Indirect estimation of fiber/polymer bond strength and interfacial friction from maximum load values recorded in the microbond and pull-out tests. Part II: Critical energy release rate

Abstract

A new approach to experimental data treatment in the pull-out and microbond tests has been developed. It uses the relationship between the maximum force recorded in these tests and the embedded length ('scale factor') to separately determine adhesional interfacial parameters (critical energy release rate, local bond strength) and interfacial friction in debonded regions. The new method does not require the measurement of the debond force, which corresponds to interfacial crack initiation, and is, therefore, much more convenient and simpler than 'direct' techniques involving continuous monitoring of crack growth. Using the equation for the current crack length as a function of the load applied to the ber, based on a fracture mechanics analysis of interfacial debonding, we modeled the pull-out and microbond experiments and obtained the maximum force versus the embedded length. By varying the critical energy release rate and interfacial frictional stress to t experimental plots, both interfacial parameters were determined for several ber-polymer pairs. Effects of specimen geometry, residual thermal stresses, and interfacial friction on the measured values are discussed. The results are compared with those obtained with our similar stress-based approach. The energy criterion works when the embedded length is not very short, and in this range of embedded length it is better than the stress criterion. Both criteria can be complementarily used for interface characterization.

Adhesional pressure as a criterion for interfacial failure in fibrous microcomposites and its determination using a microbond test

“…Many papers have been published in support of each, referring both to different theoretical models of interfacial failure and experimental results obtained in micromechanical tests. In our papers [18,26,32,[57][58][59], we consistently support the conclusion that these two parameters can equally well describe the behavior of real interfaces in micromechanical tests, but neither of them can be regarded as a ''universal'' or ''true'' interfacial parameter which is constant under any conditions.…”

“…Fig. 11 compares the behavior of F max (l e ) and s app (l e ) functions calculated for different failure criteria: s d [18,63], G ic [57] and r d . As can be seen, in the case of cylindrical geometry ( Fig.…”

“…Which criterion better describes interfacial failure in the microbond test, can only be verified experimentally. The first two criteria (s d and G ic ) have been repeatedly compared in the literature [32,57,59], and it has been found that the local IFSS failure criterion gives better results for initiation of debonding than the critical energy release rate criterion but the situation may be different for analysis of propagation of debonding. In this context, 'better results' means the independence of the specimen geometry as well.…”

“…In this paper we consider the results of microbond tests published in our earlier papers [5,6,18,57,70], as well as experimental data presented by other authors [55]. We shall not describe detailed experimental procedures unless it is absolutely necessary (e.g.…”

“…In our prior paper [57], we solved Eq. (4) for F, assuming G = G ic = const, and thus obtained the current load as a function of the crack length for G ic as a failure criterion (similarly to Eq.…”