This method is quite accurate for calculation of the fracture energy at the crack tip, especially when homogenous materials are analyzed. The mode partition can also be performed using finite element (FE) models by means of the virtual crack closure technique (VCCT) ( Krueger, 2004 Rybicki & Kanninen, 1977). Vassilopoulos, in Fatigue and Fracture of Adhesively-Bonded Composite Joints, 2015 7.1.1 Mode partitioning in asymmetric specimens The following expression ( Sethuraman & Maiti, 1988) is used to calculate the mode I strain energy release rate: Figure 14.8 shows the reference points in and around the crack tip and the corresponding terminology for the local forces and displacements. In this way, the analysis determines the strain energy release rate for crack growth in the adhesive, close to the adherend–adhesive interface. The crack was introduced on the interface (between lower adherend and adhesive), as Abdel Wahab (2000) showed that in most of the cases interfacial failure is observed for a very thin adhesive layer (<0.5 mm) and in the present case the adhesive layer thickness is 0.16 mm. The boundary conditions and crack length along with other specifications were kept exactly the same as those used in the experiments. This approach ( Sethuraman & Maiti, 1988) was implemented using crack tip singularity elements ( Barsoum, 1976). The strain energy release rate can be calculated using the virtual crack closure technique (VCCT), a well-established FM approach for analysing progressive crack growth in linear elastic problems. the interaction of Mode I and Mode II interface failure needs to be determined according to Benzeggagh and Kenane. For instance, in order to apply the popular B-K mixed mode cohesive relation in Ref. 75–77 Associated challenges are accurate measurement of crack propagation and prevention of stiffening effects such as fiber bridging which leads to significantly higher fracture energies.Īnother challenge associated with CZM is the determination of mixed mode parameters. DCB and end-notched flexure (ENF) tests are commonly used to determine G c in Mode I and Mode II, respectively. 74 Sophisticated tests and measurement techniques are necessary to ensure accurate and reliable interface quantifications in composite laminates. G c is identified as the work needed to create a unit area of a fully developed crack. Johannes Reiner, Reza Vaziri, in Comprehensive Composite Materials II, 2018 8.4.3.3.1.2 Inter-laminar modelingĪpplication of VCCT or CZM requires accurate quantification of strain energy release rates (fracture energy) G c in Mode I (opening), Mode II (in-plane shear), and Mode III (out-of-plane shear).
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