Evaluation of Fatigue Strength of Similar and Dissimilar Welded Joints of Modified 9Cr-1Mo Steel

2014 ◽  
Author(s):  
Shigeru Takaya
Keyword(s):  
Experimental Data ◽  
Fatigue Life ◽  
Fatigue Strength ◽  
Welded Joints ◽  
Strain Distribution ◽  
Welded Joint ◽  
Element Model ◽  
Fast Breeder Reactor ◽  
Weld Joints ◽  
Homogeneous Strain

This paper presents evaluation methods of fatigue strength of similar and dissimilar welded joints of modified 9Cr-1Mo steel which is a candidate structural material for a demonstration fast breeder reactor being developed in Japan. The discontinuity of mechanical properties across welded joint causes a non-homogeneous strain distribution, and this effect should be taken into account for evaluation of fatigue strength of weld joints. In this study, ‘2-element model’, which is consisted of base metal and weld metal, was employed. Firstly, strain ranges of each element are calculated, and secondly fatigue lives of each element are evaluated. Finally, shorter fatigue life is chosen as fatigue life of the weld joint. Failure position can be also estimated by this model. Evaluation results were compared with experimental data at elevated temperature, and it was shown that they agree well.

Evaluation of Fatigue Strength of Similar and Dissimilar Welded Joints of Modified 9Cr–1Mo Steel

2015 ◽  
Vol 138 (1) ◽  
Author(s):  
Shigeru Takaya
Keyword(s):  
Experimental Data ◽  
Fatigue Life ◽  
Fatigue Strength ◽  
Welded Joints ◽  
Strain Distribution ◽  
Evaluation Method ◽  
Welded Joint ◽  
Element Model ◽  
Fast Breeder Reactor ◽  
Good Agreement

This paper presents an evaluation method for the fatigue strength of similar and dissimilar welded joints of modified 9Cr–1Mo steel, which is a candidate structural material for demonstration of fast-breeder reactor being developed in Japan. The discontinuity of the mechanical properties across a welded joint causes a nonhomogeneous strain distribution, and this effect should be considered in the evaluation of the fatigue strength of welded joints. In this study, a “two-element model,” which comprises base metal and welded metal, was employed. First, the strain ranges of each element are calculated, and second, the fatigue lives of each element are evaluated. Finally, the shorter fatigue life is selected as the fatigue life of the welded joint. The failure position can be also estimated by this model. The evaluation results were compared with experimental data obtained at elevated temperature, and the results were in good agreement.

scholarly journals Fatigue Modeling and Numerical Analysis of Re-Filling Probe Hole of Friction Stir Spot Welded Joints in Aluminum Alloys

Materials ◽  
2021 ◽  
Vol 14 (9) ◽  
pp. 2171
Author(s):  
Armin Yousefi ◽  
Ahmad Serjouei ◽  
Reza Hedayati ◽  
Mahdi Bodaghi
Keyword(s):  
Experimental Data ◽  
Tensile Strength ◽  
Fatigue Life ◽  
Fatigue Strength ◽  
Fatigue Behavior ◽  
Element Model ◽  
Plastic Strain Amplitude ◽  
Friction Stir ◽  
Probe Hole ◽  
Good Agreement

In the present study, the fatigue behavior and tensile strength of A6061-T4 aluminum alloy, joined by friction stir spot welding (FSSW), are numerically investigated. The 3D finite element model (FEM) is used to analyze the FSSW joint by means of Abaqus software. The tensile strength is determined for FSSW joints with both a probe hole and a refilled probe hole. In order to calculate the fatigue life of FSSW joints, the hysteresis loop is first determined, and then the plastic strain amplitude is calculated. Finally, by using the Coffin-Manson equation, fatigue life is predicted. The results were verified against available experimental data from other literature, and a good agreement was observed between the FEM results and experimental data. The results showed that the joint’s tensile strength without a probe hole (refilled hole) is higher than the joint with a probe hole. Therefore, re-filling the probe hole is an effective method for structures jointed by FSSW subjected to a static load. The fatigue strength of the joint with a re-filled probe hole was nearly the same as the structure with a probe hole at low applied loads. Additionally, at a high applied load, the fatigue strength of joints with a refilled probe hole was slightly lower than the joint with a probe hole.

Fatigue Strength Reduction Factors for Welded Joints: Another View

2007 ◽  
Author(s):  
Arturs Kalnins
Keyword(s):  
Standard Deviation ◽  
Fatigue Strength ◽  
Fatigue Test ◽  
Test Data ◽  
Welded Joints ◽  
Welded Joint ◽  
Fatigue Curve ◽  
Strength Reduction ◽  
Initial Estimate ◽  
Curve Fit

The paper distinguishes between FSRFs that are used for two different purposes. One is to serve as a guideline for an initial estimate of the fatigue strength of a welded joint. That is the purpose of the FSRFs that are given in the ASME B&PV Code and various accompanying documents. If that estimate renders the fatigue strength inadequate, an FSRF can be sought that is limited to the joint under consideration. The paper shows how such FSRFs can be determined from fatigue test data. In order to make it possible to read the allowable cycles from the same design fatigue curve as that used for the FSRFs of the guidelines, a Langer curve [defined by equation (2) in the paper] is used to curve fit the data. The appropriate FSRF is obtained by minimizing the standard deviation between this curve and the data. The procedure is illustrated for girth butt-welded pipes. The illustration shows that for the data used in the analysis, a constant FSRF is applicable to less than one million cycles but not to the high-cycle regime.

