scholarly journals Modification of a Defect-Based Fatigue Assessment Model for Al-Si-Cu Cast Alloys

Materials ◽  
2018 ◽  
Vol 11 (12) ◽  
pp. 2546 ◽  
Author(s):  
Roman Aigner ◽  
Martin Leitner ◽  
Michael Stoschka ◽  
Christian Hannesschläger ◽  
Thomas Wabro ◽  
...  
Keyword(s):  
Fatigue Strength ◽  
Fatigue Testing ◽  
Threshold Value ◽  
Fatigue Behaviour ◽  
Mechanical Tests ◽  
Assessment Model ◽  
Fatigue Assessment ◽  
Strength Assessment ◽  
Assessment Approach ◽  
Long Life

Cast parts usually inherit internal defects such as micro shrinkage pores due to the manufacturing process. In order to assess the fatigue behaviour in both finite-life and long-life fatigue regions, this paper scientifically contributes towards a defect-based fatigue design model. Extensive fatigue and fracture mechanical tests were conducted whereby the crack initiating defect size population was fractographically evaluated. Complementary in situ X-ray computed tomography scans before and during fatigue testing enabled an experimental estimation of the lifetime until crack initiation, acting as a significant input for the fatigue model. A commonly applied fatigue assessment approach introduced by Tiryakioglu was modified by incorporating the long crack threshold value, which additionally enabled the assessment of the fatigue strength in the long-life fatigue regime. The presented design concept was validated utilising the fatigue test results, which revealed a sound agreement between the experiments and the model. Only a minor deviation of up to about five percent in case of long-life fatigue strength and up to about 9% in case of finite-lifetime were determined. Thus, the provided extension of Tiryakioglu’s approach supports a unified fatigue strength assessment of cast aluminium alloys in both the finite- and long-life regimes.

scholarly journals Probabilistic Surface Layer Fatigue Strength Assessment of EN AC-46200 Sand Castings

Metals ◽  
2020 ◽  
Vol 10 (5) ◽  
pp. 616
Author(s):  
Sebastian Pomberger ◽  
Matthias Oberreiter ◽  
Martin Leitner ◽  
Michael Stoschka ◽  
Jörg Thuswaldner
Keyword(s):  
Heat Treatment ◽  
Surface Layer ◽  
Fatigue Strength ◽  
Treatment Condition ◽  
Heat Treatment Condition ◽  
Assessment Model ◽  
Sand Cast ◽  
Strength Assessment ◽  
Long Life ◽  
Cast Surface

The local fatigue strength within the aluminium cast surface layer is affected strongly by surface layer porosity and cast surface texture based notches. This article perpetuates the scientific methodology of a previously published fatigue assessment model of sand cast aluminium surface layers in T6 heat treatment condition. A new sampling position with significantly different surface roughness is investigated and the model exponents a 1 and a 2 are re-parametrised to be suited for a significantly increased range of surface roughness values. Furthermore, the fatigue assessment model of specimens in hot isostatic pressing (HIP) heat treatment condition is studied for all sampling positions. The obtained long life fatigue strength results are approximately 6% to 9% conservative, thus proven valid within an range of 30 µm ≤ S v ≤ 260 µm notch valley depth. To enhance engineering feasibility even further, the local concept is extended by a probabilistic approach invoking extreme value statistics. A bivariate distribution enables an advanced probabilistic long life fatigue strength of cast surface textures, based on statistically derived parameters such as extremal valley depth S v i and equivalent notch root radius ρ ¯ i . Summing up, a statistically driven fatigue strength assessment tool of sand cast aluminium surfaces has been developed and features an engineering friendly design method.

