High-speed Deformation Behavior Research Articles

A novel mathematical-based approach to predict the high-speed deformation behavior of cryodeformed materials with varying stacking fault energies

Cryodeformed (CR) materials have complex microstructures containing nano-twins, dislocation clusters, tangles, and others, depending on the stacking fault energy (SFE). Such unique microstructure makes them suitable for several engineering applications under a high strain rate environment. The high-speed deformation (HSD) behavior of CR materials is difficult to understand due to their complex microstructure. The present work is focused on developing a novel mathematical modeling method to understand the high strain rate deformation of CR materials with varying SFE. The model equation correlates the microstructure-based variables to deformation-based variables like stress, strain, and strain rate. High-speed deformation was conducted using a crossbow test. Transmission electron microscopy (TEM) was conducted on these materials to validate the model output.

High-speed Deformation Behavior of a SUS316LN Austenitic Stainless Steel with Heterogeneous-nano Structure

High-speed Deformation Behavior of a SUS316LN Austenitic Stainless Steel with Heterogeneous-nano Structure

High-Speed Deformation of Pinless FSWed Thin Sheets in AA6082 Alloy

The high-speed deformation behavior of friction stir-welded thin sheets in AA6082-T6 aluminum alloy, under biaxial balanced stretching, was investigated by means of a hemispherical punch test carried out using direct tension-compression Split Hopkinson Bar. The friction stir welding process was performed on thin sheet blanks using a pinless tool; the rotational and welding speeds were kept constant during process. The dynamic tests were carried out, with a punch speed of 4500 mm/s, at different punch stroke values until failure of the friction stir welded sample. It was seen that failure occurs along the welding line at a dome height about 11% higher than that at the onset of necking. Fractographic analysis shows that deformation is localized in the fracture zone. The results were compared with those obtained on friction stir welded blanks deformed under quasi-static condition in order to evaluate the influence of the loading rate on the weld deformation and fracture mechanisms. It was shown that joints deformed under dynamic loading condition are characterized by a dome height at the onset of necking significantly higher than the one measured under quasi-static condition.

Validation of Ti-6Al-4V Alloy Mechanical Behavior Models for Conditions of Impact Damage of Turbine Engine Fan Blade

The article describes a series of experiments and calculations for verification high-speed deformation behavior and fracture models for the titanium alloy Ti-6Al-4V. Samples made of the micro-and nanocrystalline structure alloy Ti-6Al-4V were ballistically damaged in conditions that meet a ballistic damage of real turbine engine fan blades. It is found that the behavior of the microcrystalline alloy is more accurately described by the Johnson-Cook model. In the case of nanocrystalline material the best fit is achieved by using the Cooper-Symonds model. The achieved models parameters are presented.

Ball Impact Reliability of Zn-Sn High-Temperature Solder Joints Bonded with Different Substrates

In this study, the high-speed deformation behavior of solder joints formed with Pb-free Zn-Sn and commercial Pb-Sn alloys bonded on different substrates was investigated by the ball impact test method. Overall, Zn-Sn joints exhibited greater impact strength but inferior impact toughness than Pb-Sn joints. This can be ascribed to the high hardness of Zn-Sn solders resulting in partial or overall interfacial fracture. In contrast, the joints with soft Pb-Sn solders all showed a ductile fracture feature. It is suggested that, for the joints revealing brittle fracture, the impact toughness (impact energy) increased with the plastic ability of interfacial intermetallic compounds, while for those showing a ductile fracture mode, the impact energy deteriorated with a hardened solder matrix resulting from substrate dissolution.

The High-Speed Deformation Behavior of TRIP Steels

The high-speed deformation behavior of TRIP steel was investigated at strain rates ranging from 10−2 s−1 to 103 s−1. The effects of metallurgical factors, such as the rolling direction, thickness, and gage length, on the tensile properties at various strain rates were evaluated. The ultimate tensile strength, uniform elongation, strain rate sensitivity, absorbed energy, and strain-hardening exponent are reported. In general, the strength increases and the ductility decreases as the strain rate increases. The samples with a high amount of retained austenite had two distinct regions of strain rate sensitivity, showing high strain rate sensitivity over a strain rate of 102 s−1. The tensile properties were not affected by the gage length and thickness of the tensile samples; however, the rolling direction of the tensile samples affected the UTS values slightly. The absorbed energy of the TRIP steel greatly exceeded that of HSLA steel.

Effect of microstructure on the dynamic deformation behavior of dual phase steel

The high-speed deformation behavior of a commercially available dual phase steel composition was studied by means of split Hopkinson bar testing in shear punch mode. The as-received cold-rolled material was subjected to a variety of heat treatment conditions to produce several different microstructures, namely ferrite plus pearlite, ferrite plus bainite and/or acicular ferrite, ferrite plus bainite and martensite, and ferrite plus different fractions of martensite. A strong effect of microstructure on both static and dynamic properties and on the dynamic factor (ratio of dynamic to static strength) was observed. According to the variation of dynamic factor with static strength, three groups of microstructures with three distinct behaviors were identified. Under the same static strength level, the classic dual phase microstructure was found to have the highest value of dynamic factor and therefore can absorb more dynamic energy than other microstructures.

Effect of Microstructure on Static and Dynamic Mechanical Property of a Dual Phase Steel Studied by Shear Punch Testing

The high-speed deformation behavior of a dual phase steel was studied by means of dynamic Hopkinson bar shear punch testing, with an emphasis on the influence of microstructure. Dual phase microstructures with different fractions of martensite were obtained by changing heat treatment parameters during intercritical annealing. The effects of low temperature tempering (170°C, 235°C, and 300°C) and bake hardening treatment (5% pre-strain followed by holding at 170°C for 20min) were also investigated for two selected microstructures containing 22% and 61% martensite, respectively. Quasi-static shear punch property was also measured by a MTS hydraulic machine and compared with dynamic results. Additionally, quasi-static tensile tests for some specimens were also conducted for validating the shear punch data.

Application of Polyacrylate Rubber for High Performance Automotive Gaskets and Seals

Polyacrylate rubber compounds have been used for a number of years for manufacturing oil seals used in current high performance automotive engines. The work reported here was done at the time of the development of these engines, which required new sealing material. Polyacrylate rubber was already known to withstand the use temperature of 150°C with adequate oil resistance. The unknown was the mechanical performance, particularly the endurance at the service condition. A comparative study was undertaken with compounds prepared from polyacrylate and fluoro-rubber. The latter was already known to have adequate performance and, therefore, was the reference material of this study. The strategy was to conduct a minimum amount of work and to achieve the goal in the shortest time. The temperature dependence of modulus up to 200°C, high-speed deformation behavior with subsequent relaxation and endurance at 150°C indicated that polyacrylate rubber would give satisfactory performance.