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

Do transverse cracks affect the in-situ strength and fibre breaks accumulation in longitudinal plies of cross-ply laminates?

status: Published onlin

The critical fibre break cluster for longitudinal tensile failure of unidirectional composites: misconceptions and new insights

status: Published onlin

Direct comparison of the fibre break development in unidirectional carbon fibre composites under tension predicted by statistical models and measured using 4D in-situ SRCT

status: Published onlin

Mapping strains and fibre fracture in carbon fibre composites using in situ Digital Volume Correlation

This paper presents a novel application of Digital Volume Correlation (DVC) and in situ Synchrotron Radiation Computed Tomography (SRCT) to uniaxial loading in Carbon Fibre Reinforced Polymers (CFRPs). DVC is a relatively novel tool for quantifying full-field volumetric displacements and implicit strain fields [1]. To permit the application of DVC to displacements and/or strain measurements parallel to the fibre direction in well aligned unidirectional (UD) materials, a methodology was developed for the insertion of sparse populations of sub-micrometre particles within the matrix to act as displacement trackers (fiducial markers). For the novel materials systems we have developed, measurement noise is considered, along with the spatial filtering intrinsic to established DVC data processing. The evolution of individually fractured filaments into clusters of breaks is presented, together with the associated elevated strain region. A balance of spatial resolution and signal-to-noise ratio (SNR) is discussed in relation to measuring local micromechanical phenomena, such as ineffective length, within the bulk material. It is shown that novel, mechanistically consistent measurements may be made in relation to fibre failure events.status: publishe

State-of-the-art models for mechanical performance of carbon-glass hybrid composites in wind turbine blades

Wind turbine blades are a key growth market for fibre-hybrid composites, as they offer the potential for higher turbine efficiency at a reduced cost. This paper therefore overviews the developments of KU Leuven models for mechanical properties relevant to wind turbine blades, including fibre-hybridisation, size scaling effects, flexure, transverse cracking, stress relaxation and fatigue. The strengths and limitations of the models will be highlighted with a particular focus on relevance for wind turbine blades. While significant steps forward have been made, the various developments still need to be incorporated in one all-encompassing model, and further work is needed on gathering the required input data and detailed experimental validation studies.status: Published onlin

Detailed experimental validation and benchmarking of six models for longitudinal tensile failure of unidirectional composites

Longitudinal tensile failure of unidirectional fibre-reinforced composites remains difficult to predict accurately. The key underlying mechanism is the tensile failure of individual fibres. This paper objectively measured the relevant input data and performed a detailed experimental validation of blind predictions of six state-of-the-art models using high-resolution in-situ synchrotron radiation computed tomography (SRCT) measurements on two carbon fibre/epoxy composites. Models without major conservative assumptions regarding stress redistributions around fibre breaks significantly overpredicted failure strains and strengths, but predictions of models with at least one such assumption were in better agreement for those properties. Moreover, all models failed to predict fibre break (and cluster) development accurately, suggesting that it is vital to improve experimental methods to characterise accurately the in-situ strength distribution of fibres within the composites. As a result of detailed measurements of all required input parameters and advanced SRCT experiments, this paper establishes a benchmark for future research on longitudinal tensile failure