State-of-the-Art: Fatigue Life Extension of Offshore Installations

2012 ◽  
Author(s):  
Luis Lopez Martinez ◽  
Zuheir Barsoum ◽  
Anna Paradowska
Keyword(s):  
Fatigue Life ◽  
Fatigue Strength ◽  
Residual Stresses ◽  
Fatigue Test ◽  
Welded Joints ◽  
Life Extension ◽  
Stress Concentrations ◽  
Weld Geometry ◽  
Compressive Stresses ◽  
Ultrasonic Peening

The use of fatigue life improvement techniques and specifically ultrasonic peening treatment to extend the service life of offshore structures has become an accepted practice during the last five years. The understanding of the process as well as equipment’s upgrading for treatment in-situ including quality control and assurance have been developed up to a level that it has become a current practice in many parts of the world. However, the efficiency of the ultrasonic peening is strictly dependent on the deep understanding of significant fatigue parameters as weld defects, stress concentrations and residual stresses and their interaction. In this paper we attempt to present the current knowledge and the physical reasons why the ultrasonic peening treatment is able to improve the fatigue life of welded joints. The local weld geometry or stress concentration, weld imperfections as well as welding residual stresses are all modified and improved by the application of ultrasonic peening. Local weld geometry and weld process inherent weld imperfections are the factors primarily influencing the fatigue strength in welded joints. Comprehensive studies have been carried out during the last 20 years in order to detect and document the weld defects as well as to understand their origin and effect on the fatigue strength of welds. Analogous efforts have been dedicated to understand and document the influence of local weld geometries on the stress concentrations and its influence on endurance and structural integrity. Similarly, efforts have been done to understand the influence of the relaxation by external loads of the by the ultrasonic peening treatment induced compressive stresses. Fatigue test results of ultrasonic peening treated relevant weld details have been used to assess the potential life extension. The results showed four to six times fatigue life extension. The spectrum fatigue test was designed to confirm that relaxation by service loads of the induced compressive stresses during ultrasonic peening treatment would not diminish the benefit.

Numerical Simulation and Experimental Research on Fatigue Strength of the Injector Guide Pillar under Complex Loads

2010 ◽  
Vol 118-120 ◽  
pp. 196-200
Author(s):  
Jin Guo Li ◽  
Xiao Gui Wang ◽  
Zeng Liang Gao
Keyword(s):  
Experimental Data ◽  
Mechanical Properties ◽  
Numerical Simulation ◽  
Experimental Study ◽  
Fatigue Life ◽  
Fatigue Strength ◽  
Numerical Analysis ◽  
Experimental Research ◽  
Contact Surface ◽  
Electronic Measurement

Under the complex loads, the injector guide pillar (IGP) used in injection machine was failure only after 1.5-year-service. In order to determine the cause of the fracture, the numerical simulation technology was applied to analyze the mechanical properties of the IGP. The contact between the mating surfaces of the clamping mechanism was modeled; nonlinear multi-region contact of surface-surface was applied to establish the contact model of FEA. The constraint of tie was used for modeling thread joint. The simulated results indicated that the smaller area of contact surface, the higher value of stress in the neck of IGP. Electronic measurement was also used to check the results of stress in IGP obtained by FEA. It was found that the experimental data agreed well with simulated results. Based on the numerical analysis and experimental study, the structure of IGP was improved by adopting a smoother double-round neck. The fatigue life of the improved structure was longer than that of the original machine.

The Experimental Study and Numerical Estimation of Fracture Toughness of Heterogeneous Welded Joints

2013 ◽  
Vol 592-593 ◽  
pp. 173-176 ◽  
Author(s):  
Egor Moskvichev
Keyword(s):  
Mechanical Properties ◽  
Fracture Toughness ◽  
Welded Joints ◽  
Welded Joint ◽  
Element Model ◽  
Fracture Parameter ◽  
J Integral ◽  
Numerical Estimation ◽  
Mechanical Heterogeneity ◽  
Numerical Finite Element

In this paper the mechanical heterogeneity of welded joints was studied. The experimental results show that the mechanical properties and fracture toughness vary significantly in zones of welded joint. To estimate the fracture parameter J-integral a numerical finite-element model based on the random variation of yield strength was proposed.

