scholarly journals Mechanism of Precipitate Microstructure Affecting Fatigue Behavior of 7020 Aluminum Alloy

Materials ◽  
2020 ◽  
Vol 13 (15) ◽  
pp. 3248 ◽  
Author(s):  
Zhaojun Shan ◽  
Shengdan Liu ◽  
Lingying Ye ◽  
Yiran Li ◽  
Chunhua He ◽  
...  
Keyword(s):  
Aluminum Alloy ◽  
Fatigue Crack ◽  
Fatigue Strength ◽  
Fatigue Behavior ◽  
Fatigue Cracks ◽  
Aged Alloy ◽  
Soft Matrix ◽  
Crack Propagation Resistance ◽  
Boundary Precipitate ◽  
Peak Aged

The effect of different precipitate microstructures obtained by different heat treatments on fatigue behavior of 7020 aluminum alloy was investigated. The fine Guinier Preston I (GPI) zones in the under-aged alloy can be repeatedly sheared by dislocations produced in cyclic loading, making the fatigue crack initiate difficultly and fatigue crack path propagate tortuously. Fatigue strength and fatigue crack propagation resistance of the alloy with shearable precipitates are much higher than those of the alloy with unshearable precipitates. The peak-aged alloy with continuous grain boundary precipitate (GBP) and narrow precipitate free zone (PFZ) is prone to initiate fatigue cracks and reduce fatigue strength. With the growth of unshearable precipitates, the fatigue strength of the alloy firstly increases and then decreases. Precipitates with moderate size in the over-aged alloy improve the roughness-induced crack closure (RICC) effect. Soft matrix with appropriate width between the precipitates can promote the slip reversibility and relax the crack tip stress. The fatigue strength of the moderately over-aged alloy reaches to 122.1 MPa at 107 cycles of loading, and the fatigue crack growth rate (FCGR) is 35.6% slower than that of the peak-aged alloy at ΔK of 10 MPa·m1/2.

Influence of Surface Conditions on the Fatigue Behavior of A357 Aluminum Alloy

2016 ◽  
Vol 850 ◽  
pp. 113-119 ◽  
Author(s):  
Shu Nong Jiang ◽  
Shi Yuan Xu
Keyword(s):  
Aluminum Alloy ◽  
Fatigue Strength ◽  
Fatigue Behavior ◽  
Fatigue Cracks ◽  
Optical Microscope ◽  
Cast Aluminum Alloy ◽  
Cast Aluminum ◽  
Machined Surface ◽  
Surface Conditions ◽  
A357 Aluminum Alloy

The influence of surface conditions on the fatigue behavior A357 aluminum alloy was studied in this paper. Four-point bending fatigue tests method were performed to obtain the fatigue strength of A357 cast aluminum alloy specimens with different surface conditions. A joint bearing rig was designed to minimize the experimental error caused by the misalignment associated with a four-point bend test. The results showed that the fatigue strength of specimens with as-cast surfaces was higher those with machined surface roughness of Ra=1.6μm and 3.2μm, while lower than that with Ra=0.4μm. Optical microscope (OM) and scanning electron microscope (SEM) observations, indicating that the fatigue cracks initiate from machined grooves for specimens with roughness of Ra=1.6μm and 3.2μm, while subsurface crack initiates from cast defects inside the specimen with roughness of Ra=0.4. For specimens with as-cast surface, the fatigue cracks initiate from the surface irregularities or cast defects near the surface.

scholarly journals Fatigue Behavior of Non-Optimized Laser-Cut Medical Grade Ti-6Al-4V-ELI Sheets and the Effects of Mechanical Post-Processing

Metals ◽  
2019 ◽  
Vol 9 (8) ◽  
pp. 843 ◽  
Author(s):  
André Reck ◽  
André Till Zeuner ◽  
Martina Zimmermann
Keyword(s):  
Surface Roughness ◽  
Fatigue Strength ◽  
Surface Quality ◽  
Laser Cutting ◽  
Fatigue Behavior ◽  
Fatigue Cracks ◽  
Surface Condition ◽  
Mechanical Polishing ◽  
Fatigue Properties ◽  
Post Processing

