Consider a compact specimen that is loaded cyclically at a constant load amplitude with Pmax = 18 kN and Pmin = 5 kN. Using the fatigue crack growth data in Problem 5.1, calculate the number of cycles required to grow the crack from a/W = 0.35 to a/W = 0.60. Plot crack size vs. cumulative cycles for this range of a/W.

On solidification from a melt, the polymer polyethylene forms a semi-crystalline spherulite structure. (i) sketch an individual spherulite and label the amorphous and crystalline regions. (ii) draw a schematic to show the changes in specific volume with temperature during cooling from the melt, comparing it to the theoretical extremes of fully crystalline and fully amorphous (indicate tm and tg)