Fatigue Behaviour of Friction Stir Welded AZ31B Magnesium Alloy Joints

2015 ◽  
Vol 787 ◽  
pp. 355-360
Author(s):  
S. Venkatesan ◽  
G.P. Rajamani ◽  
V. Balasubramanian ◽  
G. Padmanaban
Keyword(s):  
Fatigue Strength ◽  
Fatigue Testing ◽  
Corrosion Behaviour ◽  
Testing Machine ◽  
Fatigue Behaviour ◽  
Fusion Welding ◽  
Sensitivity Factor ◽  
Metal Fatigue ◽  
Friction Stir ◽  
Fatigue Notch Factor

Friction stir welding (FSW) is a relatively better joining technique particularly for magnesium and aluminum alloys that are difficult to weld by fusion welding techniques. Fusion welding of these alloys is not preferable due to hot cracking, formation of porosity, etc. However solid state welding techniques, such as, friction sitr welding are found to offer solution to the above problems. Many research papers available in open literature focusing tensile properties, microstructural characteristics, and corrosion behaviour of friction stir welded AZ31B magnesium alloys but fatigue behaviour of these welds are not yet investigated. Hence, in this investigation, an attempt has been made to evaluate fatigue behaviour of friction stir welded rolled plates of AZ31B magnesium alloys.Fatigue experiment was conducted using servo hydraulic controlled fatigue testing machine. Fatigue strength, fatigue notch factor and notch sensitivity factor were evaluated. It is found that the fatigue strength of AZ31B welded joints is 46 MPa at 2x106cycles which is approximately 34 % lower than that of the base metal fatigue strength.

Design Analysis and Fatigue Testing of the Typical Structural Details of Aluminium Ships

2018 ◽  
Author(s):  
Huilong Ren ◽  
Kaikai Ma ◽  
Chenfeng Li ◽  
Zhichao Zhang ◽  
Weijun Xu ◽  
...  
Keyword(s):  
Fatigue Strength ◽  
Aluminium Alloy ◽  
Fatigue Testing ◽  
Hot Spot ◽  
Fatigue Tests ◽  
Material Strength ◽  
Original Design ◽  
Hot Spot Stress ◽  
Strength Assessment ◽  
Structural Details

Aluminium alloy is widely used structural design in light-weighting design. Due to the material strength loss in welding, fatigue strength of typical joints fabricated by aluminium alloy is more sensitive than steel joints. The aim of this study is to investigate one aluminium detail of the longitudinal through the transverse, with high-performance of fatigue strength compared to the original design. The alloy of longitudinal is AA6082-T6 and the other components (including plate and transverse) is AA5083-H2. Firstly, eight schemes of structural details with various configurations of bracket and / or stiffener are designed. Based on the finite element analyses, the stress distribution of panels with eight designed details is obtained under typical loading condition respectively. According to the principle of hot spot stress being minimum, the optimal detail is determined, which using stiffener reinforced on both sides of transverse. Secondly, the fatigue tests of the optimal detail were designed and carried out. The testing panels consist of 2-span and 3 longitudinal stiffeners, and the frame with optimal joints is located in the middle of the panels. The test panels were simply supported at two ends with applied cyclic loading in the middle panel. According to the designed loading scheme (loading level, frequency, etc.), the fatigue tests of the panels with typical detail were carried out. The hot stress and the cycle times of the typical detail under different load levels were obtained. Based on the test data, the S-N curve of the typical detail in aluminium alloy is established. Finally, the fatigue strength assessment of the typical detail in target ship is performed based on the Miner’s linear cumulative damage theory and established S-N curve. The results show that the fatigue life of proposed optimal detail meets the design requirements of the target ship. The S-N curve of the typical detail made of AA6082-T6 obtained in this study can be also used for other aluminium ships with similar structural details.

scholarly journals Validation Study on the Statistical Size Effect in Cast Aluminium

Metals ◽  
2020 ◽  
Vol 10 (6) ◽  
pp. 710
Author(s):  
Matthias Oberreiter ◽  
Sebastian Pomberger ◽  
Martin Leitner ◽  
Michael Stoschka
Keyword(s):  
Fatigue Strength ◽  
Size Effect ◽  
Bulk Material ◽  
Assessment Model ◽  
Cast Material ◽  
Stressed Volume ◽  
Strength Assessment ◽  
Cast Aluminium ◽  
Distribution Parameters ◽  
And Shifts

