Static behavior of thick flax/epoxy composite laminates: multi-instrumentation mechanical failure analysis

The use of thick composites in civil engineering and aeronautics fields is becoming increasingly common in primary or secondary structures, and natural fiber composites present a valuable alternative in terms of mechanical performance, cost and environmental impact. Investigating the mechanical characteristics and damage mechanisms that occur in thick flax/epoxy laminates is the primary objective of this research. Firstly, multi-instrumented bending tests and interlaminar shear tests were carried-out to assess the mechanical properties and failure characteristics of the composite. This multi-instrumentation concerns, the Acoustic Emission and the Digital Image Correlation techniques. In addition, postmortem observations utilizing Computed Tomography (CT) Scan and scanning electron microscopy (SEM) were carried out. Finite Elements and analytical models were proposed to evaluate the mechanical response. At the macroscale, results demonstrate a good correlation in the elastic zone between the numerical, analytical and the experimental. However, at the mesoscale the correlation is less evident especially close to the final failure of the laminate. Based on SEM and X-ray tomography images, the differences recorded are related mainly to the plies thickness variations and the waviness phenomenon induced by the manufacturing process.