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).     

Suitability analysis of a polymer–metal hybrid technology based on high-strength steels and direct polymer-to-metal adhesion for use in load-bearing automotive body-in-white applications

A comprehensive set of computational engineering analyses is carried out in order to assess the suitability of a “direct adhesion” polymer–metal hybrid (PMH) technology for use in load-bearing automotive body-in-white (BIW) components. Within the direct adhesion PMH technology, load transfer between stamped sheet-metal and injection-molded rib-like plastic subcomponents is accomplished through a variety of nanometer-to-micron scale chemical and mechanical phenomena which enable direct adhesion between the two materials. The resultant adhesion strength in a 5–10 MPa range has been assessed. In the present work it has been investigated if such level of adhesion strength is sufficient to restore the component's stiffness in the cases when stiffness has been compromised by substituting a twin-shell large-thickness drawing-quality-steel design of a prototypical BIW component with a single-shell lower-thickness high-strength-steel and polymer-hybridized design of the same component. The results obtained suggest that meeting the bending stiffness requirements is the most challenging task and if such requirements do not control the overall component design, weight savings in a 2.0–2.5% range can be obtained.     

Modeling design objects in CAD system for Service/Product Engineering

This paper proposes a new type of service CAD system utilized in Service/Product Engineering (SPE), a much-needed and novel engineering discipline within the background of servicification. In this research a design-object model was defined, and a prototype named Service Explorer was implemented. The model represents critical concepts such as value, costs, functions either of products or of service activities, and entities. Through its application to business cases such as selling washing machines, providing pay-per-wash service, and cleaning washing machines, the Service Explorer was proven to support designers as they describe and operate design objects. In the future we expect that the Service Explorer can help designers with generating new ideas.     

Atomistic simulation of chemical vapor deposition of (111)-oriented diamond film using a kinetic Monte Carlo method

Chemical vapor deposition (CVD) of (111)-oriented diamond film is modeled using a kinetic Monte Carlo atomic scale method. The method is parameterized by the rates of the accompanying surface chemical reactions and permits one of these reactions to take place at each simulation step. The effect of local surface structure and morphology on the rates of surface reaction is examined. Film growth at two different chemical compositions of the feed gas and two substrate temperatures is studied in order to determine the effect of these process parameters on (a) the quality of the deposed film and (b) the rate of deposition. The quality of the film is judged by concentration of the point defects (vacancies and H atoms embedded in the film) and by surface roughness. The results obtained show that the parameters that increase the deposition rate, primarily the substrate temperature and the concentration of CH4 in the feed gas, also increase the defect content and surface roughness.     

Molecular-Level Simulations of Shock Generation and Propagation in Soda-Lime Glass

A non-equilibrium molecular dynamics method is employed to study the mechanical response of soda-lime glass (a material commonly used in transparent armor applications) when subjected to the loading conditions associated with the generation and propagation of planar shock waves. Specific attention is given to the identification and characterization of various (inelastic-deformation and energy-dissipation) molecular-level phenomena and processes taking place at, or in the vicinity of, the shock front. The results obtained revealed that the shock loading causes a 2-4% (shock strength-dependent) density increase. In addition, an increase in the average coordination number of the silicon atoms is observed along with the creation of smaller Si-O rings. These processes are associated with substantial energy absorption and dissipation and are believed to greatly influence the blast/ballistic impact mitigation potential of soda-lime glass. The present work was also aimed at the determination of the shock Hugoniot (i.e., a set of axial stress vs. density/specific-volume vs. internal energy vs. particle velocity vs. temperature) material states obtained in soda-lime glass after the passage of a shock wave of a given strength (as quantified by the shock speed). The availability of a shock Hugoniot is critical for construction of a high deformation-rate, large-strain, high pressure material model which can be used within a continuum-level computational analysis to capture the response of a soda-lime glass based laminated transparent armor structure (e.g., a military vehicle windshield, door window, etc.) to blast/ballistic impact loading.     

