. Tensile strength measurements of glass fibers yield the following results in megapascals: 3035 3106 3158 3195 3205 3275 3390 3441
Estimate the Weibull modulus and scale parameter. Estimate the median strength of the distribution. If you measured the strength of a million specimens, what is the weakest strength you expect to encounter?
. You measure the strength of many specimens (volume V) of an alumina in tension and find the average strength is 400MPa and the Weibull shape parameter is 12. For the purposes of this question, you may ignore the effects of subcritical crack growth.
a. What is the largest safe tensile stress to give a failure probability of 1 in 104 for a tension specimen of the same volume (V) as the test specimens?
b. What is the largest safe tensile stress to give a failure probability of 1 in 104 for a tension specimen with 10 times the volume of the test specimens, that is, 10V?
c. If the test specimens of volume V are proof tested to a stress of 200 MPa, what is the expected failure rate during proof testing?
d. What would the mean strength of the material be for the volume V tested in three-point bending?
Q31;
. The time to failure of an alumina specimen at room temperature in air at 40% relative humidity under 290MPa tensile stress is 42 min and at 250MPa the time to failure is 200 h.
a. What is the subcritical crack propagation parameter n?
b. What is the time to failure under 200MPa and the same conditions?
c. What is the maximum stress level to give 100 years life under constant stress under these conditions?