Imperfections due to the manufacturing process can significantly affect the local fatigue strength of the bulk material in cast aluminium alloys. Most components possess several sections of varying microstructure, whereat each of them may inherit a different highly-stressed volume (HSV). Even in cases of homogeneous local casting conditions, the statistical distribution parameters of failure causing defect sizes change significantly, since for a larger highly-stressed volume the probability for enlarged critical defects gets elevated. This impact of differing highly-stressed volume is commonly referred as statistical size effect. In this paper, the study of the statistical size effect on cast material considering partial highly-stressed volumes is based on the comparison of a reference volume V 0 and an arbitrary enlarged, but disconnected volume V α utilizing another specimen geometry. Thus, the behaviour of disconnected highly-stressed volumes within one component in terms of fatigue strength and resulting defect distributions can be assessed. The experimental results show that doubling of the highly-stressed volume leads to a decrease in fatigue strength of 5% and shifts the defect distribution towards larger defect sizes. The highly-stressed volume is numerically determined whereat the applicable element size is gained by a parametric study. Finally, the validation with a prior developed fatigue strength assessment model by R. Aigner et al. leads to a conservative fatigue design with a deviation of only about 0.3% for cast aluminium alloy.

scholarly journals Recent developments and future challenges in fatigue strength assessment of welded joints

2014 ◽  
Vol 229 (7) ◽  
pp. 1224-1239 ◽  
Author(s):  
Wolfgang Fricke
Keyword(s):  
Fatigue Strength ◽  
Welded Joints ◽  
Plate Thickness ◽  
Stress Gradient ◽  
Fatigue Behaviour ◽  
Welded Structures ◽  
Strength Assessment ◽  
Propagation Law ◽  
Recent Developments ◽  
Fatigue Strength Assessment

Fatigue is an important design criterion for welded structures subjected to cyclic loading. Several approaches for fatigue strength assessment have been developed which are either based on Woehler S–N curves and damage accumulation rule or on crack propagation law. The paper briefly reviews the different approaches, highlighting their advantages and limitations. In this connection, the problematic distinction between crack initiation and propagation phases is discussed, followed by considerations about some parameters which have large influence on the fatigue behaviour of welded joints but are considered differently in the approaches, such as plate thickness and stress gradient effects, multiaxial stress states, welding-induced distortions and residual stresses. Finally, ways of improving the fatigue behaviour of welded structures, either during design by reducing the stress concentration or during fabrication by improved quality or post-weld treatment or else by special material characteristics, are addressed. Emphasis will be placed on recent developments and challenges for the future from a personal perspective of the author.

scholarly journals Fretting Fatigue Behaviour of Alloy Steel in the Very High Cycle Region

2019 ◽  
Vol 300 ◽  
pp. 18002
Author(s):  
Yoshinobu Shimamura ◽  
Reo Kasahara ◽  
Hitoshi Ishii ◽  
Keiichiro Tohgo ◽  
Tomoyuki Fujii ◽  
...  
Keyword(s):  
Fatigue Strength ◽  
Fatigue Testing ◽  
Testing Machine ◽  
Fatigue Behaviour ◽  
Fretting Fatigue ◽  
Fatigue Tests ◽  
Fatigue Properties ◽  
Test Results ◽  
Torsional Fatigue ◽  
Very High

It is well known that fretting fatigue strength is much lower than the fatigue strength of smooth specimens and the fatigue limit disappears. Many studies on fretting fatigue have been reported but most of the studies have not cover fatigue properties in the very high cycle regime more than 107 cycles. In this study, an accelerated fretting fatigue testing method was developed by using an ultrasonic torsional fatigue testing machine with a clamping fretting pad. Fretting fatigue tests of CrMo steel were conducted by using the developed method. Test results showed that fretting fatigue failure occurs in the very high cycle region.

scholarly journals Surface roughness effect on fatigue strength of aluminum alloy using revised stress field intensity approach

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
Bingfeng Zhao ◽  
Jiaxin Song ◽  
Liyang Xie ◽  
Zhiyong Hu ◽  
Jianpeng Chen
Keyword(s):  
Surface Roughness ◽  
Aluminum Alloy ◽  
Quantitative Analysis ◽  
Fatigue Strength ◽  
Stress Field ◽  
Field Intensity ◽  
Fatigue Testing ◽  
Roughness Effect ◽  
Strength Assessment ◽  
Fatigue Strength Assessment

