Analysis of strength data using two- and three-parameter Weibull models

The strength of ceramic components is adequately described using the Weibull distribution. Values of Weibull modulus and characteristic strength were obtained for two- and three-parameter models for chemically toughened glass and phosphate-bonded investment. The data for glass consisted of strength measurements from fifty specimens loaded in a similar way to operation. The data for phosphate-bonded investment was obtained by measuring four-point bend strength of fifty specimens at room temperature. All values of strength were plotted on modified Weibull probability scales on the x-axis against median ranks on the y-axis. The Weibull modulus for the two-parameter model was determined from the slope of the best fit straight line through the data. For the three-parameter model a correction was made to the “curve” of the two-parameter model by determining the probable value of the lower bound of strength. Ranks were also used to establish tolerance limits for design strengths.