Multiaxial fatigue life assessment of welded structures

2010 ◽  
Vol 77 (15) ◽  
pp. 3011-3021 ◽  
Author(s):  
Zhigang Wei ◽  
Pingsha Dong
Keyword(s):  
Fatigue Life ◽  
Multiaxial Fatigue ◽  
Life Assessment ◽  
Welded Structures ◽  
Fatigue Life Assessment

Multiaxial Fatigue Life Assessment Method Based on the Mean Value of Modified Second Invariant of the Deviatoric Stress

2014 ◽  
Vol 224 ◽  
pp. 15-20
Author(s):  
Łukasz Pejkowski ◽  
Dariusz Skibicki
Keyword(s):  
Fatigue Life ◽  
Hydrostatic Stress ◽  
Assessment Method ◽  
Mean Value ◽  
Multiaxial Fatigue ◽  
Deviatoric Stress ◽  
Life Assessment ◽  
Fatigue Life Assessment ◽  
Fatigue Life Estimation ◽  
The Mean

Stress invariants approach to the multiaxial fatigue life estimation is generally based on the root mean square value of second invariant of the deviatoric stress amplitude and the value of hydrostatic stress. Such an approach omits a significant part of the information about multiaxial load history. It is particularly noticeable in case of non-proportional loadings, which lead to a reduction of fatigue life (i.e. [1–3]). In this work a new method based on the mean value of modified second invariant of the deviatoric stress has been presented.

Fatigue life assessment of welded structures based on fracture mechanics

2015 ◽  
Vol 6 (1) ◽  
pp. 2-25
Author(s):  
A. Krasovskyy ◽  
A. Virta
Keyword(s):  
Fatigue Life ◽  
Fracture Mechanics ◽  
Welded Joints ◽  
Welding Process ◽  
Life Assessment ◽  
Lifetime Estimation ◽  
Worst Case ◽  
Welded Structures ◽  
Content Type ◽  
Fatigue Life Assessment

Purpose – Even though modern welding technology has improved, initial defects on weld notches cannot be avoided. Assuming the existence of crack-like flaws after the welding process, the stage of a fatigue crack nucleation becomes insignificant and the threshold for the initial crack propagation can be used as a criterion for very high cycle fatigue whereas crack growth analysis can be applied for the lifetime estimation at lower number of cycles. The purpose of this paper is to present a mechanism based approach for lifetime estimation of welded joints, subjected to a multiaxial non-proportional loading. Design/methodology/approach – The proposed method, which is based on the welding process simulation, thermophysical material modeling and fracture mechanics, considers the most important aspects for fatigue of welds. Applying worst-case assumptions, fatigue limits derived by the weight function method can be then used for the fatigue assessment of complex welded structures. Findings – An accurate mechanism based method for the fatigue life assessment of welded joints has been presented and validated. Originality/value – Compared to the fatigue limits provided by design codes, the proposed method offers more accurate lifetime estimation, a better understanding of interactions between welding process and fatigue behavior. It gives more possibilities to optimize the welding process specifically for the considered material, weld type and loading in order to achieve the full cost and weight optimization potential for industrial applications.

A New Multiaxial Fatigue Life Prediction Model Under Proportional and Nonproportional Loading

2010 ◽  
Vol 132 (2) ◽  
Author(s):  
Jing Li ◽  
Qiang Sun ◽  
Zhong-Ping Zhang ◽  
Chun-Wang Li ◽  
Dong-Wei Zhang
Keyword(s):  
Fatigue Life ◽  
Damage Model ◽  
Cyclic Hardening ◽  
Damage Parameter ◽  
Multiaxial Fatigue ◽  
Life Assessment ◽  
Normal Strain ◽  
Critical Plane ◽  
Nonproportional Loading ◽  
Fatigue Life Assessment

Based on the critical plane approach, the drawbacks of the Wang–Brown (WB) model are analyzed. It is discovered that the normal strain excursion in the WB model cannot account for the additional cyclic hardening well. In order to solve this problem, a new damage parameter for multiaxial fatigue is proposed. In the meantime, the procedure for multiaxial fatigue life assessment incorporating critical plane damage model is presented as well. In the new damage parameter, both strain and stress components are considered, and the effect of the additional cyclic hardening on the fatigue life during nonproportional loading is taken into account as well. In addition, the proposed model is modified when the mean stress is existence. It is convenient for engineering application because of no material constants in this parameter. The capability of fatigue life assessment for the proposed fatigue damage model is checked against the experimental data found in literature for tubular specimens of 1045HR steel, hot-rolled 45 steel, S460N steel, GH4169 alloy at elevated temperature, and the notched shaft of SAE 1045 steel, which is under cyclic bending and torsion loading. It is demonstrated that the proposed criterion gives satisfactory results for all the five checked materials.

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