Tensile Prestrain Research Articles

Interface stress transfer model and modulus parameter equivalence method for composite materials embedded with tensile pre-strain shape memory alloy fibers.

The constitutive model and modulus parameter equivalence of shape memory alloy composites (SMAC) serve as the foundation for the structural dynamic modeling of composite materials, which has a direct impact on the dynamic characteristics and modeling accuracy of SMAC. This article proposes a homogenization method for SMA composites considering interfacial phases, models the interface stress transfer of three-phase cylinders physically, and derives the axial and shear stresses of SMA fiber phase, interfacial phase, and matrix phase mathematically. The homogenization method and stress expression were then used to determine the macroscopic effective modulus of SMAC as well as the stress characteristics of the fiber phase and interface phase of SMA. The findings demonstrate the significance of volume fraction and tensile pre-strain in stress transfer between the fiber phase and interface phase at high temperatures. The maximum axial stress in the fiber phase is 705.05 MPa when the SMA is fully austenitic and the pre-strain increases to 5%. At 10% volume fraction of SMA, the fiber phase's maximum axial stress can reach 1000 MPa. Ultimately, an experimental verification of the theoretical calculation method's accuracy for the effective modulus of SMAC lays the groundwork for the dynamic modeling of SMAC structures.

Stress recovery behavior of a promising NiTiNb-SMA plate for bonded prestressed strengthening

Shape memory alloys (SMAs) are functional metallic materials, possessing a remarkable characteristic known as the shape memory effect (SME), by which a considerable recovery stress can be generated through a simple thermal activation. A NiTiNb-SMA plate is employed in this study, aimed at prestressed strengthening of steel members. To better understand the mechanism of the generation of recovery stress, tests were conducted on the NiTiNb-SMA plates (thickness 1.5 mm) to characterize the basic mechanical properties and stress recovery behavior. Tests include: tensile failure test, prestraining, activation, and re-activation. The influence of key parameters such as prestrain level and activation temperature on the stress recovery behavior of this NiTiNb-SMA plate was evaluated. Re-activation was discussed. Test results revealed that the largest recovery stress reached 448.6 MPa when the material was prestrained by 8% and activated at 180℃. This suggests that the activation temperature of 180℃ could be optimal for this material to generate sufficient recovery stress. Such a strategy should be promising for bonded prestressed strengthening, as this activation temperature would have limited influence on the adhesive bond of the bonded prestressed strengthening system.

Depth-Dependent Strain Model (1D) for Anisotropic Fibrils in Articular Cartilage.

The mechanical response of articular cartilage (AC) under compression is anisotropic and depth-dependent. AC is osmotically active, and its intrinsic osmotic swelling pressure is balanced by its collagen fibril network. This mechanism requires the collagen fibers to be under a state of tensile pre-strain. A simple mathematical model is used to explain the depth-dependent strain calculations observed in articular cartilage under 1D axial compression (perpendicular to the articular surface). The collagen fibers are under pre-strain, influenced by proteoglycan concentration (fixed charged density, FCD) and collagen stiffness against swelling stress. The stiffness is introduced in our model as an anisotropic modulus that varies with fibril orientation through tissue depth. The collagen fibers are stiffer to stretching parallel to their length than perpendicular to it; when combined with depth-varying FCD, the model successfully predicts how tissue strains decrease with depth during compression. In summary, this model highlights that the mechanical properties of cartilage depend not only on proteoglycan concentration but also on the intrinsic properties of the pre-strained collagen network. These properties are essential for the proper functioning of articular cartilage.

Effect of plastic strain on corrosion-induced hydrogen infusion and embrittlement behaviors of Zn-coated ultra-high strength steel sheet

This study examined the effects of plastic strain on the corrosion-induced hydrogen evolution, infusion, and embrittlement behaviors of ultra-high strength steel sheets with galvanized (GI) and galvannealed (GA) coatings. The tensile pre-straining of the coated steels did not increase the hydrogen permeation flux in the absence of applied cathodic polarization, in contrast to the case under cathodic polarization. This was closely associated with the rapid kinetics of corrosion scale formation under pre-strains, providing an inhibitory effect on the surface. From this aspect, the difference in the resistance to corrosion-induced hydrogen embrittlement between GI and GA-coated steels was mechanistically interpreted.

Effect of plastic strain under roller bending on fatigue properties ofextruded 6063 T66 aluminium alloy profile

The tensile plastic strain of material sampled from profiled areas under roller bending and pre-strained material was analyzed. The experimental data of high-cycle fatigue were approximated by a probabilistic Weibull cumulative distribution (P−S−N curve). The fatigue life prediction model was implemented for numerical simulations of roller bending in the LS-Dyna solver and experimental data. The cyclic behaviour of the material shows a decrease in the fatigue life distribution with increasing static failure levels. The fractographic analysis of the fracture surface shows an increased level of intergranular cracking for the tensile pre-strain as a result of the dislocation accumulation in the neighbourhood of grain boundaries. The estimation results of the proposed model show good correlation of probabilistic scatter bands (error below 10%).

