Strain sequence effect on fatigue life and fracture surface topography of 7075-T651 aluminium alloy (original) (raw)
Related papers
Structural and Fractographic Analysis of Aluminum Alloy before and After Fatigue Loading
Manufacturing Technology
The article is focused on the analysis of the structure and fracture surface of aluminum alloy specimens. Aluminum alloy AlMg9 was mainly used as an experimental material. The material from which specimens were made was supplied as cast without heat treatment, and specifically the material was produced by the continuous casting method. The structure of the test material was examined using a Neophot 32 optical microscope, and the fracture surface of the test specimen was examined using a scanning electron microscope (SEM). The fatigue life of the aluminum alloy was tested by method of a three-point bending cyclic loading using the parameters-frequency f = 100 Hz, temperature T = 22 ± 5 ℃ and stress ratio R = 0.11. The analysis showed that cast aluminum alloys are very sensitive to casting defects, such as porosity or the content and distribution of intermetallic phases. If large pores or phases are present on or near the surface of the sample, this can be the dominant cause of fatigue crack initiation and reduction of the fatigue lifetime. Aluminum Alloy Fracture Surface Structure Fatigue Bending Loading
International Journal of Fatigue, 2016
Aim of this study is an interpretation of the influence of variable-amplitude (VA) cycles superimposed to low-frequency loads on fatigue life of 7075-T651 Al-alloys. Constant-amplitude (CA) 20 kHz stress/ strain-life (S-N) and (e-N)-curves with and without superimposed mean loads serve as basis. For combined fatigue loading, lifetime measurements were performed. Lifetime estimations based on the S-N results reveal a damaging effect of the superimposed ultrasonic vibrations in the high cycle fatigue (HCF) and the very high cycle fatigue (VHCF) regimes. The CA and VA-life time results are correlated with fractographic observations. An interpretation of fatigue lives under combined low and high-frequency VA-loading is proposed considering small/short-crack propagation and arrest mechanisms.
Effect of pre-strain on the fatigue life of 7050-T7451 aluminium alloy
Materials Science and Engineering: A, 2007
The effect of pre-straining of 1%, 3%, 5%, and 7% on fatigue life of 7050-T7451 aluminium alloy has been evaluated. Using dogbone unnotched flat specimens, axial fatigue tests were conducted under a constant amplitude sinusoidal wave loading at stress ratio of 0.1 in air at room temperature. The results demonstrate a tendency of fatigue life reduction with the pre-straining level. Optical microscopy analysis revealed that the pre-straining anticipates some microstructural changes occurring during fatigue testing, such as slipped grains and persistent slip bands (PSBs) formation, which are commonly related to fatigue life reduction. However, heterogeneities observed in the material make this reduction less prominent. Statistical analysis using a bootstrap method suggests also a reduction in fatigue life with increasing the pre-strain level.
Fatigue Crack Tip Strains in 7075-T6 Aluminum Alloy
Fatigue & Fracture of Engineering Materials and Structures, 1987
The plastic enclave surrounding a fatigue crack in a 7075-T6 aluminum alloy specimen is studied using moire interferometry. Two distinct plastic zones are identified from inspection of moire interferometric fringe patterns. The sizes and shapes of the monotonic and the cyclic plastic zones are correlated with previous theoretical and experimental results. Live load strain distributions in the plastic enclave are computed from high sensitivity (0.417 micron per fringe) full-field in-plane displacement contour maps. Comparison with theoretical and experimental strain distributions are included. NOMENCLATURE crack length frequency (Hz) active grating frequency (l/mm) reference grating frequency (l/mm) stress intensity factor plane strain fracture toughness maximum stress intensity factor minimum stress intensity factor specimen length applied load applied stress ratio (
Fatigue and Crack Growth in 7050-T7451 Aluminum Alloy Under Constant- and Variable-Amplitude Loading
Journal of Engineering for Gas Turbines and Power, 2013
The 7050 aluminum alloy is used in many aerospace structural applications. Previous studies have identified that fatigue cracks develop very rough crack-surface profiles, which cause very high crack-closure levels due to a combination of plasticity, roughness and debris. Previously, tests were conducted on compact, C(T), specimens to generate crack-growth-rate data from threshold to near fracture over a wide range in stress ratios (R). New threshold testing methods, based on compression precracking, were used to generate the data in the near-threshold regime. The plasticity-induced crack-closure model, FASTRAN, was used to correlate the data over a wide range in stress ratios and crack-growth rates from threshold to near fracture. To account for the very high crack-closure levels, a very low constraint factor, like plane-stress conditions, had to be used in the model. In addition, the crack-opening loads were measured during these tests using a local strain-gauge method to generate ...
