Research On Fatigue Failure Mode And Maintenance Reinforcement Of Main Girder Structure Of Metallurgical Crane

The working level of metallurgical crane is a5-a8,with high utilization rate,heavy work,often full load operation,and the working environment is very bad.The main and auxiliary trolley lifting,starting,braking and other working conditions make the crane girder structure bear more frequent loads.In the long-term operation of metallurgical crane,the degradation problems of fatigue,strength,stiffness and other performance of metal girder structure become more and more obvious.At present,in the actual production,limited by the objective conditions,most of the crane maintenance and reinforcement measures rely on experience,which to a certain extent will not only cause a waste of resources,but also reduce the production efficiency of enterprises.The reason is that metallurgical crane is an extremely important molten metal handling machine in smelting workshop,and its safety is in the first place.Once the structure is damaged,it will seriously threaten the safety of people and property.Therefore,from the perspective of safety,enterprises can not fully use the equipment to failure state,they can not fully understand the failure mode of the main girder structure of metallurgical crane,and there are few related tests and field studies,which lead to the status quo of conservative maintenance to a certain extent.Therefore,only by fully studying the failure mode and performance deterioration of the main girder structure of metallurgical crane,can we better grasp the opportunity of maintenance and reinforcement,avoid over maintenance and conservative maintenance on the premise of ensuring the safety and reliability of the structure,and finally achieve the engineering goal of making full use of the load-bearing performance of the structure and extending its service life.In this paper,the metallurgical crane girder structure fatigue failure mode and maintenance reinforcement effect as the research topic,using the similarity theory to design the metallurgical crane girder structure scale model,carry out the scale model fatigue test,from the test results to determine the main fatigue failure mode and stiffness degradation law of the metallurgical crane girder structure,and carry out the maintenance reinforcement test research.The main research contents and conclusions are as follows(1)Based on similarity theory,the scale model of metallurgical crane girder structure is studied.Firstly,the research status of similarity theory is summarized.Secondly,based on the similarity theory,the dimension analysis method is used to determine the similarity proportion of the main physical parameters of the main girder structure,and the similarity ratio of each parameter is solved.On the premise of determining the overall length similarity ratio of the scale model,the plate thickness of the scale model and the size and shape of the internal diaphragm are analyzed and studied according to the actual production situation.Finally,the corresponding prototype finite element model and 12 kinds of scale model finite element model are established.Through the comparison of prototype field test and finite element calculation results,the best scale model design scheme is determined,and the reduction of scale model test response in the prototype is studied.(2)Scale model test of main girder structure of metallurgical crane.Taking the scale model of metallurgical crane girder structure designed and made by similarity theory as the test object,the related static and fatigue tests are carried out.The main purpose of scale model test is to determine the fatigue failure mode and stiffness degradation law of the main girder structure of metallurgical crane.In the scale model test,not only the traditional contact test methods such as strain gauge and displacement meter are used,but also the non-contact test method of digital image correlation(DIC)method is used to measure the stress and displacement.At the same time,the nondestructive testing techniques such as ultrasonic testing and ultrasonic phased array testing are used to detect the surface of the scale model and the internal cracking of the weld,These methods ensure the accuracy and reliability of the test results,and provide accurate data support for subsequent test results analysis.(3)Research on fatigue failure mode of main girder structure of metallurgical crane.By comparing the static test results of the scale model with the finite element calculation results,it is verified that the actual scale model can reflect the mechanical response and mechanical properties of the prototype,so the subsequent test results of the scale model can be effectively restored to the prototype by the similarity theory.The load displacement and load stress curves and their changing rules can be obtained from the fatigue load test results of the scale model.At the same time,the stiffness degradation function of the structure is determined and the stiffness degradation model is established according to the deflection results.Finally,combined with the results of scale model fatigue test and non-destructive testing,it can be determined that the main failure modes of the main girder structure of metallurgical crane under long-term full load are fatigue crack propagation failure and stiffness degradation failure of the main girder structure.(4)Research on maintenance and reinforcement of main girder structure of metallurgical crane.Aiming at the problem that the rigidity of the scale model of the main girder structure of the metallurgical crane is degraded and the lower deflection is too large,the scale model is strengthened by pasting CFRP cloth,and the experimental research is carried out.The test results show that: under the full load condition,the structural stiffness of the scale model strengthened by CFRP is increased by 17.4%,and the maximum deflection deformation of the scale model strengthened by CFRP is reduced by 16.7%.According to the similarity theory,it is feasible to apply CFRP to the prototype of the main girder structure of metallurgical crane for structural reinforcement,which can improve the bearing capacity and safety of the main girder structure.At the same time,the method of "shell spring shell" element simulating "CFRP adhesive layer scale model" is proposed to establish the finite element model of the main beam strengthened by CFRP.By comparing the results of finite element calculation and test,it can be verified that the established finite element model of main beam strengthened by CFRP is basically accurate,which provides a relevant finite element model establishment method for similar box structure beams strengthened by CFRP.