Multi-instrument multi-scale experimental damage mechanics for fibre reinforced composites

© Published under licence by IOP Publishing Ltd. Reliable investigation of damage in fibre reinforced composites requires concurrent in- and ex-situ application of multiple instruments at different scale: digital image correlation, acoustic emission registration, optical/electron microscopy, C-scan, X-ray imaging and micro-computed tomography. The multi-instrument experimental mechanics allows detailed damage monitoring and inspection

Micro-CT analysis of the internal deformed geometry of a non-crimp 3D orthogonal weave E-glass composite reinforcement

An investigation at the unit cell level of the sheared geometry of a single layer E-glass non-crimp 3D orthogonal woven reinforcement (commercialized under trademark 3WEAVE by 3Tex Inc.) is performed by X-ray micro-computed tomography (micro-CT) observations. The aim is to observe, understand and quantify the effect of in-plane shear deformation on the composite reinforcement geometry, at mesoscale (i.e. unit cell level). It was observed that, increasing the shear deformation, Z-yarns maintain unchanged the distance between the yarns and as consequence the yarn cross-section has a reduced variation of width, mainly in the weft direction. Furthermore, the effect of the shear angle on the textile thickness during compression is measured, this being an important parameter after the forming and molding phases of a composite component production. Compression tests and micro-CT measurements of the thickness show similar values and are in agreement with the prediction obtained assuming the theoretical invariance of the volume in the considered range of shear deformations

Formability of a non-crimp 3D orthogonal weave E-glass composite reinforcement

In this paper, the formability of a single layer E-glass non-crimp 3D orthogonal woven reinforcement (commercialized under trademark 3WEAVE by 3Tex Inc.) is experimentally investigated. The study involves the forming process of the 3D fabric on two complex moulds, namely tetrahedron and double-dome. The tests are assisted by 3D digital image correlation measurement to have a continuous registration of the fabric local deformation. Moreover, the results of bending tests in warp and weft direction are detailed to enlarge the mechanical properties data set of the 3D reinforcement, necessary for understanding its deformability capacities in forming processes. The elevated bending stiffness of the 3D fabric means that use of a blank-holder during forming is not required. The reinforcement has a good drapability and it is able to form complex shapes without defects (wrinkles and fibre distortions). The collected experimental results represent an important dataset for numerical simulations of any complex shape with the considered 3D fabric composite reinforcement

Correlations between damage initiation thresholds in textile composites and fatigue life limits

The paper explores the interrelations between damage initiation thresholds in quasi static tensile loading and tension-tension fatigue life limits. The damage initiation thresholds are determined using acoustic emission registration during a tensile test and are confirmed by X-ray observations of cracks and micrography. The paper systematise results of experiments with measurements of the static damage initiation thresholds and tension-tension fatigue S-N curves on a variety of textile composites. The following materials were studied: (1) glass/epoxy: plain weave laminates and 3D woven; (2) carbon/epoxy: twill weave laminates, 3D woven, 3D braided, NCF, NCF structurally stitched. Glass reinforced composites have the fatigue limit stress level (more then few millions cycles) close to the AE threshold strain (appearance of the first micro damage). Carbon reinforced composites, on the contrary, have the “infinite” fatigue load between the first and the second damage thresholds loads

Fatigue limit: Is there a link to the quasi-static damage?

The paper presents experimentally and numerically observed relations of the fatigue life limit and the quasi-static damage threshold, which provide rough estimation for the design strains to use under fatigue strength requirements and allow planning of the fatigue testing programs to minimize the amount of costly and time-consuming experiments with low loads and high number of cycles

Acoustic emission and damage mode correlation in textile reinforced PPS composites

The paper applies the cluster analysis methodology to thermoplastic Polyphenylene sulphide (PPS) carbon woven composites. The experimental quasi-static tensile tests were assisted by: a digital camera for digital image correlation (DIC) evaluation of the full field strain; a digital camera for local damage observation; acoustic emission (AE) sensors for measurement of the acoustic emission features during loading. The experimental data and the subsequent cluster analyses of the AE events show a similar distribution of the AE clusters for the considered thermoplastic carbon composites and other thermoset woven composites described in the literature. The boundaries of those clusters are different for some extent, while a typical damage mechanism, namely transverse cracks inside the yarns, was clearly correlated to the first cluster with lower amplitude and lower frequency acoustic events

SHAPING ANALYSIS OF A NON-CRIMP 3D ORTHOGONAL WEAVE E-GLASS COMPOSITE REINFORCEMENT

In this work, the formability of a single layer Eglass non-crimp 3D orthogonal woven reinforcement (commercialized under trademark 3WEAVE® by 3Tex Inc.), is experimentally investigated. The study involves the shaping process of the 3D fabric on two moulds, namely tetrahedral and double-dome shape. The tests are assisted by 3D digital image correlation technique to have a continuous measurement of the local deformation during forming processes. The obtained results represent useful information and comparison to predictive numerical modelling of the forming process with such 3D composite reinforcement

FORMING OF A NON-CRIMP 3D ORTHOGONAL WEAVE E-GLASS COMPOSITE REINFORCEMENT

In this work, the formability of a single layer E-glass non-crimp 3D orthogonal woven reinforcement (commercialized under trademark 3WEAVE® by 3Tex Inc.) is experimentally investigated. The first phase of the study is dedicated to the understanding and measurement of the main deformation mechanisms occurring during forming processes. The deformation during extension is investigated under biaxial loading in the in-plane tows directions (i.e. warp and weft). Particular attention is dedicated to the behaviour during shear loading because this is considered the primary deformation mechanism in the reinforcement forming. The second phase involves the forming process of the 3D fabric on two moulds, i.e. tetrahedral and double-dome shape. The tests are assisted by 3D digital image correlation (DIC) technique to have a continuous measurement of the local deformation in the fabric plane during forming processes. The obtained results represent useful information and comparison to predictive numerical modelling of the forming process with such 3D composite reinforcement