Discrete Element Modeling of Fracture Behavior of Thermal Barrier Coatings Under Bending Conditions

Abstract The bending-driven failure test is a reliable and efficient method for evaluating the quality and load-bearing capacity of thermal barrier coatings (TBCs). This study utilizes the discrete element method (DEM) to examine the damage evolution behavior and mechanical properties of TBCs with two different coating thicknesses under four-point bending (4PB) conditions at the microscale. The results reveal that during the bending process, both thin and thick coatings experience tensile instability fractures and the formation of transverse cracks perpendicular to the interface, with crack spacing ranging from approximately one to two times the coating thickness. Thicker coatings exhibit larger crack spacing and a significantly higher delamination damage evolution rate at the interface compared to thinner coatings, displaying more pronounced delamination characteristics. While thick coatings demonstrate stronger deformation resistance, their higher bending modulus and load-bearing capacity lead to the accumulation of more cracks under equivalent strain conditions, increasing the risk of crack propagation and failure. Additionally, the pores in the coating's microstructure promote crack branching and deflection, resulting in an expanded fractured area and a negative impact on the TBC system's lifespan. This study also analyzes variations in the load–displacement curve, particle contact states, strain energy, and acoustic emission counts. By integrating experimental results, it explores the relationship between different load stages and coating damage evolution. These findings provide a theoretical basis for identifying coating failure modes in 4PB tests and offer valuable insights for the design and optimization of TBC performance.