SCIENTIFIC AND TECHNICAL AEROSPACE REPORTS

A Biweekly Publication of the National Aeronautics and Space Administration
VOLUME 44, ISSUE 7 - April 07, 2006

39 STRUCTURAL MECHANICS
Includes structural element design, analysis and testing; dynamic responses of structures; weight analysis; fatigue and other structuralproperties; and mechanical and thermal stresses in structures.

For applications see 05 Aircraft Design, Testing and Performance; and18 Spacecraft Design, Testing and Performance.

20060009304 NASA Langley Research Center, Hampton, VA, USA

A Micromechanics-Based Damage Model for [+/- Theta/90n]s Composite Laminates

Mayugo, Joan-Andreu; Camanho, Pedro P.; Maimi, Pere; Davila, Carlos G.; March 2006; 43 pp.; In English; Originalcontains color and black and white illustrationsContract(s)/Grant(s): WBS 581.02.07.07Report No.(s): NASA/TM-2006-214285; L-19242; Copyright; Avail.: CASI: A03, Hardcopy

A new damage model based on a micromechanical analysis of cracked [+/- Theta/90n]s laminates subjected to multiaxialloads is proposed. The model predicts the onset and accumulation of transverse matrix cracks in uniformly stressed laminates,the effect of matrix cracks on the stiffness of the laminate, as well as the ultimate failure of the laminate. The model alsoaccounts for the effect of the ply thickness on the ply strength. Predictions relating the elastic properties of several laminatesand multiaxial loads are presented. Author

Micromechanics; Damage; Loads (Forces); Composite Materials; Laminates; Failure; Cracks

20060009470 NASA Langley Research Center, Hampton, VA, USA, Army Research Lab., Hampton, VA, USA

Effect of Reinforcement Architecture on Fracture of Selectively Reinforced Metallic Compact Tension Specimens

Abada, Christopher H.; Farley, Gary L.; Hyer, MichaelW.; March 2006; 41 pp.; In English; Original contains color and blackand white illustrationsContract(s)/Grant(s): 759.07.11Report No.(s): NASA/TM-2006-214286; L-19238; ARL-TR-3769; Copyright; Avail.: CASI: A03, Hardcopy

A computer-based parametric study of the effect of reinforcement architectures on fracture response of aluminumcompact-tension (CT) specimens is performed. Eleven different reinforcement architectures consisting of rectangular andtriangular cross-section reinforcements were evaluated. Reinforced specimens produced between 13 and 28 percent higherfracture load than achieved with the non-reinforced case. Reinforcements with blunt leading edges (rectangularreinforcements) exhibited superior performance relative to the triangular reinforcements with sharp leading edges. Relative tothe rectangular reinforcements, the most important architectural feature was reinforcement thickness. At failure, thereinforcements carried between 58 and 85 percent of the load applied to the specimen, suggesting that there is considerableload transfer between the base material and the reinforcement. Author

Computer Techniques; Aluminum; Fracturing; Loads (Forces); Blunt Leading Edges; Sharp Leading Edges; Failure

20060009472 NASA Glenn Research Center, Cleveland, OH, USA

Composite Erosion by Computational Simulation

Chamis, Christos C.; February 2006; 29 pp.; In English; SAMPE 2006 Conference and Exhibition, 30 Apr. - 4 May 2006,Long Beach, CA, USAContract(s)/Grant(s): WBS 754.02.07.03Report No.(s): NASA/TM-2006-214096; E-15300-1; No Copyright; Avail.: CASI: A03, Hardcopy

Composite degradation is evaluated by computational simulation when the erosion degradation occurs on a ply-by-plybasis and the degrading medium (device) is normal to the ply. The computational simulation is performed by a multi factorinteraction model and by a multi scale and multi physics available computer code. The erosion process degrades both the fiberand the matrix simultaneously in the same slice (ply). Both the fiber volume ratio and the matrix volume ratio approach zerowhile the void volume ratio increases as the ply degrades. The multi factor interaction model simulates the erosiondegradation, provided that the exponents and factor ratios are selected judiciously. Results obtained by the computationalcomposite mechanics show that most composite characterization properties degrade monotonically and approach ‘zero’ as theply degrades completely. Author

