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As the drive for light weighting increases the range of materials used in automobiles, the requirement for reliable ways of joining these materials grows in importance. Adhesive joining technology is capable of joining dissimilar materials and can offer improved performance over traditional methods in many situations, however, careful qualification and quality controls are needed to ensure reliable results.
Adhesive Dynamic and Static Testing
As adhesives find their way into even more arduous automotive applications, the need to understand their static and fatigue behavior under different environmental conditions grows.
A variety of techniques can be employed to test the mechanical properties (e.g. strength and stiffness) of adhesive joints. Measuring the strength of an adhesive joint between rigid parts is usually performed using a lap-shear test. Various forms of peel tests are used to measure the strength of joints between flexible and rigid/flexible parts.
Fracture toughness tests are used to explore crack growth in bonded joints under both static and fatigue loading. The results of fracture toughness tests can provide a better understanding of the mechanisms of adhesion and the reasons for joint failure.
As automotive design evolves, adhesives are rapidly replacing mechanical fasteners as a conventional solution for joining many metals, plastics, rubbers, and glass. Specially formulated adhesives used to bond structural frame assemblies, windshields, and other components can offer improved aesthetics, reduced noise & vibration (NVH), as well as reduced manufacturing costs. With increased use of adhesives however, automotive and adhesives suppliers must develop new test protocols to ensure the structural integrity of the bonds under all possible field conditions. Impact forces in a crash may cause bonded areas of the frame or windshield to fail, resulting in serious injury to vehicle passengers.
Automotive and adhesives suppliers commonly use ISO 11343 wedge-peel impact testing method to compare the relative effects of various product and process variables on impact performance. Instron has developed standard as well as custom test configurations based on ISO 11343. Including a unique support fixture and striker arrangement to impact windshield specimens bonded to auto frame components. Packaged with an Instron thermostatic chamber, this impact system can enable research and development facilities to experiment with different material compositions, cure conditions, and temperatures to optimize product performance and comply with government regulations.