Effect Of Prestrain Research Articles

Effect of pre-strain on the flux dynamics of current-carrying superconductors containing defects

This article presents a study that combines the electrostatic potential equation with the time-dependent Ginzburg–Landau equation, incorporating volume strain and utilizing Maxwell-type and current-carrying boundary conditions. Through the finite difference method, the research investigates the magnetic flux dynamics and energy variations in a type II superconductor with an artificial defect at the center, considering pre-strain, external magnetic field, and external current. The findings indicate that linear deformation and external electric field have a significant impact on the electrical properties, distribution of magnetic flux vortices, vortex dynamics, order parameter value, and overall total energy in superconductors with defects. These results contribute to a better understanding of the magnetic flux dynamics in superconductors under complex conditions.

Experimental Study on Deep-Drawing Dies Made of Pre-Stressed UHPC

Deep drawing is a cost-efficient way of producing sheet metal parts in high production volumes. Prototypes and very small series are expensive due to the cost of steel-forming tools. Ultra-high-performance concrete (UHPC) tools offer a cheap and fast alternative to conventional steel-forming tools. However, the flexural and tensile strength of UHPC limits its use in complex loading situations occurring in the forming die during deep drawing. To overcome this challenge, we propose pre-stressing UHPC by using expansive UHPC in a mechanically restrained condition. An aluminum powder-based expansive agent can be used to induce a free volume increase in UHPC specimens. With push-out test specimens, the increase in strength was tested when restraining the free volume increase with a steel reinforcement. After 3 and 12 months, no notable pre-straining effect could be measured when restraining the expansion of UHPC. Nonetheless, in deep-drawing experiments, the die made of expansive UHPC in a restrained condition withstood a maximal load during deep drawing of 110 kN. Compared to the die made from UHPC only, the failure mode changed from complete fracture to surface degradation of the drawing radius after 15 strokes.

Pre-straining effect on ferrite/pearlite anisotropic transformation strain in steels

The effect of pre-straining on ferrite/pearlite phase transformation in high strength steels is investigated. Two steels differing mainly in their Nb content (0.03C 0.68Si 1.82Mn 0.00 or 0.04Nb in mass%) are either pre-tensioned or pre-compressed and the same-directional transformation strain is measured. A crystal plasticity fast Fourier transform numerical model with back stress effect is used for further investigation and the results are compared. Experimentally, it was found that 30% pre-tension reduces the transformation strain in the same direction by 0.09% (0.00Nb) and 0.13% (0.04Nb), while 30% pre-compression increases it by 0.16% (0.00Nb) and 0.02% (0.04Nb). The numerical simulation estimates the experimentally observed anisotropic transformation strain. In the numerical simulation, even though the anisotropy in transformation plasticity has been qualitatively reproduced, a larger anisotropy effect was observed. The quantitative discrepancies found in between experimental results and numerical results are due to the annihilation of dislocations during the interval between the pre-straining and the onset of phase transformation. The anisotropy in transformation strain found in the experiments is large enough to cause an unacceptable dimensional change in e.g. heat treated steel sheet products.

Insights into multi-scale structural evolution and dielectric response of poly(methyl acrylate) under pre-strain: A simulation study.

The structural evolution of dielectric elastomer induced by pre-strain is a complex, multi-scale process that poses a significant challenge to a deep understanding of the effect of pre-strain. Through simulation results, we identify the variation in the dielectric constant and multi-scale (electronic structure, molecular chain conformation, and aggregation structure) response of poly(methyl acrylate). As the pre-strain increases, the dielectric constant initially rises (below 200% pre-strain) and then declines (above 200% pre-strain). Analysis of the charge distribution, surface electrostatic potential, HOMO-LUMO bandgap, and electron density differences reveal that adjusting chain conformation appropriately could enhance polarity domain and electron polarization. The correlation between permittivity and segment dynamics of deformed molecules is explored, encompassing segment orientation, mean shift displacement, and diffusion coefficient. Following molecular chain orientation, the kinematic capability of the chain segment improves, which leads to an increase in the number and activity of effective dipoles and the enhancement of orientation polarization. Excessive stretching restricts the polymer molecular chain mechanically, reducing the number and activity of effective dipoles and negatively impacting electron polarization. The permittivity transitions from isotropic to anisotropic behavior when the system is subjected to strain. This study provides an interesting solution for research on multiscale responses and intrinsic mechanisms of pre-strain.

