Effect Of Strain State Research Articles

Effect of strain state on the surface roughening for hydroforming of aluminum alloy tube based on cross-scale numerical modeling

The complex deformation behavior would result in surface roughening such as orange peel defect during the hydroforming process of aluminum alloy tubular parts. In order to control the surface quality of hydroformed tubular parts, the effect of strain state on the surface roughening for 2219 aluminum alloy tube was analyzed based on a cross-scale model. The model combined the crystal plasticity model and macroscopic finite element model. During the uniaxial tension, the surface morphology reveals an equiaxed pattern characteristic of orange peel due to the strain incompatibilities between grains, and the peak and valley are stretched along the tensile direction. The surface roughness under tension-compression plane strain state is the lowest due to the low through-thickness strain. In the biaxial tension region, the change rate of surface roughness gradually increases with the decrease of the second principal strain especially in the late deformation stage, and the surface features evolve from an orange peel pattern to a ridging pattern. The forming limit diagram under different strain states based on surface roughness was established to guide the optimization of hydroforming process. Compared with the one-step hydroforming, the surface roughness of the bulging peak of 2219 aluminum alloy tube using multi-step hydroforming with the axial self-feeding decreases obviously from 16.3 to 10.8 μm due to the significant reduction of the equivalent strain.

Molecular dynamics simulations of phospholipid bilayer mechanoporation under different strain states—a comparison between GROMACS and LAMMPS

Nanoscale deformation mechanisms of cellular structures could render drastically different results depending on the molecular dynamics (MD) simulator chosen. Due to different available settings, the comparison of these different MD simulators is typically an intricate task, requiring that all configurations be converted appropriately with a variety of reasonable parameter choices. The current study aims to perform and compare MD simulations of biomolecules between two common MD software packages (GROMACS and LAMMPS), in which a phospholipid bilayer is deformed under different strain states (equibiaxial, 2:1 non-equibiaxial, 4:1 non-equibiaxial, strip biaxial and uniaxial tension). The results for the stress–strain, pore nucleation and growth, and damage behavior are compared between the respective GROMACS and LAMMPS simulations. In general, GROMACS and LAMMPS produced similar deformation behavior, including damage evolution and the effect of strain state on phospholipid bilayer failure. However, GROMACS nucleated a greater number of pores at lower strains, produced lower stress values and higher damage values than LAMMPS. Multiple different setting options between GROMACS and LAMMPS, including algorithm variations, have been considered as possible explanations for the observed differences. Overall, this study will aid in the cross-check of parameter settings and simulation results in future MD research, particularly on the mechanical damage of phospholipid bilayers and other biological systems. Based on that, with future efforts, GROMACS and LAMMPS, as well as other MD programs, could be exploited synchronously with better comparability and reproducibility.

Effects of strain state and slip mode on the texture evolution of a near-α TA15 titanium alloy during hot deformation based on crystal plasticity method

A thorough understanding of the texture evolution of near-α titanium alloys during the hot metal forming can help obtain an optimal crystallographic texture and material performance. The strain state has an obvious effect on the texture evolution of near-α titanium alloys during the hot metal forming. In this paper, the texture evolution of a near-α TA15 titanium alloy during the hot metal forming under different strain states were discussed based on the crystal plasticity finite element method. It is found that the basal and prismatic slip systems are regarded as the dominant slip modes due to the similar low critical resolved shear stress during the hot metal forming of the TA15 sheet rotating the lattice around the [101¯0] and 〈0001〉 axis, respectively. Once both of them cannot be activated, the pyramidal-2 slipping occurs rotating the lattice around the [101¯0] axis. The relationship between the texture evolution and strain state is established. All the (0001) orientations form a band perpendicular to the direction of the first principal strain. The width of the band along the direction of the second principal strain depends on the ratio of the compressive effect to the tensile effect of the second principal strain. This relationship can help control the crystallographic texture and mechanical properties of the titanium alloys component during the hot metal forming.

Effect of strain state on the linear expansion coefficient of Zr-Nb-Cu-Fe amorphous alloys

The temperature dependence of changes in the size of the samples has a structural component, which can be determined with the help of dilatometry. The purpose of this work was to obtain the structure-dependent component of the coefficient of linear thermal expansion (CLTE) of Zr-Nb-Cu-Fe amorphous alloys. The samples were preliminarily hardened under conditions of pure bending test to definite degrees of plastic deformation. The obtained experimental results permit to evaluate the CLTE as a function of plastic deformation.

