The fastening bolts of the exhaust manifold are failed during the endurance test.In this paper,different test methods are used to analyze the failure parts in detail from the aspects of product performance,pre-tightening force check and assembly process.It is determined that the pre-tightening force is too small to cause fatigue fracture.In addition,many problems in the design are also found in the analysis process,such as improper material selection and no requirement for the friction coefficient of the bolts.After the corresponding improvements,the new samples are resubmitted to the customer.Then the customer's feedback is that the endurance test passed successfully.
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