Papers by Keyword: Strain Rate

Abstract: The aim of this study was to determine the compressive mechanical properties and the energy absorption characteristics of a bio-composite material based on lime, wheat straw, and additives (protein and entraining agent). The selected samples with fiber to binder ratio of 30% were subjected to compression tests at different strain rates (1 mm/min, 10 mm/min, and 100 mm/min), in the perpendicular and parallel directions to fiber orientation. Image analysis supported with Digital Image Correlation (DIC) method is performed to follow longitudinal and lateral deformations, thus making it possible to evaluate elastic properties. The results show that the highest density and compressive strength in the parallel direction are ~349 kg/m³ and ~0.101 MPa, respectively. The perpendicular specimens at 100 mm/min of speed test showed the highest values of densification strain, stress plateau, energy efficiency, and absorbed-energy of 47.27%, 0.32 MPa, 16.98 %, and 13.84 kJ/m², respectively. The values of Young’s modulus identified with DIC are significantly different from those determined by the slope of the linear part of the stress-strain curve. A slight influence of strain rate on mechanical properties is observed.

Abstract: The compressive behavior of ME20M alloy along rolling direction (RD) at a wide strain rates under low temperatures is investigated in this paper. Compressive stress-strain results reveal that the effect of strain rate on yield strength and flow stress is not obvious, especially at low temperatures. Moreover, the temperature plays an important role in compressive responses. SEM observations indicate that brittle fracture is the main fracture mode at low strain rate, and ductile fracture occurs in the failure of the alloy at high strain rate.

Abstract: The purpose of this investigation is to study the dynamic hardness of MCrAlY abradable coatings under different strain rates. A dynamic indentation device based on the split Hopkinson pressure bar system (SHPB) was used. The results show that the hardness of MCrAlY coating increased with the increase of the strain rate, which has a positive strain rate effect. In addition, the difference of the static hardness of MCrAlY coating prepared by HVOF and LPPS was only 4%, while the difference in dynamic hardness was 16%.

Abstract: Tensile, compressive and flexural (3-point bending) tests are performed on electromechanical universal testing machine (Zwick/Roell 250kN) to determine mechanical characteristics of an aluminium hybrid composite fabricated through stir casting process at different rates of quasi-static loadings in room temperature 25°C. Influence of heat treatment (annealing) is observed on the material properties. After annealing, the tensile, compressive and flexural strengths decrease while ductility, malleability and bending capability of the composite increase. Bending tests are conducted at different crosshead speeds (1-100mm/min) to study its effects on flexural stresses. It is found that the specimen geometry affects the stress-strain behaviour of the composite.

Abstract: In this paper, the high temperature flow behaviors of 6061 Al alloy was studied by thermal compression experiments. The effects of temperature, strain rate and strain on the microstructure evolution and flow behavior of the alloy were investigated by experiments. The results show that the flow stress of the alloy increases with the increase of strain rate and it decreases with the increase of deformation temperature. The flow curve reaches the dynamic equilibrium under the interaction of work hardening and dynamic softening mechanism. The uprising deformation temperature promotes thermal excitation dynamic recrystallization of deformed microstructure. With the increase of strain, the microstructure of the alloy is transformed from equiaxed crystal morphology to fibrous structure and strain-induced dynamic recrystallization occurs. As strain rate increases, the action time of dynamic softening mechanism for the studied alloy is reduced, resulting in the fraction of dynamic recrystallized structure is reduced and the flow stress increases.

Abstract: Active development of the territories of Siberia and the Far East requires the use of materials that are able to work under the combined influence of low temperatures and a complex state. When operating equipment parts at low temperatures, it is necessary to take into account the impact of static and dynamic loads, as well as the influence of an external aggressive environment. The paper studies corrosion-resistant cold-resistant metastable austenitic steels, which are widely used for manufacturing parts of low-temperature equipment. Tests were performed to assess the strength and ductility characteristics of smooth samples and samples with annular notches for static stretching in the temperature range from 293 to 77 K.

Abstract: Investigating the influence of process parameters is vital to improve the mechanical properties of nanoparticle reinforced polymer nanocomposites. In this effort, nanocomposites of polypropylene/nanoclay are prepared by the extrusion method. In order to characterize the mechanical behavior of nanocomposites over different compounding ratios, samples are prepared with 5 and 10 wt%. Effect of re-extrusion and PP-g-MA compatibilizer on the tensile performance of nanocomposites is evaluated at different strain rates. XRD evaluation of compounds indicated that re-extrusion is an important factor in increasing the exfoliation degree.

Abstract: Uni-axial compression (UAC) tests and further post deformation annealing (PDA) were done for 23Cr-6Ni-3Mo duplex stainless steel (DSS). The initial morphology was equiaxed (EQ) in nature. In the first stage of PDA, austenite showed limited static recrystallization (SRX) followed by static recovery (SRV); however ferrite showed static recovery (SRV). In the second stage of PDA, the austenite showed grain coarsening followed by disintegration of substructures (DIS); and ferrite revealed mostly SRV leading to grain coarsening. The third stage of PDA envisages substructural disintegration of unstable substructure leading to saturation in both austenite and ferrite. The sub-structural characteristics were provided by Electron backscattered diffraction (EBSD) and its post processing were done by using HKL Channel 5 software.

Abstract: In order to study the mechanism of the fatigue strengthening using laser shot peening in GH4169 alloy, micro-structural and nanoscale mechanical twins (MT) at different depth below the top surface subjected to laser shot peening processing (LSP) were investigated by means of electron backscatter diffraction (EBSD) and transmission electron microscopy (TEM) observations. In terms of the experimental observations and analyses, the formation of refined grains and nanoscale MT mechanism at the near surface of GH4169 alloy as a function of LSP treament can be summarized as follows: (i) two direction low density of MTs divide the initial coarse grains into submicron rhombic blocks; (ii) high density of MTs aligned in two directions subdivide the submicron rhombic blocks into nanoscale rhombic MT blocks; (iii) the third direction MT further refine the nanoscale rhombic MT blocks into nanoscale triangular MT blocks; (iv) some of subdivided blocks evolve into refined grains. An ultra-high strain rate induced by ultra-short laser pulse plays a key role in the formation of refined grains and nanoscale MT during plastic deformation of GH4169 alloy subjected to LSP treatment.

Abstract: The effect of strain rate on the β texture evolution during two-step hot forging of Ti-6246 alloy was investigated. The two-step forging consisted of 15% or 50% prior-β forging at 980°C and subsequent 60% or 25% forging at 870°C in the (α + β) dual-phase region. The total compression ratio was 75%, and the investigated strain rates were 0.01 and 1.0 s⁻¹. The β forging texture showed typical {001} and {111} body-centered cubic textures. With increasing compression ratio in the (α + β) region and at a strain rate of 0.01 s⁻¹, the amount of precipitated α phase increased. Dynamic recrystallization was rarely observed after forging in the (α + β) region at a strain rate of 0.01 s⁻¹. Large amounts of α precipitates lowered the {001} β texture intensity through slip transmission between the α and β phases under the Burgers orientation relationship. However, in specimens forged at a strain rate of 1.0 s⁻¹, as the compression ratio in the β single-phase region increased, the growth of dynamic-recrystallized β grains was promoted at the prior-β grain boundaries, where α-phase precipitation was not substantial. These effects resulted in a higher {001} texture intensity of the β phase in specimens forged at 1.0 s⁻¹ compared with that of the β phase in specimens forged at 0.01 s⁻¹.