Mixed mode I + II interlaminar fracture of carbon/epoxy laminates

Abstract

Abstract. This paper describes a study of the mixed mode I + II fracture of carbon/epoxy unidirectional and multidirectional specimens with symmetric, quasi-symmetric and markedly asymmetric legs. A beam model was developed for predicting the compliance and total strain energy release rate, G. Model predictions agreed well with three-dimensional finite element results for double cantilever beam, end-notched flexure and mixed mode bending tests. The mode mix was evaluated from a virtual crack closure technique limit analysis, which overcomes ambiguity in delaminations between differently oriented plies. Experimental specimen compliances were in good agreement with beam model predictions. Initiation critical strain energy release rates Gc were plotted against the mode II ratio GII/G. Fracture loci of specimens with symmetric and quasi-symmetric legs had practically identical shapes, showing a linear Gc increase with GII/G > 25 %. Moreover, Gc values of multidirectional specimens with quasi-symmetric and markedly asymmetric legs were very similar.

The use of ECT and 6PBP tests to evaluate fracture behavior of adhesively bonded steel/epoxy joints under Mode-III and Mixed Mode III/II

“…In spite of mode-I and mode-III, crack front distribution in mode-II was uniform with the exception of localized peaks at the specimen edge [36,37] and crack advance was linear and no difference was detected between crack length at the edges and in the center of the specimen. This point demonstrated that, in mode-III as mode-I loading, there was a higher potential for the growth of crack in the center width of adhesive pad, which indicated that a crack can grow in mode-I and mode-III without being noticed.…”

“…However, the plateau size presenting the amount of mode-III component remained sensibly at the same level, meaning that distribution of strain energy release rates could not explain the crack length dependence of G IIIc . Similarly, crack front in mode-I showed such a behavior in adhesive joints and composite materials such as SERR had the maximum and minimum values in the middle width of adhesive layer and at edges, respectively; leaving the edges, SERR increased and approached a constant value (plateau region) and decreased while getting closer to the edges [34][35][36].…”

Temperature Dependence of Flexural Strength of a CF-SMC Composite

“…Figure 11 illustrates the temperature dependence of fracture toughness calculated using the experiment results (average values) and Eq. (13). Fracture toughness is almost constant from 23 to 90°C.…”

“…The flexural strength using Eq. (12) together with a= 0.5 mm and G C ¼ 600J=m 2 [8,13] is depicted in Fig. 10.…”

Bilinear approximations to the mixed-mode I–II delamination cohesive law using an inverse method

“…On the one hand, the starter crack length should be close to 70% of the half-span ( Fig. 1) in order to avoid a fast, often unstable, propagation in high mode II set-ups [12,16,26]. On the other hand, spurious loading pin compression effects occur when the long fracture process zone caused by the mode II component approaches half-span.…”