Joint design stress, types

Major type of use Unstressed joints designs with caps, overlaps, stiffeners Stressed joints at sUghtly elevated temp Unstressed joints on lightweight materials joints in flexure Where highest and strictest end-service conditions must be met sometimes regardless of cost, as military uses... 

For the best possible performance, joints should be specifically designed for adhesive bonding. In a few cases only can an adhesive be used on a joint not specifically designed for adhesives - mainly cylindrical joints. Bond stresses, materials, type of adhesive, surface preparation, methods of application and production requirements can then all be considered in relation to each other at the outset. The designer should consider especially the effect of shear, tension, cleavage and peel stresses upon the joint (Fig. 1) (see Joint design strength and fracture perspectives). 

In adhesive bonding, shear is a major type of stress when one substrate is forced to move parallel and relative to the other substrate. The entire bonded area is efficiently used when joints are stressed in shear. Thus tensile-shear overlap design is a common joint design used in adhesive bonding. (See adhesives tests. Fig. A.6.)... 

Selection of joint design is influenced by limitations in production facilities, production costs, and the desired final appearance of the part. The strength of an adhesive joint is determined primarily by (1) the mechanical properties of the adherend and the adhesive, (2) the residual internal stresses, (3) the degree of tme interfacial contact, and (4) the joint geometry. Each of these factors has a strong influence on joint performance. Figure 7.1 shows the impact of structural adhesive types and cure temperature on the toughness and durability of the bond. 

Ultrasonic (processes) Process which utilizes specially designed tooling usually vibrating at 15-80 KHz. Processes are designed to cause localized heating of thermoplastic materials which, in turn, will provide some type of welded or fused joint. Benefits are elimination of fillers and minimized heat stress on surrounding materials. 

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