On the tailoring of microstructures for prescribed effective properties

The focus of this communication is the development of genetic algorithms to handle material design problems where particulate microstructures are sought which deliver prescribed effective responses. In the problem formulation, constraints are incorporated on the distortion of the otherwise smooth internal fields corresponding to a pure (inhomogeneity-free) matrix material, due to the presence of particles. The key conceptual feature is that the microstructural variables are represented by a 'genetic string', and a 'survival of the fittest' algorithm is applied to a population of such strings in order to determine an optimal set of microstructural material design parameters.     

Attachment mode performance of network-modeled ballistic fabric shielding

A central issue in the use of ballistic fabric shielding is the mode of attachment to the structure that it is intended to protect. In order to investigate this issue, a discrete multi-scale yarn-network model is developed for structural fabric undergoing ballistic impact, based on work found in Zohdi and Powell [Zohdi TI, Powell D. Multiscale construction and large-scale simulation of structural fabric undergoing ballistic impact. Comput Meth Appl Mech Eng 2006;195:94–109] and Zohdi [Zohdi TI. Modeling/simulation of progressive penetration of multilayered ballistic fabric shielding. Comput Mech 2002;29:61–7]. The model is comprised of a network of yarn with stochastic properties determined by smaller-scale fibrils, which are randomly misaligned. The effects of stochasticity on the overall response are explored, and the model is compared against macro-scale experiments. The key feature of the model is the fact that it does not depend on phenomenological parameters, and can be calibrated by simply measuring the properties of an individual, smallest-scale, fibril. The properties of a fibril are easily ascertained from a simple tension test. The response of the overall fabric model and ballistic experiments are in excellent agreement. The model indicates that fabric which is attached by being pinned at the corners generally absorbs more energy, relative to fabric clamped along the sides. The basis for this result is discussed at length in the body of this work. Furthermore, it is observed that a uniform-yarn model, one which ignores the stochastic nature of the yarn, over-estimates the amount of energy absorbed.     

Microfibril-Based Estimates of The Ballistic Limit of Multilayered Fabric Shielding

An expression relating the dominant mechanisms for the energy loss of a projectile, as it penetrates a multilayered ballistic fabric shield, is developed. The relation is a function of the projectile mass, initial velocity and fabric microscale properties, such as microfibril stiffness and critical stretch. Using the derived expression, the number of fabric layers needed to stop a projectile is determined. The analytical result compares quite well to experiments.     

Simulation of coupled microscale multiphysical-fields in particulate-doped dielectrics with staggered adaptive FDTD

This work addresses the modeling and simulation of strongly coupled electromagnetic and thermodynamic fields that arise in particulate-doped dielectrics using an adaptive staggered adaptive FDTD (finite difference time domain) method. Of particular interest is to provide a straightforward modular approach to finding the effective dielectric (electromagnetic) response of a material, incorporating thermal effects, arising from Joule heating, which alter the pointwise dielectric properties such as the electric permittivity, magnetic permeability, and electric conductivity. This is important for “thermal (damage) management” of materials used in electromagnetic applications. Because multiple field coupling is present, a staggered, temporally-adaptive scheme is developed to resolve the internal microstructural electric, magnetic and thermal fields, accounting for the simultaneous pointwise changes in the material properties. Numerical examples are provided to illustrate the approach. Extensions to coupled chemical and mechanical fields are also provided.     

On the Tailoring of Microstructures for Prescribed Effective Properties

The focus of this communication is the development of genetic algorithms to handle material design problems where particulate microstructures are sought which deliver prescribed effective responses. In the problem formulation, constraints are incorporated on the distortion of the otherwise smooth internal fields corresponding to a pure (inhomogeneity-free) matrix material, due to the presence of particles. The key conceptual feature is that the microstructural variables are represented by a genetic string, and a survival of the fittest algorithm is applied to a population of such strings in order to determine an optimal set of microstructural material design parameters.     

Ermittlung der Fließkurve im Zugversuch

Ungenauigkeit der Ermittlung der Fließkurve aus der Zugfestigkeit und der Gleichmaßdehnung. Einfluß der Dehngeschwindigkeit und der Formabweichung des Probestabes. Gleichmaßdehnung beim Faserverbundwerkstoff. Formänderungsgeschwindigkeit, Spannungszustand und Formänderungsfestigkeit nach Beginn der Einschnürung.     

Werkstoffverhalten eines metallischen Faserverbundes und seiner Komponenten bei LCF‐Wechselbeanspruchung

Behaviour of a metallic fibre composite material and its components in LCF‐test The mechanical behaviour of unidirectional metallic fiber composite materials is investigated in the low cycle fatigue tests. The material consists of a copper matrix reinforced by continuous unidirectional fibers of austenitic steel with two different volume fractions. A comparative investigation carried out on the component materials. In addiction to the result of the strain controlled tension‐compression‐tests, the fatigue life is estimated using the Manson‐Coffin relation. The fracture characteristics are studies metallographically.     

Dynamics of clusters of charged particulates in electromagnetic fields

The dynamics of rigid clusters of charged particulates is the subject of this work. The work ascertains what properties of the cluster control its dynamic response to an external electromagnetic field. A primary focus is on the role of the distribution of the charges within the cluster and the effects of the Lorentz force on the overall body's linear and angular momentum. The presentation contains a derivation of the equations governing a charged cluster's dynamics and development of corresponding numerical methods for the simulation. Numerical examples are presented, along with comparisons to qualitative analytical results, where possible. Copyright © 2010 John Wiley & Sons, Ltd.     

Modeling and simulation of progressive penetration of multilayered ballistic fabric shielding

 In this paper a simulation technique is developed to estimate the number of ballistic fabric sheets needed to stop an incoming projectile. Such sheets are free of any fortification by a resin. The computational approach is designed so that it can be easily implemented by a wide audience of researchers in the field, without resorting to more involved finite element formulations. This is achieved by taking advantage of the intrinsic characteristics of such fabric structures. Since the deformations of the fabric are (a) finite, (b) nonlinearly inelastic due to progressive fiber degradation and (c) dynamically coupled to the projectile, the system is highly nonlinear. A temporally adaptive, iterative scheme is developed to solve the system. Theoretical issues pertaining to convergence of the algorithm are investigated. Large-scale 3-D numerical examples are then given to illustrate the approach in determining the number of sheets needed to stop a projectile. Received 28 February 2002 / Accepted 2 April 2002