Nondestructive Photoelastic and Machine Learning Characterization of Surface Cracks and Prediction of Weibull Parameters for Photovoltaic Silicon Wafers

A nondestructive photoelastic method is presented for characterizing surface microcracks in monocrystalline silicon wafers, calculating the strength of the wafers, and predicting Weibull parameters under various loading conditions. Defects are first classified from through thickness infrared photoelastic images using a support vector machine learning algorithm. Characteristic wafer strength is shown to vary with the angle of applied uniaxial tensile load, showing greater strength when loaded perpendicular to the direction of wire motion than when loaded along the direction of wire motion. Observed variations in characteristic strength and Weibull shape modulus with applied tensile loading direction stem from the distribution of crack orientations and the bulk stress field acting on the microcracks. Using this method it is possible to improve manufacturing processes for silicon wafers by rapidly, accurately, and nondestructively characterizing large batches in an automated way.

Heat transfer to a moving wire immersed in a gas fluidized bed furnace

The gasified fluidized bed has been looked at as a safer replacement for heat treatment of carbon steel wire traditionally heat treated using molten lead baths. Most of the research has been conducted on heat transfer to larger diameter boiler tubes immersed in gas fluidized beds used by the power generation industry. However, there has been a lack of research on small diameter cylinders and longitudinally moving wire in heat treating systems. In 2015, Tannas developed a correlation that confirmed that the correlation previously developed for static wire under-predicts the heat transfer rate at higher wire speeds. In addition, this earlier correlation did not account for varying fluidization rates and only assumed that Nu was independent of fluidization rate for Ug/Umf > 2.5. So, the work reported here is intended to develop a new correlation that accounts for both wire motion and fluidizing rate in fluidized bed.

Heat transfer to a moving wire immersed in a gas fluidized bed furnace

The gasified fluidized bed has been looked at as a safer replacement for heat treatment of carbon steel wire traditionally heat treated using molten lead baths. Most of the research has been conducted on heat transfer to larger diameter boiler tubes immersed in gas fluidized beds used by the power generation industry. However, there has been a lack of research on small diameter cylinders and longitudinally moving wire in heat treating systems. In 2015, Tannas developed a correlation that confirmed that the correlation previously developed for static wire under-predicts the heat transfer rate at higher wire speeds. In addition, this earlier correlation did not account for varying fluidization rates and only assumed that Nu was independent of fluidization rate for Ug/Umf > 2.5. So, the work reported here is intended to develop a new correlation that accounts for both wire motion and fluidizing rate in fluidized bed.

Self-Exciting Wire Transducer for Time-Varying Strain Measurements

The solution of a system exciting wire vibrations of a wire sensor allowing one to perform time-varying measurements, including rapid changes and of a chaotic nature, are presented in this paper. The system is based on the typical two-coil solution, in which one of the coils is responsible for exciting the wire vibrations while the other coil is used for recording those vibrations. The task of maintaining and not fading away the natural vibrations of the wire was solved by the excitation of self-exciting vibrations by the impulse system synchronized using the wire motion velocity. The mathematical analysis of the wire motion in the system with the impulse generator, in which the existence of the limiting cycle of the wire natural frequency was proved, is shown in this paper. The computer simulation results, illustrating the metrological possibilities of the solution as well as an example of a physical implementation, are also presented.

Theoretical Research on Contact Length in the Rocking Motion Wire Saw

Rocking motion wire saw with the additional rocking motion of either the wire or the workpiece is a new machining method compared with the traditional wire saw. The length of contact between the wire and the workpiece changes in this new saw process. In this paper, the wire motion and the contact length were theoretically researched. Wire motion path equation with the rocking motion was established. The theoretical equation of the contact length in half a swing period was derived out. The results indicated that the wire motion was a single pendulum movement with a length line segment, which the swing pivot was moved with a feed rate. The contact length had significant changes in half a swing period in the rocking motion wire saw. The contact length varied periodically with the same amplitude in the square ingot sawing, which varied periodically with the variation amplitude in the circle ingot sawing. The contact length with the rocking motion was obviously shorter than the case without the rocking motion for either the square ingot or the circle ingot.

Numerical Investigation on the Effects of Sample Wire Motion in a Tube Furnace

A tube furnace is a heat treatment device in which a specimen is heated in the presence of an inert gas using electric heating coils embedded in a thermally insulating matrix. Heat flux and temperature gradients of sample during heat treatment in a tube furnace depend on the gas and wire velocities. These parameters were used in this paper for a 2-D axisymmetric numerical study to determine an optimized relationship between the temperature and the sample wire motion. The results show that wire velocity considerably affected the wire temperature distribution and increased the gas temperature to some extent. The phenomenon resulted in the shifting of the heating zone on the wire surface and occurrence of an inner convection heat transfer.