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MECHANICAL CHARACTERIZATION OF HEAT RESISTANT TITANIUM ALLOYS

FOR AUTOMOTIVE APPLICATIONS Author: Dr. Eng. Silvia Gaiani

Akrapovič d.d. - Technology Supervisor

ABSTRACT

In the last five years, the use of titanium

alloys for exhaust systems manufacturing in

automotive industry has increased

significantly. Due to this reason, also the

variety of heat resistant alloys available on the

market is raised considerably. In order to

better evaluate the characteristics of this wide

range of products, Akrapovič d.d. developed a

classification method which can be used to

check incoming materials and compare

properties between different alloys. Because

of the strongly anisotropic behavior of

titanium, to obtain a comprehensive overview

of the plastic performance, a testing approach

based on biaxial tensile trials has been used.

1.0 INTRODUCTION

Actually, titanium alloys used for exhaust

system fabrication are all α alloys, which use

as addition small quantities of different

alloying elements, as aluminum, copper,

niobium, silicon and iron. Addition of these

elements has increased significantly the

oxidation resistance and mechanical

properties, if compared whit the performance

of commercially pure titanium, especially

Grade 2. For production of exhaust system

dedicated to high performance bikes and cars,

Akrapovič buys several types of titanium

alloys, from different producers worldwide;

the most common purchased raw material is

in shape of coils, with a thickness between 0,5

- 1,5 mm. These advanced alloys show

excellent properties for their target

application (high strength, elevated thermal

properties, weldability); however, their use for

realizing parts with complicated shapes is still

limited, because of problems associated with

poor formability and consequently high

manufacturing costs. Formability problems of

cold rolled titanium alloys are well known

several years ago, and basically are strictly

related to the anisotropic behavior of the

materials.

Anisotropy behavior in α titanium alloys is

strictly related to two aspects mostly:

- Type of titanium lattice, which is, until

882 °C, hexagonal closed packed (HCP).

- Crystallographic orientation (texture)

For titanium, the hexagonal unit cell of the α

phase shows values of the lattice parameters

a=0.295 nm and c=0.468 nm. The resulting c/a

ratio for pure α titanium is therefore 1.587, or

rather smaller than the ideal ratio of 1.633 for

the hexagonal close-packed crystal structure.

This condition means that the three most

densely packed lattice planes are the following

(see Pic. 1):

- Two ( 0002 ) plane, also called

basal plane,

- Four {1010 } planes, also called

prismatic planes

- Six {1011} planes, also called

pyramidal plane

Looking Picture 1, it is very easy to understand

that hexagonal unit cell don't present

symmetric slip systems.

Pic.1 - Theoretical slip planes for titanium [[[[ 1]]]]

2

Combining the three different types of slip

planes mentioned above, together with the

possible slip directions there are a total of 12

slip systems. These slip systems can be

reduced to nominally 4 independent.

However, according to Von Mises principle, to

obtain a homogeneous plastic deformation at

least five independent slip systems are

required. This means that in order to have

plastic deformation, also a system with a non-

basal Burgers vector needs to be activated; for

these type of titanium alloys this non-basal

Burgers system most commonly activated is

the type <1123> {1122}. The need to activate

two different types of dislocations (a vector

basal, c vector non basal) at the same time is

strictly related also to the direction of load.

For all these reasons, plastic deformation in α

titanium alloy is also strongly dependent from

the activation of twinning deformation modes

in addition to conventional slip by

dislocations. To be more precise, these

twinning modes are probably the most

important for the deformation behavior of the

considered α titanium alloys.

Concerning the crystallographic orientation, it

is well known that during the production

process, especially during final cold rolling,

titanium α alloys show a considerable attitude

to give rise to a preferred crystallographic

orientation. When preferred orientation

exists, the structure is said to be “textured” or

that it has a strong “texture”. The orientation

of the lattice is related to many factors, like

c/a ratio, rolling conditions, annealing

temperature, etc. Most HCP alloys show a

nearly basal texture (i.e. c-axis aligned normal

to the plane of the sheet); for titanium α

alloys obtained with standard production

processes the basal planes are inclined

approximately 30° towards the transverse

direction [2]. However, certainly alloying

agents, direction of rolling, heat treatment

temperature should play an important role in

determining the final texturing direction of the

material. For sure, texture in titanium alloys

has a big impact on the final mechanical

characteristic of the product, especially

formability, because, as previously explained,

the slip planes of HCP lattice are not

symmetrically sorted.

