The effect of mode II fatigue crack growth rate on the fractographic features of CFRP composite laminates: An acoustic emission and scanning electron microscopy analysis

Abstract

The present study is focused on the characterization of the fatigue damage features in carbon/ epoxy laminates under mode-II loading conditions. To this aim, a sinusoidal cyclic load was applied to the End-Notched Flexural (ENF) specimens and the fatigue behavior of specimens was investigated. Scanning Electron Microscope (SEM) was used to identify the damage features on the fracture surface, i.e. fiber imprints, cusps, roller cusps, and striations. It was found that the fatigue damage features, such as cusps and striations, completely depended on the fatigue crack growth rate, da/dN. In addition, a linear relationship between the fatigue striation space and the strain energy release rate range (ΔGs) and the hysteresis loop area was established. The Acoustic Emission (AE) method was also employed to characterize the damage features. The obtained results showed that higher AE energy indicates larger and rougher cusps and striation features.

Acoustic emission waveforms for damage monitoring in composite materials: Shifting in spectral density, entropy and wavelet packet transform

“…Typically, in a CFRP material, which is used in this research work, the macroscopic damage modes can be generalised into matrix cracking, delamination, debonding between the matrix and the fibres, fibre breakage, fibre pullout and through-thickness (interlaminar) crack growth. 3,4,37,38 Over the years, several researchers experimentally validated the frequency band of the acoustic signal associated with the different damage processes. For example, an acoustic event generated as a consequence of matrix cracking or delamination will have the characteristic frequency range of 150 kHz–200 kHz.…”

“…At the same time, the acoustic event generated due to fibre breakage will be above 300 kHz or 350 kHz. [37][38][39][40][41][42] Although most of these results are provided through the FFT analysis and the peak amplitude values, several researchers have used CWT and WPT for proving the same. The reason for choosing CWT or WPT over the conventional FFT is because they can provide information on the acoustic waveforms in their time domain.…”

A review of FMLs performance test methods and index evaluation

“…The surface properties of carbon fiber include fiber surface roughness, fiber surface chemical properties, specific area of fiber surface, etc. The surface properties of carbon fiber directly affect the surface properties of composites, and thus affect their mechanical macroscopic properties [19,20]. In general, the rougher the carbon fiber surface, the larger the specific surface area, the better the bonding of the interface; the more polar functional groups on the carbon fiber surface, the more favorable the adhesion of carbon fiber and resin; and the macroscopic mechanical properties of carbon fiber composites.…”

Evaluation of the influence of preliminary low-velocity impacts on the residual fatigue life of CFRP composites

“…In particular, the use of acoustic emission technique allows to analyse and assesses the intensity of formation and growth of defects in the structure of the material under load. Therefore, it gives an opportunity to study damage accumulation to obtain additional experimental data on the mechanical behaviour of the studied materials under load (Brunner, 2018;Lobanov and Zubova, 2019;Jung et al, 2020;Kalteremidou et al, 2021;Mohammadi et al, 2021). The energy parameter of acoustic emission signals is often used for this purpose.…”