An analysis of void formation mechanisms in out-of-autoclave prepregs by means of X-ray computed tomography

Out-of-Autoclave prepregs consolidated through vacuum-bag-only conditions (VBO) have attracted much interest in recent years due to the need to reduce costs associated to structural composites manufacturing. These materials are specially designed to extract volatiles and air entrapments by using tow evacuation channels introduced during the production of the raw prepreg sheets. The analysis of the void distribution and evolution across the cure cycle in [+45/0/-45/90](3s) IM7/M56 laminates is carried out in this paper using X-ray tomography measurements. Laminates were stacked following both hand lay-up (HLU) and automated fiber placement (AFP), and consolidated using vacuum-bag-only conditions. Porosity in the fresh laminates was very high (approximate to 10%) and mainly concentrated in the tow evacuation channels. Once the cure cycle progress, voids from evacuation channels start to close so the final porosity was fundamentally attributed to arrested voids between adjacent plies of the laminate. In the case of HLU laminates, the residual porosity after curing was significantly higher (approximate to 2%) than the almost void-free AFP laminates.