2.0 UNIAXIAL TENSILE TESTS

Akrapovič d.d. purchases for its exhaust

system production six diffent types of titanium

alloys from three different suppliers; four of

them are mostly used for deep drawed parts,

as endcap or rosette. Executing a practical

deep drawing test under the press, the

behavior of these materials is completely

different. However, if we compare the results

of a tensile test executed along the rolling

direction the outcome are the following:

Rp 0,2

(MPa) Rm

(MPa) A80

(%) Agt

(%) Rp/Rm

(--)

Mat. 1 300,26

425,93 30,76 14,34 0,705

Mat. 2 319,63 452,43 29,93 17,48 0,706

Mat. 3 297,74 431,44 31,60 17,35 0,691

Mat. 4 476,72* 576,43 24,38 13,32 0,827

Table 1 – Tensile test in rolling direction

The results listed in Table 1 are medium value

obtained executing n°5 tensile test for every

type of materials according to standard EN

10002-1 on a specimen with L0=80 mm. (*) For

material n°4 the measured yield limit is not

Rp0,2 but REH. Looking the tensile value

obtained in rolling direction, is clearly visible

that the first three materials show similar

behavior and characteristics; unfortunately

this results was not supported from practical

deep drawing tests. For this reason, also

tensile tests in transverse direction were

performed. The obtained results are in Tab 2.

Rp 0,2

(MPa) Rm

(MPa) A80

(%) Agt

(%) Rp/Rm

(--)

Mat. 1 340,13

398,26 30,93 8,22 0,854

Mat. 2 365,51 400,40 34,56 7,22 0,913

Mat. 3 308,74 408,72 31,22 7,98 0,765

Mat. 4 550,48* 575,46 24,40 8,05 0,956

Table 2 – Tensile test in transverse direction

As it is possible to see from Table 1 and 2, the

behavior of the material in rolling and

transverse direction is strongly different. For

every material, in transverse direction Rp

value raises, becoming nearer to Rm, which is

mainly constant. In transverse direction Rm

peak is also reached at a lower elongation.

These two factors cause a big reduction of the

plastic field of the material, also if the final

elongation is basically the same.

3

Pic. 2- Comparison between rolling and transverse

tensile test results for material n°1

Pic. 3- Comparison between rolling and transverse

tensile test result for material n°3

Crossing the values obtained by tensile test in

rolling and transverse direction and the

practical results obtained in deep drawing

department, was clear that for predicting

realistic results, a more detailed investigation

which can explore deeper the problems

related to anisotropy is needed [3].

3.0 BIAXIAL TENSILE TEST

For all four materials used for deep drawing,

some tensile test using a biaxial electronic

gauge were performed according to standard

EN 10002-1 [4] on specimens with L0=80 mm.

The specimens were orientated along the

rolling direction (longitudinal), perpendicular

to the rolling direction (transverse), and at

45°degrees to the rolling direction (diagonal).

The trials were executed using two different

types of machine controls during the test:

1) Stress rate control → σrate= 12 MPa/s

2) Strain rate control → εrate= 0,00065 1/s

In the elastic field σrate value has been chosen

for staying in the boundaries suggested from

standard EN 10002-1, which for metals with E

< 150.000 recommend staying between 2 – 20

MPa/s. In the plastic field, constant strain rate

condition has been chosen because standards

require specifically for this type of control, and

recommend that strain rate doesn't exceed

0,0025 1/s. The switch between stress rate

control and strain rate control is performed at

1,5% of elongation.

