Technical Brief
April 2013
Validation of Burst Pressure Analysis and
Manufacturing Techniques for Composite Over-wrapped Pressure Vessels
GENOA provides engineers with a
validated computational approach to determine residual stresses in composite over-wrapped pressure vessels (COPV). It also identifies leakage and burst
locations, as well as associated failure modes under service.
The Challenge: To
accurately determine the onset of crack formation, leakage, slippage of gas
between dome and valve assembly, and rupture of COPVs.
Other challenges
pertain to accurate determination of the following:
- Ply
angle distribution
- Residual
stresses due to winding and curing
- Tank
reliability due to scatter in manufacturing parameters, defects, and
material properties
- Strength
allowables for risk reduction
- Rupture
due to service load: Proof, Auto-Frottage
(load, unload), Sustained Fatigue
(short, high cycles) pressurization,
- Slippage/Leakage prediction
- Damage
and failure multi-site locations
- Reliability
- Addressing
variability in tank performance
considering “As-designed” versus “As-built” and “As-is”
- Tank
certification
Another challenge
stems from the complexity of modeling and analysis of composite materials. Most
finite element analysis (FEA) solvers assess damage at the lamina level whereby
damage initiates at lower scale in the fiber, matrix, and interphase. These challenges
can be addressed through an integrated capability that couples winding analysis
with multi-scale progressive failure analysis, including modeling of defects
and uncertainty analysis.
The Solution: To utilize GENOA’s Filament Winding & Multi-Scale
Progressive Failure Analysis
Residual stresses
are calculated through GENOA’s Filament Winding (GENOA-FW) module. To calculate
residual stresses, GENOA uses design parameters, such as tape tension, internal
pressure, and curing effects. The tank finite element model is generated based
on inputted tape thickness and width, winding angles, and wrapping circuite
location during winding. The winding pattern can be optimized to reduce weight.
Tanks with metallic and plastic liners or those without liner are modeled and
analyzed with GENOA’s
FW module. Residual stresses from autofrettage are also determined with the
analysis. To ease the design of the tank, the FW module is capable of
generating two distinct FEA models using:
§
Low Fidelity: 3D thick shell elements that merges all plies into a
single element thru thickness
§
High
Fidelity: 3D solid where
plies thru thickness are modeled with layers of solid elements
With generated FEA
model and calculated residual stresses, GENOA’s multi-scale progressive failure
analysis (MS-PFA) performs leakage and burst rupture analyses. The code
integrates finite element analysis with multi-scale composite mechanics and damage
tracking and fracture. Several FEA stress solvers are used within the GENOA environment
for evaluating durability and damage tolerance of the tank. These solvers
include NASTRAN, ABAQUS, ANSYS, and nodal based MHOST [1].
MS-PFA identifies
all stages of damage evolution: damage/delamination initiation and growth, and
probabilistic fiber stress rupture fracture initiation and growth to failure.
It calculates micro-cracks, stiffness degradation in the matrix, delamination
within the plies, and fiber failure in tension and compression including
micro-buckling. The COPV tank can be evaluated with MS-PFA subject to static,
fatigue, and impact loading conditions to accommodate tank certification
process [2]. Reliability evaluation considers the
uncertainties in geometry, material, fabrication process and loading [3]. It ranks the effect of considered
random variables on leakage, delamination, and rupture of tank and determines
the scatter in burst pressure. In addition to uncertainty analysis, a test
reduction methodology for determining A- and B-basis allowable design loads is
integrated. A-basis design allowables generation can be determined with reduced
testing using B-basis values from accepted test methods or can be generated
from lamina level uncertainties [4].
Validation: Figure 1
shows a failed composite tank that was modeled and analyzed with the software. Figure 2
shows typical filament winding input requirements supporting helical and hoop
winding schemes. Data used as input includes winding schedule, tape width, and
tape tension. The tanks analyzed include spherical, and cylindrical with
geodesic domes. ASC validated its technical approach for both space and
automotive applications and subject to extreme environmental conditions
(elevated and cryogenic temperatures). Typical analysis results are used to determine
conditions for leakage, burst location, damage evolution through-the-thickness,
and reliability. Filament wound composites over-wrapped tanks were considered
in for the application of motor cases for solid rockets motor cases [3]
Deterministic evaluation of durability and damage tolerance of tank using GENOA
resulted in predicted burst pressures that are within 8.8% of the test for 4
groups of tank design. The pressurized tanks were also evaluated in presence of
uncertainties in constituent stiffness and strength and manufacturing
variables. The sensitivity analysis indicated that the fiber mis-alignment and
ply thickness are the most influential variables that affect the burst pressure
as indicated in Figure
3. Scatter in burst pressure,
A Basis Allowable as a result of considered uncertainty is shown in Figure 4.
The results show that a reliability 0f 0.999 can be achieved if burst pressure
is kept under 3033 psi. When damage
evolution through thickness is of concern, GENOA offers capability to generate
high-fidelity solid element FE models. Figure 5 shows the snap shots from automated
process to generate high-fidelity solid FE model from previously generated
shell element FE model. The high-fidelity model helped account for the
out-of-plane shear stresses, which results in delamination, more accurately. Figures 6 to 8 show
the damage evolution at the laminate level, ply-by-ply level and final burst
predictions compared to the test specimen in Figure 1.
Another validation
of the capability done under the NASA space launch initiative effort [5]
determines leakage in COPV at cryogenic temperatures. Analysis showed a large
percentage of failure in composites initiate as matrix cracking. When matrix
cracks it releases energy causing accumulation of additional cracks that continues
till a saturation point. GENOA can track this initiation, accumulation and
saturation process.
Conclusion: GENOA provided a
reliable and verifiable low as well as high fidelity simulation solution in
determining residual stresses, identifying leakage, burst locations, and
associated failure modes under service in COPV’s.
References:
1.
S. Nakazawa, “The Mhost Finite
Element Program, 3-D Inelastic Method for Hot Structure Components”, Volume 1 Theoretical Manual, NASA Technical Contract Report CR-182205,
March, 1991.
2.
C. Keddy , “Composite Overwrapped
Pressure Vessel Modeling and Analysis”, White
Sands Test Facility, Johnson
Space Center,
July 2008.
3.
G. Abumeri, F. Abdi, M. Baker, M.
Triplet and, J. Griffin “Reliability Based Design of Composite Over-Wrapped
Tanks”. SAE World Congress, 2007, 07M-312, Detroit
Mi, April 2007.
4.
G. Abumeri, F. Abdi, K.S. Raju, J.
Housner, R. Bohner and A. McCloskey: “Cost Effective Computational Approach for
Generation of Polymeric Composite Material Allowables for Reduced Testing”, Inetch Book publishing, in print for
March 2011 (Co-authored with Northrop Grumman and NIAR).
5.
F. Abdi, X. Su “Composite Tank
Permeation and Crack Density Prediction and Verification”. ASME Paper No. IMECE2003-4439
November 2003.
About AlphaSTAR
Corporation: AlphaSTAR Corporation is a
leading engineering services and software company that provides innovative physics-based
simulation technologies for structural modeling and analysis of advanced
composite structures in the aerospace, automotive, defense, and energy
industries worldwide. As
a solution provider, AlphaSTAR partners with Siemens PLM, Altair, ANSYS, MSC
Software, DS Simulia, and LSTC. AlphaSTAR is headquartered in Long Beach,
California and is the recipient of esteemed industry and technology awards for
R&D and software development. Contact marketing@alphastarcorp.com or www.alphastarcorp.com.
