Alexander J. Carpenter

Mesoscale modeling of S-2 glass/SC-15 epoxy composites: Plain-weave architecture

S-2 glass composites can readily serve as backing materials for armor systems due to their light weight and tensile properties. However, high-fidelity ballistic modeling of these composites requires accurate predictions of their nonlinear deformation and failure behaviors, which can prove challenging. This paper describes simulations of a plain-weave S-2 glass composite at the mesoscale using a mesh geometry that individually models the S-2 glass yarns, epoxy resin matrix, and yarn/matrix interfaces as separate entities. Simulation results are compared to a wide variety of mechanical tests designed to measure the response of the composite to tension, shear, and delamination. Although the individual yarns, matrix, and interfaces are described using relatively simple material models, the overall composite model can accurately reproduce behaviors such as nonlinear deformation, yarn breakage, and delamination in both tension and shear.

Gas-Pressure Bulge Forming of Mg AZ31 Sheet at 450°C

Magnesium (Mg) sheet materials, such as wrought AZ31, possess low densities and high strength- and stiffness-to-weight ratios. These properties suggest that the use of Mg sheet is viable for reducing vehicle weight, an important goal of the automotive industry. Magnesium exhibits poor ductility at room temperature, but high-temperature forming processes may be used to manufacture complex vehicle closure panels. Tensile tests are the most common method of characterizing the plastic deformation of sheet materials. However, gas-pressure bulge tests may be more representative of the stress states that occur during the manufacture of sheet metal components. This study investigates the plastic deformation of AZ31 sheet during both biaxial and plane-strain gas-pressure bulge forming at 450°C. The heights and thicknesses of formed specimens are measured and compared. The deformation behaviors of the AZ31 sheet are related to observations of grain growth and cavitation that occur during forming.

Ballistic and Material Tests and Simulations on Ultra-High Performance Concrete

Ultra-high performance concretes (UHPC), meaning concretes with compressive strengths above 150 MPa (B-150), introduce improved properties such as stiffness, compressive strength, and post-failure compliance as compared to standard concretes. Advantages are shown in standard applications of construction, yet, a large potential exists in applications of protective structures to withstand impulsive loadings of blast or direct impact. In this work an UHPC with a compression strength of 200 MPa was used to test and develop a material model to enable predictions for impact and penetration. The material was first tested to characterize the material behavior under quasistatic loading in torsion, compression and triaxial compression, up to confinement pressures of 500 MPa. Moreover, the UHPC was characterized under dynamic loading, using a Kolsky bar (Split Hopkinson Pressure Bar). Based on these lab-scale tests, a Johnson-Holmquist material model was calibrated for the numerical simulations. Finally, ballistic tests were performed with two projectile geometries, using two configurations: a standalone UHPC panel to obtain the ballistic limit, and depth of penetration (DOP) measurements, with aluminum backing, to better relate to the concrete strength during penetration conditions. Preliminary ballistic computations with the UHPC model, calibrated from the lab-scale tests for LS-DYNA, provided good predictions when compared to most of the tests.