Toughness moisture effects

Fig. 6.12. Toughness maps depicting contours of predicted fracture toughness (solid lines in kJ/m ) for (a) glass-epoxy composites as a function of fiber strength, Uf, and frictional shear stress, tf and (b) Kevlar-cpoxy composites as a function of at and clastic modulus of fiber, Ef. The dashed line and arrows in (a) indicate a change in dominant failure mechanisms from post-debonding friction, Rif, to interfacial debonding, Sj, and the effect of moisture on the changes of Of and Tf, respectively. Bundle debond length...

Table 9.13 summarizes the effect of the kind of reductant on the photochromic behavior of thionine dye. All reductants afforded transparent films upon irradiation and complete color recovery in the dark. The greatest photosensitivity was obtained with TEA as the reductant. The reversibility decreased in the order, tri->di->mono-ethanolamine. The difference cannot be explained by an electron-donating character such as the basicity of the reductant (P A a value of their ammonium salt tri-mono-ethanolamine). A potential explanation is that TEA(bp, 335.4°C/760mmHg) is so hygroscopic that the moisture absorbed in TEA and TEA itself acts as a plasticizer, providing tough films that afford higher color reversibility, as mentioned earlier. 

Chou 1. Effect of fiber orientation and moisture absorption on the interlaminar fracture toughness of CFRP laminates. Adv Compos Mater 1998 7 377-94. http //dx.doi.org/ 10.1163/156855198X00264. 

A further complication is the effect of moisture absorption and plasticization on the fracture toughness of the matrix [33,39]. As shown in Table 3.7, the moisture content of the resin can influence its fracture toughness as determined by Ki the critical stress intensity factor under mode I loading conditions. It is clear that the effect of moisture on the fracture toughness of the more brittle chemically resistant resins will be less, so that the chemically resistant resins will provide less protection to ESCC of the fibres, even in the presence of absorbed moisture [37,39]. 

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