Volume 4 - Loctite.ph

TitleDesign GuidelinesEngineers must have a good understanding of how stress isdistributed across a joint which is under an applied force. There areseveral design guidelines which should be considered when designingan adhesive joint.Bond Shear Strength Width vs OverlapAs a general rule, increase the joint width rather than the overlap area(“wider is better”).• Maximize Shear/Minimize Peel and CleavageNote from the stress distribution curve for cleavage and peel, thatthese bonds do not resist stress very well. The stress is located atone end of the bond line. Whereas, in the case of shear, both endsof the bond resist the stress.• Maximize Compression/Minimize TensileNote from the stress distribution curve for compression andtension, that stress was uniformly distributed across the bond. Inmost adhesive films, the compressive strength is greater than thetensile strength. An adhesive joint which is feeling a compressiveforce is less likely to fail than a joint undergoing tension.• Joint Width More Important Than OverlapNote from the shear stress distribution curve, that the ends of thebond resist a greater amount of stress than does the middle of thebond. If the width of the bond is increased, the bond area at eachend also increases; the overall result is a stronger joint.In this same overlap joint, if the overlapping length is greatlyincreased, there is little, if any, change in the bond strength. Thecontribution of the ends is not increased. The geometry of the endshas not changed, thus their contribution to the bond strength hasnot changed.The Loctite ® Design Guide for Bonding Plastics, Volume 4 79