Lap and strap joints

In-plane shear loading—kAherenA shear loads that produce shear stresses to the bondline in lap and strap joints. 

The effects of the eccentricity are the greatest in lap and strap joints, particularly in a single-lap joint. 

P(l) Two design methods are given for the design of lap and strap Joints a simplified procedure and a rigorous procedure (5.3.5.4 and 5.3.5.5 resnertiveivl In both nmcediires Ian and stran inints are treated... 

P(l) When lap and strap joints are loaded simultaneously by more than one of the above listed loadings, the joint resistance shall be determined using the maximum strain failure criterion applied to the resultant shear strain vector in the adhesive. 

Although stress concentrations are a problem mainly with lap and strap joints, it should be noted that stress concentrations are present also in scarf and step-lap joints. However, in scarf joints the stress concentrations are irrelevant when the scarf angle is low, typically less than 20°. in step-lap joints the stress concentrations generally have to be taken into account only at the ends of the outermost steps. 

It is important to realise that the bonded joint design may only ensure that the joint is capable of withstanding the external loads assumed in the design. Further on, in the case of certain configurations with highly eccentric load paths, such as lap and strap joints, it... 

It should to be noted that lap and strap joints are treated identically. As the numerical methods are based on lap joint analysis, applying these same methods gives equal or conservative results for strap joints, because strap joints are generally stronger than lap joints. 

Figure 4 also shows that maximum loading densities of single-lap and single-strap joints are very close to each other. This is also true for double-lap and double-strap joints, as can be seen in Table 6. These results indicate that lap and strap joints may be treated using similar design principles and design procedures. 

One point which is particularly relevant to bonded composites is the benefit to be gained from the increased stiffness of thicker sections (see Fig. 7.14). While it may be neither possible nor desirable to thicken the whole of a component, consideration should be given to increasing its thickness both within the area of the joint and for several mm beyond. This ensures that any distortion takes place away from the point where the joint is most sensitive to stress — its very edge. Although not immediately obvious, such a joint is a variant on the tapered lap and strap joints (Figs 7.12b and f). 

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