The objective is to produce a series of new computer codes that permit more accurate and efficient three dimensional inelastic structural analysis of combustor liners, turbine blades, and turbine vanes. Each code embodies a progression of mathematical models for increasingly comprehensive representaion of the geometrical features, loading conditions, and forms of nonlinear material response that distinguish these three groups of hot section components

Todd, E. S.

English

NASA Technical Reports Server

N88- 11165
3-D INELASTIC ANALYSIS METHODS
FOR HOT SECTION COMPONENTS_
E. S. Todd
United Technologies Corporation
Pratt & Whitney
The objective of this program is to produce a series of new computer codes that
permit more accurate and efficient three-dimensional inelastic structural analysis
of combustor liners, turbine blades, and turbine vanes. Each code embodies a pro-
gression of mathematical models for increasingly comprehensive representation of the
geometrical features, loading conditions, and forms of nonlinear material response
that distinguish these three groups of hot section components.
Software in the form of stand-alone codes is being developed by Pratt & Whitney
(P&W) with assistance from three uniquely qualified subcontractors: MARC Analysis
Research Corporation (MARC), United Technologies Research Center (UTRC), and the
State University of New York at Buffalo (SUNY-B). Special finite element models are
being constructed by MARC, while mechanics of materials models and constitutive
models are being assembled by UTRC. Development of advanced formulation (boundary
element) models is being shared by P&W and SUNY-B. Verification of the various
analysis packages is being done by P&W.
The technical effort of the Inelastic Analysis Methods program is divided into
two 24-month segments: a base program, and an optional program exercised at the
discretion of the government. The first year (Task I) of the base program dealt with
linear theory in the sense that stresses or strains and temperatures in generic
modeling regions are linear functions of the spatial coordinates, and solution
increments for load, temperature and/or time are extrapolated linearly from previous
information. The second half of the base program (Task II), as well as the option
program (Tasks IV and V), extend the models to include higher-order representations
of deformations and loads in space and time and deal more effectively with collec-
tions of discontinuities such as cooling holes and coating cracks. Work on Task II
(polynomial theory) has been completed, and the results are given in the Second
Annual Status Report (ref. I). Base program computer codes, hereafter referred to as
MOMM (Mechanics of Materials Model), MHOST (MARC-HOST), and BEST (Boundary Element
Stress Technology), have been developed and delivered to NASA-Lewis Research Center.
Three increasingly sophisticated constitutive models are employed by MOMM,
MHOST, and BEST to account for inelastic material behavior (plasticity, creep) in
the elevated temperature regime. The simplified model assumes a bilinear approxima-
tion of stress-strain response and glosses over the complications associated with
strain rate effects, etc. The state-of-the-art model partitions time-independent
(plasticity) and time-dependent (creep) in the conventional way, invoking the Von
Mises yield criterion and standard (isotropic, kinematic, combined) hardening rules
for the former, and a power law for the latter. Walker's viscoplasticity theory
(ref. 2), which accounts for the interaction between creep/relaxation and plasticity
that occurs under cyclic loading conditions, has been adopted as the advanced
constitutive model.
*Work done under NASA Contract NAS3-23697.
239
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https://ntrs.nasa.gov/search.jsp?R=19880001783 2020-03-20T08:34:38+00:00Z
In brief, ttOVllt is a stiffness method finite element code that utilizes one-,
t_o- and three-dimensional arrays of beam elements to simulate hot section component
behavior. Despite limitations of such beam model representations, the code will be
useful during early phases of component design as a fast, easy to use, computation-
ally efficient tool. All of the structural analysis types (static, buckling, vibra-
tion, dynamics), as well as the three constitutive models mentioned above, are pro-