The study presented investigates the fatigue strength of the (α+β) Ti-6Al-4V-ELI titanium alloy processed by laser cutting with and without mechanical post-processing. The surface quality and possible notch effects as a consequence of non-optimized intermediate cutting parameters are characterized and evaluated. The microstructural changes in the heat-affected zone (HAZ) are documented in detail and compared to samples with a mechanically post-processed (barrel grinding, mechanical polishing) surface condition. The obtained results show a significant increase (≈50%) in fatigue strength due to mechanical post-processing correlating with decreased surface roughness and minimized notch effects when compared to the surface quality of the non-optimized laser cutting. The martensitic α’-phase is detected in the HAZ with the formation of distinctive zones compared to the initial equiaxial α+β microstructure. The HAZ could be removed up to 50% by means of barrel grinding and up to 100% through mechanical polishing. A fracture analysis revealed that the fatigue cracks always initiate on the laser-cut edges in the as-cut surface condition, which could be assigned to an irregular macro and micro-notch relief. However, the typical characteristics of the non-optimized laser cutting process (melting drops and significant higher surface roughness) lead to early fatigue failure. The fatigue cracks solely started from the micro-notches of the surface relief and not from the dross. As a consequence, the fatigue properties are dominated by these notches, which lead to significant scatter, as well as decreased fatigue strength compared to the surface conditions with mechanical finishing and better surface quality. With optimized laser-cutting conditions, HAZ will be minimized, and surface roughness strongly decreased, which will lead to significantly improved fatigue strength.

Plastic Strain Distribution at the Tips of Propagating Fatigue Cracks

1976 ◽  
Vol 98 (1) ◽  
pp. 24-29 ◽  
Author(s):  
D. L. Davidson ◽  
J. Lankford
Keyword(s):  
Aluminum Alloy ◽  
Fatigue Crack ◽  
Plastic Strain ◽  
Plastic Zone ◽  
Strain Distribution ◽  
Dimensionless Parameter ◽  
Fatigue Cracks ◽  
Crack Tip ◽  
Cyclic Plastic Zone ◽  
Plastic Zones

The techniques of selected area electron channeling and positive replica examination have been used to study the plastic zones attending fatigue crack propagation in 304 SS, 6061-T6 aluminum alloy, and Fe-3Si steel. These observations allowed the strain distribution at the crack tip to be determined. The results indicate that the concepts of a monotonic and a cyclic plastic zone are essentially correct, with the strains at demarcation between these two zones being 3 to 6 percent. Strain distribution varies as r−1/2 in the cyclic zone and as ln r in the monotonic plastic zone. The strain distributions for all materials studied may be made approximately coincident by using a dimensionless parameter related to distance from the crack tip.

scholarly journals Fatigue Behavior of Conventional and Stationary Shoulder Friction Stir Welded EN AW-5754 Aluminum Alloy Using Load Increase Method

Metals ◽  
2020 ◽  
Vol 10 (11) ◽  
pp. 1510
Author(s):  
Abootorab Baqerzadeh Chehreh ◽  
Michael Grätzel ◽  
Jean Pierre Bergmann ◽  
Frank Walther
Keyword(s):  
Aluminum Alloy ◽  
Fatigue Strength ◽  
Aluminum Alloys ◽  
Efficient Method ◽  
Fatigue Behavior ◽  
Friction Stir ◽  
Stationary Shoulder ◽  
Aluminum Sheets ◽  
Load Increase ◽  
Weld Seams

The load increase method, which is highly efficient in rapidly identifying the fatigue performance and strength of materials, is used in this study to investigate friction stir welded (FSW) EN AW-5754 aluminum alloys. Previous investigations have demonstrated the accuracy and efficiency of this method compared to Woehler tests. In this study, it is shown that the load increase method is a valid, accurate and efficient method for describing the fatigue behavior of FSW weld seams. The specimen tests were performed on 2 mm thick aluminum sheets using conventional and stationary tool configurations. It is shown that an increase in fatigue strength of the FSW EN AW-5754 aluminum alloys can be achieved by using the stationary shoulder tool configuration rather than the conventional one.

