Direction Of Tensile Strain Research Articles

Deterministic domain wall rotation in a strain mediated FeGaB/PMN-PT asymmetrical ring structure for manipulating trapped magnetic nanoparticles in a fluidic environment.

The manipulation of domain walls (DWs) in strain-mediated magnetoelectric (ME) heterostructures has attracted much attention recently, with potential applications in precise and location-specific manipulation of magnetic nanoparticles (MNPs). However, the manipulation ability in these structures is restricted to magnetostrictive circular ring structures only, where the required onion state is metastable, less thermally stable, and cannot be obtained easily. This work investigates the highly shape anisotropic FeGaB magnetostrictive elliptical ring structures of different aspect ratios and trackwidths on the PMN-PT piezoelectric substrate to manipulate fluid-borne MNPs using active control of DWs. The proposed model utilizes the attribute that the required onion state in a magnetostrictive elliptical ring is thermally stable and easily obtained compared to magnetostrictive circular ring structures. By varying the trackwidth of elliptical rings, nucleated DWs are rotated at different angles to capture and transport fluid-borne MNPs. Up to a critical trackwidth, DW rotation is predicted by dominant stress anisotropy energy that leads the rotation of DWs and attached MNPs toward the dominant tensile strain direction of PMN-PT with reversibility. Increasing the trackwidth beyond the critical trackwidth caused a complete 90° rotation of DWs and attached MNPs without reversibility and is given by dominant shape anisotropy energy. The fundamental relationship of capture probability with the size and velocity of injected MNPs is also demonstrated. The nucleation and rotation of DWs are predicated using the coupled elastodynamic and electrostatic Finite Difference Method (FDM) micromagnetic model. Dynamics of MNP capture and rotation are envisaged using an analytical model.

Shear strength anisotropy of rooted soils

The shear strength of rooted soils depends on the principal stress direction owing to the anisotropy in the soil structure and root system. Existing failure criteria cannot describe the strength anisotropy of rooted soils under general loading conditions because they are mainly based on the test results of direct shear. This study presents a new generalised three-dimensional anisotropic failure criterion for rooted soils. The model employs the projection of two independent microstructure fabric tensors (soil fabric and root network) on the stress tensor. Twenty-four drained triaxial compression and extension tests were carried out to measure the strength anisotropy of silty sand vegetated with vetiver grass (Chrysopogon zizanioides L.) at different overconsolidation ratios and calibrate the material parameters for the proposed criterion. Anisotropies of both cohesion and friction angle exist in rooted soil. Roots contribute mainly to the increase in cohesion (hence root cohesion) from most of the direct shear test data. Roots with predominant orientation aligning in the tensile strain direction contribute the most to soil strength. In the case of vetiver grass, which has a taproot system, their roots show the strongest reinforcement effect in the conventional triaxial extension path, in which the maximum portion of the roots is subjected to tension.

The stability of 3D skyrmions under mechanical stress studied via Monte Carlo calculations

Using Monte Carlo (MC) simulations, we study the skyrmion stability/instability as a response to uniaxial mechanical stresses. Skyrmions emerge in chiral magnetic materials as a stable spin configuration under external magnetic field B→ with the competition of ferromagnetic interaction and Dzyaloshinskii–Moriya interaction (DMI) at low temperature T. Skyrmion configurations are also known to be stable (unstable) under a compressive stress applied parallel (perpendicular) to B→. To understand the origin of such experimentally confirmed stability/instability, we use the Finsler geometry modeling technique with a new degree of freedom for strains, which plays an essential role in DMI being anisotropic. We find from MC data that the area of the skyrmion state on the B−T phase diagram increases (decreases) depending on the direction of applied stresses, in agreement with reported experimental results. This change in the area of the skyrmion state indicates that skyrmions become more (less) stable if the tensile strain direction is parallel (perpendicular) to B→. From the numerical data in this paper, we find that the so-called magneto-elastic effect is suitably implemented in the effective DMI theory with the strain degree of freedom without complex magneto-elastic coupling terms for chiral magnetic materials. This result confirms that experimentally-observed skyrmion stability and instability are caused by DMI anisotropy.