Effect of Tensile Pre-strain on Mechanical Properties of Austenitic 301 Stainless Steel

Effect of Tensile Pre-strain on Mechanical Properties of Austenitic 301 Stainless Steel

Anisotropic effect of pre-strain on hydrogen embrittlement susceptibility in a stable austenitic stainless steel

Different pre-strain of uniaxial tensile deformation or cold rolling were applied to 0.02C–18Cr–11Ni-0.15 N austenitic stainless steel to investigate the effect of pre-strain stress modes on hydrogen embrittlement (HE). The susceptibility to HE was negligibly affected by tensile pre-strain, but it increased with the degree of pre-strain by cold rolling. This resulted from differences in strain distribution, twinning behavior, and changes in H diffusivity arising from the two deformation methods. Homogeneous strain distribution was observed after uniaxial tensile deformation, whereas the deformation was locally concentrated after cold rolling. This led to localized H adsorption to assist crack propagation. While twinning was the main deformation mechanism in the present steel, only the twins formed during cold rolling were vulnerable to stress localization owing to their crystallographic orientation. These twins acted as initiation sites for H-induced cracking and degraded the HE resistance. Finally, H diffusion was less active in tensile-strained samples, and high HE resistance was effectively maintained despite the increase of strength by pre-straining as a consequence.

Effects of Prestrain and Baking on the Tensile and Fatigue Properties of Fe–0.1C–5Mn Transformation‐Induced Plasticity Steel

This study aims to investigate the effects of uniaxial tensile prestrain (PS) and bake hardening (BH) on tensile and force‐controlled (R = 0.1) high‐cycle fatigue (HCF) properties of Fe–0.1C–5Mn medium Mn transformation‐induced plasticity (TRIP) steel. Stress‐life data of the as‐received (AR: 0% prestrain) and 10%, 15%, and 20% prestrained (PS10, PS15, PS20) samples have been generated under both baked and unbaked conditions. It is manifested that prestraining increases the HCF life of the steel. The addition of BH further increases the HCF life. The fatigue limit is greatly improved from 433 MPa (AR) to 532 MPa (BH20), and the maximum incremental value is as great as 99 MPa. It is attributed to the austenite to martensite transformation (progressive TRIP effect) that occurs during the prestraining and cyclic loading processes.

Sound Quality Performance of Orthogonal Antisymmetric Composite Laminates Embedded with SMA Wires.

Orthogonal antisymmetric composite laminates embedded with shape memory alloys (SMAs) wires have the potential to improve the sound quality of vibro-acoustics by taking advantage of the special superelasticity, temperature phase transition, and pre-strain characteristics of SMAs. In this research, space discretion and mode decoupling were employed to establish a vibro-acoustic sound quality model of SMA composite laminates. The association between the structural material parameters of SMA composite laminates and the sound quality index is then approached through methodologies. Numerical analysis was implemented to discuss the effects of SMA tensile pre-strain, SMA volume fraction, and the ratio of resin-to-graphite in the matrix on the vibro-acoustic sound quality of SMA composite laminates within a temperature environment. Subsequently, the sound quality test for SMA composite laminates is thus completed. The theoretically predicted value appears to agree well with the experimental outcomes, which validates the accuracy and applicability of the dynamic modeling theory and method for the sound quality of SMA composite laminates. The results indicate that attempting to alter the SMA tensile pre-strain, SMA volume fraction, and matrix material ratio can be used to modify loudness, sharpness, and roughness, which provides new ideas and a theoretical foundation for the design of composite laminates with decent sound quality.

The influence of equi-biaxial and uniaxial tensile pre-strain on the low cycle fatigue performance of the AA2024-T4 aluminium alloy

In the present investigation, the low cycle fatigue performance of the aluminium alloy AA2024-T4 is examined for different tensile pre-straining histories. The equi-biaxial tensile pre-strained specimens revealed identical fatigue life to the 0% pre-strained specimens, while all the uniaxial tensile pre-strained specimens showed improved fatigue life. As-received specimens exhibit noticeable cyclic hardening at all the strain amplitude. The pre-strained specimen shows an almost stable cyclic stress–strain response for each strain amplitude. The electron backscattered diffraction examination of the without pre-strained and pre-strained specimens revealed large lattice distortion in the equi-biaxial tensile pre-strained case in comparison with the other two cases.

