The Fracture Characteristics of a Near Eutectic Al-Si Based Alloy Under Compression
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THE Al-Si based cast alloys are extensively used for structural components in automotive applications because of their good castability, high strengthto-weight ratio, and wear resistance.[1–3] These components experience wide ranges of stress (strain), strain-rate, and temperature during service. Therefore, it is necessary to understand the effects of strain rate, temperature, and strain on the damage evolution of this alloy. The microstructure of a hypoeutectic Al-Si cast alloy consists of a-Al dendrite cells, eutectic (consisting of a-Al and Si particles), various intermetallic particles, and microporosity. The interplay between the composition, solidification conditions, and heat treatment of the alloy dictates the final microstructure. The mechanical properties of the alloy are influenced by dendrite arm spacing, morphology, size, and volume fraction of the eutectic Si particles,[4–7] intermetallic phases, and the precipitates formed during heat treatment. An important aspect of damage evolution in these alloys is particle fracture and debonding of Si particles.[8–10] The particle fracture occurs when the local stress exceeds its strength, whereas particle debonding SUDHA JOSEPH, Research Scholar, and S. KUMAR, Professor, are with the Department of Materials Engineering, Indian Institute of Science, Bangalore 560012, India. ASIM TEWARI, Associate Professor, is with the Department of Mechanical Engineering, IIT Bombay, Powai, Mumbai 400076, India. Contact e-mail: [email protected] Manuscript submitted April 7, 2011. Article published online December 19, 2012 2358—VOLUME 44A, MAY 2013
occurs when the stress incompatibilities between elastically strained brittle particles and a plastically deformed matrix reaches a critical value. The critical stress level developed at particle/matrix interfaces responsible for particle fracture has been studied by various analytical and numerical models. A dispersion hardening model[11,12] was used by Caceres et al. to calculate the stresses in the particles[13,14], and a dislocation pileup mechanism was used to explain the particle cracking event.[9] A fiber loading model along with the weakest link model is used by Wallin et al. to explain particle fracture.[15] A void nucleation and growth model[16–18] was used to explain the damage nucleation and damage rates. A dislocation-based constitutive model for the matrix and a load transfer model for describing the stresses in the particles were used to explain the work hardening behavior of the Al-Si alloy.[19] The same model was used to predict the damage evolution rate of the alloy. Fracturing of Si particles, formation, and growth of voids around Si particles and subsequent interlinkage of voids leads to crack propagation.[20,21] The microstructural effect on eutectic Si particle cracking has been studied by many authors.[13,14,22–26] The dependence of strain hardening rate on the sizes and shapes of the Si particles, dendrite arm spacing, and Mg content has been studied by Wang and Caceres.[27] It was also reported that t
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