68b in addition to that quasi-Figure 67 Local equivalent plastic strain at fracture as a function of the degree ofmultiaxiality ðsm=svÞ along the specimen radius at the narrowest cross-s
Trang 1aged [138] The results are represented by a continuous curve for each metry (symbols) Each point of a curve represents a location r along theradius in the smallest cross-section Only one point of each curve fulfillsthe failure criterion for ductile fracture, so that the envelope of all curvesrepresents the failure criterion For quasi-static loading (Fig 67a), the envel-ope is described by the Hancock=Mackenzie relation and for dynamic load-ing (Fig 67b) by Eq (111).
geo-The comparison between the failure criterions determined for static and dynamic loading is represented in Fig 68b in addition to that
quasi-Figure 67 Local equivalent plastic strain at fracture as a function of the degree ofmultiaxiality ðsm=svÞ along the specimen radius at the narrowest cross-section ofdifferently notched specimen of aluminum AA7075 highly over aged under (a) quasi-static, and (b) dynamic loading (From Ref 138.)
Trang 2Figure 69 The transition temperature shift due to an increase in multiaxiality
M ¼ sm=ss, prestrain e and rate of elongation
Figure 70 Influence of deformation rate and strength on the transitiontemperature shift [141] (a) J-integral-temperature curves for steel 15NiCuMoNb5.(b) Transition temperature shift as a function of yield strength (c) Measured andcalculated values for the transition temperature as a function of the machine ramvelocity v
"
Trang 3If this is the case, the brittle fracture condition is simply assumed to be
sf sI¼ 0 The microscopic cleavage strength s
f can be considered as portional to the modulus of elasticity EðTÞ The transition temperature Tt
pro-from brittle to ductile fracture can be determined by the intersection ofthe functions sfðTÞ and ssðTÞ for given values of multiaxiality M, prestrain
e, and strain rate _ee A variation of these parameters results in a shift of thetransition temperature which is determined by
Tt 1þ DT=ð@m=@TÞT¼0wherem ¼ @ ln s=@ ln _ee is the strain rate sensitivity.According to this method, the transition temperature shift can be expressedby
2 Hollomon, J.H Tensile deformation Trans AIME 1945, 126, 268–290
3 Swift, M.W Plastic instability under plane stress J Mech Phys Solid 1952, 1,1–18
4 Voce, E The relationship between stress and strain for homogenousdeformation J Inst Metals 1948, 74, 537–562
5 Mecking, H.; Kocks, U.F Kinetics of flow and strain hardening Acta Metal
1981, 29, 1865–1875
Trang 46 Follansbee, P.S.; Kocks, U.F A constitutive description of the deformation ofcopper based on the use of the mechanical threshold stress as an internal statevariable Acta Metal 1988, 36 (1), 81–93.
7 Tome, C.; Canova, G.R.; Kocks, U.F.; Christodoulou, N.; Jonas, J.J Therelation between macroscopic and microscopic strain hardening in f.c.c.polycrystals Acta Metal 1984, 32, 1637–1653
8 Voehringer, O Gefu¨ge und mechanische Eigenschaften; gesellschaft Oberursel: Germany 1990
DGM-Informations-9 Campbell, J.D.; Ferguson, W.G The temperature and strain rate dependence
of the shear strength of mild steel Phil Mag 1970, 21, 63–82
10 Campbell, J.D Dynamic Plasticity of Metals Springer Verlag: Wien, NY,1972
11 Harding, J Material behavior at high rates of strain In Impact Loading andDynamic Behaviour of Materials; Chiem, C.Y.; Kunze, H.D.; Meyer, L.W.,Eds.; DGM-Informationsgesellschaft Oberursel: Germany, 1988
12 El-Magd, E Mechanical properties at high strain rates J Phys IV 1994, 4,C8-149–C8-170
13 Perzyna, P The constitutive equation for rate sensitive plastic material Quart.Appl Math 1963, 20, 321–332
14 Ludwik, P U¨ber den Einfluß der Deformationen mit besonderer tigung der Nachwirkungserscheinungen Phys Zeitschrift 1909, 10 (suppl 12),411–417
Beru¨cksich-15 Johnson, G.R.; Cook, W.H Fracture characteristics of three metals subjected
to various strains, strain rates, temperatures and pressures Eng Fract Mech
1985, 21, 31–48
16 Gilman, J.J Micromechanics of Flow in Solids; McGraw Hill: New York, 1969
