Damage evolution and fracture events sequence in various composites by acoustic emission technique

Abstract

Three composites materials, Glare 2 fiber metal laminates, graphite/epoxy (Gr/Ep) and carbon/carbon (C/C) have been tested mechanically under quasi-static loading in uniaxial and bending modes using uniform and notched specimens. Acoustic emission (AE) technique was utilized in tracking the damage accumulation profile during loading up to fracture in terms of AE counts rate and cumulative. In addition wavelet transforms was used to process AE signals in order to obtain both frequencies and time information on the main failure mechanism and the sequential events during fracture process. This was supported by light and electron microscopies characterizations. The mechanical and acoustical responses were examined with respect to orientation and temperature effects for the Glare 2, exposure temperature effect for the Gr/Ep and porosity degree effect for the C/C. Manifestly, the AE results demonstrate different damage build-up profiles and point to a transition in failure micro-mechanisms with respect to the influence of each parameter (temperature, orientation, and density) on the specific composite tested. For the Gr/Ep, the wavelet transforms indicate the sequence of events in the fracture process, from fiber breaks followed by debonding and ending with matrix cracking. In some cases, it has been observed that the damage accumulation profile in terms of AE resembled the dependency of the crack density versus the strain predicted by a micro-mechanical damage model.

New method employing the electrical impedance for monitoring mechanical damage evolution in glass-reinforced: Applications to riveted joints

“…The damage in composite materials has been investigated by several techniques as acoustic emission [9], electrical resistance [10][11][12] and flash thermography [13]. These studies are aimed to assess the structural integrity of the material by mapping the properties of the surface as in C-scan inspection, but none has been applied to dissimilar mechanical joints.…”

Effect of Hydrolytic Ageing on Kevlar/Polyester Using Acoustic Emission Monitoring

“…We get frequency information from FFT, whereas STFFT is used to window the dominant frequency region in the FFT and converts the frequency into time domain. Hence STFFT is a useful tool to compare different failure modes with respect to duration and magnitude [26]. Variation of a waveform's frequency content at any particular point or time information of the waveform can be understood by this technique [21].…”

Failure Mechanism of Brass with Three V‐Notches Characterized by Acoustic Emission in In Situ Three‐Point Bending Tests

“…[18][19][20] AE is a kind of emission stress wave in a solid material. The AE has been generally used in engineering applications for internal defects, [21,22] crack initiation, [23,24] fatigue life, [25,26] fracture location, [27,28] evaluation of the failure mechanisms, and process and damage characterization. [29,30] In this paper, three V-notches specimens with different relative depth ratio a/h and relative distance ratio a/(a þ c) are characterized by the AE under in situ three-point bending (TPB) tests.…”