This paper is a review of low-velocity impact responses of composite materials. First the term ‘low-velocity impact’ is defined and major impact-induced damage modes are described from onset of damage through to final failure. Then, the effects of the composite's constituents on impact properties are discussed and post-impact performance is assessed in terms of residual strength.

Review of low-velocity impact properties of composite materials

Damage characterization of laminated composites has been thoroughly studied the last decades where researchers developed several damage models, and in combination with experimental evidence, contributed to better understanding of the structural behavior of these structures. Experimental techniques played an essential role on this progress and among the techniques that were utilized, acoustic emission (AE) was extensively used due to its advantages for in-situ damage monitoring with high sensitivity and its capability to inspect continuously a relatively large area. This paper presents a comprehensive review on the use of AE for damage characterization in laminated composites. The review is divided into two sections; the first section discusses the literature for damage diagnostics and it is presented in three subsections: damage initiation detection, damage type identification and damage localization, while the second section is devoted to damage prognostics and it focuses on the remaining useful life (RUL) and residual strength prediction of composite structures using AE data. In every section, efforts have been made to analyze the most relevant literature, discuss in a critical manner the results and conclusions, and identify possibilities for future work.

Damage characterization of laminated composites using acoustic emission: A review

This article presents the mechanical characterization of an eco composite consisting of a thermoplastic matrix reinforced by flax fibres. Different configurations of specimens were tested with uniaxial tensile loading and their mechanical behaviours were discussed. Moreover, the acoustic emission technique was used to detect the appearance of damage mechanisms and to follow their evolution. In addition, a list of these mechanisms was established by means of macroscopic and microscopic observations. The acoustic emission records were post processed by the k-means unsupervised pattern recognition algorithm. Depending on the specimen configuration, three or four classes of events were obtained. The acoustic characteristics of these classes were compared. Then, a correlation between these AE events classes and the damage mechanisms observed was proposed. Their effects on the mechanical behaviour of the material were investigated by means of a variable called the Sentry Function.

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Mechanical behaviour and damage mechanisms analysis of a flax-fibre reinforced composite by acoustic emission

Cluster analysis of acoustic emission signals and deformation measurement for delaminated glass fiber epoxy composites

Application of different acoustic emission descriptors in damage assessment of fiber reinforced plastics: A comprehensive review

Cluster analysis of acoustic emission signals for 2D and 3D woven glass/epoxy composites

Correlation of acoustic emission with optically observed damage in a glass/epoxy woven laminate under tensile loading

Understanding the failure mechanisms in textile composites based on acoustic emission signals is a challenging task. In the present work, unsupervised cluster analysis is performed on the acoustic ...

/pdf/cluster-analysis-of-acoustic-emission-signals-for-2d-and-3d-56vrjh13m7.pdf

Cluster analysis of acoustic emission signals for 2D and 3D woven carbon fiber/epoxy composites

Experiments were performed to study the growth of damage in fibre rein forced cross-ply carbon/epoxy composite plates subjected to transverse loads. The plates were repeatedly loaded and unloaded, with the maximum displacements of each loading cycle greater than or equal to the previous cycle. After certain loading cycles, the extent of damage was measured by a combination of C-scanning, optical microscopy, and radiog raphy. The critical strain energy release rate for delamination growth was determined by relating the delamination area to the amount of energy dissipated by the formation of that delamination.

Delamination Growth in Composite Plates Subjected to Transverse Loads

Understanding the failure mechanisms in textile composites based on acoustic emission (AE) signals is a challenging task. In the present work, unsupervised cluster analysis is performed on the AE data registered during tensile tests on 2D and 3D woven carbon and glass fibre/epoxy composites. The analysis is based on the k-means++ algorithm and principal component analysis. Peak amplitude and frequency features – peak frequency for 2D woven composites and frequency centroid for 3D woven composites – were found to be dominant in cluster analysis. Cluster bounds were identified for all composite types. These bounds do not differ with a reinforcement type, but do differ for glass and carbon reinforced composites. These bounds can be used as a starting point for AE analysis of other carbon or glass fibre/epoxy composites (Figure 1) The statistics of high frequency AE events in carbon reinforced composites are compared with the estimates obtained from a fibre bundle model based on Weibull fibre strength statistics. The number of AE events agrees well with the number of groups of carbon fibres that fail simultaneously. This finding may provide a new way to explain why the Weibull distribution predicts much more fibre breaks than measured by AE. AE events registered during tensile loading of a plain weave glass/epoxy laminate are correlated to actual damage, which is observed optically. Cracks in the transparent laminate, visible in the backlight images, are counted during the tensile test. Transversal and longitudinal cracks in the yarns and localised delaminations are distinguished. AE events are classified according to the amplitude and peak frequency of the signal into low frequency – low amplitude, low frequency – high amplitude and high frequency clusters. The latter (high frequency) AE events are assumed to be connected to the fibre breakage. The cumulative number of transversal and longitudinal matrix cracks corresponds well to the number of AE events in the low frequency – high amplitude cluster, and the number of delaminations – with low frequency – high amplitude cluster. The study validates use of cluster analysis of AE for identification of damage models in woven glass fibre reinforced laminates. Li Li, Yentl Swolws, Valter Carvelli, Stepan V. Lomov Figure 1: Cluster analysis for a glass fibre 2D woven composites The research visit of L.Li to KU Leuven was funded by Chinese Scholarship Council.

Li Li

Papers

Cluster analysis of acoustic emission signals for 2D and 3D woven glass/epoxy composites

Correlation of acoustic emission with optically observed damage in a glass/epoxy woven laminate under tensile loading

Cluster analysis of acoustic emission signals for 2D and 3D woven carbon fiber/epoxy composites

Delamination Growth in Composite Plates Subjected to Transverse Loads

Identification of the damage in woven composites based on acoustic emission cluster analysis