Scale effects in orthotropic composite assemblies as micropolar continua: A comparison between weak-and strong-form finite element solutions

The aim of the present work was to investigate the mechanical behavior of orthotropic composites, such as masonry assemblies, subjected to localized loads described as micropolar materials. Micropolar models are known to be effective in modeling the actual behavior of microstructured solids in the presence of localized loads or geometrical discontinuities. This is due to the introduction of an additional degree of freedom (the micro-rotation) in the kinematic model, if compared to the classical continuum and the related strain and stress measures. In particular, it was shown in the literature that brick/block masonry can be satisfactorily modeled as a micropolar continuum, and here it is assumed as a reference orthotropic composite material. The in-plane elastic response of panels made of orthotropic arrangements of bricks of different sizes is analyzed herein. Numerical simulations are provided by comparing weak and strong finite element formulations. The scale effect is investigated, as well as the significant role played by the relative rotation, which is a peculiar strain measure of micropolar continua related to the non-symmetry of strain and work-conjugated stress. In particular, the anisotropic effects accounting for the micropolar moduli, related to the variation of microstructure internal sizes, are highlighted

ECOTOXICOLOGICAL AND PHYSIOLOGICAL EFFECTS OF SALINITY ON AMPHIBIANS

Salinity is a persistent anthropogenic contaminant that negatively effects freshwater species, communities, and ecosystems. High-salinity wastewaters from energy extraction (wastewaters) and road salts are major contributors to increased salinity (NaCl; sodium chloride), but most studies focus on effects of NaCl roads salts. Amphibians are particularly vulnerable to contaminants such as increased salinity because of their porous skin, dependence on freshwater, and poor osmoregulatory capacity. We investigated the relative effects of wastewaters and NaCl on three species of larval amphibians with acute toxicity experiments (Chapter 1). Effects of wastewaters on larvae were predominantly due to high concentrations of NaCl and both had negative effects on survival and growth of larvae. Information on the effects of salinity on amphibian eggs is limited. Therefore, we used chronic toxicity experiments to test the relative effects of wastewaters and NaCl on eggs and larvae of two amphibian species (Chapter 2). Effects of NaCl and wastewaters were comprehensive, but similar, and negatively influenced hatching of eggs and survival, growth, and behavior of larvae. Larvae that survived exposure to increased salinity were smaller, suggesting a growth-survival tradeoff. We tested the influence of salinity on growth, survival, corticosterone (CORT; a steroid hormone) responses, and tradeoffs among traits of a larval amphibian (Chapter 3). By experimentally suppressing CORT signaling, we demonstrate that CORT mediated a growth-survival tradeoff. Suppressing CORT reduced survival further than for controls, but effects of salinity on growth and development were attenuated. Because CORT enhanced survival and influenced fitness-related traits following exposure to salinity, it could be a marker of physiological stress. Therefore, we evaluated whether CORT could be used as a biomarker of individual and population condition for freeliving larval amphibians exposed to wastewaters (Chapter 4). We provide only weak evidence that we could detect changes in waterborne CORT for free-living amphibians exposed to salinity. We provide suggestions to improve collection methods, reduce variability, and avoid confounding effects of background CORT. Background CORT was pervasive, highly variable, and may affect the physiology of larval amphibians. Collectively, this work increases our understanding of the comprehensive negative effects of wastewaters and salinity on amphibians and their physiology

Development and Characterization Testing of an Air Pulsation Valve for a Pulse Detonation Engine Supersonic Parametric Inlet Test Section

In pulse detonation engines, the potential exists for gas pulses from the combustor to travel upstream and adversely affect the inlet performance of the engine. In order to determine the effect of these high frequency pulses on the inlet performance, an air pulsation valve was developed to provide air pulses downstream of a supersonic parametric inlet test section. The purpose of this report is to document the design and characterization tests that were performed on a pulsation valve that was tested at the NASA Glenn Research Center 1x1 Supersonic Wind Tunnel (SWT) test facility. The high air flow pulsation valve design philosophy and analyses performed are discussed and characterization test results are presented. The pulsation valve model was devised based on the concept of using a free spinning ball valve driven from a variable speed electric motor to generate air flow pulses at preset frequencies. In order to deliver the proper flow rate, the flow port was contoured to maximize flow rate and minimize pressure drop. To obtain sharp pressure spikes the valve flow port was designed to be as narrow as possible to minimize port dwell time

NIH-small instrumentation program

Issued as Final report, Project no. G-32-64

Special Issue on Recent Advances in Theoretical and Computational Modeling of Composite Materials and Structures

none2The advancement in manufacturing technology and scientific research have improved the development of enhanced composite materials with tailored properties depending on their design requirements in many engineering fields, as well as in thermal and energy management. Some representative examples of advanced materials in many smart applications and complex structures rely on laminated composites, functionally graded materials (FGMs), and carbon-based constituents, primarily carbon nanotubes (CNTs), and graphene sheets or nanoplatelets, because of their remarkable mechanical properties, electrical conductivity, and high permeability. For such materials, experimental tests usually require a large economical effort because of the complex nature of each constituent, together with many environmental, geometrical, and/or mechanical uncertainties in nonconventional specimens. At the same time, the theoretical and/or computational approaches represent a valid alternative for the design of complex manufacts with more flexibility. In such a context, the development of advanced theoretical and computational models for composite materials and structures is a subject of active research, as explored here for a large variety of structural aspects, involving static, dynamic, buckling, and damage/fracturing problems at different scales.Tornabene, Francesco; Dimitri, RossanaTornabene, Francesco; Dimitri, Rossan

The strong formulation finite element method: stability and accuracy

The Strong Formulation Finite Element Method (SFEM) is a numerical solution technique for solving arbitrarily shaped structural systems. This method uses a hybrid scheme given by the Differential Quadrature Method (DQM) and the Finite Element Method (FEM). The former is used for solving the differential equations inside each element and the latter employs the mapping technique to study domains of general shape. A general brief review on the current methodology has been reported in the book [1] and recalled in the works [2,3], where a stress and strain recovery procedure was implemented. The aim of this manuscript is to present a general view of the static and dynamic behaviors of one- and two-dimensional structural components solved by using SFEM. It must be pointed out that SFEM is a generalization of the so-called Generalized Differential Quadrature Finite Element Method (GDQFEM) presented by the authors in some previous papers [4-8]. Particular interest is given to the accuracy, stability and reliability of the SFEM when it is applied to simple problems. Since numerical solutions - of any kind - are always an approximation of physical systems, all the numerical applications are compared to well-known analytical and semi-analytical solutions of one- and two-dimensional systems. Ultimately, this work presents typical aspects of an innovative domain decomposition approach that should be of wide interest to the computational mechanics community