Plastic Deformation Of Samples Research Articles

On the acoustic method of control of spatial inhomogeneity of plastic deformation of weakly anisotropic orthotropic materials

In this paper, the possibilities of using non-destructive acoustic control to determine the features of the spatial distribution of local plastic deformations during deformation of flat samples made of AMg61 alloy were investigated. The methodological features of using the acoustic anisotropy parameter to study the patterns of changes in spatial inhomogeneities of the field of local plastic deformations are analyzed. A computational and experimental method for determining the acoustic anisotropy parameter is proposed, which allows to correctly determine not only its magnitude, but also the directions of the local axes of acoustic anisotropy. The sources of errors of the proposed methodology, the limits of its applicability, as well as the requirements for hardware and software for its implementation are analyzed. The results of experimental studies carried out on samples of weakly anisotropic aluminum alloy AMg61 are compared with the representations of autowave mechanics of plasticity of metals. An engineering algorithm for determining the early localization of zones of loss of stability during plastic deformation of samples is proposed. The possibility of creating a methodology for assessing the plasticity resource of a material during its plastic shaping is shown.

Strain distribution and lattice rotations during in-situ tension of aluminum with a transmodal grain structure

Samples of aluminum were prepared using spark plasma sintering from a mixture of coarse (average particle size of 6 μm) and fine (average particle size of 1 μm) powders to achieve a heterogeneous transmodal grain size distribution covering a range of grain sizes from ≈1 to 10 μm. By careful choice of surface markers both electron back-scatter diffraction (EBSD) data, to track crystal rotations, and digital image correlation (DIC) data, to track local plastic deformation, were collected from the same region during in-situ tensile deformation up to a strain of εt = 0.126. A heterogeneous pattern of crystal rotation is observed for all grain sizes, although in some smaller grains (defined as those <4 μm diameter) no clear grain sub-division was identified. Plastic strain was more concentrated in the larger grains, but the average rotation rate of the smaller grains was found to be higher than that of larger grains, showing also a much wider spread in rotation rate. Based on the change in average orientation, a clear orientation dependence in the tensile axis rotation direction was observed for many larger grains, in agreement with previously reported data for aluminum with average grain size of 75 μm, whereas the smaller grains showed a more complex rotation behavior, with more of these grains showing unexpected tensile axis rotations. The combination of both EBSD and DIC during in-situ experiments provides a rich data set for analysis of plastic deformation in samples with a heterogeneous microstructure.

Influence of slip ratio on worn-surface microstructure and fatigue wear behavior of D2 wheel steel

To investigate the worn-surface microstructure and fatigue cracks in D2 wheel steel under the pure rolling and 0.5% slip ratio conditions, a rolling wear test using a GPM-40 wear machine to simulate the wheel/rail operation was performed. After testing, a transmission electron microscope, a scanning electron microscope with electron backscatter diffraction, and micro-hardness testers were used to characterize the microstructure and fatigue cracks. The surface microstructure and hardness of the pure rolling sample were in a steady state after 8 × 104 cycles; however, the 0.5% slip ratio sample reached a steady state after 7 × 103 cycles. Regardless of whether the test uses the slip ratio, the orientation of lamellar pearlites gradually became parallel to the surface and a portion of lamellar cementites was fragmented and dissolved during the formation of steady-state microstructure. The slip ratio accelerates this process. The hardening mechanism of the samples shows a decrease in the lamellar spacing of pearlite and the refinement of proeutectoid ferrite (PF). As the number of cycles increased, plastic deformation of samples became increasingly severe and the wear mechanism of the samples was fatigue wear in steady state. The sample surfaces formed shallow cracks, which gradually peeled off. The slip ratio accelerated the initiation and propagation of fatigue cracks because of the high friction stress on the contact surface. Most fatigue cracks initiated at the interface of pearlite and PF and in the PF region.

Electromagnetoelasticity Effect in Silicon

The paper is devoted to the study of the magnetostimulated dynamics of dislocations in silicon and the influence of electric current on this process. As a result of the conducted studies, it was found that preliminary exposure of n-and p-type silicon single crystals in a constant magnetic field (B = 1 T, exposure time up to 30 minutes) leads to an increase in mobility of dislocation segments in them during plastic deformation of samples (Т=675оС, σ=60–100 MPa, t=45–60 minutes). The quadratic dependence of the dislocation ranges on the induction of a constant magnetic field was found on the samples studied. A decrease in the activation characteristics of the process of displacement of linear defects during the flow of electric current during deformation is also detected: the transmission of electric current helps to reduce the activation energy of the process from 2.2± 0.2 eV to 0.7±0.1 eV. The observed changes are attributed to a decrease in the interaction energy of linear defects with dislocation stoppers based on the dopant.