17 Lindholm, U.S Some Experiments in dynamic plasticity under combinedstress In Mechanical Behaviour of Materials under Dynamic Loads; Lindholm,U.S Ed.; Springer-Verlag: Berlin, 1968
18 Kawate, K.; Hashimoto, S.; Kurokawa, K Analyses of high velocity tension
of bars of finite length of b.c.c and f.c.c metals with their own constitutiveequations In High Velocity Deformation of Solids; Kawata, K.; Shoiri, J.,Eds.; Springer-Verlag: New York, 1978
19 Vo¨hringer, O Habilitation Thesis, Technical University, Karlsruhe,Germany,1972
20 Macherauch, E.; Vo¨hringer, O Das Verhalten metallischer Werkstoffe untermechanischer Beanspruchung Z Werkstofftechnik 1978, 9, 370–391
21 Kocks, U.F.; Argon, A.S.; Ashby, M.F Thermodynamics and Kinetics ofSlip; Pergamon Press: New York, 1975
22 Armstrong, R.W Relation between the Petch ‘‘Friction’’ stress and thethermal activation rate equation Acta Metal 1967, 15, 667–668
23 Zerilli, F.J.; Armstrong, R.W Dislocation-mechanics-based constitutiverelations for material dynamic calculations J Appl Phys 1987, 61,1816–1825
24 Kumar, A.; Hauser, F.E.; Dorn, J.E Viscous drag on dislocations inaluminium at high strain rates Acta Metal 1968, 16, 1189–1197
Trang 525 Sakino, K.; Shiori, J Dynamic flow stress response to sudden reduction instrain rate at very high strain rates J Phys France IV 1991, (suppl III 1),C3–35.
26 El-Magd, E.; Treppmann, C Mechanical Behaviour of AA7075, Ck45Nand TiAl6V4 at High Strain Rates, Materialsweek, Munich, September 2000;
http:==www.proceedings.materialsweek.org=proceed=mw2000 786.pdf
27 El-Magd, E.; Treppmann, C Modelling of mechanical behaviour of materialsfor high speed cutting processes Third International Conference on MetalCutting and High Speed Machining, Metz, Conference Proceedings, Vol II,25–28, University Melz, France, 2001
28 Treppmann, C Fließverhalten metallischer Werkstoffe bei hohen windigkeiten Ph.D Thesis RWTH Aachen: Germany, 2001
Dehngesch-29 Dormeval, R The adiabatic shear phenomenon In Materials at High StrainRates; Blazynski, T Ed.; Elsevier Applied Science: London, 1988; 47–70
30 Troost, A.; El-Schennawi, A Zusammenhang zwischen isothermer undadiabatischer Fließkurve Mech Res Comm 1975, 1, 331–334
31 Troost, A.; El-Schennawi, A Einfluss der Umformwa¨rme auf die Fliesskurveund auf im Zugversuch ermittelte mechanische Eigenschaften Arch Eisen-hu¨ttenwes 1975, 46 ( suppl 11), 729–733
32 Doege, E.; Meyer-Nolkemper, H.; Saeed, I Fliessverkurvenatlas metallischerWerkstoffe; Hanser Verlag: Mu¨nchen 1986
33 Coffey, C.S.; Armstrong, R.W Description of the hot spots associated withlocalized zones in impact tests In Shock Waves and High-Strain RatePhenomena in Metals; Meyers, M.A.; Morr, L.E., Eds.; Plenum Press: NewYork, NY, 1981; 313–324
34 Semiatin, S.L.; Staker, M.R.; Jones, J.J Plastic instability and flowlocalization in shear at high rates of deformation Acta Metal 1984, 32,1347–1354
35 Giovanola, J.H Observation of adiabatic shear banding in simple torsion InImpact Loading and Dynamic Behaviour of Materials; Chiem, C.Y.; Kunze,H.D.; Meyer, L.W., Eds.; DGM-Informations-Gesellschaft Oberursel:Germany, 1988
36 Cho, K.M.; Lee, S.; Nutt, R.; Duffy, J Adiabatic shear band formationduring dynamic torsional deformation of an HY-100 Steel Acta Metal 1993,
41, 923–932
37 Hartmann, K.H.; Kunze, H.D.; Meyer, L.W Metallurgical effects on impactloaded materials In Shock Waves and High Strain Rate Phenomena in Metals;Meyers, M.A.; Murr, L.E., Eds.; Plenum Press: New York, 1981; 325–337
38 El-Magd, E.; Treppmann, C High speed quick-stop tests cut with the hopkinson-bar In Scientific Fundamentals of HSC; Schulz, H Ed.; KarlHanser Verlag: Mu¨nchen, 2001
split-39 El-Magd, E.; Brodmann, M Ductility of aluminium AA7075 at high strainrates J Phys IV France 2000, 10, Pr9 335–Pr9 340
40 Rix, K.F.W Konstitutive Gleichungen fu¨r metallische Werkstoffe unterZeitvera¨nderlicher Hochtemperatur-Beanspruchung Ph.D Dissertation,RWTH Aachen, 1997
Trang 641 Lemaitre, J.; Chaboche, J.L Mechanics of Solid Materials; CambridgeUniversity Press: Cambridge, 1990.
