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EWI
Columbus, OH, United States

Yang Y.-P.,EWI
Journal of Materials Engineering and Performance | Year: 2014

A framework for developing a product involving manufacturing processes was developed with integrated computational materials engineering approach. The key component in the framework is a process modeling tool which includes a thermal model, a microstructure model, a thermo-mechanical, and a property model. Using friction stir welding (FSW) process as an example, development of the process modeling tool was introduced in detail. The thermal model and the microstructure model of FSW of steels were validated with the experiment data. The model can predict reasonable temperature and hardness distributions as observed in the experiment. The model was applied to predict residual stress and joint strength of a pipe girth weld. © 2014, ASM International.


Fracture control technology has been developed to control brittle and ductile fracture initiations as well as fracture propagation in gas pipelines. The approaches developed forty years ago remain in use today for fracture initiation control, but not for ductile fracture propagation control. Different methods have been proposed for high-strength pipeline steels. This includes the two-curve model, simplified equations, corrections, correlations, alternative fracture criteria and finite element methods. This paper presents a state-of-the-art review on fracture control technology and development for modern and vintage gas transmission pipelines with critical discussions and recommendations. © 2015 Elsevier Ltd.


Zhu X.-K.,EWI
Fatigue and Fracture of Engineering Materials and Structures | Year: 2016

This paper revisits a complicated analytical solution of the stress intensity factor K adopted in a newly published British standard BS 8571:2014 for clamped single edge notched tension (SENT) specimens. Comparison with existing numerical results of K shows that the analytical K solution in BS 8571 is correct only for the crack length to specimen width ratio a/W ≤ 0.6, but incorrect for a/W > 0.6. A reinvestigation is thus performed using the crack compliance method, and a corrected K solution is obtained for the BS 8571 clamped SENT specimens over the full range of a/W. On this basis, a simple closed-form solution of K is obtained using the best curve fitting with an accuracy within 1% for crack sizes up to a/W = 0.98. Results show that the proposed closed-form solution of K agrees well with the numerical results of K for the clamped SENT specimens. © 2015 Wiley Publishing Ltd.


Zhu X.-K.,EWI
Journal of Pressure Vessel Technology, Transactions of the ASME | Year: 2016

This paper presents a critical comparison of the traditional strength criteria and the modern plastic flow criteria used in the structural design and integrity assessment of pressure vessels. This includes (1) a brief review of the traditional strength criteria used in the ASME Boiler and Pressure Vessel (BandPV) Code, (2) a discussion of the shortcomings of the traditional strength criteria when used to predict the burst pressure of pressure vessels, (3) an analysis of challenges, technical gaps, and basic needs to improve the traditional strength criteria, (4) a comparison of strength theories and plasticity theories for ductile materials, (5) an evaluation of available plastic flow criteria and their drawbacks in prediction of burst pressure of pressure vessels, (6) a description of a newly developed multiaxial yield criterion and its application to pressure vessels, and (7) a demonstration of experimental validation of the new plastic flow criterion when used to predict the burst pressure of thin-wall pressure vessels. Finally, recommendations are made for further study to improve the traditional strength design criteria and to facilitate utilization of the modern plastic flow criteria for pressure vessel design and analysis. © 2016 by ASME.


The susceptibility to stress-relaxation cracking of Alloy IN740 was evaluated using high-temperature tensile testing and Gleeble stress-relaxation testing in the temperature range from 600°-900°C and compared to Alloys IN718 and Waspaloy®. The test results indicate that the susceptibility to stress-relaxation cracking of IN740 is lower than that of Waspaloy, and it is similar to that of Alloy IN718. A ductility dip was observed in the alloys tested. IN740, IN718, and Waspalloy showed a ductility (reduction of area) minimum of 11.3% at 850°C, 8.5% at 750°C, and 4.0% at 900°C, respectively. The three alloys showed an increase of effective stress or negative-creep behavior during stress relaxation at most testing temperatures, increasing the driving force for stress-relaxation cracking. Waspaloy presented a normal stress relaxation behavior at 850°, 900°, and 950°C. Phase computational modeling predictions indicate that IN740 and Waspaloy are strengthened mainly by γ ' precipitates while IN718 is hardened by the precipitation of both gamma prime and gamma double prime. The modeling predictions show that alloys strengthened only by gamma prime (IN740 and Waspaloy) present faster precipitation reaction kinetics and experience formation of eta phase during the stress relaxation tests. The synergistic effect of stress relaxation behavior, characteristics and kinetics of precipitation reactions, and high-temperature or creep ductility may control the relative susceptibility to stress relaxation cracking of these three alloys.

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