Native extracellular matrix orientation determines multipotent vascular stem cell proliferation in response to cyclic uniaxial tensile strain and simulated stent indentation

Cardiovascular disease is the leading cause of death worldwide, with multipotent vascular stem cells (MVSC) implicated in contributing to diseased vessels. MVSC are mechanosensitive cells which align perpendicular to cyclic uniaxial tensile strain. Within the blood vessel wall, collagen fibers constrain cells so that they are forced to align circumferentially, in the primary direction of tensile strain. In these experiments, MVSC were seeded onto the medial layer of decellularized porcine carotid arteries, then exposed to 10%, 1 Hz cyclic tensile strain for 10 days with the collagen fiber direction either parallel or perpendicular to the direction of strain. Cells aligned with the direction of the collagen fibers regardless of the orientation to strain. Cells aligned with the direction of strain showed an increased number of proliferative Ki67 positive cells, while those strained perpendicular to the direction of cell alignment showed no change in cell proliferation. A bioreactor system was designed to simulate the indentation of a single, wire stent strut. After 10 days of cyclic loading to 10% strain, MVSC showed regions of densely packed, highly proliferative cells. Therefore, MVSC may play a significant role in in-stent restenosis, and this proliferative response could potentially be controlled by controlling MVSC orientation relative to applied strain.

Investigation of uniaxial ratcheting fatigue behaviours and fracture mechanism of GH742 superalloy at 923 K

In this study, the ratcheting fatigue behaviours of GH742 superalloy at 923 K were investigated through a series of symmetric and asymmetric stress-controlled tests. The effects of stress amplitude and mean stress on the fatigue behaviours were analysed through scanning electron microscopy, transmission electron microscopy and electron backscatter diffraction. The results highlight that the fatigue life significantly decreases with increasing mean stress or stress amplitude. Tensile ratcheting strain occurs and increases with the increasing number of cycles under both symmetric and asymmetric cyclic loading. The alloy initially exhibits a cyclic hardening response, followed by cyclic softening until fracture failure under symmetric and asymmetric cyclic loading. The increase in mean stress promotes the cyclic softening in the tensile strain direction to a certain extent. The fracture mode does not change with increasing mean stress. Multiple fatigue cracks initiate from the surface inclusions, crystallographic facets and slip bands, and propagate in mixed transgranular and intergranular modes. The modified Basquin equation, which considers the mean stress and stress amplitude, can accurately predict the fatigue life, and all the fatigue data are located within the 1.5X scatter band.

Study on the Correlation between the Microstructure Characteristics and Corrosion Behaviors of 2A12-T4 Aluminum Alloy under Thermal Strain

In this study, the welding thermal simulation technology was used to prepare samples under different peak temperatures and strain levels in order to reveal the effects of thermal strain on the microstructure characteristics and corrosion resistance of aluminum alloy. Furthermore, the correlation between microstructure evolution law and corrosion behavior was studied by analyzing the microstructure characteristics and performing electrochemical polarization curve tests. Results showed that the amount and distribution of the precipitated phase were the main factors affecting the corrosion behavior of aluminum alloy. The precipitated phase was distributed along the direction of tensile strain, and the grain size was coarsened from 152 to 260 μm (and even exceeded 280 μm) after experiencing peak temperatures of 300 and 400 °C. In addition, the risk of corrosion for the samples that experienced thermal strain was increased compared to those that did not undergo tensile strain. The samples that experienced a peak temperature of 300 °C presented the best corrosion resistance as the precipitated phase was evenly distributed in the matrix. However, when the peak temperature was 400 °C and the strain was 8%, the number and density of the precipitated phase increased due to the dynamic recrystallization, and the corrosion resistance of the sample became the worst. Finally, the microstructure analysis results showed that dynamic recrystallization occurred in the sample with a peak temperature of 400 °C, and the precipitated phase was mainly distributed along the grain boundaries. This led to the decrease of the corrosion resistance of grain boundaries, and the corrosion developed from pitting corrosion to intergranular corrosion.

