Andy Vanaerschot

Stochastic Characterisation of the In-Plane Tow Centroid in Textile Composites to Quantify the Multi-scale Variation in Geometry

Optical imaging is performed to quantify the long-range behaviour of the in-plane tow centroid of a 2/2 twill woven textile composite produced by resin transfer moulding. The position of the carbon fibre tow paths is inspected over a square region of ten unit cells and characterised by decomposing the centroid data into a non-periodic non-stochastic handling effect and non-periodic stochastic fluctuations. A significantly different stochastic behaviour is observed for warp and weft direction. Variability of the in-plane coordinate, identified by the standard deviation, is found to be six times higher in weft direction. The spatial dependency of deviations along the tow demonstrates a correlation length of ten unit cells for warp tows, which is twice the length computed for weft tows. The observed bundling behaviour of neighbouring tows of the same type is quantified by a cross-correlation length. Warp tow deviations affect neighbouring centroid values within the unit cell dimension, while this effect exceeds the unit cell size for weft tows. The stochastic information reflects the difference in tow tensions during the weaving of the fabric.

A stochastic multi-scale framework for textile composites to evaluate the stiffness tensor

This paper discusses the application of a multi-scale modeling technique in a stochastic framework with the aim of deriving the stiffness statistics of a composite structure. First, optical images are taken from cross sections of a laminate that consists of several layers of fabric. The characterization of these images allows constructing a dataset for each geometrical parameter of which statistical information can be extracted. Next, the model characteristics at meso- and macro-scale are calibrated, for each deterministic realization in a Monte Carlo simulation, with a sampled set from this statistical data. Several virtual composite panels are obtained and statistics of the macroscopic stiffness tensor can be derived. The procedure also permits performing a sensitivity analysis of each geometrical parameter on the stiffness values. Results are presented for the case of the laminate Young’s modulus.

Variability in Composite Materials Properties

Composite materials are created as a quite complex architecture which includes a fibre reinforcement structure and matrix material. Many material parameters play a role when composite structures are modelled, e.g. in finite element models. In addition to the properties of the raw fibre and matrix materials which are used, also geometrical parameters have a significant effect on structural characteristics. Fibre reinforcement geometry together with material properties of fibre and matrix determine homogenised material properties.The first part of the paper gives an overview of the most important processes which are used in composites processing industry. The factors which affect variability are also listed, and the effect of variability on material parameters is mentioned as well. The second part of the paper elaborates the identification of geometrical variability of the fibre reinforcement structure which is encountered with one particular type of composite material, namely a twill 2/2 carbon fibre weave with an epoxy matrix.