Low bend loss femtosecond laser written waveguides exploiting integrated microcrack

We introduce the fabrication and use of microcracks embedded in glass as an optical element for manipulating light propagation, in particular for enhancing waveguide performance in silica integrated optics. By using a femtosecond laser to induce a strong asymmetric stress pattern in silica, uniform cracks with set dimensions can be created within the substrate and propagated along a fixed path. The smoothness of the resulting cleave interface and large index contrast can be exploited to enhance waveguide modal confinement. As a demonstration, we tackle the longstanding high bend-loss issue in femtosecond laser written silica waveguides by using this technique to cleave the outer edge of laser written waveguide bends, to suppress radiative bend loss. The microcrack cross section is estimated to be 15 μm in height and 30 nm in width, for the 10 $$\times$$ × 10 μm waveguides. At 1550 nm wavelength, losses down to 1 dB/cm at 10 mm bend radius were achieved, without introducing additional scattering. Both the cleave stress pattern and waveguide are fabricated with the same multiscan writing procedure, without requiring additional steps, and re-characterisation of the waveguides after 1 year confirm excellent long term performance stability.

Mechanical analysis on cement sheath integrity under asymmetric load

In large-scale multi-section hydraulic fracturing, the stress environment of wellbore is extreme complex, often causing the unbalanced stress distribution around the wellbore. That poses great challenges to the integrity of the sheath. In this paper, firstly, triaxial compression test and triaxial cyclic test are carried out at 130 °C to study the deformation characteristics of the cement under high temperature. Then based on that, an appropriate plastic mechanics model is established. Finally, the shakedown theory is applied to analyze the model and acquires a maximum cyclic loading under asymmetric stress. The result shows that (1) the well cement, with the increase of load, shows the plastic flow characteristics and can be regarded as an ideal elastic–plastic material under high temperature. (2) During the cyclic loading and unloading process, the "hysteresis loop" becomes denser, which indicates that the accumulation rate of plastic deformation is continuously declining. The main plastic strain appears in the phase of the first loading. (3) The external pressure Pz plays a positive role in the deformation control of the sheath. With the growth of Pz, the maximum cyclic loading Pmax will also increase. (4) Asymmetric stress distribution can significantly affect the bearing capacity of the sheath. If stress difference coefficient λ = 0.3, the Pmax tends to decrease nearly by 50%. With the growth of λ, the negative influence of stress asymmetry reduces gradually. High external pressure is beneficial to reduce the negative impact of the asymmetry. With the growth of λ, the benefit tends to enhance. (5) In engineering practice, if the geology around wellhole showcases the strong asymmetry (the value of λ is large), some steps need to be adopted to reduce the stress concentration.

Transverse Vibrations of Annular Spinning Disk Subjected to Out-of-Plane Loads and Uniform In-Plane Follower Edge Forces

This paper investigated the transverse vibration natural frequency and stability of an annular spinning disk subjected to concentrated uniform in-plane edge follower forces and out-of-plane loads including mass, damper, and spring. Linear plate theory is used to derive the plate model used in this research, both symmetric in-plane stress fields, due to plate rotation, and asymmetric in-plane stress fields, due to uniform edge follower forces, are considered. The asymmetric stress, which is a function of the rotation of the plate, is obtained from the steady-state response of the coupled in-plane vibration equations. The concentrated in-plane follower edge forces are expanded as Fourier series and the produced stress fields are also achieved from the corresponding Fourier components. To explore the system stabilities, natural frequency variations, in-plane and out-of-plane loads coupling effects, and the instability types, the eigenvalues are plotted with respect to rotation speeds. Based on the eigenvalue analysis, the effects of concentrated edge uniform follower forces on a spinning disk system with out-of-plane loads were concluded.

Longitudinal Compensation Algorithm for the Stamping Fold Shift of Quadric Metal Curtain Walls

Metal curtain walls are widely applied as decorative materials for the outer walls of large buildings. However, the application of such materials in curved building surfaces is relatively complicated. The whole curved surface is divided into several small surface patches according to a specific plan. Each surface patch is shaped by stamping with a certain-shaped plane metal plate. The calculation of the flat shape of a given surface patch is a key technology. Quadric surfaces are inextensible surfaces. Flat metal materials are folded when stamped into curved surfaces. Wrinkles are distributed unevenly because the curvature of surface patches is often asymmetric. Stress pushes wrinkles from high-density regions to low-density areas, at which point a uniform distribution pattern is reached under the limiting case. An accurate surface flattening method that compensates for fold shift is regarded as a difficult technology to develop. To address these problems, this study proposed an even flattening method for quadric surfaces. The proposed method simplifies the sheet metal forming technology and achieves satisfactory accuracy in the engineering process.

FEATURES OF DURABILITY CALCULATION FOR MACHINE PARTS AND STRUCTURAL ELEMENTS UNDER HIGH ASYMMETRIC LOW-AMPLITUDE LOAD CONDITIONS

The study has been conducted by means of physical, mathematical and computer modeling integrated method use. To prove the adequacy of the results obtained the experimental procedure on the existing equipment and laboratory facilities has been applied. The method of carrying out asymmetric stress cycles with mean stress of stretching to symmetric using the proposed piecewise – linear equations for evaluating the material sensitivity to asymmetry of the cycle has also been improved. It has enabled pipe column element durability under the condition of typical asymmetric low-amplitude loading calculation.