Design and Joint Configuration

Plexus helps designers to create the right joint


Today’s designer has an exciting variety of advanced composites and materials available for product design. High-performance plastics, composites and corrosion-resistant metals offer more choices than ever before, but these additional options can create challenging assembly problems. Our technical team has a wealth of expertise and knowledge which enables them to assist engineers in the design and development of the bond joints for their projects.

With a wide range of joint design possibilities, it is important to have a good understanding of joint designing and how stress is distributed across these joints when force is applied. The design guidelines to be considered when designing an adhesive joint include;

1. Maximise Shear / Minimise Peel and Cleavage
Bonds do not resist peel and cleavage stress very well. The stress is located at one end of the bond line, whereas, in the case of shear, both ends of the bond resist stress.

2. Maximise Compression / Minimise Tensile
Tension and Compression stress are uniformly distributed across the bond. In most adhesive films, the compressive strength is greater than the tensile strength. An adhesive joint is less likely to fail under a compressive force than under tension

3. Joint Width is more important than Overlap Length
With Shear Stress the ends of the bond will resist a greater amount of stress than the middle of the bond does. If the width of the bond is increased, the bond area at each end also increases, producing a stronger joint. In this same overlap joint, if the overlapping length is greatly increased, there is little, if any, change in the bond strength because the contribution of the ends is not increased. The geometry of the ends has not changes, thus their contribution to the bond strength has not changed.

As a general rule, increase the joint width rather than the overlap length.

 

ITW Engineered Polymers