Pre-compression Deformation Research Articles

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.

Effect of pre-compression deformation on aging precipitation behavior and mechanical properties of Mg–5Sn alloy

The study aimed to investigate the impact of different aging time and the compression prior to aging on the precipitation behavior and mechanical properties of the Mg–5Sn(wt.%) alloy. The findings revealed that compression prior to aging significantly reduced the time required to reach peak aging and resulted in a higher peak hardness, reaching up to 63 H V after 5 h of aging. The pre-compression introduced dislocation densities of up to 1.916 × 1015/m2, creating more nucleation sites for precipitated phases. As a result, pre-compression aging led to an order of magnitude more precipitated phases compared to direct aging. Interestingly, the study also discovered that hardness and strength did not exhibit a traditional positive correlation. The maximum strength was not achieved when hardness reached its peak. The increased numbers of precipitated phases were closely associated with an increase in strength but did not always enhance the corresponding hardness. The deviation of the hardness along with the increased precipitated phases was mainly imputed to the softening of the precipitated phases themselves. These findings highlight the complex relationship between hardness, strength, and the microstructures of the Mg–5Sn alloy during pre-compression and aging treatment.

Evaluation of Mechanical Performance of a New Disc Spring-Cable Counter Pressure Shock Absorber

Mechanical performance evaluation of a new disc spring-cable counter pressure shock absorber is focused on in this study. The proposed shock absorber is always in a compressive working state with energy dissipation capacity under both tension and compression loadings. The design formulas of its axial bearing capacity, vertical stiffness, deformation energy of the shock absorber were derived, and the corresponding specific design process was provided in detail. Experimental and numerical investigations of the mechanical performance were conducted under static and dynamic loadings. The parameters influencing the laws of the mechanical performance of the shock absorber, including loading frequency, pre-compression deformation and loading amplitude, were investigated. The rationality of the proposed shock absorber was firstly verified through comparative analysis using experimental, numerical and theoretical calculations. The shock absorber with a friction coefficient of 0.005 between disc springs, and a friction coefficient of 0.3 between the disc spring and cover plate has the smallest error between experiment and theory for the flattening force. The bearing capacity of the shock absorber exhibits a linear relationship with the loading displacement in static loading. In dynamic loading, however, the bearing capacity shows a trend of slow growth followed by rapid growth. The energy dissipation capacity of the shock absorber shows an increase with the increase of loading displacement. The minimum equivalent damping ratio of all of the dynamic test cases is 7%, with a maximum up to 15.3%. Under the same loading frequency, the equivalent stiffness and equivalent damping ratio have a linear amplification trend with the increase of pre-compression deformation, and the maximum increase of equivalent stiffness is equal to 41.37%. Under the same loading frequency and pre-compression deformation, the energy consumption capacity can be improved by increasing the loading amplitude.

Grain size dependence of annealing strengthening of an extruded Mg-Gd-Zn alloy subjected to pre-compression deformation

In this work, pre-strain annealing strengthening (PSAS) effect was investigated in an extruded Mg-1.0Gd-1.5 Zn (wt.%) alloy with respect to different grain sizes. The evolution of microstructures was provided by scanning electron microscopy (SEM), electron backscattered diffraction (EBSD), transmission electron microscopy (TEM) and high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) under the initial state, pre-compression, intermediate annealing and re-compression conditions. The obtained results showed a grain size-dependent PSAS effect in the alloy. The sample with larger grain sizes corresponded to a higher strengthening effect, which mainly resulted from a more remarkable hindrance for the growth of existing twins and a larger proportion of activation for the nucleation of new twins. This was closely associated with the increase of back stress and friction stress for twin boundary motion impeded by the larger restraint of dislocations, the higher stress field surrounding solutes and the more Zn segregation. In addition to twinning behavior, Guinier Preston (G.P.) zones on basal 〈a〉 dislocations were found after intermediate annealing and provided an extra strengthening by inhibiting the motions of gilding pre-existing dislocations and newly formed ones, but it was independent on the grain size.

