Prediction of cracking initiation in enamel coated product and its verification by four-point bending test

The cracking of enamel coating often occurs because of excessive tensile stress under the product usage environment. The cracks loosen the enamel coating, leading to spalling and peeling and subsequent corrosion of the metal substrate. The cracking is also affected by the residual stress, which complicates the prediction of cracking initiation. The objective of this study is to predict the cracking initiation of the enamel coating by the FE-analysis. The brittle fracture properties of the enamel coating in the FE-analysis were determined by an experimental Vickers indentation fracture (VIF) test and a uniaxial tensile test. The effect of the residual stress of the enamel coating generated by the firing and cooling process on the cracking was considered and analyzed with a four-point bending model by the FE-analysis. To verify the predicted displacement up to the cracking initiation of the enamel from the FE-analysis, a four-point bending test was also performed using the same conditions as the simulation and the results were in agreement with those of the simulation.