Investigation of short-term creep deformation mechanisms in MarBN steel at elevated temperatures

This paper reports the short-term creep behavior at elevated temperatures of a MarBN steel variant. Creep tests were performed at 3 different temperatures (625oC, 650oC and 675oC) with applied stresses ranging from 160 MPa to 300 MPa, and failure times from 1 to 350 hours. Analysis of the macroscopic creep data indicates that the steady-state creep exhibits a power-law stress dependence with an exponent of 7 and an activation energy of 307 kJ.mol-1, suggesting that dislocation climb is the dominant rate-controlling creep mechanism for MarBN steel. Macroscopic plastic instability has also been observed, highlighted by an obvious necking at the rupture region. All the macroscopic predictions have been combined with microstructural data, inferred from an examination of creep ruptured samples, to build up relations between macroscopic features (necking, damage, etc.) and underlying microstructural mechanisms. Analysis of the rupture surfaces has revealed a ductile fracture mode. Electron Backscatter Diffraction (EBSD) analysis near to the rupture surface has indicated significant distortion and refinement of the original martensitic substructure, which is evidence of long-range plastic flow. Dislocation pile-ups and tangles from TEM were also observed near substructure boundaries and precipitate particles. All of these microstructural observations suggest that creep is influenced by a complex interaction between several elements of the microstructure, such as dislocations, precipitates and structure boundaries. The calculated stress exponent and activation energy have been found to agree quantitatively with the highlighted microstructural features, bearing some relationships to the true observed creep microstructures

Contact Interaction of Two Oil Lenses Floating on Surface of Deionized Water

Droplets on the surface of liquid play an important role in a variety of areas, including the petroleum industry, pollution control, and environmental processes. In this work, we study the contact interaction between two floating oil lenses on the surface of immiscible water. The contact interaction between the two floating oil lenses can be divided into three different regimes: (a) the collision involving deformation for low-viscous oils, (b) the direct coalescence for high-viscous oils, and (c) the coexistence (noncoalescence) of oil lenses at relatively high temperatures. The temperature dependence of the coalescence time for the coalescence of two silicone-oil lenses of large viscosities follows the Arrhenius equation

Contact Interaction of Two Oil Lenses Floating on Surface of Deionized Water

Droplets on the surface of liquid play an important role in a variety of areas, including the petroleum industry, pollution control, and environmental processes. In this work, we study the contact interaction between two floating oil lenses on the surface of immiscible water. The contact interaction between the two floating oil lenses can be divided into three different regimes: (a) the collision involving deformation for low-viscous oils, (b) the direct coalescence for high-viscous oils, and (c) the coexistence (noncoalescence) of oil lenses at relatively high temperatures. The temperature dependence of the coalescence time for the coalescence of two silicone-oil lenses of large viscosities follows the Arrhenius equation

Contact Interaction of Two Oil Lenses Floating on Surface of Deionized Water

Droplets on the surface of liquid play an important role in a variety of areas, including the petroleum industry, pollution control, and environmental processes. In this work, we study the contact interaction between two floating oil lenses on the surface of immiscible water. The contact interaction between the two floating oil lenses can be divided into three different regimes: (a) the collision involving deformation for low-viscous oils, (b) the direct coalescence for high-viscous oils, and (c) the coexistence (noncoalescence) of oil lenses at relatively high temperatures. The temperature dependence of the coalescence time for the coalescence of two silicone-oil lenses of large viscosities follows the Arrhenius equation

Formation of Self-Organized Gradient Stripes on Precast Poly(methyl methacrylate) Films

A “wire-on-film” template has been developed to construct surface gradient patterns on precast poly­(methyl methacrylate) films. Solvent evaporation around a Cu wire leads to the formation of self-organized gradient stripes, with the longitudinal direction of the stripes being parallel to the axis of the Cu wire. Both the spatial wavelength and the amplitude of the stripes near the Cu wire decrease with a decrease of the distance to the center of the Cu wire. The amplitude of the stripes varies linearly with the spatial wavelength for the experimental conditions used, which is a function of the diameter of the Cu wires and the film thickness. Using two parallel copper wires, we demonstrate the possibility of controlling the characteristics of the gradient stripes. A featureless zone is formed between the copper wires, the size of which is dependent on the distance between two wires and the diameter of the copper wires. The results of this study provide a simple method to fabricate gradient gratings on polymer films in an economical and efficient way

Dynamics of the Evaporative Dewetting of a Volatile Liquid Film Confined within a Circular Ring

The dewetting dynamics of a toluene film confined within a copper ring on a deformable PMMA film is studied. The toluene film experiences evaporation and dewetting, which leads to the formation of a circular contact line around the center of the copper ring. The contact line recedes smoothly toward the copper ring at a constant velocity until reaching a dynamic “stick” state to form the first circular polymer ridge. The average receding velocity is found to be dependent on the dimensions of the copper ring (the copper ring diameter and the cross-sectional diameter of the copper wire) and the thickness of the PMMA films. A model is presented to qualitatively explain the evaporative dewetting phenomenon

Structure schematic of a typical rotary SIAMS.

Attitude determination involves the integration of methodologies and systems for estimating the time varying attitude of moving objects. Strapdown Inertial Attitude Measurement System (SIAMS) is among the most widely used navigation systems. The development of cost effective Micro Electro Mechanic System (MEMS) based inertial sensors has made attitude measurement system more affordable. However, MEMS sensors suffer from various errors that have to be calibrated and compensated to get acceptable attitude results. Given the auto-compensation of inertial sensor bias in rotation error modulation, the objective of this paper is to develop a MEMS-based rotary SIAMS, in which the significant sensor bias is automatically compensated by rotating the IMU, to offer comparable performance with respect to a tactical-grade Inertial Measurement Unit (IMU). With the analysis of the relationship between the MEMS error and misalignment, a MEMS calibration model is derived, and a combined calibration method of multi position rotation is applied to estimate the deterministic sensor errors such as bias, scale factor, and misalignment. Simulation and experiment results indicate that the proposed method can further modulate and compensate the MEMS errors, thereby improving the MEMS attitude accuracy.</div

Curves of attitude error with heading changed slowly.

(a) Attitude overall view. (b) Heading partial enlarged view.</p

Mechanization of the rotary SIAMS.

Attitude determination involves the integration of methodologies and systems for estimating the time varying attitude of moving objects. Strapdown Inertial Attitude Measurement System (SIAMS) is among the most widely used navigation systems. The development of cost effective Micro Electro Mechanic System (MEMS) based inertial sensors has made attitude measurement system more affordable. However, MEMS sensors suffer from various errors that have to be calibrated and compensated to get acceptable attitude results. Given the auto-compensation of inertial sensor bias in rotation error modulation, the objective of this paper is to develop a MEMS-based rotary SIAMS, in which the significant sensor bias is automatically compensated by rotating the IMU, to offer comparable performance with respect to a tactical-grade Inertial Measurement Unit (IMU). With the analysis of the relationship between the MEMS error and misalignment, a MEMS calibration model is derived, and a combined calibration method of multi position rotation is applied to estimate the deterministic sensor errors such as bias, scale factor, and misalignment. Simulation and experiment results indicate that the proposed method can further modulate and compensate the MEMS errors, thereby improving the MEMS attitude accuracy.</div