A SIMPLE-MODEL OF THE ADHESIVE FAILURE OF A LAYER - COHESIVE EFFECTS

A fine-scale model is developed for the removal of an adhesive layer b y a uniform stress. The initial motivation of this modeling project wa s a description of the removal of a layer of filter cake from cylindri cal filters by backpulse cleaning. The model includes the bonding forc es of adhesion between the layer and a substrate, as well as the farce s of cohesion between imaginary ''gridblocks'' within the layer. For s tresses greater than a threshold value, some of the layer is removed, with the fraction removed depending upon the stress, the average adhes ive and cohesive forces, and the distribution of these forces about th eir average. The cohesive forces reduce the threshold well below the a verage strength of the adhesive force, because they increase the stres s near broken adhesive bonds. The cohesive forces also sharpen the thr eshold in the cleaning pressure significantly, so that the threshold i s very much sharper than the distribution of adhesive strengths, For m oderate filter cake thickness (moderately strong cohesive forces), the threshold becomes steplike, with no cleaning just below the threshold and complete cleaning at the threshold and above. The model also prov ides the pressure dependence of the size and shape distributions for t he fragments of the filter cake layer removed from the filter, enablin g the model to address questions of cleaning efficiency, ''patchy clea ning,'' re-entrainment, and trapping of large cake-fragments in the fi lter vessel. (C) 1997 American Institute of Physics.