ANALYSIS OF STRENGTH DATA USING 2-PARAMETER AND 3-PARAMETER WEIBULL MODELS

The strength of ceramic components is adequately described using the W eibull distribution. Values of Weibull modulus and characteristic stre ngth were obtained for two-and three-parameter models for chemically t oughened glass and phosphate-bonded investment. The data for glass con sisted of strength measurements from fifty specimens loaded in a simil ar way to operation. The data for phosphate-bonded investment was obta ined by measuring four-point bend strength of fifty specimens at room temperature. All values of strength were plotted on modified Weibull p robability scales on the x-axis against median ranks on the y-axis. Th e Weibull modulus for the two-parameter model was determined from the slope of the best fit straight line through the data. For the three-pa rameter model a correction was made to the ''curve'' of the two-parame ter model by determining the probable value of the lower bound of stre ngth. Ranks were also used to establish tolerance limits for design st rengths. The values of Weibull modulus obtained from the two-parameter and three-parameter models were similar for chemically toughened glas s but different for phosphate-bonded investment. The three-parameter W eibull distribution was found to give a more reliable estimate of the Weibull modulus for phosphate-bonded investment. (C) 1998 Chapman & Ha ll.