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All sourcesNASA NTRSDOE OSTI
NASA NTRS1988

Lewis Structures Technology, 1988. Volume 3: Structural Integrity Fatigue and Fracture Wind Turbines HOST

The charter of the Structures Division is to perform and disseminate results of research conducted in support of aerospace engine structures. These results have a wide range of applicability to practioners of structural engineering mechanics beyond the aerospace arena. The specific purpose of the symposium was to familiarize the engineering structures community with the depth and range of research performed by the division and its academic and industrial partners. Sessions covered vibration control, fracture mechanics, ceramic component reliability, parallel computing, nondestructive evaluation, constitutive models and experimental capabilities, dynamic systems, fatigue and damage, wind turbines, hot section technology (HOST), aeroelasticity, structural mechanics codes, computational methods for dynamics, structural optimization, and applications of structural dynamics, and structural mechanics computer codes.

Source record↗
NASA NTRS1988

Probabilistic Structural Analysis Methods for select space propulsion system structural components (PSAM)

The objective is the development of several modular structural analysis packages capable of predicting the probabilistic response distribution for key structural variables such as maximum stress, natural frequencies, transient response, etc. The structural analysis packages are to include stochastic modeling of loads, material properties, geometry (tolerances), and boundary conditions. The solution is to be in terms of the cumulative probability of exceedance distribution (CDF) and confidence bounds. Two methods of probability modeling are to be included as well as three types of structural models - probabilistic finite-element method (PFEM); probabilistic approximate analysis methods (PAAM); and probabilistic boundary element methods (PBEM). The purpose in doing probabilistic structural analysis is to provide the designer with a more realistic ability to assess the importance of uncertainty in the response of a high performance structure. Probabilistic Structural Analysis Method (PSAM) tools will estimate structural safety and reliability, while providing the engineer with information on the confidence that should be given to the predicted behavior. Perhaps most critically, the PSAM results will directly provide information on the sensitivity of the design response to those variables which are seen to be uncertain.

Cruse, T. A.↗
NASA NTRS1989

Computational structural mechanics for engine structures

The computational structural mechanics (CSM) program at Lewis encompasses: (1) fundamental aspects for formulating and solving structural mechanics problems, and (2) development of integrated software systems to computationally simulate the performance/durability/life of engine structures. It is structured to mainly supplement, complement, and whenever possible replace, costly experimental efforts which are unavoidable during engineering research and development programs. Specific objectives include: investigate unique advantages of parallel and multiprocesses for: reformulating/solving structural mechanics and formulating/solving multidisciplinary mechanics and develop integrated structural system computational simulators for: predicting structural performances, evaluating newly developed methods, and for identifying and prioritizing improved/missing methods needed. Herein the CSM program is summarized with emphasis on the Engine Structures Computational Simulator (ESCS). Typical results obtained using ESCS are described to illustrate its versatility.

Chamis, C. C.↗
NASA NTRS1989

Probabilistic structural analysis methods of hot engine structures

Development of probabilistic structural analysis methods for hot engine structures at Lewis Research Center is presented. Three elements of the research program are: (1) composite load spectra methodology; (2) probabilistic structural analysis methodology; and (3) probabilistic structural analysis application. Recent progress includes: (1) quantification of the effects of uncertainties for several variables on high pressure fuel turbopump (HPFT) turbine blade temperature, pressure, and torque of the space shuttle main engine (SSME); (2) the evaluation of the cumulative distribution function for various structural response variables based on assumed uncertainties in primitive structural variables; and (3) evaluation of the failure probability. Collectively, the results demonstrate that the structural durability of hot engine structural components can be effectively evaluated in a formal probabilistic/reliability framework.

Chamis, C. C.↗
NASA NTRS1992

Application of adaptive structures in the design of space structures

Future requirements for large precision structures will require a new structural design approach called Adaptive Structures: a system whose geometric and inherent structural characteristics can be changed beneficially to meet the mission requirements either through remote commands or automatically in response to external stimulations. The performance requirements and a ground validation test program for structural designs can be established by the use of Adaptive Structures. The potential value of incorporating Adaptive Structures into the structural design will be described with current analytical and experimental developments.