Influence of pre-strain and size effect on Bauschinger effect of superalloy ultrathin sheet during microscale cyclic deformation

During the fabrication of thin-walled superalloy structures, materials often undergo complex loading paths and exhibit different mechanical properties compared to those under simple loading paths. For example, when subjected to cyclic loading, superalloy ultrathin sheet exhibits pronounced Bauschinger effect. Furthermore, the achievement of precise forming in thin-walled superalloy components is hindered by size effect. To enhance the forming accuracy of superalloy components, this study systematically investigated the interplay between pre-strain, size effect, and Bauschinger effect, along with their underlying mechanisms. Cyclic deformation mechanical response of GH4169 ultrathin sheets with different thicknesses and grain sizes were thoroughly examined under diverse pre-strain conditions through cyclic shearing test. The evolution laws of Bauschinger parameters, specifically as they relate to varying pre-strains, thicknesses and grain sizes, were further determined. To rationalize these Bauschinger parameter evolution laws, electron backscatter diffraction (EBSD) and transmission electron microscopy (TEM) were used to characterize the microstructure of GH4169 ultrathin sheets. Results indicated that the primary mechanism driving Bauschinger effect in GH4169 ultrathin sheets is the arising of back stress from dislocation slip and accumulation. As the level of pre-strain intensifies, Bauschinger effect becomes more pronounced, which is attributed to the intricate interplay between the evolving densities of moving and forest dislocations. Moreover, as grain size decreases, Bauschinger effect undergoes an enhancement due to changes in moving dislocation density and grain boundary strengthening effect. Conversely, size effect inherent to GH4169 ultrathin sheets exerts a dampening influence on Bauschinger effect. This weakening is intimately tied to surface layer effect, which modulates the dislocation density within GH4169 ultrathin sheets. These intricate interactions underscore the complexity of Bauschinger effect in thin-walled superalloy structures and highlight the need for nuanced approaches in material design and processing.

On tailoring morphing mechanics of a bistable composite cylindrical shell through elastic fibre prestressing

A bistable composite cylindrical shell is a thin-walled structure that can change shape between two stable configurations under small energy input, showing great potential to be applied to space deployable mechanics. The internal stress level within a cylindrical shell plays a vital role in determining its morphing mechanics, whilst tailoring the internal stress is tricky for traditional composite manufacturing methods. In this paper, we devise a novel biaxial elastic fibre prestressing (EFP) method to systematic design and produce prestrained carbon-based composite cylindrical shells, with tailorable bistability and morphing mechanics, as well as improved load-carrying capabilities. A biaxial fibre stretching rig was devised to apply tensions on both directions of a plain-weave carbon prepreg simultaneously; prestrained cylindrical shell samples were produced with various prestrain levels to fully evaluate the fibre prestraining effects; a finite element model was established and showed good agreement with experimental observations. The fibre prestraining mechanisms were then proposed. It is found that EFP is effective in tailoring the internal strain/stress level within a composite cylindrical shell, which in turn altering the structural morphing mechanics, and able to significantly lower the maximum tensile strain during shape-changing, thus improve the load-carrying capability. These findings are expected to facilitate structural design of the deployable composite structures and flexible mechanical hinges, by allowing further design freedoms in terms of morphing mechanics and load-carrying capability.

Effect of Pre-strain on High-Temperature Oxidation Behavior of Inconel 617 Superalloy Fabricated by Wire Arc Additive Manufacturing at 900 °C

Effect of Pre-strain on High-Temperature Oxidation Behavior of Inconel 617 Superalloy Fabricated by Wire Arc Additive Manufacturing at 900 °C

Effect of pre-strain on hydrogen-induced delayed cracking and hydrogen trapping behavior in high-strength martensitic steels

Pre-strain is a key factor affecting the critical conditions for hydrogen-induced delayed cracking (HIDC). In this study, the threshold stress and critical hydrogen concentration for HIDC of MS1300 and MS1500 steels with different pre-strains were measured by constant load tensile (CLT) tests. The results demonstrated that although MS1500 has higher strength, its safe service strength is lower than that of MS1300 when the hydrogen content exceeds 0.5 wppm. Additionally, the hydrogen penetration, thermal desorption spectroscopy, and hydrogen microprinting methods were also used to analyze the hydrogen-induced failure mechanism. These studies provide an effective data reference for improving the industrial production process.