42 ABAQUS=Standard Version 6.1 In User’s Manual Volume II Hibbit,Karlsson & Sorensen, Inc.: New York, 2000
43 Hoffmann, M.; Seeger, T.A A generalized method for estimating multiaxialelastic–plastic notch stresses and strains, part 1 Trans ASME 1985, 107,250–254
44 Hoffmann, M.; Seeger, T.A A generalized method for estimating multiaxialelastic-plastic notch stresses and strains, part 2 Trans ASME 1985, 107, 255–260
45 Tipton, S.M.; Nelson, D.V Methods for estimating cyclic notch strains inSAE specimen In Multiaxial Fatigue; Socie, D.; Leese, G.E., Eds.; Society ofAutomotive Engineers Inc: Warrendale, PA, 1989; 101–106
46 Neuber, H Theory of stress concentration for shear strained prismaticalbodies with arbitrary nonlinear stress–strain law J Appl Mechanics 1961,
28, 544–550
47 Tipton, S.M Multiaxial fatigue life predictions of the SAE specimen usingstrain based approaches In Multiaxial Fatigue; Socie, D.; Leese, G.E., Eds.;Society of Automotive Engineers Inc: Warrendale, PA, 1989; 67–80
48 ASME Boiler and Pressure Vessel Code Sec III, Div I: Case N-47–33, 1995
49 Brown, M.W.; Miller, K.J High temperature low-cycle biaxial fatigue of twosteels Fatigue Eng Mat Structures 1979, 1, 217–229
50 Lohr, R.D.; Ellison, E.L.G A simple theory for low cycle multiaxial fatigue.Fatigue Eng Mat Structures 1980, 3, 1–17
51 Garud, Y.S A new approach to the evaluation of fatigue under multiaxialloadings J Eng Mat Techn ASME Trans 1981, 103, 118–125
52 El-Magd, E.; Wahlen, V Energiedissipationshypothese zur nung bei mehrachsiger Schwingbeanspruchung Z Werkstofftechnik 1994, 25,218–223
Festigkeitsrech-53 Stratmann, P.; Bowe, K.H U¨ber die Anwendung des Potentialsondenverfahrens in der Bruchmechanik Materialpru¨fung 1976, 18,339–341
Gleichstrom-54 El-Magd, E.; Mahmoud, M Verhalten gekerbter Biegeproben aus derAluminiumlegierung AA7075 im Kurzzeitermuedungsbereich Materialwis-senschaft und Werkstofftechnik 2003, 2, 242–248
55 Weaver, C.V.; Williams, J.G Deformation of a carbon–epoxy compositeunder hydrostatic pressure J Material Sci 1975, 10, 1323–1333
56 Evans, A.G.; Adler, W.F Kinking as a mode of structural degradation incarbon fiber composites Acta Metal 1978, 26, 725–738
57 Yang, W.; Wie, Y.G Progressive damage along kink bands in fiber-reinforcedcomposite blocks under compression Int J Damage Mechanics 1992, 1,80–101
58 Pattnaik, A.; Kim, C.; Weimer, R.J Deformation behavior of depleteduranium=tungsten fiber composites in compression In Compression Testing ofHomogeneous Materials and Composites; ASTM STP 808, ASTM: WestConshohoken 1983; 254–275
Trang 759 Schuerch, H Prediction of compressive strength in uniaxial boron fiber–metalmatrix composite materials J Am Inst Aeronautics Astronautics 1966, 4,102–106.
