The health monitoring of structural joints is a major concern of the engineering community and needs to be addressed with the proper consideration. Among joining techniques, the spot welding and weld-bonding (spot weld + adhesive bonding) methods are of great interest in a number of industries. Spot welding is the traditional assembly method for steel-based automotive structures, while weld-bonding is a novel technique that combines the stiffness and productivity benefits of adhesive bonding with the proven-technology attributes of spot welding. Future trends in the design and construction of vehicular structures indicate a strong diversification of material usage, with aluminum and polymeric composites projected to play a major role. While aluminum is amenable to both spot welding and adhesive bonding, composites will, most likely, be entirely adhesive bonded. Hence, the trends towards weld-bonding and adhesive bonding are clearly visible.
The paper first presents a short review of the present trends in joining techniques with special emphasis on those in present and future use in the automotive industry. This will be followed by a short review of the existing non-destructive evaluation (NDE) techniques that may be applicable to the health monitoring of spot welded and weld-bonded structures. Next, novel concepts of health monitoring utilizing an adaptive structures approach are presented. Laser ultrasound techniques; tagged adhesive methods; dielectric response techniques; electric potential methods, etc. are briefly mentioned.
Particular emphasis is placed on the electro-mechanical impedance method. This novel method is described in some detail. The electro-mechanical impedance method utilizes the coupled electro-mechanical response of piezo-electric interrogators (sensor-actuator crystals) intimately bonded to the monitored structure. An array of such structural interrogators can be envisaged to monitor the incipient local damage and crack growth in spot-welded and weld-bonded structures. Preliminary proof-of-concept demonstration tests performed with this method have shown remarkable features and ease of utilization.