Characterization of interfacial properties of composite materials by acoustic emission

Abstract

The global mechanical properties of composite structures in service depend on fiber/matrix interface and interlaminar strength. The paper proposes to use Acoustic Emission (AE) and advanced signal processing to evaluate the interlamnar performance of polymeric composites. A delaminating process simulated with a Double Cantilever Beam (DCB) in opening mode (Mode I) coupled with a n Acoustic Emission (AE) technique has been employed. Different samples were analyzed to observe the damage evolution and to evaluate the interlaminar decohesion processes. The resistance to delamination growth is expressed in terms of the interlaminar DCB mode (mode I) fracture toughness, measured by strain energy release rate, GI, dissipated per unit area of delamination growth in composite. Three categories of samples were used: two unidirectional carbon fiber/epoxy resins with one degraded by heat and one with a commercially used resin. It was found that sample that was exposed at a temperature greater than the glass transition temperature Tg of the epoxy had a higher cumulative energy release rate than the two other samples types. The original type having the lowest release rate. Acoustic emission parameters have been found to be powerful indicators of the intensity of the damage. Multivariate analysis of up to 49 parameters was performed in order to group classes of AE signals with matching characteristics. A correlation was established between the energy release rate and the acoustic emission energy.

Using Acoustic Emission to Evaluate Fracture Toughness Energy Release Rate (GI) at Mode I Delamination of Composite Materials

“…Microscopic behavior of fiber matrix interface microdamage is more difficult to be investigated, although it represents a major part of the delamination process. For monitoring microscopic events, Acoustic Emission (AE) is an appropriate tool (Refahi Oskouei & Ahmadi, 2010;Ndiaye et al, 2000;R'Mili et al, 2008;Cesari et al, 2007;Huguet et al, 2002). However, the interpretation of the signals and, hence, the evaluation of the damage stages is a major problem of the AE method.…”

“…During the last 30 years, in few papers the AE has been considered as a tool to predict the delamination fracture toughness (Benmedakhene et al, 1999;Ndiaye et al, 2000;Niebergall et al, 1999;Bohse, 2000;Lorriot, Wu & Dzenis, 2003;Bohse & Brunner, 2008). Except the paper (Ndiaye et al, 2000), in all other works the mode I fracture toughness is estimated by conventional formulas provided by normative and the AE information are used to have a phenomenological description of the delamination progression.…”

“…The transition point in the bilinear relation enabled the estimation of the critical strain release rate (G Ic ) value. The G Ic obtained by this approach was then compared to the values obtained by both ASTM D5528 standard test method (ASTM, 1994) and (Ndiaye et al, 2000) approaches. It was possible to obtain a very good agreement between the results from the new approach to the ones obtained by the ASTM D5528.…”

“…Except the paper (Ndiaye et al, 2000), in all other works the mode I fracture toughness is estimated by conventional formulas provided by normative and the AE information are used to have a phenomenological description of the delamination progression. The paper presented by (Ndiaye et al, 2000) used the AE information to estimate the G Ic , nevertheless their approach has some limitations concerning the theoretical approach and some details about that will be discussed later in the present paper.…”

“…This analysis is inspired by the work of (Ndiaye et al, 2000) where the cumulative of G I is related to the cumulative of the AE event energy, see Fig. 11 (A); a different approach is nevertheless proposed considering the plot of cumulative G I (G I CUM) versus the integral of the sentry function, Int(f), see Fig.…”