Efficient frequency-domain based fatigue life estimation of spot welds in vehicle components

Abstract

The estimation of the damage and fatigue life of spot welds in vehicle components with hundreds or thousands thereof within reasonable computation time is a challenge even for recent computers in automotive industry. Hence, an advanced procedure in the frequency-domain is proposed. Whereas the general frequency-domain approach is well-established, it nevertheless becomes efficient for a large number of spot welds only with a package of measures. Among others, a two-scale FE-method using a pre-processed data base for various spot weld/sheet geometries and specified basic load cases, application of the cutting-plane method, and a priori stress estimations to reduce the number of spot welds to be checked completely are suggested. By the example of a tank of a cooling medium in a vehicle it is shown that the proposed algorithm may reduce the computation time as compared to time-domain calculations substantially. Effiziente Frequenzbereichs-Methode zur Abschätzung der Ermüdungsfestigkeit von Schweißpunkten in Fahrzeugkomponenten Zusammenfassung Eine rechenzeitgünstige Lebensdauerabschätzung einer großen Anzahl von Schweißpunkten in Fahrzeugkomponenten stellt auch für moderne Computer eine Herausforderung dar. Es wird deshalb eine neue Vorgehensweise im Frequenzbereich vorgeschlagen. Während die allgemeine Methode wohlbekannt ist, wird sie für große Anzahlen von Schweißpunkten dennoch erst durch mehrere Zusatzmaßnahmen effizient. Es werden unter anderem eine Zweiskalen-FE-Methode unter Verwendung einer Datenbank für diverse Schweißpunkt-/Blechgeometrien unter definierten Einheits-Belastungen vorgeschlagen, Anwendung der Schnittebenenmethode und A-priori-Spannungsabschätzungen zur Reduktion der vollständig zu untersuchenden Schweißpunkte. Am Beispiel eines Kühlmitteltanks in einem Fahrzeug wird gezeigt, daß die vorgeschlagene Vorgehensweise eine signifikante Rechenzeitreduktion gegenüber Zeitbereichs-Berechnungen ermöglicht.

The Influence of the Motor Traction Vibration on Fatigue Life of the Bogie Frame of the Metro Vehicle

“…ere are only a few research studies about motor vibration fatigue on the metro bogie frame. Some studies show that ① the vertical vibration of the frame suspension traction motor has an evident impact on the frame fatigue strength [6]; ② decoupling optimization of the motor suspension system can effectively improve the vibration isolation to reduce the fatigue damage of the motor seat [7,8]. e above studies have confirmed the importance of the influence of the motor vibration on the fatigue strength of the frame from the obverse and reverse, but have not been studied in detail.…”

Computationally effective spot‐weld fatigue life estimation for vehicle components

“…Essentially, for spot-weld fatigue analyses in timedomain two basic approaches have been followed: First, there are simple FE-models with only a few elements which allow for a rather gross approximation of the stress state only [1]. Subsequently, several measures to speed up frequency-domain fatigue analyses for vehicle components with huge numbers of spot-welds -as implemented in the program FEMSITE of MAGNA STEYR -are outlined [5]. Although the necessary CPU-time is a crucial issue especially in time-domain calculations, it is relevant in frequency-domain methods, too.…”

“…Indeed, whereas the general frequency-domain approach is well-established [3,4], there still is room for improvements with respect to specific problems. Subsequently, several measures to speed up frequency-domain fatigue analyses for vehicle components with huge numbers of spot-welds -as implemented in the program FEMSITE of MAGNA STEYR -are outlined [5].…”

“…2 General frequency-domain approach for fatigue life estimation Figure 1 presents a sketch of the applied basic procedure (for one channel excitation). For the sake of brevity, a few specific characteristics shall be pointed out only: (i) Since the focus is on computational efficiency, just the (maximum) normal stress criterion is applied for fatigue life estimation; (ii) an estimate of the stress Probability Density Function from a stress PSD is obtained by the widely-used Dirlik method [3,5]; this method cannot capture non-zero mean values of the stresses, but they can be added afterwards; (iii) finally, for the damage and the fatigue life estimation, the Smith Watson Topper parameter curve (PSWT) is used [6]. For vehicle components with many spot-welds, in the aforementioned algorithm now the following particular/additional measures are taken.…”

“…2b presents a comparison of CPU-times of time-domain and frequency-domain calculations for different numbers of spot-welds in a vehicle body-in-white. As a supplement, it shall be mentioned that the difference in the damage-values for a single spot-weld predicted by both methods is only of the order of 10% [5].…”