Pic. 4 – Biaxial testing equipment

Performing these tensile tests with biaxial

gauge allow to determinate many different

parameters, which are very important to

predict the plastic behavior of the material:

- General tensile properties (Rp, Rm, A80,

Agt, E modulus)

- Poisson coefficient in elastic field and in

plastic field (νEL and νPL)

- Strain hardening exponent and strain

hardening coefficient (n and K)

- Plastic strain ratio index (r, planar

anisotropy, normal anisotropy)

- Strain-rate sensitivity coefficient and

strain hardening coefficient (m and C)

In order to obtain complete information about

plastic behavior of the alloy, also some

Erichsen cupping tests (performed according

to ISO 20482 [5]) have been executed.

The obtained results, which for every

characteristic are calculate as mean value of

three tests, are listed in the following

paragraphs.

4

3.1 General tensile properties

The collections of data obtained during testing

are listed in the sequel (Table 3, 4 and 5).

Young’s modulus is evaluated using the

method called “Cord Modulus”; this

calculation determines the slope of the

stress/strain curve using two specific points on

the diagram. Furthermore, a straight line

between this lower and upper bounds

previously chosen is constructed. The two

boundaries are different for every material,

because the extension of the elastic field is

not constant. Furthermore, to evaluate Yield

strength limit (Rp0,2) we use the method called

“Offset Yield”. Basically the offset yield

calculation constructs a line parallel to the line

detected for evaluating E modulus and than

offset it by an amount that you specify. In our

case the offset is 0,2% of initial length L0, and

the offset yield point is where the offset line

intersects the diagram σ−ε. Only material n°4

uses a different method because instead of

Rp0,2 the upper and lower limits REH and REL are

evaluated.

Table 3 – Tensile test in rolling direction (L)

Table 4 – Tensile test in diagonal direction (D)

Table 5 – Tensile test in transverse direction (T)

3.2 Poisson coefficient

According to the standard ASTM E132 [6],

Poisson coefficient ν is an absolute value of

the ratio between transverse strain and

longitudinal strain. Poisson's ratio is variable in

case the material is not isotropic; in our case

we evaluated it, according to standard, as the

ratio between the average transverse strain εt

and the average longitudinal strain εl using the

same range used for calculating E modulus

(variable for every material). Moreover, also a

single value of ν at 0,25% elongation has been

considered.

Also in the plastic field Poisson ratio has been

calculated using average value in the range

between 2% of elongation and Rm. The

obtained data are listed below.

Table 6 – Poisson ratio in rolling direction (L)

Table 7 – Poisson ratio in diagonal direction (D)

Table 8 – Poisson ratio in transverse direction (T)

Pic. 5 – Trend of Poisson Ratio (elastic and plastic field)

Rp0,2 (MP)

Rm

(MPa)

A80 (%)

Agt

(%) Rp/Rm

(--) E

(MPa) M1 293,2 414,9 35,3 15,5 0,706 100.719

M2 321,8 455,6 30,8 17,8 0,706 98.539

M3 291,5 415,0 35,7 18,5 0,702 92.674

M4 433,5 521,6 24,6 14,2 0,831 91.667

Rp0,2 (MP)

Rm

(MPa)

A80 (%)

Agt

(%) Rp/Rm

(--) E

(MPa) M1 325,6 389,1 33,6 9,6 0,836 101.405

M2 324,2 378,5 38,2 12,1 0,856 98.285

M3 297,6 381,1 41,3 13,9 0,781 96.091

M4 473,1 489,1 26,3 10,2 0,967 98.167

Rp0,2 (MP)

Rm

(MPa)

A80 (%)

Agt

(%) Rp/Rm

(--) E

(MPa) M1 336,5 393,8 27,5 7,8 0,854 103.230

M2 366,6 401,9 34,9 7,1 0,912 99.525

M3 297,1 390,3 36,3 8,6 0,761 94.534

M4 541,0 545,8 31,5 8,1 0,991 109.208

νννν0,25%

(--) ννννelastic

(MPa)

ννννplastic

(%)

M1 0,399 0,343 0,731

M2 0,343 0,300 0,562

M3 0,364 0,316 0,588

M4 0,315 0,321 0,435

νννν0,25%


(MPa)

