Fatigue Behavior Of Aluminum Alloy Research Articles

Probabilistic fatigue cumulative damage model considering the randomness of load and material properties

A probabilistic fatigue cumulative damage model that can be applied to the fatigue life prediction of aluminum alloy under spectrum loading is proposed in this paper. The model is constructed by a novel nonlinear cumulative damage model, the P–S–N curve, and the probabilistic load–exceedance curve. It introduces the randomness of the loading process and fatigue resistance of the material to the deterministic model. In this model, it is derived that the cumulative damage under fleet spectrum loading exhibits an approximate lognormal distribution, and a method to calculate the distribution parameters is provided. Finally, the validity of the proposed probabilistic model is verified through fatigue tests on 2297-T87 aluminum–lithium alloy specimens under random loading, demonstrating its capability to capture the probabilistic nature of the fatigue behavior of aluminum alloy effectively.

Corrosion mechanism and fatigue behavior of aluminum alloy with high silicon content

The corrosion and corrosion-assisted fatigue life degradation behaviors of Al–8Si alloy is investigated. The test results show that galvanic cells are formed in the inter-dendrites due to high Si concentration, leading to pitting corrosion. The Al2Cu phase and the Si-rich phase precipitate at the grain boundaries in the inter-dendrites, among which the Al2Cu phase is the most critical factor leading to intergranular corrosion. Subsequently, intergranular corrosion gradually develops into intragranular corrosion attributed to the higher dislocation energy in fine-grained Al grains. Additionally, it is found by comparing the corrosion potential and corrosion rate that high Si concentration would cause the decrease in corrosion resistance. Finally, the fatigue test results show that the corrosion could reduce fatigue life of Al–8Si alloy by 79.77% on average. Therefore, the corrosion-induced fatigue life degradation is very worth to be considered in structures.

Effect of primer and sealant in refill friction stir spot welded joints on strength and fatigue behaviour of aluminium alloys

The refill friction stir spot welding (RFSSW) is one of the promising friction stir welding (FSW) methods consisting in the joint creation by plunging and retracting the rotating tool into the overlapped sheets without an exit hole after welding.This work aims to fulfil a knowledge gap related to use of aluminium semi-products in a final configuration state (including anodizing, primer and sealant application) for RFSSW process by means of the lap-shear and cross-tension mechanical test, fatigue performance, metallographic and fractographic analyses, and digital image correlation (DIC) technique. Sheet semi-products of thicknesses from 2 to 3 mm made of AA7050-T7451 and AA2024-T3 aluminium alloys in bare and/or anodised condition were used for the lap-joint specimens manufacturing and five various material joint combinations were analysed.The effect on static strength for the joint configurations with primer and sealant was studied and compared with the bare materials’ RFSSW joints. Fatigue tests showed that the primed configurations exhibited a higher scatter of the results and a different slope of fatigue curve with a higher fatigue limit value as compared with the bare material’s joints exhibiting a higher ultimate static strength.

Evaluation of creep-fatigue life and strength for AA7001-T6 under constant amplitude loading

Aluminum alloys were widely used in the construction, automotive, marine, and aviation industries due to their low specific strength, ease of manufacture, and low weight. The fatigue behavior of aluminum alloys at different temperatures is investigated. Thanks to the rapid development of armament in recent years, 7XXX ultra-high strength aluminum alloys are now used more frequently because of their non-corrosive qualities and low weight. Aluminum alloy 7001-T6 behavior is examined at the Company State for Engineering, Rehabilitation, and Inspection (SIER) in Iraq, where chemical analysis of the AA7001 is supported. Most engineering components that operate at high temperatures will eventually fail from fatigue strain, creep damage is a time-dependent process that is primarily influenced by the history of stress and temperature applied to the component. When the two damaging factors combine their effects, This study used AA7001-T6 to conduct experiments on mechanical characteristics (UTS, YS, E, and ductility) and the interaction between creep and fatigue at four distinct temperatures: room temperature (25, 150, 280, and 330) °C, the UTS, YS, and E were lowered by 37.2, 37.2, and 24) %, respectively, as compared to the result at room temperature, but the ductility increased by 28.27 %. It has been noted that rising temperatures cause mechanical and fatigue characteristics to decline. Experimental S-N fatigue test findings showed a significant loss of fatigue strength, After 107cycles, the endurance fatigue limit was reduced from 208 MPa at (RT) to 184 MPa at 330 °C, an 11.5 % reduction. Overall, it can be said that AA7001-T6 demonstrates a significant drop in mechanical and fatigue properties at high temperatures

