In-situ synchrotron computed tomography tensile testing of composite specimens to estimate fibre strength Weibull parameters

Abstract

A methodology is presented for the retrieval of fibre strength Weibull parameters using in-situ synchrotron computed tomography tensile testing of unidirectional composite specimens. Only fibre breaks that did not fail due to stress concentrations caused by other breaks are considered in this methodology. After the selection of the fibre breaks, the Weibull strength parameters were estimated through non-linear regression as well as least-squares fitting of linear regression in logarithmic scale. The two methods yield different estimated parameters, with the non-linear regression showing a better correlation with the observed fibre strength probability. The estimated Weibull parameters differed between specimens of the same fibre and matrix type, indicating that the strength distribution of fibres can vary within a given material batch. The measured Weibull scale parameters of the carbon fibres was estimated to be larger than the parameters measured in the single fibre tensile testing. This strength increase can be evidence of the higher strength of fibres when embedded in resin compared to when tested in air. The effect of fibre pre-selection in single fibre tensile tests was eliminated in the performed impregnated specimen tests, removing one source of uncertainty of the fibre strength Weibull parameters.