COURSE UPDATE
• Final MAE 4291 Senior Design 1 Presentations:
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November 3 and 5
Same format as Mid-Term Updates (details to come)
Reverse order from Mid-Term Updates (?) or do you prefer something else?
Send a draft by November 1 and I will review
• Answers to Mid-Term Briefing Questions
– How many teams still need to turn this in? Submitted by Wednesday at 11am?
– I would like to pass these out the entire class
• Hazard Analysis due 10/15
– I’m getting feedback from Greg Peebles this week
• Human Safety Analysis
– Originally due on 11/3 (when final presentations were later)
– Now due on 11/10 (are teams OK with this or more time?)
OVERVIEW
• Important aspect of design for aerospace, mechanical, electrical, thermal,
chemical or other applications is selection of best materials
• Systematic selection of best material for a given application usually
depends on 2 aspects:
1. Properties
2. Cost
• A few examples:
– Thermal blanket must have poor thermal conductivity in order to
minimize heat transfer for a given temperature difference
– Large amounts of copper in superconducting magnets: copper needed
for low resistance path for large currents in case superconductivity lost
– Samarium-Cobalt Permanent Magnets on DS-1
– SR-71 structure: 85% titanium and 15% composite
– Hummer armor – should it be stiff or deflect against a bomb blast
ROD VERSUS PLATES
• Systematic selection for applications requiring multiple criteria is
more complex
• Example 1: Rod
– Design a rod that is stiff and light-weight
– Requires a material with high Young's modulus and low density
– If rod pulled in tension, specific modulus, or modulus divided by
density E/ρ, will determine best material
• Example 2: Plate
– Design a plate that is stiff and light-weight
– Plate's bending stiffness scales with thickness cubed
– Best material for a stiff and light plate is determined by cube root
of stiffness divided density ³√E/r
ASHBY PLOTS
• Ashby plot is a scatter plot which displays two or more properties of a materials
• Example of stiff, light part would have Young's modulus on one axis and density
on other axis, with one data point on graph for each candidate material
– On such a plot, it is easy to find not only material with highest stiffness or
lowest density, but that with best ratio E/ρ.
– Ashby plot on next slide shows density versus Young's modulus
• Metals are represented by blue squares, ceramics by green, and polymers by red
• Using a log scale on both axes facilitates selection of material with best plate
stiffness ³√E/r.
– Second plot shows same materials attributes for a database of approx 100
materials
• Materials families (polymers, foams, metals, etc.) are identified by the larger
colored bubbles
EXAMPLE OF ASHBY PLOT
METALS
CERAMICS
POLYMERS
EXAMPLE OF ASHBY PLOT
MATERIALS SELECTION RESOURCES
• http://www-materials.eng.cam.ac.uk/mpsite/interactive_charts/
– Excellent plots of properties for various materials and useful for observing
primary trends
– ‘Hover’ over material label to see details within materials sub-class
– Think about how each chart can be used in an engineering context
• http://www.matweb.com/index.aspx
• http://www.matweb.com/tools/contents.aspx
– Probably the most comprehensive materials database ever created
– Worth spending a few hours sifting and surfing this site in preparation for
selecting materials for your project
YOUNG’S MODULUS VS. COST
STRENGTH VS. DENSITY
STRENGTH VS. COST
STRENGTH VS. MAXIMUM SERVICE TEMPERATURE
COST ISSUES
• Cost of materials plays a very significant role in their selection
• Most straightforward way to weight cost against properties is to develop a
monetary metric for properties of parts
• For example, life cycle assessment can show that reducing weight of a car by 1 kg
averages around $5, so material substitution which reduces weight of a car can cost
up to $5 per kilogram of weight reduction more than original material
• For commercial aircraft: $450/kg
• Spacecraft: $20,000/kg
• However, geography- and time-dependence of energy, maintenance and other
operating costs, and variation in discount rates and usage patterns (distance driven
per year in this example) between individuals, means that there is no single correct
number for this
COST ISSUES
• As energy prices increase and technology improved, automobiles have substituted
increasing amounts of light weight magnesium and aluminum alloys for steel
• Aircraft are substituting carbon fiber reinforced plastic and titanium alloys for
aluminum
• Satellites have long been made out of exotic composite materials.
• Cost per kg is not only important factor in material selection
• An important concept is 'cost per unit of function'.
