Material defects critical factors

It s time to pause a moment and see where we are. First, all materials are weaker than they could be because of cracks, defects in the crystalline lattice, and so on. This is something that some materials scientists like to tackle by making more perfectly ordered materials. Even so, it is not necessarily the measured tensile strength that is the most critical factor in choosing a material for a structural application, but its work of fracture, its resistance to the growth of cracks. This property also plays into impact strength. When you hit a ceramic vase with a hammer... 

If the material has a critical stress intensity factor of 1.8 MN m and it is known that the moulding process produces defects 40 m long, estimate the maximum repeated tensile stress which could be applied to this material for at least 10 cycles without causing fatigue failure. 

A very wide sheet of grp which is known to contain intrinsic defects 1 mm long, is subjected to a fluctuating stress which varies from 0 to 80 MN/m. How many cycles would the sheet be expected to withstand if it is made from (a) chopped strand mat (CSM) and (b) woven roving (WR) reinforcement. The crack growth parameters C and n, and the critical stress intensity factors, Kc, for these materials are... 

Structure identification problems in polymer science generally entail identification of chain ends, main-chain repeat units and their sequences, and chain defects. All these factors influence the pearance of the polymer s NMR spectra, and are critical in determining the material s final physical and mechanical properties. 

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