Damage initiation and propagation

Pneumatic stress-induced failures of elastomers are simulated in the laboratory. The samples, polydimethylsiloxane, are saturated with carbon dioxide gas at high pressure and the ambient pressure is rapidly reduced while the processes damage initiation and propagation are monitored visually. In some cases, there appears to be a relation between the failure mechanism and the diffusion of the gas from the sample to the ambient. The reasons for this effect are not clear, although some speculations are provided. 7 refs. 

In this model the Chang and Chang [87] failure criterion was used to calculate damage initiation and propagation. Chou and Ko [88] fiber imdulation model based on the unidirectional fiber tow properties was used to calculate the woven fabric properties. The dynamic response of the helmet system was almost identical in the case of carbon and glass woven fabric reinforcements. 

Thus the question arises as to what forms of haem proteins and transition metals are available in vivo that are capable of mediating the formation of damaging initiating or propagating species, since the majority of the iron and haem proteins in the human body are protected in vivo from exerting pro-oxidant activities by their compart-mentalization within their functional locations in the haem and non-haem iron-containing proteins and enzymes. 

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