Polymer composites and adhesives have been utilized in the field of the automobile and the aircraft where the light-weight structures are required. Cyclic loads are applied for long time on the structural components. As fatigue strength is much lower than static strength and the fracture mechanisms under cyclic loading are totally different from that under monotonic loading, the evaluation of fatigue properties is indispensable as well as static properties. Fatigue crack growth resistance is also important factor on the basis of damage tolerance design because crack growth is main mechanism of the fatigue fracture. In this paper, the bending fatigue properties of carbon fiber reinforced acrylic composites, the fatigue crack propagation resistance of the epoxy resin modified with carbon nanotubes or core-shell rubber particles and fatigue adhesion properties of epoxy adhesive with sacrifice particles were reviewed.

Thermosets with excellent heat resistance are produced by the thiol-ene reaction of maleimide copolymers containing an unsaturated group in the side chain using a polyfunctional thiol cross-linking agent. In this study, several maleimide copolymers containing unsaturated groups in the side chain were synthesized by radical copolymerization of N-n-butylmaleimide with allyl methacrylate and vinyl methacrylate. In addition, a part of the methyl esters of copolymers of N-phenylmaleimide or N-n-butylmaleimide and methyl acrylate was converted to the allyl esters by transesterification. These maleimide copolymers containing unsaturated groups were heated in the presence of random silsesquioxane（SQ）modified with mercapto groups and triallyl isocyanurate（TAIC）in order to fabricate thermosets. The reactions of the unsaturated groups and the mercapto group were followed by IR spectroscopy, and the relationship between the repeating structure of the maleimide copolymer and the cross-linking formation was clarified. Thermogravimetric analysis was performed for the precursor polymers and their thermosets in order to determine thermal decomposition temperatures and residual weights at a high temperature. Based on the results of transmittance measurements, tensile tests, and dynamic mechanical analysis of the thermosets, the effects of repeating structures and cross-linking structures on optical and mechanical properties were clarified. It was found that the thermosets obtained by thiol-ene reaction of N-n-butylmaleimide/acrylate copolymer with allyl groups have the most excellent thermal stability, transparency, and mechanical properties.

The effect of heating time on the indentation hardness, composite modulus, and adhesive strength of one-component moisture-curing cyanoacrylate adhesives was investigated experimentally. As a result, it is revealed that the heat treatments after curing decreased the hardness of the adhesives and increased their ductility. Moreover, the effect of the reheated time on the adhesive strength was investigated using a cylindrical butt joint under the combined stress after the adhesive cured. As a result, it was proved that the tensile strength was higher than the shear strength before heating and that the tensile strength, shear strength and combined strength increased after heating. It was also proved that the tensile strength and the shear strength became almost equivalent after heating. The above experiment suggested that the brittle fracture dominated the fracture surface before heating and that both the brittle fracture and the ductile fracture occurred after heating. It was clarified that the heat treatment increased the adhesive strength even though the heat treatment reduced the hardness of the adhesives and the composite elastic modulus. FTIR analysis revealed that the methyl group contained in the adhesive decreased after the heat treatment, which presumed that the methyl group was one of the factors that affected adhesive strength.