Surface Properties of Ultrasonic Vibration-Assisted ELID Grinding ZTA Ceramics

This study aimed to explore the evolution of surface properties of nanocomposite ceramics during ultrasonic vibration-assisted electrolytic in-process dressing (UVA-ELID) grinding. First, the trajectory of the grain was analyzed, and the motion was simulated using MATLAB to demonstrate the mechanism of UVA-ELID grinding. The critical grinding depth was also calculated under the effect of ultrasonic vibration. Then, the conventional ELID (C-ELID) and UVA-ELID grinding were compared. The surface properties, including surface residual stress, surface microstructure, surface roughness, and surface morphology, were used to evaluate the effectiveness and feasibility of UVA-ELID grinding. Whether it was conventional C-ELID or UVA-ELID grinding, the residual compressive stress was introduced into the machined surface, while the former was lower than the latter. The microstructure of the UVA-ELID grinding was evenly distributed, and the ductility removal occurred during material removal. The surface roughness of Ra and Rz was reduced by 14.5% and 20.6%, respectively, during the UVA-ELID grinding. The surface morphology was dramatically changed with the help of ultrasonic vibration. In a word, for nanocomposite ceramic, the UVA-ELID grinding can significantly improve surface performance and achieve a better machining effect.

Design and Fabrication of Laser Protective Lenses Based on Multilayered Notch Filter with Low Residual Stress and Low Surface Roughness

We present a new laser protective lens based on a multilayered notch filter design with low residual stress and low surface roughness. An18-layer notch filter was prepared by electron beam evaporation with an ion-assisted deposition technique, which was composed of SiO2 and Nb2O5 with a center wavelength of 532 nm. The optical transmittance, residual stress, surface roughness, and surface morphology were measured by a UV/VIS/NIR spectrophotometer, Twyman–Green interferometer, scanning probe microscope, Linnik microscopic interferometer, and field-emission scanning electron microscopy (FE-SEM). The transmittance of the notch filters at center wavelength is 0.2%, and the average transmittance of the transmission band is about 70%. The residual stress of the notch filter is −0.298 GPa, and the root mean square surface roughness is 1.88 nm. The experimental results show that the optical transmittance meets the design requirements.

Limited Stress Surface Model for Bending and Torsion Fatigue Loading with the Mean Load Value

In this study, a linear model of the transformation of the stress amplitude due to the mean value was used. The coefficient of the material sensitivity to cycle asymmetry with consideration of the dependence of this coefficient on the number of fatigue loading cycles is also used. A three-parameter surface model of limited stresses is proposed in this paper. The model is verified using the results of fatigue tests for cyclic bending and torsion under mean loads. The tests are performed for two types of alloy steels—S355J0 and S355J2G1W. Comparison of the allowable stress amplitudes obtained experimentally with those predicted using the proposed model shows errors of no more than 18%, with the area of the surface with the largest error being relatively small.

4D Printing of Smart Polymer Nanocomposites: Integrating Graphene and Acrylate Based Shape Memory Polymers

The ever-increasing demand for materials to have superior properties and satisfy functions in the field of soft robotics and beyond has resulted in the advent of the new field of four-dimensional (4D) printing. The ability of these materials to respond to various stimuli inspires novel applications and opens several research possibilities. In this work, we report on the 4D printing of one such Shape Memory Polymer (SMP) tBA-co-DEGDA (tert-Butyl Acrylate with diethylene glycol diacrylate). The novelty lies in establishing the relationship between the various characteristic properties (tensile stress, surface roughness, recovery time, strain fixity, and glass transition temperature) concerning the fact that the print parameters of the laser pulse frequency and print speed are governed in the micro-stereolithography (Micro SLA) method. It is found that the sample printed with a speed of 90 mm/s and 110 pulses/s possessed the best batch of properties, with shape fixity percentages of about 86.3% and recovery times as low as 6.95 s. The samples built using the optimal parameters are further subjected to the addition of graphene nanoparticles, which further enhances all the mechanical and surface properties. It has been observed that the addition of 0.3 wt.% of graphene nanoparticles provides the best results.

A full relativistic thin disc - the physics of the plunging region and the value of the stress at the ISCO

The widely used Novikov-Thorne relativistic thin disc equations are only valid down to the radius of the innermost-stable circular orbit (ISCO). This leads to an undetermined boundary condition at the ISCO, known as the inner stress of the disc, which sets the luminosity of the disc at the ISCO and introduces considerable ambiguity in accurately determining the mass, spin and accretion rate of black holes from observed spectra. We resolve this ambiguity by self-consistently extending the relativistic disc solution through the ISCO to the black hole horizon by calculating the inspiral of an average disc particle subject to turbulent disc forces, using a new particle-in-disc technique. Traditionally it has been assumed that the stress at the ISCO is zero, with material plunging approximately radially into the black hole at close to the speed of light. We demonstrate that in fact the inspiral is less severe, with several (∼4 − 17) orbits completed before the horizon. This leads to a small non-zero stress and luminosity at and inside the ISCO, with a local surface temperature at the ISCO between ∼0.15 − 0.3 times the maximum surface temperature of the disc, in the case where no dynamically important net magnetic field is present. For a range of disc parameters we calculate the value of the inner stress/surface temperature, which is required when fitting relativistic thin disc models to observations. We resolve a problem in relativistic slim disc models in which turbulent heating becomes inaccurate and falls to zero inside the plunging region.

Analytical Solution for Buckling Behavior of FGM Plate Considering Surface Effect Based on General Third-Order Plate Theory and Non-local Theory

In this paper, the buckling characteristic of FGM plate considering the surface effect is studied based on general third-order plate theory and non-local theory. The surface effect of FGM plate is captured by the surface elasticity theory. The Kirchhoff hypothesis is released by employing parabolic variation of transverse shear strains. By using Navier solution technique, analytical solutions of buckling loads of FGM plate with surface effect are given, and detailed parametric studies are presented to show the relationship between surface effects and the plate thickness, power-law index, surface residual stress, surface moduli and non-local parameter. Furthermore, the surface effect on the buckling characteristic of FGM plate is also discussed.

A Two-Step Annealing Method to Enhance the Pyroelectric Properties of Mn:PIMNT Chips for Infrared Detectors

Mn:0.15Pb(In1/2Nb1/2)O3-0.55Pb(Mg1/3Nb2/3)O3-0.30PbTiO3 (Mn:PIMNT) pyroelectric chips were prepared by a two-step annealing method. For the two steps, annealing temperatures dependence of microstructure, defects, surface stress, surface roughness, dielectric properties and pyroelectric properties were studied comprehensively. The controlling factors influencing the pyroelectric properties of the Mn:PIMNT crystals were analyzed and the optimum annealing temperature ranges for the two steps were determined: 600–700 °C for the first step and 500–600 °C for the second step. The pyroelectric properties of the thin Mn:PIMNT chips were significantly enhanced by the two-step annealing method via tuning oxygen vacancies and eliminating surface stress. Based on Mn:PIMNT pyroelectric chips annealed at the most favorable conditions (annealed at 600 °C for the first step and 500 °C for the second step), infrared detectors were prepared with specific detectivity D* = 1.63 × 109 cmHz1/2W−1, nearly three times higher than in commercial LiTaO3 detectors.