Tensile Fracture of Laminates with Cracks

Abstract

In this paper a method, called the Damage Zone Model (DZM), is used for predicting strength of composites with through-the-thickness cracks. The DZM is based on the two fundamental parameters unnotched tensile strength (σ 0 ) and apparent fracture energy (G* c ). The damage zone, developed at a notch in the composite, is modelled as a crack with cohesive forces acting on the crack surfaces. Redistribution of stresses and change in stiffness is accounted for in the model. For comparison, strengths are also calculated by semi-empirical methods such as the inherent flaw and the point stress criteria.Experimental results for three point bend (TPB), single edge notch (SEN) and compact tension (CT) quasi-isotropic carbon/epoxy specimens are presented. Some results for specimens made from randomly oriented short glass fiber/polyester specimens are also discussed. The damage zone model is shown to accurately predict fracture load, loaddeformation behaviour and damage zone sizes in these types of laminates.

Size Effect Law and Critical Distance Theories to Predict the Nominal Strength of Quasibrittle Structures

“…In the generalized bridging crack model, the stress profile at the FPZ is obtained by means of the application of the cohesive law [32,108,[127][128][129][130][131][132][133][134][135][136]. The bridging crack model assumes that the FPZ is localized in a plane, while the rest of the specimen follows the bulk material response, usually assumed as linear.…”

Tensile Fracture of Laminates with Holes

“…For all cases studied so far [24,30], a linear relationship between crack opening and cohesive stress has proven to give good results, Figure 2b. It is important to note that the area below the Q-v curve is equivalent to the apparent fracture energy G* and that the maximum value ao of the stress is the unnotched tensile strength of the laminate.…”

“…Moreover, the extension of the damage zone is obtained as a result of 260 the analysis, and computed zone sizes are in the same order of magnitude as the experimentally determined sizes. In a related paper the method is also shown to accurately predict fracture of laminates with cracks [24]. The method was originally developed by Hillerborg et al [25][26][27][28] for fracture analysis of concrete beams.…”

Finite fracture mechanics analysis of crack onset at a stress concentration in a UD glass/epoxy composite in off-axis tension

“…Such models incorporate specific assumptions concerning strength criteria of the plies and stiffness reduction upon element failure [21], and are capable of yielding generally accurate prediction of progressive damage. Modeling failure process at a stress concentration as a propagation of a cohesive zone [22][23][24][25][26][27] led to introduction of an (apparent) critical energy release rate (ERR) as a material parameter in addition to the unnotched strength. However, the material parameters have to be determined for each layup considered.…”