The shear response of a Nicalon-reinforced ceramic-matrix cloth plies are combined to produce the desired thickness and composite was investigated using Iosipescu tests. Damage can be laid up to form complex geometric shapes using polymer was characterized by X-ray, optical, and SEM techniques. composite techniques. The formed part is then vacuum bagged The large inelastic strains which were observed were attriband fired in an autoclave. uted to rigid body sliding of longitudinal blocks of material.The fiber cloth consists of many tows in 15 m diameter SiC These blocks are created by the development and extension filaments in an eight-harness satin weave architecture. The SiC of intralaminar cracks and ply delaminations. This research (Nicalon), NL202 grade with 11.8% oxygen content, is manreveals that the debonding and sliding characteristics of ufactured by Nippon Carbon Co. There are 8.7 tows/cm running the fiber-matrix interface control the shear strength, strain in each direction with each tow containing approximately 500 softening, and cyclic degradation of the material.filaments. The matrix slurry is created by mixing alumina particles in I. Introduction phosphoric acid. The alumina and phosphoric acid react to form aluminum phosphate (AlPO 4 ). The resulting matrix is highly A LOW-COST ceramic-matrix composite (CMC) is being devel-porous and contains particles of aluminum phosphate in both oped by McDonnell Douglas Technologies Inc. (MDTI). quartz and cristobalite forms and unreacted alumina. 8 It has potential commercial applications in jet engine exhaust For this research, MDTI supplied plates from two batches of ducts, leading edges, nose cones, and other hot moderately the CMC. The plates were made from four plies and were stressed environments. An understanding of the mechanical nominally 1.27 mm thick. A micrograph of a polished cross behavior of this material is needed to help make improvements section is shown in Fig. 1. The batches are compositionally and to design components.identical-40% fibers, 40% matrix, and 20% porosity by volResearch on CMCs has generally focused on their tensileume. Yet, tensile tests indicated a dramatic difference in the behavior. Recent investigations have defined the relationship between matrix cracking, sliding, and the tensile inelastic strains and hysteresis. 1-3 With this research, the tensile behavior is fairly well understood. More recently, investigators have begun to examine CMC behavior when shear loads are applied. [4][5][6][7] These studies indicate that many CMCs have significant inelastic shear deformations and large shear failure strains. Although the ultimate tensile strains of the constituents are less than 1%, the composite shear strains at failure exceed 2-3%. There is no clear understanding of the damage mechanisms which are responsible for this behavior. To address this issue, this research examines the shear damage mechanisms in the MDTI CMC. This paper is organized as follows. First, Iosipescu shear and push-out test results are presented. Thes...
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