Wada, Ben K.↗
NASA NTRS1994

A PDE-based methodology for modeling, parameter estimation and feedback control in structural and structural acoustic systems

A problem of continued interest concerns the control of vibrations in a flexible structure and the related problem of reducing structure-borne noise in structural acoustic systems. In both cases, piezoceramic patches bonded to the structures have been successfully used as control actuators. Through the application of a controlling voltage, the patches can be used to reduce structural vibrations which in turn lead to methods for reducing structure-borne noise. A PDE-based methodology for modeling, estimating physical parameters, and implementing a feedback control scheme for problems of this type is discussed. While the illustrating example is a circular plate, the methodology is sufficiently general so as to be applicable in a variety of structural and structural acoustic systems.

Banks, H. T.↗
NASA NTRS1994

Experimental validation of an integrated controls-structures design methodology for a class of flexible space structures

This paper describes the first experimental validation of an optimization-based integrated controls-structures design methodology for a class of flexible space structures. The Controls-Structures-Interaction (CSI) Evolutionary Model, a laboratory test bed at Langley, is redesigned based on the integrated design methodology with two different dissipative control strategies. The redesigned structure is fabricated, assembled in the laboratory, and experimentally compared with the original test structure. Design guides are proposed and used in the integrated design process to ensure that the resulting structure can be fabricated. Experimental results indicate that the integrated design requires greater than 60 percent less average control power (by thruster actuators) than the conventional control-optimized design while maintaining the required line-of-sight performance, thereby confirming the analytical findings about the superiority of the integrated design methodology. Amenability of the integrated design structure to other control strategies is considered and evaluated analytically and experimentally. This work also demonstrates the capabilities of the Langley-developed design tool CSI DESIGN which provides a unified environment for structural and control design.

Maghami, Peiman G.↗
NASA NTRS1996

The Use of Structural-Acoustic Techniques to Assess Potential Structural Damage From Sonic Booms

The potential impact of supersonic operations includes structural damage from the sonic boom overpressure. This paper describes a study of how structural-acoustic modeling and testing techniques may be used to assess the potential for such damage in the absence of actual flyovers. Procedures are described whereby transfer functions relating structural response to sonic boom signature may be obtained with a stationary acoustic source and appropriate data processing. Further, by invoking structural-acoustic reciprocity, these transfer functions may also be acquired by measuring the radiated sound from the structure under a mechanical drive. The approach is based on the fundamental assumption of linearity, both with regard to the (acoustic) propagation of the boom in the vicinity of the structure and to the structure's response. Practical issues revolve around acoustic far field and source directivity requirements. The technique was implemented on a specially fabricated test structure at Edwards AFB, CA with the support of Wyle Laboratories, Inc. Blank shots from a cannon served as our acoustic source and taps from an instrumented hammer generated the mechanical drive. Simulated response functions were constructed. Results of comparisons with corresponding measurements recorded during dedicated supersonic flyovers with F-15 aircraft are presented for a number of sensor placements.

Garrelick, Joel↗
NASA NTRS2002

Monitoring of Structural Integrity of Composite Structures by Embedded Optical Fiber Sensors

