The effects of superimposed hydrostatic pressure on deformation and fracture: Part II. Particulate-reinforced 6061 compo
- PDF / 1,963,096 Bytes
- 7 Pages / 597.28 x 785 pts Page_size
- 27 Downloads / 238 Views
I.
INTRODUCTION
T H E fracture behavior o f many particulate-reinforced composites may be considered "quasi-brittle." It is typically observed that the ductility in such systems is l o w e r than that o f the monolithic matrix, while examination o f fracture surfaces reveals a combination o f brittle features (e.g., fractured reinforcement) and ductile fracture (e.g., matrix failure between reinforcement), t',2,3J The m e c h a nisms o f strengthening and o f microscopic damage and failure in metal-matrix composites are issues o f academic and practical importance. Many different m e c h anisms have been proposed as affecting the strength o f the composite. These mechanisms include: (1) load transfer between the matrix and reinforcement, ~45,~ (2) enhanced dislocation density in the matrix,tSl (3) matrix and interfacial precipitation, tl,6-8~ (4) overall strengthening directly attributable to the strengths o f the individual components o f the composite by the mixture theories,t9~ (5) strengthening arising from constrained plastic flow and triaxiality in the ductile matrix due to the presence o f brittle reinforcements, ts'l°] (6) residual stresses generated during cooling from the processing temperature as a result o f thermal contraction mismatch between the components, tH,12,~31 and (7) barrier strengthening models where the reinforcements act as barriers to dislocation movement, t14,~5~ In addition to the wide range o f viewpoints currently available on the strength o f metal-matrix composites, a variety o f microscopic failure mechanisms have also been reported in the literature, including D.S. LIU, Graduate Student, and J.J. LEWANDOWSKI, Associate Professor, are w i t h the Department o f Materials Science and Engineering, Case Western Reserve University, Cleveland, OH 44106. This article is based o n a presentation made in the symposium °'QuasiBrittle Fracture" presented during the TMS fall meeting, Cincinnati, OH, October 2 1 - 2 4 , 1991, under the auspices of the TMS Mechanical Metallurgy C o m m i t t e e and the A S M / M S D F l o w and Fracture Committee. METALLURGICAL TRANSACTIONS A
(1) ductile failure in the matrix o f the composite due to the nucleation, growth, and coalescence o f v o i d s , [16A7! (2) void formation at the reinforcement-matrix interface w h i c h leads to the debonding o f the reinforcement from the matrix and possible w h i s k e r pullout during tensile loading,Its.19,20] (3) ductile failure in the matrix o f the composite in regions adjacent to the reinforcement, tl'7,21-23J and (4) fracture o f the reinforcement, followed by fracture o f the matrix. [1,7,21 231 The propensity for quasi-brittle fracture in metal-matrix composites is closely associated with its yielding and flow characteristics. Although studies on the yielding and flow mechanisms at ambient temperature are necessary to understand the basic parameters which control quasi-brittle fracture, the plastic behavior in these materials at room temperature is limited because o f their relatively low ductility. The e
Data Loading...
