Post on 28-Oct-2014
Properties and Testing of Materials
خواص واختبار المواد
بسم اهلل الرحمن الرحيم
Determination of Fracture Toughness“Plane-Strain Fracture Toughness of Metallic Materials”
متانة االنهيارتعيين
Toughness
• Toughness measurement by calculating the area under the stress-strain curve from static tests
• Material fractures occur by progressive cracking
Notch Toughness
Defined as “the ability of a material to absorbenergy”, (usually when loaded dynamically) in thepresence of a flaw
Laboratory measurement of impact energy by
Charpy test (V-notch impact specimen)
Izod test
Dynamic tear test …
The general purpose of the various kinds of notch-toughness tests is to model the behavior of actual structures so that the laboratory test results can be used to predict service performance.
Impact Energy
Introduction
Hardness Strength
Impact Energy Toughness
Laboratory measurement of impact energy
Charpy test
Izod test
…
Sensitivity of Impact Test Data
• Test conditions
• Notch sharpness
• Nature of stress concentration at notch tip
• Test temperature
• Internal atomic structure of the material
Ductile to brittle transition temperature
Most structural steels can fail in either a ductile 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 stress.
Brittle or cleavage fractures generally occur with 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???
•Alloy Loses toughness and it is susceptible
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.
Fracture Toughness
Fracture Toughness the most widely 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.
Fracture Toughness
The value of Fracture 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 MPam ( for plane strain conditions in which the
specimen thickness is comparatively large ).
Fracture Toughness
KIc (plane strain conditions).
Kc (plane stress conditions).
ASTM E 399
Failure Modes by cracking
Types of relative movements of two crack surfaces
Failure Modes by cracking
The opening mode,
Mode I
The sliding or shear mode, Mode II
The stress field at the crack tip can be treated as one or a combination of
the three basic types of stress fields
The tearing mode,
Mode III
KIc 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
under plane-strain conditions.
KIc 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,
loading rate, and constraint as follows:
Kc = critical stress-intensity factor for static loading and plane-stress
conditions of variable constraint. Thus, this value depends on specimen
thickness and geometry& crack size.
KIc = critical-stress-intensity factor for static loading and plane-strain
conditions of maximum constraint. Thus, this value is a minimum value
for thick plates.
KId = critical-stress-intensity factor for dynamic (impact) loading and plane-
strain conditions of maximum constraint.
KIc Fracture toughness
Kc, KIc, or KId = C a ,
C = constant, function of specimen and
crack geometry,
= nominal stress, ksi (MN/m2),
a = flaw size, in. (mm).
KIc Fracture toughness
KIC test procedure
1 – Determine critical specimen size dimensions
2 – Select a test specimen and prepare shop drawing3 – Fatigue crack the test specimen (by cyclic loading)
4- Obtain test fixtures and displacement gauges
5- Alignment, positioning of loads, loading rate, friction, eccentricity, …
6- Test record of the load displacement.
7- Measurements of specimen dimensions and fractures to calculate KQ
(B, S, W, a).
8- Analysis of P- records.
9- Calculation of conditional KIc (KQ).
KIC test procedure
1 – Determine critical specimen size dimensions
2
2
2
0.5
5.2
5.2
ys
Ic
ys
Ic
ys
Ic
KdepthSpecimenW
KthicknessSpecimenB
Kdepthcracka
KIC test procedure
4- Obtain test fixtures and displacement gauges
5- Alignment, positioning of loads, loading rate, friction, eccentricity, …
Tensile cracking experimental setup
Instron Screw Machine
PC
AESystem
Pin grips
MTSExtensometer
AEsensor
KIC test procedure
6- Test record of the load displacement.
7- Measurements of specimen dimensions and fractures to calculate KQ (B, S, W, a).
8- Analysis of P- records.
9- Calculation of conditional KIc (KQ).
KIC test procedure
• Calculation of conditional KIC (KQ) for SBTS
2
9
2
7
2
5
2
3
2
1
23
7.386.378.216.49.2W
a
W
a
W
a
W
a
W
a
WB
SPK
Q
Q
• 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
2
9
2
7
2
5
2
3
2
1
21
9.6380.10177.6555.1856.29W
a
W
a
W
a
W
a
W
a
WB
PK
Q
Q
• PQ = Load as determined
• B = Thickness of specimen
• W = Width of specimen
• a = Crack length as determined
ASTM E 399 – 90Plane-Strain Fracture Toughness of Metallic Materials
1- This test method covers the determination of the plane strain fracture toughness (KIc) 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 strength ratio Rsx where x refers to the specific specimen configuration being tested. This strength ratio is a function of the 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 part gives general information concerning the recommendations and requirements for KIc 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 by this method. In addition, an annex is provided for the specific procedures to be followed in rapid-load plane-strain fracture toughness tests.
ASTM C1018
Flexural Toughness and First Crack Strength of Fiber Reinforced Concrete (Using Beam With
Third Point Loading)
ASTM C1018
Flexural Toughness and First Crack Strength of Fiber Reinforced Concrete (Using Beam With
Third Point Loading)
ASTM C1018
Flexural Toughness and First Crack Strength of Fiber Reinforced Concrete (Using Beam With
Third Point Loading)
ASTM C1018
Flexural Toughness and First Crack Strength of Fiber Reinforced Concrete (Using Beam With
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
2
.
00 )(
m
J
m
N
A
mgWG
lig
f
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 (m2)
Alig.