60 El Magd, E.; Mahmoud, M.; Vervoort, S Finite Elemente Simulation desFaserverhaltens metallischer Verbundwerkstoffe bei LCF-Beanspruchung ZMetallkunde 2001, 92, 191–196
61 Ahlquist, C.N.; Nix, W.D The measurement of internal stresses during creep
of Al and Al–mg alloys Acta Metal 1971, 19, 373–385
62 Nix, W.D.; Ilschner, B Mechanism controlling creep of single phase metalsand alloys In Proceedings of the Fifth International Conference on Strength ofMetals and Alloys; Haasen, P.; Gerold, V.; Kostors, G., Eds.; PergammonPress: Oxford, 1980; 1503–1514
63 Estrin, Y.; Mecking, H A unified phenomenological description for work ening and creep based on the one-parameter model Acta Metal 1984, 32, 57–70
hard-64 Reppich, B.; Heilmaier, M.; Wunder, J.; Baumeister, H.; Huber, T Mechanicalanalysis of the creep behavior of iron-base superalloys In Microstructure andMechanical Properties of Metallic High-Temperature Materials, DFG-ResearchReport; Mughrabi, H Ed.; Wiley-VCH: Weinheim, 1999
65 Mughrabi, H Dislocation wall and cell structures and long-range internalstresses in deformed metal crystals Acta Metal 1983, 31, 1367–1379
66 Nicolini, G Mikrostuktur und Zeitstandverhalten teilchengeha¨rteter temperaturwerkstoffe Ph.D Dissertation, RWTH Aachen, 1998
Hoch-67 Kachanov, L.M The Theory of Creep In Engl Transl; Kennedy, A.J Ed.;Boston Spa: Wetherby, 1960
68 Rabotnov, Y.N Creep Problems in Structural Members: In Engl Transl.;Lecki, F.A Ed.; North Holland Publishing Company: Amsterdam, 1969
69 Shaker, C Zeitstandverhalten metallischer Werkstoffe bei Zeitvera¨nderlicherBeanspruchung; Ph.D Dissertation, RWTH Aachen, 1991
70 El-Magd, E Hochtemperatur-Werkstofftechnik; RWTH Aachen, Umdruck, 1999
LFW-71 Norton, F.N The Creep of Steel at High Temperature; McGraw-Hill:New York, 1929
72 El-Magd, E.; Pantelakis, P.; Jaeger, K Influence of stress and temperaturechanges on the creep damage rate Res Mechanica 1987, 21, 55–72
73 Neubing, H.C.Production and properties of aluminum powder for powdermetallurgy PMI 1981, 13, 74–78
74 El-Magd, E.; Ismail, Y.; Brockmann, G.J.; Baumgarten, J Influence of thedispersoid material and forming process on the creep behaviour of dispersionstrengthened aluminium Mat-wiss u Werkstofftech 1996, 28, 34–39
75 Li, Y.; Langdorn, T.G An examination of creep data for an Al–mgcomposite Met Trans A 1997, 28, 1271–1273
76 Orlova, A.; Kucharova, K.; Brezina, J.; Krejci, K.; Cadek, J Hightemperature creep in Al4C3 Dispersion strengthened aluminium alloys intension and compression Scr Metal Mater 1993, 29, 63–68
77 Ismail, Y.; Nicolini, G.; El-Magd, E Deformation behaviour of particlestrengthened P=M-aluminium alloys under creep loads Metall 1997, 51, 557–563
Trang 878 Kro¨pfl, I.; Vo¨hringer, O.; Macherauch, E Creep behaviour of dispersionhardened aluminium materials Proceedings of the Second InternationalConference on Mechanics of Time Dependent Materials, USA=CA: Pasadena,1998.
