Discrete Element Simulation of Transverse Cracking During the Pyrolysis of Carbon Fibre Reinforced Plastics to Carbon/Carbon Composites

TL;DR

This study uses a discrete element simulation to analyze transverse cracking in carbon fiber reinforced plastics during pyrolysis, revealing how micro-structure, ply thickness, and process conditions influence crack development and damage.

Contribution

It introduces a novel discrete element model for simulating transverse cracking during pyrolysis, incorporating fiber-matrix interactions and disorder effects.

Findings

Crack segmentation occurs after distributed cracking under heating.

Micro-structure damage depends on ply thickness and disorder.

Simulation results align with experimental data and analytical models.

Abstract

The fracture behavior of fiber-ceramics like C/C-SiC strongly depends on the initial damage arising during the production process. We study the transverse cracking of the 90{\deg} ply in [0/90]S cross-ply laminates due to the thermochemical degradation of the matrix material during the carbonization process by means of a discrete element method. The crack morphology strongly depends on the fiber-matrix interface properties, the transverse ply thickness as well as on the carbonization process itself. To model the 90{\deg} ply a two-dimensional triangular lattice of springs is constructed where nodes of the lattice represent fibers. Springs with random breaking thresholds model the disordered matrix material and interfaces. The spring-lattice is coupled by interface springs to two rigid bars which capture the two 0{\deg} plies or adjacent sublaminates in the model. Molecular dynamics simulation is used to follow the time evolution of the model system. It was found that under gradual heating of the specimen, after some distributed cracking, segmentation cracks occur in the 90{\deg} ply which then develop into a saturated state where the ply cannot support additional load. The dependence of the micro-structure of damage on the ply thickness and on the disorder in spring properties is also studied. Crack density and porosity of the system are monitored as a function of the temperature and compared to an analytic approach and experiments.