Identifying the Poly Methyl Methacrylate behavior during free thermoforming using experimental tests and numerical simulation

Thermoforming is one of the new methods for forming of polymer sheets. Free thermoforming is one of the thermoforming methods in which shaping is done with air pressure or vacuum without the plug mold. In this paper, free thermoforming of Poly Methyl Methacrylate (PMMA) has been investigated by experimental tests and finite element simulation. The main purpose of this article is the identification of the real behavior of PMMA during free thermoforming to achieve maximum workable air pressure with respect to initial thickness. For this, at first, tensile and relaxation tests have been done in working temperature (160◦C). Then the process was simulated by Abaqus software with considering four types of the material property: three hyperelastic models (Ogden, Mooney-Rivlin, and Marlow) and a hyperviscoelastic model. After that, experimental tests were done, and the samples final shape were compared with simulation results. Accordingly, the simulation results obtained based on the Marlow hyperelastic model showed the best agreement with the experiments compared to others. After that, maximum workable air pressure versus plate initial thickness and minimum thickness of the deformed plate were achieved by finite element simulation

Nonlinear Buckling Analysis of Cylindrical Nanoshells Conveying Nano-Fluid in Hygrothermal Environment

The present work addresses the critical buckling of circular cylindrical nano-shells containing static/dynamic nanofluids under the influence of different thermal fields that can also lead to appear the effect of thermal moisture so-called hygrothermal forces fields. To this end, the classical Sanders theory of cylindrical plates and shells is generalized by utilizing the non-classical nonlocal elasticity theory to derive the modified dynamic equations governing the nanofluid-nanostructure interaction (nano-FSI) problem. Then, the dimensionless obtained equations are analytically solved using the energy method. Herein, the applied nonlinear heat and humidity fields are considered as three types of longitudinal, circumferential, and simultaneously longitudinal-circumferential forces fields. The mentioned cases are examined separately for both high- and room-temperatures modes. The results show a significant effect of nanofluid passing through the nanostructure and its velocity on the critical buckling strain of the nano-systems, especially at high temperatures