Chapter 25. Determination of Strength of Double-Layer Brittle Coatings on Metallic Substrates by Four-Point Bend Test

Summary

Apparent strength of ZrO₂/Al₂O₃ double layer coatings on Al-alloy substrate was measured by four-point bend test. First, an analytical relationship between the strength and failure load was derived through the strength of materials approach. Second, failure load for the brittle coatings was determined experimentally. Finally, strength was calculated based on where the failure occurred. Since failure load strongly depends on residual stresses, the apparent strength determined reflects the effect of residual stresses. Calculations require the geometric dimensions as well as the elastic modulus of all three constituents.