Test method for time-scaled fatigue tests of gear transmission systems

Abstract

Under real operating conditions, gear transmissions usually suffer a wide spectrum of loads. The required runtimes, which have to be reached without any damage may cover long periods of time. Tests with the load spectrum in its whole extension are both time and money consuming. The use of shortened test methods can reduce the required testing time and lead to cost savings. In this paper, an extensive test methodology for time-scaled fatigue tests of transmission systems under variable load is presented. The method in general is divided in two steps. In a first step, a load spectrum truncation is performed based on a detailed system analysis of the gearbox. Exemplary the gearing itself is investigated regarding the main damage mechanisms pitting and tooth breakage as well as micropitting and sliding wear. Nevertheless the shown method is also applicable for further components in the transmission. The observed damage mechanisms are investigated locally and analyzed by means of a local damage accumulation. Based on the evaluated (local) Miner sums both the decisive damage mechanism and the damage location can be identified. This approach allows a truncation of the load spectrum without change of the main damage mechanism. An increase of load-levels on the one hand and omission of low loads on the other hand result in a reduced test time. A further reduction of test time is possible by performing and evaluating shortened test runs with the truncated load spectrum without reaching any failure criteria in a second step. The described evaluation is mainly based on destructive and non-destructive examination methods on gears as well as statistical methods which help to estimate the remaining service life of pre-damaged parts. With the described method, a realistic truncation by factor 5 to 20 is possible depending on the original load spectrum and transmission design.