• For example, if key design objective was stiffness of a plate of material, then
designer would need a material with optimal combination of density, Young's
modulus, and price
• Optimizing complex combinations of technical and price properties is a hard
process to achieve manually, so rational material selection software is an important
tool – but lets see what we can do by hand…
BOEING 747 VERSUS 787: COMPOSITES
BOEING 787 MATERIALS DETAILS
• First major airliner to use composite materials for most of its construction
• Boeing claims the 787 will be at least 20% more fuel-efficient than current
competing aircraft
– One third of the efficiency gain will come from the engines
– another third from aerodynamic improvements
– increased use of lighter weight composite materials, and the final third from advanced systems
• The 787 features lighter-weight construction. Its materials (by weight) are: 50%
composite, 20% aluminum, 15% titanium, 10% steel, 5% other.[75] Composite
materials are significantly lighter and stronger than traditional aircraft materials,
making the 787 a very light aircraft for its capabilities.[76] By volume, the 787
will be 80% composite. Each 787 contains approximately 35 tonnes of carbon fiber
reinforced plastic, made with 23 tonnes of carbon fiber.[77] Composites are used
on fuselage, wings, tail, doors, and interior. Aluminum is used on wing and tail
leading edges, titanium used mainly on engines with steel used in various places
• Higher humidity in the passenger cabin is possible because of the use of
composites (which do not corrode).
• http://en.wikipedia.org/wiki/Boeing_787
BOEING 787 MATERIALS DETAILS
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The 787's all-composite fuselage makes it the first composite airliner in production. While the Boeing
777 contains 50% aluminum and 12% composites, the numbers for the new airplane are 15%
aluminum, 50% composite (mostly carbon fiber reinforced plastic) and 12% titanium. Each fuselage
barrel will be manufactured in one piece, and the barrel sections joined end to end to form the fuselage.
This will eliminate the need for about 50,000 fasteners used in conventional airplane building.
According to the manufacturer the composite is also stronger, allowing a higher cabin pressure during
flight compared to aluminum. It was suggested by many that the risks of having a composite fuselage
have not been fully assessed and should not be attempted. It was also added that carbon fiber, unlike
metal, does not visibly show cracks and fatigue and repairing any damage done to the aircraft would
not be easy.[96] Boeing has dismissed such notions, insisting that composites have been used on wings
and other passenger aircraft parts for many years and they have not been an issue. They have also
stated that special defect detection procedures will be put in place to detect any potential hidden
damage.
Another concern arises from the risk of lightning strikes. The 787 fuselage's composite could have as
much as 1,000 times the electrical resistance of aluminum, increasing the risk of damage during a
lightning strike
In 2006, Boeing launched the 787 GoldCare program. This is an optional, comprehensive life-cycle
management service whereby aircraft in the program are routinely monitored and repaired as needed.
This is the first program of its kind from Boeing: Post-sale protection programs are not new, but have
usually been offered by third party service centers. Boeing is also designing and testing composite
hardware so inspections are mainly visual. This will reduce the need for ultrasonic and other non-visual
inspection methods, saving time and money
BOEING 787 MATERIALS DETAILS
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According to Boeing Vice President Jeff Hawk, who heads the effort to certify the 787 for airline
service, a crash test involving a vertical drop of a partial fuselage section from about 15 feet onto a one
inch-thick steel plate went ahead as planned August 23, 2007 in Mesa, Arizona. Boeing spokeperson
Lori Gunter stated on September 6, 2007 that results matched what Boeing's engineers had predicted.
As a result the company can model various crash scenarios using computational analysis rather than
performing more tests on actual pieces of the plane
However, it has also been suggested by a fired Boeing engineer that in the event of a crash landing,
survivable in a metal plane, the composite fuselage could shatter and burn with toxic fumes
Boeing had been working to trim excess weight since assembly of the first airframe began in 2006.
This is typical for new aircraft during their development phase. The first six 787s, which are to be used
as part of the test program, will be overweight according to Boeing Commercial Airplanes CEO Scott
Carson. After the flight test program, these aircraft will be delivered to airline customers All Nippon
Airways, Northwest Airlines and Royal Air Maroc at speculated deeper than usual discounts.[107] The
first 787 is expected to be 5,000 lb (2,270 kg) overweight. The seventh and subsequent aircraft will be
the first optimized 787s and are expected to meet all goals.[108] Boeing has redesigned some parts and
made more use of titanium.[38] According to ILFC's Steven Udvar-Hazy, the 787-9's operating empty
weight is around 14,000 lb (6,350 kg) overweight, which also could be a problem for the proposed 78710.
