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At least 1,243 records · Page 69
All sourcesNASA NTRSDOE OSTI
DOE OSTI2022

Elastic Solutions to 2D Plane Strain Problems: Nonlinear Contact and Settlement Analysis for Shallow Foundations

The classical Neumann boundary value problem of an isotropic, homogeneous elastic half-plane under plane strain conditions is readdressed as the limiting case of the fully three-dimensional problem. Analytical solutions of the stress and strain tensors are obtained by taking the limit from known three-dimensional solutions. It is shown that the displacement fields for the plane strain problem are not well defined. A small number of simple expressions are developed, which provide a general solution for linearly-varying traction over arbitrary regions on the boundary. A simple, efficient, and rapidly convergent algorithm is developed which uses these solutions as analytic elements and provides a solution approach to the general boundary value problem. The method is verified against known solutions for Hertzian contact between parallel cylinders. Two numerical examples are presented for the analysis of shallow foundation systems. In the first, the boundary conditions are informed by analytical elastoplastic calculations and a strain influence analysis is performed and compared with the Schmertmann method. Subsequently, empirical laboratory contact traction distributions measured by Bauer et al., in both the normal and tangential directions are employed as boundary conditions for an analysis of the underlying stress field.

42 ENGINEERING↗
DOE OSTI2021

New Solids in As-O-Mo, As(P)-O-Mo(W) and As(P)-O-Nb(W) Systems That Exhibit Nonlinear Optical Properties

Interactions between well-mixed fine powders of As 2 O 3 , P 2 O 5 , MoO 3 , WO 3 and Nb 2 O 5 at different stoichiometry in quartz ampoules under vacuum at ~1000 °C in the presence of metallic molybdenum (or niobium), over several weeks, led to shiny dichroic crystalline materials being formed in cooler parts of the reaction vessel. An addition of small quantities of metals-Mo or Nb-was made with the aim of partially reducing their highly oxidized Mo(VI), W(VI) or Nb(V) species to corresponding Mo(V), W(V) and Nb(IV) centers, in order to form mixed valence solids. Sublimed crystals of four new compounds were investigated using a variety of techniques, with prime emphasis on the X-ray analysis, followed by spectroscopy (diffusion reflectance, IR, Raman and EPR), second harmonic generation (SHG), thermal analysis under N 2 and air atmosphere, and single crystals electrical conductivity studies. The results evidenced the formation of new complex solids of previously unknown compositions and structures. Three out of four compounds crystallized in non-centrosymmetric space groups and represent layered 2D polymeric puckered structures that being stacked on each other form 3D lattices. All new solids exhibit strong second-harmonic-generation (SHG effect; based on YAG 1064 nm tests with detection of 532 nm photons), and a rare photosalient effect when crystals physically move in the laser beam. Single crystals’ electrical conductivity of the four new synthesized compounds was measured, and the results showed their semiconductor behavior. Values of band gaps of these new solids were determined using diffusion reflectance spectroscopy in the visible region. Aspects of new solids’ practical usefulness are discussed.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2020

Tunable diode laser absorption spectroscopy with corrected laser ramping nonlinearities

A tunable diode laser absorption spectroscopy device includes a tunable diode laser. A laser driver is configured to drive the diode laser and ramp it within a particular frequency range. An analyte gas container, a reference gas container, and a fringe generating device are configured to receive the laser therethrough. An optical detector is configured to detect the laser after it has passed through the analyte gas container and/or the reference gas container, and the in-line fringe generating device. An acquisition card is configured to sample an output of the optical detector. A spectral analyzer is configured to receive output data from the acquisition card, determine a spectrum of the output data, decouple the fringe spectrum from the measured spectrum, calibrate the spectrum based on an expected ideal spectrum of both the fringe and reference gas, and determine a composition of the analyte based on the calibrated spectrum.

42 ENGINEERING↗
DOE OSTI2020

Polar oxysulfide for nonlinear optical applications

Single crystals of a new noncentrosymmetric polar oxysulfide SrZn2S2O (s.g. Pmn21) grown in a eutectic KF—KCl flux with unusual wurtzite-like slabs consisting of close-packed corrugated double layers of ZnS3O tetrahedra vertically separated from each other by Sr atoms and methods of making same.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