A new 2D discrete model applied to dynamic crack propagation in brittle materials

In this work, a 2D discrete model (DM) applied to the dynamic crack propagation in brittle materials is developed and implemented. The proposed model is based on a particular discretization of Navier’s equations, presenting similarities to the Born model, with the advantage that the constants appearing in it are explicitly related to the elastic properties. This model overcomes the limitations in the choice of Poisson’s ratio present in other discrete models. Three numerical examples are presented to show the capability of this method in modelling wave propagation and dynamic fracture problems. The obtained results are in agreement with experimental and numerical results reported by other researchers.     

A novel technique for time-resolved detection and tracking of interfacial and matrix fracture in layered materials

A novel experimental technique is developed for time-resolved detection and tracking of damage in the forms of delamination and matrix cracking in layered materials such as composite laminates. The technique is non-contact in nature and uses dual or quadruple laser interferometers for high temporal resolution. Simultaneous measurements of differential displacement and velocity at individual locations are obtained to analyze the initiation and progression of interfacial fracture and/or matrix cracking/delamination in a polymer matrix composite laminate system reinforced by graphite fibers. The measurements at multiple locations allow the speeds at which interfacial crack front (mode-I) or matrix cracking/delamination front (mode-II dominated) propagates to be determined. Experiments carried out use three-point bend configurations. Impact loading is achieved using a modified Kolsky bar apparatus with a complete set of diagnostics for load, deformation, deformation rate, and input energy measurement. This technique is used to characterize the full process of damage initiation and growth. The experiments also focused on the quantification of the speed at which delamination or damage propagates under primarily mode-I and mode-II conditions. The results show that the speed of delamination (mode-I) or the speed of matrix cracking/delamination (primarily mode-II) increases linearly with impact velocity. Furthermore, speeds of matrix failure/delamination under primarily mode-II conditions are much higher than the speeds of mode-I crack induced delamination under mode-I conditions.