Method of measurement and determination on fracture toughness of structural materials at high temperature

Patent metadata

Field	Value
Publication number	US-9939359-B2
Application number	US-201414915659-A
Country	US
Kind code	B2
Filing date	Sep 25, 2014
Priority date	Sep 25, 2014
Publication date	Apr 10, 2018
Grant date	Apr 10, 2018

Abstract

Disclosed is a method of measurement and determination on fracture toughness of structural materials at high temperature, comprising: preliminary assessing the ductility of a material based on a high-temperature uniaxial tensile test and the fracture characteristic; designing and manufacturing a CT specimen; conducting a monotonic loading fracture test on the CT specimen at high temperature; modifying a load-displacement curve output by a testing machine; determining a passivation coefficient M for the crack of the structural material; reversely recursing instant load-displacement data pairs corresponding to the instant crack length; calculating a J_R crack extension resistance curve of the tensile test; examining the validity of the J_R crack extension resistance curve and the fracture toughness J IC ; calculating the fracture toughness per equivalent of the structural material K IC . The present invention overcomes the difficulty of placing an extensometer inside a high-temperature furnace.

First claim

What is claimed is:

1. A method of measurement and determination on fracture toughness of structural materials at high temperature, comprising the steps of:
conducting a high-temperature tensile test on a standard tensile specimen of a structural material to obtain high-temperature tensile mechanical properties of the structural material, and determining that the structural material exhibits a ductile fracture behavior;
preliminarily estimating the fracture toughness K IC of a compact tension (CT) specimen of the structural material at high temperature to obtain width (W) and thickness (B) of the CT specimen, wherein,

J
IC

=

K
IC
2

⁡

(

1
-

v
2

)

E

,

⁢

W
=

a
0

+

b
0

≥

2
×
10
⁢

⁢

J
IC

⁢

/

⁢

σ
Y

,

⁢

σ
Y

=

(

σ
ys

+

σ
uts

)

2

,

⁢

2
≤

W
⁢

/

⁢
B

≤
4

E, v stand for elastic modulus and Poisson ratio of the structural material respectively, the unit of E is MPa; a 0 , b 0 stand for initial average crack length and initial ligament size of the CT specimen respectively, the unit is mm, σ ys , σ uts stand for yield strength and tensile strength of the structural material respectively, the unit is MPa;
inducing a fatigue crack with a length of 1.0˜2.0 mm on the CT specimen through a high frequency fatigue testing machine, then grooving a side slot with a depth of 10% B at both sides of the CT specimen with a crack surface along the thickness direction;
measuring the thickness (B) and width (W) of the CT specimen, and placing the CT specimen into a heating equipment with a furnace having an upper, lower and middle part, and heating;
turning on an INSTRON or MTS testing machine, monotonic loading the CT specimen, and obtaining a load-displacement curve of the CT specimen by a load displacement transmission device on the testing machine;
cooling the CT specimen to room temperature, opening the furnace's cavity, tensing the CT specimen till fracture through a testing machine, then measuring an initial crack length a 0 i and a final average crack length a f i at nine spots on the crack surface by an optical microscopy or a camera to obtain an initial average crack length a 0 and a final crack length a f of the crack, wherein,

a
0

=

1
8

⁡

[

1
2

⁢

(

a
0
1

+

a
0
9

)

+

∑

i
=
2

8

⁢

⁢

a
0
i

]

,

⁢

a
f

=

1
8

⁡

[

1
2

⁢

(

a
f
1

+

a
f
9

)

+

Assignees

• Univ East China Science & Tech
• Shanghai Electric Power Equipment Co Ltd Shanghai Steam Turbine Factory

Inventors

• Xuan Fuzhen
• Wang Haitao
• Wang Qiongqi
• Mei Linbo
• Liu Xia
• Huang Yuhui

Classifications

• G01N3/18 Primary

  Performing tests at high or low temperatures · CPC title

• G01N2203/0069

  Fatigue, creep, strain-stress relations or elastic constants · CPC title

• G01N3/00

  Investigating strength properties of solid materials by application of mechanical stress · CPC title

• G01N2203/006

  Crack, flaws, fracture or rupture · CPC title

• G01N2203/0017

  Tensile · CPC title