Effect of pre-compression on microstructural evolution, mechanical property and strengthening mechanism of AZ31 alloy

The effect of pre-compression deformation on the microstructural evolution, mechanical property and deformation behavior of AZ31 magnesium alloy was studied. The alloy was microstructurally characterized with a combination of optical microscopy, electron backscatter diffraction, X-ray diffraction and energy-dispersive spectrometer. The results indicate that average number of twins per grain and dislocation density increases with an increase in compressive pre-deformation level. Stress–strain curves of low pre-strained samples (0%, 1% and 3%) present concave-up features, whereas concave-down shapes are detected for high pre-strained samples (6% and 8%) in uniaxial compression tests. The corresponding underlying deformation mechanism transists from a twin-dominated mechanism to a slip-dominated mechanism. This deformation mechanism transition is related to {10–12} twinning, which leads to grain refinement and crystal orientation change, as well as increased dislocation density. The yield strength linearly increases with increasing equivalent grain size regardless of the deformation mechanisms. Quantitative analysis reveals that the contributions from texture strengthening, twinning/grain boundary strengthening and dislocation strengthening increase as pre-compression level increases. Texture strengthening is the dominant strengthening mechanism for high pre-strained samples.

Effect of pre-strain levels and high temperature annealing on the formability of AZ31 Mg alloy thin sheet during stretch deformation

Pre-compression deformation at different strain levels (1.58%, 3.32%, 5.38% and 7.78%) along transverse direction (TD) are conducted to introduce (10–12) tensile twins at room temperature. The static recrystallization process is induced by annealing at 450 °C for 2 h. Then the stretch deformation is conducted at room temperature to investigate the fracture and formability of Mg sheet. The c-axis of grains tiltes from normal direction (ND) to transverse direction (TD) due to the tensile twins; however, the TD-rotated texture is inherited by the new recrystallized grains. The grains grow up and the size increases gradually as the pre-strain levels increasing. Due to the rotated orientation, the basal slips are favored and a larger Schmid factor is obtained on the pre-strained samples. The yield strength reduces, and the ductility increases. Besides, the strain hardening coefficient (n-value) increases and Lankford value (r-value) decreases at the same time. Owing to the TD-rotated orientation, the increased n-value and reduced r-value, the stretch formability is enhanced greatly. The Erichen value (IE-value) increases largestly from 2.83 mm to 5.74 mm which improves by 102.8%.

Effect of Precompression Deformation on the Strain-Controlled Low-Cycle Fatigue Behavior of Extruded AZ31 Magnesium Alloy

In this work, the effect of precompression along the extrusion direction on the strain-controlled low-cycle fatigue behavior of an extruded AZ31 magnesium alloy was investigated. After precompression deformation occurred, the tensile yield strength decreased, whereas the tensile yield strength and ultimate tensile strength increased gradually as precompression deformation increased. The shape of the stress–strain hysteresis of a specimen with 5% precompression deformation changed from asymmetrical to symmetrical compared with that of the as-extruded specimen. Hence, the whole process was likely dominated by twinning–detwinning behavior. Fractographic analysis revealed that the crack propagation region of the specimen with 5% precompression deformation was flatter than that of the as-extruded specimen because of the compressive mean stress and finer grains in the specimen with 5% precompression deformation. The fatigue lives of the as-extruded and precompression specimens were predicted by the Coffin–Manson model, the Ellyin energy model, the Smith–Watson–Topper model, the Fatemi–Socie model, and the Jiang model, respectively. The life predicted by the Ellyin energy model and the Jiang model was consistent with the experimental data.

Enhanced Stretch Formability of AZ31 Magnesium Alloy Thin Sheet by Induced Precompression and Sequent Annealing.

