The cause of the Challenger disaster was that the seals had not been tested at extremely low temperatures, so some of the seals failed. This is a problem with the step/perform tests on the prototype/testing in the engineering design process.

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)