The Effect of Polyurea Coating on Fatigue Life of Mild Steel

The main objective of this study is to investigate experimentally the effect of polyurea coating on fatigue strength of grade-A marine steel (Mild steel). Some preliminary specimens are prepared by different cutting and surface finishing methods, using two types of primer. Based on roughness measurement of surface and pull-off test results, the milling method for cutting and grinding machine method for surface preparation with Rayston as a primer are used. Mechanical properties of steel and coating are determined by applying tensile tests on five specimens. The results of tensile tests show that polyurea coating is low-strength, high-ductile material with good energy absorption capability. Then thirty specimens are fabricated and high-cycle axial fatigue tests with a stress ratio of 0.05 and maximum stress as a fraction of yield stress are employed. The fatigue strength of coated specimens can be as more than 128% of uncoated specimens in high-cycle fatigue. This is due to the high absorption of energy by coating when the applied stress is in the elastic range of steel. In low cycle fatigue tests, the results of coated specimens are almost the same as for uncoated specimens. It was concluded that the type of primer has a very significant effect on the adhesion and fatigue strength of coated specimens.