vided by !401,1M.Capabilities of the code have been tested for a variety of simple
problem discretizations (ref. l).
The MHOST code employs both shell and solid (brick) elements in a mixed method
framework to provide comprehensive capabilities for investigating local (stress/
strain) and global (vibration, buckling) behavior of hot section components• Over
the last decade, in order to support their commercially available software, the i4ARC
Corporation has accumulated a great deal of technical expertise creating new, im-
proved algorithms that will significantly reduce CPU (central processing unit) time
requirements for three-dimensional analyses. The MHOST code development has taken
advantage of this expertise• Second generation (Task II) MHOST code is operational
and has been tested with a variety of academic as well as engine-related configura-
tions (ref. l).
Successful assembly of the all-new BEST code was possibly the most important
accomplishment of tile base program effort• The challenge of extending basic theory
and algorithms to encompass inelastic dynamic effects in three-space was met by com-
bining the special skills and efforts of the research and programming teams at SUNY-B
and P&W. As with HOt_4 and f4HOST, the second version of BEST is executable and has
been exercised with both small and large test cases (ref. l). While MHOST and BEST
are currently viewed as complementary, they are also competitors; and overall perfor-
mance on large inelastic models will be watched with interest as the codes mature•
Experimental data from the Benchmark Notch Test program (ref. 3) are being used
to verify the stress analysis capabilities of the Inelastic Methods codes. Nominal
dimensions of the benchmark notch specimen are shown in figure I. Finite element and
boundary element meshes for one-quarter of the specimen gage section are shown in
figure 2. Measured notch root stress-strain behavior for initial uploadings of sever-
al specimens is summarized in figure 3. Correlation between the MHOST predictions and
the measured strains is very good (fig. 4). Simulation of first-cycle notch root be-
havior with BEST has also proven to be quite accurate (fig. 5).
Work on Task IV (special functions theory) and application of the codes to repre-
sentative turbine blade and vane configurations is in process, and will be described
at the Fourth Annual HOST Workshop•
l •
•
i
REFERENCES
Wilson, R. B.; Bak, M. J.; Nakazawa, S., and Banerjee, P. K.: "3-D Inelastic
Analysis 14ethods for Hot Section Components (Base Program): Second Annual
Status Report" (Draft), March 1985.
Walker, K. P.: "Research and Development Program for Nonlinear Structural
Modeling _ith Advanced Time-Temperature Dependent Constitutive Relationships,"
NASA CR-155533, November 25, 1981.
Domas, P. A.; Sharpe, W. N.; Ward, M.; and Yau, J.: "Benchmark Notch Test for
Life Prediction," i_ASA CR-165571, June 1982.
240
Benchmark Notch Specimen
71.12
(2.80) \
Radius \
7.11 _(0.28) \ \
Radius _
----_. -- _,__
! _* -1_-I_9,,
B-_C-symCenter"he
24.13n/ I /-R,-19.05
(0.95) I / 1 / [(_0.75)
 . ao,us?( _i_k_ '
l- ,1 5o.8o t
254.00 (2.00)
(1o.oo)
PO No
1
2
19.05 Dia.
(0.75)
Ym. Centedine
25.40 Dia.
, ,.J (1.00)
B
17.958
(0.707)
24.13
(0.95)
Dimensions in mm (inches)
Fi gure 1
Meshes Used In Benchmark Notch Analysis
Finite Element Model A Finite Element Model x,,f_,,t \ ,._
. Co_
 ou da e,e en   e'Mixed Variationo L - LinearQ - Quadratic
Fi gure 2
R
4.902
(0.193)
241
8OOO
7000
6000
5000
0 4000
c
E
•_ 3000
200O
1000
0
8OOO
7000
6000
5000 -
0
4000 -
C
E
o 3000 -
2000 -
1000
0
0
Notch Strain Vs. Load - First Quarter Cycle
I I i I I I 1 I
GE/LSU Data (ref. 3)
• -Test 6
o - Test 8
× - Test 9
- Test 10
- Test 11 A
Three Term Regression
To GE / LSU Data
I I I I I I I ,
2 4 6 8
Concentrated Microstrain
Figure 3
10
E3
Benchmark Notch - Calculated Vs. Measured Strains
I I I I ! I I 1
* - MHOST, Coarse Mesh
x - MHOST, F_ne Mesh
Three Term Regression
To GE / LSU Data
2 4 6 8
Concentrated Microstrain
Figure 4
10
E3
242
8OOO
6O0O
4000
(,i
"_ 2000
E
"__ o
O3
-2000
-4000
-6000
Cyclic Behavior At Root Of Specimen Notch
I I I I I I I
.. BEST3D - 20% Load Step
w .Q.:,.._f- n GE/LSU Data
Test 7 - 1st Cycle
I I I I I I I
-4 0 4 8E3
Notch Strain - Microstrain
Figure 5
243


3-D inelastic analysis methods for hot section components

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