During fabrication of glass lens by precision glass molding (PGM), residual stresses are setup, which adversely affect the optical performance of lens. Residual stresses can be obtained by measuring the residual birefringence. Numerical simulation is used in the industry to optimize the manufacturing process. Material properties of glass, contact conductance and friction coefficient at the glass-mold interface are important parameters needed for simulations. In literature, these values are usually assumed without enough experimental justifications. Here, the viscoelastic thermo-rheological simple (TRS) behavior of glass is experimentally characterized by the four-point bending test. Contact conductance and friction coefficient at P-SK57™ glass and Pt-Ir coated WC mold interface are experimentally measured. A plano-convex lens of P-SK57™ glass is fabricated by PGM for two different cooling rates and whole field birefringence of the finished lens is measured by digital photoelasticity. The fabrication process is simulated using finite element method. The simulation is validated, for different stages of PGM process, by comparing the load acting on the mold and displacement of the molds. At the end of the process, the birefringence distribution is compared with the experimental data. A novel plotting scheme is developed for computing birefringence from FE simulation for any shape of lens
Process parameters of Precision Glass Molding (PGM) are often sought by Finite Element (FE) simulation. Mechanical as well as thermal boundary conditions (BCs) are necessary for FE simulation in which mechanical BCs are usually known or easily determinable. However, most of the thermal BCs are generally assumed in the FE simulation as they cannot be measured directly. The focus of this article is to propose a novel method for evaluating the thermal BC of glass-N 2 gas. FE simulations as well as thermal cycling experiments are carried out for a glass disk specimen for three different cooling rates. CFD analysis of N 2 flow in the PGM machine is performed to understand the heat extraction mechanism. Based on this, adhoc values for equivalent heat transfer coefficient (h eqv ) are obtained by lumped system analysis. A novel methodology is then proposed for obtaining accurate h eqv values by measurement of integrated residual birefringence in glass using digital photoelasticity. FE simulation is repeated for different values of h eqv until the integrated birefringence based on simulation matches with that of the experiment. For the same cooling rates, two aspherical glass lenses are molded and their residual birefringence is measured and compared with the glass disk specimen.
Experimental observations of domain formations and pattern transitions in soft particulate composites under large deformations are reported herein. The system of stiff inclusions periodically distributed in a soft elastomeric matrix experiences dramatic microstructure changes upon the development of elastic instabilities. In the experiments, the formation of microstructures with antisymmetric domains and their geometrically tailored evolution into a variety of patterns of cooperative particle rearrangements are observed. Through experimental and numerical analyses, it is shown that these patterns can be tailored by tuning the initial microstructural periodicity and concentration of the inclusions. Thus, these fully determined new patterns can be achieved by fine tuning of the initial microstructure.
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