Atomistic study of internal stress effect on scratching behavior in titanium single crystal

The internal stress effect on the scratching behavior in titanium single crystal is investigated by molecular dynamics simulations. It is introduced by applying the compressive/tensile pre-strain in this work. The friction force in the model with compressive pre-strain is higher than that with tensile pre-strain, which is related to the atomistic spacing and the distribution of pile-up. The dislocation mechanism is systematically illustrated that three types of <a> dislocations of edge dislocation loop, prism edge dislocation and screw dislocation dominate the plastic deformation. The coupling of dislocation loop and screw dislocation in the model with tensile pre-strain causes much more defects to remain in the matrix. However, when the model is applied by small compressive pre-strain, the dislocations left in the matrix are obviously decreased, reducing the internal crystal damage. Overall, the compressive/tensile internal stress has a distinguishing effect on the scratching behavior, which can be used for altering the friction and wear property of titanium.

Effect of Tensile Pre-strain and Specimen Orientation on Tearing Resistance Parameters of DP 780 Steel Sheet Determined Using Essential Work of Fracture Method

Effect of Tensile Pre-strain and Specimen Orientation on Tearing Resistance Parameters of DP 780 Steel Sheet Determined Using Essential Work of Fracture Method

Fabrication and Actuation Performance of Selective Laser Melting Additive-Manufactured Active Shape-Memory Alloy Honeycomb Arrays

Shape-memory alloy (SMA) honeycomb arrays have drawn worldwide attention for their potential active applications in smart morphing wings. However, the manufacturing of complex active SMA honeycomb arrays via conventional processes is a difficult task, and the actuation performance of the honeycomb arrays has not yet been well–investigated. In this work, the active SMA honeycomb arrays were fabricated by selective laser melting (SLM) additive manufacturing, and their actuation performance was investigated. The results show that the SLM–fabricated active SMA honeycomb arrays can generate obvious actuation performance during the transformation and exhibit a higher maximum actuation stress of 2.53 MPa at a R/t ratio of 4 and a tensile pre–strain of 35%. This research will contribute to the design and further improvement of active SMA honeycomb arrays based on SLM additive manufacturing, promoting the engineering applications for smart morphing wings.

Mesoscopic numerical study on ductile fracture in TRIP steel under reverse loading

The aim of this study is to elucidate the fracture mechanism of transformation-induced plasticity (TRIP) steel under reverse loading using a ductile damage simulation method. First, the fracture limit of a TRIP steel under the reverse path is experimentally investigated and compared with the results of a dual-phase (DP) steel without a retained austenite. In both steels, the reduction in fracture strain by compressive pre-strain is smaller than that by tensile pre-strain. The difference between the effects of tensile and compressive pre-strain is even larger in the TRIP steel than in the DP steel. These results are analyzed via numerical calculations using a model that extends the ductile damage theory proposed by Ohata et al. to account for the microstructural changes caused by martensitic transformation. The results indicate that the development of damage in the TRIP steel strongly depends on the fraction and distribution of the hard martensite generated by the transformation. Moreover, when TRIP steels are subjected to compressive pre-strain, martensitic transformation occurs less likely than when they are subjected to tensile pre-strain. This leads to less heterogeneity and less void formation within the microstructure. As a result, the fracture strain decrease in TRIP steel due to compressive pre-strain is smaller than that in DP steel.

An Energy-Based Method for Lifetime Assessment on High-Strength-Steel Welded Joints under Different Pre-Strain Levels.

Pre-loading on engineering materials or structures may produce pre-strain, especially plastic strain, which would change the fatigue failure mechanism during their service time. In this paper, an energy-based method for fatigue life prediction on high-strength-steel welded joints under different pre-strain levels was presented. Tensile pre-strain at three pre-strain levels of 0.2%, 0.35% and 0.5% was performed on the specimens of the material Q345, and the cyclic stress and strain responses with pre-loading were compared with those without pre-loading at the same strain level. The experimental work showed that the plastic strain energy density of pre-strained welded joints was enlarged, while the elastic strain energy density of pre-strained welded joints was reduced. Then, based on the strain energy density method, a fatigue life estimation model of the high-strength-steel welded joints in consideration of pre-straining was proposed. The predicted results agreed well with the test data. Finally, the validity of the developed model was verified by the experimental data from TWIP steel Fe-18 Mn and complex-phase steel CP800.

Thermal Modal Performance of Composite Laminates Embedded with Anti-Symmetric Oblique Coupling Gradient Pre-Strained SMA Wires for Suppressing Resonance

As an extension of conventional gradient, anti-symmetric oblique coupling gradient has a superior modal modification ability on composite laminates embedded with pre-strained shape memory alloys (SMA) wires, which is beneficial to suppress modal resonance of composite laminates in the thermal environment. This paper presents an anti-symmetric oblique coupling gradient model of SMA along the thickness direction. That is, the gradient model of SMA wires’ orientation and the positive and negative gradient model of SMA volume fraction. Considering the internal force of composite laminates composed of the pre-strain recovery force of SMA and the thermal expansion force of the substrate, the free vibration equation of composite laminates with additional internal forces energy is derived from first-order shear plate theory and Hamilton principle. The influence of coupling gradient parameters on the thermal modal performance of SMA composite laminates is analyzed and verified by experiments. The proposed anti-symmetric oblique coupling gradient SMA wires’ distribution form effectively exerts the recovery stress generated by SMA tensile pre-strain, i.e., effectively improves the stiffness and critical buckling temperature. Coupling gradient distribution broadens the frequency modulation range, which makes the fine regulation of the natural frequency and critical buckling temperature feasible.

