• Composite Materials Show Their Strength

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    • Abstract: You know a topic is hot when people don’t want to talk about it for fear of divulging their design choices ... Technology Corporation and Optistruct software. from Altair Engineering to analyze the ...

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Composite Materials Show their Strengths
From golf clubs to the Space Shuttle, composite constructions result
in tough stuff.
By Pamela J. Waterman
Composite Materials Show their Strengths
From golf clubs to the Space Shuttle, composite constructions result
in tough stuff.
By Pamela J. Waterman
You know a topic is hot when people don’t want to talk about it for fear of divulging their design choices
and techniques to the competition. Right now, that topic is composites as industries look to cut weight,
increase durability, and save operating costs for customers. Despite the reticence to speak among some
players, DE managed to get a look at some parts and products that bring composite performance to new
heights. (For related analysis software information, see “The Life of Composite Materials,” May 2007 DE.)
Far Beyond Golf Clubs
For decades, outdoor enthusiasts have
been familiar with the traditional
benefits of composite materials,
whether trimming the weight of bicycle
parts or improving the clout of a golf
club. But in more recent years,
engineers and designers have identified
many more desirable properties, such
as thermal conductivity and insulation,
and have used FEA tools to help take
advantage of these characteristics in a
wide range of composite applications.
As far back as the early 1990s, Noran The electronics housing of this Proba 2 micro-satellite,
Engineering participated in the Phase I currently made of aluminum, was used as the basis for a
design stage of the X-33 aircraft, a comparative study based on ANSYS software to evaluate the
technology demonstrator for NASA’s properties of composite materials for a lighter-weight design.
“next-generation” of reusable space (Image courtesy ANSYS and Verhaert Design and
launch vehicles intended to reduce both Development)
business and technical risks. One of the
vendor teams, led by McDonnell Douglas, used NEiNastran to analyze the performance of a proposed
lightweight thermal protection system (TPS) made of a high-temperature ceramic matrix composite called
carbon-silicon carbide (C/SiC).
Composites play a critical role in rockets due to their light weight, and are used in two general categories.
For the primary and secondary structures, as well as integral load-carrying fuel tanks and non-integral tanks
— all relatively “cool” surfaces — ordinary organic composites such as graphite-epoxy are sufficient.
However, “hot” areas such as the leading edge of the space shuttle or the overall TPS structure require the
thermal properties of the more exotic C/SiC composites.
McDonnell Douglas successfully demonstrated that NEiNastran provided accurate structural and thermal
analysis results for a C/SiC system encapsulated with fibrous insulation and laminated to an external metal
layer. (The X-33 program itself was later awarded to a Lockheed-Martin team, then subsequently lost its
funding and was cancelled.) More recently, Scaled Composites, the aerospace composites development
company that won Burt Rutan’s SpaceShipOne contract, chose NEiNastran software as part of its analysis
tool portfolio.
Less Weight, More Challenging
It’s hard to imagine an application where
weight matters more than in the payload of a
rocket. Componeering, an analysis company
in Helsinki, Finland, relied on the advanced
analysis capabilities of ANSYS software to
create a laminated composite housing
material that would give them the
comparable thermal and mechanical behavior
of the original aluminum while cutting back
on overall mass.
The project involved a low-orbiting
microsatellite, generally much smaller than a
telecommunications satellite. Componeering
needed to determine the thermal balance,
General stress analysis of initial X-33 design, as an structural integrity and resonant frequencies
example of a reusable NASA launch vehicle with throughout the tight spaces, without applying
composite material elements. (Image courtesy Noran extreme simplifications. The designers
Engineering, Inc.) evaluated material selection, number of
layers, layer orientations, and stacking
sequence for a design that embedded a layer of tungsten foil inside a carbon-fiber-reinforced plastic
(CFRP) laminate.
Engineers studied laminate through-the-thickness direction and modeled the mechanical interfaces and
adhesively bonded joints, including materials, surface roughness, and contact pressure. They performed
both conduction and radiative heat-transfer analyses, used that information to directly analyze structural
performance, and verified the results through vacuum-chamber testing of a prototype.
The designers then exported the results to Componeering’s own ESAComp software for postprocessing to
generate laminate layups and material data, including coefficient of thermal expansion (CTE). The
composite design was stiffer, had better thermal properties, and offered a 29 percent weight savings over
aluminum.
