Nanoscale evaluation of multi-layer interfacial mechanical properties of sisal fiber reinforced composites by nanoindentation technique

Abstract The multi-layer structure of plant fibers has been revealed qualitatively by qualitative microscopic characterization and associated with multi-stage failure behaviors of plant fiber reinforced epoxy composites. To quantitatively evaluate the nanoscopic mechanical properties of sisal fiber (a typical plant fiber) reinforced epoxy composites (SFRCs) involving the unique structural characteristics, elastic modulus and hardness of the epoxy matrix and cell wall layers of sisal fiber along with interfacial mechanical properties were measured by applying the nanoindentation technique. A series of indents were conducted at selected positions from the matrix to each layer of the fiber cell walls to ascertain transition zones of the multi-layer interfaces. Single-step and multi-step nanoindentation methods were respectively employed on the multi-layer interfaces of SFRCs to present their distinct mechanical properties in terms of modulus and hardness, energy dissipation, crack initiation and propagation upon compressive loading. This study measures the transition zones of the multi-layer interface and the interfacial failure load, which consequently facilitates a quantitative analysis of fracture mechanisms for SFRCs with a multi-scale and multi-layer structure.