The Influence of Internal Stresses on the Microbond Test II: Physical Aging and Adhesion

Abstract

The present work investigated the effects of physical aging on interfacial adhesion and internal stresses using single-fibre model composites. First, the stress state of the interface and its evolution upon aging were studied for the microbond geometry. This stress analysis was used with experiments to determine an intrinsic interfacial shear strength. Second, this stress analysis, including aging effects, was used in a fracture mechanics or energy release rate analysis of the microbond test, which involves the energy necessary to propagate a crack instead of the minimum stress to initiate a crack. These methods were tested for both freshly cured and aged epoxy droplets on glass fibres, and were shown to yield similar results. It was found that neither the interfacial shear strength nor the interfacial toughness were changed by physical aging of the polymer matrix when the relaxation of internal stresses and shift of relaxation times of the matrix due to physical aging were accounted for. Thus, the intrinsic shear strength and toughness of the fibrematrix interface were determined.KEY WORDS: microbond test, adhesion, intrinsic strength, internal stresses, physical aging, energy release rate, interfacial toughness. the reinforcing fibre, the polymer matrix and the fibre-matrix interface [1,2].

Accelerated thermal ageing of epoxy resin and 3-D carbon fiber/epoxy braided composites

“…This is probably attributed to the post-curing of epoxy resin, which has been confirmed in section 3.3. Physical ageing (the decreasing of free volume of the resin) may also account for the change[39]. The specimens aged at 110 ℃ exhibit an initial increase in modulus and then decline marginally after 1-day ageing.…”

Enhanced Interfacial Shear Strength and Critical Energy Release Rate in Single Glass Fiber-Crosslinked Polypropylene Model Microcomposites

“…This is not surprising, since, as was shown in Reference [30], the relationship between G ic and τ d is a quadratic equation:Gic=[c0(ΔT)2+c1ΔTτd+c2τd2]df, where ∆ T = T test − T ref is the difference between the test temperature and the reference stress-free temperature; c 0 , c 1 , and c 2 are functions of material constants but not of specimen geometry; and d f is the diameter of fiber. For polymer matrices, T ref is considered to be equal to the glass transition temperature ( T g ) if T g > T test , but T ref = T test (i.e., ∆ T = 0) if T g < T test [31]. In the case of PP, the glass transition temperature amounted to −10 °C, which was lower than the test temperature during the pull-out test (25 °C).…”

Interlaminar fracture toughness improvement in composites with hyperbranched polymer modified resin

“…This value is then reported as a function of the embedded length and an intrinsic value of the interfacial shear strength s 0 is obtained according to Mendels et al [20,21]:…”