MATERIALS SCIENCE & ENGINEERING A ELSEVIER Materials Science and Engineering A232 (1997) l-10 High strain-rate compression testing of a short-fiber reinforced aluminum composite M. Guden, I.W. Hall * Mechanical Engineering and Materials Science Program, University of Delaware, Newark, DE 19716, USA Received 22 August 1996; received in revised form 3 December 1996 Abstract Compression behavior of 15-267/$/o Saffilr” short-fiber reinforced Al- l.l’iwt.%Cu alloy metal matrix composites has been determined over a strain-rate range of approximately lop4 to 2 x lo3 s- I. The strain-rate sensitivity of composite samples at 4% strain, tested parallel and normal to the plane of reinforcement,was found to be higher than that of unreinforced alloy in the strain-rate range studied. Quantitative analysis of fiber fragment lengths from samples tested to different strain levels showed that, at smallstrains,high strain-rate testing induced a relatively shorter fiber fragment length distribution in the composite compared to quasi-static testing.At quasi-static strain rates,the fiber strengthening effect wasfound to increase with increasing V?h and was higher in samples tested parallel to the planar random array. The observed anisotropy of the composite at quasi-static strain rates was also observed to continue into the high strain-rate regime. Microscopic observations on composite samples tested quasi-statically and dynamically to a range of strainsshowed that the major damage process involved during compression testing was fiber breakage followed by the microcracking of the matrix at relatively large strains. Fiber breakage modes were found to be mostly shearing and buckling. 0 1997Elsevier Science S.A. Keywords: Compression testing; Metal matrix composites; Strain-rate sensitivity 1. Introduction Metal matrix composites (MMCs) are f%rding steadily more applications in the aerospace, automobile and defense industries. In many of these applications, high strain-rate loading may occur, for example, in the sudden impact of foreign objects on aircraft turbine blades or collisions of cars. Therefore, the high strain- rate mechanical response of MMCs is important in present and future applications in these industries. Knowledge of the quasi-static response of MMCs is needed and constitutes the basic material parameter database for designing with MMCs for structural appli- cations at present. Parameters such as yield strength and modulus are well known and have been studied widely at quasi-static strain rates. The associated frac- ture mechanisms in MMCs at these rates are also well determined. However, few studies have been conducted on the high strain-rate response of MMCs and most of * Corresponding author. Tel.: + 1 302 S312062; fax: + 1 302 8314545; e-m& haU@me.udel.edu. 0921-5093/97/S17.00 Q 1997 Elsevier Science S.A. All rights reserved. PII SO921-5093(96)10880-7 these have concentrated on particulate and whisker reinforced composites. The main aim of the present study has been to determine the possible rate sensitivity of a short-fiber MMCs properties as compared with the unreinforced alloy. Harding and Taya [l] carried out tensile testing on Sic whisker (SIC,) reinforced 2124 aluminum alloy over the strain-rate range from 10m3 to 1.5 x lo3 s-l and observed that the yield stress, Young’s modulus and fracture strain of the composite increased with the strain rate. Vaziri et al. [2] performed compression tests on SIC and Al,O, particle reinforced 6061 alloys and found a higher strain-rate sensitivity of the flow stress for the composite when compared with the monolithic alloy. Yadav et al. [3] observed the same effect for Al,O, particulate reinforced 6061 alloy and suggested that the higher rate sensitivity of the composite is due to the imposed strain rate rather than the changing of the internal structure. In the examples given above, no significant fracture of the remforcement is expected during quasi-static or dynamic loading due to its low aspect ratio. However,