Real time monitoring of the mechanical integrity and stresses on key aerospace composite structures like aircraft wings, walls of pressure vessels and fuel tanks or any other structurally extended components and panels as in space telescopes is very important to NASA. Future military and commercial aircraft as well as NASA space systems such as Space Based Radar and International Space Station will incorporate a monitoring system to sense any degradation to the structure. In the extreme flight conditions of an aerospace vehicle it might be desirable to measure the strain every ten centimeters and thus fully map out the strain field of a composite component. A series of missions and vehicle health management requirements call for these measurements. At the moment thousands of people support a few vehicle launches per year. This number can be significantly reduced by implementing intelligent vehicles with integral nervous systems (smart structures). This would require maintenance to be performed only as needed. Military and commercial aircrafts have an equally compelling case. Maintenance yearly costs are currently reaching astronomical heights. Monitoring techniques are therefore required that allow for maintenance to be performed only when needed. This would allow improved safety by insuring that necessary tasks are performed while reducing costs by eliminating procedures that are costly and not needed. The advantages fiber optical sensors have over conventional electro-mechanical systems like strain gauges have been widely extolled in the research literature. These advantages include their small size, low weight, immunity to electrical resistance, corrosion resistance, compatibility with composite materials and process conditions, and multiplexing capabilities. One fiber optic device which is suitable for distributed sensing is the fiber Bragg grating (FBG). Researchers at NASA MSFC are currently developing techniques for using FBGs for monitoring the integrity of advanced structural materials expected to become the mainstay of the current and future generation space structures. Since carbon-epoxy composites are the materials of choice for the current space structures, the initial study is concentrated on this type of composite. The goals of this activity are to use embedded FBG sensors for measuring strain and temperature of composite structures, and to investigate the effects of various parameters such as composite fiber orientation with respect to the optical sensor, unidirectional fiber composite, fabrication process etc., on the optical performance of the sensor. This paper describes an experiment to demonstrate the use of an embedded FBG for measuring strain in a composite material. The performance of the fiber optic sensor is determined by direct comparison with results from more conventional instrumentation.

Albert J. Osei↗
DOE OSTI2025

Lattice Structured Lightweight Structural Materials

The development of lightweight structural materials is crucial for enhancing the performance and deployment feasibility of fission batteries. This study aims to produce lightweight structural materials whose strength-to-weight ratios exceed those of current widely used structural materials. To achieve this, advanced modeling and simulation tools were employed to design lattice structures with different lattice parameters and different lattice types. A process was successfully developed for transforming lattice-structured models into Multiphysics Object Oriented Simulation Environment (MOOSE) inputs. Finite element modeling (FEM) was used to simulate the uniaxial tensile testing of the lattice-structured parts to investigate the stress distribution at a given displacement. The modeling results showed that the lattice-structured sample displayed a lower Young’s modulus in comparison to the solid material; the increase in solid shell thickness and blend radius enhances the mechanical performance; and the effect of unit cell size on macro scale stress is minimal. Tensile testing was conducted on the solid and lattice-structured materials fabricated by laser powder bed fusion (LPBF) additive manufacturing. The experimental results agreed well with the model prediction. The approach of using modeling as a guiding tool for preliminary material design can significantly save time and cost for new material development.

lightweight material↗
DOE OSTI2014

Calcium substitution in rare-earth metal germanides with the hexagonal Mn{sub 5}Si{sub 3} structure type. structural characterization of the extended series RE{sub 5–x}Ca{sub x}Ge{sub 3} (RE=Rare-earth metal)

Reported are the synthesis and the structural characterization of an extended family of rare-earth metal–germanides with a general formula RE{sub 5–x}Ca{sub x}Ge{sub 3} (RE=Y, Ce–Nd, Sm, Gd–Tm and Lu; x<2). All twelve phases are isotypic, crystallizing with the Mn{sub 5}Si{sub 3} structure type (Pearson index hP16, hexagonal space group P6{sub 3}/mcm); they are the Ca-substituted variants of the corresponding RE{sub 5}Ge{sub 3} binaries. Across the series, despite some small variations in the Ca-uptake, the unit cell volumes decrease monotonically, following the lanthanide contraction. Temperature dependent DC magnetization measurements reveal paramagnetic behavior in the high temperature range, and the obtained effective moments are consistent with free-ion RE{sup 3+} ground state, as expected from prior studies of the binary RE{sub 5}Ge{sub 3} phases. The onset of magnetic ordering is observed in the low temperature range, and complex magnetic interactions (ferromagnetic/ferrimagnetic) can be inferred, different from the binary phases RE{sub 5}Ge{sub 3}, which are known as antiferromagnetic. In order to understand the role of Ca in the bonding, the electronic structures of the La{sub 5}Ge{sub 3} and the hypothetical compounds La{sub 2}Ca{sub 3}Ge{sub 3} and La{sub 3}Ca{sub 2}Ge{sub 3} with ordered metal atoms are compared and discussed. - Graphical abstract: The family of rare-earth metal–calcium–germanides with the general formula RE{sub 5–x}Ca{sub x}Ge{sub 3} (RE=Y, Ce–Nd, Sm, Gd–Tm and Lu) crystallize in the hexagonal space group P6{sub 3}/mcm (No. 193, Pearson symbol hP16) with a structure that is a variant of the Mn{sub 5}Si{sub 3} structure type. - Highlights: • The newly synthesized RE{sub 5–x}Ca{sub x}Ge{sub 3} (RE=Y, Ce–Nd, Sm, Gd–Tm and Lu) constitute an extended family. • The structure is a substitution variant of the hexagonal Mn{sub 5}Si{sub 3} structure type. • Ca-uptake is the highest in the early members, and decreases for the late rare-earth metal analogs. • Experimental and theoretical work suggest limiting solubility range RE{sub ≈3}Ca{sub ≈2}Ge{sub 3}.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2019