79 El-Magd, E.; Nicolini, G Creep behavior and microstructure of strengthened PM-Aluminium materials at elevated temperatures In Mughrabi,
dispersion-H , et al Eds.; DFG-report, Microstructure and Mechanical Properties
of Metallic High-Temperature MaterialsWiley-VCH,Eds Germany=Weinheim 1999; 18–33
80 Reppich, B.; Brungs, F.; Hu¨mmer, G.; Schmidt, H Modelling of the creepbehaviour of ODS-platinum-based alloys; In Creep and Fracture of Engineer-ing Materials and Structures; Wilshire, B.; Evans, R.W., Eds.; The Institute ofMetals: London, 1990; 141–168
81 Guttmann, V.; Tirum, J On the influence of thermal pretreatment on creepand microstructure of alloy 800 Z Metallkunde 1990, 81, 428–432
82 Diglio, M.R.; Straube, H.; Sprradek, K.; Degischer, H.P Rupture Ductility
of Creep Resistant Steels Strang, A The Institute of Metals: London,1990
83 Martin, J.W Micromechanisms in Particle-Hardened Alloys; CambridgeUniversity Press: Cambridge, UK, 1980; 162–187
84 El-Magd, E.; Nicolini, G.; Farag, M.M Effect of carbide precipitation on thecreep behaviour of alloy 800 HT in the temperature range 700–9008C Met.Mat Trans A 1996, 27 (3), 747–756
85 Lifshitz, I.M.; Sloyozov, V.V The kinetics of precipitation from saturated solid solutions J Phys Chem Solids 1961, 19, 35–50
super-86 Kranz, A.; El-Magd, E Creep behavior of the particle strengthenedaluminium alloy AA 2024 In Creep and Fracture of Engineering Materialsand Structures; Parker, J.D Ed.; IOM-Communications: London, 2001;241–250
87 Cotrell, A.H Theory of brittle fracture in steel and similar metals Trans.Metal Soc AIME 1958, 212, 192–203
88 Baluffi, R.W.; Seigle, L.L Growth of voids in metals during diffusion andcreep Acta Metal 1957, 5, 449–454
89 Hull, D.; Rimmer, D.E The growth of grain-boundary voids under stress.Phil Mag 1959, 4, 673–687
90 Raj, R.; Ashby, M.F Intergranular fracture at elevated temperature ActaMetal 1975, 23, 653–666
91 Edward, G.H.; Ashby, M.F Intergranular fracture during power-law creep.Acta Metal 1977, 27, 1505–1518
92 Dyson, B.F Constrains on diffusional cavity growth rates Metal Sci 1976,
10, 349–353
93 Svoboda, J.; Cˇadek, J Modelling of intergranular cavity growth with specialreference to the mechanism of coupled diffusion and power-law creep Mat.Sci Eng 1987, 93, 135–149
94 Wilkenson, D.S The effect of a non-uniform void distribution on grainboundary void growth during creep Acta Metal 1988, 36, 2055–2063
Trang 995 Lindborg, U Nucleation and growth of creep cracks in an austenitic steel.Acta Metal 1969, 17, 157–166.
96 El-Magd, E.; Walkenhorst, H.W Investigation on inter-crystalline creep crackgrowth of the austenitic steels X6CrNi18-11 and X8 CrNiMoNb 16 16 SteelRes 1990, 61 (1), 39–44
97 El-Magd, E.; Walkenhorst, H.W.; Freres, P Rate of growth of wedge typeinter-crystalline creep micro-cracks In Creep and Fracture of EngineeringMaterials and Structures; Wilshire, B.; Ewans, R.W., Eds.; The Institute ofMetals: London, 1993; 99–108
98 El-Magd, E.; Freres, P Statistical and computational modelling of initiation andgrowth of intercrystalline creep cracks Comp Mat Sci 1994, 3 (2), 159–168
99 Freres, P.; El-Magd, E Investigation of the influence of a multi-axial state ofstress on the behaviour of intercrystalline creep micro-cracks ComputationalMaterials Science, 1996, 5, 101–110
100 El-Magd, E Simulation of material behavior under impact loading.Computational Materials Sci 1993, 1, 333–342
101 Dackweiler, G Verhalten Metallischer Faserverbundwerkstoffe beihohen Verformungsgeschwindigkeiten Ph.D Dissertation, RWTH Aachen,1990
102 El-Magd, E Simulation of material behavior under dynamic loading.Computers Industrial Eng 1999, 37, 195–198
103 Paffrath, W Verhalten ferritischer Gusseisen bei hohen windigkeiten im Temperaturbereich zwischen 93 K und 293 K Ph.D.Dissertation, RWTH Aachen, 1989
Verformungsgesch-104 El-Magd, E.; Brodmann, M Der Einfluss von Scha¨digung auf dieadiabatische Fließkurve der Aluminiumlegierung AA7075 unter Schlagzug-beanspruchung Z Metallkunde 1999, 90, 732–737
