Steam pressure induced in crack-like cavities in moisture saturated polymer matrix composites during rapid heating

The time history of steam pressure inside an isolated “crack-like” micro-cavity in a polymer matrix composite is studied by assuming that the chemical potential of water is continuous across the cavity/polymer interface. Steam pressure inside the cavity is due to rapid heating of moisture-saturated composites from its initial temperature to a final temperature Tf. Exact closed form solutions are obtained for a “crack-like” cavity inside an infinite and a finite plate. For the case of an infinite plate, the exact solution shows that the steam pressure approaches the saturated steam pressure psat(Tf) at a characteristic time tc≅25h2Df(Mwpsat(Tf)RTfψ0)2, where h is the cavity height, Df is the diffusivity of water at Tf, Mw is the molecular weight of water, ψ0 is the initial moisture concentration of the composite and R is the universal gas constant. When moisture is allowed to escape from the composite, such as in the case of a finite plate, the maximum steam pressure depends on a single dimensionless parameter α=LRTfψ0hMwpsat(Tf), where L is the thickness of the composite plate. For large α, the maximum steam pressure approaches psat(Tf). However, the maximum steam pressure can be significantly less than psat(Tf) when α ⩽ 4. The present model can also be used to study the 'popcorning' observed in electronic packages.