Effect of Pre-strain and Strain Rate on Deformation and Fracture Behavior of Automotive Grade Interstitial Free Steel Sheets

Effect of Pre-strain and Strain Rate on Deformation and Fracture Behavior of Automotive Grade Interstitial Free Steel Sheets

The effect of pre-strain on textures, nano-twins and mechanical properties of a novel Nickel-based superalloy GH4251 with low stacking fault energy

By means of appropriate cold rolling pre-deformation, the tensile strength and plasticity of a novel polycrystalline precipitation-strengthened Nickel-based superalloy with low-stacking fault energy at 750 °C can be enhanced. The findings indicate that such pre-deformation leads to the emergence of microscopic substructures, including dislocations, anti-phase boundaries (APBs), stacking faults, and Lomer-Cottrell Locks (L-C locks). It is observed that the presence of these substructures is increased with the degree of pre-deformation. At the 15 % pre-deformation, a few deformation twins are detected near the grain boundaries, and their occurrence rises further in specimens subjected to 25 % pre-deformation. In addition, the nano-twins formation presents a strong correlation with the intensification of Brass-type textures. Notably, after the cold rolling pre-deformation, the alloy's yield strength as well as tensile strength at 750 °C is enhanced in contrast to those without pre-deformation, which is attributed to plentiful factors, such as low recovery and recrystallization activation energy, high-density nano-twins, grain refinement, and conducive crystallographic orientation for nano-twin mechanism activation caused by cold rolling pre-deformation. The specimen with 25 % pre-deformation exhibits relatively high tensile ductility. In this study, the relationships between pre-cold rolling deformation, microstructure, texture, and mechanical properties are comprehensively explored, indicating that the cold rolling pre-deformation holds promise for enhancing Nickel-based superalloys' strength and plasticity.

Effect of pre-strain on thermal aging of austenitic stainless steel weld metal

Austenitic stainless steel welds (ASSWs) suffer from severe pre-strain during assembly process, which threatens the long-term operation safety of pipelines in nuclear power plant. In this work, the 316L weld metals (WMs) with 0 % and 8 % pre-strain were thermally aged at 400 °C for up to 39000 h to investigate the pre-strain effect on thermal aging of ASSWs. The results showed that the pre-strain caused work hardening and further promoted the hardening of thermally aged ferrite. After thermal aging for 39000 h, the nano-hardness increment of ferrite with 8 % pre-strain was about 1.6 GPa more than that without pre-strain. By microstructure characterization, it is found that the high dislocation density induced by pre-strain promoted spinodal decomposition and G-phase precipitation. The spinodal decomposition morphology and corresponding element concentration fluctuations were more obvious in the WM with 8 % pre-strain. Moreover, the size and density of G-phase along dislocations were larger in the ferrite with 8 % pre-strain than those without pre-strain.

Effect of strain ratio and pre-strain on the low-cycle fatigue behavior of 4130X steel at different strain amplitudes

This study investigates the impacts of strain ratio and pre-strain on the low-cycle fatigue properties and microscopic damage mechanisms of 4130X steel across varying strain amplitudes. Under symmetric loading, initial cycles at low strain amplitudes demonstrate clear peak/valley stress hardening followed by cyclic softening in later stages of fatigue. In contrast, the hardening behavior vanishes at higher strain amplitudes. Increasing strain ratio and pre-strain cause the initial hardening behavior at low strain amplitudes to gradually disappear. Additionally, at lower strain amplitudes, fatigue life decreases as strain ratio and pre-strain rise, attributed to substantial tensile mean stress. Microscopic examination reveals that symmetric cyclic loading at low strain amplitudes releases stress concentrations caused by quenched and tempered processing and reduces both dislocation density and localized plastic strain. Conversely, at higher strain ratios and pre-strains, increased tensile mean stresses not only intensify dislocation multiplication, resulting in high dislocation density, but also activate multi-slip system, leading to dislocation cross-slip. Moreover, at a high strain amplitude of 0.45 %, pre-strain aids in martensite recovery and promotes dislocation annihilation during recovery, thus inducing cyclic softening. Finally, the fatigue lives under varied loading conditions are compared with the fatigue design curve prescribed by ASME VIII-II code.

