Mean stress dependence of fatigue strength and subsurface crack initiation in Ti–15Mo–5Zr–3Al alloy

2000 ◽  
Vol 281 (1-2) ◽  
pp. 268-274 ◽  
Author(s):  
Keiro Tokaji ◽  
Hiroyasu Kariya
Keyword(s):  
Fatigue Strength ◽  
Crack Initiation ◽  
Mean Stress ◽  
Stress Dependence ◽  
Subsurface Crack

scholarly journals The relationship between the Dang Van criterion and the traditional bulk fatigue criteria

2003 ◽  
Vol 38 (3) ◽  
pp. 201-206 ◽  
Author(s):  
G Peridas ◽  
A. M Korsunsky ◽  
D. A Hills
Keyword(s):  
Crack Initiation ◽  
Fatigue Limit ◽  
Mean Stress ◽  
Stress Dependence ◽  
Biaxial Fatigue ◽  
Formal Relationship ◽  
Crack Initiation Criterion ◽  
The Relationship ◽  
Fatigue Criterion ◽  
Dang Van Criterion

A formal relationship is established between the traditional bulk fatigue criteria such as the Goodman rule and the Sines criterion, and the recent crack initiation criterion of Dang Van. The constants implied by the Dang Van procedure may be formally connected to the fatigue limit and mean stress dependence given by the Goodman rule, under conditions of uniaxial loading. The biaxial fatigue criterion of Sines is also compared with the Dang Van procedure. The similarity in the approaches may be further extended to permit finite initiation times to be estimated by the Dang Van criterion when the fatigue limit is exceeded.

Experimental Study on Fatigue Strength of Welded Joints Under Storm Loading

2011 ◽  
Author(s):  
Chang-Hyun Moon ◽  
Kiyoshi Hashimoto ◽  
Yooseok Song ◽  
Kyung-Su Kim ◽  
Sunghoon Kim ◽  
...  
Keyword(s):  
Fatigue Life ◽  
Fatigue Strength ◽  
Crack Initiation ◽  
Welded Joints ◽  
Maximum Stress ◽  
Stress Amplitude ◽  
Offshore Structures ◽  
Variable Load ◽  
Mean Stress ◽  
Storm Model

Welded joints are important for fatigue strength evaluation of ship and offshore structures. However, current techniques for fatigue evaluation of welded joint under variable load is not accurate enough. Also, it cannot consider the effect of load history which is one of the important features for the variable loads. Therefore, many experimental attempts are conducted for storm model to consider the variable loading. However, studies of storm loading usually ignore the effect of calm sea loading which constitute a large portion of the marine phenomena. Because it has been believed that the contribution of calm sea loading is not dominant for fatigue life in storm loading. In this paper, fatigue tests are conducted for the specimens with transverse attachment made of high tensile steel under variable amplitude axial loading based on storm model. Considered loadings include repeated single storm, 6 or 8 kind storms sequenced randomly, and storms including calm sea condition while the mean stress and the maximum stress of loadings are changed. Moreover, the effect of three variables are investigated; 1) root mean square (RMS) value of stress amplitude, 2) mean stress shift and 3) maximum stress which can characterize the storm loading on fatigue life. In addition, experiments with calm sea loading are conducted and the effect of calm sea loading is also investigated. The storm and calm sea loadings are generated from IACS-34 wave scatter diagram. 5% strain drop criteria is introduced to define crack initiation life. Experimental results including the test results from previous study are evaluated and compared with DNV-CN 30.7 (2005) and Matsuoka’s method for the estimation of crack initiation and propagation life. From the result, it is concluded that the fatigue strength under storm loading can be evaluated by RMS value of stress amplitude. And mean stress shift is more likely to relate to fatigue strength than maximum stress. The effectiveness of the calm sea loading is depend on the existence of mean stress shift. Regarding fatigue life evaluated by DNV and Matsuoka method, both of them have almost same accuracy.

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.

Fatigue Assessment of Welded Joints Taking Into Account Effects of Residual Stress

2010 ◽  
Author(s):  
Nur Syahroni ◽  
Stig Berge
Keyword(s):  
Residual Stress ◽  
Fatigue Strength ◽  
Welded Joints ◽  
Fatigue Testing ◽  
International Association ◽  
Hot Spot ◽  
Mean Stress ◽  
Element Analysis ◽  
Structural Rules ◽  
Fatigue Design

Residual stress may have a significant effect on the fatigue strength of welded joints. As a non-fluctuating stress, it has an effect similar to that of the mean stress. Recently the International Association of Ship Classification Societies (IACS) has issued Common Structural Rules (CSR) for respectively tankers (IACS 2006a) and bulk carriers (IACS 2006b). The effect of mean stress in fatigue design is taken into account in both sets of rules. However, the treatment is quite different, in particular with regard to residual stress and shakedown effects. In the present paper a comparative study of fatigue design procedures of the IACS rules is reported, with emphasis on residual stress effects. Testing was carried out with longitudinal attachment welds in the as-welded condition. The initial residual stress was measured by a sectioning method using strain gages. Hot spot stress was determined experimentally by strain gauges and numerically by finite element analysis using different types of elements. Fatigue testing was carried out and SN-curves were plotted according to the relevant stress as specified by the rules. In order to investigate the shake-down effect of residual stress, testing was performed for several pre-load conditions which could be taken to represent maximum load levels in a load history. The aim of the study is to contribute towards better understanding of the effect of residual stress and shakedown on fatigue strength of welded joints.

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