Effect of elastic modulus and position of polyurea coating on flexural strength of coated ceramic tiles by experiments and finite element analysis

The mechanism of a polyurea coating on the flexural strength of coated ceramic tiles was studied by three-point bending together with FEM simulation. The influence of Young’s modulus and the coating position of the polyurea on the coated ceramic sample were investigated. The back-coated ceramic with lower modulus polyurea (PUR240 MPa) could show higher flexural strength due to the cushion effect that reduces tensile stress around the bottom center of the substrate. The higher modulus polyurea coating (PUR866 MPa) has a significant influence on the flexural strength of the coated ceramic sample. In back-coating, the higher modulus coating increased the flexural strength of the coated ceramic sample by nearly twofold, compared to lower modulus. This higher modulus coating enhanced the stress distribution as well as storage energy in the sample. According to the results of the FEM simulation, the mechanism which influences the stress distribution within samples during the three-point bending test was investigated. The cushion effect shows a main contribution in stress distribution by a lower modulus coating. The cushion effect occurs near the supporting pins and contributes to the stress dissipation and the reduction of stress concentration at the center-bottom of the substrate. In contrast, a thickening effect plays an important role in the case of higher modulus polyurea coatings. The center-back-coated with higher modulus polyurea acts to increase the thickness of the ceramics and dominates the effect on the flexural strength of the coated ceramic sample.