Multiscale shear failure mechanisms within a prestrained composite

AbstractThe elastic fiber prestressing (EFP) technique has been developed to balance the thermal residual stress generated during curing of a polymeric composite, where continuous fibers were prestretched under either constant stress or constant strain throughout the curing process. The tension was only removed after the resin was fully cured. It has been demonstrated that EFP is able to enhance the shear properties of the composite, while the underlying mechanics is still unknown. Here, we investigated the multiscale shear failure mechanisms induced by the EFP within a carbon composite. A bespoke biaxial fiber prestressing rig was developed to apply biaxial tension to a plain‐weave carbon prepreg, where the constant strain‐based EFP method was employed to produce prestrained composites with different prestrain levels. Effects of EFP on macro‐scale shear failure were subsequently characterized through mechanical tests and micro‐morphological analysis. Both the micro‐ and meso‐scale representative volume element (RVE) finite element models were established and experimentally verified. These were then employed to reveal the underlying stress evolution mechanics induced by EFP. It is found that EFP would improve the shear performance of a composite by enhancing the fiber/matrix interfacial bonding strength. This attributes to the elastic strain recoveries of the prestrained fibers locked within a polymeric composite, which generate compressive stresses to counterbalance the external loading. The multiscale shear failure mechanisms were then proposed. These findings are expected to facilitate structural design and application of the EFP for aerospace composites.Highlights Biaxial tension is applied to produce prestrained woven composite. Prestrain effects on microstructural stress evolution mechanics are revealed. Multiscale shear failure mechanisms are proposed for prestrained composites.

Effect of pre-strain on dynamic mechanical properties of Ti-6Cr-5Mo-5V-4Al titanium alloy

Abstract The effect of quasi-static pre-deformation on the dynamic properties of Ti-6Cr-5Mo-5V-4Al titanium alloy was studied. The results revealed that as the pre-tension deformation increased, the average dynamic flow stress was slightly decreased while the dynamic uniform plastic strain and the maximum absorbed energy were improved obviously and the largest value existed when the deformation reached 6.8%. As the pre-tension deformation progressively increased, the dynamic performance exhibited a marked decline. Conversely, with the increase of the pre-compression deformation, the dynamic flow stress experienced a substantial enhancement, but the dynamic uniform plastic and the maximum absorbed energy significantly declined which showed that the pre-compression deformation did harm to the dynamic mechanical properties of Ti-6Cr-5Mo-5V-4Al titanium alloy.

Enhanced spall strength of an Al0.1CoCrFeNi high-entropy alloy by the pre-strain method

The effects of pre-strain on spallation damage of an Al0.1CoCrFeNi high-entropy alloy are investigated with plate impact loading. During the pre-strain process, Kink bands and dislocations are generated in the microstructures. Pre-strain smears elastic–plastic transition upon shock loading and improves spall strength via dislocation strengthening. Although the level of pre-strain does not affect the ductile damage mode, it has a pronounced effect on damage evolution.

Cyclic response and stability of shape memory alloy cables considering training, displacement history, and prestrain effects

Superelastic shape memory alloy (SMA) cables have been considered in the development of various seismic protection technologies. The cyclic nature of seismic loads necessitates a comprehensive understanding of the mechanical behavior of SMA cables under repeated loading conditions. As SMAs undergo repeated phase transformation cycles, alterations in their properties occur due to defects generated and modified during the transformation. When utilizing superelasticity, this response can be stabilized after numerous transformation cycles. In various applications, components made of SMAs undergo a stabilization process referred to as training to enhance the predictability of the alloy’s response. Despite the widespread acceptance of training cycles to achieve stable cyclic response, a well-defined protocol is lacking. This study investigates the effects of various factors, including training strain amplitude, repeated loading, low-cycle fatigue loading, loading at high strain amplitudes, displacement loading history, and prestrain on the cyclic response of a large-diameter SMA cable. A total of 14 SMA cable specimens are tested under various tensile loading conditions. The experimental results, including stress-strain curves and various response parameters such as peak stress, residual strains, energy dissipation capacity, and equivalent viscous damping are examined in detail. The results indicate that training SMA cables at a strain amplitude near the end of phase transformation plateau leads to a highly stable cyclic response. However, it is worth noting that, in comparison to untrained cables, training induces a softening effect in the cable response.

