Two mechanisms of the fragmentation of thin coatings on rubber substrates

The fragmentation of thin platinum films, nanometers thick, deposited on isoprene rubber and poly(ethylene terephthalate) substrates was studied. Light and scanning electron microscopy was used. The length of a fragment depends on the thickness of the coating film and the tensile stress applied to the specimen. An equation describing the tensile stress in an elastic coating fragment is derived. The equation is used to analyze the fragmentation of a coating film under tension. Two stages of fragmentation are distinguished. At low strains, when the length of the fragments is lower than the ineffective length, fragmentation is occasional, as determined by defects in the coating. At high strains, the mechanism of fragmentation changes to the division of the fragments into halves. The division repeats when the load is doubled. During this stage of fragmentation, the crack density is proportional to the applied stress and reversibly proportional to the thickness of the coating. (C) 2001 John Wiley & Sons, Inc.