Failure analysis on abnormal cracking of polycarbonate plates used in the gearbox oil level gauge for high-speed train

The gearbox of bogie is the core transmission component of the high-speed train. Once its parts have problems, this will cause hidden danger to the running of the train. Therefore, the safety of the gearbox parts must be paid special attention. The failed samples studied in this paper were the polycarbonate (PC) plates used in the gearbox oil level gauge and seven PC plates were found failure during routine maintenance for a certain type of high-speed train. Among them, five plates had cracks parallel to the oil level and close to the middle area, while other two plates had cracks near the circular arc area and lay at an angle of 45 degrees with the level line. In order to find out the root cause of their failure, a variety of material analysis methods were used to examine the properties of the materials, and the fracture morphologies were studied in detail by means of macro and micro observations. The analysis results show that the causes of the failed PC plates could be divided into two types, one was caused by environmental stress cracking and thermal fatigue and the other was caused by forced installation when the length of the PC plate was a little larger. According to the correct determination of the failure causes, the pertinent countermea-sures like length reduction of the PC plate and spraying special transparent coating on the PC plate have been put forward, which have been proven very effective after execution.