Deformation Behavior and Fatigue Analysis of Magnesium Wrought Alloys under Variable Amplitude Loading

Abstract

The deformation behavior and the fatigue life of AM50 magnesium alloy sheet metals under variable amplitude loading were determined experimentally via strain-controlled tests. Hysteresis loops were recorded precisely to evaluate its shapes and to calculate the fatigue life. A strong basal texture is responsible for non-symmetric and sigmoidal shaped hysteresis loops. Thus, the shape of inner hysteresis loops in variable amplitude tests highly depends on the mean stress. To evaluate the influence of the mean strain on the fatigue life, tests with different load sequences were carried out. For a fatigue calculation, the Smith-Watson-Topper and two energy based fatigue models were compared, where all in all the energy based fatigue models achieved the best results.

An energy‐based approach for uniaxial fatigue life estimation under asymmetric cyclic loading

“…In contrast to Equation (4), Lin et al 24 and Dallmeier et al 25 considered that negative stresses σ min are much less effective than positive stresses σ max when jσ min j < jσ max j. One of these models shown in the literature 25,26 is…”

“…The stress distribution of the beam should be solved first. Taking elastic deformation as an example, Figure 9 shows this stress distribution of the beam mid-section along the x-direction under maximum force F max = 72.2 N, including normal stress σ x and shear stress τ xy which are calculated by Equations ( 24) and (25), respectively.…”

“…It is well established in the existing literature [23][24][25]40 that the tensile-compression state exhibits a marked impact on the fatigue life of metallic materials. Meanwhile, the test data introduced in Section 3.1 shows that although the maximum tensile deformation of metallic material remains unchanged during the action of asymmetric cyclic load, the higher the compressive deformation, the lower the number of cycles.…”

“…Thus, the model of the energy that causes material damage per fatigue cycle is critical. In literatures, the model or energy criterion for this energy is based on total strain energy, [12][13][14][15][16][17] plastic strain energy, [18][19][20][21] elastic strainenergy density, [22][23][24][25][26] the equivalent strain energy computed by the Huber-Mises criterion, 27 the entropy (based on the unified mechanic's theory) calculated with the plastic strain energy, 28 and so on.…”

“…Among them, for fatigue under asymmetric cyclic loading, the combination of peak stress and strain range is generally used to characterize the energy parameter. Other scholars, such as Koh, 22 Lazzarin et al, 23 and Dallmeier et al, 25,26 applied stress range to calculate the energy parameters. These parameters have energy characteristics but have an overlooked problem which is introduced in Section 2.1.…”