The high-cycle fatigue and fracture behavior of aluminum alloy 7055
Materials Science and Engineering: A, 2000
This paper highlights the results of a study on the high-cycle fatigue, deformation and fracture behavior of aluminum alloy 7055. Specimens of the alloy, in the T7751 temper, were cyclically deformed over a range of stress amplitudes at both ambient and elevated temperatures. While an increase in test temperature was found to have a detrimental influence on cyclic fatigue life of the transverse orientation specimens, little influence was found on the longitudinally oriented specimens. The macroscopic fracture mode was essentially identical regardless of the orientation of the test specimen with respect to the wrought rolled plate. Cyclic fatigue fracture, on a microscopic scale, revealed features reminiscent of locally ductile and brittle mechanisms. The microscopic fracture behavior was a function of test temperature. The mechanisms governing cyclic fatigue life and fracture behavior are discussed in light of the mutually interactive influences of microstructural effects, matrix deformation characteristics and test temperature.
Influence of mechanical properties on load sequence effect and fatigue life of aluminium alloy
JOURNAL OF MECHANICAL ENGINEERING AND SCIENCES
Most of the structural components in real applications are subjected to variable amplitude loading. The load sequence may have a significant effect on the number of cycles to failure. However, the relationship between the mechanical behaviour of material and the load sequence effects has scarcely been reported. Therefore, this paper discusses the influence of mechanical properties on the load sequence effect and fatigue life behaviour of aluminium alloys AA6061 and AA7075. Tensile and fatigue tests were performed according to ASTM E8 and ASTM E466, respectively. The variable amplitude loading signal was obtained from the engine mount bracket of an automobile in normal driving conditions. Constant amplitude loading, and high-to-low and low-tohigh spectrum loadings were derived from the variable amplitude loading to assess the effects of load sequence on fatigue life. The results showed that AA7075 has better fatigue life properties compared to AA6061. Both alloys were significantly influenced by load sequences. The number of cycles to failure for low-to-high spectrum loading is about 56 % higher than the CAL for AA6061 compared to about 82 % higher than the CAL for AA7075. Thus, it can be concluded that the load sequence effect was more pronounced on AA7075 compared to AA6061.
Comparison of Fatigue Life Cycle of Different Aluminium Alloy AA 5083 - AA6062
International Journal of Scientific Research in Science, Engineering and Technology, 2019
Fatigue failure is one of the main reasons for the mechanical failure in engineering materials. To improve the fatigue strength of the material one of the most used method is surface treatment of the materials in which hardness, wear resistance and aesthetics is improved. In this paper a comparative study of fatigue of two different aluminium alloy [AA 5083-AA6062] was conducted. CT specimen of both the alloys was formed as per ASTM-E647 Standard. The result shows that the fatigue life of AA5083 greater than AA6062. In this paper fracture that occur in material during fatigue testing and effect of fatigue life on material is studied. The main purpose of the research presented herein was to study the fatigue crack propagation under loading mode I.
Effects of Geometrical Cross- Section on Fatigue Strength of Aluminum Alloy (6063)
2011
This research constructs a relationship between the geometrical cross section and the fatigue strength of aluminum alloy (6063). Different geometrical cross section specimens were manufactured with the same section space, the specimens were tested under bending and unbending loading conditions. The strain was calculated and fatigue curves were drawn for all different forms of sections. After studying and analyzing the results, it became clear that increasing the sides in any form increases the fatigue strength as the strain is fixed. Fatigue curve equations were derived using computing techniques and connected to find a mathematical relationship between the geometrical shape of the section and fatigue strength. Equation were derived in order to determine the stress or strain, a specimen of a certain section figure can endure to fail under the effect of a number of cycles. The results show a good agreement when applying the same conditions for all specimens.
Procedia Engineering, 2013
Constant amplitude data obtained from smooth specimens have been used for many years to evaluate the fatigue life of components. However, most of the loadings used in real applications are variable or random. This paper discussed the analysis on fatigue signal of Al 6061 specimen under three types of loading sequences, i.e. constant loading (CL), Hi-lo (HL) and Lo-hi (LH) associating with Integrated Kurtosis-based Algorithm for Z-filter (I-Kaz) technique. Fatigue test was performed according to the ASTM E466-96 standard with attachment of 2 mm strain gauge at the gauge of flat dumbbell shape specimen. Fatigue test was carried out at all the three types of loading stress at the sampling frequency of 8 Hz. Series of strain data were collected throughout the test from initial until failure occur using a data acquisition system. The respective I-kaz coefficients and the three dimensional plot s were used to analyse and interpret the strain signals. Fatigue damage for thress loading sequences were compared, and it was found that the I-kaz coefficient was linearly correlate to fatigue damage, hence, it is worth to see the capability of this method to representing the fatigue damage of metallic materials.