MATERIALS SELECTION PROCESS: DIXON AND POLI
EXAMPLE WITH METALS
EXAMPLE: FISHING REEL EXAMPLE
• Options:
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Injection molding
Cast aluminum/die or mold
Wrought aluminum/stamping
Wrought steel/stamping
EXAMPLE 2: THRUST STAND
• Continue literature survey and review of existing and hobby thrust stands
• Rework of dimensions and performance of most likely candidate rockets to be
tested
• Large parametric investigation of multiple designs:
– Structural integrity
– Rigidity
– Weight
– Manufacturability
– Modularity
– Portable
– Flexibility of design for future enhancements
• Novel calibration and testing plan
• Quadra-axial feature (torque) presents unique design challenges
FINAL DESIGN
OTHER DESIGNS CONSIDERED
• Original concept from
response to RFP
• Feasible and practical design,
but new features and rigidity
now included
• Next generation design considered
a tubular elements for enhanced
rigidity
• Triangular cross section
• Feasible and practical design, but
easier to implement current design
CONCEPTUAL DESIGN
Solid rocket motor up to
12 inch diameter and 12 ft long
KEY FEATURES
• Horizontal and vertical capabilities
• Factor of safety of 15 on structural design, factor of safety of 5 on sensors on
nominal maximum thrust conditions
• Accommodate wide range of rocket sizes and thrusts
• Low friction, free rotation orthogonal force measurement system
• No residual orthogonal force due to mounting on forward array
• Corrosion resistant
• Optimized strength-to-weight ratio
• Rapid turn time between tests
• Readily modifiable to hybrid and liquid rockets (in the future)
LITERATURE REVIEW
• Review of numerous thrust stands
• Review of wide range of commercial hobby, amateur, and high-powered rocketry
solid and hybrid rocket motor classes
• Review of university / small corporation rocketry needs
• Materials, instrumentation, and manufacturability options
Rocket Motor
Diameter
Thrust
Burn Time
Loki Research: H or I class
1.14 inches
51 lbf
~ 2 sec
Loki Research: K or L class
2.12 inches
284 lbf
~ 3 sec
Loki Research: O or P class
5.98 inches
1,873 lbf
~ 6 sec
Atlantic Research SR45-AR-1 solidfuel rocket
4.5 inches
336 lbf
29 seconds
Loki Dart:
JPL 132A solid-fuel rocket
3 inches
2,030 lbf
1.9 seconds
Super Loki:
Aero Dyne SR110-AD-1
4 inches
5,520 lbf
2.1 seconds
MATERIALS SELECTION MATRIX
STAND MATERIALS SELECTION
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Stress corrosion cracking (SCC) is a mechanism of material breakdown which is
precipitated by subjecting materials to high stress coupled with a corrosive environment
Various aluminum materials can provide an adequate yield strength to meet our needs
(roughly 50-ksi for cross-sections considered), however, availability and corrosion
resistance is questionable for our purposes.
– 7075 is available in sheet and plate only
– Highly corrosive rocket exhaust plume
316L stainless steel offers a material that is highly resistant to corrosive environments
with no additional surface treatment needed
– Readily available in desired cross-section 3x3x0.25 in
– Relatively low cost $5,500 for 80-ft
– Due to low carbon content (< 0.02 %) of alloy produces welds that are extremely strong
– Molybdenum-3%, Chromium-18%, and Nickel-14% content account for superior
corrosion resistance of 316L
– 317L offers an alternative that is more resistant to chloride formation but its availability
is limited and cost is roughly twice 316L
Recommendation to proceed with constructing rocket thrust stand from 316L material
PARAMETRIC CASES INVESTIGATED
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Investigated Configurations:
– Triangular cross section with circular tubing:
• Benefits – Easy to manufacture; Inexpensive to make
• Disadvantages – Very heavy; Larger size; Material not readily available
– Square cross section with square tubing:
• Benefits – Material readily available; Relatively light weight; Smaller size
• Disadvantages – Longer machining time
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Investigated square frame dimensions:
– 4 x 4 inch with 0.25, 0.5 and 1 inch wall thickness (Most heavy)
– 3.5 x 3.5 inch with 0.25 and 0.5 inch wall thickness (Best)
– 3.0 x 3.0 inch with 0.25 and 0.5 inch wall thickness (Best)
– 2.5 x 2.5 inch with 0.25 and 0.5 inch wall thickness (Material unavailable)
– 2 x 2 inch with 0.5 inch wall thickness (Insufficient strength)
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Over 30 detailed ANSYS simulations completed18
WEIGHT VS. WALL THICKNESS PARAMETERIZATION
2500
SS 316L - 3x3
weight (lb)
2000
SS 316L - 2.5x2.5
Focus on 0.25 inch
wall thickness design
1500
SS 316L - 2x2
1000
Al 6061 T6 - 3x3
Al 6061 T6 - 2.5x2.5
500
Al 6061 T6 - 2x2