High cycle fatigue behavior of bimetallic Al 7025/CP-Mg rods produced by rotary swaging

This study aims to investigate the monotonic uniaxial tensile/compressive properties and the high cycle fatigue behavior of aluminum alloy 7025 (Al 7025)/commercially pure magnesium (CP–Mg) bimetallic rods produced via rotary swaging method at ambient temperature. In these lightweight bimetallic rods, the outer layer of aluminum can protect the magnesium core from corrosion and improve the rods' mechanical properties. The microhardness and microstructure were studied in the cross-section of the rods to investigate the manufacturing process effects on the starting materials. Based on the obtained results, under the compressive loading, the ultimate strength of the Al/Mg sample increased by 34% compared with the pure magnesium sample. Furthermore, while only 31% of the bimetallic cross-section is composed of aluminum, the tensile and compressive yield strengths of Al/Mg specimens are closer to those of the aluminum specimens. Microhardness results and the microstructural evaluation indicate that no significant chemical interface is formed between the layers. According to the fatigue test results, adding the outer layer of aluminum can increase the fatigue life more than ten times, compared with the monolithic magnesium specimens. The aluminum layer acts as a deterrent agent, delaying crack initiation and causing such substantial life improvement. The aluminum layer plays a more significant role at the lower stress levels, where most of the fatigue life is spent on crack initiation. Based on the finite element analysis, compared to the monolithic magnesium specimen at the same position, adding an aluminum layer around the magnesium core causes a 46.8% reduction in the maximum stress at the surface of the magnesium core in the bimetallic specimen. The fractography shows that the cracks initiated at the surface and propagated through the aluminum sleeve are barricaded by Al/Mg interface, resulting in new crack initiation sites on the magnesium core.

On the low-cycle fatigue behavior of aluminum alloys under influence of tensile pre-strain histories and strain ratio

The present study attends to the effect of tensile pre-strain histories and strain ratio on cyclic deformation behavior of 6061 aluminum alloy and 2024 aluminum alloy. Low-cycle fatigue tests performed in this study covered two areas; Under fully reversed conditions, with 8% tensile pre-strain, 4% tensile pre-strain, and 0% tensile pre-strain, at strain amplitudes varying in the range 0.6–1.75%; Under strain-controlled circumstances at three different strain ratios [−1, 0, and 0.5] with strain amplitudes varying in the range 0.60–1.75%. The outcomes indicate that the material demonstrates a cyclic strain-softening behavior whose degree rises with rising values of strain ratio and reducing values of strain amplitude. The material demonstrates a non-Masing behavior for higher strain amplitudes amid the interval [1.00%−1.75%]. The material demonstrates a nearly-Masing behavior for lower strain amplitudes amid the interval [0.6%−0.85%]. Under non-zero mean strain, a total relaxation of mean stress is observed at higher strain amplitudes, whereas at lower strain amplitudes, no such behavior is observed.

Fatigue Life Prediction of AA6063-T6 under Erosion Condition

The study of fatigue behavior of aluminum alloy 6063 exposed to periodic fatigue stresses was studied in laboratory conditions under the two conditions of the presence of the first indentation in the first test, then the presence of the phenomenon of erosion in the second test resulting from the projection of pure water Jet on samples of the same metal used in The first test. The purpose of these tests was to estimate the practical life of these samples and the resulting accumulation by using upward and downward variable stresses. A mathematical model was built to calculate the life of the samples in the above conditions, and the results of the estimated life of the samples calculated by the model showed a large convergence with the results of the estimated life of the samples practically calculated. So this mathematical model can be used to estimate the life of samples made of different minerals under these same conditions, after knowing the (S-N) curve for each metal and the amount of the value of the fatigue notch factor (Kf), which can be calculated from special tables without referring to performing practical tests for them.

