Prediction of Microcracking Distributions in Composite Laminates Using a Monte-Carlo Simulation Method

Abstract

Space structures are subject to thermal and mechanical loads. Matrix cracks can form in composite components, which results in a change in their thermal and elastic properties. The objective of this study is to develop a method to predict transverse microcracking in general composite laminates subject to thermal and mechanical loads. The approach combines probabilistic and analytical components in an incremental damage method. The probabilistic components include a distribution of flaws characterized by a Weibull probability function, seeding of flaws at random locations, inspection of flaws in random order for crack initiation, and inspection of cracks in random order for extension. The analytical components include fracture mechanics based energy criteria that uses a shear lag derivation of the stress and displacement fields. Degradation of material properties, temperature-dependent material properties, and a material variations model are incorporated into the method. This method is implemented through a computer program that predicts crack densities, crack distributions, and degraded laminate properties as functions of an arbitrary thermomechanical load profile. Parametric analyses are used to understand the behaviors predicted by the method and their sensitivities to model parameters. Predictions are compared to previously collected data and observations for different laminate configurations and material systems. For both thermal and mechanical loads, crack density predictions capture general trends and agree with much of the data. The method shows improvements on the current state of the art in several areas. The effective flaw model predicts the initiation and gradual accumulation of cracks. The material variations model allows the method to emulate the intrinsic variability of the crack data. The method predicts crack distributions and their evolution as cracking progresses. This evolution can include the formation of different crack types and patterns. The effect of ply thickness on this evolution is correctly predicted. The success of the method shows its superiority as a tool for predicting cracking. By replicating complex observed behavior using a relatively simple method, the work supports the physical soundness of the method and increases our understanding of the mechanisms of microcracking in composite laminates.

Accelerated Tests of Environmental Degradation in Composite Materials

“…Reduced ;;tresses at free edges for certain ply angles have been analyzed [48] and used to explain some of the observed cracking behaviors. An extension by Michii, which incorporates a Monte Carlo simulation method [49], accounts for much of the observed statistical nature of microcracking. The method 'seeds' effecdve flaws at random places on the edge of the specimen to act as crack initiation sites, while material property variations are modeled to vary about a mean value.…”

“…Prior work [49] has shown that classical microcracking analyses predict considerable data scatter if one considers factors such as material variations. The current study was also limited in the number of specimens available for testing at each condition.…”

Predictive modeling of microcracking in carbon‐fiber/epoxy composites at cryogenic temperatures

“…Because of this, many attempts have been made to predict the generation of thermal stresses in composite materials, the onset of microcracking, and the distribution and origination of microcracks during failure. Shear lag analyses, variational and strain energy release rate approaches, Monte Carlo simulations, and in situ strength analyses are among the approaches that have been used to address this problem 8, 18–22. Various degrees of success have been achieved with these analyses, but they are often unnecessarily complex and fail to account for the changes in the material properties with temperature.…”