Effect of Ultrasonic Impact Treatment on Fatigue Life in Butt Welded Joints of Austenitic Stainless Steel

2010 ◽  
Author(s):  
Yu Togasaki ◽  
Takashi Honda ◽  
Tetsuya Sasaki ◽  
Atsushi Yamaguchi ◽  
Hirokazu Tsuji
Keyword(s):  
Residual Stress ◽  
Stainless Steel ◽  
Fatigue Life ◽  
Stress Concentration ◽  
Austenitic Stainless Steel ◽  
Welded Joints ◽  
Diffraction Method ◽  
Weld Toes ◽  
Ultrasonic Impact Treatment ◽  
Weld Joints

Ultrasonic impact treatment (UIT), which is a type of peening method, is usually used as a post-weld treatment for mild steel in order to improve the fatigue strength of its welded joints. As there is insufficient fatigue data available on welded joints of austenitic stainless steel treated by UIT, the authors decide to conduct fatigue tests on butt welded joints of austenitic stainless steel treated by UIT. The results were compared with the fatigue lives of as-weld joints to investigate the effect of UIT on the fatigue lives of welded joints of austenitic stainless steel. The fatigue lives of butt welded joints treated by UIT were more than 1.5 times longer than those of as-weld joints. The following were considered as possible reasons for this improvement in fatigue life: change in residual stress near the weld toes, relaxation of stress concentration at the weld toes, and refinement of grains under the weld toes. The residual stress measured near the weld toes by using the X-ray diffraction method was transformed from tension to compression by the application of UIT. The stress concentration factors at the welded toes were reduced about 10% by the application of UIT.

A Study of Fatigue-Life Estimation and Reliability Analysis for Dental Implants

2012 ◽  
Author(s):  
Yuo-Tern Tsai ◽  
Y. K. Lu ◽  
Y. Y. Hsu ◽  
J. B. Lu
Keyword(s):  
Experimental Data ◽  
Fatigue Life ◽  
Fatigue Strength ◽  
Dental Implants ◽  
Fatigue Testing ◽  
Simulation Analysis ◽  
Linear Regression Method ◽  
Estimation Model ◽  
Life Estimation ◽  
Fatigue Life Estimation

Recently, dental implants (DIs) are extensively utilized on edentulous patients. The bio-compatibility & physical properties of DIs are severely specified since it belongs to the products of biomedicine. Generally, DIs must pass a series of tests before they are approved to use in human body. In this paper, a method of probabilistic fatigue-life estimation was proposed to fulfill reliability life prediction of DIs. The probabilistic form of fatigue-life evaluation is developed based on material constants namely fatigue strength coefficient and fatigue strength exponent. The procedure is developed based on the shift of the fatigue-life curve to the desired value of the probability of occurrence. This estimation model yields the life distribution in respect of the scatter of the cyclic properties of DIs. The CAD models of DIs are first constructed to perform computer simulation analysis for establishing the fracture spots. The stress analysis and life estimation were carried out by ANSYS software. The simulation results are further compared with the experimental data obtained by fatigue testing to determine the estimated model of fatigue life. The parameters of the model were determined by linear regression method based on the combination of the simulated and experimental data. The reliabilities of DIs were further investigated to provide an index of life-safety of DI at different cyclic loads. The analyzed results may be useful while programming the fatigue testing of DIs.

Development of High Chromium Steel for SFR in Japan and Creep-Fatigue Assessment of the Welded Joint

2008 ◽  
Author(s):  
Takashi Wakai ◽  
Nobuhiro Isobe ◽  
Shingo Date ◽  
Tai Asayama ◽  
Shigenobu Kubo
Keyword(s):  
Fatigue Strength ◽  
Grain Boundaries ◽  
Welded Joints ◽  
Ferritic Steel ◽  
Welded Joint ◽  
Assessment Procedure ◽  
Test Results ◽  
Strength Assessment ◽  
High Chromium ◽  
Creep Fatigue

This paper describes the provisional material specifications of the high chromium (Cr) ferritic steel for the Sodium cooled Fast Reactor (SFR) and development of creep-fatigue assessment procedure for the welded joint made of the steel. Based on the test results, it was revealed that tungsten (W) should be diminished to achieve better creep-fatigue strength and toughness after long term aging at elevated temperature. Metallurgical examinations using a scanning electron microscope showed that W precipitated on the grain boundaries as “Laves phase” during aging process. The toughness of the steel which contained much W might be degraded by such coarse precipitations on the grain boundaries. As a result, provisional specifications of the high Cr ferritic steel for SFR pipes and tubes were proposed. Creep-fatigue strength assessment procedure for the welded joints made of the steels was also investigated. An assessment procedure using 2-element model was proposed and verified by comparing with some creep-fatigue test results. The creep-fatigue lives observed in the experiments were well predicted by the proposed assessment procedure, but the failure of the welded joints really occurred in the heat affected zone (HAZ) in some creep-fatigue tests. Since the HAZ was not taken into account in the procedure, there were obviously some rooms for improvement. Creep-fatigue failure mechanisms of the welded joint must be investigated and the characteristics of the HAZ must be formulated for more precise creep-fatigue strength assessment.

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