Epoxy network Fatigue

Figure 13.11 Paris diagrams for fatigue crack propagation of polyldimethyl-siloxane)-modified epoxy networks. (Rey et a/., 1999 with kind permission from Kluwer Academic Publisher.)... 

Fig. 21 In situ visualization pictures showing damage a in a fretting contact between an unmodified DGEBA/DDM epoxy network and a glass sphere, and b in a similar contact with a DGEBA/DDM network modified with the acetamide derivative shown in Table 1. The magnitude of the maximum tensile stress at the edge of the contact was found to be similar in both cases. Contact fatigue cracks were only observed in the neat DGEBA/DDM system...

The degradation of the matrix in a moist environment strongly dominates the material response properties under temperature, humidity, and stress fatigue tests. The intrinsic moisture sensitivity of the epoxy matrices arises directly from the resin chemical structure, such as the presence of hydrophilic polar and hydrogen grouping, as well as from microscopic defects of the network structure, such as heterogeneous crosslinking densities. 

Properties of the thermosetting polymers are controlled by the molecular composition and structure such as the stoichiometric ratio between the reagents, and the cross-link density of the network. Accordingly, fatigue crack propagation of an Epon 828 MDA epoxy has been examined [96] with respect to amine epoxy ratio and cross-link density. 

---