Ronald D. Kriz

DIVERSE: a framework for building extensible and reconfigurable device independent virtual environments

We present DIVERSE, a highly modular collection of complimentary software packages designed to facilitate the creation of device independent virtual environments. DIVERSE is free/open source software, containing both end-user programs and C++ APIs (Application Programming Interfaces). DgiPf is the DIVERSE graphics interface to OpenGL Performer/sup TM/. A program using DgiPf can run on platforms ranging from fully immersive systems such as CAVEs/sup TM/ to generic desktop workstations without modification. We describe DgiPfs design and present a specific example of how it is being used to aid researchers.

DIVERSE: a framework for building extensible and reconfigurable device-independent virtual environments and distributed asynchronous simulations

We present DIVERSE, a highly modular collection of complimentary software packages designed to facilitate the creation of device-independent virtual environments and distributed asynchronous simulations. DIVERSE is free/open source software, containing both end-user programs and C++ application programming interfaces (APIs). DPF is the DIVERSE graphics interface to OpenGL Performer. A program using the DPF API can run without modification on platforms ranging from fully immersive systems such as CAVEs to generic desktop workstations. The DIVERSE toolkit (DTK) contains all the nongraphical components of DIVERSE, such as networking utilities, hardware device access, and navigational techniques. It introduces a software implementation of networks of replicated noncoherent shared memory. It also introduces a method that seamlessly extends hardware drivers into interprocess and Internet hardware services. We will describe the design of DIVERSE and present a specific example of how it is being used to aid researchers.

Axial shear waves in fiber-reinforced composites with multiple interfacial layers between fiber core and matrix

Abstract Effects of interfacial material properties on the overall dispersion and attenuation of axial shear waves in a multiphase fiber-matrix composite are investigated. The fiber-matrix composite consists of identical fibers that are embedded in a matrix. Multiphase interfacial regions are assumed to exist between the fiber core and the matrix, and their material properties (shear modulus μ and density ρ) are assumed to have linear or exponential variation between fiber core and matrix. Only the case of axial shear waves is studied; thus, the effective axial shear modulus (M), axial shear wave phase speed (B), and axial shear wave specific damping capacity (Ψ) are obtained. The analyses indicate, among others, that the effective mechanical properties of the multiphase composite depend on (in addition to the fiber volume, c, and dynamic parameters In) the variations of material properties in the interfacial region. Numerical computations show the following: 1. The effective axial shear wave phase speed (B) of the composite with multi-interfacial region does not vary with driving frequencies when the frequency range is under 30 Khz. Specifically, for frequency range under 30 Khz, the multiphase composite is indispersive. 2. For the same composite, a higher frequency range will beget higher attenuation. 3. Under the same frequency, certain composites will have higher attenuation; composites with thicker interfacial region, composites with less smooth variation of the interfacial region, and composites with exponential variation (compared with those of linear variation) of the interfacial region.

Science at the speed of thought

Scientific discoveries occur with iterations of theory, experiment, and analysis. But the methods that scientists use to go about their work are changing [1]. Experiment types are changing. Increasingly, experiment means computational experiment [2], as computers increase in speed, memory, and parallel processing capability. Laboratory experiments are becoming parallel as combinatorial experiments become more common. Acquired datasets are changing. Both computer and laboratory experiments can produce large quantities of data where the time to analyze data can exceed the time to generate it. Data from experiments can come in surges where the analysis of each set determines the direction of the next experiments. The data generated by experiments may also be non-intuitive. For example, nanoscience is the study of materials whose properties may change greatly as their size is reduced [3]. Thus analyses may benefit from new ways to examine and interact with data.

MULTIPLE WAVE SCATTERING IN FIBER-REINFORCED COMPOSITES : MICROMECHANICAL VIEWPOINT

Abstract In this study multiple wave scattering phenomena in fiber-matrix composites are investigated from a successive-event perspective. Following the general multiple scattering principle in a successive-event approach, the wave functions (axial shear displacement waves for our case) are calculated and summed for consecutive scattering events. The result thus obtained (an explicit solution) is proved to be the same as the one obtained from the many-body approach (an implicit solution) by previous investigators. After proving the mathematical exactness of the multiple scattering approach, we study the energy transferability by considering the extinction cross-section of each scattering event. Asymptotic analyses are performed for the extinction cross-section for the Rayleigh limit (low frequency limit). The analytical result for the Rayleigh limit shows that the shear wave diminishing power factor has a simple relation with the shear modulus, μ, of both the matrix and fiber. In addition, the order of magnitude of the extinction cross-section for each succeeding event is always O(k13a4), where k1 is the wave number associated with the matrix and ‘ a’ is the fiber radius. Numerical computations are performed for the first five scattering orders, with a specific arrangement of a two-fiber system and over a wide range of frequencies. The results show that at higher frequencies the extinction cross-sections for the first five scattering orders tend to be in the same order of magnitude for this particular arrangement of fiber-matrix system. Finally, the widely used quasi-crystalline approximation in the statistical-averaging technique for wave theory is proven to be valid from the successive-event viewpoint.

