The effect of fiber orientation on matrix plasticity and fracture behavior of SiC fiber-reinforced titanium matrix compo
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The effect of fiber orientation on the matrix plasticity and fracture behavior of SCS-6 fiber-reinforced Ti-15V-3Al-3Cr-3Sn composites was studied. The laminates used in this study were [0] 6 , [0/±45] s , and [90/+45] s . Three-point bending tests were conducted on chevron-notched specimens to determine the crack initiation energy, fracture toughness, and fracture strength as a function of notch length. The critical energy release rate was determined from the slope of the crack initiation energy versus notch length curve. The damage evolution and development of the matrix plastic deformation zone at the notch tip during the crack initiation and propagation as a function of fiber orientation were also determined. The relationships among the crack-tip matrix plastic deformation zone size, the critical energy release rate, and notch strength of the composites were discussed.
I. INTRODUCTION Titanium matrix composites reinforced with continuous ceramic fibers are promising materials for high temperature structural applications due to their excellent high temperature specific properties. However, because of their inhomogeneity and anisotropic nature, the initiation and propagation of microscopic damage which leads to the failure of the composites are different from that seen in conventional isotropic materials. Recently, the damage evolution at the crack-tip of several notched unidirectional SCS-6/Ti alloy matrix composites under static and dynamic loading has been characterized.1"3 The results indicate that the crack initiation and propagation mechanisms are strongly dependent on the fiber strength, interfacial shear strength, and matrix toughness. Crack splitting, interfacial debonding, matrix plastic deformation and/or cracking, and multiple fiber breakage are the major mechanisms at the crack-tip damage zone. The results also indicate that the critical crack initiation energy was dependent on the fiber strength and matrix yield strength. However, quantitative relationships among these damage mechanisms, energy absorbing capability, and notch strength of the composite have not yet been fully established. Angle-ply laminates are developed primarily for use in multiaxial loading conditions such as hypersonic airframes. In an angle-ply composite, the fiber orientation and lay-up sequence are additional factors that affect the fracture behavior and damage mechanisms. When a notched angle-ply composite is under mechanical loading, the stress distribution and microstructural damage in each layer differ depending on the specific fiber orientation. As a result, the fracture behavior of the J. Mater. Res., Vol. 9, No. 7, Jul 1994
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notched angle-ply composite would be more complicated than that in a unidirectional composite. It is essential to gain a thorough understanding of the fracture modes and energy absorbing mechanisms of metal matrix composites before they can be safely implemented into structural components. In this paper, the effect of the fiber orientation on
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