Degradation; Erosion; Void Ratio; Computer Programs

20060009495 Los Alamos National Lab., NM USA

Effects of Various Blowout Panel Configurations on the Structural Response of Los Alamos National Laboratory Building 16-340 to Internal Explosions

January 2005; 168 pp.; In English Report No.(s): DE2005-861280; LA-14196-T; No Copyright; Avail.: National Technical Information Service (NTIS)

The risk of accidental detonation is present whenever any type of high explosives processing activity is performed. These activities are typically carried out indoors to protect processing equipment from the weather and to hide possibly secret processes from view. Often, highly strengthened reinforced concrete buildings are employed to house these activities. These buildings may incorporate several design features, including the use of lightweight frangible blowout panels, to help mitigate blast effects. These panels are used to construct walls that are durable enough to withstand the weather, but are of minimal weight to provide overpressure relief by quickly moving outwards and creating a vent area during an accidental explosion. In this study the behavior of blowout panels under various blast loading conditions was examined. External loadings from explosions occurring in nearby rooms were of primary interest. Several reinforcement systems were designed to help blowout panels resist failure from external blast loads while still allowing them to function as vents when subjected to internal explosions. The reinforcements were studied using two analytical techniques, yield-line analysis and modal analysis, and the hydrocode AUTODYN.Ablowout panel reinforcement design was created that could prevent panels from being blown inward by external explosions. This design was found to increase the internal loading of the building by 20%, as compared with nonreinforced panels. Nonreinforced panels were found to increase the structural loads by 80% when compared to an open wall at the panel location. NTIS

Blowouts; Explosions; Panels

20060009943 NASA Glenn Research Center, Cleveland, OH, USA

Probabilistic Structural Evaluation of Uncertainties in Radiator Sandwich Panel Design

Kuguoglu, Latife; Ludwiczak, Damian; March 2006; 23 pp.; In English; Earth and Space 2006, 5-8 Mar. 2006, Houston, TX, USA; Original contains color and black and white illustrations Contract(s)/Grant(s): WBS 22-794-20-69 Report No.(s): NASA/TM-2006-214116; E-15451; Copyright; Avail.: CASI: A03, Hardcopy

The Jupiter Icy Moons Orbiter (JIMO) Space System is part of the NASA’s Prometheus Program. As part of the JIMO engineering team at NASA Glenn Research Center, the structural design of the JIMO Heat Rejection Subsystem (HRS) is evaluated. An initial goal of this study was to perform sensitivity analyses to determine the relative importance of the input variables on the structural responses of the radiator panel. The desire was to let the sensitivity analysis information identify the important parameters. The probabilistic analysis methods illustrated here support this objective. The probabilistic structural performance evaluation of a HRS radiator sandwich panel was performed. The radiator panel structural performance was assessed in the presence of uncertainties in the loading, fabrication process variables, and material properties. The stress and displacement contours of the deterministic structural analysis at mean probability was performed and results presented. It is followed by a probabilistic evaluation to determine the effect of the primitive variables on the radiator panel structural performance. Based on uncertainties in material properties, structural geometry and loading, the results of the displacement and stress analysis are used as an input file for the probabilistic analysis of the panel. The sensitivity of the structural responses, such as maximum displacement and maximum tensile and compressive stresses of the facesheet in x and y directions and maximum VonMises stresses of the tube, to the loading and design variables is determined under the boundary condition where all edges of the radiator panel are pinned. Based on this study, design critical material and geometric parameters of the considered sandwich panel are identified. Author

Sensitivity Analysis; Structural Analysis; Panels; Design Analysis; Performance Tests; Structural Design; Tensile Stress

Source: NASA