In this study, precompression deformation with a strain level of 5.38% along the transverse direction (TD) at room temperature was conducted on a AZ31 magnesium alloy thin sheet with thickness of 1mm. Then subsequent annealing treatment was carried out at various temperatures (200, 300, 400, and 500 °C) to induce static recrystallization (SRX) and grain growth. The stretch formability was also investigated using the hemispherical test. The results showed that the twinning texture induced by the precompression process was nearly inherited by recrystallized grains after annealing process. Grains grew up and the size increased with the increase of annealing temperature. The largest grain size was obtained when annealing at 400 °C. The mechanical properties including strength and ductility decreased due to the development of coarse grains, however, the stretch formability was enhanced significantly. Indeed, the IE-value increased from 2.83 mm in the as-received Mg alloy sheet to 5.78 mm in the precompressed and 400 °C annealed specimens, leading to an improvement of 104%. This was ascribed to the rotated grain orientation and higher activity of (10–12) twins in coarse grains.

Effect of pre-plastic-deformation on mechanical properties of TiZr-based amorphous alloy composites

Phase transformation behaviors can modulate the stress distribution under loading and enhance the plasticity and work hardening ability of amorphous alloy composite. Effect of pre-plastic deformation on the phase transformation kinetics and the mechanical properties of the TiZr-based amorphous alloy composite were studied systematically in the current work. The plasticity of the composites was improved by lateral pre-compression deformation and pre-tensile deformation. However, the plasticity reduced after axial pre-compression deformation. These results were attributed to the distinguish of the directions between the pre-existing shear bands formed during pre-plastic deformation and new developed shear bands during the final compression, which can favor the severe interaction of shear bands.

Effects of pre-compression deformation on nanoindentation response of Zr65Cu15Al10Ni10 bulk metallic glass

Nanoindentation experiments were conducted on Zr65Cu15Al10Ni10 bulk metallic glass samples with pre-compression deformation (PCD) under various conditions. By analyzing indentation hardness, residual morphology, pile-up, and serrated flow, the effects of PCD on nanoindentation response were comparatively investigated. Experimental results indicate that 9 kN PCD induced remarkable decrease of indentation hardness, i.e. softening of the material, while for the 18 kN and 25 kN PCD samples, hardness values very close to that of the as cast sample were obtained. Furthermore, PCD also changed the mechanical heterogeneity, i.e., distribution of soft and hard regions in the bulk metallic glass. Residual morphologies and load-displacement curves of the 9 kN and 18 kN PCD samples showed opposite features in aspects of macroscopic shear bands, pile-up width, pile-up height, and serrated flows, suggesting different plastic flows during nanoindentation. To rationalize these phenomena, a competing mechanism between shear bands and compressive residual stress was discussed.

Enhancement of orientation gradients during simple shear deformation by application of simple compression

We use a multi-scale, polycrystal plasticity micromechanics model to study the development of orientation gradients within crystals deforming by slip. At the largest scale, the model is a full-field crystal plasticity finite element model with explicit 3D grain structures created by DREAM.3D, and at the finest scale, at each integration point, slip is governed by a dislocation density based hardening law. For deformed polycrystals, the model predicts intra-granular misorientation distributions that follow well the scaling law seen experimentally by Hughes et al., Acta Mater. 45(1), 105–112 (1997), independent of strain level and deformation mode. We reveal that the application of a simple compression step prior to simple shearing significantly enhances the development of intra-granular misorientations compared to simple shearing alone for the same amount of total strain. We rationalize that the changes in crystallographic orientation and shape evolution when going from simple compression to simple shearing increase the local heterogeneity in slip, leading to the boost in intra-granular misorientation development. In addition, the analysis finds that simple compression introduces additional crystal orientations that are prone to developing intra-granular misorientations, which also help to increase intra-granular misorientations. Many metal working techniques for refining grain sizes involve a preliminary or concurrent application of compression with severe simple shearing. Our finding reveals that a pre-compression deformation step can, in fact, serve as another processing variable for improving the rate of grain refinement during the simple shearing of polycrystalline metals.

