Material%20 selection%20for%20aircraft%20compressor%20blade
Post on 25-Jun-2015
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MATERIAL SELECTION FOR AIRCRAFT COMPRESSOR BLADEAhmad Bamasq
Ahmad Al Dakhil
Outline• Introduction• Constrains• Selection Procedure• Decision• Future approach• References
Introduction• The majority of the thrust for propulsion in a modern
commercial jet engine comes from a large diameter fan at the front of the engine, which is driven by the low-pressure turbine at the rear of the engine. The fan, similar to a room fan, consists of multiple blades that rotate about the fan axis at high speed, and push the air backward past the engine.
Constrains: Mass & Shape• It is desired to minimize the weight of the fan blade to
decrease engine weight and then the takeoff weight. The mass of the blades rotating at high speed creates high stresses in the blades. It also requires the fan disk should be strong enough to hold the blades.
• The blade has a specified size and shape.
Constrains: Strength• The blade is to withstand rotational stresses equivalent to
70,000 psi (483 Mpa) in a material with density of titanium (4500 kg/m3).
• We can find relation of σ/ρ > 107333 Pa / (kg/m3)
Constrains: Fracture Toughness • Tolerance to damage (dents, cracks) from impact of
foreign objects (rocks, birds) is also important. A .02” (0.51 mm) deep impact-induced crack should not propagate under the cyclic loads imposed by centrifugal force.
• Fast fracture will occur if the fracture toughness • (Kc) > σ (πa)1/2
• (Kc) > ρ107333 (π 0.00051)1/2
• (Kc) / ρ > 4300 Pa (m)1/2 / (kg/m3)
Constrains: Cost & Temperature • Cost is always a constraint in jet engines, particularly
commercial ones, and it is desired (though not essential) to keep blade cost below $2000.
• The maximum service temperature is 200 C
Design Requirements
Aircraft compressor blades. Function
Size and shape are specified .
Strength: must not fail under design stresses.
High fracture toughness.
Maximum service temperature is 200 C
Constraints
Minimize mass Objective
Choice of material Free variables
Indexes
• σ/ρ > 107333 Pa / (kg/m3)
• (Kc) / ρ > 4300 Pa (m)1/2 / (kg/m3)
Tensile strength / Density1000 10000 100000
Frac
ture
toughnes
s /
Den
sity
10
100
1000
10000
Nickel-based superalloys
Titanium alloys
Wrought magnesium alloys
Low alloy steel Stainless steel
CFRP, epoxy matrix (isotropic)
Tensile strength / Density1000 10000 100000
Frac
ture
toughnes
s /
Den
sity
10
100
1000
10000
Titanium alloys
Nickel-based superalloys
Wrought magnesium alloys
Low alloy steel Stainless steel
CFRP, epoxy matrix (isotropic)
Tensile strength / Density200000 300000 400000 500000 600000 700000
Frac
ture
toughnes
s /
Den
sity
5000
10000
15000
20000
25000
Titanium alloys
Age-hardening wrought Al-alloys
Low alloy steel
Stainless steel
Wrought magnesium alloys
Nickel-based superalloys
CFRP, epoxy matrix (isotropic)
Materials for bladesIt is much lighter than normal (metallic) blade and very strong but it’s expensive. CFRB
Titanium has very good balance between weight, drag and durability against vibrations, damage - such as bird strikes - and erosion through sand, and rain. However, it’s expensive.
Titanium alloys
Both have much bigger density Steel & Nickel alloys
Lighter and cheaper than Ti but the safety is low. Al & Mg alloys
Ti blade vs. composite blade• Today, the largest engine producers are Roll Royce and General
Eclectic. RR use hollow Ti blades while GE uses a composite blade.• • The choice of blade construction depends on a number of
considerations, thus there is no clear ‘right or wrong’ answer. Each blade has advantages and disadvantages.
‘Preferred’ material Factor
Composites Fatigue strength
Ti alloys Impact strength
Both about equally (high) Cost
Depends on fan diameter Weight
Both appear adequate Durability
• All RR aircraft engines use hollow titanium fan blades including the Trent 1000 engine which is used in Boeing 787 Dreamliner.
• RR claims that CFRP blade is not aerodynamically efficient as Ti blade. It has to be thicker to have the strength to deal with actual requirements. In addition, Ti blades are more economical.
• However, Rolls-Royce is planning to replace the Ti blades by CFRB blades.
• Rolls-Royce and GKN have developed a CFRP blade that is as thin as the titanium blades with manufacturing costs.
• This fan blade has already undergone ground tests, including blade-off and bird strike tests.
• It is to begin flight tests on a Trent 1000 in the 2013 in Boeing 787.
• It could become available on a new engine in the end of the decade (beyond the Trent XWB).
• Since 1995, GE uses a CFRB fan blades for their engines.
• Starting from GE90 for Boeing 777 and now: GEnx for Boeing 787 Dreamliner which has both a front fan case and fan blades made of carbon fiber composites.
• The CFRP with has titanium leading edge for extra protection were a lightweight and durable solution.
• Each fan blade weighs between 15 and 22 Kg. Every engine contains 22 of these fan blades, which add approximately 900 kg to the engine's thrust capability, providing better fuel burn.
References• http://www.me.jhu.edu/hemker/MatSel/Labs/Lab%202%20
Fan%20Blade.doc• http://www.sciencedirect.com/science/article/pii/S0921509
398011794• http://www.flightglobal.com/news/articles/rolls-royce-come
s-full-circle-362251/• http://www.geaviation.com/aboutgeae/presscenter/ge90/g
e90_20041116.html• http://www.compositesworld.com/articles/aviation-outlook-
composites-in-commercial-aircraft-jet-engines
Thanks ..!
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