Fatigue properties of wood at different load ratios tested at 50 Hz and 20 kHz

Abstract

Fatigue properties of sycamore maple (Acer pseudoplatanus) under cyclic tension, cyclic compression and tension-compression loading at 50 Hz are investigated. Furthermore, for the first time, fatigue test results of wood generated with the ultrasonic fatigue testing technique at 20 kHz under tension-compression loading are presented. Cyclic properties are in line with the static properties -with the tensile strength being more than two times the compressive strength. Mean lifetimes of 10 6 cycles are found if the maximum tensile stress for cyclic tension is 69 % � 8 % of the tensile strength and if the maximum compressive stresses for cyclic compression and tension-compression are 75 % � 7 % and 54 % � 4 % of the compressive strength, respectively. Tension-compression loading at 20 kHz delivers lifetimes comparable to servo-hydraulic tests at 50 Hz, and no pronounced frequency effect on fatigue lifetime is found. Ultrasonic fatigue testing is therefore, in principle, appropriate for accelerated fatigue testing of wood up to the very high cycle fatigue regime. Tests up to 10 9 cycles show no evidence of a fatigue limit for sycamore maple. Keywords: Sycamore maple / cyclic tension / cyclic compression / cyclic tensioncompression / ultrasonic fatigue testing / very high cycle fatigue Die Ermüdungseigenschaften von Bergahorn (Acer pseudoplatanus) wurden unter Zugschwell-, Druckschwell-und Wechselbeanspruchung bei 50 Hz untersucht. Zudem wurden erstmalig Versuche mit dem Ultraschall-Ermüdungsprüfverfahren bei 20 kHz unter Wechselbeanspruchung an Holz durchgeführt. Die zyklischen Festigkeiten zeigen ein ähnliches Verhalten wie die statischen Festigkeiten -die Zugfestigkeit beträgt mehr als das Doppelte der Druckfestigkeit. Mittlere Lebensdauern von 10 6 Lastzyklen ergaben sich, wenn die maximale Zugspannung unter Zugschwellbeanspruchung 69 % � 8 % der Zugfestigkeit und wenn die maximale Druckspannung unter Druckschwell-bzw. unter Wechselbeanspruchung 75 % � 7 % bzw. 54 % � 4 % der Druckfestigkeit beträgt. Die bei 50 Hz und 20 kHz ermittelten Lebensdauern stimmen gut überein und es zeigt sich kein wesentlicher Ein-

Interior micro‐defect induced cracking mechanism and life prediction of carburized Cr−Ni steel based on double nonlinear damage under variable amplitude loading

“…With the continuous progress of production technology, modern service parts are developing towards long service life and high reliability. That is, in machinery, navigation, aerospace, automobile and other industries, many key parts are required to withstand alternating loads of more than 10 8 cycles before they can be damaged [1]. Therefore, very‐high‐cycle fatigue failure has become one of the main failure modes of components, and has been paid more and more attention by researchers [2].…”

“…(1) Depressive decohesion of spherical carbide; (2) Hydrogen embrittlement-assisted cracking; (3) Polygonization and debonding [29,30]. In addition, there are several opinions about the formation of fine grain zone: (1) The grain refinement around the inclusion under cyclic loading will lead to the formation of fine grain zone; (2) The cyclic compressive stress around the inclusion makes the upper and lower concave convex surfaces contact and collide with each other, resulting in the formation of fine grain zone; (3) The compressive stress refinement of micro grains at the crack tip induces the formation of fine grain zone [31][32][33]. Although interior fatigue failure is still a controversial issue, these models more or less reflect the very-high-cycle fatigue characteristics of materials under constant amplitude loading.…”