ννννplastic

(%)

M1 0,395 0,356 0,796

M2 0,369 0,343 0,685

M3 0,405 0,314 0,710

M4 0,343 0,333 0,617

νννν0,25%


(MPa)

ννννplastic

(%)

M1 0,395 0,351 0,813

M2 0,389 0,333 0,737

M3 0,561 0,341 0,769

M4 0,335 0,322 0,655

5

3.3 Strain hardening exponent and coefficient

According to standards ISO 10275 [7] and

ASTM 646 [8], the strain hardening exponent

n is defined as the exponent of true plastic

strain in Hollomon equation, which describes

a relation between true stress σ and true

strain ε in the plastic region. This equation can

be taken as follows:

ε� (1)

Equation 1 can be transformed in logarithmic

one as follows:

(2)

Pic. 6 - Difference between true stress –true strain

curve and engineering stress – engineering strain curve

From a practical point of view, strain

hardening exponent “n” is the parameter that

provides an indication about the increase in

hardness and strength occurring during plastic

deformation of the material.

The n value has been calculated using a linear

regression of the logarithm of true stress vs.

the logarithm of true strain; the obtained

values are listed in Table 9.

Table 9 – Strain hardening exponent and coefficient

3.4 Plastic strain ratio index

A parameter than can be used to have an

impression of anisotropic properties of the

alloys is the ″plastic strain ratio″ r; according

to standards ISO 10113 [9] and ASTM E517

[10] this value is defined as follows:

��

�� (Lankford value) (3)

Where εw is the width strain and εt is the

transverse strain. Moreover, performing

tensile test with double extensimeter in

different direction (rolling direction 0°,

transverse direction 90°, diagonal direction

45°) and evaluating Lankford value in every

orientation, also other parameter are

definable as follow:

�0°+2�45°

+�90°

4 (normal anisotropy) (4)

∆��°��°

��°�

(planar anisotropy) (5)

Pic. 7- Normal and planar anisotropy [[[[Ref. 2]]]]

The obtained values are listed in Table 10.

Table 10 – Strain ratio index

ROLLING DIAGONAL TRANSVERSE

n (--)

K

(MPa)

n (--)

K

(MPa)

n

(--) K

(MPa) M1 0,138 629,9 0,104 550,8 0,087 534,5

M2 0,134 680,4 0,093 518,8 0,067 517,1

M3 0,139 623,3 0,103 533,6 0,080 520,5

M4 0,138 795,5 0,105 693,1 0,093 758,4

rL

(--) rD

(--)

rT

(--)

(--) ∆∆∆∆r (--)

M1 4,202 5,764 6,224 5,488 -0,551

M2 1,601 2,861 3,386 2,677 -0,367

M3 1,754 3,147 3,703 2,937 -0,418

M4 0,888 1,994 2,496 1,843 -0,302

6

3.5 Strain rate sensitivity

The rate at which strain is applied to the

tension specimen has an important influence

on the stress-strain curve. Strain rate should

be defined as follows:

= �ε

�� (6)

The strain-rate dependence of flow stress at

constant strain and temperature is given by:

σ = C· m

(7)

Where:

m = strain-rate sensitivity coefficient

C = strain hardening coefficient

In order to determine the strain rate

sensitivity, we use the speed change

performed at 1,5 % of elongation. In that

point, we change the test speed and also the

type of control of the machine from stress to

strain.

Pic. 8 - Rate change during test [[[[Ref. 2]]]]

The strain-rate sensitivity, at constant strain

and temperature, can be determined from

equation 8:

(��

��)

(�

�

)

(8)


Table 11 – Strain hardening exponent and coefficient

3.6 Erichsen cupping test

The tests have been performed using a

standard tool; the geometry of this tool is in

accordance with the prescription of standard

ISO 20482. According to standard, the

specimens have been slightly lubricated with a

graphite based lubricant; the speed of the

crosshead during the test has been kept

constant at 8 mm/min. The torque applied to

the two screws, which lock the specimen in

the correct position in 15 N·m, in order to

obtain a holding load equal to 10 KN.