Micro-mechanical investigation of fatigue behavior of Al alloys containing surface/superficial defects

A crystal plasticity finite element (CPFE) simulation framework has been proposed in this study for the prediction of combined detrimental effect of mean stress and defects on the fatigue behavior of aluminum alloy. Experimental data for mean-stress effect on fatigue life and crack growth behavior was obtained on metal inter gas (MIG) welded joints of Al-5083/Al-5.8%Mg alloy plates and has been detailed in authors’ previous work, referred later. The present study focuses on its prediction using computational framework only. A 2D representative model for material’s microstructure was used for the simulations, generated using an anisotropic tessellation algorithm using the EBSD measurements data. A total of 10 different microstructure models were generated for each loading condition using six-node plane strain type quadratic triangular (CPE6) elements of mesh size 6 μm. Two different types of cases were investigated: one without defect and other with a semi-circular surface defect. The simulated loadings at different stress ranges and stress ratios (R-ratio) were similar to the experimental conditions for the better comparison of the results. Significant heterogeneity in the distribution of R-ratios and the far-field applied R-ratio was observed. When defect was not considered, a clear deviation in the predicted fatigue lives from the experimental data was observed at different R-ratios: the predicted fatigue lives were higher than the experimentally observed fatigue lives. This was probably because of not considering the detrimental effect of defects on fatigue lives. But, when the defects were considered, the predicted results for different R-ratios were consistent with the experimental fatigue lives. The proposed CPFE simulation framework not only predicted well the effect of defects and mean stress on the fatigue lives, but also the scatter induced in them due to the defects.

Investigating the effect of cold expansion process on the fatigue behavior of aluminum alloy 7075-T6 in double-lap shear joints

In this paper, the effect of cold expansion process on the fatigue behavior of 7075-T6 aluminum alloy has been investigated both by numerical modeling and conducting experimental tests. In the experimental part, one batch of the specimens without cold expansion and two other batches after being subjected to cold expansions of 1.5% and 4.7% were subjected to cyclic loading in a double-lap shear joint. In the numerical part, finite element simulations of the cold expansion process and loading of the joint were performed and the effect of this process on the stress distribution and the location of the critical zone of the fatigue crack initiation were surveyed. Tangential stresses at different angles around the hole were extracted from the finite element analysis, and after determining the angular position of the surfaces with maximum stresses, crack initiation location in the thickness direction is predicted with an acceptable approximation. The S–N diagrams obtained from the experiments show that the cold expansion process increases fatigue life, and this increase is much more pronounced in lower loads. Also by increasing the percentage of cold expansion from 1.5% to 4.7%, this increase is more appreciable.

Correlation between Thermal Behaviour of AA5754-H111 during Fatigue Loading and Fatigue Strength at Fixed Number of Cycles.

The characterization of the fatigue behaviour of aluminium alloys is still capturing the attention of researchers. As it is well known in literature, for certain alloys, in a specific range of cycles number, the S-N curves do not present any asymptote. So that, problems result in the assessment of the fatigue life. In these conditions, the concept of the fatigue limit has to be replaced by the fatigue strength at a fixed number of loading cycles. Temperature acquisitions during fatigue tests allow for a specific analysis that can support the researchers in understanding the complex processes that are involved in fatigue and their influence on fatigue life, even for aluminium alloys. In fact, the analysis of the surface temperature signal that was detected during a self-heating test provides a curve that is characterized by a distinct slope-change point at a specific stress value. Even though researchers have been investigating fatigue life characterisation and temperature variations for more than a decade, it is not clear what this point represents in terms of fatigue strength. The aim of the present paper is to find out a possible correlation between the thermal behaviour of AA5754-H111 undergoing self-heating testing procedure and fatigue strength at a specific loading cycles.