Synthesis and structure of Sr 14 Zn 1+ x As 11 and Eu 14 Zn 1+ x As 11 (x ≤ 0.5). New members of the family of pnictides isotypic with Ca 14 AlSb 11 , exhibiting a new type of structural disorder

Systematic investigation of the ternary systems A–Zn–As (A = Sr, Eu) led to the discovery of two new ternary phases, Sr 14 Zn 1+x As 11 and Eu 14 Zn 1+x As 11 (x ≤ 0.5). Both title compounds were structurally characterized by single-crystal X-ray diffraction. The basic structure of these new arsenides is akin to that of the numerous other pnictides adopting the tetragonal Ca 14 AlSb 11 structure type (space group I4 1 / acd (No. 142); Z = 8). The main difference is the presence of an interstitial Zn atom, located in a nearly trigonal-planar coordination environment of three As atoms. Four such fragments share common edges with the regular ZnAs 4 tetrahedron, to form an unusual new structural unit with the formula [Zn 1+x Sb 8] . The small uptake of additional zinc is needed to augment the overall valence electron count, thereby driving the system to an electronically charge-balanced state. Upon partial substitution of the nominally divalent Sr with a trivalent La, the equivalent of electron doping, the structure rids itself of the interstitial zinc, as demonstrated on the example of Sr 13.30(2) La 0.70 ZnAs 11 , which was also structurally characterized by single-crystal X-ray diffraction as part of this study. In conclusion, electronic structure calculations for the idealized composition Sr 14 ZnAs 11 confirm the speculated electron-deficient assignment, and suggest intrinsic semiconducting behavior for the one-electron richer Sr 14 Zn 1+x As 11 (x = 0.5) and Sr 13 LaZnAs 11 , respectively.

36 MATERIALS SCIENCE↗
DOE OSTI2021

Structural analysis of the catalytic domain of Artemis endonuclease/SNM1C reveals distinct structural features

The endonuclease Artemis is responsible for opening DNA hairpins during V(D)J recombination and for processing a subset of pathological DNA double-strand breaks. Artemis is an attractive target for the development of therapeutics to manage various B cell and T cell tumors, because failure to open DNA hairpins and accumulation of chromosomal breaks may reduce the proliferation and viability of pre-T and pre-B cell derivatives. However, structure-based drug discovery of specific Artemis inhibitors has been hampered by a lack of crystal structures. Here, we report the structure of the catalytic domain of recombinant human Artemis. The catalytic domain displayed a polypeptide fold similar overall to those of other members in the DNA cross-link repair gene SNM1 family and in mRNA 3'-end-processing endonuclease CPSF-73, containing metallo-β-lactamase and β-CASP domains and a cluster of conserved histidine and aspartate residues capable of binding two metal atoms in the catalytic site. As in SNM1A, only one zinc ion was located in the Artemis active site. However, Artemis displayed several unique features. Unlike in other members of this enzyme class, a second zinc ion was present in the β-CASP domain that leads to structural reorientation of the putative DNA-binding surface and extends the substrate-binding pocket to a new pocket, pocket III. Moreover, the substrate-binding surface exhibited a dominant and extensive positive charge distribution compared with that in the structures of SNM1A and SNM1B, presumably because of the structurally distinct DNA substrate of Artemis. The structural features identified here may provide opportunities for designing selective Artemis inhibitors.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2020

