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.
Instron’s range of electromechanical and dynamic testing machines are well suited for all types of adhesive joint testing. A range of grips and fixtures are available to assess the strength of adhesives. Tests on lap-shear specimens are commonly performed using either; wedge action grips, screw operated side action grips or pneumatic grips. Peel test fixtures include; 90° peel, variable angle, floating roller and rotating wheel types. Specialty fixtures such as the climbing drum peel fixture are available for testing the adhesive bonds in sandwich core materials. Bluehill® Universal software is ideal for static adhesive testing and an optional Adhesives Application Module includes a number of pre-configured test methods to ASTM, EN and ISO standards.
Fatigue tests on adhesive joints can be performed on dynamic machines using fatigue rated mechanical or hydraulic grips. Adhesives are often tested under various environmental conditions, in this case, Instron environmental chambers are available.
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.
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