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

Abstract

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.

Review and Assessment of Fatigue Delamination Damage of Laminated Composite Structures

“…It is obvious that there is no general model that can comprehensively consider influence factors of fatigue delamination onset. There are few phenomenological models [1,2,58,80,90] for fatigue delamination onset in composite materials, and there is a lack of experimental verification.…”

“…Moreover, the damage caused by fatigue delamination is irreversible and often leads to a serious decline in the performance of components and even flight accidents. Therefore, research on the initiation and propagation law [1,2], the failure mechanism [3,4], and the numerical simulation [5,6] of delamination under fatigue loads is important for the damage tolerance and durability design of composite laminated structures.…”

Review and Assessment on Fatigue Delamination Damage of Laminated Composite Structures

“…Moreover, the damage of fatigue delamination is irreversible, which often leads to a serious decline in the performance of components and even flight accidents. Therefore, the researches on initiation and propagation law [1,2], the failure mechanism [3,4] and the numerical simulation [5,6] of delamination under fatigue loads are the significant issues to the damage tolerance and durability design of composite laminated structures.…”

Applying the new experimental midpoint concept on strain energy density for fracture assessment of composite materials

“…In the FPZ, several mechanisms such as the nucleation of micro-cracks cause the dissipation of energy and prevent catastrophic failure [55][56][57][58][59]. The effects of the FPZ, where micro-cracks nucleate and propagate, have been studied and a criterion derived based on dissipated energy in the FPZ [60]. Given the fracture toughness based on the maximum strain energy release rate (SERR), a rather accurate approximation of fracture based on the fracture mechanics becomes possible [61].…”