A simple ballistic material model for soda-lime glass

Various open-literature experimental findings pertaining to the ballistic behavior of glass are used to construct a simple, physically based, high strain-rate, high-pressure, large-strain constitutive model for this material. The basic components of the model are constructed in such a way that the model is suitable for direct incorporation into standard commercial transient non-linear dynamics finite-element based software packages like ANSYS/Autodyn [ANSYS/Autodyn version 11.0, User documentation, Century Dynamics Inc. a subsidiary of ANSYS Inc.; 2007.] or ABAQUS/Explicit [ABAQUS version 6.7, User documentation, Dessault systems, 2007.]. To validate the material model, a set of finite element analyses of the Edge-on-Impact (EOI) tests is carried out and the results compared with their experimental counterparts obtained in the recent work of Strassburger et al. [Strassburger E, Patel P, McCauley JW, Kovalchick C, Ramesh KT, Templeton DW. High-speed transmission shadowgraphic and dynamic photoelasticity study of stress wave and impact damage propagation in transparent materials and laminates using the edge-on impact method. In: Proceedings of the twenty-third international symposium on ballistics. Spain: April 2007, and Strassburger E, Patel P, McCauley W, Templeton DW. Visualization of wave propagation and impact damage in a polycrystalline transparent ceramic-AlON. In: Proceedings of the twenty-second international symposium on ballistics. Vancouver, Canada: November 2005.]. Overall, a good agreement is found between the computational and the experimental results pertaining to: (a) the front-shapes and propagation velocities of the longitudinal and transverse waves generated in the target during impact; (b) the front-shapes and propagation velocities of the “coherent-damage” zone (a zone surrounding the projectile/target contact surface which consists of numerous micron- and sub-micron-size cracks); and (c) the formation of “crack centers”, i.e. isolated cracks nucleated ahead of the advancing coherent-damage zone front. Relatively minor discrepancies between the computational and the experimental results are attributed to the effects of damage-promoting target-fixturing induced stresses and cutting/grinding-induced flaws located along the narrow faces of the target and the surrounding regions.     

Seat-cushion and soft-tissue material modeling and a finite element investigation of the seating comfort for passenger-vehicle occupants

Improved seating comfort is an important factor that most car manufacturers use to distinguish their products from those of their competitors. In today’s automotive engineering practice, however, design and development of new, more comfortable car seats is based almost entirely on empiricism, legacy knowledge and extensive, time-consuming and costly prototyping and experimental/field testing. To help accelerate and economize the design/development process of more-comfortable car seats, more extensive use of various computer aided engineering (CAE) tools will be necessary. However, before the CAE tools can be used more successfully by car-seat manufacturers, issues associated with the availability of realistic computer models for the seated human, the seat and the seated-human/seat interactions as well as with the establishment of objective seating-comfort quantifying parameters must be resolved.In the present work, detailed finite element models of a prototypical car seat and of a seated human are developed and used in the investigation of seated-human/seat interactions and the resulting seating comfort. To obtain a fairly realistic model for the human, a moderately detailed skeletal model containing 16 bone assemblies and 15 joints has been combined with an equally detailed “skin” model of the human. The intersection between the two models was then used to define the muscular portion of the human. Special attention in the present work has been given to realistically representing/modeling the materials present in different sections of the car seat and the seated human. The models developed in the present work are validated by comparing the computational results related to the pressure distribution over the seated-human/seat interface with their open-literature counterparts obtained in experimental studies involving human subjects.     

Implication of elastic coherency in secondary hardening of high Co-Ni martensitic steels

Composition and stoichiometry of coherent M₂C carbide precipitates, (M=Cr, Mo, Fe), in two high Co-Ni martensitic steels have been calculated using thermodynamic conditions for mechanical, chemical and interfacial equilibrium between the ferrite (tempered martensite) and the M₂C phase. Compared to the corresponding incoherent equilibrium compositions, our calculations at the standard secondary hardening temperature of 783 K predict a substantial carbon deficiency and a measurable solubility of iron in the M₂C phase, both of which have been verified experimentally. These deviations from the incoherent equilibrium compositions are found to be in line with the influence of these constituents in lowering the strain energy by reducing the principal strains of the M₂C stress-free transformation strain.     

Friction Stir Weld Failure Mechanisms in Aluminum-Armor Structures Under Ballistic Impact Loading Conditions

A critical assessment is carried out of the microstructural changes in respect of the associated reductions in material mechanical properties and of the attendant ballistic-impact failure mechanisms in prototypical friction stir welding (FSW) joints found in armor structures made of high-performance aluminum alloys (including solution-strengthened and age-hardenable aluminum alloy grades). It is argued that due to the large width of FSW joints found in thick aluminum-armor weldments, the overall ballistic performance of the armor is controlled by the ballistic limits of its weld zones (e.g., heat-affected zone, the thermomechanically affected zone, the nugget, etc.). Thus, in order to assess the overall ballistic survivability of an armor weldment, one must predict/identify welding-induced changes in the material microstructure and properties, and the operative failure mechanisms in different regions of the weld. Toward this end, a procedure is proposed in the present study which combines the results of the FSW process modeling, basic physical-metallurgy principles concerning microstructure/property relations, and the fracture mechanics concepts related to the key blast/ballistic-impact failure modes. The utility of this procedure is demonstrated using the case of a solid-solution strengthened and cold-worked aluminum alloy armor FSW-weld test structure.     

A new meshless “fragile points method” and a local variational iteration method for general transient heat conduction in anisotropic nonhomogeneous media. Part II: Validation and discussion

Abstract

In the first part of this two-paper series, a new computational approach is presented for analyzing transient heat conduction problems in anisotropic nonhomogeneous media. The approach consists of a truly meshless Fragile Points Method (FPM) being utilized for spatial discretization, and a Local Variational Iteration (LVI) scheme for time discretization. In the present article, extensive numerical results are provided as validations, followed by a discussion on the recommended computational parameters. The FPM?+?LVIM approach shows its capability in solving 2?D and 3?D transient heat transfer problems in complex geometries with mixed boundary conditions, including preexisting cracks. Both functionally graded materials and composite materials are considered. It is shown that, with appropriate computational parameters, the FPM?+?LVIM approach is not only accurate, but also efficient, and has reliable stability under relatively large time intervals.     

Linear Friction Welding Process Model for Carpenter Custom 465 Precipitation-Hardened Martensitic Stainless Steel

An Arbitrary Lagrangian-Eulerian finite-element analysis is combined with thermo-mechanical material constitutive models for Carpenter Custom 465 precipitation-hardened martensitic stainless steel to develop a linear friction welding (LFW) process model for this material. The main effort was directed toward developing reliable material constitutive models for Carpenter Custom 465 and toward improving functional relations and parameterization of the workpiece/workpiece contact-interaction models. The LFW process model is then used to predict thermo-mechanical response of Carpenter Custom 465 during LFW. Specifically, temporal evolutions and spatial distribution of temperature within, and expulsion of the workpiece material from, the weld region are examined as a function of the basic LFW process parameters, i.e., (a) contact-pressure history, (b) reciprocation frequency, and (c) reciprocation amplitude. Examination of the results obtained clearly revealed the presence of three zones within the weld, i.e., (a) Contact-interface region, (b) Thermo-mechanically affected zone, and (c) heat-affected zone. While there are no publicly available reports related to Carpenter Custom 465 LFW behavior, to allow an experiment/computation comparison, these findings are consistent with the results of our ongoing companion experimental investigation.