Damage Layer Evolution of a Breakwater Under Seawater Attack: Testing and Modeling

This paper presents experimental and theoretical methods to study the damage layer evolution of a breakwater made with concrete hollow squares in marine environment.Wetting time was directly related to the performance degradation of the breakwater by observation.The thickness of damage layer was detected by means of ultrasonic testing.Meanwhile,some samples drilled from concrete hollow squares were analyzed by SEM and XRD in order to illustrate the damage mechanism.Subsequently,a theoretical model containing wetting time ratio was established to simulate the damage layer evolution based on Fick’s second law,which could be suggested to predict the service life of concrete structures in marine environment.

Raman Back-scattering study of Damaged and Strain Subsurface Layers in GaAs Wafers

The damaged and strain subsurface layers of semi insulating(SI) GaAs substrate were characterized non destructively by Raman back scattering.The study shows that the thicknesses of the damaged and strain layers are less than 3μm.The damaged and strain layer can be removed after being etched in H 2SO 4·H 2O 2·H 2O for 1.5 min.

Research on Chemical Mechanical Planarization for Functional Ceramics

Presently, the products of functional ceramic are widely applied in the light & mechatronics fields such as communication, aeronautic and astronautic engineering, military affairs and home-use electrical appliance etc. It’s performance of working is mainly determined by the physical performance of the surface. And therefore the roughness and the affected layer’s depth of the final processing surface have a direct influence to the performance of the device. It is obvious that how to guarantee the processing quality of functional ceramic is a kernel problem whether it can achieve the purpose of application or not. Ultra-precision planarization is usually as the final processing method of functional ceramic substrates, and the mirror surface of Ra 0.01～0.002 μm can be obtained by ultra-precision polishing. For the ultra-precision planarization processing of functional ceramic material, simplex chemical or mechanical polishing method is very difficult to achieve the technic demands, and furthermore various defects of processing exist in the surface of crystal after planarization. However, chemical mechanical planarization (CMP) which has emerged recently as a new indispensable processing technique for higher degree planarization of functional ceramic is be able to satisfy the processing requests from the aspects of processing performance and rate. The current paper systematically introduces the processing course of functional ceramic by using chemical mechanical planarization. In addition, material removal mechanism is analyzed, and the choosing of processing conditions and components and effect of polishing slurry are discussed. Then the present research status and development trend of CMP technology for functional ceramic are discussed. Finally the current existing main questions and their solutions are presented.

Hardening Effect on Machined Surface for Precise Hard Cutting Process with Consideration of Tool Wear

During hard cutting process there is severe thermodynamic coupling effect between cutting tool and workpiece, which causes quenching effect on finished surfaces under certain conditions. However, material phase transformation mechanism of heat treatment in cutting process is different from the one in traditional process, which leads to changes of the formation mechanism of damaged layer on machined workpiece surface. This paper researches on the generation mechanism of damaged layer on machined surface in the process of PCBN tool hard cutting hardened steel Cr12MoV. Rules of temperature change on machined surface and subsurface are got by means of finite element simulation. In phase transformation temperature experiments rapid transformation instrument is employed, and the effect of quenching under cutting conditions on generation of damaged layer is revealed. Based on that, the phase transformation points of temperature under cutting conditions are determined. By experiment, the effects of cutting speed and tool wear on white layer thickness in damaged layer are revealed. The temperature distribution law of third deformation zone is got by establishing the numerical prediction model, and thickness of white layer in damaged layer is predicted, taking the tool wear effect into consideration. The experimental results show that the model prediction is accurate, and the establishment of prediction model provides a reference for wise selection of parameters in precise hard cutting process. For the machining process with high demanding on surface integrity, the generation of damaged layer on machined surface can be controlled precisely by using the prediction model.