Mode II Fatigue Crack Behavior in Compact Tension Shear Specimen

2005 ◽  
Vol 297-300 ◽  
pp. 1592-1597 ◽  
Author(s):  
Sam Hong Song ◽  
Jeong Moo Lee
Keyword(s):  
Fatigue Crack ◽  
Crack Surface ◽  
Notch Root ◽  
Fatigue Behavior ◽  
Fatigue Cracks ◽  
Load Condition ◽  
Compact Tension ◽  
Initial Crack ◽  
Shear Loading ◽  
Mode Ii

The need for research on fatigue behavior of mechanical element under mixed-mode loading has been increasing as the user environment today becomes more and more complicated. However there haven’t been enough investigations on behavior in shear loads comparing to those under tensile loading conditions. So, for this paper, we investigated the characteristics and properties of initiation and propagation behavior for fatigue crack observed for different shapes of the initial crack and magnitudes of load in the modified compact tension shear (CTS) specimen subjected to mode II load. In the low-load condition, the secondary fatigue crack was created in the notch root due to friction on the pre-crack surface grew to a main crack. In the high-load condition meanwhile, fatigue crack under shear loading propagated branching from the pre-crack tip. Influenced by the shear loading condition, fatigue crack propagation was retarded in the initial propagation region due to the decrease in crack driving force and friction on the crack surface. In both cases, however, fatigue cracks grew in tensile mode. The propagation direction of fatigue crack under mode II loading was approximately at a 70 degree angle from the initial crack, regardless of its shape and load magnitude.

Effect of Pre-Strain on Fatigue Properties of NHH Rail

2004 ◽  
Vol 261-263 ◽  
pp. 1239-1244
Author(s):  
Wen Xian Sun ◽  
S. Nishida ◽  
Nobusuke Hattori ◽  
X.L. Yue
Keyword(s):  
Fatigue Crack ◽  
Fatigue Strength ◽  
Fatigue Test ◽  
Fatigue Cracks ◽  
Fatigue Tests ◽  
Fatigue Properties ◽  
Slip Lines ◽  
Propagation Behavior ◽  
Strain Process ◽  
Initiation And Propagation

In the present study, fatigue tests have been performed to study the effect of pre-strain on fatigue properties of NHH (New Head-Hardened) rail. The objectives of this study were: (1) to observe the microscopic behavior of specimens during pre-strain process, (2) to research the influence of pre-strain on fatigue strength of NHH rail and (3) to investigate initiation and propagation behavior of the fatigue crack. The results showed that plastic pre-strain decreased the fatigue strength of NHH rail; fatigue limits had no obvious variation among the different pre-strain ratios. Fatigue cracks initiated in the microscopic cracking or slip lines that were originated in the pre-strain process and propagated from these sites in the later fatigue test.

Fatigue Crack Growth of LC9 Aluminum Alloy under Flying Loading with Corrosion Damage

2014 ◽  
Vol 488-489 ◽  
pp. 66-69
Author(s):  
Xu Dong Li ◽  
Zeng Jie Cai ◽  
Zhi Tao Mu
Keyword(s):  
Aluminum Alloy ◽  
Fatigue Crack ◽  
Fatigue Crack Growth ◽  
Crack Growth ◽  
Fatigue Cracks ◽  
Corrosion Damage ◽  
Growth Behavior ◽  
Transport Aircraft ◽  
Suitable Parameter ◽  
Corrosion Pits

This paper investigates the growth behavior of fatigue cracks initiated at corrosion pits in laboratory coupons of LC9 aluminum alloy subjected to a transport aircraft loading spectrum. Corrosion pits were introduced by exposing the coupons to EXCO solution for a variety of periods to produce corrosion damage varying from mild to severe. In general, the presence of corrosion damage reduced the fatigue lives of components to a severe extent. It was found that the depth of the corrosion pit was a suitable parameter for characterizing the corrosion damage and for predicting the fatigue life of the coupons using commercial fatigue crack growth software

Effect of Forging Force on Fatigue Behavior of Spot Welded Joints of Aluminum Alloy 5182

2006 ◽  
Vol 129 (1) ◽  
pp. 95-100 ◽  
Author(s):  
B. H. Chang ◽  
D. Du ◽  
B. Sui ◽  
Y. Zhou ◽  
Z. Wang ◽  
...  
Keyword(s):  
Residual Stress ◽  
Aluminum Alloy ◽  
Welded Joints ◽  
Fatigue Behavior ◽  
Fatigue Cracks ◽  
Element Analysis ◽  
Aluminum Alloy 5182 ◽  
Forging Force ◽  
Positive Effect ◽  
Spot Welded

