Edge Debonding Research Articles

Separation failure in a class of bonded plates

Separation failure of bonded elastic plates is considered for a class of mathematically one-dimensional structural configurations under various loading and support conditions. These include configurations simulating those of lap joints and ‘patched’ plates in which intermediate edge debonding occurs as a result of applied in-plane tension, three-point loading, and applied transverse pressure. The problems are approached from a unified point of view, as moving boundary problems in the calculus of variations. In this way a self-consistent mathematical model for the intact segment of the composite structure, for the debonded segments of the composite structure, and for the individual plate segments along with the corresponding boundary and matching conditions are obtained, as well as the transversality conditions which define the moving boundaries of a contact zone and of the bonded region itself. The latter establishes the energy release rates for the debonding structures. Numerical results based on analytical solutions then establish delamination paths or threshold curves which predict the onset and propagation characteristics of the evolving structures. These characteristics are seen to be dependent upon the loading conditions, the support conditions, the relative stiffnesses and lengths of the two primitive plates, and on the initial size of the bonded region.

Integrity of edge-debonded patch on cracked panel

The structural integrity of reinforced cracked panels with patches that are partially damaged is analyzed by assessing the load carrying capacity and failure instability of the system. Two typical types of path edge debonding are considered; they are referred to as collinear and transverse debonding with respect to the crack plane. The former refers to debonding over a region ahead of only one of the crack tips where the load and geometry are symmetric across the crack plane while the latter is concerned with debonding over a region to the side of the crack where symmetry is no longer preserved across the crack plane. Finite elements are employed to obtain the stresses and strains from which the strain energy densities can be determined for analyzing the failure behavior of the patched panels. The local and global maximum of the minimum strain energy density function, designated by [( dW/ dV ) min max] L at L and [( dW/ dV ) min max] G at G, are found and applied to define failure instability. The distance l betwen L and G serves as a measure of crack instability; it increases with the debonded area. That is, debonding tends to enhance failure instability by fracture initiating from the existing crack. For approximately the same area of debonding, crack initiation for collinear debonding would be more unstable as compared with transverse debonding for loads directed normal to the crack. Introduced also is a Patch Effectiveness Index (PEI) that serves as a measure of the load carrying capacity of the damaged patch. In this case, transverse debonding is more detrimental than collinear debonding because a more significant reduction in the load transfer path occurs in the former case. In general, both l and PEI would have to be considered for assessing the integrity of the damaged patch.