BK50A2700 Selection Criteria of Structural Materials

Lesson 12014

REPETITION 1:Material selection based on strength propertiesMaterial selection based on manufacturabilityReliability based material selection

Lesson 12014

The goal of this lesson

Our goal is, that after this lesson, students are able to recognize the importance of affecting loading cases, optional manufacturing technologies and the reliability based aspects for material selection.

Material selection based on strength properties

Note!The key for proper material selection based

on the required strength properties is to recognize the affecting loading cases!TensileCompressionBendingShearCombined loadingDynamic / static loading, fatigueThermal loading, corrosion assisted loading

DIFFERENT LOADING CASES

A= STATIC LOADINGB= DYNAMIC LOADING/ PULSATING LOADINGC= DYNAMIC LOADING/ REPEATED LOADINGD= DYNAMIC LOADING/ ASYMMETRIC REVERSED LOADINGE= DYNAMIC LOADING/ SYMMETRIC REVERSED LOADING

TIME

FORCE

LOADING CASE:PULSATING LOADING

LOADING CASE:REVERSED LOADING

σa = stress amplitudeσm = mean stress

σ

σm

σa

σa

t

σ

σmσa

σat

σa = stress amplitudeσm = mean stress

CASE: FATIGUE FAILURE OF A SPRING

DIMENSIONS- Effective cross- sectional area- Thickness, diameter- Geometrical restrictions- Weight

GEOMETRY- Changes of cross- section areas- Joints - Groves, shoulders, threads holes, notches- Geometry related to the loading angle

MATERIAL PROPERTIES- Tensile, compression, bending, torque- Fatigue failure- Strength, ductility- Notch sensitivity- Yeld strength ratio- Environmental conditions

Key seat Circlip seatRelief groove End of the worm gear thread

STRESS

TEMPERATURE

200 400 600 800 1000 1200 1400 1600 18000

0.05

0.1

0.15

0.2

0.25

0.3

0.35

MATERIAL COEFFICIENT “a” OF STEELS FOR NOTCH SENSITIVITY CALCULATIONS

ULTIMATE TENSILE STRENGTH [Mpa]

MA

TE

RIA

L C

OE

FF

ICIE

NT

a

STEELS

CAST IRONS

COPPER ALL

OYS

TITANIU

M A

LLOYS

MAGNESIU

M A

LLOYS

ALUM

INIU

M A

LLOYS

NICKEL-

SUPERALLOYS

NANOFIBRE C

OMPOSIT

ES

POLYM

ER MATRIX

COM

POSITES

POLYM

ERS0

500

1000

1500

2000

2500

3000

3500

4000

4500

ULTIMATE TENSILE STRENGTHS OF DIFFERENT MATERIAL GROUPS

UL

TIM

AT

E T

EN

SIL

E S

TR

EN

GT

H [

MP

a]

1400 MPa

1800 MPa

BH HSLA DP TRIP CP MART0

200

400

600

800

1000

1200

1400

1600

1800

COMPARISON OF HIGH STRENGTH STEELS

HSS/ AHSS/ UHSS -STEELS

UL

TIM

AT

E T

EN

SIL

E S

TR

EN

GT

H [

MP

a]

-20

-10

0

10

20

30

40

50

60

70

TO

TAL

WE

IGH

T

BO

DY

WE

IGH

T

FU

EL

CO

NS

UM

PT

ION

CO

2-E

MIS

SIO

NS

MA

NU

FAC

TU

RIN

G

CO

ST

S

-10% -20% -5% -6% 0% -11% -3% -2% -3%

+ 65%

EFFECTS OF CHANGING THE CAR BODY MATERIAL

CHANGE: STEEL AHSS-STEEL CHANGE: AHSS-STEEL ALUMINIUM

CH

AN

GE

%

TO

TAL

WE

IGH

T

BO

DY

WE

IGH

T

FU

EL

CO

NS

UM

PT

ION

CO

2-E

MIS

SIO

NS

MA

NU

FAC

TU

RIN

G

CO

ST

S

Note!Typically the increase of the strength of the

material requires some compromises with other material properties!

Remember that the increase of the strength of the material is NOT the only option to increase the strength of the construction!

E.g. the by changing the direction of the affecting load some materials become acceptable (e.g. ceramic materials withstand compression loading better than tensile loading)

PROPERTIES G

ET WORSE

STRENGHT RANGE DECREASES

PROPERTIES GET WORSE

PROPERTIES IM

PROVEPROPERTIES IMPROVE

STRENGTH RANGE INCREASES

MACHINABILITYHEAT CHANGE RESISTANCE ABILITY TO ABSORB VIBRATIONSCASTABILITYTHINNEST POSSIBLE WALL THICKNESS

SURFACE ROUGHNESSHEAT RESISTING STRENGTHMODULUS OF ELASTICITYWEAR RESISTANCE

MACHINABILITYHEAT CHANGE RESISTANCE ABILITY TO ABSORB VIBRATIONSCASTABILITYTHINNEST POSSIBLE WALL THICKNESS

SURFACE ROUGHNESSHEAT RESISTING STRENGTHMODULUS OF ELASTICITYWEAR RESISTANCE

COMPARISON OF CAST IRONS

Material selection based on manufacturability

Note!For objective and systematic material

comparison and selection numerical characteristics are required to describe manufacturability:Machinability (cutting, milling, drilling etc.)WeldabilityFormability (bending, deep drawing etc.)CastabilityAspects of powder metallurgyAspects of polymer and composite technology