Pic. 9 – Erichsen equipment


ROLLING TRANSVERSE

F (N)

E.I. (mm)

F (N)

E.I. (mm)

M1 18.920 7,773 20.122 7,995

M2 24.099 8,612 24.886 8,892

M3 24.123 10,257 24.494 10,514

M4 25.939 9,117 26.338 9,250

Table 12 – Erichsen cupping test results


m (--)

C

(MPa)

m (--)

C

(MPa)

m

(--) C

(MPa) M1 0,032 387,2 0,064 550,1 0,047 501,1

M2 0,032 426,2 0,037 441,8 0,056 580,8

M3 0,064 509,3 0,058 497,5 0,075 593,4

M4 0,027 487,6 0,049 465,5 0,051 598,2

7

4.0 CONCLUSION

The trials performed with a biaxial electronic

gauge had the purpose to investigate in depth

the plastic properties of the four materials

used by Akrapovič for deep drawed parts. The

performed trials allow finding a precise

relation between the experimental collected

values and the practical results obtained

during formability tests carried out in

production.

In order to investigate about plastic properties

of titanium heat resistant alloys, the best way

to take advantage by the series of data

collected during these trials is use them as

material data for some FEA (Finite Elements

Analysis) activities. In fact, FEA simulations are

important instruments in trying to predict

formability of materials. Anyway, the accuracy

of these numerical analysis depend on the

preciseness of the constitutive model used to

describe the behavior of the alloy; in case of

anisotropic materials, mathematical models

are just developed taking in account all the

plastic parameters evaluated during biaxial

tests, like Poisson and strain hardening

coefficients, plastic strain ratio and so on. For

simulating deep drawing, 3D parameter Barlat

equation has been chosen; this model was

developed by Barlat and Lian in 1989 for

modeling sheets with anisotropic behavior

loaded in plane stress condition [12].

According to this equation, the anisotropic

yield criterion Φ is defined in the following

equation (9):

� ��

� ��

��

σ��

Where: σY = yield stress

K1, K2 = principal values of stress

deviator

a, c = anisotropic material coefficient

(Calculated using r0, r45, r90)

m = Barlat coefficient depending on

type of lattice

This macroscopic yield criterion, expressed in

terms of the principal values of stress

deviator, has been used several times to

predict the anisotropic behavior of hexagonal

closed packet metals (i.e. titanium,

magnesium and zirconium alloys) obtaining

very good results. Using this model the

anisotropy of the material and the yielding

asymmetry between tension and compression

is perfectly represented [13].

The first trial actually under development is a

model for simulating Erichsen cupping test.

This choice has been made because Erichsen is

a symmetric model with a single axial load;

moreover, practical tests with this equipment

have been already carried out, and the

collection of experimental results is ready for

comparison with the theoretical results.

Pic. 10, 11 – FEA model of Erichsen cupping test

5.0 REFERENCES

1. G. Lutjering, J.C. Williams, Titanium – Springer,

second edition

2. T.L. Sullivan, Texture strengthening and

fracture toughness of titanium alloy sheet at

room and cryogenic temperature – N.A.S.A.

Technical Note D-4444

3. K.S. Chan, D.A. Koss, Deformation and fracture

of strongly textured Ti alloy sheet in uniaxial

tension – Office of Naval Research, technical

report n°19

8

4. EN 10002/1 - Metallic materials - Tensile

testing - Part 1: Method of test at ambient

temperature

5. ISO 20482 - Metallic materials - Sheet and

strip - Erichsen cupping test

6. ASTM E132 - Standard Test Method for

Poisson's Ratio at Room Temperature

7. ISO 10275 – Metallic materials - Sheet and

strip - Determination of tensile strain hardening

exponent

8. ASTM E646 – Standard Test Method for

Tensile Strain-Hardening Exponents (n-Values) of

Metallic Sheet Material

9. ISO 10113 – Metallic materials – Sheet and

strip – Determination of plastic strain ratio

10. ASTM 517 - Standard Test Method for

Plastic Strain Ratio r for Sheet Metal

11. ASM Metal Handbook Vol. 08 – Mechanical

testing and evaluation

12. F. Barlat, J. Lian, Plastic behavior and

stretchability of sheet metals, Part. 1: A function

for orthotropic sheet under plane stress

condition - International journal of plasticity,

Vol. 5 (1989) pp. 51-66

13. F. Barlat, O. Cazacu, B. Plunkett, Orthotropic

yield criterion for hexagonal closed packed

metals – International journal of plasticity 22

(2006)

