Ahigh-strength pressure vessel steel (hy130) has a yield strength (y. s.) of 1,460 mpa and a kic of 98 mpa m1/2. calculate the size of a surface crack that will lead to catastrophic failure at an applied stress of
(a) 1/2 y. s. and
(b) 2/3 y. s. (y = 1) (see example 8.2)

The force acting on a beam was measured under the same operating conditions and a sample of 5 data points was collected. this process was repeated by 3 observers. the pooled standard deviations of these 3 data sets was 1.21. determine the true mean force using all pooled data (with a 95% probability). the result should look like this: true mean = mean +/- margin of error