Composite pipe reducing tee (reinforced) This composite multibranch pipe
developed using COSMOSM. The Finite manifold section model was developed
Element Model, developed using the using COSMOSM. Five discrete
COSMOS Command Language, enables composite materials are defined
dimensional parameters, mesh density, and through the pipe walls. Input
materials to be quickly changed to assess a parameters including geometry can be
wide range of size configurations. (Image quickly changed to regenerate an FE
courtesy of Grantec Engineering Consultants, model to assess various configurations.
Inc.) (Image courtesy of Grantec
Engineering Consultants, Inc.)
Stronger than Steel?
ESG Engineering, a design and analysis company in Tempe, Arizona, wanted to get ahead of the curve
demonstrating their expertise in composite analysis to client companies in the aerospace and automotive
worlds. It performed its own case-study analysis on a typical vehicle side door designed to compare both
performance and cost factors for parts made of conventional stamped steel versus those of fiber-filled
composites.
The original 3D CAD door design consisted of inner and outer steel panels (each approximately 0.7mm
thick), an intrusion bar, and a number of local reinforcements in the hinge and latch areas. Total assembly
count: nine parts. For the alternate design, the engineers evaluated a simple assembly of just two glass-
fiber/polyamide composite shells (each 2.65mm thick), with local reinforcements in the inner shell and no
intrusion bar.
The project was based on the following three design requirements: the geometry of the original door was
left unchanged; composite rupture at smaller deformation levels was allowed as long as the desired strength
and energy absorption was achieved; and impact testing required ramming a 12-in. diameter cylinder
sideways into the panels to create a static deformation at various depths of intrusion per standard
automotive testing.
ESG used LS-DYNA from Livermore Software
Technology Corporation and Optistruct software
from Altair Engineering to analyze the strength of
both materials. The proposed composite design
showed higher strength and energy absorption than
steel at displacements below 8 in. and had a mass
that was 60 percent of the original. Typical
automotive industry design requirements such as
dent resistance, local structural resistance to
buckling, and overall stiffness were also shown to be
on par or better than standard designs. An optimized
design would improve even these results.
Serious About Safety
Engine maintenance can account for up to 40 percent
Stress analysis of proposed advanced thermal of the total lifetime support costs for military
protection system for a vehicle such as the X-33. aircraft. Much of that comes from replacing parts
Designed of composite materials (improved early as a preventive safety measure, even though
carbon fiber protected by silicon-carbon matrix) they have experienced relatively low numbers of
that would eliminate the current practice of stress cycles. With more and more composites in
recoating Space Shuttle tiles for waterproofing critical subsystems, it’s important to predict not only
after each flight. (Image courtesy Noran total lifetime, but actual life based on the projected
Engineering, Inc.) severity of small failures. The Royal Australian Air
Force turned to the Australian Defence Organization
to investigate such probabilities. The group used
ABAQUS analysis software from Simulia to predict
just where the problems would occur, and then
identified the risk involved in crack growth over
time.
ABAQUS customers such as Boeing know that this
software has long been capable of modeling
nonlinear damage and fractures in composites. Its
latest revision is also capable of predicting the
durability of the adhesives used in composite
laminate manufacturing as well as final part
assembly. While traditional aircraft used riveted
metal sheets (and every drilled hole compromised strength), designs with today’s composites offer equal or
superior performance when properly analyzed and assembled. (See sidebar, “ABAQUS V6.7 Unifies FEA
with Pre- and Postprocessing.”)
The Acid Test ABAQUS V6.7 Unifies FEA with
When you’ve been successfully transferring corrosive Composite Pre- and Postprocessing
fluids through stainless-steel power-plant piping for years,
switching to fiber reinforced plastic (FRP) pipes simply to
trim costs isn’t enough. Proving that FRP will do the job In May, Simulia released ABAQUS V6.7
equally well was the task taken on by analyst Richard with enhancements that let designers,
Grant of Grantec Engineering Consultants. A long-time engineers, and manufacturing staff the
user of COSMOS analysis tools from SolidWorks Corp., capability model the entire composite design
he finds the flexibility of the COSMOSM command process. Though always capable of analyzing
language gives him the speed he needs to analyze the composites, V6.7 now lets users start with the
complexities of composite structural behavior. geometry or mesh, incorporate material
properties, run the design through the
The piping design in question had a thin liner surrounded ABAQUS solvers, and directly produce
by four additional layers that could vary in their individual draping and fiber-orientation calculations.
designs. By scripting an analysis sequence, Grant could
quickly change parameters like the internal diameter (ID) Greg Brown, Simulia Product Manager for
of the main pipe, the IDs of the branches, the thickness of CAE, notes, “There are lots of niche tools out
layers, and any material properties to evaluate the effect of there, but the real advantage of V6.7 is
reinforcements around nozzle openings. Automatic incorporating [the information] into a general
remeshing made it easy to do multiple studies of pipe nonlinear FEA program, with all pre- and
diameters ranging from 12 in. to 48 in. while comparing postprocessing included.”
structural results to ASME code requirements.
