On the in-plane deformability of cross-plied unidirectional prepreg

Abstract

PostprintThis is the accepted version of a paper published in Journal of composite materials. This paper has been peer-reviewed but does not include the final publisher proof-corrections or journal pagination. AbstractThe work presented herein aims to investigate the in-plane properties of cross-plied unidirectional prepreg using the bias extension method. The study is focusing on different generations of carbon fibre/epoxy material systems and testing is performed at elevated temperatures to enhance formability. Using digital image correlation (DIC), the specimen deformation and fibre rotation is captured during tests. The study shows that most cross-plied unidirectional material deforms at different characteristic length scales as deformation continues: first seemingly continuous and later in form of bands.Further, the different type of prepreg materials investigated behaves differently; for one type the pin-jointed net theory fit well, enabling simple estimation of resulting fibre angle, while for the another two not. Different loading speed and temperatures are investigated in order to pin-point its influence on the deformability.

On the interply friction of different generations of carbon/epoxy prepreg systems

“…This work aims to characterise the interply friction for four different non-bleeding, thermoset prepreg materials, for which initial tests in the workshop have indicated a more complex behaviour than purely hydrodynamic. In an earlier study [2] it was seen that although having seemingly similar characteristics (i.e. comparable type of fibres, matrix, fibre volume fraction, etc), the materials have shown significantly different interply friction.…”

“…This is done by forcing the different layers to deform by intraply deformation (within the prepreg ply) and interply deformation (in-between the prepreg plies); both in the plane and due to bending of the fibres out of the plane. While previous studies [1,2] have shown large differences in the in-plane deformation behaviour in general (between different generations of prepreg materials), this paper focuses only on the in-plane interply deformation, or more exactly the resistance to interply deformation, by measuring the friction in-between separate prepreg plies.…”

“…Other examples effecting the quality of the final component are prepreg not properly laid up [3], slippage in corner areas and the different thermal expansion coefficients of the material and the tool [4,5]. During forming experiments, it has been shown that the microscopic thermoplastic particles used as tougheners (craze stoppers) greatly influence the degree of sliding within and between thermoset prepreg layers [1]. However, also process settings such as sliding rate, i.e.…”

“…However, also process settings such as sliding rate, i.e. matrix shear rate, and matrix temperature has experimentally been shown to significantly influence the interply friction coefficient [2].…”

In-plane deformation of multi-layered unidirectional thermoset prepreg – Modelling and experimental verification

“…During in-plane shear the fibres reorient to conform to the shape of the tool, which is often seen as the most important measure when it comes to forming. For weaves, a limit of in-plane shear deformation is often defined as the shear locking angle, although this does not seem to exist in the same way for cross-plied UD prepreg [11,16,17].…”