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Notes for IUPUI ME 344
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10/15/2015
3
Ductile and Brittle Fractures
66
Brittle Fracture of Ceramics
• Surface of a 6-mm diameter fused silica rod.
• Characteristic fracture behavior in ceramics– Origin point
– Initial region (mirror) is flat and smooth
– After reaches critical velocity crack branches
• mist
• hackle
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7
Fatigues Testing
(After H.W. Hayden, W.G. Moffatt, and J.Wulff, “The structure and Properties of Materials,” vol. III, Wiley, 1965, p.15.)
Figure 7.17
Figure 7.18
Figure 7.16
Endurance Limit modifications
Reversed Bending 1.0
Reversed Axial 0.71
Reversed Torsional 0.6
T < 450 C 1.0
450 < T < 550 C 1-5.8-3 (T – 450C)
D < 8mm 1
8 < D < 250 mm 1.189 D-0.097
10/15/2015
8
Fatigue Crack Propagation Rate
(After “Metals Handbook,” Vol 8, 9th ed., American Society of Metals, 1985, p.388.)
Fatigue Crack Growth rate Versus ΔK
)()(.
)(
ALogKLogm
KALogdN
daLog m
(After P.C. Paris et al. Stress analysis and growth of cracks, STP 513 ASTM, Philadelphia, 1972, PP. 141-176
10/15/2015
10
Creep Test
High temperatureor stress
Medium temperatureor stress
Low temperatureor stress
Figure 7.27
Figure 7.28
Copper Alloy
Larsen Miller Parameter
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11
How long will a steel connector rod last if used in service at 430 C and 180 Mpa? A test at 520 C at 180 MPa failed after 300 hours.
L.M. Diagram of several alloys
Figure 6.37
After N.R. Osborne et. al., SAMPE Quart, (4)22;26(1992)
Fig. 7.32
LM for 0.2% strain