Highly Stretchable, Directionally Oriented Carbon Nanotube/PDMS Conductive Films with Enhanced Sensitivity as Wearable Strain Sensors.

Recent interest in the fields of human motion monitoring, electronic skin, and human-machine interface technology demands strain sensors with high stretchability/compressibility (ε > 50%), high sensitivity (or gauge factor (GF > 100)), and long-lasting electromechanical compliance. However, current metal- and semiconductor-based strain sensors have very low (ε < 5%) stretchability or low sensitivity (GF < 2), typically sacrificing the stretchability for high sensitivity. Composite elastomer sensors are a solution where the challenge is to improve the sensitivity to GF > 100. We propose a simple, low-cost fabrication of mechanically compliant, physically robust metallic carbon nanotube (CNT)-polydimethylsiloxane (PDMS) strain sensors. The process allows the alignment of CNTs within the PDMS elastomer, permitting directional sensing. Aligning CNTs horizontally (HA-CNTs) on the substrate before embedding in the PDMS reduces the number of CNT junctions and introduces scale-like features on the CNT film perpendicular to the tensile strain direction, resulting in improved sensitivity compared to vertically-aligned CNT-(VA-CNT)-PDMS strain sensors under tension. The CNT alignment and the scale-like features modulate the electron conduction pathway, affecting the electrical sensitivity. Resulting GF values are 594 at 15% and 65 at 50% strains for HA-CNT-PDMS and 326 at 25% and 52 at 50% strains for VA-CNT-PDMS sensors. Under compression, VA-CNT-PDMS sensors show more sensitivity to small-scale deformation than HA-CNT-PDMS sensors due to the CNT orientation and the continuous morphology of the film, demonstrating that the sensing ability can be improved by aligning the CNTs in certain directions. Furthermore, mechanical robustness and electromechanical durability are tested for over 6000 cycles up to 50% tensile and compressive strains, with good frequency responses with negligible hysteresis. Finally, both types of sensors are shown to detect small-scale human motions, successfully distinguishing various human motions with reaction and recovery times of as low as 130 ms and 0.5 s, respectively.

Superplastic Deformation Behavior and Cavity Formation of Ti55 Titanium Alloy

Ti55 is a type of new near-α titanium alloy featuring good heat resistance and thermal stability at a temperature below 550°C. This paper explores the superplastic behaviors of Ti55 titanium alloy sheets at high temperature. The results showed that at a strain rate between 8.3×10-4 and 1.32×10-2s-1 and a deformation temperature between 885 and 935°C, this material exhibited favorable superplasticity. A 872% tensile elongation was achieved even at a high temperature of 925°C and a high strain rate of 1.32×10-2s-1. For a deformation temperature of 925°C and a strain rate range of 8.3×10-4～1.32×10-2s-1, the strain rate sensitivity index (m) was equal to or higher than 0.38, which depends on the specific strain rate and reached its peak at 6.64×10-3s-1. The study showed that tiny cavities tended to appear around the rare earth phase particles. As the deformation temperature and the deformation strain rate increased, both size and volume fraction of the cavities decreased significantly. When the plastic deformation further increased, the cavities experienced not only longitudinal aggregation along the tensile strain direction, but also transverse aggregation normal to the tensile strain direction. The typical high-temperature ductile fracture morphology is related to both aggregation and growth of the large number of microscopic cavities and dimples.

