structural analysis and model validation for the jwst...
Post on 20-Mar-2018
218 Views
Preview:
TRANSCRIPT
MSC Software Confidential 2012 Aerospace Users Symposium
Structural Analysis and Model Validation for
the JWST ISIM Structure Using MSC
NASTRAN 2012 Aerospace Users Symposium
Presented By: John Johnston
September 18, 2012
MSC Software Confidential 2012 Aerospace Users Symposium
• This presentation describes the structural modelling, analysis,
and model validation completed to verify the performance of the
James Webb Space Telescope (JWST) Integrated Science
Instrument Module (ISIM) metering structure.
• Topics:
– JWST and the ISIM Structure
– Structural Modelling, Analysis, and Model Validation Approach
– Structural Model Architecture
– Distortion Analysis
– Dynamics Analysis
– Strength Analysis
Overview
2
MSC Software Confidential 2012 Aerospace Users Symposium
James Webb Space Telescope (JWST)
3
• JWST is a large, infrared-
optimized space telescope
consisting of an Optical
telescope element (OTE),
Integrated science instrument
module (ISIM), a Spacecraft, and
a Sunshield.
• ISIM consists of the JWST
science instruments, fine
guidance system, ISIM Structure,
and thermal and electrical
subsystems.
• JWST's instruments are designed
to work primarily in the infrared
range of the electromagnetic
spectrum, and operate at
cryogenic temperatures (~35 K).
MSC Software Confidential 2012 Aerospace Users Symposium
Integrated Science Instrument (ISIM) Structure
4
• The JWST ISIM Structure is a
precision optical metering structure
that supports the JWST science
instruments and guider.
• Needs to meet stringent
performance requirements at both
ambient temperatures for launch and
cryogenic operating temperatures
on orbit.
• Structural analysis was completed
for both these environments using
MSC NASTRAN to simulate key
aspects of structural performance,
including stress, dynamics, and
distortion.
MSC Software Confidential 2012 Aerospace Users Symposium
• ISIM Structure design, analysis, and fabrication development employed an
incremental building blocks approach starting with coupons, then joints,
followed by a sub-assembly, and finally the flight space hardware.
• The development of new analysis approaches followed this same approach with
incremental model validation for strength, dynamics/stiffness, and thermal
distortion at each level of assembly.
ISIM Modeling, Analysis, and Model Validation
5
• These efforts recently culminated
in the successful completion of
qualification testing for the flight
hardware and model correlation
studies demonstrating that our
finite element analyses accurately
simulate the complex behavior of
the flight hardware.
• This presentation will describe the
innovative analyses completed
during the development and
qualification of the ISIM Structure.
MSC Software Confidential 2012 Aerospace Users Symposium
• ISIM structural models have been developed for generating performance predictions
at the system and detailed component levels.
• An integrated ISIM structural model is used for both system performance predictions
and derivation of load sets for detailed stress analysis.
• Detailed stress models are used for component and joint analysis.
Structural Model Architecture
6
MSC Software Confidential 2012 Aerospace Users Symposium
Integrated ISIM System Model
7
• High fidelity NASTRAN structural
model.
– 1.5 million nodes
– ~ 5M DOFs
• Composite frame structure is modeled
using solid elements to capture fine
details such as bond lines and bond
shapes.
• Model is linked to a materials database
specifically generated for the program,
and utilizes temperature-dependent
CTE and stiffness properties to
accurately predict thermal distortion
and stiffness behavior at both
cryogenic and room temperatures.
• Full physical model used for static
analysis, and reduced Craig-Bampton
model used for dynamic analysis.
MSC Software Confidential 2012 Aerospace Users Symposium
Dynamics Analysis
8
• The integrated ISIM model is used for
dynamic analysis to predict:
– Normal modes (frequencies, mode shapes) via
MSC NASTRAN SOL 103
– Response during vibration testing and launch
via coupled loads analysis (loads, accelerations,
and displacements) using normal modes results
in custom application software.
• Model Reduction:
– All subsystems and component models are
reduced to Craig-Bampton models on
NASTRAN DMIG. Modes to 400 Hz are
retained for the subsystem and component
models.
– DMIG Craig-Bampton models are incorporated
into the ISIM structure model and an ISIM
Element Craig-Bampton model is generated
with 36 boundary degrees-of-freedom (6 DOFs
at base of each KM) and cantilevered modes
retained to 200 Hz.
1 23.86 3.81 33.30 721.98 30.16 1090.77 57.24
Mode # Freq (Hz) V1 (kg) V2 (kg) V3 (kg) Rv1 (kg-m2) Rv2 (kg-m2) Rv3 (kg-m2)
MSC Software Confidential 2012 Aerospace Users Symposium
Dynamic Model Validation
9
• Dynamic model validation was
completed through correlation with
test results from two modal survey
tests:
– ISIM Breadbox subassembly
– Flight ISIM Structure with payload mass
simulators
• The subassembly test provided early
validation of the modeling approach
and led to the adoption of the high
fidelity distortion model as the
baseline for dynamics analysis.
