Reduction of Residual Stresses in Sapphire Cover Glass Induced by Mechanical Polishing and Laser Chamfering Through Etching

Sapphire is a hard and anti-scratch material commonly used as cover glass of mobile devices such as watches and mobile phones. A mechanical polishing using diamond slurry is usually necessary to create mirror surface. Additional chamfering at the edge is sometimes needed by mechanical grinding. These processes induce residual stresses and the mechanical strength of the sapphire work piece is impaired. In this study wet etching by phosphate acid process is applied to relief the induced stress in a 1” diameter sapphire cover glass. The sapphire is polished before the edge is chamfered by a picosecond laser. Residual stresses are measured by laser curvature method at different stages of machining. The results show that the wet etching process effectively relief the stress and the laser machining does not incur serious residual stress

Sliding Mode Path following and Control Allocation of a Tilt-Rotor Quadcopter

A tilt-rotor quadcopter (TRQ) equipped with four tilt-rotors is more agile than its under-actuated counterpart and can fly at any path while maintaining the desired attitude. To take advantage of this additional control capability and enhance the quadrotor system’s robustness and capability, we designed two sliding mode controls (SMCs): the typical SMC exploits the properties of the rotational dynamics, and the modified SMC avoids undesired chattering. Our simulation studies show that the proposed SMC scheme can follow the planned flight path and keep the desired attitude in the presence of variable deviations and external perturbations. We demonstrate from the Lyapunov stability theorem that the proposed control scheme can guarantee the asymptotic stability of the TRQ in terms of position and attitude following via control allocation

Sliding Mode Path following and Control Allocation of a Tilt-Rotor Quadcopter

A tilt-rotor quadcopter (TRQ) equipped with four tilt-rotors is more agile than its under-actuated counterpart and can fly at any path while maintaining the desired attitude. To take advantage of this additional control capability and enhance the quadrotor system’s robustness and capability, we designed two sliding mode controls (SMCs): the typical SMC exploits the properties of the rotational dynamics, and the modified SMC avoids undesired chattering. Our simulation studies show that the proposed SMC scheme can follow the planned flight path and keep the desired attitude in the presence of variable deviations and external perturbations. We demonstrate from the Lyapunov stability theorem that the proposed control scheme can guarantee the asymptotic stability of the TRQ in terms of position and attitude following via control allocation

Measurement of Elastic Properties of Brittle Materials by Ultrasonic and Indentation Methods

The measurements of acoustic properties of three brittle materials i.e., ITO (alkaline earth boro-aluminosilicate) glass, bulk metallic glass (BMG) and nickel-based superalloy (CM247LC) are conducted in this work to obtain various properties. The elastic moduli of materials are derived from the results by simple acoustic speed-elasticity relationship and compared with the data obtained with nanoindentation. The difference between the Young’s modulus of ITO glass by ultrasonic and nanoindentation is 0.83%, a perfect match within range error. As for BMG, the difference (Young’s modulus) is 23.59%, and 5.11% for the CM247LC superalloys. The pulse-echo method proves to be reliable for homogeneous amorphous glass, however, the elastic moduli of metallic glass and CM247LC superalloy by ultrasonic are quite different from those by nanoindentation. The difference is large enough to cover the maximal error associated with the nanoindentation method. The relationship of acoustic speed and elastic constants must be reviewed in dealing with compound materials

Reduction of Residual Stresses in Sapphire Cover Glass Induced by Mechanical Polishing and Laser Chamfering Through Etching

Sapphire is a hard and anti-scratch material commonly used as cover glass of mobile devices such as watches and mobile phones. A mechanical polishing using diamond slurry is usually necessary to create mirror surface. Additional chamfering at the edge is sometimes needed by mechanical grinding. These processes induce residual stresses and the mechanical strength of the sapphire work piece is impaired. In this study wet etching by phosphate acid process is applied to relief the induced stress in a 1” diameter sapphire cover glass. The sapphire is polished before the edge is chamfered by a picosecond laser. Residual stresses are measured by laser curvature method at different stages of machining. The results show that the wet etching process effectively relief the stress and the laser machining does not incur serious residual stress