اثبات استحکام محیط مکانیکی
Abstract
1-Introduction
2-Recalling about the method according to the standard
3-Focus on ERS, XRS, FDS and XFS approach
4-Conclusions
References
Abstract
The new standard of strength proof related to mechanical environment – design and implementation of environmental tests – includes new methods of assessment and synthesis of mechanical stresses. This paper proposes to remind the innovations and to constitute a constructive approach, based on their implementation and on the first experiences. The new standards contain new estimators of fatigue damage spectra and shock response spectra. In particular, the major novelty includes a statistical estimation for a given risk of overtaking of the stresses extrema and the damage extrema, which are computed from the measures performed on a duration much shorter than the in service real one. The purpose of these standards is to insure the mechanical design taking into account severe environments which may not have been measured. The authors propose to recall the fundamentals and to perform an analysis based on comparative results. Especially, will its use make the products more reliable? Will the use of these standards become widespread?
Introduction
The new standard AFNOR XP X50-144 « Demonstration of the resistance to environmental conditions — Design and Carrying of environmental tests” offers a synthesis and a guideline of all the tools and methods used to specify an accelerated mechanical endurance test of a specimen. Some of these methods have already been presented in military guidelines as NORMDEF 0101 [1]. The purpose of these methods is to specify an accelerated test performed on usual test bench (vibrating table) based on an equivalent damage between the real measured mechanical environment and the test. This is why these methods are also commonly named “tailoring process for mechanical environment”, in opposition to the historical standards based on fallback approach that do not take into account the measured environment and which often produces a test too severe. In particular, these methods take into consideration two mechanisms of damage: the first one for which a threshold stress value is exceeded, as the yield strength for metallic specimen. The second one, based on accumulated fatigue damage due to stress cycles. The equivalence of damage related to the first mechanism is treated with the Extreme Response Spectrum (ERS), as the equivalence of the second mechanism is reached with the Fatigue Damage Spectrum (FDS).