The determination of key resin parameters to support FE modelling of composite forming

Aim:
The identification and validation of techniques to provide accurate input data for FE models of composite forming.
Objectives:
1. To identify what are the material related input parameters required to produce accurate simulations of the forming of organic matrix composites
2. To isolate those parameters relevant to the resin and the research techniques currently used to measure these parameters
3. To identify the challenges and limitations of these techniques and develop improved techniques for more accurate measurements and contribute to the development of an in-house capability
4. To validate the approaches used through properly designed forming trials supported by FE modelling
Background
There is increasing use of Carbon and Glass Fibre Composites (CFCs and GFCs) across a range of market sectors, notably in aerospace and transport. One of the great challenges, particularly for larger parts e.g. aircraft wing sections, or sections on Wind turbines, is to manufacture the parts within tight geometric tolerances. Key to this is tool design. For aerospace the tooling is often made of Invar – a low expansion metallic alloy that demonstrates a similar thermal expansion coefficient to the CFC component. More recently there has been a move towards the use of CFC tooling to better account for differentials in thermal expansivity. Irrespective of the tooling material, tooling costs are high and lead-times for tooling delivery are often protracted. A major factor in optimising the tooling geometry is the prediction of springback when a component is removed from a set of tools. There are a number of issues affecting this one of the major one’s being the residual stresses that are built up within a component due to the cross-linking of the resin that binds the fibres and the thermal shrinkage following forming. The cross linking process itself causes the resin properties to change with time and is an exothermic reaction that is supported by tool heating. The overall process modelling challenge is then a coupled problem involving transitory chemical, thermal and mechanical effects. This is shown schematically in Fig. 1. In order to properly analyze this, a representative material dataset is required. The focus of this doctorate programme will be to identify which variables are important to adequately represent the changing resin properties and then to identify, develop and test suitable techniques for measuring such variables.

Fig. 1. Factors influencing distortion predictions in FEM of composite forming.
To support this research the University of Strathclyde has excellent materials characterization capabilities and it is anticipated that the equipment at both the AFRC and Advanced Materials Research Laboratory (AMRL) will be involved in facilitating successful outcomes to this work.
Aim: The identification and validation of techniques to provide accurate input data for FE models of composite forming.