6.0 CONTACTS

Dr. Eng. Silvia Gaiani

Akrapovič d.d.

Malo Hudo 8 – Ivancna Gorica (SLO)

[email protected]

TITANIUM 2008Las Vegas, Nevadag

21 – 24 September 2008

MECHANICAL CHARACTERIZATION OF HEAT RESISTANT TITANIUM ALLOYS

FOR AUTOMOTIVE APPLICATIONSDr. Eng. Silvia Gaiani

Akrapovič d.d. – Technology Supervisor

TITANIUM 2008Las Vegas NevadaLas Vegas, Nevada


In the last five years, the marketdemand of high performancedemand of high performancecars and bikes oblige vehiclesmanufacturer to design andproduce engines increasinglyp g g yextreme and powerful

This aspect obliges consequentlythe exhaust systems producersthe exhaust systems producersto use materials which presentawfully high mechanical andphysical characteristicsphysical characteristics



Titanium alloys have the following benefits:following benefits:

Low Density

Excellent Heat Resistance(low oxidation at elavated temperature)

Interesting Mechanical Properties

Weldability

TITANIUM 2008Las Vegas, Nevadag


Titanium alloys have the following problems:

High Manufactoring Costs

Poor Formability

TITANIUM 2008Las Vegas Nevada Formability problems of titanium are related to its Las Vegas, Nevada


Formability problems of titanium are related to its type of lattice, which is Hexagonal Close Packed (HCP)

HCP lattice shows the following singularity:

Properties ara related to the ratio between height and widthof the lattice (c/a ratio for Titanium is 1,587)( / )

Depending on c/a ratio, only 4 independentslip system are active, and they’re not enoughto allow plastic deformation (minimum 5)to allow plastic deformation (minimum 5)

To allow plastic deformation, also a systemwith a non-basal Burger vector must be

ti t d Th t it t ti t thiactivated. The oppurtunity to activate thisplane is tightly related to the direction ofthe load

If stress axis // to c axis → NO ACTIVATION

TITANIUM 2008Las Vegas, Nevada


TWINNING occours when two separate crystalsshare a part of the same lattice in a symmetricalshare a part of the same lattice in a symmetricalmanner. Deformation twinning is important forplasticity of the HCP metals, in some conditionsdepending from stress direction and temperature

TEXTURING is a preferential orientation of the

p g pis also predominant than dislocation slipping

crystallographic structure. Texture is mainlydeterminated from cold rolling conditions, heattreatments, alloying elements.

Because of the reasons mentioned above TitaniumBecause of the reasons mentioned above, Titaniumalloys exhibit a strong anisotropic behavior


21 – 24 September 2008 AKRAPOVIČ TECHNOLOGY

Tube Production Bending Hydroforming Deep Drawing

Welding Rolling Machining Surface Finishing



For the production of exhaust systems forbikes and cars Akrapovič d d uses sevenbikes and cars, Akrapovič d.d. uses sevendifferent types of titanium alloys.Some of these alloys are standard alloyslike Grade 2 Grade 5 Grade 9 and gradelike Grade 2, Grade 5, Grade 9 and grade37; other alloys are patented products.

Deep drawing and tube bending are thep g gtechnologies where titanium formabilityproblems are more noticeable.Therefore, on the four types of alloys, yp ymore used for these purposes, a completemechanical characterization has beencarried out in order to better understandcarried out in order to better understandthe behavior of these different materials.

