MATLS 3M03 Final Exam| questions and answers | latest update
What are some examples of flaws/imperfections of - Casting Defects (Result of shrinkage of metal during solidification/release of
materials? gases dissolved in the liquid metal. Control methods include x-ray)
- Machining (i.e. Surface Tear). Control using fluorescent dye inspection.
- Operational (Visual control/inspection required)
How do defects impact the stress experienced on a Defects in the material are obstacles for flow. Lines get denser in the region
near material? How does this compare to the yeild stress of the the defect. The local stress concentration increases.
material
As the crack tip radius (row) decreases, the stress at the tip increases significantly.
As the crack radius (a) increases past the tolerable crack size, the material can
fracture at a stress lower than the yield stress
, What is Griffiths criterion? Are there limitations? The criterion is the energy associated with the advancement of the crack per
unit area of the crack.
The region of material within a semicircle radius of a is considered stress-free.
When the crack advances by a delta a, the new volume shown in red becomes
stress free.
This is only applicable to brittle materials, since metals range in a Griffiths
criterion of 100-1000 J/m^2, whereas glass is a constant 10 J/m^2.
What is the irwin-orowan modification? There is a plastic region (a blue-hatched region) of size rp at the tip of the crack
that contributes to the high Gc in metals. When the crack advances by delta a, the
plastic region follows, and the new region of the material undergoes plastic
deformation (the red-hatched region).
Essentially, the size of the plastic zone (rp) is linked to the material yield strength.
What is the difference between the shape factor in an
infinite plate vs. a finite plate?
What orientation of the crack in a material produces the When the crack is normal to applied stress. Stress is proportional to
cos^2(alpha). highest experienced stress.
What is toughening in terms of toughness mechanics? Increasing the work required for crack propagation.
For Metals and Composites: Stronger, brittle materials are less tough, and weaker, more ductile materials
are more tough. Thus, stronger materials have a smaller plastic zone and more
tough
- Which types of materials have a larger plastic zone (rp)? materials have a higher plastic zone.
- How does rp contribute to fracture toughness of the The size of the plastic zone (rp) is proportional to
Gc. materials?
TLDR: rp and Gc decrease due to higher material strength and lower fracture
toughness.
What are some examples of flaws/imperfections of - Casting Defects (Result of shrinkage of metal during solidification/release of
materials? gases dissolved in the liquid metal. Control methods include x-ray)
- Machining (i.e. Surface Tear). Control using fluorescent dye inspection.
- Operational (Visual control/inspection required)
How do defects impact the stress experienced on a Defects in the material are obstacles for flow. Lines get denser in the region
near material? How does this compare to the yeild stress of the the defect. The local stress concentration increases.
material
As the crack tip radius (row) decreases, the stress at the tip increases significantly.
As the crack radius (a) increases past the tolerable crack size, the material can
fracture at a stress lower than the yield stress
, What is Griffiths criterion? Are there limitations? The criterion is the energy associated with the advancement of the crack per
unit area of the crack.
The region of material within a semicircle radius of a is considered stress-free.
When the crack advances by a delta a, the new volume shown in red becomes
stress free.
This is only applicable to brittle materials, since metals range in a Griffiths
criterion of 100-1000 J/m^2, whereas glass is a constant 10 J/m^2.
What is the irwin-orowan modification? There is a plastic region (a blue-hatched region) of size rp at the tip of the crack
that contributes to the high Gc in metals. When the crack advances by delta a, the
plastic region follows, and the new region of the material undergoes plastic
deformation (the red-hatched region).
Essentially, the size of the plastic zone (rp) is linked to the material yield strength.
What is the difference between the shape factor in an
infinite plate vs. a finite plate?
What orientation of the crack in a material produces the When the crack is normal to applied stress. Stress is proportional to
cos^2(alpha). highest experienced stress.
What is toughening in terms of toughness mechanics? Increasing the work required for crack propagation.
For Metals and Composites: Stronger, brittle materials are less tough, and weaker, more ductile materials
are more tough. Thus, stronger materials have a smaller plastic zone and more
tough
- Which types of materials have a larger plastic zone (rp)? materials have a higher plastic zone.
- How does rp contribute to fracture toughness of the The size of the plastic zone (rp) is proportional to
Gc. materials?
TLDR: rp and Gc decrease due to higher material strength and lower fracture
toughness.
