G. Arakere

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).

Fully coupled thermomechanical finite element analysis of material evolution during friction-stir welding of AA5083

Abstract Interactions between the rotating and advancing pin-shaped tool (terminated at one end with a circular—cylindrical shoulder) with the clamped welding plates and the associated material and heat transport during a friction-stir welding (FSW) process are studied computationally using a fully coupled thermomechanical finite element analysis. To surmount potential numerical problems associated with extensive mesh distortions/entanglement, an arbitrary Lagrangian—Eulerian (ALE) formulation was used, which enabled adaptive remeshing (to ensure the continuing presence of a high-quality mesh) while allowing full tracking of the material-free surfaces. To demonstrate the utility of the present computational approach, the analysis is applied to the case of FSW of AA5083 (a solid—solution strengthened and strain-hardened/stabilized Al—Mg wrought alloy). To account for the competition between plastic deformation-controlled strengthening and dynamic recrystallization-induced softening phenomena during the FSW process, the original Johnson—Cook strain and strain-rate hardening and temperature-softening material strength model is modified using the available recrystallization kinetics experimental data. Lastly, the computational results obtained in the present work are compared with their experimental counterparts available in the open literature. This comparison revealed that general trends regarding spatial distribution and temporal evolutions of various material-state quantities and their dependence on the FSW process parameters are reasonably well predicted by the present computational approach.

Computational Analysis of Material Flow During Friction Stir Welding of AA5059 Aluminum Alloys

Workpiece material flow and stirring/mixing during the friction stir welding (FSW) process are investigated computationally. Within the numerical model of the FSW process, the FSW tool is treated as a Lagrangian component while the workpiece material is treated as an Eulerian component. The employed coupled Eulerian/Lagrangian computational analysis of the welding process was of a two-way thermo-mechanical character (i.e., frictional-sliding/plastic-work dissipation is taken to act as a heat source in the thermal-energy balance equation) while temperature is allowed to affect mechanical aspects of the model through temperature-dependent material properties. The workpiece material (AA5059, solid-solution strengthened and strain-hardened aluminum alloy) is represented using a modified version of the classical Johnson-Cook model (within which the strain-hardening term is augmented to take into account for the effect of dynamic recrystallization) while the FSW tool material (AISI H13 tool steel) is modeled as an isotropic linear-elastic material. Within the analysis, the effects of some of the FSW key process parameters are investigated (e.g., weld pitch, tool tilt-angle, and the tool pin-size). The results pertaining to the material flow during FSW are compared with their experimental counterparts. It is found that, for the most part, experimentally observed material-flow characteristics are reproduced within the current FSW-process model.

Process Modeling of Ti-6Al-4V Linear Friction Welding (LFW)

A fully coupled thermomechanical finite-element analysis of the linear friction welding (LFW) process is combined with the basic physical metallurgy of Ti-6Al-4V to predict microstructure and mechanical properties within the LFW joints (as a function of the LFW process parameters). A close examination of the experimental results reported in the open literature revealed that the weld region consists of a thermomechanically affected zone (TMAZ) and a heat-affected zone (HAZ) and that the material mechanical properties are somewhat more inferior in the HAZ. Taking this observation into account, a model for microstructure-evolution during LFW was developed and parameterized for the Ti-6Al-4V material residing in the HAZ. Specifically, this model addresses the problem of temporal evolution of the prior β-phase grain size (the dominant microstructural parameter in the HAZ) during the LFW process. This model is next combined with the well-established property versus microstructure correlations in Ti-6Al-4V to predict the overall structural performance of the LFW joint. The results obtained are found to be in reasonably good agreement with their experimental counterparts suggesting that the present computational approach may be used to guide the selection of the LFW process parameters to optimize the structural performance of the LFW joints.

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...

