Mohamed Nasr Saleh

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

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.

Detection of Impact Damage in Carbon Fiber Composites Using an Electromagnetic Sensor

ABSTRACT This article presents a comprehensive experimental study of impact damage detection for carbon fiber-reinforced polymer (CFRP) composites using an electromagnetic (EM) sensor with coupled spiral inductors (CSI). Two representative types of damage are detected and evaluated, i.e., barely visible impact damage (BVID) and delamination. A multifrequency inspection is performed, where the resultant images indicate the potential of the CSI sensor in the characterization of damage extent. The accuracy and efficiency of the CSI sensor are compared with the open-ended waveguide imaging, near-field microwave microscopy, microwave time-domain reflectometry, the complementary split-ring resonator, and ultrasonic scanning. Applications and limitations of these nondestructive testing (NDT) methods for identifying impact damage are discussed. There is a free edge effect on the electromagnetic signal, which is illustrated for the first time with the proposed EM technique. Detection of the air gap produced by inserting a thin piece into a machined subsurface groove is carried out. It is found that the developed CSI sensor is able to accurately resolve the location and extent of the air gap. The experimental results demonstrate that the sensor could offer an alternative relatively low cost method that can be fully automated for structural monitoring of aircraft and other composite structures.

Acoustic Emission of 3D Angle Interlock Glass Fibre Composites

It is a big challenge to relate acoustic emission (AE) signal events to specificdamage modes developed in composites under hygro-thermo-mechanical loading.This study provides further insight into the AE monitoring of a 3D angle interlock(AI) glass fibre composite and has revealed the complex nature of the relationshipbetween the principal characteristics of recorded AE events on the one hand and themechanical behaviour of the material on the other. Because the tested material here is transparent, the development of cracks can be observed in-situ during the test using optical images on the specimen. This paper presents experimental results on the use of AE on 3D AI glass fibre composites for structural health monitoring (SHM) of matrix cracks, during quasi-static tension of flat plates.

The effect of the through-thickness yarn component on the in- and out-of-plane properties of composites from 3D orthogonal woven preforms

Abstract Development of three-dimensional (3D) weaving technology introduced new and enhanced features to the 2D weaving technology. 3D Orthogonal Woven (3DOW) preforms have a through-thickness yarn component that significantly enhances the out-of-plane properties and delamination resistance. In this study, a range of 3DOW E-glass preforms were woven using 3D weaving technology and then converted into composites, using vacuum assisted resin transfer molding technology. The composite samples had varying Z to Y-yarn/ layer ratio, the objective is to study the effect of changing the Z to Y-yarn/ layer ratio on the in-plane and out-of-plane mechanical properties. The study concludes that changing the amount of Z-yarn in the structure has negligible effect on the tensile (in-plane), yet, it has a significant effect on the drop weight impact properties (out-of-plane). Moreover, it had a strong effect on the failure mechanisms, and as the amount of Z-yarn is reduced, delamination became more significant.

Stabilising and Trimming 3D Woven Fabrics for Composite Preforming Applications

The work presented here focusses on the developments in the stabilising and trimming of 3D woven preforms. Dry fibre preforms are notoriously difficult to trim; once a fabric is cut, it loses its edge stability and consequently the fabric frays. The result is an unstable fabric which can easily be displaced/ distorted prior to composite manufacturing. In this work, three stabilisation and three trimming techniques were investigated. Of the stabilisation techniques these included powder binder, thermoplastic binder yarn (activated to give fabric stabilization); and polyester stitching. The stabilised fabrics were trimmed to near-net-shape using different trimming techniques. The trimming techniques investigated were laser, clicker press and ultrasonic knife. Each stabilisation method was trialled with each trimming method to assess the most suitable combination. The assessment of quality and suitability was made by observing the level of stabilisation, amount of fraying fibres, quality of the cut, ease of application and repeatability of the process. This paper details the assessments made for each combination alongside practical application conclusions. The key findings were; cutting by means of a laser is capable of sealing the fabric edges, producing high edge quality. Stitching as a method of stabilising is not sufficient in preventing fibres from moving during the cutting process, hence producing an unclean cut.