Failure Analysis of the Fracture of a Spring Hanger

Abstract

The small spring hanger analyzed in this paper is made of 60Si2MnA spring steel. In the past, this kind of hanger has performed well in the acceptance test and is used by many customers; however, in a recent batch of these hangers, the first tested hanger accidentally fractured in the lifting test. Thus, the acceptance test failed. Then, the tensile test was performed on a random sample of hangers from the same batch, and the tensile strength was found to be much lower than the design requirements. In fact, the tensile strength was 30% less than the normal strength, which can result in low stress fractures at loads below the normal bearing capacity of the material. In order to find out the cause of the failure and to solve the fracture problem, a fault tree was built according to the fracture shape and manufacturing process of the hangers. The fracture morphology and the mechanical properties of the hangers were examined, and the working conditions, manufacturing process, and production site were all investigated. A verification test of production was also conducted after data collection and preliminary analysis. Results of the fault tree and the verification test indicated that the main cause of hanger failure was that the dehydrogenation treatment was not carried out in a timely manner after chemical plating of the hangers in this batch; the poor dehydrogenation effect led to hydrogen brittleness failure of the hanger. This failure analysis shows that for spring steel bearing parts, effective dehydrogenation treatment should be conducted immediately after plating so as to prevent hydrogen brittleness and ensure reliability and safety of the product.