Design And Analysis Of Multi-station Fatigue Test Rig For Large Cantilever Members

Excavators play a vital role in various engineering fields,and their high-quality development is conducive to the development of Chinese construction machinery and equipment to the forefront of the world.The fatigue reliability of excavator working devices is one of the main factors that restrict domestic excavators to seize the market.Bench fatigue test is an important method used to study the fatigue performance of excavator working device.Developing test tooling separately for different types of excavators requires great human and material resources in the design and installation process,which increases the test cost and prolongs the development cycle.At the same time,non-self-balancing design will seriously damage the laboratory foundation.In order to solve these problems,a set of fatigue test bench suitable for large cantilever members and multi-station is designed based on the fatigue test of excavator working device with the mass of 6t,8t and 20 t developed by a company.The main research contents of this paper are as follows:(1)The relevant standards and research status of the excavator working device fatigue test were analyzed and summarized,and the loading requirements of the 6t,8t and 20 t excavator working device fatigue test were obtained,and the multi-station design parameters of the fatigue test bench were defined.According to the design requirements,the overall scheme of multi-station fatigue test bench of large cantilever member with double longitudinal beam structure is determined.Combined with the mechanics principle,drawing software is used to complete the structural design of the fatigue test bench of the boom and bucket rod of 6t,8t and 20 t excavator respectively.The analysis of the joint hinge points and the longitudinal beam bearing capacity of the multi-station fatigue test bed of large cantilever member under the action of the ultimate load shows that the dynamic load self-balance of the double longitudinal beam fatigue test bed has been realized and the foundation bearing capacity has been greatly improved.(2)Using ANSYS software and finite element simulation analysis,the modeling of 6t,8t and 20 t excavator working device fatigue test bench was completed respectively,and the strength,stiffness and stability analysis under ultimate tensile and compression loads were carried out.The static strength and deformation results show that all the components meet the relevant design parameters.At the same time,in order to determine the loading frequency of the test load block,the modal analysis module in ANSYS is used to carry out numerical simulation calculation to obtain the natural frequency of the fatigue test platform.The results show that the natural frequency of the fatigue test bench is far away from the loading frequency of the fatigue test and the resonance failure is avoided.(3)In order to ensure that the multi-station fatigue test bench of large cantilever members has good anti-fatigue performance,the fatigue life of weld structure was evaluated based on hot spot stress method and the fatigue life of bolt group and suspender joint structure was evaluated based on nominal stress method.Meanwhile,the influence of preload on the fatigue life of suspender structure was studied.The analysis results show that the fatigue life of the fatigue test bench meets the application requirements.The application of preload will increase the fatigue life of derrick structure.According to the fatigue test method and loading requirements of the program,the fatigue loading test was carried out on the 20 t excavator manipulator arm.The test results show that the equivalent working time of the 20 t excavator manipulator arm is 7921.38 hours,and the rationality of the fatigue test bench analysis results is verified,and the overall design is safe and reliable.