Predictions of High Strain Rate Failure Modes in Layered Aluminum Composites
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TRODUCTION
LAYERED or laminated metallic composites can be designed for desired thermo-mechanical behavior, and failure tolerance and mitigation, such that composite behavior can be potentially superior to that of any single constituent. Ultrathin laminates produced by the deposition technique can have high tensile strengths at low temperature.[1] Roll-bonded laminates can also have desirable ductility, impact, corrosion, and wear.[2] Most investigations pertaining to aluminum alloy layered composites, however, are based on low and moderate strain rate studies such as the three-point bend test[3,4] and the Charpy impact test.[3–6] There have been experimental[7,8] and modeling[8,9] investigations that have focused on the dynamic behavior of layered metallic composites; however, most of these investigations have focused on phenomenological aspects. Aluminum alloys can have high strength and they are particularly useful for lightweight application such as aerospace, armor, and automotive applications. The 2xxx and 7xxx series Al-alloys are known to have higher strength than other series alloys. However, 7xxx series alloys are more susceptible to stress corrosion cracking.[10] Hence, 2xxx series Al-alloys are more desirable for high strength applications. Moreover, 2139 aluminum alloy has very high ductility and toughness, which have been shown to be applicable for damage-tolerant systems.[11,12] The 2195 aluminum alloy has significantly PRASENJIT KHANIKAR, Graduate Research Assistant, and M.A. ZIKRY, Professor, are with the Department of Mechanical and Aerospace Engineering, North Carolina State University, Raleigh, NC 27695-7910. Contact e-mail: [email protected] Manuscript submitted April 5, 2013. Article published online October 31, 2013 60—VOLUME 45A, JANUARY 2014
higher strength than the 2139 alloy due to the presence of lithium (Li). Both alloys have low densities and are hence well suited for high strength and lightweight applications. Hence, one of the objectives of this investigation was to determine what the optimal arrangements of 2195 alloy and 2139 alloy would be for a metallic layered composite of these aluminum alloys that would combine strength and toughness for high strain rate applications. It will be assumed that the interface is hot roll bonded, because hot roll bonding can produce higher bond shear strength than that of cold roll bonding.[13] A detailed computational study can provide insights on high strain rate behavior, which are difficult, if not impossible, to obtain experimentally. The interrelated effects of wave propagation, shear strain localization, geometrical softening and thermal softening, and dislocation density evolution on microstructural features, such as grain boundaries (GBs), dispersed particles, and precipitates, are investigated. A dislocation density crystalline plasticity finite strain formulation has been used to investigate the variation of layer thicknesses and the effects of dispersed particles, precipitates, and interfaces, such as GBs and bonded surfaces, on failures modes,
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