Shakedown behaviors of railway ballast under cyclic loading

Based on laser scanning technique and discrete element program, the fine mesoscopic model of irregular ballast particles was simulated well by series of bonded disc clusters, then the large-scale static and cyclic loading tests were used to determine the parameters of the discrete element model. On this basis, the plastic deformation and shakedown behaviors of ballast samples under cyclic loading were studied, and the effects of cyclic loading amplitude, confining pressure and loading frequency were discussed. The results show that, in plastic shakedown state, broken ballast particles were rare and the strain rate of the sample decreased rapidly with the increase of the number of load cycles; in plastic creep state, ballast particles were broken at the beginning of cyclic loading and then appeared stable deformation; in incremental collapse state, ballast particles were broken in initial cyclic loading, but the plastic deformation of the sample was mainly due to the rapid shear failure. The stress limits of ballast samples for different shakedown states increased with raising the confining pressure, but the influence of the loading frequency on the stress limits related to the stress levels of confining pressure, and accordingly, the empirical exponential models of the relationships between the stress limits (i.e. maximum principal stress) and the ratios of corresponding maximum principal stress to minimum principal stress were established.

Compressive failure mechanism and buckling analysis of the graded hierarchical bamboo structure

Bamboo is a unique unidirectional biocomposite, which consists of vascular bundles (VBs) as the reinforcement and parenchyma cells (PCs) as the matrix. The non-uniform distribution of VBs embedded in the matrix makes bamboo a functionally graded material. In order to investigate the compressive behavior of bamboo as a function of its components, compression tests were performed on specific bamboo samples with different VB volume fraction (V vb), collected from different positions in the culm wall. The results show that both compressive strength and modulus increased linearly with V vb, while the plastic deformation of samples in the compression decreased with increasing V vb. This indicates that VBs dominate the compressive strength and modulus of bamboo, while the ductile performance of the bamboo is determined by the foam-like PCs. Scanning electron microscope observation indicated that VBs buckling were the main cause of failure. The Euler theory was applied to investigate the buckling behavior of bamboo blocks, showing that theoretical buckling strength when only considering the effect of VBs was much lower than with the test results, with the theoretical buckling strength being closer to test results when considering both the effect of VBs and PCs. It is therefore necessary to consider the contribution of PCs to resist buckling in bamboo, as their foam-like structure can effectively prevent the large-scale buckling of VBs.

Induced magnetic anisotropy in low-carbon steel plates subjected to plastic deformation by stretching

Experimental studies of induced magnetic anisotropy in plastically deformed low-carbon steel were carried out. The measurements were performed on samples in the form of discs. The maximum energy of the induced magnetic anisotropy was observed at a relative elongation of ~12% upon an increase in the plastic deformation of samples. At higher degrees of deformation the energy of the induced magnetic anisotropy is reduced, which indicates a decrease in the residual mechanical stresses in the material.

Effect of weft density and percentage of stainless steel fiber content of weft yarn on electrical properties of woven fabric strain sensors

Textile-based strain sensors have been used in smart textiles frequently. In this study, effect of percentage of stainless steel fiber of spun yarn (i.e. 28 and 40%) and weft density (i.e. 14, 18, and 22 per cm) of conductive yarn on performance and sensitivity of woven fabrics strain sensor under tensile cyclic loading in 3 mm elongation and also behavior of woven fabric strain sensors under simple tensile loading, was studied. Our finding showed the interaction between weft density and percentage of conductive fiber of spun yarns on performance and sensitivity of strain sensors under cyclic loading. Samples prepared by conductive yarns with 40% stainless steel fiber showed no clear cyclic variation in 18 and 22 weft per cm. This trend for samples woven with conductive yarn with 28% stainless steel fiber was only observed in 22 weft per cm. All samples showed the same trend of resistance variation during simple tensile loading, although the level of resistance variation was different. The slope of resistance variation during tensile cyclic loading confirmed plastic deformation of samples. Finally, by comparing the sensitivity of strain sensors during cyclic loading no obvious advantage was obtained for samples woven with conductive yarn with 40% stainless steel fiber compared with samples woven with conductive yarn with 28% stainless steel fiber.