0
0
0.2
0.4
0.6
thickness (in)
0.8
1
1.2
STRUCTURAL FRAME
• Made from 316L 3x3 inch square tube stock
with 0.25 inch wall thickness
• Frame includes several cross members for
rigidity
• Gusset plates for rigidity/stiffness
• Numerous mounting holes to allow for
location of forward and aft mounting braces to
accommodate rockets of any size
• Versatile and adjustable anchoring system
STRUCTURAL ANALYSIS: ANSYS WORKBENCH
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Worst case scenario:
– 150,000 lbf axial thrust, 10,000 lbf lateral thrust, 6,000 lbf-in moment
– Yield strength design criteria: all equivalent stresses less than yield strength of material
Results
– Equivalent (von-Mises) stresses in stand structural members are below yield
– Deformations < than 0.11 inch (2.8 mm)
Equivalent (von-Mises) Stress
Total Deformation
MODAL ANALYSIS: ANSYS WORKBENCH
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Seek first natural frequency and mode shape
Results
– First frequency @ 69 Hz
– Deformed vs. undeformed
MATERIALS SELECTION ASSIGNMENT
• For Wednesday’s lecture:
• Think about 4 or 5 major components of your design
– What will these components be made of?
– Most important – how do you justify the choice?
– What metrics will you use to justify the choice?
• Materials selection slides included in next design presentation
• Materials selection section included in final report
STEEL PRICES: 2000-MID 2008
US STEEL (NYSE: X): 2006-CURRENT
LIGHT SWEET CRUDE (AMEX: OIH): 2006-CURRENT
COPPER PRICES
GOLD PRICES
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October 22, 2008: Gold futures tumbled 4.3% Wednesday to the lowest level in one year, while copper
futures were set for their worst year since 1988 in a broad sell-off that was sending stocks and
commodities sharply lower. Gold for December delivery fell $32.80, or 4.3%, to end $735.20 an ounce
on the Comex division of the New York Mercantile Exchange, the lowest closing level since October,
2007. Gold has fallen nine out of the past 10 trading sessions. Meanwhile, December copper slumped
14.15 cents, or 7.1%, to $1.8655 a pound. The metal has dropped 39% so far this year, heading for the
biggest yearly percentage drop since 1988, when trading data first became available on the Nymex.
MATERIALS SELECTION ASSIGNMENT
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Part 1: Materials selection for project prototypes
– Develop a list of criteria for 4 or 5 individual components of your design
• Example criteria: corrosion resistance, weldability, strength, hardness, etc.
– Select material properties that quantify important criteria and serve as material property metrics
• Example metrics: density, cost, tensile strength, CTE, etc.
– Examine a range of candidate materials using your metrics
• Note: if you already have a material selected, such as aluminum, survey other types of
aluminum for your metric ranges and cost.
– Perform an engineering trade-off between two or three of your variables
• Example 1: trade wall thickness vs. strength vs. cost on a component
• Example 2: trade weight vs. cost vs. fabrication time
– Identify 4-5 potential vendors of your materials including actual quotes and availability
• Note: usually McMaster-Carr is most expensive
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Part 2: Materials selection if your project went into production
– What are components of your design that would have to be examined from materials perspective?
– How would you develop a model to trade materials vs. cost vs. time?
– How would you reexamine (or redesign) a component with manufacturability in mind?
MID-TERM QUESTIONS/ANSWERS
• Examine all questions and answers for each team from the Mid-Term presentations
– Regarding the questions:
• How good were the questions themselves?
• Could the questions have been more poignant?
– Regarding the answers:
• How good were the answers to each question?
• Could the answers have been more specific / Did the answering team actually answer the
question that was being asked?
• Come up with 3-4 questions for each team that you think should be answered at
this point in the semester
– Don’t repeat questions ‘blindly’ but re-phrase them so they are more specific and
directly ask what you feel should be answered/addressed
– Write-up questions and submit by 10 am on October 27, 2008
– In lecture on October 27, 2008 I will submit collated questions to each team *before*
the final presentations – no team caught off guard
– During the week of October 27 – October 31, we meet to together and decide which
questions need to be answered/addressed
– Interweave answers to questions in final presentation
– Audience re-assesses how well these questions have now been answered