Influence of salt corrosion on the fatigue behaviour of aluminium alloys for chassis components under constant and variable amplitude loading

AbstractThis paper presents an approach to assessing the cumulative fatigue under spectrum loading and simultaneous salt corrosion for aluminium alloys. Fatigue tests, in air and in 5 % sodium chloride solution, were performed with two different structural aluminium alloys (EN AW‐6082 T6 and EN AW‐7075 T73) using unnotched and notched specimens. The alloy EN AW‐7075 T73 proved to be unsuitable for automotive applications due to its high susceptibility to corrosion. For fatigue lifing, a modified cumulative damage calculation based on the material susceptibility, which comprises the influence of salt corrosion on fatigue lifetime, has been proposed. On this basis, potential structural aluminium alloys for chassis applications can be evaluated and selected, prior to validation tests.

Effect of electrical discharge machining on corrosion and corrosion fatigue behavior of aluminum alloys

Electrical discharge machining (EDM) is often used in the manufacturing of fatigue test coupons because it allows for the production of complex shapes and sharp starting notches. However, the effect that the machining process has on the corrosion susceptibility due to the surface alterations is unknown. This work focuses on the effect the machining method has on the corrosion and corrosion fatigue behavior of aluminum alloys. The study is aimed at understanding the influence of EDM processes on environmentally assisted cracking evaluations, namely crack growth rate. Conventional milling and electrical discharge machining were the machining process examined in this study; the machining parameters used were best practices for laboratory fatigue sample production. The following aluminum alloys (AA) 2024-T351, 5083-H116, 6061-T6 and 7075-T651 were evaluated in this study. EDM was performed using a 0.152 mm (0.006 in.) hard brass wire. Surface quality evaluations, microstructural analysis, electrochemical tests and corrosion fatigue testing in sodium chloride (NaCl) solution were completed. The study found corrosion rates are affected by the EDM machining in all aluminum alloys. In final testing, crack growth rate tests were completed in sodium chloride solution with starter notches that were traditionally cut and EDM machined for 7xxx and 2xxx series alloys. The testing showed accelerated fatigue crack growth rates for the samples with EDM notches as compared to cut notches.

Fatigue behavior of Al2024 alloy-matrix nanocomposites reinforced with multi-walled carbon nanotubes

Abstract Fatigue behavior of aluminum alloy 2024 (Al2024) matrix composites reinforced with multi-walled carbon nanotubes (MWCNTs) is investigated under the tension–compression fatigue test condition. Tensile and fatigue strength of the Al2024/MWCNT composites increases with increasing the MWCNT content. Al2024/4 vol.% MWCNT composite shows the notably enhanced fatigue strength of 600 MPa at the 2.5 × 106 cycles and the ratio of tensile strength to fatigue strength of 0.78. When the composite is cyclically loaded, the developed incompatibility between the matrix and the fiber induces the fiber pull-out (not shown under tension) and it acts as a bridge when the cracks propagate. Thus, as the content of MWCNT increases in the composite, the prevailing bridging behavior of MWCNTs enhances the number of fatigue cycle, thereby increasing the fatigue strength.

Preliminary evaluation of the fatigue behaviour of aluminium alloy in corrosive environment

Purpose – The purpose of this paper is to investigate the effect of fatigue life reduction of 2024 Al alloy for aerospace components due to the corrosive (exfoliation) environment. Both standard fatigue tests on prior corroded samples and fatigue tests conducted with the samples in corrosive solution are developed to define some guidelines for the inclusion of such effect in design and to improve aircraft life management. Design/methodology/approach – The effect of corrosion is taken into consideration, introducing specific concentration factors into the life estimation relationship. Differences between fatigue in corroded specimens and fatigue in presence of corrosive environment are emphasized. No crack propagation is considered. Two alternative procedures are considered in the analysis: “a-procedure” based on maximum stress calculated on un-corroded sample section; “b-procedure” based on stress calculated on final residual section, including corrosion. Findings – Related concentration factors are deriv...