Stoichiometry effects on core structure and mobility in B2 NiAl

Abstract The effects of stoichiometry deviation on the core structure and motion of dislocations in B2 NiAl are studied. Vacancies and antisites are introduced into numerous positions in embedded atom simulation blocks containing [100](001) as well as [100](011) pure edge dislocations. The interaction of these point defects with the dislocation is quantified by calculating the change in total energy experienced by the simulated lattice. An off-stoichiometry Ni-rich alloy is generated by randomly substituting Ni atoms for Al atoms as well as simply deleting Al atoms from the perfect lattice structure. It was found that a 2% deviation from stoichiometry affects the shapes of dislocation cores in that they tend to lose their preference for the well-defined crystallographic planes seen in the stoichiometric alloy. Stoichiometry deviations also increase the non-planar spreading of the core as visualized using the strain invariant method. It was found that Al vacancies are strongly attracted to the dislocation ...

Effect of stress on energy flux deviation of ultrasonic waves in GR/EP composites

Ultrasonic waves suffer energy flux deviation in graphite/epoxy because of the large anisotropy. The angle of deviation is a function of the elastic coefficients. For nonlinear solids, these coefficients and thus the angle of deviation is a function of stress. Acoustoelastic theory was used to model the effect of stress on flux deviation for unidirectional T300/5208 using previously measured elastic coefficients. Computations were made for uniaxial stress along the chi /sub 3/ axis (fiber axis) and the chi /sub 1/ axis for waves propagating in the chi /sub 1/ chi /sub 3/ plane. These results predict a shift as large as three degrees for the quasi-transverse wave. It is noted that the shift in energy flux offers a new nondestructive technique for evaluating stress in composites.<<ETX>>

Shear waves in fiber-reinforced composites with interfacial cracks

Abstract An ensemble-average statistical method is used to calculate the overall effective mechanical properties of fiber-reinforced composites with interfacial cracks. The cracks here are specifically the fiber-matrix interfacial cracks which occur during the manufacturing process or are from inherent material defects. The problem starts with the establishment of the Helmholtz equations and boundary conditions followed by a full scale solution of the multiple scattering equations. Then by considering the low frequencies limit and the statistics of randomly spatial distribution of the fibers, a manageable homogeneous linear matrix equation is obtained. In a homogenized point of view the macroscopic mechanical properties of the composite system are derived. The calculated average mechanical properties include the overall effective shear modulus μ, the average shear wave phase speed B , and the average specific damping capacity Ψ of the composite system. The shear modulus corresponds to the elasticity of the static state, while the shear wave phase speed and damping capacity correspond to the viscoelasticity of the dynamic state of the composite. The results show that, among others: 1. the fiber-reinforced composites with interfacial cracks are transversely anisotropic material systems possessing viscoelastic behavior 2. the axially shear modulus of the composite, as the half crack length (δ) increases, is in a ‘decreasing steps’ fashion for which finite numerical jumps exist between those steps 3. 3. for a fiber-reinforced composite with interfacial cracks, the composite system with 1/2 π half crack length is the least attenuated and is nearly transversely isotropic 4. the composite is a non-dispersed material system in low frequency ranges.

Combined Research and Curriculum Development of Web and Java Based Educational Modules with Immersive Virtual Environments

A Java framework is described for creating an interface with legacy code on a Web browser. This interface was created in the development of modules for teaching a senior level (I) and first-year graduate level course (II) on the Mechanical Behavior of Materials. Both courses incorporate the results of state-of-the-art simulation techniques. The modules make extensive use of materials available through the Internet. When appropriate, students study structure property relationships predicted by simulations in an immersive environment called a CAVETM. Simulation results span various length scales, starting at the atomistic level that use embedded atom method techniques, and continuing with simulations at the continuum level that use finite element method techniques. Modules for the second course focus on a scale between the atomistic and continuum level where mechanical behavior is predicted by simulations that used a variety of numerical techniques. These modules use legacy code written by the researchers teaching these classes. Considerable attention was given to creating a Web-based interface that allows researchers easily to construct, and students easily to use, interfaces that access legacy code in an interactive format. Hence, researchers and instructors can focus more on content development and students can focus more on experimenting with possible parametric combinations in their solutions.

SIMULATION AND VISUALIZATION OF STRESS WAVE PROPAGATION IN COMPOSITE LAMINATE WITH INTERPHASE LAYER

Abstract In order to obtain a physical interpretation of experimental data obtained in ultrasonic-acoustic measurements, we simulate the experiment by numerical calculation on a supercomputer. The composite we discuss here is a two dimensional rectangular beam which has one reinforcement layer located at middepth. The Finite Strip Method (FSM) is used to formulate the composite and modal analysis and Duhatnel integral equation are also used to obtain its dynamic response for the impulsive incident wave. Making use of the Visualization Technique of Stress Wave Propagation (VTSWP) we obtain the animated simulation of stress wave propagation in a composite. The effect of gradient distribution of the stiffness in the interphase layer on the wave energy transmission from matrix to fiber is also analyzed as an amplitude transmission coefficient (ATC).