive stress is experimentally studied. These diagrams are found to reach the martensitic inelasticity diagram corresponding to the compression of initially fully twinned martensite when the stress increases. The cross hardening on compression is shown to be more intense than that on tension. The phase-structural strain deviator can be considered as a state parameter for a shape memory alloy.

A new spallation mechanism of thermal barrier coatings and a generalized mechanical model

Multilayer thermal barrier coating (TBC) systems typically consist of three layers of materials: A thermal barrier top coat (TC), a thermally-grown oxide (TGO), and a bond coat (BC) in addition to the substrate. Local strain energy concentrations, called ‘pockets of energy concentration (PECs)’ in this work, often occur around the interface between the TGO and the BC. They have various causes, including local phase changes, and non-uniform creep and plastic relaxation. It is discovered that both PECs and buckling drive the spallation of a TBC in a new spallation mechanism. A PEC-based mechanical model is developed that describes, explains and predicts how blisters nucleate in a TBC under constant biaxial compressive residual stress, steadily and then unsteadily grow, and finally spall off. Two conditions are established for the occurrence of TBC spallation, which depend on the compressive residual strain energy density in the TC and the TGO, and the interface fracture toughness. Experimental validation of the model was performed using aircraft jet engine turbine blades with electron beam physical vapor deposition (EBPVD) TBCs. The predictions from the developed PEC-based mechanical model for the radii of spallation in the TBC are in a good agreement with experiment results.

Determination of residual stress and interface adhesion toughness of thin films by blisters

Circular blisters and telephone cord blisters (TCBs) can spontaneously occur in thin films under constant bi-axial compressive residual stress. In this work, new mechanical models are used in conjunction with measurements of blister morphology parameters to determine the residual stress in films and the adhesion toughness at interfaces. These new models are based on the hypothesis that pockets of energy concentration (PECs) drive the nucleation and growth of blisters instead of buckling, as in the conventional models, since the thin films are under constant compressive residual stress. Predictions from the models are in excellent agreement with independent experimental data.