Fracture and Failure Theory. Defining Failure Failure can be defined in a variety of ways: Unable to...
-
Upload
luis-wicker -
Category
Documents
-
view
216 -
download
0
Transcript of Fracture and Failure Theory. Defining Failure Failure can be defined in a variety of ways: Unable to...
![Page 1: Fracture and Failure Theory. Defining Failure Failure can be defined in a variety of ways: Unable to perform the to a given criteria Fracture Yielding.](https://reader036.fdocuments.us/reader036/viewer/2022062421/56649c855503460f9493bcd5/html5/thumbnails/1.jpg)
Fracture and Failure Theory
![Page 2: Fracture and Failure Theory. Defining Failure Failure can be defined in a variety of ways: Unable to perform the to a given criteria Fracture Yielding.](https://reader036.fdocuments.us/reader036/viewer/2022062421/56649c855503460f9493bcd5/html5/thumbnails/2.jpg)
Defining Failure
Failure can be defined in a variety of ways: Unable to perform the to a given
criteria Fracture Yielding …… ……
![Page 3: Fracture and Failure Theory. Defining Failure Failure can be defined in a variety of ways: Unable to perform the to a given criteria Fracture Yielding.](https://reader036.fdocuments.us/reader036/viewer/2022062421/56649c855503460f9493bcd5/html5/thumbnails/3.jpg)
Failure of Structural Materials
Yielding is often considered “impending failure” The deformations associated with
yield provide a warning The service life is effectively ended if
a materials yields under service, in most cases.
![Page 4: Fracture and Failure Theory. Defining Failure Failure can be defined in a variety of ways: Unable to perform the to a given criteria Fracture Yielding.](https://reader036.fdocuments.us/reader036/viewer/2022062421/56649c855503460f9493bcd5/html5/thumbnails/4.jpg)
Tresca Yield Criterion
Ductile Materials Assumes slip occurs
during yielding
“yielding begins when max. shear stress reaches the shear stress obtained in a simple tension test at yield”
max= (σ1 –σ2)/2
![Page 5: Fracture and Failure Theory. Defining Failure Failure can be defined in a variety of ways: Unable to perform the to a given criteria Fracture Yielding.](https://reader036.fdocuments.us/reader036/viewer/2022062421/56649c855503460f9493bcd5/html5/thumbnails/5.jpg)
Tension in x and y directions
xy
![Page 6: Fracture and Failure Theory. Defining Failure Failure can be defined in a variety of ways: Unable to perform the to a given criteria Fracture Yielding.](https://reader036.fdocuments.us/reader036/viewer/2022062421/56649c855503460f9493bcd5/html5/thumbnails/6.jpg)
Tension in x and y directions
xy
![Page 7: Fracture and Failure Theory. Defining Failure Failure can be defined in a variety of ways: Unable to perform the to a given criteria Fracture Yielding.](https://reader036.fdocuments.us/reader036/viewer/2022062421/56649c855503460f9493bcd5/html5/thumbnails/7.jpg)
von Mises Yield Criterion
Separates “hydrostatic pressure” from “distortion stresses”Bases on “Energy of distortion is equal to energy of distortion at yield of a simple tension test”
2231
232
221 2 y
![Page 8: Fracture and Failure Theory. Defining Failure Failure can be defined in a variety of ways: Unable to perform the to a given criteria Fracture Yielding.](https://reader036.fdocuments.us/reader036/viewer/2022062421/56649c855503460f9493bcd5/html5/thumbnails/8.jpg)
Comparison of Theories
![Page 9: Fracture and Failure Theory. Defining Failure Failure can be defined in a variety of ways: Unable to perform the to a given criteria Fracture Yielding.](https://reader036.fdocuments.us/reader036/viewer/2022062421/56649c855503460f9493bcd5/html5/thumbnails/9.jpg)
Surface Energy and Fracture
Energy required to generate new surfaces
Griffith crack theory Crack will propagate if elastic strain
energy is equal to energy of newly created surface
![Page 10: Fracture and Failure Theory. Defining Failure Failure can be defined in a variety of ways: Unable to perform the to a given criteria Fracture Yielding.](https://reader036.fdocuments.us/reader036/viewer/2022062421/56649c855503460f9493bcd5/html5/thumbnails/10.jpg)
2a
r
Kr
2
1
rr
Real Distribution
Plastic Zone
![Page 11: Fracture and Failure Theory. Defining Failure Failure can be defined in a variety of ways: Unable to perform the to a given criteria Fracture Yielding.](https://reader036.fdocuments.us/reader036/viewer/2022062421/56649c855503460f9493bcd5/html5/thumbnails/11.jpg)
Stress Intensity
The Stress Intensity Factor is a constant that defines the stress distribution near a crack
2a
r
Kr
2
1
rr
FactorIntensity Stress 1 aK
r
Kr
2
1
r = distance from crack tip.
![Page 12: Fracture and Failure Theory. Defining Failure Failure can be defined in a variety of ways: Unable to perform the to a given criteria Fracture Yielding.](https://reader036.fdocuments.us/reader036/viewer/2022062421/56649c855503460f9493bcd5/html5/thumbnails/12.jpg)
Fracture Toughness, KIc
Fracture toughness, KIc
Material property Used to predict the crack size that can be
tolerated c = KIc/(a)1/2
KIc increases with thickness KIc decreases with temperature
increase
![Page 13: Fracture and Failure Theory. Defining Failure Failure can be defined in a variety of ways: Unable to perform the to a given criteria Fracture Yielding.](https://reader036.fdocuments.us/reader036/viewer/2022062421/56649c855503460f9493bcd5/html5/thumbnails/13.jpg)
Stress Concentrations
Stress risers occur at discontinuities
SCF is related to hole shape and size 2a
rr
max
ave
Factorion Concentrat Stress ave
max
TK