Comparison Research on Mechanical Properties of High Temperature Alloy after Laser Peened and Ultrasonically Peened

For comparative study of the influence of laser shock peening and ultrasonic shot peening on the mechanical property of superalloy K403, untreated, ultrasonic shot peening with 850°C heat preservation, laser shock (heat preservation, Hp), the fatigue testing of samples under four states were conducted at room temperature, and the analysis of two techniques’ influence on the mechanical properties of K403 was done by hardness tester, profile tester, scanning electron microscopy (SEM). The results indicated that LSP with Hp, LSP, USP with Hp can improve the fatigue life of K403 respectively for 2.4, 2.25, 1.4 times more longer than untreated sample; the increase of micro-hardness gradient after LSP were smaller than after USP. The SEM studies showed that the γ' phase distortion was elongated and the plastic deformation of samples by LSP was larger than by USP.

Initial Aspects of Low-Cycle Fatigue Fracture of Martensitic Steels

This study deals with the SEM and optical microscopic characterization of fatigue plastic deformation process during fatigue crack initiation to understand where, why and how cracks initiate under conditions of low cycle fatigue. Samples were prepared from the 13Х11Н2В2МФ high-chromium stainless steel used for fusion power applications. The low-cycle tests were conducted at room temperature with the standard V-notched samples prepared from conventional stainless steel. The following characteristics were studied during fatigue tests: 1 macrocrack propagation, 2. interaction between macrocrack and isolated microcracks, 3. interaction between macrocrack and slip bands, 4. interaction between macrocrack and microstructure elements of the steel. The above experiments show that during macrocrack propagation a plastic zone is formed around it, where isolated microcracks and slip bands of 2-3 different directions are observed. Measurement of plastic zone dimensions after different number of cycles of deformation show that plastic zone size increases during the first stage of cyclic deformation (until definite number of cycles are completed), and then remains unchanged. The observations show that main crack is composed of individual micro-components, the lengths of which are in a good correlation with the dimensions of microstructure elements of the steel (former austenite grains, martensite crystals). It was revealed that during growth, as a rule, macrocrack rarely propagates along isolated microcracks and slip bands. Direction of macrocrack propagation changes while passing from one microstructure element to another, so that main direction is the same. No preferable transcrystalline or intercrystalline propagation of macrocrack has been observed in the investigated steel. It is shown that after subsequent fatigue tests, dimensions of the previously created slip bands increase, and additional new slip band are also formed. The sites and frequency of slip bands’ formation in plastic zone are also studied. It was observed that the boundaries and mainly the sites of intersection of martensite crystals are the sites of isolated (rough) microcracks’ formation. The dimensions of slip bands are comparable with those of martensite crystals. The angles between the main crack propagation direction and slip bands varied from 30o to 60o, however, most of the slip bands were oriented at 45o to the main crack. Based on the obtained results a conclusion is made that plastic deformation in samples go inhomogeneously. In plastic zones, along with the heavily deformed areas, almost non-deformed areas are also observed. The speed of fatigue fracture increases with the increase in frequency and amplitude of deformations. Generally, the annealed samples are destructed prematurely in comparison with non-annealed ones of the investigated steel.

Modeling Cutting: Plastic Deformation of Polymer Samples Indented With a Wedge

An experiment was designed to relate force to plastic deformation caused by a wedge indenting the edge surface of a polymer sample. The experiment reveals the primary phenomena observed in industrial converting processes of cutting and slitting of thin polymer films. The thin film was modeled using a polycarbonate rectangular block, which was indented with a metallic half-round wedge that represents the industrial cutter blades. The wedge radius and sample size were selected to scale to the ratio of slitting blade radius and industrial film thickness. A compression test frame impressed wedges into polymer samples with measurements of both force and displacement recorded. These experiments clearly revealed the shape of the plastic deformation zone ahead of and around the wedges. Data from the experiments showed increasing cutting force with wedge displacement until the sample fractured. Plastic deformation of the samples was examined: the out-of-plane plastic volume was shown to equal the volume displaced by the wedge. Cracks that developed from the side of the wedge tip during indention propagated with near steady-state loads under edge surface indention.

