Initial Damage Evolution Of Bubbles At The Interface Of Concrete Epoxy Coating Under Regular Wave

Periodic impact load on coating surface of structures aggravates the initial damage evolution of bubbles at the interface between concrete and coating,which leads to premature mechanical denudation and failure of the coating and greatly shortens the service life of structures.Based on ABAQUS finite element software,cohesive element is used to simulate bonding action of concrete and epoxy coating,user-defined materials of cohesive element for monotone damage and fatigue damage are developed,cohesive model for initial damage of air bubbles at interface of concrete and epoxy coating is established,and evolution law of initial damage of air bubbles at interface of concrete and epoxy coating under periodic impact load of regular wave is studied.The main research contents and conclusions are as follows:(1)The dynamic response law of bubble initial damage at the interface between concrete and epoxy coating in the initial application stage under regular wave.Under the periodic impact load of regular wave,the stress and strain of the coating and cohesive element around the initial damage of air bubbles are positively correlated with the wave load,and increase or decrease with the wave load.The dynamic response around the initial damage of a single bubble is concentrated at the bottom of the bubble initial damage,and the stress-strain of the semi-short axle is larger than that of the semi-long axle in the initial damage of a single elliptical bubble,while the dynamic response of the initial damage of multiple bubbles is concentrated at the middle of the bottom of the initial damage of the two bubbles.The stress-strain value of cohesive element is larger than that of coating.Under the periodic impact load of regular wave for a long time,the coating mainly suffers from interfacial debonding damage.(2)The effects of different factors(area,generation degree,eccentricity and relative distance)on the dynamic response of bubble initial damage.Under the influence of a single factor,the maximum strain of cohesive element of single bubble initial damage increases with the increase of area and decreases with the increase of generation degree.With the increase of the initial damage eccentricity of single bubble,the stress and strain of cohesive element concentrate to the semi-short axle of the initial damage of bubble,and the maximum strain of cohesive element increases gradually,and the increasing rate increases gradually.When the relative distance of multi-bubble initial damages is small,the cohesive element strain is concentrated in the middle of the bottom of bubble initial damages.With the increase of relative distance,the strain in this part gradually decreases.The maximum strain of cohesive element of multi-bubble initial damages is always located in the bottom of the bubble initial damages where the connecting line between the two centers passes,which is the nearest distance between the bottom of two bubble initial damages,and the maximum strain decreases gradually with the increase of relative distance.When the relative distance between the initial damage of two circular bubbles is greater than 5R and the relative distance between the initial damage of two elliptical bubbles is greater than 5SR,the influence between the initial damage of bubbles is small.(3)The evolution law of bubble initial damage at the interface of concrete and epoxy coating under long-term action of regular wave.The initial damage evolution process of bubbles can be divided into fatigue damage accumulation stage and debonding region expansion stage.Fatigue damage accumulation stage:the stress and strain of cohesive element for single and multiple bubbles are concentrated at the bottom of bubble initial damage and the middle part of the bottom of two bubble initial damages respectively.Under the action of regular wave periodic impact load,the fatigue damage accumulation at this part is faster and the debonding occurs first;The stress and strain of the semi-short axle at the bottom of the initial damage of the elliptical single bubble is larger than that of the semi-long axle,the fatigue damage accumulates faster,and the debonding occurs first.Debonding region expansion stage:the debonding region of single bubble initial damage expands outward with the shape of the bottom of bubble initial damage as the prototype,and the area expansion rate of debonding region gradually increases,and finally forms a circular debonding region;Due to the phenomenon of"convergence",the interface of concrete coating with multi-bubble initial damages takes the lead in debonding from t the bottom of the bubble initial damage where the connecting line between the two centers passes,and then the debonding area gradually expands,and finally forms a circular debonding area.(4)The effects of different factors(area,generation degree,eccentricity and relative distance)on the initial damage evolution of bubbles.Under the influence of single factor,the initial debonding time of single bubble initial damage decreases with the increase of bubble initial damage area,and finally tends to a stable value.The initial debonding time of single bubble initial damage increases with the increase of bubble initial damage generation degree.When the bubble is flat,the initial debonding time tends to be stable.With the increase of the initial damage eccentricity of single bubble,the initial debonding time decreases and the change rate increases gradually.Initial debonding time of two circular bubbles increases with the increase of relative distance,but interaction will be weak when relative distance is 5R,and initial debonding time tends to be stable.Therefore,the coating process should be further improved to minimize the number and size of bubble initial damage,so as to increase the initial debonding duration and prolong the service life of the coating.