Chapter 8: Failure Flashcards
Ductile metals exhibit———plastic deformation with———energy absorption before fracture.
A.) substantial, high
B.) little, low
C.) substantial, low
A.) substantial, high
A stable crack will extend with———in the applied stress.
- no change
- a decrease
- an increase
An increase
Ductile fracture requires———strain energy compared to brittle fracture.
- higher
- lower
- equivalent
Higher
What type of fracture is this?
A mode of fracture attended by extensive gross plastic deformation
Ductile Fracture
What type of fracture is this?
Fracture that occurs by rapid crack propagation and without appreciable macroscopic deformation
Brittle Fracture
———materials show virtually 100% reduction in area at fracture.
- brittle
- Moderately ductile
- highly ductile
Highly ductile
Most ductile materials experience a ——— amount of necking before fracture.
- significant
- moderate
- negligible
Moderate
The long axis of an elliptical crack during the process of ductile fracture is———to the direction of the applied stress.
- parallel
- perpendicular
- unrelated
Perpendicular
Fractographic studies are performed using a(n)———microscope.
- optical
- scanning electron
- transmission electron
Scanning electron
A scanning electron fractograph showing spherical dimples is indicative of fracture from———stress.
- tensile
- compressive
- shear
Tensile
A scanning electron fractograph showing parabolic dimples is indicative of fracture from———stress.
- tensile
- compressive
- shear
Shear
The fracture surface of a brittle fracture is———.
- curved
- smooth
- flat
Flat
Cracks in a transgranular fracture propagate———grain boundaries.
- until
- through
- along
Through
Cracks in an intergranular fracture propagate———grain boundaries.
- until
- through
- alone
Along
What type of fracture is this?
Fracture of polycrystalline materials by crack propagation through the grains
Transgranular fracture
What type of fracture is this?
Fracture of polycrystalline materials by crack propagation along grain boundaries.
Intergranular fracture
The magnitude of localized stress is highest———the crack tip.
- at
- near
- far from
At
A maximum stress much higher than the applied stress results from a———micro crack with a———tip radius of curvature.
- short, small
- long, large
- long, small
Long, small
The———is a measure of the degree to which an external stress is amplified at a crack tip.
- stress concentration factor
- modulus of elasticity
- specific surface energy
Stress concentration factor
In the example above, if the applied stress is increased to stress= 80MPa, then the critical crack length, a, will be equal to———um.
- 16.4
- 2.05
- 4.1
2.05
What is this equation?
Stress(m)= 2*stress(0)((a/pt)^1/2
Tensile loading, computation of maximum stress at a crack tip
What is this equation?
K(t)=stress(m)/stress(0)=2(a/pt)^1/2
Tensile loading, computation of maximum at a crack tip
Stress(c)=((2Ey(s))/pi*a)^1/2
Critical stress for crack propagation in brittle material
The magnitude of localized stress is highest———the crack tip.
- at
- near
- far from
At
A maximum stress much higher than the applied stress results from a———micro crack with a———tip radius of curvature.
- short, small
- long, large
- long, small
Long, small
The———is a measure of the degree to which an external stress is amplified at a crack tip.
- stress concentration factor
- modulus of elasticity
- specific surface energy
Stress concentration factor
In the example above, if the applied stress is increased to stress= 80MPa, then the critical crack length, a, will be equal to———um.
- 16.4
- 2.05
- 4.1
2.05
K(c)=Ystress(c)squrt(pi*a)
Fracture toughness-dependence on critical stress for crack propagation and crack length
K(Ic)=Ystresssqurt(pi*a)
Plane strain fracture toughness for mode 1 crack surface displacement
Fracture toughness is common in units of———.
- MPa
- MPa*m
- MPa*squrt(m)
MPa*squrt(m)
Plane strain fracture toughness is used when the specimen thickness is———the crack dimensions.
- much greater than
- equal to
- much less than
Much greater than
The plane strain fracture toughness, K(Ic) decreases with———strain rate the———temperature.
- increasing, increasing
- decreasing, decreasing
- increasing, decreasing
Increasing, decreasing
Stress(c)=(K(Ic))/(Ysqrt(pia))
Computation of design
a(c)= 1/pi((K(Ic))/(stressY))^2
Computation of maximum allowable flaw length
If K(Ic) and stress(c) are determined by design constraints, then a(c) is———.
- variable
- fixed
- irrelevant
Fixed
A———can be used to find internal or surface flaws in in-service components and during quality control in manufacturing.
- destructive test
- non-destructive test
- tensile test
Non-destructive test
A———is used to design to account for flaws which result in lower strength and toughness.
- safety factor
- critical crack length
- critical stress
Safety factor
A technique of fracture Analysis used to determine the stress level at which preexisting cracks of known size will propagate, leading to fracture.
Fracture mechanics
A small flaw (internal or surface) or a structural discontinuity at which an applied tensile stress will be amplified and from which cracks may propagate.
Stress raiser
The measure of a material’s resistance to fracture when a crack is present
Fracture toughness (K(c))
The condition, important in fracture mechanical analyses, in which, for tensile loading, there is zero strain in a direction perpendicular to both the stress axis and the direction of crack propagation; this condition is found in thick plates, and the zero-strain direction is perpendicular to the plate surface.
Plane strain
For the condition of plane strain, the measure of a material’s resistance to fracture when a crack is present.
Plane strain fracture toughness (K(Ic))
Impact testing is used to determine fracture characteristics at———temperature and———loading rates.
- high, high
- low, low
- low, high
Low, high
In the———impact test, the specimen is supported on both sides with impact on the side opposite the v-notch.
- charpy
- izod
- v-notch
Charpy
The———is calculated from the difference between the initial height, h, and the maximum height, h’, of the impact hammer.
- plane strain fracture toughness
- yield strength
- energy absorption
Energy absorption
The ductile-to-brittle transition is related to the———dependence of the measured impact energy absorption.
- initial hammer height
- temperature
- applied force
Temperature
The ductile-to-brittle transition occurs at approximately———degrees C for A283 steel.
- 0
- 50
- 100
50
Increase the carbon content of a steel alloy will———the ductile-to-brittle transition temperature.
- increase
- decrease
- not change
Increase
One of two tests that may be used to measure the impact energy or notch toughness of a standard notched specimen. An impact blow is imparted to the specimen by means of a weighted pendulum.
Charpy test
One of two tests that may be used to measure the impact energy of a standard notched specimen. An impact blow is imparted to the specimen by a weighted pendulum.
Izod test
A measure of the energy absorbed during the fracture of a specimen of standard dimensions and geometry when subjected to very rapid (impact) loading Charpy and Izod impact tests are used to measure this parameter, which is important in assessing the ductile-to-brittle transition behavior of a material.
Impact energy (notch toughness)
The transition from ductile to brittle behavior with a decrease in temperature exhibited by some low-strength steel (BCC) alloys; the temperature range over which the transition occurs is determined by Charpy and Izod impact tests.
Ductile-to-brittle transition
Stress(m)= (stress(max)-stres(min))/2
Mean stress for cyclic loading-dependence on maximum and minimum stress levels
Stress(r)= stress(max)-stress(min)
Computation of range of stress for cyclic loading
Stress(a)= stress(r)/2= stress(max)-stress(min)/2
Computation of stress amplitude for cyclic loading
R=stress(min)/stress(max)
Computation of stress ratio
Failure, at relatively low stress levels, of structures that are subjected to fluctuating and cyclic stresses
Fatigue