Effect of strain states during cold rolling on the recrystallized grain size in an aluminum alloy

The evolution of texture and microstructure during recrystallization was tracked for a number of differently cold-rolled aluminum sheets and through-thickness layers which were differentiated by different strain states due to prior deformation. The results substantiate a correlation between recrystallization texture and the amount of shear applied during cold rolling as well as a decrease in the final grain size with increasing effective strain during deformation.

Effect of strain path change on recrystallisation in copper

The effect of different modes of deformation on the subsequent recrystallisation kinetics of copper has been studied. Combinations of uniaxial tension, uniaxial compression and plane strain compression were used to give linear, reversed, and orthogonal strain paths. The rate of recrystallisation, determined using hardness tests and isochronal annealing, did not correlate with any simple strain measure. Correlation with final flow stress was moderate, and was slightly better with as deformed hardness. Deviations from such simple relationships were due partly to an overall effect of strain state, although the largest differences were associated with transient behaviour at small second stage deformations.

Effect of Strain State on a Yield Anisotropy Model for Materials Strengthened by Plate-Shaped Precipitates

The effect of texture and crystallographic alignment of precipitate particles on yield anisotropy are examined in an Al-Cu-Mg-Ag precipitation hardening alloy. Three variants of the plastic inclusion model, involving different degrees of relaxation of the axisymmetric strain requirement, were used to model yield anisotropy in this material. Comparing model results to yield anisotropy measurements for a C415 (Al-Cu-Mg-Ag) extrusion reveals that the best agreement is obtained when modest departures from axisymmetric strain are allowed.

Effects of strain state on the kinetics of strain-induced martensite in steels

This paper deals with the quantitative prediction of the volume fraction of strain-induced martensite produced in a steel that undergoes a thermomechanical loading. This issue is relevant for several steels with a low stacking fault energy, where a significant amount of transformed martensite drives many mechanical properties. Practical situations range from the optimization in the rolling process of a sheet to the improvement of the toughness of the final product. The model relies on the assumption that the martensite ( α′) is nucleated within a grain at the intersections of shear bands formed by the movement of partial dislocations on certain of the twelve {111} γ 〈2̄11〉 γ systems (subscript γ refers to the austenitic, or mother, phase). A modified Taylor-based numerical calculation is performed on a polycrystalline aggregate in order to obtain the intensity of the shear, and hence the volume fraction of martensite in each grain. Results are found to model and predict various experimental results obtained mainly on 304L stainless steel under different strain states.

Recent advances in biomedical polyurethane biostability and biodegradation

This paper summarizes our recent efforts to better understand the effects of antioxidants, the effects of strain-state, mechanistic studies of soft segment cleavage by reactive oxygen radicals, and the effects of different soft segment chemistries on the biostability/biodegradation of polyether polyurethanes (PEUUs). In vivo cage implant system studies and in vitro cobalt ion/hydrogen peroxide studies have been carried out on PEUUs and the polymers have been analysed by attenuated total reflectance and Fourier transform infrared (ATR-FTIR) spectroscopy, and scanning electron microscopic (SEM) characterization of the PEUU surfaces. The natural antioxidant, vitamin E, has been shown to inhibit biodegradation and enhance biostability of PEUUs. Studies of the effect of stress state on PEUU biodegradation demonstrate that stress can inhibit biodegradation. While polyether soft segments may be cleaved by the presence of reactive oxygen radicals, the presence of oxygen has a profound effect in accelerating biodegradation. The biodegradation of polyurethanes may be inhibited by substituting different chemistries such as polydimethylsiloxanes, polycarbonates, and hydrocarbon soft segments for the polyether soft segments. To safely utilize polyurethanes in long-term biomedical devices, the biodegradation mechanisms of polyurethane elastomers must be fully understood and subsequently prevented. © 1998 SCI.

The effect of strain state on the biostability of a poly(etherurethane urea) elastomer.