105 Knott, J.F Micromechanisms of fibrous crack extension in engineering alloys.Met Sci 1980, 14, 327–336
106 Meakin, J.D.; Petch, N.J Atomistic aspects of fracture In Fracture of Solids;Drucker, D.C.; Gilman, J.J., Eds.; John Wiley & Sons: New York, 1963; 393–415
107 Ghosh, A.K A criterion for ductile fracture in sheets under biaxial loading.Met Trans A 1976, 7, 523–533
108 Atkins, A.G.; Mai, Y.M Fracture strains in sheet metalforming and specificessential work of fracture Eng Fracture Mech 1987, 27, 291–297
109 Gurland, J.; Plateau, J The mechanism of ductile rupture of metals containinginclusions Trans ASM 1963, 56, 442–451
110 Le Roy, G.; Embury, J.D.; Edward, G.; Ashby, M.F A model of ductilefracture based on the nucleation and growth of voids Acta Met 1981, 29,1509–1522
111 Jun, S.; Zengjie, D.; Zhonghua, L.; Mingjing, T Fracture strength ofspheroidal carbide particle Int J Fract 1990, 42, 39–42
112 Gurson, A.L Continuum theory of ductile rapture by void nucleation andgrowth Part I—yield criteria and flow rules for porous ductile media J Eng.Mat Tech 1977, 99, 2–15
Trang 10113 Needleman, A.; Rice, J.R Limits to ductility set by plastic flow localization.
In Mechanics of Sheet Metal Forming; Koisten, D.P.; Wang, N.M., Eds.;Plenum Press: New York, 1978; 237
114 Fowler, J.P.; Worswick, M.J.; Pilkey, A.K.; Nahme, H Damage leading toductile fracture under high strain-rate conditions Met Trans A 2000, 31,831–844
115 Argon, A.S.; Im, J.; Safoglu, R Cavity formation from inclusions in ductilefracture Met Trans A 1975, 6, 825–837
116 Beremin, F.M Cavity formation from inclusions in ductile fracture of A508steel Met Trans A 1981, 12, 723–731
117 Ashby, M.F Work hardening of dispersion crystals Phil Mag 1966, 14 (2),1157–1178
118 Tanaka, K.; Mori, R.; Nakamura, T Cavity formation at the interface ofspherical inclusion in a plastically deformed matrix Phil Mag 1970, 21, 267–279
119 Chu, C.C.; Needleman, A Void nucleation effects in biaxially stretched sheets
J Eng Mater Tech 1980, 102, 249–256
120 Rice, J.R.; Tracy, D.M On the ductile enlargement of voids in triaxial stressfields J Mech Phys Solids 1969, 17, 201–217
121 Hancock, J.W.; Mackenzie, A.Z On the mechanisms of ductile failure in strength steels subjected to multi-axial stress-state J Mech Phys Solids 1976,
high-24, 147–169
122 Rousselier, G.; Phan-Ngoc, K.; Mottet, G Elastic–plastic behaviour lawincluding ductile fracture damage SMIRT Paris 1981, 1, 119–128
123 Thomason, P.F Ductile fracture and the stability of incompressible plasticity
in the presence of microvoids Act Met 1981, 29, 763–777
124 Thomason, P.F An assessment of plastic-stability models of ductile fracture.Act Met 1982, 30, 279–284
125 Thomason, P.F A three-dimensional model for ductile fracture by the growthand coalescence of microvoids Acta Met 1985, 33, 1087–1095
126 Marini, B.; Mudry, F.; Pineau, A Ductile rupture of A508 steel undernonradial loading Eng Fract Mech 1985, 22 (3), 375–386
127 Holland, D.; Halim, A.; Dahl, W Influence of stress triaxiality upon ductilecrack propagation Steel Res 1990, 61, 504–506
128 McClintock, F.A A Criterion for ductile fracture by the growth of holes
J Appl Mech 1968, 35, 363–371
129 Tvergard, V On localization in ductile materials containing spherical voids.Int J Fract 1982, 18 (4), 237–252
130 Needleman, A.; Tvergaard, V An analysis of ductile rupture in notched bars
J Mech Phys Solids 1984, 32, 461–490
131 Needleman, A.; Tvergaard, V Effect of material rate sensitivity on failuremodes in the Charpy V-notch test J Mech Phys Solids 1986, 34, 213–241
132 Carroll, M.M.; Holt, A.C Static and dynamic pore-collapse relations forductile porous materials J Appl Phys 1972, 43 (4), 1626–1636
133 Johnson, G.R.; Cook, W.H Fracture characteristics of three metals subjected
to various strains, strain rates, temperatures and pressures Eng Fract Mech
1985, 21, 31–48
Trang 11134 El-Magd, E Influence of strain rate on ductility of metallic materials SteelRes 1997, 68 (2), 67–71.
