T. He

Material Modeling and Ballistic-Resistance Analysis of Armor-Grade Composites Reinforced with High-Performance Fibers

A new ballistic material model for 0°/90° cross-plied oriented ultra-high molecular weight (UHMW) polyethylene fiber-based armor-grade composite laminates has been constructed using open-literature data for the fiber and polymeric-matrix material properties and the general experimental/field-test observations regarding the deformation and failure modes in these types of materials. The present model is an extension of our recently developed unit cell-based ballistic material model for the same class of composites (M. Grujicic, G. Arakere, T. He,W.C. Bell, B. A. Cheeseman, C.-F. Yen, and B. Scott, A Ballistic Material Model for Cross-Plied Unidirectional Ultra-High Molecular-Weight Polyethylene Fiber-reinforced Armor-Grade Composites, Mater. Sci. Eng, A 2008, 498(1-2), p 231-241) which was found to be physically sound, but computationally not very efficient. The present model is constructed in such a way that it can be readily integrated into commercial finite element programs like ANSYS/Autodyn (ANSYS/Autodyn version 11.0, User Documentation, Century Dynamics Inc., a subsidiary of ANSYS Inc., 2007), as a User Material Subroutine. To validate the model, a series of transient nonlinear dynamics computational analyses of the transverse impact of armor-grade composite laminates with two types of bullets/projectiles is carried out and the computational results compared with their experimental counterparts. Relatively good agreement is found between the experiment and the computational analysis relative to: (a) the success of the armor panels of different areal densities in defeating the bullets at different initial bullet velocities; (b) postmortem spatial distribution of the damage modes and the extents within the panels; (c) the temporal evolution of the armor-panel back-face bulge; and (d) The existence of three distinct armor-penetration stages (i.e., an initial filament shearing/cutting dominated stage, an intermediate stage characterized by pronounced filament/matrix debonding/decohesion, and a final stage associated with the extensive filaments extension and armor-panel back-face bulging).

Experimental Characterization and Material-Model Development for Microphase-Segregated Polyurea: An Overview

Numerous experimental investigations reported in the open literature over the past decade have clearly demonstrated that the use of polyurea external coatings and/or inner layers can substantially enhance both the blast resistance (the ability to withstand shock loading) and the ballistic performance (the ability to defeat various high-velocity projectiles such as bullets, fragments, shrapnel, etc. without penetration, excessive deflection or spalling) of buildings, vehicles, combat-helmets, etc. It is also well established that the observed high-performance of polyurea is closely related to its highly complex submicron scale phase-segregated microstructure and the associated microscale phenomena and processes (e.g., viscous energy dissipation at the internal phase boundaries). As higher and higher demands are placed on blast/ballistic survivability of the foregoing structures, a need for the use of the appropriate transient nonlinear dynamics computational analyses and the corresponding design-optimization methods has become ever apparent. A critical aspect of the tools used in these analyses and methods is the availability of an appropriate physically based, high-fidelity material model for polyurea. There are presently several public domain and highly diverse material models for polyurea. In the present work, an attempt is made to critically assess these models as well as the experimental methods and results used in the process of their formulation. Since these models are developed for use in the high-rate loading regime, they are employed in the present work, to generate the appropriate shock-Hugoniot relations. These relations are subsequently compared with their experimental counterparts in order to assess the fidelity of these models.

Material‐modeling and structural‐mechanics aspects of the traumatic brain injury problem

Purpose – This paper aims to conduct a combined Eulerian/Lagrangian fluid/solid transient non‐linear dynamics computational analysis of the interaction between a single planar blast wave and a human head in order to assess the extent of intra‐cranial shock wave generation and its potential for causing traumatic brain injury.Design/methodology/approach – Two levels of blast peak overpressure were selected, one corresponding to the unprotected lung‐injury threshold while the other associated with a 50 percent probability for lung injury caused death. Collision of the head with a stationary/rigid barrier (at an initial collision velocity of 5 m/s) was also analyzed computationally, since blunt‐object impact conditions may lead to mild traumatic brain injury (mTBI), i.e. concussion.Findings – A comparison between the two blast and the single blunt‐object impact cases with the corresponding head‐to‐head‐collision results showed that, while the von Mises stress‐based head‐to‐head collision mTBI thresholds are n...

Development and parameterization of an equilibrium material model for segmented polyurea

Purpose – The purpose of this paper is to develop and parameterize a time‐invariant (equilibrium) material mechanical model for segmented polyureas, a class of thermoplastically linked co‐polymeric elastomers, using experimental data available in open literature.Design/methodology/approach – The key components of the model are developed by first constructing a simple molecular‐level microstructure model and by relating the microstructural elements and intrinsic material processes to the material mechanical response. The new feature of the present material model relative to the ones currently used is that the physical origin and the evolution equation for the deformation‐induced softening and inelasticity observed in polyureas are directly linked to the associated evolution of the soft‐matrix/hard segment molecular‐level microstructure of this material. The model is first developed for the case of uniaxial loading, parameterized using one set of experimental results and finally validated using another set ...

Development and parameterization of a time-invariant (equilibrium) material model for segmented elastomeric polyureas

A time-invariant (equilibrium) material mechanical model for segmented polyureas, a class of thermoplastically linked co-polymeric elastomers, is developed and parameterized using experimental data available in open literature. The key components of the model are developed by first constructing a simple molecular-level microstructure model and by relating the microstructural elements and intrinsic material processes to the material mechanical response. The new feature of the present material model relative to the ones currently used is that the physical origin and the evolution equation for the deformation-induced softening and inelasticity observed in polyureas are directly linked to the associated evolution of the soft-matrix/hard-segment molecular-level microstructure of this material. The model is first developed for the case of uniaxial loading, parameterized using one set of experimental results, and finally validated using another set of experimental results. The validation procedure suggested that the model can reasonably well account for the equilibrium mechanical response of polyureas under the simple uniaxial-loading conditions. In the last portion of this study, a general finite-strain three-dimensional material model for polyureas was developed and cast as a subroutine suitable for linking with commercial finite-element programs.

Development, parameterization, and validation of a visco-plastic material model for sand with different levels of water saturation

A new material model for sand has been developed in order to include the effects of the deformation rate and the degree of saturation on the constitutive response of this material. The model is an extension of the original high strain-rate compaction model for sand developed by Laine and Sandvik and an elastic—visco-plastic material model for sand recently proposed by Tong and Tuan in which these effects were neglected. The new material model was parameterized using the available experimental data for sand with different levels of saturation tested mechanically at different strain rates. The model is next used, within a non-linear-dynamics transient computational analysis, to study: (a) various phenomena associated with the explosion of shallow-buried and ground-laid mines and (b) the dynamic behaviour of a vehicle during an off-road ride. The computational results are then compared with the corresponding experimental results. This comparison suggested that the newly developed material model for sand captures the essential features of the dynamic behaviour of sand with different levels of saturation when subjected to realistic high and low strain-rate loading conditions.