Effect Of Prestrain Research Articles

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 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.

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.

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.

Effect of Pre-strain on Microstructure and Stamping Performance of High-strength Low-alloy Steel

Effect of Pre-strain on Microstructure and Stamping Performance of High-strength Low-alloy Steel

Forming limit and failure characterization of as-received and bi-axial prestrained Cu-Cr-Zr-Ti alloy sheets in the context of multistage forming

The characterization of forming limit utilizing Cu-Cr-Zr-Ti alloy sheets during the multistage forming process is imperative for successfully fabricating thrust chamber liners used in satellite launch vehicles. Therefore, the present work studies the effect of prestrain on the forming limit and failure behaviour of this alloy under different deformation paths. A stretch-forming setup was utilized to induce 8% equi-biaxial prestrain (EBP), and subsequently, these prestrained specimens were deformed till the onset of failure using the same setup. After prestraining, a shift in the failure strains was observed in the principal strain space, whereas it was found to be absent in the polar effective plastic strain, principal stress and effective plastic strain-stress triaxiality loci. The cup height along different deformation paths was marginally decreased in the prestrained specimens because of the reduction in failure strains, and the fracture occurred in the prestrained region. Further, failure analysis revealed intergranular cracks in the specimens deformed along plane strain and uniaxial deformation paths due to the presence of micron-size Cr-rich precipitates along grain boundaries. However, intergranular and transgranular cracks were present in the prestrained specimens, which were deformed equi-biaxially similar to the as-received specimens. The presence of nano-size Cr-rich precipitates inside the grains acted as nucleation sites for voids during equi-biaxial stretching, leading to transgranular cracks. It was also observed that failure in the prestrained and as-received specimens occurred at a similar effective plastic strain value due to the combined effect of void density and void size. Based on experimental observations, it was inferred that the forming limit of Cu-Cr-Zr-Ti sheets under a two-stage forming process was primarily affected by the presence of micro and nano-size Cr-rich precipitates.

Effect of Pre-strain on Microstructure and Corrosion Behavior of a Novel High-Zn Containing Al-Zn-Mg-Cu Alloy

Effect of Pre-strain on Microstructure and Corrosion Behavior of a Novel High-Zn Containing Al-Zn-Mg-Cu Alloy

Biaxial Tensile Testing of Cruciform Samples to Determine the Impact of Pre-Strain on the Forming Limit Diagram of Aluminum Alloy 5052 through Finite Element Simulation

The present work focuses on the effect of pre-strain on the forming limit curves (FLCs) of aluminium alloy 5052 sheet of 2.5 mm thickness using cruciform samples. To identify the effect of pre-strain on the FLC, the finite element simulations are performed on cruciform samples. The cruciform samples are deformed to a small level of pre-strain in different strain paths. Thereafter, the further deformation under the various strain paths to measure the effect of pre-strain on the forming limits are carried out. Pre-strain in uniaxial, plane strain and biaxial loading conditions are considered in this work. For each case, i.e., uniaxial, plane strain and biaxial conditions two pre-strain conditions are considered. The cruciform samples are carefully thinned in the central region to promote development of large plastic strains there and eventually to neck and fail. The output obtained through simulations are presented in terms of forming limit curves for various strain paths.

Effect of pre-strain on microstructure evolution and fracture behavior of undermatching X80 pipeline steel girth weld

This work aims to study the effect of pre-strain on the fracture behavior of X80 pipeline girth weld joint, a comprehensive analysis was conducted on the microstructure and mechanical properties of the girth weld before and after pre-strain treatment. The mechanical properties were evaluated through tensile testing, Charpy impact testing, and digital image correlation (DIC) strain analysis. Furthermore, the microstructure and fracture morphology of the girth weld were observed using optical electron microscopy (OM) and scanning electron microscopy (SEM). The results show that the application of pre-strain treatment leads to dislocation accumulation at the grain boundary of X80 pipeline girth weld, resulting in stress concentration and subsequent formation of damage holes. This process disrupts the continuity of chain M-A island and initiates small cracks at the grain boundary, ultimately causing a significant decrease in impact toughness and impact work from 177 J to about 10 J.

Oxidation Behavior of Pre-Strained Polycrystalline Ni3Al-Based Superalloy.

The harsh service environment of aeroengine hot-end components requires superalloys possessing excellent antioxidant properties. This study investigated the effect of pre-strain on the oxidation behavior of polycrystalline Ni3Al-based superalloys. The growth behaviors of oxidation products were analyzed by scanning electron microscope, transmission electron microscope, X-ray Photoelectron Spectroscopy and Raman spectroscopy. The results indicated that the 5% pre-strained alloys exhibited lower mass gain, shallower oxidation depth and more compact oxide film structures compared to the original alloy. This is mainly attributed to the formation of rapid diffusion paths for Al atoms diffusing to the surface under 5% pre-strain, which promotes the faster formation of protective Al2O3 film while continuing to increase the pre-strain to 25% results in less protective transient oxidation behavior being aggravated due to the increase in dislocation density within the alloy, which prevents the timely formation of the protective Al2O3 film, resulting in uneven oxidation behavior on the alloy.

Tunable viscoelasticity of bulk fullerene network via high-temperature annealing

Although the experimental transformation of C60 bulk into various functional carbon materials at a certain temperature and pressure has been extensively explored, the understanding of the structural transformation mechanisms and the energy dissipation mechanisms of the derived topologies at the atomic scale is still poor. By using the molecular dynamics (MD) simulations method, the structural transformation of C60 bulk to various carbon materials is studied. Besides, the mechanisms of energy dissipation of three typical structures are revealed and the effects of loading frequency, temperature, loading amplitude, and pre-strain on the storage, loss modulus, and dumping ratio of three typical structures were investigated by dynamic mechanical analysis (DMA). The results show that due to the difference in structural morphology and mechanical behaviors under cyclic loading, three typical structures show different viscoelastic mechanical properties which could also be tuned by changing related parameters. This work systematically investigates the viscoelastic mechanical properties of bulk fullerene network during different annealing processes and corresponding energy dissipation mechanisms and provides important references for further design and application.