135 Brodmann, M Scha¨digungsmodell fu¨r schlagartige Beanspruchung lischer Werkstoffe, Ph.D Dissertation, RWTH-Aachen, 2001
metal-136 Avrami, M Kinetics of phase change I J Chem Phys 1939, 7, 1103–1112
137 Curran, D.R.; Seaman, L.; Shockey, D.A Linking dynamic fracture tomicrostructural processes In Shock Waves and High Strain Rate Phenomena inMetals; Meyers, M.A.; Murr, L.E., Eds.; Plenum Press: New York, 1981;129–165
138 El-Magd, E.; Brodmann, M Influence of precipitates on ductile fracture ofaluminium alloy AA7075 at high strain rates Mat Sci Eng A 2001, 307,143–150
139 El-Magd, E.; Brodmann, M Ductility of Aluminium Alloy AA7075 at highstrain rates EURODYMAT Krakow, Nov 2000
140 Ritchie, R.O.; Knott, J.F.; Rice, R On the relationship between critical tensilestress and fracture toughness in mild steel J Mech Phys Solids 1973, 21,395–410
141 Falk, J.; Dahl, W Influence of loading rate on the transition behaviour ofstructural steels J Phys IV 1991, 1, C3=613–C3–621
Trang 12Tribology and the Design of
Surface-Engineered Materials
for Cutting Tool Applications
German Fox-Rabinovich and George C Weatherly
McMaster University, Hamilton, Ontario, Canada
excel-be used, that marks modern manufacturing trends
The theme of this chapter is the role played by physico-chemicalinteractions in modifying and controlling the friction and wear of thetribo-couple (i.e., the critically loaded surfaces of the cutting tool and theworkpiece) during high-speed cutting operations The chapter is dividedinto three sections In the first section, the characteristic features of
Trang 13friction and the role of ‘‘self-organizing systems’’ in helping to control thewear processes are described A ‘‘self-organizing system’’ is one thatresponds to the external mechanical, thermal, and chemical forces with
a positive feedback loop that leads to an improvement in the wear acteristics of the couple Two types of stable secondary structures formed
char-at the surface of the tool have been identified in ‘‘self-organizing tems’’ They are usually oxide films, either highly plastic or refractoryand less plastic that form under machining conditions by reaction ofthe tool material with oxygen
sys-The second section develops these ideas of self-organization for somecommon tool materials, and shows how they can be understood andexploited for alloys such as high-speed tool steels (HSS), cemented car-bides, and cermets A deep level of understanding of the complex inter-actions that lead to the formation of stable secondary structures has comefrom the use of techniques such as Auger spectroscopy and electron energyloss spectroscopy, which have been extensively used to study the wear cra-ters formed during machining These studies, when coupled to more con-ventional wear and friction experiments, clearly demonstrate the positiverole of secondary structures in reducing the wear rate in the initial (run-in) phase of wear In addition, the formation of secondary structures isshown to prolong the steady-state wear regime, with positive benefits onthe overall life of the cutting tool
In the third section, a number of recent trends to enhance the mance of cutting tools are discussed These include the use of monolithic ormulti-layered coatings, substrate modification, surface-engineered tools,and multi-layered self-lubricating coatings Throughout the discussion, therole of secondary structures is highlighted, and the concept of a ‘‘smart’’coating that can respond to the cutting environment (with a positive feed-back) is proposed Finally we propose that any future development ofimproved cutting tools will depend on a better understanding of the nature
perfor-of the secondary structures Examples are given as to how these ments might be exploited for high-speed machining operations
improve-II TRIBOLOGICAL ASPECTS OF METAL CUTTING
A Cutting Tool Wear Mechanisms
Metal cutting is associated with mechanical and thermal processes thatinvolve intensive plastic deformation of the workpiece ahead of the tooltip, and severe frictional conditions at the interfaces of the tool, chip, andthe workpiece Most of the work of plastic deformation and friction is