scholarly journals Fatigue Behavior and Fracture Mechanism of a Hot Rolled AA7020 Aluminum Alloy

2019 ◽  
Vol 9 (03) ◽  
Author(s):  
Ashish Thakur
Keyword(s):  
Aluminum Alloy ◽  
Fatigue Strength ◽  
Crack Initiation ◽  
Crack Growth ◽  
Fracture Mechanism ◽  
Fatigue Behavior ◽  
Constant Load ◽  
Fracture Mechanisms ◽  
Hot Rolled ◽  
Aa7020 Aluminum Alloy

Fatigue tests of smooth specimens and CT specimens of a hot rolled AA7020 Aluminum alloy have been performed in laboratory at ambient temperature. Fatigue strength and fatigue crack propagation (FCP) characteristic were evaluated and fracture mechanism was discussed on the basis of crack initiation, small crack growth, and fracture surface analysis. The growth behavior of small and large cracks has been investigated on 7020 alloy.The FCP resistance was found significantly lower than that of other aluminum alloys. The crack growth measurements were performed in CT specimens at constant load ratios ranging from R = 0.1–0.5. The fatigue strength at 104 cycles was 110 MPa that led to a considerably fatigue ratio of 0.1, fatigue failure did not occur. There existed two different modes of crack initiation depending on applied stress level. Above 200 MPa, cracks initiated at the specimen surface in transgranular or intergranular manner due to cyclic slip deformation, while below that stress subsurface crack initiation took place. The growth of small cracks initiated at the surface coincided with the FCP characteristic after allowing for crack closure for large cracks, but the operative fracture mechanisms were different between small and large cracks.

Effect of Processing Layer on Fatigue Strength of Extruded AZ61 Magnesium Alloy

2013 ◽  
Vol 577-578 ◽  
pp. 429-432 ◽  
Author(s):  
Yukio Miyashita ◽  
Kyohei Kushihata ◽  
Toshifumi Kakiuchi ◽  
Mitsuhiro Kiyohara
Keyword(s):  
Fatigue Crack ◽  
Fatigue Life ◽  
Fatigue Strength ◽  
Magnesium Alloy ◽  
Crack Initiation ◽  
Crack Growth ◽  
Fatigue Crack Initiation ◽  
Fatigue Tests ◽  
Crack Growth Resistance ◽  
Az61 Magnesium Alloy

Fatigue Property of an Extruded AZ61 Magnesium Alloy with the Processing Layer Introduced by Machining was Investigated. Rotating Bending Fatigue Tests were Carried out with the Specimen with and without the Processing Layer. According to Results of the Fatigue Tests, Fatigue Life Significantly Increased by Introducing the Processing Layer to the Specimen Surface. Fatigue Crack Initiation and Propagation Behaviors were Observed by Replication Technique during the Fatigue Test. Fatigue Crack Initiation Life of the Specimen with the Processing Layer was Slightly Longer than that of the Specimen without the Processing Layer. Higher Fatigue Crack Growth Resistance was also Observed when the Fatigue Crack was Growing in the Processing Layer in the Specimen with the Processing Layer. the Longer Fatigue Life Observed in the Fatigue Test in the Specimen with the Processing Layer could be Mainly due to the Higher Crack Growth Resistance. it is Speculated that the Fatigue Strength can be Controlled by Change in Condition of Machining Process. it could be Effective way in Industry to Improved Fatigue Strength only by the Cutting Process without Additional Surface Treatment Process.

scholarly journals Properties of the Fine Granular Area and Postulated Models for Its Formation during Very High Cycle Fatigue—A Review

2020 ◽  
Vol 10 (23) ◽  
pp. 8475
Author(s):  
Jan Patrick Sippel ◽  
Eberhard Kerscher
Keyword(s):  
Fatigue Strength ◽  
Crack Initiation ◽  
Crack Growth ◽  
High Performance ◽  
High Cycle Fatigue ◽  
The Other ◽  
Cycle Fatigue ◽  
Very High Cycle Fatigue ◽  
Open Questions ◽  
Very High

Understanding the mechanisms leading to very high cycle fatigue is necessary to make predictions about the behavior under various conditions and to ensure safe design over the whole lifetime of high-performance components. It is further vital for the development of possible measures to increase the very high cycle fatigue strength. This review therefore intends to give an overview of the properties of the fine granular area that have been observed so far. Furthermore, the existing models to describe the early crack initiation and crack growth within the very high cycle fatigue regime are outlined and the models are evaluated on the basis of the identified fine granular area properties. The aim is to provide an overview of the models that can already be considered refuted and to specify the respective open questions regarding the other individual models.

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.

