Abstract
It has been accepted not only that effective proof testing of ceramic materials demands rapid loading and unloading to prevent strength degradation but also that especially rapid unloading results in a truncation strength of σp (the stress just before very rapid unloading). Such an accepted interpretation in proof testings as above has been rechecked from an analytical point of view. The analysis reveals that as the loading and unloading rates increase, weaker samples tend to survive more easily. As a consequence. the truncated strength is not characterized analytically, and the Weibull curve will not have asymptote. The present analytical results come to the conclusion that the established theory in proof testing can not be accepted from the physical point of view.