A concept for defining the mixed-mode behaviour of tough epoxy film adhesives by single specimen design

• Published in: Journal of adhesion science and technology 2020-09, Vol.34 (18), p.1982-1999
• Main Authors: Jokinen, Jarno, Orell, Olli, Wallin, Markus, Kanerva, Mikko
• Format: Article
• Language: English
• Subjects: Adhesive; Computer simulation; Crack closure; Criteria; digital image correlation; Digital imaging; epoxy; Finite element method; mixed-mode testing; virtual crack closure technique
• ISSN: 0169-4243; 1568-5616
• DOI: 10.1080/01694243.2020.1746606

Fracture modes I and II interact in mixed-mode loading conditions, and the interaction is typically taken into account using a mixed-mode fracture criterion. In this work, a concept for defining the criterion is developed through an experimental-numerical simulation analysis. The mixed-mode behaviour for the criterion is tested and analysed with a single specimen design. The design of the specimen simplifies the measurement when complex test arrangements and preparations for various specimen geometries are excluded in practice. Here, the mixed-mode fracture behaviour of the specimen is analysed in detail using digital image correlation (DIC). The DIC data are used in collaboration with a finite element-based crack onset analysis, including the virtual crack closure technique, in order to consider the typical simplifications and their effects on the mixed-mode criterion. As a benchmark case, the fracture criterion is determined for an epoxy film adhesive FM 300-2 using the developed approach. The developed approach was shown to be feasible and effective for defining the mixed-mode fracture criterion. The determined Power law criterion's exponents were below unity, which points out that the common (presumed) exponent values in the current literature are actually unconservative.