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Wilson, D. W.

Publications and source records attributed to Wilson, D. W..

13 records
All sourcesNASA NTRSDOE OSTI
NASA NTRS2011

Optical Design and Performance of the Ultra-Compact Imaging Spectrometer

We present the optical design and performance of the Ultra-Compact Imaging Spectrometer (UCIS) currently under development at Caltech's Jet Propulsion Laboratory. The new instrument demonstrates a low optical bench mass of less than 0.5 kg and compact size that enables Mars Rover or other in situ planetary applications. UCIS is a F/4, wide field (30deg) design, covering the spectral range 500-2600 nm and is enabled by a simple all aluminum two-mirror telescope and Offner spectrometer. We discuss here the optical design and alignment method that enables this compact and low mass imaging spectrometer and demonstrate successful spectrometer alignment with smile and keystone levels at 2-3% of a pixel width.

Imaging spectroscopy↗
NASA NTRS2011

Progress in implementation of the Portable Remote Imaging Spectrometer (PRISM) coastal ocean sensor.

PRISM is a pushbroom imaging spectrometer currently in its second year of development at the Jet Propulsion Laboratory, intended to address the needs of airborne coastal ocean science research. We give an overview of the instrument functionality and then describe progress in component and subsystem fabrication. In the second year, all critical components have been received and most have been integrated into their respective subsystems. The design of the vacuum enclosure has also been completed. We present results from the telescope and spectrometer sub-assemblies, the focal plane electronics, and the overall system assembly implementation.

Yee, K.↗
NASA NTRS2002

Diffractive optics for particle velocimetry and sizing

Beam-shaping diffractive optical elements are used to create structured light patterns in fluid flows. Particle scattering results in detected signals that can be used to determine the particle size and velocity.

diffractive optics laser velocimetry↗
NASA NTRS1998

New Convex Grating Types for Concentric Imaging Spectrometers

The properties of convex gratings fabricated by electron-beam lithography are investigated. Three grating types are shown. These gratings allow the optical designer to fully realize the considerable advantages of concentric spectrometer forms.

spectrometers concentric imaging electron beam↗
NASA NTRS1983

Mechanically fastened joints in woven fabric composites

Strength analysis for composite bolted joints involves the mating of a stress analysis with an appropriate mode specific failure criterion for each of the primary failure modes. The stress analysis and failure criteria are independent of each other and can be manipulated separately in order to optimize the strength analysis package formed by their coupling. Material properties tests were conducted on rubber toughened graphite-epoxy material to measure the basic strength and stiffness in the warp and fill directions and in shear. Test matrices are summarized for investigations of laminate configuration, stacking sequence, fastener diameter, edge distance, fastener half spacing, laminate thickness, and fastener torque. A three dimensional finite element analysis computer program was written and failure criteria for net tension, shearout, and bearing were determined.

Wilson, D. W.↗
NASA NTRS1981

Mechanical characterization of PMR-15 graphite/polyimide bolted joints

Data are presented for the static and viscoelastic performance of Celion 6000/PMR-15 graphite/polyimide composite belted joints over the 21 to 315 C temperature range. Two laminate configurations were obtained by sectioning a panel into subpanels oriented parallel and perpendicular to the laminate principal direction. Three replicates of each specimen geometry were tested at each of the test temperatures for the two laminate configurations, and failure load was defined as the maximum load attained as indicated by the load/deflection curve. Effects of strain-rate on strength and failure mode behavior were assessed at room temperature for strain rates of 0.002, 0.01, 0.10, and 1.00/s, and creep behavior was examined for the case of bearing deformations at temperatures of 21 and 177 C. Results are presented, including: (1) two distinct mechanisms were responsible for bearing failure and related to laminate configuration, (2) the + or - 45 deg plies carried the shearing load in composite bolted joints, and (3) the material exhibited strain-rate sensitivity which varied with laminate configuration.

Wilson, D. W.↗
NASA NTRS1981

Analysis of the shearout failure mode in composite bolted joints

A semi-empirical shearout strength model has been formulated for the analysis of composite bolted joints with allowance for the effects of joint geometry. The model employs a polynomial stress function in conjunction with a point stress failure criterion to predict strength as a function of fastener size, edge distance, and half spacing. The stress function is obtained by two-dimensional plane-stress finite element analysis using quadrilateral elements with orthotropic material properties. Comparison of experimentally determined shearout strength data with model predicted failures has substantiated the accuracy of the model.

Wilson, D. W.↗
NASA NTRS1980

Failure analyses of composite bolted joints

The complex failure behavior exhibited by bolted joints of graphite epoxy (Hercules AS/3501) was investigated for the net tension, bearing and shearout failure modes using combined analytical and experimental techniques. Plane stress, linear elastic, finite element methods were employed to determine the two dimensional state of stress resulting from a loaded hole in a finite width, semiinfinite strip. The stresses predicted by the finite element method were verified by experiment to lend credence to the analysis. The influence of joint geometric parameters on the state of stress and resultant strength of the joint was also studied. The resulting functional relationships found to exist between bolted joint strength and the geometric parameters, were applied in the formulation of semiempirical strength models for the basic failure modes. A point stress failure criterion was successfully applied as the failure criterion for the net tension and shearout failure modes.

Wilson, D. W.↗
NASA NTRS1979

Behavior of composite bolted joints at elevated temperature

Experimental results from an investigation which examines the combined effects of temperature, joint geometry and out-of-plane constraint upon the response of mechanically fastened composite joints are presented. Data are presented for simulated mechanically fastened joint conditions in two laminate configurations fabricated from Hercules AS/3501-6 graphite-epoxy. Strength and failure mode results are presented for the test temperatures of 21 C, 121 C and 177 C and for a range of the geometric parameters W/D and e/D from 3.71 to 7.43 and 1.85 to 3.69, respectively. A hole diameter, D of 5.16 mm was utilized for all tests. Pin bearing tests with out-of-plane constraint were conducted at room temperature only. All elevated temperature data were generated for pin bearing conditions. Ultrasonic C scan inspection of the failed specimens was employed to assess the damage region and to determine failure mode. Comparative data are presented for pin bearing and out-of-plane constraint conditions for the above mentioned joint configurations. The joint under pin loading was modeled by two dimensional finite element methods. Predicted net section strain concentrations were compared with experimental results.

Wilson, D. W.↗