The unified approach considers such factors
Grantec Engineering also has years of experience as contact and plasticity as well as fastening
analyzing the structure of large ships, offshore structures, and bonding techniques for calculating
and submerged equipment. Grant says that COSMOSM durability in parts made from carbon fiber-
gives him the ability to readily handle designs with both reinforced plastics or uni- or bidirectional
complex geometries and intense loading by the forces of fabrics. For example, users can take a ply-
ocean waves or seismic shocks. stacking design generated in CATIA, analyze
the linear and non-linear performance in
High-Flying Ideas ABAQUS, modify the stack parameters, and
UGS has had composite analysis capabilities for years in export the data back to CATIA in a closed-
both its NX and Femap lines, as evidenced by the success loop sequence. The process incorporates a
of the design program for Adam Aircraft’s A500, a plug-in of Advanced Fiber Modeler and
pressurized twin-engine aircraft (with both engines Composites Link software from Simulayt.—
mounted along the centerline) featuring carbon-fiber PW
composite (CFC) airframe construction. When Adam
Aircraft decided on a CFC skin in the late 1990s, the idea seemed unusual to the conservative general
aviation crowd; later, Boeing’s decision to use composites for its 787 Dreamliner made it seem obviously
the right choice — just ahead of its time.
The Colorado company chose UGS software because of the ease of interoperability between NX (which
enabled surfacing and analysis functions of the sleek composite design) and Solid Edge (whose modeling
capabilities generated parts and molds). By using products built on the Parasolid geometric kernel, no time
or effort was wasted with data translation. The A500 was FAA certified in 2005, and the company now has
back orders for about 70 planes.
The NX 5 Advanced FEM package (NX 5 was announced in April) includes updates to the Laminate
Composites add-on. Sample preprocessing features include the ability to define laminates in MS Excel for
import to NX or vice versa; change properties of any ply material prior to solution; combine fiber and
matrix properties to create ply materials; and incorporate micromechanical structure definitions. Users can
interface with Nastran, ANSYS, and ABAQUS solvers, and improved postprocessing tools help engineers
identify problem areas, quickly recompute ply results, and generate margins of safety based on different
criteria.
Many Players, Many Angles
Knowledge and resources for making the most efficient use of composites also come from users across the
manufacturing spectrum. Software such as FiberSIM from Vistagy captures the nuances of the actual
composite lay-up approach to help manufacturing teams translate a CAD design into real parts more
rapidly, efficiently, and accurately. And suppliers such as Specialty Materials (formerly part of Textron
Systems) deliver the real goods with such offerings as titanium metal matrix composite (MMC)
preimpregnated sheets.
The Adam Aircraft A500 is a pressurized centerline-mounted twin-engine plane
with a carbon-fiber composite skin designed with NX and Solid Edge software from
UGS. (Image courtesy UGS)
Just remember, for technology that seems heavy on verbiage, it’s actually very light stuff, and for many
applications, it’s the right stuff, too.
More Information Resources for the Hardware Side
of the Composite World
Altair Engineering, Inc.
Troy, MI
altair.com Whether you’re looking at machines or materials, check these
out:
ANSYS
Canonsburg, PA Materials
ansys.com Applied Sciences Inc.
apsci.com
Componeering Inc. W.L. Gore & Associates
(Convergent Mechanical Solutions) gore.com
Seattle, WA
bconverged.com Specialty Materials, Inc.
specmaterials.com
COSMOS, the Analysis
Division of SolidWorks Yokohama Aerospace America, Inc.
Santa Monica, CA yaainc.com
cosmosm.com
Machinery
ESG Engineering Century Design Inc.
Tempe AZ centurydesign.com
Livermore Software Technology
Corporation
Livermore, CA
lstc.com
Noran Engineering Inc.
Westminster, CA
nenastran.com
Simulayt Ltd.
Brookwood, Woking, Surrey, UK
simulayt.com
Simulia, Inc. /Abaqus
Providence, RI
simulia.com
UGS/Siemens
Plano TX
ugs.com
Vistagy, Inc.
Waltham, MA
vistagy.com
Contributing Editor Pamela J. Waterman is an electrical engineer and freelance technical writer based in
Arizona. You can contact her about this article via e-mail here.
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