Wind-Turbine Gear-Box Roller-Bearing Premature-Failure Caused by Grain-Boundary Hydrogen Embrittlement: A Multi-physics Computational Investigation

To help overcome the problem of horizontal-axis wind-turbine (HAWT) gear-box roller-bearing premature-failure, the root causes of this failure are currently being investigated using mainly laboratory and field-test experimental approaches. In the present work, an attempt is made to develop complementary computational methods and tools which can provide additional insight into the problem at hand (and do so with a substantially shorter turn-around time). Toward that end, a multi-physics computational framework has been developed which combines: (a) quantum-mechanical calculations of the grain-boundary hydrogen-embrittlement phenomenon and hydrogen bulk/grain-boundary diffusion (the two phenomena currently believed to be the main contributors to the roller-bearing premature-failure); (b) atomic-scale kinetic Monte Carlo-based calculations of the hydrogen-induced embrittling effect ahead of the advancing crack-tip; and (c) a finite-element analysis of the damage progression in, and the final failure of a prototypical HAWT gear-box roller-bearing inner raceway. Within this approach, the key quantities which must be calculated using each computational methodology are identified, as well as the quantities which must be exchanged between different computational analyses. The work demonstrates that the application of the present multi-physics computational framework enables prediction of the expected life of the most failure-prone HAWT gear-box bearing elements.     

Multi-Length Scale-Enriched Continuum-Level Material Model for Kevlar®-Fiber-Reinforced Polymer-Matrix Composites

Fiber-reinforced polymer matrix composite materials display quite complex deformation and failure behavior under ballistic/blast impact loading conditions. This complexity is generally attributed to a number of factors such as (a) hierarchical/multi-length scale architecture of the material microstructure; (b) nonlinear, rate-dependent and often pressure-sensitive mechanical response; and (c) the interplay of various intrinsic phenomena and processes such as fiber twisting, interfiber friction/sliding, etc. Material models currently employed in the computational engineering analyses of ballistic/blast impact protective structures made of this type of material do not generally include many of the aforementioned aspects of the material dynamic behavior. Consequently, discrepancies are often observed between computational predictions and their experimental counterparts. To address this problem, the results of an extensive set of molecular-level computational analyses regarding the role of various microstructural/morphological defects on the Kevlar^® fiber mechanical properties are used to upgrade one of the existing continuum-level material models for fiber-reinforced composites. The results obtained show that the response of the material is significantly affected as a result of the incorporation of microstructural effects both under quasi-static simple mechanical testing condition and under dynamic ballistic-impact conditions.     

Two-Level Weld-Material Homogenization for Efficient Computational Analysis of Welded Structure Blast-Survivability

The introduction of newer joining technologies like the so-called friction-stir welding (FSW) into automotive engineering entails the knowledge of the joint-material microstructure and properties. Since, the development of vehicles (including military vehicles capable of surviving blast and ballistic impacts) nowadays involves extensive use of the computational engineering analyses (CEA), robust high-fidelity material models are needed for the FSW joints. A two-level material-homogenization procedure is proposed and utilized in this study to help manage computational cost and computer storage requirements for such CEAs. The method utilizes experimental (microstructure, microhardness, tensile testing, and x-ray diffraction) data to construct: (a) the material model for each weld zone and (b) the material model for the entire weld. The procedure is validated by comparing its predictions with the predictions of more detailed but more costly computational analyses.     

Design-optimization and material selection for a femoral-fracture fixation-plate implant

The problem of size/thickness optimization of a distal femoral-fracture fixation-plate is addressed computationally using a combined finite-element/design-optimization procedure. To obtain realistic physiological loading conditions associated with normal living activities (cycling, in the present case), a musculoskeletal multi-body inverse-dynamics analysis is carried out of a human riding the bicycle. While optimizing the design of the femoral-fracture locking-plate, realistic functional requirements pertaining to attain the required level of fracture-femur fixation and longevity/lifecycle were used. It is argued that these types of analysis should be used to complement pre-clinical implant-evaluation tests, the tests which normally include a limited number of physiological loading conditions and single pass/fail outcomes/decisions with respect to a set of lower-bound implant–performance criteria.     

Comparative Discrete-Particle Versus Continuum-Based Computational Investigation of Soil Response to Impulse Loading

Two representative soil models are compared and contrasted within two transient nonlinear dynamics computational analyses. The first soil model is representative of a discrete-particle group of models, while the other is a typical continuum-type consolidated-soil model. The two computational analyses involved: (a) the case of a soil slug impacting a rigid flat surface and (b) the case of detonation of a mine shallow buried in soil and the interaction of the resulting gaseous detonation products, mine fragments, and soil ejecta with a plate-like deformable steel target. The results obtained show that the use of the computationally more expensive particle mechanics-based soil models is fully justified only in the case of loose (low-density) soil. In addition, the magnitude of the particle-to-particle coefficient of restitution has been found to have a second-order effect on the extent of momentum transferred from the moving soil to the target and that it may be substantially different from its effective counterpart for the entire loose-soil agglomerate.