Effects of pre-strain on hydrogen-induced stress corrosion cracking behavior of Q345R steel in hydrofluoric acid vapor environment

This study investigates microstructure, hydrogen diffusion properties, and stress corrosion cracking (SCC) behavior of Q345R steel subject to pre-applied strains of 1 %, 3 %, and 5 %. The relationship between microstructure and SCC susceptibility in hydrofluoric acid (HF) vapor is examined. It is found that pre-strain cannot change the microstructure of Q345R steel but increases dislocation density. The increasing SCC sensitivity of Q345R steel in HF vapor is associated with the dislocation density induced by pre-strain. With increasing pre-strain, dislocation density and reversible hydrogen trap increase, and interaction between hydrogen and dislocation accelerates hydrogen-induced SCC. In addition, irreversible hydrogen traps caused by high pre-strain can severely aggravate hydrogen-induced SCC, resulting in high SCC vulnerability.

Effects of cold rolling pre-strain on abnormal grain growth behavior in longitudinal welds of 2196 Al-Cu-Li profiles

The dramatic abnormal grain growth (AGG) in longitudinal weld of 2196 Al-Cu-Li extrusion profiles during solution treatment leads to performance deterioration. In this paper, the profile was subjected to cold rolling with different reduction along transverse direction (TD) and extrusion direction (ED) before T6 treatment, and the effects of above processes on the AGG behavior were clarified. The cold rolling changed the morphology and orientation of grains in the longitudinal weld area, and the number of Cube grains that can work as AGG precursor decreased. Meanwhile, numerous dislocations and stored strain energy promoted the DRX of the whole section, thus AGG process transformed to synchronous grain growth. However, the increasing grain boundary energy stimulated grain growth, thus this method could not suppress AGG completely. Grains of welding area have special rotation path when they were cold rolled along ED, the Cube grains transformed to the Copper grains during rolling, hence the growth advantage of welding area disappeared and then transformed to R-Copper texture after solution treatment, which improved the homogeneity of microstructure, thereby removed the local strain concentration and local brittle failure of welding area induced by AGG, and improved the comprehensive properties of the profiles.

Corrosion behavior and mechanical integrity of Zn-based guided bone generation (GBR) membrane subjected to U-bending deformation

To study the effect of pre-strain on corrosion behavior of pure Zn strip/membranes, the U-bending treatment, immersion and mechanical tests were conducted. The pre-strain accelerated the corrosion rates of both pure Zn strips or membranes with an elevated ratio of 78.02 % (strips), 27.33 % (300 μm), 32.09 % μm/yr (600 μm) and 52.77 % μm/yr (1000 μm). Besides, the finite element simulation results indicated that stress concentration occurred at the maximum deflection sites, leading to the rupture of surface protective layer and formation of micro cracks. Moreover, the applied strain would accelerate the mechanical integrity decay of pure Zn membranes.

Small punch evaluation of mechanical properties for 310S stainless steel considering pre-strain effect

Strain strengthening technology is widely used in practical engineering to increase the allowable stress of materials in pressure vessel manufacturing. Small punch analysis was performed using less material in this study to analyse the influence of pre-strain on the mechanical properties of 310S stainless steel. The results indicated that the material yield strength and ultimate tensile strength increased with pre-strain deformation. Similarly, the small punch characteristic parameters increased owing to the influence of the pre-strain, proving that the small punch test could estimate the evolution of mechanical properties along with pre-strain deformation. Small punch characteristic parameters at different deformation stages were analysed. In addition to the maximum load, small punch parameters at the inflection point were used in the ultimate tensile strength estimation. The small punch deformation features and stress distribution were discussed based on numerical simulations. Finally, an ultimate tensile strength estimation method based on membrane stretching model was proposed. Additionally, the strain hardening parameters considering the effect of pre-strain deformation were discussed.