Low-pressure turbine disc fi rtree slots’ life and reliability enhancement by ultrasonic surface hardening

The possibility of life and reliability enhancing of AL-31F low pressure turbine disc’s fir-tree slots by ultrasonic hardening is considered. Having disc’s material properties studied, working stress derivation is executed which was further used for following comparative fatigue tests. Also, Davidenkov method residual stress analysis is carried out which showed 95.3 % change to compression stress for circumferential residual stress and 80.9 % change to compression stress for axial residual stress which proves possibility of fir-tree slots’ life and reliability enhancement by ultrasonic hardening. Comparative fatigue tests with N = 4•10 5 cycles basis showed that the hardened samples standing out the cycle basis during higher oscillatory amplitudes (and, thus, affecting loads) than the non-hardened basic ones.

Effect of Initial Residual Stress on Machining Deformation of a Casing Part

Initial residual stress of blank is the main cause for the workpiece machining deformation. Based on the simplified equivalent model and the finite element analysis method, the effects of initial residual stress in bidirectional, axial direction and tangential direction on the deformation of an aluminum alloy conical case were studied respectively. The deformations of case were judged by flatness and roundness error of the end face of the case. From the results, it can be seen that the influence of the initial axial residual stress on the roundness error of the end face is greater than that of the radial residual stress; among all the errors, the roundness error of the large end face is much larger than that of other errors. It is shown that the roundness error of the large end face and the initial axial residual stress of the workpiece are the most important issues to be controlled in actual machining process. This conclusion has certain guiding significance for practical application.

Residual Stress Relief in 2219 Aluminium Alloy Ring Using Roll-Bending

Relieving the residual stress in components is essential to improve their service performance. In this study, a roll-bending process was proposed to reduce the quenching residual stress in a large-size 2219 Al alloy ring. The roll-bending effect on quenching residual stress was evaluated via the finite element method (FEM) combined with experiment. The effect of radial feed quantity, friction coefficient, and roller rotational speed during the roll-bending process on quenching residual stress was analyzed. A set of optimized roll-bending parameters with radial feed quantity, friction coefficient, and roller rotational speed was obtained. The results reveal that the best reduction rates of circumferential and axial residual stress reached 61.72% and 86.24%, respectively. Furthermore, the difference of the residual stress reduction effect between the roll-bended ring and the three-roller bended beam was analyzed.

Design and optimization of a low voltage RF switch MEMS capacitance using genetic algorithm and Taguchi method

Purpose This paper aims to design, optimize and simulate the Radio Frequency (RF) micro electromechanical system (MEMS) Switch which is stimulated by electrostatically voltage. Design/methodology/approach The geometric structure of the switch was extracted based on the design of Taguchi-based experiment using the mathematical programming and obtaining objective function by the genetic meta-heuristic algorithm. Findings The RF parameters of the switch were calculated for the design of Taguchi-based S11 = −5.649 dB and S21 = −46.428 dB at the working frequency of 40 GHz. The pull-in voltage of the switch was 2.8 V and the axial residual stress of the proposed design was obtained 28 MPa and the design of Taguchi-based S11 = −4.422 dB and S21 = −48.705dB at the working frequency of 40 GHz. The pull-in voltage of the switch was 2.5 V and the axial residual stress of the proposed design was obtained 25 MPa. Originality/value A novel complex strategy in the design and optimization of capacitive RF switch MEMS modeling is proposed.

Optimization of shunt capacitive RF MEMS switch by using NSGA-II algorithm and uti-liti algorithm

The present paper aimed at designing, optimizing, and simulating the RF MEMS Switch which is stimulated electrostatically. The design of the switch is located on the CoplanarWaveguide (CPW) transmission line. The pull-in voltage of the switch was 2V and the axial residual stress of the proposed design was obtained at 23MPa. In order to design and optimize the geometric structure of the switch, the desired model was extracted based on the objective functions of the actuation voltage and the return loss up-state and also the isolation down-state using the mathematical programming. Moreover, the model was solved by the NSGA-II meta-heuristic algorithm in MATLAB software. In addition, the design requirements and the appropriate levels for designing the switch were obtained by presenting the Pareto front from the beam actuation voltage and also the return loss up-state and isolation down-state. Finally, the RF parameters of the switch were calculated as S11=-2.54dB and S21=-33.18dB at the working frequency of 40GHz by extracting the appropriate parameters of the switch design through simulating a switch designed by the COMSOL Multiphysics software 4.4a and the advanced design system (ADS).

