Understanding the effect of void morphology and characteristics on laminate mechanical properties

Due to the nature of composite materials, it is almost impossible to manufacture defect-free parts. The presence of micro-defects, such as porosity, is commonly observed, and it is been shown that porosity has a detrimental effect on the matrix-dominated mechanical properties. Most researchers have attempted to evaluate the behaviour of composites with defects by correlation of the average void content to the particular mechanical property. However different materials, stacking sequences and processing parameters can affect the distribution and morphology of the pores. It is crucial to understand the variations in void morphology, such as the pore size, shape or distribution, and how these parameters affect the progressive failure behaviour of composite structures. In this work, two carbon/epoxy toughened prepreg systems were investigated, namely the Hexcel® IM7/and the Hexcel® IMA/M21. To introduce inter-ply voids, cross-ply laminates were manufactured using a novel controlled heat and pressure curing process. To characterise the voids, micro X-ray Computed Tomography (CT) was used, giving high resolution information about pore size, location and shape in three dimensions. This information was used in this study to develop a methodology to characterise the effects of porosity on the matrix-dominated material properties.