Adhesive Strength Evaluation of Plasma Sprayed Coatings by Tesile Pin Test

Applicability of Stress Singularity Parameter for Evaluating Adhesive Strength of Coating Film (Phase 1)

Abstract

Selecting the tensile pin test from among the test procedures for evaluating the adhesive strength of sprayed coatings, the authors devised an adhesive strength evaluation technique.
The results obtained are summarized as follows;
1) The fracture net stress (σ_net)_cr obtained by the pin test is influenced by the coating thickness and pin diameter, and thus dose not necessarily use as an index of the adhesive strength.
2) In the vicinity of the coating edge of the pin test, the stress σ_y in load direction is inversely proportional to the square root of the distance x from the coating edge to the center of pin.
This stress singularity is expressed as follows;
σ_y= κ/√x = F_I×σ_net/√x
in which κ is an index representing the size of the field of singular stress.
3) The pin test results, when sorted out using the stress singularity parameter k_cr universal values were given regardless of changes in coating thickness and pin diameter, suggesting that employing k_cr enables the adhesive strength to be quantitatively evaluated.