A Concurrent Product-Development Approach for Friction-Stir Welded Vehicle-Underbody Structures

High-strength aluminum and titanium alloys with superior blast/ballistic resistance against armor piercing (AP) threats and with high vehicle light-weighing potential are being increasingly used as military-vehicle armor. Due to the complex structure of these vehicles, they are commonly constructed through joining (mainly welding) of the individual components. Unfortunately, these alloys are not very amenable to conventional fusion-based welding technologies [e.g., gas metal arc welding (GMAW)] and to obtain high-quality welds, solid-state joining technologies such as friction-stir welding (FSW) have to be employed. However, since FSW is a relatively new and fairly complex joining technology, its introduction into advanced military-vehicle-underbody structures is not straight forward and entails a comprehensive multi-prong approach which addresses concurrently and interactively all the aspects associated with the components/vehicle-underbody design, fabrication, and testing. One such approach is developed and applied in this study. The approach consists of a number of well-defined steps taking place concurrently and relies on two-way interactions between various steps. The approach is critically assessed using a strengths, weaknesses, opportunities, and threats (SWOT) analysis.

The effect of up‐armoring of the high‐mobility multi‐purpose wheeled vehicle (HMMWV) on the off‐road vehicle performance

Purpose – A parallel finite‐element/multi‐body‐dynamics investigation is carried out of the effect of up‐armoring on the off‐road performance of a prototypical high‐mobility multipurpose‐wheeled vehicle (HMMWV). The paper seeks to investigate the up‐armoring effect on the vehicle performance under the following off‐road maneuvers: straight‐line flatland braking; straight‐line off‐angle downhill braking; and sharp left turn.Design/methodology/approach – For each of the above‐mentioned maneuvers, the appropriate vehicle‐performance criteria are identified and the parameters used to quantify these criteria are defined and assessed. The ability of a computationally efficient multi‐body dynamics approach when combined with a detailed model for tire/soil interactions to yield results qualitatively and quantitatively consistent with their computational counterparts obtained using computationally quite costly finite element analyses is assessed.Findings – The computational results obtained clearly reveal the comp...

Application of Topology, Size and Shape Optimization Methods in Polymer Metal Hybrid Structural Lightweight Engineering

Application of the engineering design optimization methods and tools to the design of automotive body‐in‐white (BIW) structural components made of polymer metal hybrid (PMH) materials is considered. Specifically, the use of topology optimization in identifying the optimal initial designs and the use of size and shape optimization techniques in defining the final designs is discussed. The optimization analyses employed were required to account for the fact that the BIW structural PMH component in question may be subjected to different in‐service loads be designed for stiffness, strength or buckling resistance and that it must be manufacturable using conventional injection over‐molding. The paper demonstrates the use of various engineering tools, i.e. a CAD program to create the solid model of the PMH component, a meshing program to ensure mesh matching across the polymer/metal interfaces, a linear‐static analysis based topology optimization tool to generate an initial design, a nonlinear statics‐based size and shape optimization program to obtained the final design and a mold‐filling simulation tool to validate manufacturability of the PMH component.

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.

The Potential of a Clinch-Lock Polymer Metal Hybrid Technology for Use in Load-Bearing Automotive Components

In order to help meet the needs of automotive original equipment manufacturers and their suppliers for a cost-effective, robust, reliable polymer-metal-hybrid (PMH) technology which can be used for the manufacturing of load-bearing body-in-white (BIW) components and which is compatible with the current BIW manufacturing process chain, a new approach, the so-called direct-adhesion PMH technology, was recently proposed (Grujicic et al., J. Mater. Process. Technol., 2008, 195, p 282-298). Within this approach, the necessary level of polymer-to-metal mechanical interconnectivity is attained through direct adhesion and mechanical interlocking. In the present work, a new concept for mechanical interlocking between the metal and plastics is proposed and analyzed computationally. The approach utilizes some of the ideas used in the spot-clinching joining process and is appropriately named clinch-lock PMH technology. To assess the potential of the clinch-lock approach for providing the required level of metal/polymer mechanical interlocking, a set of finite-element based sheet-metal forming, injection molding and structural mechanics analyses was carried out. The results obtained show that stiffness and buckling resistance levels can be attained which are comparable with those observed in the competing injection overmolding PMH process but with an ~3% lower weight (of the polymer subcomponent) and without the need for holes and for overmolding of the free edges of the metal stamping.