Mechanical Behavior of Coating Cracks Based on Distributed Dislocation Method
In the preparation of coating materials,defects such as pores and microcracks are often produced in the coating and the interface,and the propagation of cracks in the coating is a way of coating failure.In this paper,the mechanical properties and interaction of surface cracks and inner cracks in elastic coatings under uniaxial tensile load are solved theoretically.The method is also suitable for multiple cracks.According to the superposition principle,the problem becomes two sub-problems.The distributed dislocation principle was adopted for the crack problem.After superposition,the integral equation was solved by numerical solution method,and the dislocation density function was solved.The stress intensity factor(SIF)at the crack tip was calculated by interpolation method,and the propagation direction of the crack was calculated by maximum circumferential stress theory.The stress field of the model was obtained by substituting the dislocation density function back into the integral equation under global coordinates.The method was verified by setting the same modulus of the coating and the substrate and degrading the model to an infinite semi-planar sub-surface crack problem.The SIF at the surface crack tip and the stress at the coating interface were calculated under different coating moduli and crack lengths.The effect of the microcrack on the SIF of the surface crack tip at any point was calculated,and the affecting zones of the microcrack with 60° inclination angle,the surface crack with 2l/h=0.2 and 2l/h=0.04,and the microcrack with 2a/h=0.01 and 2a/h=0.018 were given.Finally,the effect of the inner inclined crack on the SIF and the propagation direction of the surface crack tip were analyzed,and the possible propagation direction of the surface crack was given.According to the data analysis,the SIF of the surface crack tip at the coating harder than the substrate was larger,which enhanced the crack propagation,and that at the coating softer than the substrate was opposite.The longer the surface crack was,the greater the effect of the coating modulus on the SIF was.In the region below the surface crack of the soft coating and on both sides of the hard coating,the interfacial crack was easier to initiate.The larger difference between the moduli of the coating and the substrate,the longer the surface crack,the easier crack initiation at the interface,and the surface micro-crack had little effect on the interface.The effect of microcracks on the surface cracks was mainly concentrated in the two similar butterfly wing regions above and below the surface crack tip.The inclined microcrack made the affecting zone decrease and rotate,while the short surface crack and relatively long microcrack had a large affecting zone.The inner inclined crack tip enhanced the equivalent stress intensity factor(ESIF)of the surface crack tip,while the crack of two sides weakened the ESIF of the surface crack tip.In conclusion,the inner crack on both sides of the surface crack has an attractive effect on the propagation of the surface crack.When the internal crack is located below the surface crack,the propagation angle points to the crack plane.When the crack on the surface of the coating continues to expand,it is easier to form intersection with the crack on the left side and the lower side.
coating crackdistributed dislocationstress intensity factorinterfacial stresspropagation direction
国家科技期刊平台
NSTL
万方数据
