Prediction technique for dynamic stress on bellows exhaust pipe (2) (Dynamic stress analysis of multilayer bellows using equivalent stiffness model)

Abstract

We developed a new prediction technique for dynamic stress on a bellows with low computational load, to secure the strength reliability of the multilayer bellows used in the engine exhaust system of hydraulic excavators. In this developed technique, dynamic stress is predicted by constructing the bellows finite element model with single-layer shell elements having stiffness equivalent to that of the multilayer bellows and selecting appropriate excitation conditions for each stress-generating factor. The stress time waveform calculated by the developed prediction technique was verified by actual measurement results, and the following conclusions were obtained: (a) The causes of dynamic stress on the bellows were specified and classified into the two classifications. One is the deformation of the bellows caused by relative displacement. The other is the deformation caused by the bellows vibration modes; (b) Appropriate excitation conditions of the bellows model are forced displacement input for predicting dynamic stress caused by relative displacement, and forced acceleration input for predicting dynamic stress caused by the bellows vibration modes; (c) The calculation results derived by using the above model and the excitation inputs were verified by measuring a vibration bench test. The calculated stress had relative agreement with measured stress in the test.

Keywords

• hydraulic excavator
• bellows
• multilayer
• excitation
• transient response analysis
• impulse testing