ICOPE-15-C153 Application of the Three-Dimensional Reconstruction in Fatigue Behavior of Aluminum Alloy

ICOPE-15-C153 Application of the Three-Dimensional Reconstruction in Fatigue Behavior of Aluminum Alloy

Effect of Particle Size on the Fatigue Behaviour of Al–Cu–Mg/Bean Pod Ash Particulate Composites

The fatigue behaviour of aluminium alloy (Al–Cu–Mg)/bean pod ash (BPA) particulate composites was investigated. The composites were produced by stir-casting and double layer feeding method using two particle sizes of BPA (100 µm and 55 nm). The fatigue strength tests were conducted on these specimens with a stress ratio of (R) −1. The results obtained show that composite specimens have longer fatigue lives than matrix alloy. The fatigue limit of 167, 135 and 75 Mpa were obtained for the nano-particle (55 nm), micro-particle (100 µm) BPA composites and unreinforced alloy respectively. The Al–Cu–Mg alloy/BPA nano-particles have lower probability of fracture particles. Hence, low cost BPA nano-particles can be used to enhance the fatigue strength of aluminum matrix composites for automobile industry.

Influence of casting defects on fatigue behaviour of A356 aluminium alloy

The fatigue behaviour of A356 cast aluminium alloy under 104 cycles was investigated by a servo-hydraulic machine at the temperature of 150°C. The specimens for the fully reversible tension compression tests were cut from cylinder head castings of automobile engines. The testing data were treated by S–N curve and the staircase method and the mean values of fatigue property coincided with each other by these two methods, though the data scattered with different casting defects. The fracture surfaces of fatigue specimens were examined by OM, SEM and EDS. It was found that in most of the specimens two or more fatigue crack initiations appeared at a fracture surface. Compared with casting defects such as oxide film, inclusion and blowhole, shrinkage porosity is more detrimental to the fatigue behaviour of aluminium alloy castings.

Fatigue Behavior of Aluminum Alloys under Multiaxial Loading

Fatigue Behavior of Aluminum Alloys under Multiaxial Loading

Influence of Load Signal Form and Variable Amplitude Loading on the Corrosion Fatigue Behaviour of Aluminium Alloys

Aluminium alloys are used for a large variety of safety relevant applications for example in the automotive and aviation industries. With the introduction of high strength but possibly less corrosion resistant alloys it is essential to determine if an enhanced sensitisation against corrosion comes into effect under simultaneous mechanical and corrosive loading. Within this work corrosion fatigue tests under constant and variable amplitude loading were carried out on aluminium alloys established for chassis applications such as EN AW-5018 with slightly elevated magnesium content (AlMg3.5Mn), EN AW-6082-T6, EN AW-6110A-T6 and EN AC‑42100-T6 as well as alloys sensitised to corrosion. Sensitisation was obtained by a borderline (17 h at 130 °C) and an excessive (500 h at 130 °C) thermal ageing treatment and elevated copper contents for the forged and cast alloys. Aforementioned alloys and material conditions were assessed concerning the impact of mechanical loading conditions such as load signal type (sinusoidal and square-wave signal), strain rate and load spectra on the damaging process and on corrosion fatigue life. Fatigue tests were complemented by simultaneous determination of electrochemical characteristics as well as the type of corrosion by metallographic investigations.

High-cycle fatigue simulation for aluminium alloy using cohesive zone law

This article describes high-cycle fatigue simulation for 7050-T7451 aluminium alloy using cohesive zone law. A three-dimensional finite element model is developed for fatigue behaviour of aluminium alloy subjected to cyclic bending. A bilinear, cycle-dependent cohesive zone law is implemented with a help of experimental S-N (stress amplitude–number of cycles to failure) data. In the finite element model, a cycle jump strategy is used including stiffness degradation and reduction of fracture energy during cyclic loadings. Additionally, bending experiments are conducted with unnotched specimens and S-N curves are determined. Direct comparison of S-N curves between the simulation and the experiment is performed on bilogarithmic scale. Results show that the proposed method provides a good means of simulating high-cycle fatigue behaviour of aluminium alloys.