Strength parameters of some brittle dental materials : Weibull statistics
There are many factors affecting the mechanical strength of a material. The effects of specimen size and strain rate (crosshead speed of testing) on the compressive, diametral tensile and flexural strengths some of the brittle dental materials are the main factors investigated in this study. The study was composed of two parts. The first part was to study the effect of specimen size and strain rate (crosshead speed of testing) on the compressive, diametral tensile and flexural strengths of a material tested. Weibull and Normal statistics were used to analyse the data. The analysis showed that specimen size and strain rate (crosshead speed of testing) affect the strength of a brittle materials. The optimum specimen size and crosshead speed of testing were determined for the compressive, diametral tensile and flexural tests. These specimen size and crosshead speed of testing are the 'test parameters'. The analysis also showed that the Weibull statistics was more adaptable method used in assessing the strength of a brittle materials. Therefore the value of Weibull modulus, characteristic strength and a stress at an arbitrary failure probability of 0.01 percent are the 'strength parameters' concluded from the analysis. In addition the relationship between Weibull modulus and deviation coefficient(%) and the relationship between deviation coefficient(%), mean strength and characteristic strength were established from the results of this investigation. A good correlation coefficient were obtained for these relationships. In the second parts of the study, 'strength parameters' some of brittle dental materials were determined by using the I test parameters If ound in the first -part' of the study. In addition the relationships found -in''the 'first part of the study were used, as -a model to estimate the 'strength parameter', from a-mean strength and and standard deviation of a small sample (a sample of 5 specimens). The results of this study showed --that a stress' at an arbitrary failure probability of 0.01 percent for' the small sample was not significantly varied from the stress at the same arbitrary failure probability of the large sample size.