ASTM E 399 – 90

Properties and Testing of Materials

Determination of Fracture Toughness “Plane-Strain Fracture Toughness of Metallic Materials”

Toughness •

Toughness measurement by calculating the area under the stress-strain curve from static tests

•

Material fractures occur by progressive cracking

Stress Concentration at crack tip by Photo-elasticity

Notch Toughness 

Defined as “the ability of a material to absorb energy”, (usually when loaded dynamically) in the presence of a flaw

Laboratory measurement of impact energy by 

Char Charp py test test (V-n (V-not otch ch impa impact ct sp spec ecim imen en))



Izod Izod test test



Dyna Dynami micc tear tear tes estt …

The general purpose of the various kinds of notchtoughness tests is to model the behavior of actual structures so that the labora laboratory tory test results can be used to predict service performance.

Impact Energy Introduction 

Hardness

Strength



Impa Impact ct Ener Energy gy

Toughness

Laboratory measurement of impact energy 

Char Charp py tes estt



Izod test



…

Impact Energy



Charpy test

Charpy Impact Test Stress concentrating notch

Sensitivity of Impact Test Data

•

Test conditions

•

Notch sharpness

•

Nature of stress concentration at notch tip

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Test tempe temperature rature

•

Internal atomic structure of the material

Sensitivity of Impact Test Data

Ductile to brittle transition temperature Most structural steels can fail in either a ductile ductil e or brittle manner depending on several conditions such as temperature, loading rate, and constraint. Ductile fractures are generally preceded by large amounts of plastic deformation and usually occur at 45 ° to the direction of the applied a pplied stress. Brittle or cleavage fractures generally occur with w ith little plastic deformation and are usually normal to the direction of the principal stress.

Ductile to brittle transition temperature Why is it of great practical importance??? Lose s toughness and it is susceptible •Alloy Loses to catastrophic failure below this transition temperature •It is a design criterion of great importance. Several disastrous failures of ships occurred because of this phenomenon.

Plane stress & Plane strain

 1s  E s   s xx

s ZZ



1 s

E



x

(    )

0

s xx

s

s yy

  s yy

1 s

E

( yy    xx ) s

s

s

Microscopic Fracture Surface

Fracture Toughness oughness Fracture Toughness the most widely w idely used material property “single parameter” from fracture mechanics”. It is represented by the symbol KIC, defined as “The critical value of the stress intensity factor at crack tip necessary to produce catastrophic failure under simple uni-axial loading. loading .

Fracture Toughness oughness The value of Fracture Fract ure Toughness Toughness is given by: (1)

Y

is a dimensionless geometry factor f is the overall applied stress at failure a is the length of the surface crack or one half of an internal crack KIc have the units of MPa m ( for plane strain conditions in which the specimen thickness is comparatively large ).

Fracture Toughness oughness KIc (plane strain condition conditions). s). Kc (plane stress conditions conditions). ). ASTM E 399

Failure Modes by cracking

Types of relative movements of two crack surfaces

The opening mode, Mode I

The sliding or shear mode, Mode II The tearing mode, Mode III The stress field at the crack tip can be be treated as one or a combination of

Failure Modes by cracking

Typical Fracture Toughness values

KIc Fracture toughness K Ic represents the inherent ability of a material to withstand a given stress-field intensity at the tip of a crack and to resist progressive tensile crack extension unde underr plan planee-st stra rain in cond condit itio ions ns.. K Ic represents the fracture toughness of the material and has units of (MN/m3/2).

KIc Fracture toughness Is the material-toughness property depends on the particular material, load loadin ing g ra rate te,, and and cons consttra rain intt as follo ollows ws:: K c = critical stress-intensity factor for static loading and plane-stress condit nditiions of variable constraint. Thus, this value depends on specimen thic thickn knes ess s and and geom geomet etry ry& & cr crac ack k si size ze.. K Ic = critical-stress-intensity factor for static loading and plane-strain conditions of maximum constraint. Thus, this value is a minimum value for for thic thick k plat plates es.. K Id = cr crit itic ical al--stre stress ss-i -int nten ensi sity ty fac acto torr for for dyna dynami mic c (imp (impac act) t) load loadin ing g and and pla lane ne-stra strain in cond condit itio ions ns of maxi maximu mum m cons constr trai aint nt..

KIc Fracture toughness K c , K Ic , or K Id = C

a,

C = constant, function of specimen and crack cr ack geom geomet etry ry,, = nominal stress, ksi (MN/m2), a = flaw size, in. (mm).