Behaviour of model footing resting on sand reinforced with number of layers of coir geotextile

Several methods of ground improvement techniques were developed and tried for stabilizing weak soils. The technique of reinforcing the soil becomes one of the important methods. The performance of granular soils which are strong in compression and shear, but weak in tension can be substantially improved by introducing reinforcing element in the direction of tensile strain. Compared to the numerous works done in the area of bearing capacity of unreinforced soil, less work has been done in the determination of bearing capacity of reinforced soil. In this present investigation, bearing capacity of coir geotextile reinforced sand was determined for number of layers of geotextile. The comparison was made with the parameters like peak stress, bearing capacity ratio, and settlement reduction factor for different d/B ratios. The experimental values of bearing capacity were validated with theoretical values.

Strain Relaxation of Monolayer WS2 on Plastic Substrate

Strain‐dependent electrical and optical properties of atomically thin transition metal dichalcogenides may be useful in sensing applications. However, the question of how strain relaxes in atomically thin materials remains not well understood. Herein, the strain relaxation of triangular WS2 deposited on polydimethylsiloxane substrate is investigated. The photoluminescence of trions (X–) and excitons (X0) undergoes linear redshifts of ≈20 meV when the substrate tensile strain increases from 0 to 0.16. However, when the substrate strain further increases from 0.16 to 0.32, the redshifts cease due to strain relaxation in WS2. The strain relaxation occurs through formation of wrinkles in the WS2 crystal. The pattern of wrinkles is found to be dependent on the relative angle between an edge of the triangular WS2 crystal and tensile strain direction. Finite element simulations of the strain distribution inside the WS2 crystals explain the experimental observations.

Diametral compression of pultruded composite rods

Diametral compression tests were performed on pultruded composite rods comprised of unidirectional glass or carbon fibers in a common matrix. During compression tests, acoustic emission (AE) activity was recorded and images were acquired from the sample for analysis by digital image correlation (DIC). In both composite systems, localized tensile strain developed in the transverse plane under the load platens prior to failure, producing non-linearity in the load–displacement curve and AE signals. In situ SEM diametral compression tests revealed the development of matrix microcracking and debonding in regions of localized strain, perpendicular to the tensile strain direction (parallel to the load axis). Comparison of linear finite element simulations and experimental results showed a deviation from linear elastic behavior in the load displacement curve. The apparent transverse modulus, in plane shear modulus, and transverse tensile strength of the GF rod was greater than that of the CF rod, and fracture surfaces indicated greater fiber/matrix adhesion in the GF system compared to the CF system. A mixed mode fracture surface showed that two failure modes were active – matrix tensile failure and matrix compression failure by shear near the loading edge.

Molecular Dynamics Simulations of the Effect of the Composition of the Intergranular Film on Fracture in Si3N4

Molecular dynamics computer simulations were used to study the fracture behavior of silica, multicomponent silicate, and oxynitride intergranular films (IGFs) between silicon nitride crystals as a function of composition, film thickness, and crystallographic orientation. The maximum fracture strength is higher in the IGF between prism surfaces than between basal surfaces. This is caused by the preferential segregation of specific species to the basal surfaces in contrast to the prism surfaces, effectively modifying the composition within the glassy portion of the IGF, with a subsequent effect on strength. The ordering observed in the thinner IGFs causes an increase in strength in the linear portions of the stress/strain curves, effectively increasing fracture stress. The simulations show that the force/atom in the 1 nm SiO2 IGF in the direction of tensile strain is more similar to that in β‐cristobalite than to v‐SiO2, whereas such data in the 2 nm SiO2 IGF is more similar to v‐SiO2. Simulations of the multicomponent silicate IGFs show the expected effect of lowering fracture strength with increasing modifier content in the silicate IGF, similar to that of bulk glasses. Similar to experimental studies, a decrease in strength is observed in silicon oxynitride IGFs with increasing oxygen concentration.

