Study of Asymmetric Test Configurations by Means of Standard and Revised Virtual Crack-Closure Techniques

The objective of this article is to compare the standard two-step virtual crack-closure technique (VCCT) and the revised I–II and II–I VCCT developed by Valvo by studying two asymmetric test configurations commonly used to produce mixed-mode delamination in composite laminates—the asymmetric double cantilever beam (ADCB) and asymmetric end-notched flexure (AENF) configurations—via finite element modelling (FEM). Scientific literature has revealed that highly asymmetric specimens may exhibit negative components of the energy release rate (ERR) under certain specific loading conditions when using the standard VCCT. The revised VCCTs establish an alternative ERR partition with energetically orthogonal components to solve this inconsistency. This study aims to better understand the mechanisms involved in the revised VCCTs. This study demonstrates that, when using the revised methods, there is a transfer of energy between modes I and II, unlike when using the standard VCCT. The values of the mode I and mode II components of the ERR produced by the standard VCCT fall between the values produced by the revised I–II and II–I VCCTs for the test configurations. Nevertheless, as expected, the total ERR calculated using the three procedures is the same. Finally, some considerations are drawn for the scenario when contact occurs between the specimen arms in the AENF configuration, as it can also lead to unrealistic negative mode I ERR values in the FEM analysis.