From a large number of tests on a certain material, it has been learned that 50% of them will break when loaded in tension at stress equal to or less than 520 MPa and that 30% will break at stress equal to or less than 500 MPa. Assume that the fracture statistics follow a Weibull distribution.
A. What are the values of σ o and m in the equation Ps = exp[-(σ/σo)m ]?
B. What is the maximum permissible stress if the probability of failure is to be kept less than 0.001% (i.e., one failure in 100,000)?