Ph.D. (Engg): Effect of Surface Roughness on Mechanical Strength of Adhesively Bonded CFRP Joints – Experimental and Numerical Studies

This dissertation focuses on surface preparation and its effect on the shear strength of adhesively bonded Single Lap Joints (SLJs) in Carbon Fiber Reinforced Polymer (CFRP), their fracture properties, and the associated Non-Destructive Evaluation (NDE) parameters. The surface preparation was carried out using different grades of emery paper so that the interfaces of different roughness were available for bonding. The morphology of the interfaces before bonding was captured with the light interferometry [Micro-System Analyzer (MSA)]. Then, roughness parameters were characterized by contact-based measurements. The correlations of the contact angle between the droplet of liquid and the bonding interface with varied surface roughness and the increase in area with respect to the smoothest surface were established. CFRP, one of the most preferred composite materials in the aerospace industry, has been chosen in this study.

A band of NDE techniques was utilized to evaluate the effects of surface roughness in ABJs of CFRP adherends. This included Ultrasonic Testing (UT), Infra-Red Thermography (IRT), Acoustic Wave Propagation (AWP), Acoustic Emission Testing (AET), X-ray Radiography Testing (XRT), and Digital Image Correlation (DIC).

In the FEA model it is difficult to model micro-roughness on the adherend of mesoscale. Hence, an approach was presented to model the fracture in rough interfaces. Modelling of joints with varied roughness was considered, and fracture properties were implemented in the commercial FEA software Abaqus. The surface-to-surface interactions were modelled for each interface. The interaction was based on the Cohesive Zone Model (CZM). Traction separation laws were derived from experimental fracture energies.

Speaker: Laxmikant Mane Sarjerao

Research Supervisor: Prof Bhat M Ramachandra