Effect of high strain rate on plastic deformation of a low alloy steel subjected to ballistic impact

Odeshi, A.G.; Al-Ameeri, S.; Bassim, M.N.

doi:10.1016/j.jmatprotec.2005.02.157

Cited by 91 publications

(46 citation statements)

References 29 publications

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“…12 by the white etching bands. This microscopic evidence for the occurrence of TASB, which has been previously observed by other investigators, 16,32) was further confirmed in this work by microhardness results that indicated a change from 270 HV in the undeformed zone to roughly 400-430 HV in the ASB and approximately 510-570 HV measured inside the TASB region. Hence during impact loading such as the DWCT or fastening forging, the inhomogeneous conditions for deformation coupled with the thermal instabilities has a high probability for void initiation and coalescence as well as microcrack formation.…”

Section: Resultssupporting

confidence: 92%

Characterization of Internal Voids and Cracks in Cold Heading of Dual Phase Steel

2005

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In this work, the mechanism of void and microcrack formation along the adiabatic shear bands (ASB) was studied for processing dual phase steel by cold heading. Experimental investigation along with finite element simulation has confirmed that this mechanism depends on two types of instabilities, namely geometrical and thermal instabilities. The geometric instability occurs in the presence of second phase particles (inclusions) and in relation to the material flow orientation, whilst the thermal softening arises due to the localized plastic deformation inside the ASB. Progressive deformation was observed to cause the elongation of voids in the direction of shearing that formed microcracks in the ASB of the cold headed specimen. In addition, transformed bands were observed in the highly deformed zones as a result of the temperature in the ASB exceeding the Ac 3 transformation temperature 847°C. The superposition of the location of the ASB region containing the voids and micro-cracks with the phase transformation zone indicates that the development of optimized processing conditions is particularly critical for preventing fracture during cold heading of dual phase steels.KEY WORDS: dual phase steel; cold heading; adiabatic shear bands; voids; cracks; inclusions.rials. However, most of the plastic work (90-95 %) is converted into heat causing a local temperature increase and a flow stress decrease. Thus, a competing mechanism between the work hardening and the thermal softening commences and continues in the deformation zone. As the work hardening mechanism dominates over the thermal softening at the beginning, an increase in the flow stress occurs and with continuing deformation, the thermal softening mechanism can progressively dominate over work hardening increases, which then triggers unstable deformation. This instability condition will force the deformation to localize into a narrower band that through further localization can lead to final failure. 4)There are two types of ASBs, namely the deformed adiabatic shear bands (DASBs) and the transformed adiabatic shear bands (TASBs). DASBs occur in materials that do not undergo phase transformation, or when the local increased temperature in the band is not high enough to cause phase transformation. The damage and fracture process in DASBs involves a number of metallurgical events involving different steps between void nucleation and crack propagation. The initial phase of damage coincides with void nucleation at inclusion edges or at grain boundaries due to the interaction of local stresses and dislocations phenomena. The damage in the material is then driven by the accumulated plastic strain and affected by the stress triaxiality. 5) Moreover, deformation under compressive loads shows that when there is compressive (negative) stress triaxiality, the formability is greater than in the tensile loading state, i.e. positive stress triaxiality.6) It is therefore a competition between the stress triaxiality levels reached in the specimen and the high plastic strains, w...

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Section: Resultssupporting

confidence: 92%

Characterization of Internal Voids and Cracks in Cold Heading of Dual Phase Steel

2005

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“…This deformation mode is commonly observed in ballistic impacts, explosive fragmentation, and high-speed metal forming and fabrication [9][10][11][12] and has important implications in terms of loading conditions. It is widely believed that the formation of adiabatic shear bands is the result of a thermally-induced plastic instability effect, which suppresses work hardening in the deformed region.…”

Section: Introductionmentioning

confidence: 99%

Adiabatic Shearing Localisation in High Strain Rate Deformation of Al-Sc Alloy

et al. 2010

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Aluminium-scandium (Al-Sc) alloy is subjected to shear deformation at high strain rates ranging from 3:0 Â 10 5 s À1 to 6:2 Â 10 5 s À1 using a compressive-type split-Hopkinson pressure bar (SHPB). The effects of the strain rate on the shear stress, adiabatic shear band characteristics, and fracture features of the Al-Sc alloy are systematically examined. The results show that both the shear stress and the strain rate sensitivity increase with an increasing strain rate. In addition, it is shown that an adiabatic shear band is formed within the deformed specimens for all values of the strain rate. As the strain rate is increased, the width of the shear band decreases, but the microhardness increases. Moreover, the distortion angle and the magnitude of the local shear strain near the shear band both increase with an increasing strain rate. At a strain rate of 3:0 Â 10 5 s À1 , the fracture surface is characterised by multiple transgranular clearage fractures. However, for strain rates greater than 4:4 Â 10 5 s À1 , the fracture surface has a transgranular dimple-like characteristic, and thus it is inferred that the ductility of the Al-Sc alloy improves with an increasing strain rate.

