Material Allowables

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Material Allowables

Material Allowables


Class Objectives

• Classes of Allowables

• Property Distribution

Material Specifications

• Test Requirements

q

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

$ Fullscale

tests

Component

tests

$ Analysis

$

$

Sub Sub-component component tests

Structural elements tests $

Allowable development

Material specification development

$

Material screening and selection $

Design and Analysis of Aircraft Structures

$

verification

Design-value

development

Material

property

evaluation

14-5


Allowables Ensure the Structural

Integrity of the Final Product

Allowables Design Requirements

• Static Allowables Properties and Bases

Allowables Development and Publication

• Presentation of Design Manuals and

Examples of Use

Design and Analysis of Aircraft Structures

14-6


Allowables Are Required by FAA

to Certify All Aircraft Structures

FAA requirement

FAR 25-613 25 613

Design and Analysis of Aircraft Structures

MMaterial t i l strength t th

and design values

14-7


Within Boeing, Allowable Development Is the Responsibility of

the Stress Methods and Allowables (SMA) Group

Structural Damage

Technology (SDT)

Central

Engineering

SMA

Methods Allowables

Design and Analysis of Aircraft Structures

Boeing Materials

Technology (BMT)

14-8


Allowables Ensure the Structural

Integrity of the Final Product

Allowables Design Requirements

• Static Allowables Properties and Bases

Allowables 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:

Mechanical properties having a level of statistical

assurance – general case

• DDesign i value: l

A mechanical property value based on the allowable

adapted p to the criteria and analysis y method used –

specific case

Design and Analysis of Aircraft Structures

14-10


Strength Is an Allowables Domain

Mechanical

Properties

St Strength th properties ti ( (reduced) d d)

Ftu, Fty, Fsu Elastic properties (typical)

EE, GG, u

Physical properties (typical)

w, k

Design and Analysis of Aircraft Structures

14-11


Classes of Allowables

“A” BBasis i • 99% probability b bilit with ith 95% confidence fid

“B” BBasis i

• 90% probability with 95% confidence

Point

Design

• Associated with a unique q structure and

valid only for that particular configuration

“S” Basis

Design and Analysis of Aircraft Structures

• Specification acceptance value

with no statistical significance—

this is not an allowable!

14-12


The Allowable Need is Dependent

Upon the End User

Material

controlled by -

Vendor

Preliminary

specifications:

XBMS, XBAC

Firm specifications:

BMS, BAC,

AMS*, MIL*, QQ*

Allowables Design/analysis

Estimated

design values

Trade studies

initial design

Preliminary Preliminary

allowables design

Firm

allowables

*No longer Government monitored

Design and Analysis of Aircraft Structures

Firm design g

drawing release

- hardware

fabrication

14-13


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 p limits

– Weibull distribution

– Normal distribution

– Lognormal distribution

Design and Analysis of Aircraft Structures

14-15


Unknown Distribution

Nonparametric analysis

• “A” A 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

Material

controlled by

Vendor Estimated design

values

Preliminary

specifications:

XBMS, XBAC

Allowables Design/analysis

Preliminary

allowables

Trade studies’

initial design

Preliminary design

Firm specifications: Firm allowables Firm design drawing

AMS*, MIL*, QQ*,

release hardware

BMS, BAC fabrication

Design and Analysis of Aircraft Structures

14-17


Allowables Ensure the Structural

Integrity of the Final Product

Allowables Design Requirements

• Static Allowables Properties and Bases

Allowables Development and Publication

• Presentation of Design Manuals and

Examples of Use

Design and Analysis of Aircraft Structures

14-18


Allowables Development Requirements

• Program g request q

• Firm specification

• Test program planning

• Specimen fabrication and testing

Allowables development

• DDocument t D6 D6-57037, 57037 “P “Procedure d ffor MMaterial t i l

Selection and Development of

Design/Producibility Data”

Design and Analysis of Aircraft Structures

14-19


Requirements for Development

of Metal Allowable

• Existence of a material specification

• TTen lots l t of fmaterial t i lf from at tl least tt two production d ti heats h t

for each test

• Thi Thickness k range of f the th 10 lots l t to t be b tested t t d should h ld span

the thickness range covered by the material specification

• All tests are performed in accordance with the applicable

standard specifications

• Specific standard properties (tension (tension, compression

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 2 0 for each grain direction and each lot

Design and Analysis of Aircraft Structures

14-20


Allowables

Typical Allowables Test Program for Metallic Materials

Tension

(L) 90 + 10

(LT)

10

Compression

(L)

10

(LT)

10

Shear

(L)

10

(LT)

10

Bearing, e/D=1.5 (L)

10

(LT)

10

Bearing, g, e/D=2.0 (L) ( )

10

(LT) 10

Design and Analysis of Aircraft Structures

14-21


Allowables Ensure the Structural

Integrity of the Final Product

Allowables Design Requirements

• Static Allowables Properties and Bases

Allowables Development and Publication

• Presentation of Design Manuals and

Examples of Use

Design and Analysis of Aircraft Structures

14-22


BDM-4090

7075

Design and Analysis of Aircraft Structures

14-23


BDM-4090

7075

Design and Analysis of Aircraft Structures

14-24


BDM-4090

7075

Design and Analysis of Aircraft Structures

14-25


BDM-4090

7075

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 p at 250°F service

temperature 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%) =

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

2024-T3

P

BACR15BB6D

t = 0.050

t = 0.050

Design and Analysis of Aircraft Structures

0.43

(minimum

typical)

P

14-32


Example

Solution

Design and Analysis of Aircraft Structures

14-33


Example

Solution

Answer = 910 lbs

Design and Analysis of Aircraft Structures

14-34


Tension

Fasteners

Design and Analysis of Aircraft Structures

14-35

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