AbstractThe fatigue strength of a component is known to highly depend on its surface quality, and it is thus necessary to develop a reliable and appropriate mathematical model for fatigue strength assessment that consider the effect of surface roughness. In this paper, different underlying physical mechanisms of the roughness effect at different regions of specimens were studied by fatigue testing of 7N01 aluminum alloy. For a quantitative analysis of the surface roughness effect, a revised stress field intensity approach for a fatigue strength assessment of microsized notches was proposed as a theoretical support. In the new model, a new form of weight function was built to adapt the characteristics of microsized notches. In addition, the effect of the field radius was fundamentally weakened on solution of the stress field intensity and the difficulty of fatigue failure region definition in the traditional method was overcome correspondingly in the proposed model, which made the calculated field strength accurate and objective. Finally, to demonstrate the validity of the revised approach quantitatively, specimens with conventionally sized notches were subjected to stress field intensity calculations. The results showed that the revised approach has satisfactory accuracy compared with the other two traditional approaches from the perspective of quantitative analysis.

scholarly journals Assignment of fatigue strength requirements and development of algorithms for ship fatigue assessment

2020 ◽  
Vol S-I (2) ◽  
pp. 89-96
Author(s):  
M. Kuteinikov ◽  
◽  
S. Nikonov ◽  
I. Surikova ◽  
◽  
...  
Keyword(s):  
Fatigue Strength ◽  
North Atlantic ◽  
Calculation Procedure ◽  
Fatigue Assessment ◽  
Strength Assessment ◽  
Fatigue Strength Assessment

Guidelines on Fatigue Assessment of Ships published by Russian Maritime Register of Shipping (RS) in 2020 suggests a calculation procedure for fatigue strength assessment of ships in order to ensure additional notation signs FTL(years) and FTL(years) Spectral North Atlantic developed with consideration of the peculiarities typical for modern procedures of this kind. The paper describes the main points of these Guidelines, dwelling upon the challenges in related calculations. The results of this work made it possible to outline the ways of further studies intended to improve these Guidelines.

Fatigue Life Improvement of Welded Elements and Structures by Ultrasonic Impact Treatment

2011 ◽  
Author(s):  
Yuriy Kudryavtsev ◽  
Jacob Kleiman
Keyword(s):  
Mechanical Properties ◽  
Fatigue Life ◽  
Fatigue Strength ◽  
Residual Stresses ◽  
Fatigue Testing ◽  
Highway Bridges ◽  
Surface Layers ◽  
Ultrasonic Impact Treatment ◽  
Stress Relieving ◽  
Life Improvement

The ultrasonic impact treatment (UIT) is relatively new and promising process for fatigue life improvement of welded elements and structures. In most industrial applications this process is known as ultrasonic peening (UP). The beneficial effect of UIT/UP is achieved mainly by relieving of harmful tensile residual stresses and introducing of compressive residual stresses into surface layers of a material, decreasing of stress concentration in weld toe zones and enhancement of mechanical properties of the surface layers of the material. The UP technique is based on the combined effect of high frequency impacts of special strikers and ultrasonic oscillations in treated material. Fatigue testing of welded specimens showed that UP is the most efficient improvement treatment as compared with traditional techniques such as grinding, TIG-dressing, heat treatment, hammer peening and application of LTT electrodes. The developed computerized complex for UP was successfully applied for increasing the fatigue life and corrosion resistance of welded elements, elimination of distortions caused by welding and other technological processes, residual stress relieving, increasing of the hardness of the surface of materials. The UP could be effectively applied for fatigue life improvement during manufacturing, rehabilitation and repair of welded elements and structures. The areas/industries where the UP process was applied successfully include: Shipbuilding, Railway and Highway Bridges, Construction Equipment, Mining, Automotive, Aerospace. The results of fatigue testing of welded elements in as-welded condition and after application of UP are considered in this paper. It is shown that UP is the most effective and economic technique for increasing of fatigue strength of welded elements in materials of different strength. These results also show a strong tendency of increasing of fatigue strength of welded elements after application of UP with the increase in mechanical properties of the material used.

Sign in / Sign up

Export Citation Format

Share Document