Research On The Failure Detection And Performance Optimization Of The Threaded Connection Structure In Automobile Chassis

The main connection of car connection is threaded connection,the threaded connection of the chassis is especially important for the safety and driving experience of the vehicle,the joints of the chassis are connected with a variety of failure problems due to the complex force.At present,there is a lack of theoretical basis for the design and development of the connection structure.Most of them depend on the standard and test,the repair cost is high and the development cycle is long.In order to improve the connection reliability of the threaded connection structure of the chassis,and solved the failure problem that often appears in the chassis.This paper is aimed at the reliability of the overall connection of the screw joints in the chassis,the study is carried out based on the actual failure.Firstly,the fatigue fracture and looseness of screw joint structure are studied by finite element method.The effect of each influencing factor on failure is analyzed and a reliable finite element model is obtained.Then using the case reasoning method in the field of artificial intelligence,the empirical model of the case reasoning about the matrix is obtained by integrating the detection,research and analysis of the actual failure problem.Finally,the multi-objective optimization method is adopted.Multi-objective optimization is performed for the overall reliability of screw joints in the chassis of CN200 model.The main research contents are as follows:1.Establish the stress model of thread connection fatigue process,analyze the fatigue properties of thread fasteners under different initial axial force and stress amplitude.Establishment of the ‘critical slip' of the connected parts that causes the screw fastener to rotate and loosen.It lays a theoretical foundation for the following finite element research and multi-objective optimization.2.Set up the finite element parameterized model of thread fastener,aimed at the influence factors of threaded connection fatigue performance related(initial pre-tightening force,stress amplitude)and loose coupling related influencing factors(friction coefficient,initial pre-tightening force,the thickness of the connection).The mechanism of failure problem is investigated by combining the force characteristics of the chassis.3.By establishing a case reasoning model,integrate the detection,research and processing experience of failure problems.In this paper,the failure detection results are described by means of digital,unified,standardized invalidation characteristics and their failure reason relationship matrix.The cause of each failure problem is weighted to represent the main failure reasons in the corresponding failure characteristics.4.For the overall connection performance of the front and lower arm of the chassis and the front point of the auxiliary frame,the multi-objective optimization of the thickness of the joint surface of the auxiliary frame,the contact outer diameter and the liner length of the auxiliary frame are carried out.The optimal Latin hypercube method is used for the simulation sampling design.The Kriging approximation model was established by MATLAB.Finally,an NSGA-II multi-objective optimization algorithm is adopted for multi-objective optimization.The optimal combination of each parameter is obtained to improve the overall connection performance.