A Micromechanics-Based Damage Model for the Strength Prediction of Composite Laminates

The prediction of the failure of composite laminates subjected to multi-axial loading in regions with mild stress gradients is of considerable interest for some aerospace applications such as pressurized vessels. In such components, which are devoid of notches or other stress concentrations, matrix cracks can accumulate prior to the localization of damage along a narrow fracture path. The prediction of the onset of ply damage can be accomplished by using ply-level failure criteria [

1

]–[

2

]. To predict ultimate failure of a laminate the ‘ply-discount’ method is normally used. The ply discount method reduces by an empirical amount the elastic properties of a damaged ply as a function of the type of damage predicted. Such an approach is not rigorous for the simulation of the progressive accumulation of transverse matrix cracks.

The main objective of the current work is to develop an alternative method to predict the onset of ply damage and ultimate failure of a laminate. The failure criteria used to predict damage onset are the LaRC03 failure criteria [

2

]. A micromechanical model of a laminate containing matrix transverse cracks under multi-axial loading is proposed. The model proposed can predict the increased strength of a ply when it is embedded in a multidirectional laminate, and it relates the multi-axial strain state to the density of transverse matrix cracks. Based on the micromechanical analyses, a new model is formulated in the framework of damage mechanics. The characteristics of the constitutive model are based on the micromechanical model. Several examples relating the applied loads to the stiffness of a multidirectional laminate are presented.