Fatigue Crack Growth Behavior of Threaded Pipe Couplings

2011 ◽  
Author(s):  
Jeroen Van Wittenberghe ◽  
Patrick De Baets ◽  
Wim De Waele
Keyword(s):  
Fatigue Crack ◽  
Fracture Surface ◽  
Crack Initiation ◽  
Crack Growth ◽  
Fatigue Behavior ◽  
Crack Opening ◽  
Bending Test ◽  
Crack Initiation And Propagation ◽  
Accurate Knowledge ◽  
Initiation And Propagation

Threaded couplings are used in various applications to connect steel pipes. To maintain a secure connection, such couplings are preloaded and during service additional dynamic loads can act on the connections. The coupling’s threads act as stress raisers, initiating fatigue cracks, which can cause the connection to fail in time. Accurate knowledge of the fatigue behavior, taking into account crack initiation and propagation is necessary to understand the fatigue mechanisms involved. In this study, the fatigue behavior of tapered couplings with NPT threads is studied. This is done by analyzing the results of an experimental four-point bending test. The fatigue crack propagation is monitored using an optical dynamic 3D displacement measurement device and LVDTs to measure the crack opening. At certain times during the test, the load ratio is changed to apply a number of beach marking cycles. This way a fine line is marked in the fracture surface. These marked crack shapes are used as input for a finite element model. The measured deflection and crack opening are compared to the results of the numerical simulations. Using this methodology a distinction is made between fatigue crack initiation and propagation. By analyzing the fracture surface it was observed that once the crack is initiated, it propagates over a wide segment of the pipe’s circumference and subsequently rapidly penetrates the wall of the pipe. The observed crack growth rates are confirmed by a fracture mechanics analysis. Since the appearing long shallow crack is difficult to detect at an early stage the importance is demonstrated of accurate knowledge of the fatigue behavior of threaded connections in order to define acceptable flaw sizes and inspection intervals.

Effect of the Rheocasting Process and of the SLS Layer on the Fatigue Behavior of 357 Aluminum Alloy

2014 ◽  
Vol 217-218 ◽  
pp. 227-234 ◽  
Author(s):  
Alain Abou Antoun ◽  
Myriam Brochu ◽  
Heinrich Möller
Keyword(s):  
Aluminum Alloy ◽  
Crack Initiation ◽  
High Cycle Fatigue ◽  
Fatigue Behavior ◽  
Fatigue Properties ◽  
Cycle Fatigue ◽  
Initiation Mechanism ◽  
Liquid Segregation ◽  
Surface Liquid ◽  
Effect Of Surface

Two objectives were targeted: 1) compare the high cycle fatigue behavior of rheocast aluminum alloy 357 prepared by the swirl enthalpy equilibration device (SEED) and by the Council for Scientific and Industrial Research (CSIR) process, and 2) study the effect of surface liquid segregation (SLS) on the fatigue behavior of the CSIR material. Rectangular hourglass specimens machined from rheocast plates were tested at four stress amplitudes in axial fatigue with a stress ratio of R = -1 and a frequency of 20 Hz. Results obtained for SLS free specimens show that the SEED and the CSIR processes produce rheocast materials with comparable high cycle fatigue properties, 115 MPa at 107 cycles. In order to study the influence of surface liquid segregation, slightly polished specimens with a remaining SLS of nearly 750 microns thick were also tested. According to the results, the SLS reduces the average fatigue strength by approximately 5% (110 MPa vs. 115 MPa at 107 cycles). For SLS free specimens, the fatigue crack initiated at shrinkage cavities, oxide films or in the alpha globules. On the other hand, for specimens with SLS, no crack initiation in the alpha globules was observed. The main crack initiation mechanism was identified to be a deformation incompatibility between regions characterized by higher silicon content compared to nominal eutectic regions. The originality of the work is provided by the rigorous comparative analysis of the fatigue performance of components produced in two different rheocasting facilities, but tested in a single laboratory. It is also the first fundamental research published on the mechanical effect of surface liquid segregation. It confirms that SLS should be removed in critical areas in order to optimize the fatigue resistance of rheocast components.

scholarly journals 405 Crack growth and Fatigue Strength of Bent Aluminum Alloy under Plane Bending

2012 ◽  
Vol 2012.48 (0) ◽  
pp. 114-115 ◽  
Author(s):  
Kei OHKAWA ◽  
Atsushi KUDO ◽  
Takehiro ANDO ◽  
Isao OHKAWA
Keyword(s):  
Aluminum Alloy ◽  
Fatigue Strength ◽  
Crack Growth ◽  
Plane Bending

An energetic method to evaluate the macro and micro high-cycle fatigue behavior of the aluminum alloy

2017 ◽  
Vol 232 (8) ◽  
pp. 1456-1469 ◽  
Author(s):  
Junling Fan ◽  
Xinglin Guo ◽  
Yanguang Zhao
Keyword(s):  
Aluminum Alloy ◽  
Fatigue Life ◽  
Fatigue Strength ◽  
Energy Dissipation ◽  
High Cycle Fatigue ◽  
Fatigue Behavior ◽  
Cycle Fatigue ◽  
Thermal Signal ◽  
Dissipation Mechanism ◽  
Good Agreement

An energetic method is proposed to rapidly evaluate the macro- and microfatigue behavior of aluminum alloy in high-cycle fatigue. The theoretical correlation between the thermal signal and the energy dissipation during the fatigue process is established for the irreversible dissipation mechanism description. The energetic method is applied to predict the fatigue strength and the entire fatigue life of the aluminum alloy. Moreover, the energy dissipation is properly used to evaluate the microplastic behavior at the grain scale, which is responsible for the progressive movements of the internal microstructures. Experiments were carried out to validate the current energetic method, and good agreement was obtained between the predicted results and the traditional results. Thus, the current energetic method is confirmed to be promising for the macro and micro high-cycle fatigue behavior assessment.

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