Development of a physics-based theory for mixed mode I/II delamination onset in orthotropic laminates

• Published in: Theoretical and applied fracture mechanics 2019-10, Vol.103, p.102303, Article 102303
• Main Authors: Daneshjoo, Z., Amaral, L., Alderliesten, R.C., Shokrieh, M.M., Fakoor, M.
• Format: Article
• Language: English
• Subjects: Delamination; Flux density; Fracture testing; Heat treating; Laminated composite; Laminates; Mixed mode I/II loading; Physics; Strain energy density; Strain energy release rate
• ISSN: 0167-8442; 1872-7638
• DOI: 10.1016/j.tafmec.2019.102303

•Quasi-static delamination growth is scrutinized with physics-based principles.•SED approach is augmented to explain the physics of mixed mode delamination growth.•A physics-based relation between crack growth at different mode mixities is proposed.•Data from the literature is used to evaluate the critical SED approach.•Mixed mode I/II fracture data is obtained from mode I data and material properties. This paper demonstrates how the critical strain energy density in the delamination tip vicinity may be used to explain the physics of delamination growth under mixed mode I/II. A theory previously proposed to physically relate mode I and mode II delamination growth is further extended towards describing the onset of mixed mode I/II delamination. Subsequently, data from the literature is used to demonstrate that this new concept of the critical strain energy density approach indeed explains, based on the physics of the problem, the strain energy release rate level at which crack onset occurs. This critical strain energy density for the onset of delamination appears to be independent of the opening mode. This means that, in order to characterize the fracture behaviour of a laminate, fracture tests at only one loading mode are necessary. Because the load level at which the physical delamination onset occurs at the microscopic level is much lower than the traditional engineering definition of macroscopic onset, further work must reveal the relationship between the macroscopically visible delamination onset, and the microscopic onset.