The structural engineer is faced with unique problems when dealing with aeropropulsion systems. He is faced with extremes in operating temperatures, rotational effects, and behaviors of advanced material systems which combine into complexities that require advances in many scientific disciplines involved in structural analysis and design procedures. This presentation provides an overview of the complexities of aeropropulsion structures and the theoretical, computational, and experimental research conducted to achieve the needed advances

Nichols, Lester D.

English

NASA Technical Reports Server

AEROPROPULSION STRUCTURES 
L e s t e r  D. N i c h o l s  
Aeropropulsion systems present unique problems to the structural engineer. 
extremes in operating temperatures, rotational effects, and behaviors of advanced 
material systems combine into complexities that require advances in many scientific 
disciplines involved in structural analysis and design procedures. 
provides an overview of the complexities of aeropropulsion structures and the theo- 
retical, computational, and experimental research conducted to achieve the needed 
advances. 
The 
This presentation 
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https://ntrs.nasa.gov/search.jsp?R=19880006404 2020-03-20T07:55:26+00:00Z
ORIGINAL PAGE IS 
OF POOR QUALITY: STRUCTURES DIVISION 
The Structures Division is engaged principally in developing validated analysis 
methods for predicting the performance of the structural components and systems of 
aerospace propulsion machinery. 
behavior characteristics, such as instantaneous o r  time-dependent stresses and 
deformations, structural dynamics, aeroelasticity, material behavior, and structural- 
life-related phenomena. 
stand complex structural and material behaviors in order to develop theoretical 
models that emulate them. 
Performance here refers to a diversity of operating 
Experiments are used both to validate methods and to under- 
The structures of aeronautical propulsion systems have a unique combination of 
complexities: 
have rotating components with complex dynamic behavior, and are constructed of 
lightweight advanced material systems with unique characteristics. 
they operate with long life in extremely harsh loading environments, 
STRUCTURES DIVISION 
BUSINESS: AEROSPACE PROPULSION STRUCTURES 
PRINCIPAL PRODUCT: 
> 
VALIDATED METHODS TO PREDICT THE 
STRUCTURAL PERFORMANCE OF AEROSPACE 
' f  IPROPULSION SYSTEMS 
STRUCTURES OF PROPULSION SYSTEMS ARE 
UNIQUE: 
EXTREME LOADING ENVIRONMENTS -1 
HIGH-SPEED ROTATING STRUCTURES 
ADVANCED MATERIAL SYSTEMS 
CD-87-28940 
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AEROPROPULSION SYSTEMS REPRESENT COMPLEX STRUCTURAL PROBLEM AREAS 
Propulsion systems present a number of complex structural problems from different 
sources. Because of the loading environment materials exhibit two forms of nonlinear 
behavior: plasticity (considered to be instantaneous response), and creep (deforma- 
tion and stress relaxation accumulating with time). Advanced material systems, 
because of their microstructures, represent local complexities that have to be 
included in global analysis methods. Single-crystal, directionally solidified, or 
fiber-reinforced materials result in anisotropic and nonhomogeneous local structures 
that must be mathematically characterized over wide ranges of nonlinear response and 
over the predicted structure life. 
CD-87-28941 
OHGINAJ; PAGE IS 
OF. POOR QUALITY 
AEROPROPULSION SYSTEMS REPRESENT COMPLEX 
STRUCTURAL PROBLEM AREAS 
MATERIAL NONLlNEARlTlES 
- PLASTICITY 
- CREEP 
COMPLEX MATERIAL PROPERTIES 
- ISOTROPIC/ANISOTROPIC 
- HOMOGENEOUS/NONHOMOG 
I DIRECTION ALLY SOLIDIFIED I I  SINGLE CRYSTAL 
Si3N4 
CARBON/ 
CARBON 
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AEROPROPULSION SYSTEMS REPRESENT COMPLEX STRUCTURAL PROBLEM AREAS (concl'd) 
Another source of complexity is the large deflection associated with flexible 
structures, usually coupled with aerodynamic and thermal effects. Furthermore 
descriptions of the loading environments and the material properties may not be 
available except in the form of a probability distribution. 
structural integrity and life are among the most vexing and most important consider- 
ations. All these complexities and their possible interactions have to be considered 
in developing credible methods for predicting the structural behavior of propulsion 
sys terns. 
Phenomena related to 
AEROPROPULSION SYSTEMS REPRESENT COMPLEX 
STRUCTURAL PROBLEM AREAS (concl'd) 
DESCR'PT'oNS s 
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ORIGINAL PAGE IS 
&.!IE POOR QUALITY 
PARTICIPATING DISCIPLINES 
I .  
Research is needed in a number of scientific disciplines to solve the complex 
?rcY,lems facing the structural designer of aeropropulsion systems. The nonlinear- 
ities cf material behavior require major advances over conventional finite element 
o r  5cur?dary element methods. 
ities offered by the upcoming multiprocessor computer revolution. 
These advances also have to reflect the new opportun- 