The effect of deformation state on degradation of a PEUU without added stabilizers was examined in an oxidative environment that simulates the in vivo biodegradation of the polymer. Polymer tubes were stressed uniaxially and biaxially over glass mandrels and treated in 20% hydrogen peroxide/0.1 M cobalt chloride solution for 12 days at 37 degrees C. The amount of degradation was determined from the ATR-FTIR peak height of the amorphous aliphatic ether absorbance at 1110 cm-1. If a uniaxial stress was applied, degradation was inhibited and the amount of surface ether remaining after treatment increased linearly with strain. If the stress was biaxial, the amount of degradation was not reduced unless the strain was greater than 200%. Decreased degradation correlated with the amount of soft-segment orientation. The decreased degradation rate was attributed to compaction of the polyether phase by orientation, which resulted in lower permeability to oxidative agents, particularly oxygen. Macroscopic damage was confined to a thin peeling surface layer if the stress was uniaxial. In comparison, biaxially stressed PEUU ruptured.

Void formation during tensile testing of dual phase steels

The effects of martensite volume fraction (MVF) and strain state on necking behavior, post-uniform elongation, and the nucleation and growth of voids in thin sheet dual phase steel, strained in tension, were investigated. Steel containing, in weight percent, 0.08C, 1.45Mn, and 0.21Si, was cold rolled 50 pct and intercritically annealed to produce dual phase microstructures. The effects of MVF were evaluated with a series of constant geometry tensile samples with martensite volume fractions between 5 and 40 pct. The effects of strain state within the neck were evaluated with a series of constant thickness samples with 20 pct MVF and with width variations between 3 and 25 mm. A transition from diffuse to localized necking, as well as a decrease in post-uniform elongation, occurred with both an increase in MVF and sample width. Metallographic analysis of deformed samples revealed that the void nucleation occurs primarily at martensite particles by three distinct mechanisms. The void size and density in the necked region increased toward the fracture surface in all samples and the void density was significantly higher for the samples which exhibited localized necking. However, independent of neck geometry, voids were nucleated uniformly throughout the samples, and were associated with the martensite. The difference in void size and density between the samples with different necking behavior indicates that void growth is a consequence of the strain gradient while the shape of the voids depends on both the strain state and strain gradient. The implications of the void structure analysis are interpreted based on the dual phase microstructure.

Effects of Strain State and Strain Rate on Deformation-Induced Transformation in 304 Stainless Steel: Part I. Magnetic Measurements and Mechanical Behavior

The γ→α transformation in 304 stainless steel can be induced by plastic deformation at room temperature. The kinetics of strain-induced transformations have been modeled recently by Olson and Cohen. We used magnetic techniques to monitor the progress of the γ→α transformation in 304 stainless steel sheet loaded in uniaxial and biaxial tension at both low (10-3 per second) and high (103 per second) strain rates. We found that using the von Mises effective strain criterion gives a reasonable correlation of transformation kinetics under general strain states. The principal effect of increased strain rate was observed at strains greater than 0.25. The temperature increase resulting from adiabatic heating was sufficient to suppress the γ→α transformation substantially at high rates. The consequences of the γ→α transformation on mechanical behavior were noted in uniaxial and biaxial tension. Uniaxial tension tests were conducted at temperatures ranging from 50 to -80°C. We found that both the strain hardening and transformation rates increased with decreasing temperature. However, the martensite transformation saturates at ≈85 pct volume fraction α. This can occur at strains less than 0.3 for conditions where the transformation is rapid. Once saturation occurs, the work hardening rate decreases rapidly and premature local plastic instability results. In biaxial tension, the same tendency toward plastic instability associated with high transformation rates provides a rationale for the low biaxial ductility of 304 stainless steel.

Effects of Strain State and Strain Rate on Deformation-Induced Transformation in 304 Stainless Steel: Part II. Microstructural Study

The γ→α transformation in 304 stainless steel was induced by plastic deformation under various conditions of strain, strain state, and strain rate, and the transformation microstructures were examined by transmission electron microscopy (TEM). The nucleation of α martensite embryos was always confined to microscopic shear band (faults, twins, and e-martensite) intersections. In cases where shear bands consisted of bundles of intermixed faults, twins, and e-martensite, α nucleated preferentially only within specific portions of the intersection volume. At sufficiently large strains α appeared to grow into polyhedral shapes. We postulate that growth occurs by repeated nucleation of new α embryos and coalescence of such embryos into polyhedral shapes. These shapes can grow either within an active slip plane or out of it, depending on how many shear band intersections are produced during deformation. Actual measurements of the number of intersections indicated that more intersections are formed in biaxial tension per unit effective strain than in uniaxial tension. This accounts for the more irregular, blocky α morphology observed in biaxial tension. At high strain rates we also found an increase in the number of intersections. However, adiabatic heating at large strains and high rates restricts repeated nucleation and coalescence and limits the amount of α transformation product.