Experimental Experimental determination of KIc

KIC test procedure 1 – Determine critical specimen size dimensions 2 – Select a test specimen and prepare shop drawing 3 – Fatigue crack the test specimen (by cyclic loading) loadin g) 4- Obtain test test fixtures fixtures and displacement displacement gauges gauges

5- Alignment, positioning of loads, loading loadin g rate, friction, eccentricity, eccentricity, … 6- Test record record of the load displacement. displacement.

7- Measurements Measurements of specimen dimensions and fractures fractures to calculate calculate KQ (B, S, W, a). 8- Analy Analysis sis of P- records. 9- Calcul Calculatio ation n of conditi conditional onal KIc (KQ ).

KIC test procedure 1 – Determine critical specimen size dimensions

a  crack depth

 K Ic    2.5      ys 

 K Ic  I c  B  Specimen thickness  2.5      ys  W  Specimen depth

 K Ic  I c   5.0      ys 

2

2

2

CTS, Slow bend Specimens Specimens

KIC test procedure 2 – Select a test specimen and prepare shop drawing

Specimen Design

KIC test procedure 3 – Fatigue crack the test specimen (by cyclic loading)

KIC test procedure

4- Obtain Obtain test fixtures fixtures and displacement displacement gauges gauges 5- Alignment, positioning of loads, loading loading rate, rate, friction, eccentricity, eccentricity, …

Gauges for CTS

Gauges for Slow bend test specimen

Testing Machine

Tensile cracking experimental setup setu p Instron Instron Screw Screw Machine Machine Pin grips

PC MTS Extensometer AE sensor

AE System

Fracture Toughness Specimens

KIC test procedure 6- Test recor record d of the load displacement. displacement. 7- Measuremen Measurements ts of specimen dimensions and fractures to calculate KQ (B, S, W, a). 8- Anal Analys ysis is of of P- records. 9- Calcula Calculation tion of of conditio conditional nal KIc (KQ ).

Load – Displacement Curve

P- test record 5% offset line

Determination of P Q

KIC test procedure Calculation of conditional conditional K IC (KQ ) for SBTS • Calculation 1 3 5 7 9   PQ S 2 2 2 2 2 a a a a a           2.9     4 . 6 21 . 8 37 . 6 38 . 7 K Q            3   W   W   W   W   B W 2   W  

• PQ = Load as determined • B = Thickness of specimen • S = Span length • W = Depth of specimen • a = Crack length as determined

KIC test procedure • Calculation of conditional KIC (KQ ) for CTS K Q 

PQ B W

1

2

1 3 5 7 9   2 2 2 2 2 a   a   a   a   a  29.6   185.5   655.7  1017.0   638.9     W   W   W   W   W    

• PQ = Load as determined • B = Thickness of specimen • W = Width of specimen • a = Crack length as determined

ASTM E 399 – 90 Plane-Strain Fracture Toughness of Metallic Materials

1- This test method covers the determination determination of the plane strain strain fracture fracture toughness (K Ic) of metallic materials by tests using a variety of fatigue-cracked specimens having a thickness of 0.063 in. (1.6 mm) or greater. 2- This test method also covers the determination of the specimen specimen strength ratio Rsx where x refers refers to the specific specimen configuration being tested. This strength strength ratio is a function of the t he maximum load the specimen can sustain, its initial dimensions and the yield strength of the material. 3- This test method is divided into two main parts. The first first part gives general information information concerning the recommendations recommendations and requirements for K Ic testing. The second part is composed of annexes that give the displacement gage design, fatigue cracking procedures, and special requirements for the various specimen configurations covered covered by this method. In addition, an annex is provided for the specific procedures to be followed in rapid-load rapid-load plane-strain fracture toughness tests.






ASTM C1018 Flexural Toughness Toughness and First Crack Strength of Fiber Reinforced Concrete (Using Beam W ith Third Point Loading)





RILEM 50-FMC Determination of the Fracture Energy of Mortar and Concrete by Means of Three-Point Bend Tests on Notched Beams

Alig.

G f 

(W 0  mg  0 )

Alig .

 N  J   m  m 2    

W0 = area under the load – deflection curve (N/m) m = m1 + m2 δ = deformation at the final failure of the beam (m) Alig. = area of the ligament at mid span (m 2)

Thanks

ASTM E 399 – 90

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