Fatigue crack growth in AlCu4Mg1 under nonproportional bending-with-torsion loading
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FATIGUE CRACK GROWTH IN AlCu4Mg1 UNDER NONPROPORTIONAL BENDING-WITH-TORSION LOADING D. Rozumek1,2 and Z. Marciniak1 We present the experimental results on fatigue crack growth for AlCu4Mg1 aluminum alloy under proportional and nonproportional bending with torsion obtained at the Opole University of Technology. Specimens with square sections and stress concentrators in the form of external one-sided sharp notches were used. The tests were performed in a high-cycle fatigue mode for the stress ratio R = 1 and the phase shift between the bending and torsion loads equal to = 0, 45°, and 90°. Three loading paths were used: line, ellipse, and circle. The fatigue crack growth was cyclically measured with the use of an optical microscope (with a magnification of 25 diameters), strain gauges, and a computer to record the signals of loading. In the tested specimens, it was possible to observe the growth of cracks conforming with the mixed mode I + III. The crack growth was nonuniform on both sides of the specimen surface. However, the difference between the crack lengths was rather small. In the biaxial tests, the influence of bending was six times greater due to the notches in the bending plane. The experimental results are described by range of the stress intensity factor K . Keywords: fatigue crack growth rate, out-of-phase loading, mixed mode I + III, notch.
The development of some modern mechanical structures must include the problems connected with strength and fatigue life. The phenomenon of fatigue crack growth observed in numerous structures and devices is of especial importance. Crack growth under simple loading (e.g., tension, bending or torsion) is often discussed in the literature, while the problems connected with multiaxial loading are studied fairly rarely [1, 2]. The solved problems of crack growth under complex stress states usually deal with proportional loads [3–5]. The tests of fatigue crack growth under nonproportional loads are rarely performed because it is difficult to describe the experimental results. Some data concerning these tests are published in [6]. The authors tested the growth of short fatigue cracks in the mixed mode I + II. The obtained results were described with the help of the J -integral, and new relations were proposed for the correlation of the test results expressed by using the J -integral and the influence of surface roughness. In [7], the authors presented fatigue-crack paths for two steels subjected to nonproportional tension-compression with torsion. Various theoretical models were applied for the description of the test results. The aim of the present paper is to study the fatigue crack growth rate in plane specimens under proportional and nonproportional bending with torsion. The tested specimens were made of AlCu4Mg1 aluminum alloy. Tested Materials and Experimental Procedures Specimens with square sections were tested. 1 2
Opole University of Technology, Opole, Poland. Corresponding author; e-mail: [email protected].
Published in Fizyko-Khimichna Mekhanika Materia
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