Residual stress constitutes an integral part of the total stress acting on any component in service.It is imperative to determine residual stress to estimate the life of critical engineering components, especially those that are welded. The stresses caused by non-uniform temperature distribution due to welding and the effect of these multiaxial stresses upon service performance are discussed. A controlled thermal severity test (CTS) was performed on mild steel plates bolted together, with anchor welds deposited on opposite sides. After cooling, bithermal and trithermal test welds were deposited one after the other. Varying welding stresses were deliberately introduced by using different thicknesses of both plates to change the thermal severity numbers (TSN). The main experimental technique used here to determine the magnitude and nature of residual stress is based on X-ray diffraction (XRD). It was utilised to develop and standardise other techniques. The XRD method is based on the peak shift in the diffraction pro le due to the presence of stress using a sin 2 y method. The peak shift is determined by orienting the sample at different angles ¡y to the incident X-ray beam. The semidestructive technique of hole drilling and use of a strain gauge was also employed to determine residual stress in CTS specimens. The magnitude, nature, and direction of principal stresses were determined by relieving stresses through incremental blind hole drilling and measuring strain values at each step. The surface displacements arising due to hole drilling can also be determined by laser holography. A sandwich holography technique was developed to avoid unwanted rigid body motions of samples due to hole drilling when relieving stresses. Stress values were obtained by measuring fringe displacement between two exposures of a sandwich hologram, due to hole drilling. Results on the change in residual stress values with TSN are discussed. The residual stress values determined by XRD and sandwich holography were found to be comparable, and stress values obtained by hole drilling/strain gauge measurement were higher than these values. The reasons are discussed.MST/5352
Modified Sierpinski gasket fractal patch antenna for earth exploration satellite services has been proposed in this article. The proposed antenna is designed up to third iterative fractal geometry on the FR4 substrate having dielectric constant of 4.4 with height of 0.8 mm. The proposed design shows multiband characteristics at 2.8, 6.1, 7.96, 16, and 17 GHz frequencies. The maximum gain of the proposed design is 9.6 dBi has been achieved in Ku‐band. The resonating performance characteristics and radiation characteristics of the final iteration are investigated using simulator and experimentally to verify the results of the proposed design. The simulated and measured performance parameters show quite resemblance. Further, proposed design has been simulated on the micro‐machined high resistive silicon substrate which causes the improvement in gain and efficiency. Micro‐machined fractal antenna is compatible with monolithic microwave integrated circuits (MMICs).
Abstract-In this paper, a new compact tri-band bandpass metamaterial (MTM) filter based on meander line with a rectangular stub is proposed and designed. The pseudo connections between meander line and ports generate interdigital capacitor (IDC) to provide series capacitance. Meander line with a rectangular stub realizes a virtual ground concept here. To validate the MTM property of the proposed filter structure, a dispersion diagram is plotted. The proposed filter offers measured first passbands from 1.88-4.0 GHz; second band starts from 5.4-5.9 GHz; third passband ranges from 7.1-7.4 GHz. It has insertion losses of 0.8 dB, 1.5 dB and 2.0 dB at 2.1 GHz, 5.7 GHz and 7.3 GHz centre frequencies, respectively. The designed filter will cover S band (2-4 GHz), ISM band (5.725-5.875) and fixed satellite services (7.25-7.3 GHz). Further, the designed filter shows electrical size of 0.14λ 0 ×0.13λ 0 at zeroth order resonance (ZOR) frequency 2.1 GHz.
Abstract-In this paper, a compact triple-band bandpass filter based on composite right/left handed (CRLH) approach has been proposed. The zeroth order resonance (ZOR) frequency of the designed filter can be controlled effectively by varying the series parameters. A new circular interdigital capacitor is integrated to provide series capacitance. The number of passbands depends on number of rings of circular interdigital capacitor (C-IDC). In order to validate metamaterial behavior, a dispersion diagram has been plotted for the designed filter. The proposed filter offers measured 3 dB fractional bandwidth of 71% at 1.7 GHz, 24% at 2.9 GHz and 12% at 4.1 GHz as center frequencies. The designed filter will be suitable for different wireless applications such as global navigation satellite systems (1.559-1.610 GHz), GSM1800, indoor femtocells (2.5-2.7 GHz), air traffic surveillance (2.7-2.9 GHz) and fixed satellite services (3.8-4.2 GHz). The size of the proposed filter is 0.13λ 0 × 0.11λ 0 , where λ 0 is the free space wavelength at ZOR frequency of 1.7 GHz.
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