Effect of twinning and detwinning on the spring-back and shift of neutral layer in AZ31 magnesium alloy sheets during V-bend

Abstract In order to investigate the effect of twinning and detwinning on springback and shift of neutral layer, pre-stretch (PRS) of 3% and 5%, and pre-compression (PRC) of 1%, 3% and 5% along rolling direction was conducted in an AZ31 magnesium alloy sheets at room temperature. 90° V-bending tests were performed at 423 K with various pre-strained samples. The results show that springback increases after both PRS and PRC deformation. The coefficient of neutral layer ( k-value ) decreases with the increase of the levels of PRS and PRC. After PRS, twinning in an inner compressive region during bending is restrained and tension–compression asymmetry decreased. After PRC, detwinning occurs which implying that it dominates the deformation in the outer tensile region, while in inner compressive region twinning still governs the deformation. Twinning and detwinning leads to a decrease of asymmetry mechanism between the outer and inner layers. The decrease of asymmetry mechanism after PRT and PRC results in a drop of the neutral layer offset.

Analysis of TF Insert Coil

The United States ITER Project Office (USIPO) is responsible for the design of the oroidal Field (TF) insert coil, which will allow validation of the performance of significant lengths of the conductors to be used in the full scale TF coils in relevant conditions of field, current density and mechanical strain. The Japan Atomic Energy Agency (JAEA) will build the TF insert which will be tested at the central solenoid model coil (CSMC) test facility at JAEA, Naka, Japan. Three dimensional mathematical model of TF insert was created based on the initial design geometry data, and included the following features: orthotropic material properties of superconductor material and insulation; external magnetic field from CSMC, temperature dependent properties of the materials; precompression and plastic deformation in lap joint. Major geometrical characteristics of the design were preserved including cable jacket and insulation shape, mandrel outline, and support clamps and spacers. The model is capable of performing coupled structural, thermal, and electromagnetic analysis using ANSYS. Numerical simulations were performed for room temperature conditions; cool down to 4 K, and the operating regime with 68 kA current at 11.8 Tesla background field. Numerical simulations led to the final design of the coil producing the required strain levels on the cable, while simultaneously satisfying the ITER magnet structural design criteria.

Improving low-cycle fatigue properties of rolled AZ31 magnesium alloy by pre-compression deformation

The effect of pre-compression deformation on the low-cycle fatigue properties and cyclic deformation behavior of as-rolled AZ31 alloy was investigated by performing the stress-controlled low-cycle fatigue tests at room temperature. Fatigue properties and cyclic damage process should be closely related to the twins. The present work aimed to investigate the deformation mechanism and fatigue life caused by the introduced {10−12} twinning–detwinning from the viewpoint of stress amplitude. The results reveal that the twins contribute to the fatigue properties and cyclic damage process of AZ31 alloy. There were noticeable changes in hysteresis loops, microstructures and fatigue lives when the stress amplitude increased from 120 to 150MPa. The fatigue life of pre-compressed samples was more superior to that of the as-rolled sample under different stress amplitudes, especially under the stress amplitude close to the tensile yield strength of the as-rolled sample.

Mechanical behaviours of workhardening and worksoftening bulkmetallic glasses

The workhardening Cu47·5Zr47·5Al5and the worksoftening Zr52·5Cu17·9Ni14·6Al10·0Ti5·0bulk metallic glasses before and after precompression deformation were characterisedfor thermal and mechanical behaviours. The predeformation introduces excessivefree volume in both glasses. Cu47·5Zr47·5Al5and Zr52·5Cu17·9Ni14·6Al10·0Ti5·0exhibit substantial workhardening and worksoftening behaviours respectively.For Cu47·5Zr47·5Al5, the precompressionhas a negligible effect on serrations in the plastic flow during nanoindentation,which is related to the hardening of a shear band, while for Zr52·5Cu17·9Ni14·6Al10·0Ti5·0, the precompression moderates serrations in the plasticflow during nanoindentation, which is associated with the softening of a shearband. Strengthening from mechanically induced nanocrystallites at shear bandsis responsible for the workhardening of Cu47·5Zr47·5Al5,which overwhelms softening due to the introduction of excessive free volume.