Experimental measurement and predictive modelling of bending behaviour for viscous unidirectional composite materials

Abstract

It is widely accepted that the key deformation mechanisms during forming of viscous textile composite (prepreg) sheets are in-plane shear and out-of-plane bending. This paper focuses on the bending deformation mechanism, including experimental characterisation and theoretical modelling of bending behaviour during viscous composite forming. Experimental measurements are obtained by means of a large-displacement buckling test at a variety of displacement rates and temperatures. Some important aspects, such as viscoelastic behaviour, are also investigated. A bending model based on elastic theory combined with uniaxial continuum theory for ideal fibrereinforced fluids for viscous shear deformation has been developed, using material parameters obtained from industrial manufacturers as input data, such as composite geometry, fibre properties, fibre volume fraction and matrix rheology. Model predictions demonstrate that the model can capture the main characteristics of material properties, such as rate dependence. This bending model can be used in formability analysis for viscous unidirectional composite materials, and might be applied in a finite element forming simulation to account for the bending stiffness.

Comprehending the Bending: A Comparison of Different Test Setups for Measuring the Out-of-Plane Flexural Rigidity of a UD Fabric

“…slope, decreases with an increase in curvature. This phenomenon can for the specimens be explained by micro-buckling of the UD rovings between the stitches which was observed during the test for large curvatures and also previously reported on a UD carbon fiber prepreg [13]. The FCT, VCT and RBT agree well for low curvatures which is also their region of highest fidelity: For FCT and VCT the low curvatures are measured furthest away from the fixation and for the RBT, the low curvatures occur in the beginning of the test where sliding friction is negligible.…”

“…Kocik et al [12] used the maximum critical force recorded at buckling as the basis for determining the bending stiffness. See also the study by Wang et al [13] in which a BT was used for comparison with their fabric bending model.…”

Curvature determination in the bending test of continuous fibre reinforcements

“…As shown in Figure , first, a still image of bending deflection shape of sample is taken by a high resolution CCD camera (2048 × 2048 pixel); then image processing technique is employed to extract the midline of bending deflection shape; third, a curve function is used to fit it; finally, the curvature and corresponding moment along the midline are calculated with the fitting curve, the slope of moment–curvature curve is the bending stiffness of sample. Compared with the available bending test methods, this bending test approach is easy to operate, and the setup is simple. It allows to measure large enough bending deformation and to get a wide range of moment–curvature relation.…”

Viscoelastic bending model for continuous fiber-reinforced thermoplastic composites in melt

“…Various experimental setups have been developed for characterizing the bending behavior of continuous fiber-reinforced composites at process conditions [3,7,8,[10][11][12]. Fig.…”

“…Wang et al [10] designed a setup to measure the bending stiffness of thermoset composites, which resembles the buckling of a column with two fixed ends (Fig. 1(c)).…”