Design and Analysis for EPB Shield Bracket Based on Ansys

According to the structural characteristics of EPB shield bracket, the author establishes 3D solid model by Solidworks and corresponding finite element model of the bracket portion which is connected to the cutterhead by ANSYS WORKBENCH software. Through the static analysis of bracket’s stress characteristics under extreme conditions, we get its stress, deformation and safety coefficient distribution law under the maximum constraint conditions. After getting the maximum equivalent stress, the analysis of the calculation results shows that this kind of bracket with good static characteristics can meet the design strength requirement. This paper points out the weak position of bracket’s strength, and provides some reference data for the structural optimization design, as well as some basic data for both the structural design of bracket and the construction maintenance. Moreover, the structure analysis in the process of the grid selection and the key technology of the post-processing method are discussed in detail. The design example shows the effectiveness of the method.


Introduction
Shield tunneling machine is a special machine for tunneling, and the shield bracket is one of the main working partsof shield tunneling equipment.The structure of shield bracket is directly related to the quality of the tunnel project and the costs and service life of cutting tool.Because the overall size of shield bracket is larger while its local design size is relatively small and design installation and testing are very complex with high cost and complex on-site maintenance, high requirements on bracket design are put forward.
With complex cutterhead design structure and great construction intensity, the bracketwhich transfers power to the cutterheadis required to be with high strength.Therefore, it is needed to check the bracket's strength so as to ensure the project needs.Because of the restrictions of the shield tunneling machine itself and construction environment, both the costs and conditions of multiple tests in physical environment are difficult to achieve the requirements.As a result, under the condition of simulation, using 3D modeling software and finite element analysis software to make mechanical analysis and intensity checking can quickly optimize the cutterhead bracket design.Reasonable structure, as one of the key technologies of the shield, can not only ensure the high-efficiency operation of the shield construction machine, but also improve the service life of cutterheadand many other parts of the machine and narrow tool cost.
The work to research shield bracket has not been done clearly before.This paper puts forward a simulation design method specialized for the strength of shield bracket, and it combinesthe analysis of the stress and strain fields of the structure element with the shield bracketwhich isdesigned and checked by Ansys, one kind of powerful analysis system, the targeted physical experiment strength analysiscan be realized so as to finish the rapid and effective design.w ( 2l 1 )l   ems in elastic d finally is the of the stress and the defor he cloud atlas stress variation loud atlas for s n Applied Scienc 30 criterion.
here is the stre     According to the calculation results, under the extreme condition, the bracket equivalent stress mostly distributes between 0.0197 MPa and 83.212 MPa , and the stress distributions are rather even.The maximum equivalent stress is 187.2MPa , which is less than the material allowable stress 275 MPa ; the minimum safety coefficient is 1.4; the biggest Von-Mises stress occurs in the bracket root, while through the measurement in field experiment, the maximum equivalent stress is 166 MPa , so they have a difference of 12%, which can meet the requirements.Although shield construction machine operates continuously, and bracket shall not be replaced in a construction process except in special circumstances, the alternating stress changeslightly, this kind of design schema can meet the construction requirements.Much more attention should be paid on the bracket which can be strengthened properly without impacting the material cost and operating condition, so as to improve the overall performance.
The whole design is safe, and from the view of stress analysis, there is great potential about the ability of the material's resistance to damage, and stress concentration may exist in the maximum equivalent stress of node, for the cutterhead, as the stress surface, is approximately simplified to arigid body structure in order to study the bracket intensity.But the stress value is far lower than the ultimate strength of material, and the stress concentration will not affect bracket stiffness.In actual work process, the power transferred from the cutterhead special structure will not cause stress concentration.

Conclusion
Using Solidworks and ANSYS to analyze the stress characteristics of bracket in shield construction machine under extreme conditions, the bracket's stress, deformation and safety coefficient distribution rules are obtained.
Through analyzing the designed bracket with actual situation, physical experiment will be more targeted for the test of shield construction machine bracket.Thus shield construction machine bracket which can meet the practical construction requirements shall be designed, as well as reduce the design and experiment cost.Besides, the study results can provide design reference for the similar bracket structure design and engineering construction maintenance.