A cross-sectional aeroelastic analysis and structural optimization tool for slender composite structures

A fully open-source available framework for the parametric cross-sectional analysis and design optimization of slender composite structures, such as helicopter or wind turbine blades, is presented. The framework—Structural Optimization and Aeroelastic Analysis (SONATA)—incorporates two structural solvers, the commercial tool VABS, and the novel open-source code ANBA4. SONATA also parameterizes the design inputs, postprocesses and visualizes the results, and generates the structural inputs to a variety of aeroelastic analysis tools. It is linked to the optimization library OpenMDAO. This work presents the methodology and explains the fundamental approaches of SONATA. Structural characteristics were successfully verified for both VABS and ANBA4 using box beam examples from literature, thereby verifying the parametric approach to generating the topology and mesh in a cross section as well as the solver integration. The framework was furthermore exercised by analyzing and evaluating a fully resolved highly flexible wind turbine blade. Computed structural characteristics correlated between VABS and ANBA4, including off-diagonal terms. Stresses, strains, and deformations were recovered from loads derived through coupling with aeroelastic analysis. The framework, therefore, proves effective in accurately analyzing and optimizing slender composite structures on a high-fidelity level that is close to a three-dimensional finite element model.

42 ENGINEERING↗
DOE OSTI2016

New insights into the application of the valence rules in Zintl phases—Crystal and electronic structures of Ba{sub 7}Ga{sub 4}P{sub 9}, Ba{sub 7}Ga{sub 4}As{sub 9}, Ba{sub 7}Al{sub 4}Sb{sub 9}, Ba{sub 6}CaAl{sub 4}Sb{sub 9}, and Ba{sub 6}CaGa{sub 4}Sb{sub 9}

Crystals of three new ternary pnictides—Ba{sub 7}Al{sub 4}Sb{sub 9}, Ba{sub 7}Ga{sub 4}P{sub 9}, and Ba{sub 7}Ga{sub 4}As{sub 9} have been prepared by reactions of the respective elements in molten Al or Pb fluxes. Single-crystal X-ray diffraction studies reveal that the three phases are isotypic, crystallizing in the orthorhombic Ba{sub 7}Ga{sub 4}Sb{sub 9}-type structure (space group Pmmn, Pearson symbol oP40, Z=2), for which only the prototype is known. The structure is based on TrPn{sub 4} tetrahedra (Tr=Al, Ga; Pn=P, As, Sb), connected in an intricate scheme into 1D-ribbons. Long interchain Pn–Pn bonds (d{sub P–P}>3.0 Å; d{sub As–As}>3.1 Å; d{sub Sb–Sb}>3.3 Å) account for the realization of 2D-layers, separated by Ba{sup 2+} cations. Applying the classic valance rules to rationalize the bonding apparently fails, and Ba{sub 7}Ga{sub 4}Sb{sub 9} has long been known as a metallic Zintl phase. Earlier theoretical calculations, both empirical and ab-initio, suggest that the possible metallic properties originate from filled anti-bonding Pn–Pn states, and the special roles of the “cations” in this crystal structure. To experimentally probe this hypothesis, we sought to synthesize the ordered quaternary phases Ba{sub 6}CaTr{sub 4}Sb{sub 9} (Tr=Al, Ga). Single-crystal X-ray diffraction work confirms Ba{sub 6.145(3)}Ca{sub 0.855}Al{sub 4}Sb{sub 9} and Ba{sub 6.235(3)}Ca{sub 0.765}Ga{sub 4}Sb{sub 9}, with Ca atoms preferably substituting Ba on one of the three available sites. The nuances of the five crystal structures are discussed, and the chemical bonding in Ba{sub 7}Ga{sub 4}As{sub 9} is interrogated by tight-binding linear muffin-tin orbital calculations. - Graphical abstract: The new Zintl phases—Ba{sub 7}Al{sub 4}Sb{sub 9}, Ba{sub 7}Ga{sub 4}P{sub 9}, and Ba{sub 7}Ga{sub 4}As{sub 9}, and their quaternary variants Ba{sub 6}CaTr{sub 4}Sb{sub 9} (Tr=Al, Ga)—crystallize in the Ba{sub 7}Ga{sub 4}Sb{sub 9} structure type. The structures are based on TrPn{sub 4} tetrahedra (a perspective of the crystal structure is shown, as viewed along the c axis). - Highlights: • Ba{sub 7}Al{sub 4}Sb{sub 9}, Ba{sub 7}Ga{sub 4}P{sub 9}, and Ba{sub 7}Ga{sub 4}As{sub 9} are new compounds in the respective phase diagrams. • The quaternary phases Ba{sub 6}CaTr{sub 4}Sb{sub 9} (Tr=Al, Ga) show nearly ordered Ba/Ca distribution. • Very weak Pn–Pn bonds and pairing distortion are observed for Ba{sub 7}Ga{sub 4}Pn{sub 9} (Pn=P, As).

