Transverse Crack Detection in 3D Angle Interlock Glass Fibre Composites Using Acoustic Emission

Abstract

In addition to manufacturing cost and production rates, damage resistance has become a major issue for the composites industry. Three-dimensional (3D) woven composites have superior through-thickness properties compared to two-dimensional (2D) laminates, for example, improved impact damage resistance, high interlaminar fracture toughness and reduced notch sensitivity. The performance of 3D woven preforms is dependent on the fabric architecture, which is determined by the binding pattern. For this study, angle interlock (AI) structures with through-thickness binding were manufactured. The AI cracking simulation shows that the transverse component is the one that leads to transverse matrix cracking in the weft yarn under tensile loading. Monitoring of acoustic emission (AE) during mechanical loading is an effective tool in the study of damage processes in glass fiber-reinforced composites. Tests were performed with piezoelectric sensors bonded on a tensile specimen acting as passive receivers of AE signals. An experimental data has been generated which was useful to validate the multi-physics finite element method (MP-FEM), providing insight into the damage behaviour of novel 3D AI glass fibre composites. MP-FEM and experimental data showed that transverse crack generated a predominant flexural mode A0 and also a less energetic extensional mode S0.

Early Damage Detection in Composites during Fabrication and Mechanical Testing

“…Some of these are shown in Figure 1 . Researchers have used many different methods to distinguish these damage mechanisms during mechanical testing, including, but not limited to, classification of acoustic signature [ 16 , 32 ], amplitude and frequency distribution analysis [ 16 , 32 , 33 , 34 , 35 , 36 , 37 , 38 ], and analysis of different features of the waveform [ 32 , 39 ]. Figure 2 shows a typical AE signal and the parameters that are commonly used for analysis of AE-generating damage events.…”

“…The layered nature of FRP composites allows small sensors to be integrated, thus allowing real time process monitoring. Optical fibres [ 13 , 14 , 15 ] and piezoelectric sensors [ 12 , 16 , 17 , 18 , 19 , 20 ] have been introduced for SHM in composite materials.…”

The effect of z-binding yarns on the electrical properties of 3D woven composites

“…Damage modes in composites can be generally grouped into two categories: first, intra-laminar cracking (diffused damage [10], transverse cracking [11][12][13], local delamination [14][15][16], fibre breakage [17,18]) and second, inter-laminar damage (delamination or separation between plies/yarns [19,20]). Detecting damage in 3D woven composites is even more challenging since the z-binding yarns also contribute to the damage initiation and development [9,[19][20][21][22][23][24]. Due to the high stress concentration at the interlacement points between z-binding yarns and in-plane yarns, localised damage occurs at those locations.…”

Characterisation of Damaged Tubular Composites by Acoustic Emission, Thermal Diffusivity Mapping and TSR-RGB Projection Technique

“…Forty years of research have led to the agreement that there are four main damage mechanisms identifiable in composite materials by their acoustic emission Bsignature^ [36,37]: (i) matrix cracking, (ii) interfacial debonding, (iii) fibrematrix friction/fibre pull-out, and (iv) fibre breakage. Researchers have used many different methods to distinguish these damage mechanisms during mechanical testing including, but not limited to, classification of acoustic signature [20,[37][38][39], amplitude and frequency distribution analysis [20,, and analysis of different features of the waveform [37,44]. Figure 3 shows a typical AE signal and the parameters that are commonly used for analysis of AE-generating damage events.…”

“…The use of structural health monitoring (SHM) systems has sparked interest in recent years as they can be integrated directly into a composite structure during manufacture [18,19]. Sensors and embedded networks can be used to monitor various parameters such as local stress, strain, temperature, impact, delamination, and crack propagation in-situ and in real time [19][20][21][22][23][24]. Where the use of SHM and NDE are combined, it becomes possible to carry out Bfocused^inspections using non-destructive techniques, saving both time and money.…”