Shortcomings in characterizing the material behavior under cyclic thermomechanical 
mission loads are major obstacles to improved accuracy and computational efficiency. 
Combining the required advances in constitutive modeling with the mechanics of 
fiber-reinforced composites compounds the complexity. 
PARTICIPATING DISCIPLINES 
ADVANCED ANALYSIS METHODS 
- FINITE ELEMENT METHODS e 
- BOUNDARY ELEMENT METHODS 
MATERIAL BEHAVIOR MODELING 
- CONSTITUTIVE MODELING 
- MECHANICS OF COMPOSITES 
awm 
- 
STRESS 
p!" 
2- 
PREDICTION OF TENSILE REPONSES AT l8OOF 
AXIAL STRAIN (in/;.) CD-87-28943 
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PARTICIPATING DISCIPLINES (cont'd) 
Nonlinear dynamics and aeroelasticity are needed to predict the operating character- 
istics of rotating, flexible bladed systems so that acceptable operating envelopes 
can be defined. 
PARTICIPATING DISCIPLINES (cont'd) 
I COMPONENT DYNAMICS I 
II 
STRUCTURAL DYNAMICS - 
- COMPONENT DYNAMICS 
- SYSTEM DYNAMICS 
- VIBRATION CONTROL 
- AEROELASTICITY %- 
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PARTICIPATING DISCIPLINES (cont’d) 
I Methods for predicting various structural-integrity-related behaviors of advanced 
material systems are needed in order to realize future aeropropulsion concepts with 
their demands for lighter structures operating in extremely hostile environments. 
PARTICIPATING DISCIPLINES (cont’d) 
STRUCTURAL INTEGRITY PREDICTION 
- STRENGTH 
- STATIC AND DYNAMIC STABILITY 
- THERMOMECHANICAL FATIGUE AND FRACTURE 
CRACK SIZE CD-87-28945 
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PARTICIPATING DISCIPLINES (concl'd) 
The final intent of the structural designer is not just to analyze trial design 
concepts, but also to approach an optimum design. 
optimization methods are needed to guide the human designer through the complex 
interactions of the design variables toward an optimum design. 
capabilities are needed in dynamics and in high temperatures to study new phenomena 
and to validate theoretical models. 
Multidisciplinary design 
Experimental 
PARTI C I PATI N G DISC I PLI N ES (co ncl ' d) 
INTEGRATED MULTIDISCIPLINARY 
ENGINE ANALYSIS AND OPTIMIZATION 
EXPERIMENTAL METHODS 
J ROTORSTAGE 
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STRUCTURES WORK ELEMENTS 
The three fundamental structures work areas are structural mechanics, structural 
dynamics, and life prediction methods. The structural mechanics work is focused on 
the mechanics of materials in order to develop models for their behavior under 
cyclic thermomechanical mission load conditions. 
advanced integrated structural analysis methods being developed. 
These models are needed in the 
Under structural dynamics the aeroelasticity of flexible, rotating bladed systems is 
important for advanced propulsion design concepts. Developments in vibration control 
and systems dynamics are needed to ensure safe and efficient operation of rotating 
propulsion structures, particularly as they become lighter and operate at higher 
speeds. 
The life prediction focus is on understanding, predicting, and controlling 
structural failures caused by fatigue and fracture. A wide range of advanced 
materials and material systems is being considered, many of them more brittle and 
therefore less forgiving. 
STRUCTURES WORK ELEMENTS 
STRUCTURAL PERFORMANCE 
CONSTITUTIVE RELATIONSHIPS MODELING AND EXPERIMENTS 
MECHANICS OF COMPOSITES 
VIBRATION CONTROL 
SYSTEM DYNAMICS 
AEROELASTICITY 
STRUCTURAL LIFE PREDICTION 
INTERACTIVE EFFECTS ON FATIGUE LIFE 
DAMAGE INITIATION MODELING 
CRACK GROWTH 
MECHANICS OF FRACTURE 
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STRUCTURES WORK ELEMENTS (concl'd) 
The structural designer needs input data from all disciplines in the interdisci- 
plinary chain of activities during product design. 
analysis methods are being developed for cyclic thermomechanical mission loads. 
Under computational methods the program architectures and algorithms are being 
developed that best utilize advances in computer technology. Mission load environ- 
ments and also the properties of advanced material systems can often be best 
described in probabilistic terms. This provides designers with more information on 
which to base designs. 
methods for integrated multidisciplinary design optimization. Experimental methods 
are needed for two purposes: 
and to test models for validation. The capabilities developed are distributed to 
users and are also employed in providing consultation to and participation in major 
NASA projects. 
Advanced computational mechanics 
Integrated analysis methods are coupled with optimization 
to study and understand phenomena and formulate models, 
STRUCTURES WORK ELEMENTS (concl'd) 
INTEGRATED ANALYSIS AND APPLICATIONS 
COMPUTATIONAL MECHANICS 
COMPUTATIONAL METHODS 
PROBABILISTIC METHODS 
OPTIMIZATION AND TAILORING 
NONDESTRUCTIVE EVALUATION 
CONCEPT EVALUATION 
PROJECT SUPPORT AND CONSULTATION 
CD-87-28948 
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Aeropropulsion structures

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