On the low-cycle fatigue behavior of aluminum alloys under influence of tensile pre-strain histories and strain ratio

The present study attends to the effect of tensile pre-strain histories and strain ratio on cyclic deformation behavior of 6061 aluminum alloy and 2024 aluminum alloy. Low-cycle fatigue tests performed in this study covered two areas; Under fully reversed conditions, with 8% tensile pre-strain, 4% tensile pre-strain, and 0% tensile pre-strain, at strain amplitudes varying in the range 0.6–1.75%; Under strain-controlled circumstances at three different strain ratios [−1, 0, and 0.5] with strain amplitudes varying in the range 0.60–1.75%. The outcomes indicate that the material demonstrates a cyclic strain-softening behavior whose degree rises with rising values of strain ratio and reducing values of strain amplitude. The material demonstrates a non-Masing behavior for higher strain amplitudes amid the interval [1.00%−1.75%]. The material demonstrates a nearly-Masing behavior for lower strain amplitudes amid the interval [0.6%−0.85%]. Under non-zero mean strain, a total relaxation of mean stress is observed at higher strain amplitudes, whereas at lower strain amplitudes, no such behavior is observed.

Significant Bauschinger effect and back stress strengthening in an ultrafine grained pure aluminum fabricated by severe plastic deformation process

Bauschinger test in uniaxial tension-compression mode was carried out for the first time on the pure Al specimens having homogeneous ultra-fine grained (UFG) microstructures fabricated by equal-channel angular pressing (ECAP) and subsequent annealing processes. Significant Bauschinger stress (transient softening), Bauschinger energy parameter and their strong dependences on the tensile plastic pre-strain at the very early stage of the tensile deformation were measured in the UFG specimens, in sharp contrast to their coarse-grained (CG) counterpart. The grain size dependence of the Bauschinger effect in pure Al was qualitatively discussed in terms of the back stress arising from the formation of dislocation pile-up against the grain boundary during plastic deformation.

Multistage strain aging phenomenon of low-carbon steels with rolling pre-strain

In this study, a multistage strain aging method that used rolling pre-strain (compression) was developed to study the effects of temperature, and inter-pass time on static strain aging behavior of low carbon steel. An increase in hardness and strength caused by work hardening due to the forming process and aging at every stage of aging that is calculated separately. To comparing the effects of multistage aging against typical strain aging, the samples were rolled and subjected to the aging process both exist in typical one-stage aging that setting a 20% rolling pre-strain and in multiple stages pre-strain by setting a 5% rolling ratio in four stages. The mechanical properties of aged samples are compared with each other to study the effects of time and temperatures on strength and hardness. To evaluate the effects of pre-strain type (tensile or compression) on mechanical properties, one sample was subjected to tensile and compared with rolling pre-strain samples in similar conditions. The results show that in multistage static strain aged samples with rolling pre-strain, the peak of the strain stress curve occurs in 10–15 min rather than samples that aged after tensile pre-strain. Multistage strain aging increased samples’ strength by 10% and reduced their plasticity by 5%. To evaluate the effects of temperature on the time, we propose the maximum hardness and strength, the aging temperature of the samples was increased to 250 °C and it was observed that the maximum hardness and strength time is reduced by 10 min.

Quasi-Random Gratings Enabled by Wrinkled Photoresist Surfaces on a Rigid Substrate.

Micro- and nanoscale surface wrinkling has been widely studied in artificial systems, mostly in soft substrates like polydimethylsiloxane or polystyrene, where the wrinkling dynamics are triggered by thermal stresses or tensile prestrains. Here, we introduce a new wrinkling regime based on photoresist layers on top of a rigid substrate. By introducing a bending deformation, combined with fluorine-based plasma treatment, wrinkles with a characteristic wavelength less than 1 μm can be created. By adding micropatterns on photoresists with standard UV exposure, ordered wrinkles can also be realized. This technique is demonstrated to be applicable in several commercially available photoresists, and the wrinkled patterns can be employed conveniently to create high-aspect-ratio silicon gratings and large-area silicon dioxide membranes. This unique strategy broadens the spectrum of available materials to create wrinkled surfaces in a controllable manner and provides a platform for the easier fabrication of wrinkle-based devices.