White Paper: Materials

Developing Surface Treatment Processes for Bonding Dissimilar Materials

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A recent concept in automotive lightweighting is the joining of dissimilar materials. The purpose is to tailor the materials in a structure to ensure that each part of the structure has the optimum mechanical properties and the minimum weight. An example would be the bonding of aluminum stiffening ribs to a polymeric body panel.

The concept of “joining” has many subtleties. The purpose of the joint (or interface) between the components is to transfer the applied load from one component to the next. If the means of joining is by welding, the stress distribution is evenly distributed throughout the joint; however, dissimilar materials are almost never able to be welded and mechanical fasteners (bolts or rivets) are frequently used. All of the transferred stress in a structure joined with mechanical fasteners is concentrated in the fasteners and the holes through which they pass. To resist fracture, the material must be made thicker and heavier in order to sustain these stress concentrations, which negates much of the advantage to be derived from multi-material structure design.

From a structural standpoint, adhesive bonding provides the advantages of welding with the ability to use multiple materials. Stresses in bonded structures are uniformly distributed and allow the absolute minimum gage materials while retaining excellent mechanical properties such as strength, stiffness, and impact resistance.

This paper discusses the use of contact angle measurements using the Surface Analyst™ to speed up evaluation and development of several representative surface preparation processes while providing quality assurance measurements that are easily transferred to manufacturing for monitoring and quality control. The Surface Analyst is a fast, easy, accurate, and non-destructive instrument used by manufacturers with critical surface requirements — a common concern in lightweighting.

Studying and comprehending the relationship between a contaminant surface and the effects it can have on a bond will help develop more productive monitoring and cleaning procedures for surface preparation processes.

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