The damage evolutions under low velocity impact were investigated using epoxy composite beams reinforced by S-2 glass, basalt, and Twaron 1000 fiber (identified as GFRP, BaFRP, and AFRP, respectively). GFRP showed a mutational damage mode, while BaFRP and AFRP represented a progressive one. The damage modes, the reductions in flexural strength and modulus in the direction of the impact face and the back face were compared based on the difference in fiber properties combined with fractography. The dominant factors for damage evolution were analyzed. There existed critical impact energy for initial damage, standing for the change in damage mode and dividing the post-impact flexural properties variation into two linear parts.

The load applied on the specimen in common dynamic mechanical thermal analysis (DMTA) is of the order of several Newtons to several tens of Newtons, far lower than that in service life. In this study a dynamic mechanical thermal analyser (EPLEXOR 500, with a total load up to 500 N) was applied to investigate the effects of static load and dynamic load (sine-wave load) on the dynamic viscoelasticity of unidirectional carbon fibre reinforced epoxy resin composites. The effects of the load on the dynamic viscoelasticity of polymer matrix composites (PMCs) are expressed mainly in two ways. On the one hand, the load affects the magnitude of the dynamic viscoelastic parameters. The storage modulus increases with increasing static load and decreases with increasing dynamic load. Such variations are obviously related to the interaction between the two kinds of load. The increase in load, whether static or dynamic, can result in a decline in the loss tangent. On the other hand, there exists a frequency-temperature-load equivalence for a carbon fibre-reinforced polymer's dynamic viscoelasticity. An increase in static load raises the glass-transition temperature and pushes the frequency spectrum curve towards a low frequency, while the effects of dynamic load are the reverse.

The load dependences of dynamic viscoelasticity of casting novolac epoxy 648 and its composites, reinforced by glass fiber (GFRP) or carbon fiber (CFRP), were investigated by dynamic mechanical thermal analysis under high loads. The fiber property and load pattern were considered to analyze the complicated variations in storage modulus and loss tangent with the change of loads. The load effects are comprehensively addressed by a phenomenological theory about suppression effect of static load on the motion of microstructure units, combined with the influence of shear stress and interface properties between fiber and resin.

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