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“…In Refs [196,197], the experiments on steels with different microstructures indicate that for the same strain rates, different microstructures in the same kind of alloy will lead to different degrees of susceptibility to ASBs. It was explained that the presence of defects like second-phase particles, precipitates or other inhomogeneity in the microstructure of metallic materials can increase their susceptibility to strain localization and formation of ASBs.…”

Section: Adiabatic Shear Bandmentioning

confidence: 99%

“…Materials may crack at the site of shear bands with low ductility once the shear bands forms [179][180][181][182][183]. During high strain rate deformations, the heat generated by plastic deformation fails to dissipate thus the elevated temperature will contribute to outweigh thermal softening effects over that of strain and strain rate hardening, which leads to the initiation of shear localization.…”

Section: Adiabatic Shear Bandmentioning

confidence: 99%

“…Aside from strain, strain rate and temperature, the initial microstructure of the materials under impact also have great influence on the formation of ASBs. Lee et al [129] found that "the nucleation and formation of the shearHongyi Zhan 38 The University of Queensland band were influenced significantly by the initial microstructure and hardness of the matrix material".In Refs [196,197], the experiments on steels with different microstructures indicate that for the same strain rates, different microstructures in the same kind of alloy will lead to different degrees of susceptibility to ASBs. It was explained that the presence of defects like second-phase particles, precipitates or other inhomogeneity in the microstructure of metallic materials can increase their susceptibility to strain localization and formation of ASBs.…”

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confidence: 99%

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The dynamic response of β titanium alloys to high strain rates at room and elevated temperatures

Zhan¹

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Titanium and its alloys fulfil a wide range of applications involving aerospace, biomedical, chemical and petroleum industries due to their extraordinary properties such as high specific strength, excellent biocompatibility and corrosion resistance. Among different types of titanium alloys, β titanium alloys have a unique range of properties such as an excellent combination of high strength and fracture toughness and low Young's modulus. Therefore, the usage of β titanium alloys in the manufacturing of some key components in aerospace and biomedical industries has continually increased in the past decade.Nowadays many commercial manufacturing processes for metallic materials such as machining, explosive welding, hot forging and extrusion employ high strain rates and are conducted at elevated temperatures. Also, high-strain-rate deformation can be encountered in collisions such as in car crashes, bird strikes on airplanes and micrometeorite impacts on space structures. Hence a large number of studies have been conducted on the dynamic response of metallic materials including copper, steels, tantalum, Ti-6Al-4V alloy and commercially pure titanium to high strain rates. Due to limited knowledge of the dynamic behaviour of β titanium alloys, this thesis mainly investigates the stress-strain behaviour and microstructural evolution of β titanium alloys under high strain rates at room and elevated temperatures.Split Hopkinson Pressure Bar compressive tests were carried out on two new types of β titanium alloys with different levels of β phase stability, the Ti-6Cr-5Mo-5V-4Al (wt. %) and Ti-25Nb-3Zr-3Mo-2Sn (wt.%) alloys, at strain rates ranging from 10 -3 s -1 to 10 4 s -1 and temperatures ranging from 293K to 1173K. The Ti-6Cr-5Mo-5V-4Al alloy, with relatively high β phase stability, represents an alloy type which can be engineered through heat treatment or thermo-mechanical processing to achieve a superior combination of strength and fracture toughness. While the Ti-25Nb-3Zr-3Mo-2Sn alloy with relatively low β phase stability represents an alloy type which can be applied in biomedical applications due to their low Young's modulus and superelastic properties.For the Ti-6Cr-5Mo-5V-4Al alloy, dislocation slip is dominant at all testing strain rates and temperatures in this research. The flow stress increases with increasing strain rate but decreasing temperature. Also, it is more sensitive to temperature than strain rate. At ambient temperatures, the strain hardening rate exhibited by the Ti-6Cr-5Mo-5V-4Al alloy at high strain rates is much lower than that at quasi-static strain rates, which is attributed to the thermal softening effect brought byHongyi Zhan II The University of Queensland adiabatic heating. While for the Ti-25Nb-3Zr-3Mo-2Sn alloy, multiple deformation mechanisms including dislocation slip, {332} <113> and {112} <111> mechanical twinning, stress-induced martensitic α" and ω phase transformations can be activated simultaneously and among them {332} <113> twinning is dominant at 293K regardless of...

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Effect of high strain rate on plastic deformation of a low alloy steel subjected to ballistic impact

Cited by 91 publications

References 29 publications

Characterization of Internal Voids and Cracks in Cold Heading of Dual Phase Steel

Characterization of Internal Voids and Cracks in Cold Heading of Dual Phase Steel

Adiabatic Shearing Localisation in High Strain Rate Deformation of Al-Sc Alloy

The dynamic response of β titanium alloys to high strain rates at room and elevated temperatures

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