Fracture of aluminium reinforced with densely packed ceramic particles: link between the local and the total work of fracture

Abstract

Model composites of pure Al reinforced with 50% ceramic particles are produced by infiltration. The composite fracture energy is measured by J -integral testing. Marked R-curve behaviour is found. The J-R curves exhibit a break in their slope at a well-defined point. This point is shown to denote the onset of macroscopic crack propagation and is used to assess the composite toughness.Toughness reaches values as high as 40 MPa ffiffiffiffi m p . Quantitative metallography and stereoscopic reconstructions of fracture surfaces are used to estimate the local work of fracture in the process zone. The measured (total) fracture energy is about ten times the estimated local fracture energy, for all composites. The main contribution to their total fracture energy is thus from plastic dissipation around the crack-tip; however, the toughness is still dictated by the local fracture energy. This study hence experimentally substantiates the ''valve'' concept in fracture mechanics.

Fracture of aluminium reinforced with densely packed ceramic particles: influence of matrix hardening

“…A few composites were additionally tested by Jintegral testing, according to ASTM E-1737, as in [15] using the same pre-cracking procedure (described in [33]). J-R curves were measured with the single-specimen method, using the compliance method to compute the crack length.…”

“…J-R curves were measured with the single-specimen method, using the compliance method to compute the crack length. The critical fracture parameter was taken at the initiation of ductile tearing according to the method described in [15].…”

“…It was reported in a previous paper on the fracture of pure Al reinforced with densely packed alumina particles [15] that such composites can actually be made quite tough, with fracture toughness values as high as 40 MPa p m despite the high ceramic loadings. By varying systematically the particle size as well as its type, a direct and linear correlation was found between the local work of fracture spent in creating the fracture surface, 2c pz and the macroscopic fracture energy at the initiation of ductile tearing, J c .…”

“…Two compositions, namely Al-2wt%Cu and Al-4.5wt%Cu, were selected; these are within the solubility limit of Cu in Al near the eutectic [28]. The fracture characteristics of these Al-Cu matrix composites can thus be directly compared with those of pure Al matrix composites of [15]: they all exhibit a similar microstructure made of stiff ceramic particles embedded within a single-phase, ductile matrix.…”

Increasing the Strength/Toughness Combination of High Volume Fraction Particulate Metal Matrix Composites using an Al‐Ag Matrix Alloy

“…The elevated toughness of these composites is achieved by meeting certain critical microstructural conditions, defined and explained in. [1][2][3][4] To summarize, these include: (i) the initial (high) quality of the stiff ceramic particles used, which must be free of stress concentration sites and internal defects, (ii) the presence of a ductile matrix free of brittle second phases, (iii) a capacity for composite bulk plastic deformation, made possible in spite of the high ceramic loadings by the fact that only the metal is continuous in their microstructure. These characteristics combined produce, in the composite, a local fracture cohesive law, [5,6] that features both (i) an elevated peak stress and (ii) a high local fracture energy.…”