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Material AllowablesMaterial Allowables
Class Objectives
• Classes of Allowables• Property DistributionProperty Distribution• Material Specifications• Test Requirementsq
Design and Analysis of Aircraft Structures 14-2
Design and Analysis of Aircraft Structures 14-3
Design and Analysis of Aircraft Structures 14-4
Investigation of Methods and Allowables
Full $Analysis verification
Full-scaletests
$$Component
tests
Sub component tests $$
Design-value development
Sub-component tests
Structural elements tests $$
$
Material property
evaluation
Allowable development
Material specification development
Material screening and selection $
$$
Design and Analysis of Aircraft Structures 14-5
Material screening and selection $
Allowables Ensure the StructuralIntegrity of the Final Product
Allowables Design Requirements• Allowables Design Requirements• Static Allowables Properties and Bases• Allowables Development and PublicationAllowables Development and Publication• Presentation of Design Manuals and
Examples of Use
Design and Analysis of Aircraft Structures 14-6
Allowables Are Required by FAAto Certify All Aircraft Structures
FAA requirement
FAR 25-613FAR 25 613
M t i l t thMaterial strengthand design values
Design and Analysis of Aircraft Structures 14-7
Within Boeing, Allowable Development Is the Responsibility of the Stress Methods and Allowables (SMA) Group
Structural Damage Technology (SDT)
Boeing Materials Technology (BMT)
CentralEngineering
SMASMA
Methods Allowables
Design and Analysis of Aircraft Structures 14-8
Methods Allowables
Allowables Ensure the StructuralIntegrity of the Final Product
Allowables Design Requirements• Allowables Design Requirements• Static Allowables Properties and Bases• Allowables Development and PublicationAllowables Development and Publication• Presentation of Design Manuals and
Examples of Use
Design and Analysis of Aircraft Structures 14-9
Allowables and Design Value
Definitions• Allowables:Allowables:
Mechanical properties having a level of statistical assurance – general caseD i l• Design value:A mechanical property value based on the allowable adapted to the criteria and analysis method used –p yspecific case
Design and Analysis of Aircraft Structures 14-10
Strength Is an Allowables Domain
St th ti ( d d)Strength properties (reduced) Ftu, Fty, Fsu
MechanicalProperties Elastic properties (typical)
E G uE, G, u
Physical properties (typical)Physical properties (typical)w, k
Design and Analysis of Aircraft Structures 14-11
Classes of Allowables
“A” B i 99% b bilit ith 95% fid“A” Basis
“B” B i
• 99% probability with 95% confidence
• 90% probability with 95% confidence“B” Basis
Point
• 90% probability with 95% confidence
• Associated with a unique structure andDesign
“S” Basis
qvalid only for that particular configuration
• Specification acceptance value “S” Basis with no statistical significance—
this is not an allowable!
Design and Analysis of Aircraft Structures 14-12
The Allowable Need is Dependent Upon the End User
Design/analysisMaterial
Allowables Design/analysis
Trade studies
controlled by -
Vendor
Allowables
Estimatedinitial design
Preliminary
Vendor
Preliminaryspecifications:
design values
Preliminary Preliminarydesign
Firm design
specifications:XBMS, XBAC
Firm specifications:
Preliminaryallowables
gdrawing release
- hardware fabrication
Firm specifications:BMS, BAC,
AMS*, MIL*, QQ*
Firmallowables
Design and Analysis of Aircraft Structures 14-13
fabrication
*No longer Government monitored
Material Property Population Distribution
Frequency
A B Typical Property
Design and Analysis of Aircraft Structures 14-14
Probability Distribution
A formula that gives the probability that a value fall within prescribed limitsp
– Weibull distribution– Normal distribution
Lognormal distribution– Lognormal distribution
Design and Analysis of Aircraft Structures 14-15
Unknown Distribution
