Issue 49

A. Kumar et alii, Frattura ed Integrità Strutturale, 49 (2019) 515-525; DOI: 10.3221/IGF-ESIS.49.48 525 Response at 100 Hz frequency A further estimation of fatigue life was done by exciting the ALIP body at 100 Hz to consider Double Supply Frequency (DSF) [1]. As the frequency of excitation is high, the analysis was run for about 30 cycles. A similar transient simulation was done as described earlier to estimate the transient stress response. The mean stress in this case remains the same as earlier i.e. ~ 48 MPa while the stress range has reduced to 3.29 MPa. The fatigue life under the constant stress amplitude is, N= 8.784 × 10 9 cycles i.e. the welded joint can withstand a continuous operation for 1016 days or approximately 2.78 years, if it continues to vibrate at 100 Hz at 200°C. C ONCLUSION he stress response obtained under the sinusoidal excitation given near the base comprises of two parts. In the first part, stress amplitudes are high and decreases exponentially with time and its frequency is equal to the natural frequency of the waveguide. This response is governed by solution of homogenous part of the governing differential equation and it limits the number of start-ups (or sudden transients) that the weld can withstand. The second part, which is the solution of particular integral, is stabilized stress cycle with same frequency as the frequency of excitation. The stress amplitude in this region remains constant and hence it limits the time for which the weld can be continuously subjected to such vibrations. It is evident that the fatigue life of the weld is the determining criteria for a reliable period of operation of the waveguide. The fatigue life of the weld has been estimated and the minimum fatigue life of weld for 300 mm long waveguide vibrating at 10 Hz continuously is around 260 days. In an attempt to enhance this fatigue life, a reduction in the overall length by 100 mm was done and its effect on stress and life were obtained. This modification leads to a reduction in the stress due to self-weight from 96 MPa to 48 MPa. The constant stress range has reduced from 10.6 MPa to 5.8 MPa when the ALIP vibrates at 10Hz thereby increasing the minimum fatigue life of the weld to 1716 days, however for 100 Hz frequency the life of the weld has been estimated as 1016 days under continuous operation. Hence, the use of a 200 mm long waveguide is a preferable choice. R EFERENCES [1] Hideo, Araseki et.al . (2004). Magnetohydrodynamic instability in annular linear induction pump Part I. Experiment and numerical analysis, Nuclear Engineering and Design 227 (2004) 29–50 [2] Mannan, S.L. et. al. (April, 2003). Selection of Materials for Prototype Fast Breeder Reactor, Transactions- Indian Institute of Metals 56(2) [3] Boiler and Pressure Vessel Code (BPVC) ASME (2013). II Materials Part D Properties (Customary) [4] Harvey,John F. Theory and design of pressure vessels, Van Nostrand Reinhold Company, New York. [5] Thomson,W. T. Theory of Vibration, CBS Publishers and Distributors, New Delhi, Third Edition. [6] Rao, Singiresu S. (2004). Mechanical Vibrations, Pearson Education Pte. Ltd. [7] Boiler and Pressure Vessel Code (BPVC) ASME (2010). SECTION VIII, DIVISION 2, Part 5, Fatigue Assessment of Weld-Elastic Analysis and Structural Stress. T