EFFECT OF DYNAMIC PERTURBATION AND CONTACT CONDITION ON EDGE-DEFINED FIBER GROWTH-CHARACTERISTICS

Sapphire fibers for use in both optical sensors and structure composit es have been manufactured using the edge-defined film-fed growth (EFG) process. A thermocapillary model based on a combined Lagrangian/Euler ian method has been developed to simulate the dynamic characteristics of the EFG process, subject to the pull speed perturbations. The menis cus behavior is governed by the Young-Laplace equation subject to a sp ecified contact condition at the trijunction point. Two models have be en investigated at the trijunction point, including a conventionally a dopted static model which fixes the contact angle, and a dynamic model which regulates the contact angle according to the speed and directio n of the instantaneous movement of the trijunction point. It has been predicted, and observed experimentally, that the fiber diameter respon ds to the pull speed perturbation at the corresponding frequency, but the sensitivity of the response decays as the frequency increases. Whi le both the static and dynamic models at trijunction points cause the crystal to vary in size in response to the external fluctuations, thei r effects are noticeably different, indicating that the conventional m odels are not adequate to yield accurate predictions in the solidifica tion characteristics dynamically.