Research On Mechanical Response And Damage Mechanism Of Steel Structure Coating Under Impact Load

The central and western regions of Inner Mongolia are located at the forefront of Siberia and Mongolia’s cold high pressure,with frequent cold air intrusion,strong winds in winter and spring,and four deserts and two sandy lands.Steel structure facilities such as steel structure workshops,Bridges,long-span structures,tower mast structures,etc.are extremely vulnerable to impact damage from windy sand hard particles and high-altitude falling objects in windy weather.Organic coatings are widely used in the protection of steel structures due to their good corrosion resistance and flexibility.The surface coating of steel structure is serviced under complex working conditions such as particle impact,collision,erosion,etc.And it is prone to damage and failure,especially the damage at the interface between the coating and the substrate,which is difficult to be found,causing the coating material to produce micro-cracks or even breakage and peeling,The steel structure is prone to corrosion,resulting in a decrease in the bearing capacity of the components,which seriously affects the durability and safety of the structure.This paper used a combination of mechanics theory,numerical simulation and experiment to study the mechanical response of the steel structure coating under impacting loads in the elastic phase,elastoplastic phase and the cracking delamination phase,and analyzed the deformation mechanism of the steel structure coating in different stages And failure modes.This project was funded by the National Natural Science Foundation of China(Grant No.11862022;11162011);the Natural Science Foundation of Inner Mongolia Autonomous Region(Grant No.2018MS05047);the Inner Mongolia Autonomous Region Youth Science and Technology Talent Support Program(Grant No.NJYT-17-A09).The specific research contents are as follows:1.The theoretical analysis of the mechanical response of the steel structure coating in the elastic contact stage and the elasto-plastic contact stage under the impacting load was carried out,and the deformation mechanism of the coating in the elasto-plastic contact stage was obtained.According to the physical characteristics of the impacting object in the regional environment,having applied the elastic contact theory to establish a semi-infinite body model of the sphere impact,and having analyzed the distribution of the surface stress field of the coating during the elastic contact between the rigid sphere and the coating;having applied the rigid plastic theory to establish the elastoplastic compression of the rigid sphere Into the model,having analyzed the distribution law of the coating surface and internal stress field of the coating in the elasto-plastic response stage;having analyzed the dangerous area of the coating under load and the cause of deformation according to the distribution law of the stress field of the coating in the elasto-plastic response stage.The coating danger zone is at the position of the elastoplastic boundary(a is the contact radius),where the hoop tensile stress of the material is the largest,and the coating material yields and deforms at this boundary.2.Based on the basic parameters of the polyurethane coating material measured by the test method,the ABAQUS analysis software was used to establish a two-dimensional plane simulation model of the polyurethane coating micro-indentation test process.Through the inversion analysis method,the actual stress-strain curve of the polyurethane coating material during compression was obtained,which provides parameters for the subsequent finite element simulation simulation to characterize the plastic properties of the polyurethane coating.3.The mechanical response of the steel structure coating under the impact load in the elastic contact phase,the elastic-plastic contact phase and the damage failure phase was analyzed by finite element simulation,and the failure mode of the coating under different impact loads was obtained.The ABAQUS software was used to establish the coating model of the tungsten carbide ball impacting steel structure under different impact loads based on the cohesive element.Having analyzed the stress field distribution law of the coating surface and inside under the maximum contact radius under different impact loads,and carried out the tangential stress wave propagation law at the interface during the entire impact process,and studied damage variables at the interface.The study found:(1)After the coating response enters the elasto-plastic response stage,the surface stress of the coating and the normal stress distribution curve at the interface basically keep the same shape as the impact load increases.The normal stress at the interface increases with the distance from the center point.The distribution change law is a smooth curve,the change is relatively stable,and the maximum stress locats at the contact center point.(2)During the entire impact process,the initial moment when the sphere touches the coating surface and is squeezed is the key moment to determine the interface shear stress distribution.If the interface is damaged,delamination failure will occur when the sphere rebounds.(3)When the rigid ball impact velocity is 6mm/s,the coating is deformed.When the rigid ball impact speed is 1m/s,the coating will appear pits and bulge deformation.when the rigid ball impact velocity is 2m/s,the tensile stress on the coating surface is 2MPa.At an impact velocity of 3.2m/s,the interface first has the largest shear stress at a distance of 1 mm from the center point,and the interface begins to fail at this point.As the contact radius increases,the damage starts to expand toward the center point.The delamination phenomenon shows that the shear stress is the main factor leading to the failure of the interface.4.Having used the ball pressure impact meter to set different impact heights to conduct impact tests on the steel structure coating.The damage process of the steel structure coating under different impact loads can be divided into three stages: the first stage is coating deformation that shape is spherical crown shape.The second stage is the appearance of swelling,radial cracks and obvious interfacial delamination of the coating.The third stage is the peeling of the coating.