Effect of tensile strain on morphology and dielectric property in nanotube/polymer nanocomposites

As an electrically conducting filler, multiwall carbon nanotube (MWNT) with a great slenderness ratio was introduced into poly(vinylidene fluoride) (PVDF) to form the MWNT/PVDF nanocomposites. Dielectric properties of these composites before and after stretching were studied at wide frequency ranges from 102to107Hz. The results showed that the dielectric constant and conductivity after stretching were always lower than those before stretching. In the composites with high concentration of MWNT, the decreases in dielectric constant and conductivity were very significant. Rearrangement of MWNT in the composites along with the tensile-strain direction could be charge with the results of dielectric properties.

Anisotropic diffusion of Cu adatoms on strained Cu (1 1 1) surface

Diffusion of Cu atoms on a strained Cu (111) surface was studied by molecular dynamic simulation using an EAM potential. The anisotropic diffusion behaviour is found when the uniaxial strain is imposed on the surface, which does not exist under the biaxial strain. The migration of the adatom is suppressed along the tensile strain direction. The results suggest that different island morphology can be obtained by controlling anisotropic diffusion of adatoms on the strained surfaces during film growth.

Crustal movement and deformation in Taiwan and its coastal area

Based on the station velocity data obtained from Fujian coastal GPS network and Taiwan-Luzon GPS network and the data obtained from IGS permanent stations commonly used in the data processing of both networks, the uniformity of reference frames and velocity fields of both GPS networks is realized. It has been discovered from the analysis on the velocity field in Taiwan and its coastal areas that the horizontal crustal movements in the coastal area of Fujian, Taiwan Strait and the northern part of Taiwan Island are fully consistent. The movement direction is around 26.0°E by S and the rate is about 39 mm/a. The opposite variation occurs in the coastal mountain area in the eastern part of Taiwan Island with the movement direction of 30.0°N by W and the movement rate of about 33.3 mm/a. In the southern end of Taiwan Island, the movement direction is 50.0°S by W and the movement rate is about 13 mm/a. If the geometric center of Fujian coast is used as the reference datum, Taiwan Island has a consistent (except its north end) NW-trending movement with the direction of around 50.0°N by W. The maximum rate of 61 mm/a occurs along the eastern coast and decreases gradually towards west. The analysis of strain field indicates that Taiwan and its coastal area have a uniform strain field with the principal compressive strain direction of N48.0°W and the principal tensile strain direction of N42.0°E. The principal compressive strain rate along the eastern coast of Taiwan Island is 3.436×10−7/a, which decreases gradually towards west and reaches 1.861×10−8/a to Fujian coast. The collision and underthrust of Philippine Sea plate with Eurasian plate in the eastern part of Taiwan Island can be considered as the principal force for the crustal movement, deformation and great earthquake occurred in Taiwan and its coastal area. The direction of principal compressive stress in the area is about N55.0°W.

Quasi–static studies of the deformation and failure ofβ–HMX based polymer bonded explosives

This paper describes research into the low strain rate mechanical properties of polymer bonded explosives (PBXs) and follows on from that presented by Palmer and co-workers in 1993. PBXs are highly filled composite materials comprised of crystals of a secondary explosive supported in ca .5–10% (by mass) polymeric binder. In general, the modulus of the binder is 10 5 times lower than that of the crystalline explosive, resulting in the behaviour of the composite being heavily influenced by the properties of the binder despite the low concentration present. The Brazilian test, in which a disc of material is loaded diametrically in compression, has been used to generate tensile failure in the materials studied. Three methods of microscopy have been used to examine the nature of failure in two UK compositions and one US material (PBX 9501). Pre– and post–failure optical and electron microscopy examinations of the materials have been undertaken to gain a greater understanding of the role of the microstructure and this has been aided by the use of an environmental scanning electron microscope to follow real-time failure in the PBXs. Failure in all three compositions has been observed to start around the edges of larger filler particles perpendicular to the direction of tensile strain. Compositions with rubbery binders have been observed forming binder filaments which bridge the crack walls, while clean crystal faces are observed on the larger particles. In a composition with a nitrocellulose-based binder, hair-like features of nitrocellulose have been seen sticking out from the failure surfaces and the rougher crack walls.