TITANIUM 2008Las Vegas, Nevada UNIAXIAL TENSILE TESTSg

21 – 24 September 2008UNIAXIAL TENSILE TESTS

*REH instead that RP0 2

LONGITUDINAL → TRANVERSE

Rp raises

REH instead that RP0,2

Rp raises

Rm decreases

Total elongation is equal butTotal elongation is equal, butelongation at Rm is strongly reduced


21 – 24 September 2008 BIAXIAL TENSILE TESTS

Performing biaxial tensile tests, manyi t h t i ti b d t i t dimportan characteristic can be determinated:

General tensile properties Rp, Rm, A80, Agt, E

Poisson coefficient in elastic field νEL and inplastic field νPL

Strain hardening exponent n and strainhardening coefficient K

Plastic strain ratio index r, planar anisotropy ř, normal anisotropy Δr

Strain-rate sensitivity coefficient m and strain hardening coefficient C

To complete plastic properties characterizationp p p palso Erichsen cupping tests have beenperformed


21 – 24 September 2008GENERAL TENSILE PROPERTIES

Rp0,2

(MP)Rm

(MPa)A80

(%)Agt

(%)Rp/Rm

(--)E

(MPa)

LLIN

G

M1 293,2 414,9 35,3 15,5 0,706 100.719M2 321,8 455,6 30,8 17,8 0,706 98.539

RO

L M3 291,5 415,0 35,7 18,5 0,702 92.674M4 433,5* 521,6 24,6 14,2 0,831 91.667

GO

N

M1 325,6 389,1 33,6 9,6 0,836 101.405M2 324,2 378,5 38,2 12,1 0,856 98.285

DIA

G

M3 297,6 381,1 41,3 13,9 0,781 96.091M4 473,1* 489,1 26,3 10,2 0,967 98.167

AN

SV

M1 336,5 393,8 27,5 7,8 0,854 103.230M2 366,6 401,9 34,9 7,1 0,912 99.525

TR

A M3 297,1 390,3 36,3 8,6 0,761 94.534M4 541,0* 545,8 31,5 8,1 0,991 109.208

*REH instead that RP

TITANIUM 2008POISSON COEFFICIENT Las Vegas, Nevada

21 – 24 September 2008POISSON COEFFICIENT

Poisson Coefficient: ν =

Poisson's ratio is variable in case thematerial is not isotropic; in elastic field it isthe mean value in the same range used togcalculate E modulus (variable for everymaterial). Moreover, also a single value ofν at 0,25% elongation has beenconsidered.In plastic field is the mean value between2% and Rm peak.

ROLLING DIAGONAL TRANSVERSEν0,25%

(--)νelastic

(MPa)νplastic

(%)ν0,25%

(--)νelastic

(MPa)νplastic

(%)ν0,25%

(--)νelastic

(MPa)νplastic

(%)M1 0,399 0,343 0,731 0,395 0,356 0,796 0,395 0,351 0,813M2 0,343 0,300 0,562 0,369 0,343 0,685 0,389 0,333 0,737M3 0,364 0,316 0,588 0,405 0,314 0,710 0,561 0,341 0,769M4 0,315 0,321 0,435 0,343 0,333 0,617 0,335 0,322 0,655

TITANIUM 2008 S G OTITANIUM 2008Las Vegas, Nevada


STRAIN HARDENING EXPONENT ANDSTRAIN HARDENING COEFFICIENT

Hollomon Equation:

I l ith i l In logarithmic scale:

ROLLING DIAGONAL TRANSVERSEn K n K n K

(--) (MPa) (--) (MPa) (--) (MPa)M1 0,138 629,9 0,104 550,8 0,087 534,5M2 0,134 680,4 0,093 518,8 0,067 517,1M3 0 139 623 3 0 103 533 6 0 080 520 5M3 0,139 623,3 0,103 533,6 0,080 520,5M4 0,138 795,5 0,105 693,1 0,093 758,4

TITANIUM 2008Las Vegas Nevada PLASTIC STRAIN RATIO INDEX Las Vegas, Nevada

21 – 24 September 2008PLASTIC STRAIN RATIO INDEX

Plastic Strain Ratio:

N l i tNormal anisotropy:

Planar anisotropy:

rL

(--)rD

(--) rT

(--)ř

(--)Δr(--)( ) ( ) ( ) ( ) ( )

M1 4,202 5,764 6,224 5,488 -0,551M2 1,601 2,861 3,386 2,677 -0,367M3 1 754 3 147 3 703 2 937 -0 418M3 1,754 3,147 3,703 2,937 -0,418M4 0,910 1,994 2,515 1,853 -0,281

TITANIUM 2008Las Vegas Nevada STRAIN-RATE SENSITIVITY COEFFICIENT

=

Las Vegas, Nevada21 – 24 September 2008

STRAIN RATE SENSITIVITY COEFFICIENT

=Strain rate:

Strain-rate equation: σ=C ·

Strain-rate sensitivity:

In order to determinethe strain rate


m( )

C(MPa)

m( )

C(MPa)

m( )

C(MPa) sensitivity, the speed

change performed at1,5 % of elongationh b d

(--) (MPa) (--) (MPa) (--) (MPa)M1 0,032 387,2 0,064 550,1 0,047 501,1M2 0,032 426,2 0,037 441,8 0,056 580,8M3 0 064 509 3 0 058 497 5 0 075 593 4 has been used.M3 0,064 509,3 0,058 497,5 0,075 593,4M4 0,027 487,6 0,049 465,5 0,051 598,2

TITANIUM 2008Las Vegas Nevada ERICHSEN CUPPING TESTS Las Vegas, Nevada


ERICHSEN CUPPING TESTS

According to standard, the speed of thecrosshead during the test has been keptconstant at 8 mm/min. The torque applied tothe two screws, which lock the specimen inth t iti i 15 N i d tthe correct position in 15 Nm, in order toobtain a holding load equal to 10 KN.

ROLLING TRANSVERSEROLLING TRANSVERSEF

(N)E.I.

(mm)F

(N)E.I.

(mm)M1 18.920 7,773 20.122 7,995M2 24.099 8,612 24.886 8,892M3 24.123 10,257 24.494 10,514M4 25.939 9,117 26.338 9,250



All the information collected with biaxiall testing are used for FEA simulation testing are used for FEA simulation

To describe anisotropic behavior of Titanium ll th h th ti l d l i th alloys, the chosen mathematical model is the

3D parameter BARLAT equation.This equation describe yielding condition as follow:follow:

The first simulation test is Erichsen cupping test, in order to able to compare theoretical and experimental resultsp

TITANIUM 2008Las Vegas Nevada THERMAL PROPERTIES DETERMINATIONLas Vegas, Nevada


To investigate about thermal properties and

THERMAL PROPERTIES DETERMINATION

oxidation resistance of different alloys, also somedurability test are performed on a roller bench

Using an infrared thermal camera, all thetemperature variations occuring during theaccelerated durability test performed on a specialaccelerated durability test performed on a specialbench can be evaluated in real time

TITANIUM 2008Las Vegas Nevada MICROSTRUCTURAL EXAMINATIONSLas Vegas, Nevada

21 – 24 September 2008MICROSTRUCTURAL EXAMINATIONS

On parts submitted to funcionality and durability test,

i t t l microstructural and grain size examinations are normally are normally performed in order to guarantee guarantee quality and reliability of the exhaust systemsy



Defects measurments and examinations

TITANIUM 2008Las Vegas Nevada

MACROSCOPIC EXAMINATION OF WELDSLas Vegas, Nevada


Härteverlauf über Schweißnähte

240

Härte HV 0,5 über Schweißnaht 8 Härte HV 0,5 über Schweißnaht 12

GEOMETRY AND MICROARDNESS MEASURMENT

140

160

180

200

220

Härt

e HV

0,5

100

120

0,00 1,00 2,00 3,00 4,00 5,00 6,00 7,00 8,00 9,00 10,00 11,00 12,00 13,00 14,00

Weg x in mm



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