• The flight test provided final
validation of structural modes to 100
Hz.
• Pretest analyses were completed to
determine instrumentation locations,
shaker drive points for excitation, and
target modes.
Modal Fixture
ISIM Modal Test
ConfigurationModal Facility Platform
with T-Slots
MSC Software Confidential 2012 Aerospace Users Symposium
Dynamic Model Validation - cont
10
• Model validation objectives were successfully completed for significant
modes for both the subassembly and flight structure tests:
– Frequency match within 5%
– Cross-orthogonality between model and test modes:
• Absolute value of diagonal terms between 0.9 and 1.1
• Absolute value of off-diagonal terms less than 0.2
Analysis Mode 1 2 3 4 5 6 7 8 10
Mode Description 23.44 26.44 27.82 30.38 32.68 35.88 39.51 45.01 51.73
Test Mode freq % diff 1.0% 2.9% -0.5% 2.1% 2.1% 1.9% 1.1% 3.0% 0.8%
ISIM V3 1 23.2 0.98 -0.05 0.15 0.01 -0.05 -0.04 -0.03 0.01 0.00
ISIM V2 2 25.7 0.05 0.99 -0.07 0.11 -0.02 0.01 0.00 0.02 0.00
ISIM V2, MIRI & NIRSpec V3 out of phase 3 28.0 0.11 -0.10 -0.96 0.17 -0.13 -0.07 -0.05 0.02 -0.01
ISIM RV3 4 29.8 -0.04 -0.09 0.18 0.98 0.00 -0.02 0.00 -0.02 -0.02
FGS V1 5 32.0 0.06 0.00 -0.09 0.05 0.99 -0.05 -0.04 0.01 0.00
NIRCam V1 6 35.2 -0.04 0.03 0.06 -0.03 -0.04 -0.99 0.03 -0.05 0.05
ISIM Rv1 7 39.1 -0.04 0.00 0.04 -0.01 -0.03 -0.01 -0.99 0.00 0.03
NIRSpec V1, ISIM RV2 8 43.7 -0.02 -0.01 0.01 -0.01 0.01 -0.05 0.00 0.99 0.01
NIRCam V2, MIRI V1 & V2 11 51.3 0.02 0.00 -0.01 -0.01 0.03 0.06 -0.01 -0.03 0.96
ISIM Final Cross-Orthogonality: Test modes > 5% Modal Effective Mass
Flight Structure Modal Survey Correlation Results
MSC Software Confidential 2012 Aerospace Users Symposium
Distortion Analysis
11
• The integrated ISIM model is used for distortion analysis to predict:
– Thermal distortion for cooldown to cryogenic temperatures and cryogenic thermal stability
– Gravity distortion under 1 G loading
• Linear static analysis using MSC NASTRAN SOL 101.
• In addition to standard analyses using nominal material properties, stochastic
analysis is completed to quantifying the error bounds and uncertainties in
predictions due to variations in model parameters associated with material,
manufacturing, and spatial variability.
• This effort is presented in greater detail by Emmanuel Cofie at this symposium.
Deformation
Plots for
Ambient to
Cryogenic
Distortion
MSC Software Confidential 2012 Aerospace Users Symposium
Thermal Distortion Model Validation
12
• Two major cryogenic environmental
tests were then completed as part of the
ISIM Structure verification program:
– The Cryoset Test was completed in May
2010 for thermal distortion performance
characterization.
– The Cryoproof Test was completed in
October 2010 for demonstration of cryogenic
strength.
• During each of these tests, the hardware
under test was thermal cycled between
ambient and cryogenic temperatures
with metrology performed via
photogrammetry (PG) at the warm and
cold states.
• Thermal distortion predictions were
validated through comparison with PG
data.
MSC Software Confidential 2012 Aerospace Users Symposium
Thermal Distortion Model Validation – cont
13
• Detailed structural models were
completed including the flight
hardware and associated
mechanical ground support
equipment in the test setup.
• Temperature sensor
measurements are used to
generate a temperature value for
each node in the flight hardware
and MGSE structural models via
temperature mapping.
• Model validation criteria satisfied:
– Nominal predictions with MUF=1.6
bound the measured performance
– Stochastic model predictions
including 2-sigma uncertainty
bandwidth with MUF=1.4 envelop
measured performance
MSC Software Confidential 2012 Aerospace Users Symposium
Strength Models and Analysis - Overview
14
• Detailed stress analysis was
completed to verify the structural
integrity of the ISIM Structure.
• Development and validation of
methodologies for the analysis of
the bonded joints, particularly at
cryogenic temperatures, was a
major focus of the analysis effort.
• Bonded joint analysis is based on a
semi-empirical method anchored in
joint model validation.
