Determination of Threshold Stress Intensity for Crack Growth at High Temperature in Silicon Carbide Ceramics |
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Authors: | ERIC J MINFORD RICHARD E TRESSLER |
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Affiliation: | Department of Materials Science and Engineering, The Pennsylvania State University, University Park, Pennsylvania 16802 |
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Abstract: | A method for estimating the threshold stress intensity for crack growth is presented. The technique requires prior knowledge of the flaw population of a material and uses applied static loads followed by fast fracture to assess the effect of initial applied stress intensity on flaw behavior. The technique was applied to a hot-pressed Sic at 1200° and 1400°C in a nonoxidizing atmosphere. At 1400°C with a static load time of 4 h, the threshold stress intensity was determined to be ∼ 1.75 MPa·m1/2 with a slight tendency toward higher fracture stress with increasing initial stress intensity below the threshold. At 1200°C for a static load time of 4 h, apparent strengthening was observed below a threshold stress intensity of ∼2.25 MPa·m1/2. This strengthening effect appears to result from stress relaxation in the crack-tip region, probably by plastic deformation which involves the oxide grain-boundary phase. |
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