Estimation of interfacial shear strength: an application of a new statistical theory for single fiber composite test

A simple procedure is proposed for estimating the effect of different sizin gs on the strength of fiber/matrix interface. This procedure is based on a newly developed statistical theory for single-fiber composite tests. This p rocedure is used to evaluate the interfacial shear strength of HTA carbon f iber in an epoxy matrix with two different sizings. Pt is shown that if the experiment data are presented in the form of the normalized variables, (l) over bar(f)/delta(c), and sigma/sigma(c), the two sets of data correspondi ng to the two different sizings can be collapsed into a single curve which can be obtained theoretically. Excellent agreement between experiments and theory is found. An argument is presented for the use of the interfacial sh eer strength as an engineering parameter to characterize interface adhesion . We also investigate the effect of residual stresses due to thermal-expans ion coefficient mismatch between the fiber and the matrix on the interpreta tion of single-fiber composite tests. We found that the: experimentally det ermined Weibull parameters are very sensitive to the effect of these residu al stresses and must be taken into consideration when interpreting single-f ilament composite tests. (C) 1999 Elsevier Science Ltd. All rights reserved .