VTechWorks staff will be away for the Thanksgiving holiday beginning at noon on Wednesday, November 27, through Friday, November 29. We will resume normal operations on Monday, December 2. Thank you for your patience.

Browsing by Author "Antoine, Guillaume O."

Now showing 1 - 2 of 2
  • Thumbnail Image
    Computational Design of Transparent Polymeric Laminates subjected to Low-velocity Impact
    Antoine, Guillaume O. (Virginia Tech, 2014-11-07)
    Transparent laminates are widely used for body armor, goggles, windows and windshields. Improved understanding of their deformations under impact loading and of energy dissipation mechanisms is needed for minimizing their weight. This requires verified and robust computational algorithms and validated mathematical models of the problem. Here we have developed a mathematical model for analyzing the impact response of transparent laminates made of polymeric materials and implemented it in the finite element software LS-DYNA. Materials considered are polymethylmethacrylate (PMMA), polycarbonate (PC) and adhesives. The PMMA and the PC are modeled as elasto-thermo-visco-plastic and adhesives as viscoelastic. Their failure criteria are stated and simulated by the element deletion technique. Values of material parameters of the PMMA and the PC are taken from the literature, and those of adhesives determined from their test data. Constitutive equations are implemented as user-defined subroutines in LS-DYNA which are verified by comparing numerical and analytical solutions of several initial-boundary-value problems. Delamination at interfaces is simulated by using a bilinear traction separation law and the cohesive zone model. We present mathematical and computational models in chapter one and validate them by comparing their predictions with test findings for impacts of monolithic and laminated plates. The principal source of energy dissipation of impacted PMMA/adhesive/PC laminates is plastic deformations of the PC. In chapter two we analyze impact resistance of doubly curved monolithic PC panels and delineate the effect of curvature on the energy dissipated. It is found that the improved performance of curved panels is due to the decrease in the magnitude of stresses near the center of impact. In chapter three we propose constitutive relations for finite deformations of adhesives and find values of material parameters by considering test data for five portions of cyclic loading. Even though these values give different amounts of energy dissipated in the adhesive, their effect on the computed impact response of PMMA/adhesive/PC laminates is found to be minimal. In chapter four we conduct sensitivity analysis to identify critical parameters that significantly affect the energy dissipated. The genetic algorithm is used to optimally design a transparent laminate in chapter five.
  • Thumbnail Image
    Effect of Curvature on Penetration Resistance of Polycarbonate Panels
    Antoine, Guillaume O.; Batra, Romesh C. (2016-09-13)
    Three-dimensional transient deformations of clamped flat and doubly curved polycarbonate (PC) panels impacted by a rigid smooth hemispherical-nosed circular cylinder have been numerically studied by the finite-element (FE) method to delineate effects of the panel radius of curvature to its thickness ratio on their penetration resistance. The PC is modeled as thermoelastoviscoplastic with the effective plastic strain rate depending upon the hydrostatic pressure. The effective plastic strain of 3.0 at failure is ascertained by matching for one set of flat panels the computed and the experimental minimum perforation speeds. It is found that a negative curvature (i.e., the center of curvature toward the impactor) of a panel degrades its penetration performance, and the positive curvature enhances it especially for thin panels with thickness/radius of curvature of 0.01. However, the benefit is less evident for panels with the panel thickness/radius of curvature of 0.04 or more. For positively curved thin panels, an elastic hinge forms around the central impacted area during an early stage of deformations, and subsequent deformations occur within this region. No such hinge is observed for flat plates, negatively curved panels of all the thicknesses, and positively curved thick panels. Furthermore, the maximum effective stress induced in regions surrounding the impacted area is less for positively curved panels than that for flat panels. The dominant failure mechanism is found to be the deletion of failed elements due to the effective plastic strain in them exceeding 3.0 rather than due to plug formation. For an example problem, the dependence of the effective plastic strain rate upon the hydrostatic pressure and the consideration of the Coulomb friction at the contact surfaces exhibited minimal effects on the penetration characteristics. This information should be useful for designers of impact-resistant transparent armor, such as an airplane canopy, automobile windshield, and goggles.