Predicting compression failure of 2D woven carbon-epoxy composite

Carbon-epoxy composite is applied in many high-tech products because of the excellent strength and stiffness to weight ratios. The composite consists of strong and stiff carbon fibers which are embedded in epoxy resin to bind them (see Figure 1). At Fokker Landing Gear thick-walled composite landing gear parts are being developed which are built by stacking many layers of woven carbon textile at various angles (the layup). The compression strength of the composite is one of the most important material properties that determine the load carrying capability of the landing gear. By experiments it is shown that the compression strength of the main load carrying layers depends on the test method and the layup.

MSc student: Jonas Freund
Daily supervisor: dr. ir. Joris Remmers
Company supervisor: Wouter Wilson
Company involved:
Fokker Landing Gear

In this MSc project the experiments are simulated by finite element (FE) models and continuum damage mechanics to predict the strength and gain better understanding of the influence of layup and test method. The FE model distinguishes itself from many traditional models because it is based on non-locality. Local strains are averaged in a certain volume to obtain non-local strains (see Figure 2). This method is used to avoid mesh sensitivity and to capture fiber failure by proposing that a fiber buckles if its averaged strain exceeds a threshold value. Buckling is intrinsically related to length which is represented by a characteristic length parameter that defines the volume in which the strains are averaged.

Simulations are performed (see Figure 3) for the different test methods and layups. The conclusions are as follows; the reason why strength depends on the test method is because the compression load is applied to the specimen in different ways, i.e. the boundary conditions play an important role. Layup influence on strength is better captured by including expansion effect of layers in the stacking direction. A reason for this is that fiber buckling is stabilized by lateral pressure.