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2024

A structure-preserving machine learning framework for accurate prediction of structural dynamics for systems with isolated nonlinearities

The nonlinearities present in structural systems are often found in isolated regions within the structure, such as those containing joints or interfaces. However, despite the localized nature of these nonlinearities their presence serves to couple together the modes of the underlying linear system and significantly complicate the development of appropriate reduced-order models; the localized nonlinearities have a global effect on the dynamics of the system. Further, in the presence of evolving structural health the nonlinearities can arise from accumulating damage, with dynamics distinct from those observed in the healthy state. The present work develops a data-driven formulation to identify and include the contributions of the isolated nonlinearities on the dynamics of the underlying linear structure. A novel coordinate separation is developed that decomposes those nonlinearities restricted to the isolated subdomain from the known linear system defined over the entire domain, and the influence of the isolated nonlinearities is reintroduced as an appropriately identified traction at the boundary of the isolated subdomain, referred to as the deviatoric force. In the region exterior to the nonlinear subdomain the response of the ideal linear system recovers that of the original nonlinear system. In this work, the deviatoric force component is predicted using a structure-preserving multilayer perceptron, based only on measured responses at the boundary of the isolated subdomain. Therefore introduction of the perceptron is able to bypass the direct numerical simulation of the nonlinearities within the isolated subdomain. This approach is illustrated through a simple structural system in which an interior region contains cubic nonlinearities and hysteretic damping. Once trained, the machine learning system is able to accurately predict the deviatoric force so that the ideal system recovers the response of the original system in the region outside the isolated nonlinear subdomain. Moreover, the data-driven approach is able to accurately predict the response when the system is subject to differing initial conditions and external excitation without the need for retraining, so that the proposed approach provides a robust description of the structural dynamics of the overall system.

Machine learning↗
DOE OSTI2018

Structural Comparison of Various Silkworm Silks: An Insight into the Structure–Property Relationship

Silkworm silk has attracted considerable attention in recent years due to its excellent mechanical properties, biocompatibility, and promising applications in biomedical sector. However, a clear understanding of the molecular structure and the relationship between the excellent mechanical properties and the silk protein sequences are still lacking. This study carries out a thorough comparative structural analysis of silk fibers of four silkworm species (Bombyx mori, Antheraea pernyi, Samia cynthia ricini, and Antheraea assamensis). A combination of characterization techniques including scanning electron microscopy, mechanical test, synchrotron X-ray diffraction, Fourier transform infrared spectroscopy (FTIR), and NMR spectroscopy was applied to investigate the morphologies, mechanical properties, amino acid compositions, nanoscale organizations, and molecular structures of various silkworm silks. Furthermore, the structure–property relationship is discussed by correlating the molecular structural features of silks with their mechanical properties. Here, the results show that a high content of β-sheet structures and a high crystallinity would result in a high Young’s modulus for silkworm silk fibers. Additionally, a low content of β-sheet structures would result in a high extensibility.

59 BASIC BIOLOGICAL SCIENCES↗