Onset Frequency of Fatigue Effects in Pure Aluminum and 7075 (AlZnMg) and 2024 (AlCuMg) Alloys

Abstract

Abstract:The viscoelastic response of pure Al and 7075 (AlZnMg) and 2024 (AlCuMg) alloys, obtained with a dynamic-mechanical analyzer (DMA), is studied. The purpose is to identify relationships between the viscoelasticity and fatigue response of these materials, of great interest for structural applications, in view of their mutual dependence on intrinsic microstructural effects associated with internal friction. The objective is to investigate the influence of dynamic loading frequency and temperature on fatigue, based on their effect on the viscoelastic behavior. This research suggests that the decrease of yield and fatigue behavior reported for Al alloys as temperature increases may be associated with the increase of internal friction. Furthermore, materials subjected to dynamic loading below a given threshold frequency exhibit a static-like response, such that creep mechanisms dominate and fatigue effects are negligible. In this work, an alternative procedure to the time-consuming fatigue tests is proposed to estimate this threshold frequency, based on the frequency dependence of the initial decrease of the storage modulus with temperature, obtained from the relatively short DMA tests. This allows for a fast estimation of the threshold frequency. The frequencies obtained for pure Al and 2024 and 7075 alloys are 0.001-0.005, 0.006 and 0.075-0.350 Hz, respectively.

Viscoelastic behavior of a novel aluminum metal matrix composite and comparison with pure aluminum, aluminum alloys, and a composite made of Al–Mg–Si alloy reinforced with SiC particles

“…1 and Fig. 2 for the various materials are qualitatively similar in most cases and show some common features that were discussed in [4,6,7,13]. The novel AMC shows higher stiffness than the A356 alloy matrix (see Fig.…”

“…For DMA also, rectangular plates with dimensions equal to those mentioned above were machine cut from ingots of A356 alloy and the novel AMC. More details on the studied material and experimental set up can be found for pure aluminum in [4,5], for AA 7075 and 2024 in [13], for AA 6061 reinforced with SiC particles in [8], and for the A356 alloy and the novel AMC in [1,12]. The latter two materials were also analyzed with optical microscope.…”

“…Thus, the objective of this research is to characterize the influence of the temperature, loading frequency and microstructure on the viscoelastic behavior of this novel, low-cost AMC, and compare it with that reported for pure aluminum [4,5] and commercial, age-hardenable aluminum alloys (AA) 7075 (Al-Zn-Mg) and 2024 (Al-Cu-Mg) [6,7], and another AMC made of AA 6061 (Al-Mg-Si) matrix and SiC particles [8]. Studying the viscoelastic behavior of materials, a consequence of mechanical relaxation phenomena under dynamic loading, is interesting because it offers an alternative method for analyzing the microstructure and enables a deeper understanding of properties like mechanical damping and yielding [9], and ultimately fatigue, because metals are subjected to dynamic loading in most structural applications.…”

Mechanical, Thermal and Rheological Properties of Polyethylene-Based Composites Filled with Micrometric Aluminum Powder

“…where c, f, i and m subscripts are related to composite, filler, interphase, and matrix, respectively, while ϕ stands for the volume fraction of each phase. Fillers introduced into polymer matrices, mainly mineral or metallic ones, are significantly more rigid, so their damping is very low [26]. Therefore, their influence on the adhesion factor can be neglected.…”

Very High Cycle Fatigue of Butt-Welded High-Strength Steel Plate

“…The fatigue tests were performed at room temperature. However, heat was generated in the middle of the specimen owing to stress concentration and the internal friction of the steel material [22]. Compressed air was blown on the middle section of the specimen for cooling purposes to avoid experimental errors and any resulting changes in the resonant frequency from the generated heat.…”