– Strength allowables derived from
extensive coupon test program
– Modeling and analysis approach
utilizes common mesh size for
derivation of allowables from
coupon tests, validation of method
through joint level tests, and flight
joint analysis.
Phase-2 Test Program – Development Joints
Phase-1 Test Program – Allowable Coupons
Bonded Joint Analysis
Procedure
Basic Coupon Testing
• FWT Coupons for Peel
• DSJ Coupons for Shear
• RT and Cryo
• Coupons Modeled/analyzed
per Analysis Procedure
Develop Failure Criteria
(Allowables) from Coupon
Test Results
Development Joint TestingDev Joint Test/Analysis
Correlation and Validation
ISIM Flight Structure
Design and Analysis
MSC Software Confidential 2012 Aerospace Users Symposium
Strength Models and Analysis - Ambient
15
• Ambient bonded joint strength
analysis was completed using global
joint models:
– Global models for allowable coupons,
development joints, and flight joints are
all modeled per the same methodology.
– Eight noded hex elements at critical
bond areas with 2.5mm X 2.5mm in-
plane dimensions.
– Smeared laminate orthotropic properties
for composite elements.
– Analysis layers at bonded interfaces for
critical interlaminar failure modes.
• Failure modes assessed include:
– Composite interlaminar failure
– Composite in-plane failure
– Metallic ultimate/yield failure
• Linear static analysis using MSC
NASTRAN SOL 101.
Gusset
Tube
Plug
Adhesive
Adhesive
2.5 mm
X
2.5mm
Composite Analysis Plies
at Bonded Interfaces
RBE3
Global Joint FEM
Approach for Ambient Strength
MSC Software Confidential 2012 Aerospace Users Symposium
Strength Model Validation - Ambient
16
• Model validation for ambient bonded
joint strength was completed through
correlation of analysis predictions
with test results from the destructive
testing of seven joint configurations.
• Basic plug joint model and analysis
results shown in figure at right.
– Predicted failure load (B-basis strength) =
48.8 kips
– Predicted failure load (average strength) =
60.5 kips
– Average failure load = 58.5 kips (0.1%
COV)
• All RT development joints failed above
flight predictions demonstrating that
the flight analysis methodology for
bonded joints at RT is validated and
conservative.
X
Y
Z
Global FEM
Interlaminar Stress from Global FEM
MSC Software Confidential 2012 Aerospace Users Symposium
Strength Models and Analysis - Cryogenic
17
• Cryogenic bonded joint strength
analysis was completed using global-
local joint models:
– Global model approach is the same as
ambient case
– Local models based on refined mesh for
cryogenic adhesive failure mode.
– Loading of local models includes thermal
loads plus boundary displacements mapped
from global joint models to local models.
• Failure modes assessed include:
– Composite interlaminar failure (global)
– Composite in-plane failure (global)
– Metallic ultimate/yield failure (global)
– Adhesive maximum principal stress failure
(local)
• Linear static analysis using MSC
NASTRAN SOL 101.
Global FEM displacements
applied at cut boundaries
Global
FEM
Local FEM
Global FEM
Cut Boundary
Cut Boundary
Cut Boundary
Cut Boundary
Cut Section of Critical Bond Area
Clip
Tube
Plug
Global-Local Joint FEM
Approach for Cryogenic
Strength
MSC Software Confidential 2012 Aerospace Users Symposium
Strength Model Validation - Cryogenic
18
• Model validation for cryogenic bonded
joint strength was completed through
correlation of analysis predictions with
test results from the destructive testing
at cold survival temperature (27 K) for
three joint configurations that cover the
basic bonded joint types.
• Basic plug joint model and analysis
results shown in figure at right.
– Predicted failure load (B-basis strength) =
15.7 kips
– Predicted failure load (average strength) =
18.6 kips
– Average failure load = 21.4 kips (8% COV)
• All cryo development joints failed
above flight predictions demonstrating
that the flight analysis methodology for
bonded joints at cryo is validated and
conservative.
Global FEM Local FEM
Adhesive Stress from Local FEM
Invar
Adhesive cracks
Cut fiber
Turning the corner and propagating along interface
Cross section view of Invar plug-composite tube sample (S/N002) tested at 19K
To the Invar
interface
To the tube
interface
MSC Software Confidential 2012 Aerospace Users Symposium
Summary
19
• The development and validation of
modeling and analysis capabilities for
predicting dynamic, distortion, and
strength performance of the JWST
ISIM Structure was successfully
completed.
• The approaches were grounded in
initial constituent materials testing,
benchmarked to test results at the
bonded joint/subassembly level, and
verified for the flight hardware.
• Integration and test at the next level of
assembly (ISIM Element) is underway
and will culminate with additional
cryogenic thermal-optical
performance tests and a full suite of
ambient mechanical environmental
tests.
Fully Verified Flight ISIM Structure
Ready for Integration and Test at
the next level of assembly
top related