Development of Process Induced Residual Stress During Flow Forming of Tubular 15-5 Martensitic Stainless Steel

Flow forming is a near net shape process for manufacturing of dimensionally accurate hollow components such as shaft in gas turbines, that is currently at its development stage for aerospace industry. The process has several advantages such as reducing material wastage, extremely fast manufacturing time, and eliminating extra manufacturing processes such as machining. Due to the nature of this complicated cold deformation process, significant magnitude of residual stress is introduced into the component. Understanding the magnitude and distribution of residual stress is essential to tailor the flow forming process to achieve parts within dimensional tolerances and desired mechanical properties. The present research is aiming to explore the generation and evolution of residual stress at various stages of flow forming process in a tubular component made from martensitic 15Cr-5Ni stainless steel, using different techniques of neutron scattering, x-ray diffraction (XRD) and hole-drilling based on electronic speckle pattern interferometry (ESPI). Residual stress measurements were carried out in preformed and flow formed components at surface, near-surface and in the bulk of components using XRD, ESPI based hole-drilling and neutron diffraction techniques. These measurements were conducted at different levels of reduction in the thickness of the original part (i.e. after 20% and 40%), by applying identical forming parameters for all samples. The XRD results show significant change in hoop and axial residual stress levels with a reduction in the wall thickness. This is more pronounced for the axial component where the average stress switches from relatively high tensile (∼ 450MPa) in the original part to significant compressive stress (∼ −600MPa) in the formed part, after 20% of reduction. The bulk residual stress components measured in the middle of thickness of the parts, using neutron scattering, show a general increase in the magnitude of residual stress by higher level of deformation (i.e. reduction in the wall thickness). The measured bulk stress components through the thickness were tuned to tensile after reducing the wall thickness by 40%. The results of XRD and neutron diffraction stress measurements suggest that the residual stress along the length of the samples (i.e. axial direction) is consistent with ±800 MPa and ±400 MPa after 20% and 40% reduction by forming process, respectively. The results of ESPI based hole-drilling show tensile hoop residual stress (≈600 MPa) and an abrupt fluctuation (i.e. tension-compressive-tension) in the axial residual stress near the surface of the part following flow forming. The stresses measured by ESPI based hole-drilling are complementary to the results of the XRD on surface and neutron diffraction in the bulk to reconstruct the residual stress profile form the surface through to the bulk.

Residual Stress in the Welding Joint of Layered Cylindrical Vessels Including the Weld Clad Effect

Layered cylindrical vessels are widely used in process industries. The weld clad is applied before the girth welding of layered-to-layered sections. In this paper, a numerical method was used to predict residual stresses in a layered-to-layered joint with weld clad. The results showed that high residual stresses were generated in the weld and heat affect zone (HAZ), and a discontinuous stress distribution was generated. The through-wall axial residual stress at the weld centerline (WCL) was predominately tensile. The axial residual stress in each layer at the HAZ demonstrated a bending type distribution. The through-wall hoop residual stress at the WCL was predominately compressive in the V-groove zone, and it was tensile in the U-groove zone. The weld clad can decrease the peak residual stress in the tip of the interlayer gaps.

Bounding Residual Stress Intensity Factor Profiles for Fracture Assessment of Pipe Girth Welds

The effect of residual stress on potential crack growth and fracture in welded structures is usually assessed through its contribution to the stress intensity factor (SIF) for the crack size and shape of interest. The idea of defining bounding residual SIF profiles for surface breaking circumferential cracks in pipe butt welds was presented at ASME PVP2013. The limiting profiles were based on through-thickness residual stress measurements for eight pipe girth welds. This paper presents new axial residual stress measurements made using the contour method for an Esshete 1250 stainless steel pipe girth weld. A wide variation in the through-wall distribution of axial residual stress around the circumference of the pipe is observed which has a significant effect on calculated values of SIF for postulated surface breaking circumferential cracks. Nonetheless, SIFs based on all of the new measurements (a total of 14 profiles) are comfortably bounded by the simple SIF prescriptions previously published.

Characterization of the Electrically-Actuated Micro Circular Plate

In this study presents a hybrid numerical scheme comprising the differential transformation method and the finite difference approximation technique to analyze the nonlinear dynamic response of the micro circular plate. The analysis takes account of the axial residual stress and hydrostatic pressure acting on micro circular plate upper surface. The effects of the residual stress, initial gap height, and thickness on the pull-in voltage of the micro circular plate are systematically explored. Overall, the proposed method provides an accurate and versatile means of analyzing the complex nonlinear behavior of the electrostatically-actuated microstructures.