FRACTURE STATISTICS OF SINGLE-FIBER COMPOSITE SPECIMENS

The failure of unidirectional composite materials is subject to wide dispersion owing to the occurrence of flaws or imperfections in the fibres. Fracture modelling requires the use of statistical models to deal with this variability in strength. We are currently developing an original and general approach that combines random models of defects with mechanical models and tests on composite materials. The present study is devoted to the problem of the characterisation of single fibres. The fragmentation test is used to study the flaw population along the fibre as a function of applied stress. Each fracture is due to a flaw in the fibre with a critical stress, sigma(c), less than the applied stress sigma. We can estimate the flaw distribution as a function of stress by means of a multifragmentation test. Various density functions are proposed and tested and good agreement is found between the experimental data and theoretical results. Following the proposed model, which has been verified experimentally, numerical simulations were carried out to study the validity of the parameters of the model.