Single Lap Joint Configuration Research Articles

Debonding of Stitched Composite Joints under Static and Fatigue Loading

An experimental study was conducted to examine the effects of stitches on the static and fatigue failure of two different single lap joint configurations. To monitor damage growth, X-rays were taken periodically during the fatigue tests. The study showed that a 21/2 fold increase in static strength due to stitching. A similar increase was found in fatigue strength for a given fatigue life. Additionally, stitching significantly changed the pattern of damage growth.

Use of thin adherends in adhesively bonded joints under different loading modes

The adhesive bonding technique is especially suited to the joining of thin materials. An adhesive joint consists of a structural adhesive and an adherend. When designing the joint, focusing on the behaviour of the adhesive is important. However, if the material to be joined is thin, then it becomes much more important to concentrate on the material properties. In the present work, two adhesives with different mechanical behaviour and two thin adherend materials, steel and aluminium, were selected for the production of adhesive joints. The single lap joint configuration was subjected to tests under bending load and also under tensile load. The results show that adherend plasticity plays an important part in the joint failure; specimens under bending load experienced high plastic deformation of adherends, depending on the strength of the adherend material. Overlap increase did not seem to affect the joint strength. When the joints were tested under tensile loading, it was observed that the load bearing capacity of adhesives was an important parameter influencing the joint strength, and that an increase in overlap seemed to contribute to the joint performance. In general, the results obtained imply that it is vital that the adherends used remain in their elastic deformation region to obtain a joint strength that reflects the mechanical behaviour of the adhesive used.

Analytical and Experimental Studies of the Debonding of Stitched and Unstitched Composite Joints

The effect of stitches on the failure of a single lap joint configuration was determined in a combined experimental and finite element study. The experimental program was conducted to determine debond growth under static monotonic loading. The stitches were shown to delay the initiation of the debond and provide load transfer after total debonding of the lap joint. The experimentally determined debond length versus applied load was used as an input parameter in the finite element analysis of both stitched and unstitched configurations. The strain energy release rates at the debond front were calculated using plate elements. Discrete nonlinear spring elements were used to model the stitches and multipoint constraints were used to model the contact problem. Models of the unstitched configuration showed significant values of mode I and II strain energy release rates across the width of the joint and showed that mode III is zero at the centerline but increases near the free edge. Models of the stitched configuration showed that the stitches were effective in reducing the mode I component to zero, but had less effect on modes II and III.