PRODUCT DESIGN

OPTIONAL MATERIALS OF THE PRODUCT

OPTIONAL MANUFACTURING TECHNOLOGIES

• CHARACTERISTICS FOR COMPARISON

DETAILED DESIGN OF MANUFACTURING

MAX

MIN

CHARACTERISTICS AND NUMERICAL VALUES TO DESCRIBE MACHINABILITY

Cutting speed v, cutting depth a, feed s, wear of the cutting edge

Cutting power P, cutting forces F, tolerance grade IT, surface roughness Ra, chip size

MATERIAL: ALUMEC® • COPPER ALLOYED COLD-DRAWN ALUMINIUM ALLOY WITH HIGH STRENGTH AND GOOD MACHINABILITY

EFFECTS OF CUTTING FORCES ON THE PERPENDICULARITY OF THE MW-FILTER’S RESONATOR PINS SHOULD BE TAKEN INTO CONSIDERATION IN MATERIAL SELECTION

Type of joint

Heat input min/max

Filler material

Weld protection

Suitability of the welding process

Heat treatments

Quality control

Required actions before

welding

Welded product or material

Required actions during

welding

Required actions after

welding

Effective welding time (burn time ratio)

Joint and process preparations

Groove preparations

FRIPFRIP

GLUED SEAM

FPEELING FPEELING

GLUED SEAM

SURFACE LAYER

BASIC MATERIAL (THE BODY)

Example of glued components

MATERIAL A:THE ELONGATION OF BOTH PARTS IS L3L4

STRETCHED SEAML1L2

(GLUED JOINT)

L3

L4

L1

L2

F

F

MATERIAL BTHE ELONGNATION IS LARGER THAN IN MATERIAL A L5L6 AND L3=L5 , BUT L6>L4

STRETCHED SEAM L1L2

(GLUED JOINT)

L3

L4

L1

L2

F

F

MATERIAL ATHE ELONGNATION IS L3L4

L5

L6

F

FThe thickness ”a” of the glued seam

Plate thickness ”t”

Overlapping length ”l”

Shear modulus ”G” of the glued seam

Plate’s modulus of elasticity ”E”

FF

τmax

𝝌= 𝐾× 𝑙√𝑡

❑

χ×τm/τmax

Basic material 1

Basic material 2

Glued seam

Coating 1

Coating 2

Requirements profile

Properties profile

Deriving the necessary material

properties of

the glued seam from

the requirements

of the joint

Original milled MW-filter construction with the fitting joint of the SMA-connector pin

Developed sheet metal construction with a glued joint

Special geometry of the centre pin for the glued joint

Glued joint(Elecolit® conductive adhesive)

Note!Sometimes optional materials can be selected

by utilizing appropriate coatings for cost effective base materials

Analogic to the previous glued joint of two different materials, the properties of the coating and the base material should be tuned to match with each other!

Material characteristics to describe material’s formability

Smallest allowed bending radiusrmin

Required number of forming stages

Required forming force

Required elevated forming temperature

Smallest allowed wall thickness in deep drawing related to the drawing speed

Produced maximum decrease of the cross-section [%] by one forming stage

rmin1

rmin2

A2A

1

Freq

Freq

T1 [°C]

F

T2 [°C]

F

T1 >> T2

N= 1 2 3 4 5 smin

v, F

Reliability based material selection

Note!Both the material properties and the

affecting loads vary based on the given limits in material standards and during the different functional conditions!

Therefore there is a real risk that the failure might take place when the material properties are at their minimum and the affecting load is at its maximum!

Reliability based material selection offers a tool to estimate the probability of the failure risk.

Gathering the statistical data to describe the variation of the component’s load bearing capacity

Gathering the statistical data to describe the load variation of the component

Distribution curve fits for the variations of load and load bearing capacity

Calculation of the wanted size of the overlapping area of the distributions to find out the reliability level

Stage 1 Stage 2 Stage 3 Stage 4

DISTRIBUTION OF THE LOAD BEARING CAPACITY f(R)

DISTRIBUTION OF THE AFFECTING LOAD f(S)

R S

AD

STRESSRESISTANCE

PROBABILITY

f(S)f(R)

ENDURANCE CONDITION R>S

<

Parameter ƞ”sharpness”

Parameter β”shape”

Parameter γ”position”

3-PARAMETER WEIBULL-DISTRIBUTION CURVE

=1.17 =3.57f(x)

xo xTHE SHAPE OF THE WEIBULL DISTRIBUTION CURVE WITH DIFFERENT SHAPE PARAMETER VALUES

Almost normal distribution

FAILURE

NORMAL DISTRIBUTION LOADWEIBULL DISTRIBUTION MATERIAL PROPERTIES

TOOLS FOR RISK ANALYSIS

Risk analysis of dangerous scenarios

Effect tree analysis (ETA)

Failure analysisForecasting potential damages and failures

Failure mode and effects analysis (FMEA)

Reaction matrix

Malfunction analysis

Why-because analysis (WBA) and Cause-effect analysis (CEA)

Fault tree analysis (FTA)

Analysis of consequences