Cohesive zone property measurement by a hybrid experimental and numerical method using ball indentations

Although there are several techniques available for the evaluation of various interfacial cohesive zone properties of coatings, each has difficulties and limitations. For instance, the four-point bend method is often plagued by excessive deformation and plasticity without any coating delamination, and the button test is limited by the constant stress distribution assumption. Given such issues, a new hybrid numerical/experimental technique has been developed that is based on ball indentations, which can usually induce delamination regardless of the materials used. Using this method, indentations were first made on coated samples (nickel-on-steel and aluminum-on-aluminum for the current study) to intentionally create localized, circular delaminations, the initiation and dimensions of which were functions of the applied loads. Numerical models using finite element analysis were then used with the known indentation loads to inversely evaluate the cohesive zone properties, which reproduced the experimental results. The technique was validated based on the successful prediction of the indentation results evaluated using properties from four-point bend results.