Numerical Simulation Of The Failure Of Coating Fracture

Thechnology of wear-resisting coating is widely applied to the contacted surfaces of many machines, which can improve the capability of resisting frictional wear on the local contact areas, prolong the work-life and ruduce the cost. However, during the process of manufacture there must be some flaws inevitably within the interfaces or coatings, where it is easy to form the critical cracks, making coatings failure and peeled off under sliding contact. Surface cracks, which are most likely to be found in many structures in service, such as pressure vessels, pipeline systems and aircraft components, have been recognized as a major origin of potential failure for such components. The study of fatigue crack propagation from such defects as the foundation of application for engineer has been an important subject.The j-integral value, stress and strain of crack and crack propagation in coating under the indenting by rigid sphere are studied by use of the finite element methods in diamond-like ceramic and TiN coating. Fatigue of the coating was calculated under different loads, substrates and crack parameters for surface crack and interface crack. The influence of indentor radius on the plastic deformation has been discussed and some important results are as follows: (1) The influence of the ratio of ceramic coating thickness to indentor radius on the failure of coating, plastic deformation of substrate and crack propagation are obvious. (2)The propagation of crack in ceramic coating is assumes to be of semi-elliptical shape under normal contact with a rigid sphere. (3)Fatigue life of ceramic coating is mainly decided by substrate and load, the lower substrate elastic moduli and load, the more cycles of fatigue. (4) The influence of parameters on j-integral value, which contains the thickness of ceramic coating and adhesive layer, substrate material and the ratio of center point to interface point of crack and center point of crack to thickness of coating are obvious. (5) The stress and strain in pivotal point of TiN coating has been discussed when the crack is in existence and inexistence. The distinction of stress and strain in coating is great.(6) The three j-integral values of crack front become different when they are plastic in TiN coating. (7)The equation of crack propagation in plastic coating has been set up .The crack propagation in TiN coating interface and surface which is different from the ceramic coating has been discussed. (8) The life of fatigue is longer when the elastic moduli of substrate become smaller under a definite load, coating thickness and crack parameter.