Influence of tensile strain on smooth muscle cell orientation in rat blood vessels.

Blood vessels are subject to tensile stress and associated strain which may influence the structure and organization of smooth muscle cells (SMCs) during physiological development and pathological remodeling. This study focused on the influence of the major tensile strain on the SMC orientation in the blood vessel wall. Several blood vessels, including the aorta, the mesenteric artery and vein, and the jugular vein of the rat were used to observe the normal distribution of tensile strains and SMC orientation; and a vein graft model was used to observe the influence of altered strain direction on the SMC orientation. The circumferential and longitudinal strains in these blood vessels were measured by using a biomechanical technique, and the SMC orientation was examined by fluorescent microscopy at times of 10, 20, and 30 days. Results showed that the SMCs were mainly oriented in the circumferential direction of straight blood vessels with an average angle of approximately 85 deg between the SMC axis and the vessel axis in all observed cases. The SMC orientation coincided with the principal direction of the circumferential strain, a major tensile strain, in the blood vessel wall. In vein grafts, the major tensile strain direction changed from the circumferential to the longitudinal direction at observation times of 10, 20, and 30 days after graft surgery. This change was associated with a decrease in the angle between the axis of newly proliferated SMCs and that of the vessel at all observation times (43 +/- 11 deg, 42 +/- 10 deg, and 41 +/- 10 deg for days 10, 20, and 30, respectively), indicating a shift of the SMC orientation from the circumferential toward the longitudinal direction. These results suggested that the major tensile strain might play a role in the regulation of SMC orientation during the development of normal blood vessels as well as during remodeling of vein grafts.

Material model for the analysis of reinforced concrete surface structures

A material model for the analysis of reinforced concrete surface structures is developed. The constitutive model employs the smeared crack concept, i.e. only average stresses are considered at an integration point. While uncracked concrete is modelled with a plasticity approach, the paper focuses on the numerical treatment of cracked reinforced concrete in a state of plane stress. Special attention is given to the modelling of the tension stiffening effect, the re-orientation of the principal tensile strain direction and the compressive strength of cracked concrete. The material model has been implemented in the finite element program SEGNID and tested extensively. Here the comparisons of calculated and experimentally measured results on reinforced concrete surface structures-several panels, a plate subjected to torsion and a free-formed shell-are presented.

Discussion of “the direction of tensile strain and ‘roping’ phenomenon in ferritic stainless steels”

Discussion of “the direction of tensile strain and ‘roping’ phenomenon in ferritic stainless steels”

The direction of tensile strain and the “roping” phenomenon in ferritic stainless steels

Recent observations that rolling direction surface striations are generated by tensile elongation transverse to the rolling direction have cast doubt on the validity of the plastic buckling model for roping in ferritic stainless steels. Moreover, these observations are seemingly incompatible with the transverse cross section undulations which characterize the roping morphology. To clarify this situation, detailed profilometric evaluations have been performed on roping prone type 434 stainless steel strip elongated at angles of 0, 30, 45, 60 and 90 deg to the rolling direction. In all cases, light surface striations were produced parallel to the rolling direction. However, the amplitude of the characteristic cross section undulation was quite dependent on the tensile strain axis orientation. The undulation or corrugation amplitude was greatest for tensile elongation in the rolling direction and decreased as the tensile axis diverged from the rolling direction to a point where noundulations were apparent for the case of tensile elongation transverse to the rolling direction. Thus, it is concluded that the acceptibility of the plastic buckling model is not called to question by the results of tensile elongation transverse to the rolling direction and that roping, in the general sense, is not developed by such transverse elongation. The compatibility of the plastic buckling model with observed corrugation development upon 45 deg extension is demonstrated.