Nonparametric analysis• “A” basis allowable: lowest of 299 test pointsA basis allowable: lowest of 299 test points • “B” basis allowable: lowest of 29 test points
Design and Analysis of Aircraft Structures 14-16
Allowable Need Is Dependent Upon the End Use
MaterialMaterialcontrolled by Allowables Design/analysis
Vendor Estimated design values
Trade studies’ initial design
Preliminary specifications: XBMS, XBAC
Preliminary allowables
Preliminary design
XBMS, XBAC
Firm specifications: AMS*, MIL*, QQ*,
Firm allowables Firm design drawing release hardware
Design and Analysis of Aircraft Structures 14-17
BMS, BAC fabrication
Allowables Ensure the StructuralIntegrity of the Final Product
Allowables Design Requirements• Allowables Design Requirements• Static Allowables Properties and Bases• Allowables Development and PublicationAllowables Development and Publication• Presentation of Design Manuals and
Examples of Use
Design and Analysis of Aircraft Structures 14-18
Allowables Development Requirements
• Program requestg q• Firm specification• Test program planning• Specimen fabrication and testing• Allowables development
D t D6 57037 “P d f M t i l• Document D6-57037, “Procedure for Material Selection and Development of Design/Producibility Data”
Design and Analysis of Aircraft Structures 14-19
Requirements for Developmentof Metal Allowable
• Existence of a material specification
T l t f t i l f t l t t d ti h t• Ten lots of material from at least two production heats for each test
Thi k f th 10 l t t b t t d h ld• Thickness range of the 10 lots to be tested should span the thickness range covered by the material specification
All tests are performed in accordance with the applicable• All tests are performed in accordance with the applicable standard specifications
• Specific standard properties (tension compression• Specific standard properties (tension, compression, shear, and bearing) are tested at room temperature to determine Ftu, Fty, Ein, Fcy, Csu, Fbru, and Fbry for e/d = 1.5 and e/D = 2 0 for each grain direction and each lot
Design and Analysis of Aircraft Structures 14-20
and e/D = 2.0 for each grain direction and each lot
Allowables
Typical Allowables Test Program for Metallic Materials
Tension
Compression
(L)(LT)(L)
90 + 101010Compression
Shear
(L)(LT)(L)(LT)
10101010
Bearing, e/D=1.5
Bearing, e/D=2.0
(LT)(L)(LT)(L)
10101010g, ( )
(LT) 10
Design and Analysis of Aircraft Structures 14-21
Allowables Ensure the StructuralIntegrity of the Final Product
Allowables Design Requirements• Allowables Design Requirements• Static Allowables Properties and Bases• Allowables Development and PublicationAllowables Development and Publication• Presentation of Design Manuals and
Examples of Use
Design and Analysis of Aircraft Structures 14-22
BDM-40907075
Design and Analysis of Aircraft Structures 14-23
BDM-40907075
Design and Analysis of Aircraft Structures 14-24
BDM-40907075
Design and Analysis of Aircraft Structures 14-25
BDM-40907075
Design and Analysis of Aircraft Structures 14-26
Sample Problem
• What is the tensile ultimate strength B allowable of .5-inch thick 7075-T651 bare plate at 250°F service ptemperature after exposure to 350°F for 1,000 hours?
Design and Analysis of Aircraft Structures 14-27
Example Solution
38%
Design and Analysis of Aircraft Structures 14-28
Example Solution
Answer = (79 ksi)(38%) =(79 ksi)(38%) =
30 ksi
Design and Analysis of Aircraft Structures 14-29
Joint Strength BDM-4301
Design and Analysis of Aircraft Structures 14-30
Joint Strength Single Shear
Design and Analysis of Aircraft Structures 14-31
Sample Problem: Find the Joint Capability With BACR15BB6D Fastener
BACR15BB6D P
t = 0.0502024-T3
0.43(minimumtypical)P
t = 0.050
Design and Analysis of Aircraft Structures 14-32
Example Solution
Design and Analysis of Aircraft Structures 14-33
Example Solution
Answer = 910 lbsAnswer 910 lbs
Design and Analysis of Aircraft Structures 14-34
Tension Fasteners
Design and Analysis of Aircraft Structures 14-35