Sıvı kalıplama kompozit imalat yönteminde kullanılan kumaşlar için geçirgenlik ölçüm yöntemleri

Liquid Composite Molding (LCM) processes are commonly used in the composite manufacturing industries by impregnating a stationary fiber preform placed in the mold cavity. However, to produce fully impregnated high quality end products, and provide a repeatable process, process parameters such as injection gate and vent locations and conditions, and fill time should be designed by using a process model instead of trial-and-error approach commonly used in the industry. Reliability and accuracy of the process model requires correctly measured permeability data. It is very common to see that the permeability data in the literature has a large scatter; and there is no universal agreement among the modelers about which characterization procedure (unsteady versus steady; 1D versus 2D; constant injection pressure versus constant injection flow rate) should be used for permeability measurement. Permeability measurement experiments have some issues about accuracy, repeatability and the error sensitivity as studied in this study. To investigate the sources of errors and propose methods to minimize these errors, four different types of experimental procedure for three different fabric types were performed. Non-repeatable specimen preparation, deflection of mold parts and expansion of injection equipment and tubing were observed to be the main sources of the error. Results showed that the unsteady permeabilities of the fabric preforms were up to 91% higher than the steady permeabilities. For the same fabric type, it was observed that different characterization procedures resulted in more than one order of magnitude variation. Besides constructing a permeability database, the suggestions given in this study are beneficial to minimize the anticipated sources of error and they give guidance to the experimenters to obtain more reliable and accurate results.