Dual Laser Beam Asynchronous Dicing of 4H-SiC Wafer

SiC wafers, due to their hardness and brittleness, suffer from a low feed rate and a high failure rate during the dicing process. In this study, a novel dual laser beam asynchronous dicing method (DBAD) is proposed to improve the cutting quality of SiC wafers, where a pulsed laser is firstly used to introduce several layers of micro-cracks inside the wafer, along the designed dicing line, then a continuous wave (CW) laser is used to generate thermal stress around cracks, and, finally, the wafer is separated. A finite-element (FE) model was applied to analyze the behavior of CW laser heating and the evolution of the thermal stress field. Through experiments, SiC samples, with a thickness of 200 μm, were cut and analyzed, and the effect of the changing of continuous laser power on the DBAD system was also studied. According to the simulation and experiment results, the effectiveness of the DBAD method is certified. There is no more edge breakage because of the absence of the mechanical breaking process compared with traditional stealth dicing. The novel method can be adapted to the cutting of hard-brittle materials. Specifically for materials thinner than 200 μm, the breaking process in the traditional SiC dicing process can be omitted. It is indicated that the dual laser beam asynchronous dicing method has a great engineering potential for future SiC wafer dicing applications.

Thermal–Fluid–Solid Coupling Analysis on the Temperature and Thermal Stress Field of a Nickel-Base Superalloy Turbine Blade

Based on the establishment of the original and improved models of the turbine blade, a thermal–fluid–solid coupling method and a finite element method were employed to analyze the internal and external flow, temperature, and thermal stress of the turbine blade. The uneven temperature field, the thermal stress distribution characteristics of the composite cooling turbine blade under the service conditions, and the effect of the thickness of the thermal barrier coating (TBC) on the temperature and thermal stress distributions were obtained. The results show that the method proposed in this paper can better predict the ablation and thermal stress damage of turbine blades. The thermal stress of the blade is closely related to the temperature gradient and local geometric structure of the blade. The inlet area of the pressure side-platform of the blade, the large curvature region of the pressure tip of the blade, and the rounding between the blade body and the platform on the back of the blade are easily damaged by thermal stress. Cooling structure optimization and thicker TBC thickness can effectively reduce the high temperature and temperature gradient on the surface and inside of the turbine blade, thereby reducing the local high thermal stress.

Effect of the growth pulling direction on 3D anisotropic stress during different stages of semitransparent Li2MoO4 growth

The three dimensional thermal stress field is calculated at different growth stages for LMO crystals grown in an inductively heated Czochralski furnace using the anisotropy and temperature-dependency of the mechanical...

Scaling Analysis of the Thermal Stress Field Produced by a Moving Point Heat Source in a Thin Plate

This study presents a scaling analysis of thermally induced stresses and strains produced during welding and additive manufacturing of thin structures such as plates or walls. The order of magnitude scaling (OMS) technique was used to develop an appropriate dimensionless formulation, to obtain asymptotic expressions, and to determine the limits of validity. Nonlinear finite element simulations of welding procedures were performed to validate the asymptotic model; plasticity and temperature dependent materials properties for structural steel, stainless steel, and aluminum were considered. Thermal stresses cause plasticity when the temperature reaches a critical temperature termed the first yield temperature. The model developed is valid when the first yield isotherm is elongated, which is the case for most welding and metal additive manufacturing applications. A rigorous novel expression for the criterion of applicability is presented and utilized for prediction of the width of the plastic zone surrounding a weld or additive manufacturing bead. Extrapolations beyond the region of applicability show a consistent trend, which is captured in the form of a general dimensionless empirical expression. This work establishes the foundation for the estimation of forces and distortions induced by welding or additive manufacturing processes, and also the incorporation of effects of departure from idealizations.