Acoustic emission characterization of local bending behavior for adhesively bonded hybrid external patch repaired glass/epoxy composite laminates

This article investigates the influence of homogeneous and hybrid external patches based on glass and Kevlar plain weave woven fabrics on local bending response of adhesively bonded external patch repairs in damaged glass/epoxy composite laminates. The intent of using hybrid external patches was to combine the excellent high displacement to failure property of Kevlar fiber as a ductile reinforcement with the superior mechanical property of glass fiber as a brittle reinforcement. The undamaged normal specimens were taken as the standard specimen for evaluation of residual mechanical properties. In all hybrid patches, the proportion of Kevlar and glass fibers was equal (i.e. 50% of Kevlar and 50% of glass by volume fraction), while lay-up configurations were different. This further allowed studying the associated effects of hybridization and lay-up configuration on local bending response of the repaired laminates. All the specimens were subjected to cyclic quasi-static indentation tests with a step loading method. The indentation tests have also been monitored in real time by acoustic emission system. The acoustic emission results illustrated various damage profiles and correlates with the mechanical test results to point out the load to a transformation in damage mechanisms during indentation loading with respect to the effect of each patch material on the performance of the repaired glass/epoxy specimens. Results showed that hybridization and lay-up configurations of the external patches played a significant role on local bending response (i.e. ultimate load, stiffness, residual deformation, displacement to failure, and damage pattern) of the repaired glass/epoxy specimens. Specimens repaired using intra-ply hybrid patches showed the best local bending response.

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Effect of fibre content on the mechanical properties of hemp fibre woven fabrics/polypropylene composite laminates

Polymers and Polymer Composites ◽

10.1177/09673911211023942 ◽

2021 ◽

pp. 096739112110239

Author(s):

Sheedev Antony ◽

Abel Cherouat ◽

Guillaume Montay

Keyword(s):

Mechanical Properties ◽

Polymer Matrix ◽

Composite Laminates ◽

Volume Fraction ◽

Fibre Volume Fraction ◽

Fibre Volume ◽

Woven Fabrics ◽

Fibre Content ◽

Viscoelastic Behaviour ◽

Hemp Fibre

Nowadays natural fibre composites have gained great significance as reinforcements in polymer matrix composites. Composite material based on a polymer matrix reinforced with natural fibres is extensively used in industry due to their biodegradability, recyclability, low density and high specific properties. A study has been carried out here to investigate the fibre volume fraction effect of hemp fibre woven fabrics/PolyPropylene (PP) composite laminates on the tensile properties and impact hammer impact test. Initially, composite sheets were fabricated by the thermal-compression process with desired number of fabric layers to obtain composite laminates with different fibre volume fraction. Uniaxial, shear and biaxial tensile tests were performed and mechanical properties were calculated. Impact hammer test was also carried out to estimate the frequency and damping parameters of stratified composite plates. Scanning Electron Microscope (SEM) analysis was performed to observe the matrix and fibre constituent defects. Hemp fabrics/PP composite laminates exhibits viscoelastic behaviour and as the fibre volume fraction increases, the viscoelastic behaviour decreases to elastic behaviour. Due to this, the tensile strength increases as the fibre content increases. On the other hand, the natural frequency increases and damping ratio decrease as the fibre volume fraction increases.

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Damage Characterization in Glass/Epoxy Composite Laminates under Normal and Oblique Planes of Cyclic Indentation Loading with AE Monitoring

Materials Evaluation ◽

10.32548/2021.me-04126 ◽

2021 ◽

Vol 79 (1) ◽

pp. 61-77

Author(s):

A Jayababu ◽

V Arumugam ◽

B Rajesh ◽

C Suresh Kumar

Keyword(s):

Compressive Strength ◽

Acoustic Emission ◽

Cyclic Loading ◽

Composite Laminates ◽

Epoxy Composite ◽

Damage Resistance ◽

Damage Initiation ◽

Residual Compressive Strength ◽

Cyclic Indentation ◽

Indentation Damage

This work focuses on the experimental investigation of indentation damage resistance in different stacking sequences of glass/epoxy composite laminates under cyclic loading on normal (0°) and oblique (20°) planes. The stacking sequence, such as unidirectional [0]12, angle ply [±45]6S, and cross ply [0/90]6S, were subjected to cyclic indentation loading and monitoring by acoustic emission testing (AE). The laminates were loaded at the center using a hemispherical steel indenter with a 12.7 mm diameter. The cyclic indentation loading was performed at displacements from 0.5 to 3 mm with an increment of 0.5 mm in each cycle. Subsequently, the residual compressive strength of the post-indented laminates was estimated by testing them under in-plane loading, once again with AE monitoring. Mechanical responses such as peak load, absorbed energy, stiffness, residual dent, and damage area were used for the quantification of the indentation-induced damage. The normalized AE cumulative counts, AE energy, and Felicity ratio were used for monitoring the damage initiation and propagation. Moreover, the discrete wavelet analysis of acoustic emission signals and fast Fourier transform enabled the calculation of the peak frequency content of each damage mechanism. The results showed that the cross-ply laminates had superior indentation damage resistance over angle ply and unidirectional (UD) laminates under normal and oblique planes of cyclic loading. However, the conclusion from the results was that UD laminates showed a better reduction in residual compressive strength than the other laminate configurations.

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