Prediction technique for dynamic stress on bellows exhaust pipe (1) (Finite element (FE) modelling of bellows exhaust pipe)

A bellows is a type of flexible joint. It has sufficient strength to withstand increases in internal pressure and flexibility so that it can expand and contract because it has an accordion-like structure with many-plates. In the hydraulic excavator, the bellows exhaust pipe connects the engine and the muffler. It is heated by high-temperature exhaust gas and also exposed to thumping vibration from the engine and the body. To ensure pipe reliability in these harsh conditions, we have to develop a technique to evaluate the bellows strength accurately in the design phase. In this study, on the basis of theoretical formulas listed in the Japanese Industrial Standards (JIS), we developed a bellows analytical model by using single shell elements with equivalent stiffness. Also, we modified the model by considering the contact effect to achieve higher accuracy. Then we evaluated the bellows exhaust pipe model which contains modified bellows models by comparing calculation results and measurements in the modal testing and the tensile shear test. From the results, we confirmed that the developed model can imitate the vibration characteristics and stress distribution accurately. In the next step, we will develop a prediction technique for dynamic stress on the bellows that occurs when the excavator is operating.