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Exam/HW review
Bridgman correction
Strain rate effects
Compression testing
Bauschinger effect
Yield prediction
Exam: mean = 79.8
standard deviation = 11.9
Exam review:
Exam review:
Exam review:
Exam review:
Exam review:
HW #4 review:
HW #4 review:
True strain at necking: Bridgman correction
Week 7 Read: 3.7 Tuesday class
True strain at necking: Bridgman correction
Week 7 Read: 3.7 Tuesday class
True strain at necking: Bridgman correction
During necking: uniaxial stress state develops into triaxial stress state.
R2/a1lna/R21/1/
Part of the stress that contributes to uniaxial yielding
Measured stress
Week 7 Read: 3.7 Tuesday class
True strain at necking: Bridgman correction
Week 7 Read: 3.7 Tuesday class
True strain at necking: Bridgman correction
Week 7 Read: 3.7 Tuesday class
True strain at necking: Bridgman correction
trueBtrue B
Empirically for steel: B = 0.83 – 0.186logtrue
Bridgman correction factor
Week 7 Read: 3.7 Tuesday class
Stress-strain diagrams: trends: strain-rate
Week 7 Read: 3.7 Tuesday class
Stress-strain diagrams: trends: strain-rate
Week 7 Read: 3.7 Tuesday class
Blast impact on composite material (Courtesy of Arun Shukla, URI)
Stress-strain diagrams: trends: strain-rate
Within reasonable boundaries for the strain rate limited effect on UTS
Week 7 Read: 3.7 Tuesday class
113
122
131
10
10
10
s
s
s
T,ln
lnm
m: strain rate sensitivity
Stress-strain diagrams: trends: strain-rate
mK
• Tensile tests:
at > 10-2 s-1 inertia and wave propagation
effects become important.
• Forming processes: rolling, wire drawing with high
strain rates.
• Al (alloys): m ~ 0, typically m ~ 0.02-0.2 for T < 0.9 Tm
1214 1010 ss
Week 7 Read: 3.7 Tuesday class
Week 7 Read: 3.7 Tuesday class
Stress-strain diagrams: trends: strain-rate
Within reasonable boundaries for the strain rate limited effect on UTS
Week 7 Read: 3.7 Thursday class
113
122
131
10
10
10
s
s
s
T,ln
lnm
m: strain rate sensitivity
Stress-strain diagrams: trends: strain-rate
mK
• Tensile tests:
at > 10-2 s-1 inertia and wave propagation
effects become important.
• Forming processes: rolling, wire drawing with high
strain rates.
• Al (alloys): m ~ 0, typically m ~ 0.02-0.2 for T < 0.9 Tm
1214 1010 ss
Week 7 Read: 3.7 Thursday class
Week 7 Read: 3.7 Thursday class
Difference between fcc and bcc metal strain rate sensitivity
Week 7 Read: 3.7 Thursday class
Difference between fcc and bcc metal strain rate sensitivity
Week 7 Read: 3.7 Thursday class
Example 1:
Week 7 Read: 3.7 Thursday class
The tensile stress in one region of an HSLA steel sheet (m = 0.005) is 1 %
higher than in another region. What is the ratio of the strain rates in the two
regions without strain hardening?
Combined strain and strain rate
Week 7 Read: 3.7 Thursday class
Combined strain and strain rate
Week 7 Read: 3.7 Thursday class
Physical origin of strain rate sensitivity
Week 7 Read: 3.7 Thursday class
Compression Testing
Week 7 Read: 3.7 Thursday class
(a) Stress–strain (engineering and true) curves for 70–30 brass in compression. (b) Change of shape of specimen and barreling.
Compression Testing
Week 7 Read: 3.7 Thursday class
(a) Distortion of Finite Element Method (FEM) grid after 50% reduction in height h of specimen under sticking-friction conditions. (Reprinted with permission from H. Kudo and S. Matsubara, Metal Forming Plasticity (Berlin: Springer, 1979),p. 395.) (
(b) b) Variation in pressure on surface of cylindrical specimen being compressed.
Compression Testing
Week 7 Read: 3.7 Thursday class
Bauschinger Effect
Ratio of compressive flow stress (0.2% plastic strain) and tensile flow stress at different levels of plastic strain for different steels. (After B. Scholtes, O. Vöhringer, and E. Macherauch, Proc. ICMA6, Vol. 1 (New York: Pergamon, 1982), p. 255.)
Week 7 Read: 3.7 Thursday class
Bauschinger Effect – explanation attempts
Week 7 Read: 3.7 Thursday class
