Experimental and numerical study on fracture behaviour of bamboo fibres reinforced epoxy composites

The usage of natural fibres as reinforcement in composite materials is gaining the attraction of both academic and industrial sectors. However, there is lack of information and understanding on how the natural fibres influence the fracture toughness behaviour of the composites. In this work, experimental and numerical study on fracture behaviour of bamboo fibre reinforced epoxy composites is presented. Optimum NaOH concentration for treatment of bamboo fibres was determined through single fibre tensile test results and by microscopic inspection of fibre surface through Scanning Electron Microscopy (SEM). The results demonstrated that 6% NaOH treated fibre showed maximum ultimate tensile strength of 234 MPa. For interfacial adhesion between fibre and the matrix, single fibre fragmentation test was carried out followed by SEM. The results showed that treating fibres with 6% NaOH helps to improve interfacial adhesion between fibre and the matrix. For experimental purpose, bamboo fibre reinforced composite was fabricated using 6% NaOH treated bamboo fibres of length 10 mm, 20 mm and 25 mm with random distribution in epoxy matrix. In order to find out mechanical properties of bamboo fibre reinforced epoxy composite, tensile test was carried out as per ASTM D-638. Highest Ultimate tensile strength of 32.05 MPa and poison’s ratio of 0.35 was observed for composite having fibre length of 25 mm. This is because the greater length of fibre provides more surface contact area between fibre and matrix resulting in a stronger fibre matrix bond which ultimately increases the ultimate tensile strength of the composite. Mode-I plane strain fracture toughness (KIC) of bamboo fibre reinforced epoxy composites was investigated based on Linear Elastic Fracture Mechanics (LEFM) approach as per ASTM D-5045. Results of the Mode-I plane strain fracture toughness test showed that composites having 25 mm length of fibres had the largest KIC value of 2.67 MPa.m1/2, whereas composites with 10 mm fibre length showed lowest value of fracture toughness KIC of 1.61 MPa.m1/2. This result is also due to the fact that there is stronger contact between longer length of fibres with matrix and the phenomenon of fibre bridging is more dominant in case of longer fibres than the smaller ones resulting in higher KIC value for composite having 25 mm long fibres. Failure mechanism on fractured surfaces was determined through SEM. The results revealed that fibre breakage, matrix cracking, fibre matrix debonding and fibre pull out from the matrix are the major causes of failure of composite. Overall linear elastic relationship was observed in the Force-Displacement curve during the fracture toughness test due to brittle failure of the epoxy matrix. This helps supporting the use of LEFM approach to calculate fracture toughness test under plain strain condition. Simulation/modelling of crack propagation in compact tension specimen was carried out using FEA software ABAQUS®. Stress intensity factor results obtained through, contour integral method in ABAQUS, were consistent with the results obtained through experiments. Crack propagation was also simulated successfully