Effect of microstructure on the nucleation and initiation of adiabatic shear bands (ASBs) during impact

Yiadom, Solomon Boakye; Khan, Abdul Khaliq; Bassim, Nabil

doi:10.1016/j.msea.2014.07.095

Cited by 32 publications

(15 citation statements)

References 28 publications

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“…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. Similar studies conducted by Boakye et al [198] also confirms that "the initiation of ASBs in AISI 4340 steel during impact occurs when the microstructure is highly inhomogeneous". In the past thirty years, many studies have been conducted on the microstructure of adiabatic shear bands in different metals and alloys.…”

Section: Adiabatic Shear Bandsupporting

confidence: 82%

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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Section: Adiabatic Shear Bandsupporting

confidence: 82%

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

Zhan¹

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“…It is inferred that a prior heat treatment on the Algotuf steel could increase its strength and impact resistance because of carbide precipitation. It has been reported that the prior deformation microstructure has a lot of effect on the dynamic properties and susceptibility of structural steels to shear strain localization during deformation at high strain rates and large strains [3,4]. Thus, structural steels can be heat treated to produce a strong microstructure that is resistant to strain localization during deformation at high strain rates [4].…”

Section: Discussionmentioning

confidence: 99%

“…Deformation of materials at quasi-static or intermediate strain rates is characterized by slip and twinning mechanisms [1,2]. However, at high strain rates such as impact, explosive forming, and ballistics, plastic deformation is characterized by strain localization along narrow bands [3,4]. This results in crack nucleation and propagation and subsequent fracture and fragmentation.…”

Section: Introductionmentioning

confidence: 99%

Characterization of the dynamic behaviour of ALGOTUF armour steel during impact and in torsion

Bassim

Boakye‐Yiadom

Toussaint

et al. 2015

EPJ Web of Conferences

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Abstract. Algotuf is a new steel which is proposed as a candidate for armour material. To assess this application, a study of the impact properties of this steel was conducted at the University of Manitoba using two types of Hopkinson Bar systems, namely a torsional bar equipment and a direct impact system capable of producing high strain rates and large strains. Stress strain curves for the steels were obtained in pure shear and in compression. Temperatures of 25 • C, 200 • C and 500 • C were used in the testing. Following the testing, a microstructural examination of the specimens tested was carried out to investigate the effect of microstructure on the mechanism of failure of this material. It was found that, above a value of impact momentum corresponding to a high strain rate, adiabatic shear bands are formed. The microscopic examination showed that the initiation of these shear bands corresponded at locations where martensitic laths were present and around regions of maximum shear stresses. Generally, the shear bands act as precursors to the formation of microcracks that may lead to failure. On the other hand, the high strength and formability of the steel makes it suitable for use as an armour material.

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“…The machined specimens were impacted at high strain rates and large strains using the Direct Impact Hopkinson Pressure Bar (DIHPB) at different projectile velocities resulting in several impact momentums. During the impact, an AISI 4340 steel projectile (18.67 N, 38 mm diameter by 127 mm length) with a hardness of 47HRC is fired by a gas gun, and strikes the specimen attached to a transmitter bar at a high impact velocity [4,5].…”

Section: Methodsmentioning

confidence: 99%

“…1. The predominant platelet carbides were aligned on the lath boundaries (interlath carbides) and within the laths the tempered steel specimens have been published in references [4,5]. Figure 2 shows the trajectory of an evolved ASB in a single steel specimen impacted at 51 kg · m/s.…”

Section: Microstructural Evolution Of Shear Bands In Steel During Impactmentioning

confidence: 99%

Mechanism of grain refinement and its effect on Adiabatic Shear Bands in 4340 steel and pure copper during impact

Bassim

Boakye‐Yiadom

2015

EPJ Web of Conferences

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Abstract. Pre-deformation and post-deformation microstructure characterization was conducted on tempered 4340 steel and commercial pure copper specimens under impact to determine the microstructural changes and the mechanism of grain refinement that occur during the evolution of ASBs. It was observed that the movement and multiplication of dislocations, elongation of grains, breaking of elongated grains, rotation, carbide fragmentation and boundary refinement of broken grains occur simultaneously during the evolution of ASBs in the impacted 4340 steel specimens. The extent of these mechanisms depends on the imposed local strain and strain rate. Extensive grain refinement coupled with high density of dislocations results in the shear band structures being more susceptible to crack nucleation and propagation. In copper, it was observed that sequential occurrence of emergence of dislocations, dislocation cell formations with varying cell boundaries and cell interiors, dynamic recovery and extensive micro-twinning results in the formation of the shear bands. The structure within the evolved shear bands becomes less brittle after the onset of dynamic recovery and micro-twinning. The differences in the mechanism of grain refinement and evolution of the shear bands in both materials is attributed to the differences in the mobility of dislocations, the rate of strain hardening and strain hardening exponents in both materials studied.

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Effect of microstructure on the nucleation and initiation of adiabatic shear bands (ASBs) during impact

Cited by 32 publications

References 28 publications

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

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

Characterization of the dynamic behaviour of ALGOTUF armour steel during impact and in torsion

Mechanism of grain refinement and its effect on Adiabatic Shear Bands in 4340 steel and pure copper during impact

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