Effects of oxygen on the deformation behaviour in single-phase γ-TiAl alloys

Abstract The effect of the interstitial solute element oxygen on the mobility of dislocations in single-phase γ-TiAl alloys has been assessed experimentally. Thus polycrystalline samples of alloys of Ti-52 at.% with oxygen impurity levels of either 750 or 1250wt p.p.m. have been deformed at room temperature. It has been found that, while extensive glide of dislocations with Burgers vectors b given by b = 1/2(110) is observed for higher purity specimens, their activity is very much reduced at increasing levels of oxygen impurity contents. Thus, plastic deformation of samples with an oxygen level of 1250 wt p.p.m. is provided essentially by glide of superdislocations with b = (101), accompanied by superlattice extrinsic stacking fault formation. Possible mechanisms for this effect are discussed.

On the fine-grained-lamellar microstructure transformation in Zn-20.2% Al-1.8% Cu alloy

It is known that fine-grained and lamellar microstructures of Zn-22% A1 eutectoid alloy can be obtained by quenching or slow cooling, respectively, of their f c c phase a/, from above the eutectoid temperature (551 K). Also, a lamellar microstructure arises from the isothermal heating of finegrained samples at temperatures below 551 K [1]. On the other hand, certain transformations can be produced by plastic deformation of Zn-22% AI: a fine-grained microstructure arises from hightemperature deformation of lamellar microstructures (although it is not essential to have temperatures above the eutectoid temperature) [2]. Finally, a fine-grained microstructure appears on necking zones of plastically deformed Zn-A1 lamellar eutectoid alloy (in the range 300-473 K) [3]. The main object of this letter is to report some experimental results related to microstructural transformations occurring in a Zn-20.2% A1-1.8% Cu alloy during certain thermomechanical treatments of lamellar and fine-grained samples. In our experiments we found that the samples of Zn-20.2% A1-1.8% Cu alloy follow the same general microstructure transformations scheme shown by the eutectoid Zn-22% A1 alloy. For instance, quenching or slow cooling of the 0/-phase from a temperature above the eutectoid point gave, respectively, fine-grained or lamellar microstructures. Also, isothermal heating of fine-grained samples gave lamellar microstructures, but for low temperatures (T = 373 K) the rate of transformation was very low. The plastic deformation of samples with lamellar structure produced a finegrained microstructure on necking zones. Therefore, the addition of Cu near the eutectoid composition of Zn-22% A1 alloy does not give rise to any major change in the general transformation scheme of this type of alloy. Another general result is that transformations from lamellar to fine-grained microstructures (or vice versa) are possible only by the simultaneous existence on the samples of the cr(fcc structure, Al-rich) and fi(hcp structure, Zn-rich) phases. In other words, if in a given part of the sample the fl-phase is chemically removed from the alloy, then no microstructural transformation was detected (as is shown below). Scanning electron microscopy (SEM) images from

On the Nature of the Cavitation Phenomenon in Superionic Cu2−xSe

The pore generation due to the cavitation phenomenon in superionic Cu2−xSe samples doped with In, Al, Cd, Sn, In + Sb, Zn, Er, and Sb is investigated at temperatures of T = 1000 K. Some dopants (Cd and Sb) are observed to magnify the effect, while the other ones reduce it greatly. The possible reasons for the phenomenon observed such as gas distension, nonequilibrium vacancy coagulation (Frenkel effect), and plastic deformation of samples are discussed. [Russian Text Ignored].

Structural superplasticity of Fe-Mn-C alloys

1. Ternary Fe-Mn-C alloys containing 12–45% Mn and 1.2–2.5% C exhibit structural superplasticity after deformation in tension at 770–950°C at strain rates of (0.2–2)·10−3 sec−1 both in air and in vacuum. 2. Plastic deformation of samples with an original uneven structure is accompanied by refining and homogenization of the structure due to recrystallization of the alloy and diffusion of carbon, but the plasticity is far lower in this case.

Metallographic observation of cleaved grains in polycrystalline beryllium

In recent studies of cleaved grain densities in CIP/HIP P-1 beryllium, different densities were observed for the same amount of plastic deformation in samples prepared by two different metallographic procedures. One polishing procedure was exclusively mechanical while the other included a final etch-polish step. This work addressed the reason for the difference in observed cleaved grain densities. Results showed that stress corrosion cracking in the presence of residual stresses and the etchant did not occur. The difference arose because some cracks were covered up during mechanical polishing.