Using experimental and finite element analysis methods, the effects of electrode forging force are investigated on fatigue behavior and residual stress of spot welded joints of aluminum alloy 5182. Results show that applying forging force significantly reduces the residual stresses in the heat affected zone and the fatigue cracks no longer initiate from there; instead, all cracks begin from the nugget edge. In addition, the mitigation of residual stress by forging force decreases the driving force for crack propagation and leads to longer fatigue life. It can be concluded that applying forging force appropriately has a positive effect on the fatigue strength of resistance spot welded joints.

Fatigue Behavior and Damage Mechanism of a Cast Aluminum Alloy in Very High Cycle Regime

2011 ◽  
Vol 264-265 ◽  
pp. 706-711
Author(s):  
Hong Qian Xue ◽  
E. Bayraktar ◽  
Claude Bathias
Keyword(s):  
Aluminum Alloy ◽  
Fatigue Crack ◽  
Fatigue Fracture ◽  
Loading Condition ◽  
Fatigue Behavior ◽  
Axial Loading ◽  
Cast Aluminum Alloy ◽  
Cast Aluminum ◽  
Fatigue Fracture Surface ◽  
Very High

An improved understanding of fatigue behavior of a cast aluminum alloy (2-AS5U3G-Y35) in very high cycle regime was developed through ultrasonic fatigue test in axial and torsion loading, cyclic loading in axial and torsion at 35 Hz and 20kHz with R=-1 was used respectively to demonstrate the effect of loading condition. S-N curves obtained show that fatigue failure occurred in range of 105 -1010 cycles in axial or torsion loading, the asymptote of S-N curve is inclined gently, but no fatigue limit under torsion and axial loading condition. Fatigue fracture surface shows fatigue crack essentially initiated from the surface of the specimens subjected to cyclic torsion load, it is different from the fatigue fracture characteristic in axial loading which fatigue crack initiate from subsurface defect in very high cycle regime. Fatigue initiation is on the maximum shear plane, the overall crack orientation is observed on a typical spiral 45° to the fracture plane, which is the maximum principle stress plane, however, shear strip are very clear in the torsion fatigue fracture surface, the torsion fracture is actually in shear fracture.

Fatigue behavior of an Fe48Cr15Mo14Er2C15B6 amorphous steel

2007 ◽  
Vol 22 (2) ◽  
pp. 544-550 ◽  
Author(s):  
D.C. Qiao ◽  
G.Y. Wang ◽  
P.K. Liaw ◽  
V. Ponnambalam ◽  
S.J. Poon ◽  
...  
Keyword(s):  
Fatigue Crack ◽  
Crack Propagation ◽  
Fatigue Crack Propagation ◽  
Fatigue Behavior ◽  
Fatigue Cracks ◽  
Fatigue Crack Initiation ◽  
Al Alloy ◽  
Test Environment ◽  
Sinusoidal Waveform ◽  
Amorphous Steel

Four-point-bend fatigue experiments were conducted on the Fe48Cr15Mo14Er2C15B6 bulk metallic glass (BMG), amorphous steel, under load control, employing an electrohydraulic machine, at a frequency of 10 Hz (using a sinusoidal waveform) with an R ratio of 0.1, where R = σmin./σmax. (σmin. and σmax. are the applied minimum and maximum stresses, respectively). The test environment was laboratory air. Fe48Cr15Mo14Er2C15B6 exhibited a high fatigue-endurance limit (682 MPa), which is found to be greater than those of the Zr-based BMG, Al-alloy, and high-nitrogen steel. However, the stress versus number of fatigue cycles curve of Fe48Cr15Mo14Er2C15B6 has a significantly brittle fracture mode. Some fatigue cracks initiated from the inclusions or porosities, and the fatigue-crack propagation region was large. However, other cracks initiated from the outer tensile surface of the specimen, and the fatigue-crack propagation region was very small. The mechanisms of fatigue-crack initiation are suggested.

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