儀器壓痕法斷裂韌性檢測(cè)方法.ppt

Evaluation of Fracture Toughness of MaterialsUsing Instrumented Indentation Technique: Ductile/Brittle Fracture Models2013. 08. 30. Won Je Jo Introduction Indentation Fracture Toughness Models- Brittle fracture model- Ductile fracture model Verification of the Models- Comparison between fracture test results and IIT results- Applications at low temperature Basic concept of indentation fracture toughness Fracture test Crack propagation and fracture Indenter IIT No crack and no fracture Issue of indentation fracture toughness What is a correlation between fracture test and IIT? In the case of metals, 2 Constraint effect ahead of a crack tipPlastic region constrained by elastic regionbeneath an indenter3 R=250mIndenter Material : API X70loading Constraint effect 0.0 0.1 0.2 0.3 0.4 0.5 0.60123 456 3.0- y=3.011771-exp-4.57486(x+0.31229)t max V / V max 0.0 0.1 0.2 0.3 0.4 0.5 0.601 23456 3.2- y=3.298311-exp-3.65099(x+0.27357)t max hmax / R 2.1 3.22.3 3.0Triaxiality of crack tip Triaxiality of indentation4 Indentation fracture toughness )1( 2 EJK CJC Analogous situation ?JCK5 Energy concept)1( 2 EJK CJC CJ = Required energy for crack propagationEquivalent fracture energy in Indentation Analysis of indentation process 6 Indentation process Formation of a plastic zone to the surface7 Formation of a fully-developed plastic zone (c/a is constant)Expansion of plastic zone (c/a increase)ca ca AssumptionOnset of formation of a fully-developed plastic zone=Maximum strain energy beneath the indenter Formation of equivalent fracture energyh* 8 c/a hh* Brittle materials Ductile materialsFracturesurface Deformation Relatively little or no deformation Large plastic deformationCriterion Stress controlledcritical fracture stress at the crack tip (sf) Strain controlledcritical fracture strain at the crack tip (ef)Formation offracture energy When stress reached critical fracture stress When strain reached critical fracture strain Fracture Behavior 9Brittle Fracture Model Ductile Fracture Model Brittle Fracture Model 10 Criterion 11 L (kgf) h max (m) Critical indentation depth (h*) cmm pp rrCritical stress(pressure) at h*Criterion Assumption Onset of formation to a fully-developed plastic zone=Formation of Equivalent fracture energy dtdctime sizezone plastic finalexpansionofRate constant/ acdtdadtdc expansion core of rate ;dtda zone plastic developed-fully12 Application of indentation theoriesStep 1 Yielding right outside the contact areaFormation of a plastic zone to the surfaceeorycontact th elastic Hertz Step 2Expansion of the plastic zoneFormation of fully-developed plastic zone theory)plastic-(elastic modelcavity Expanding cah*13 Hertz elastic contact theoryStress outside the contact area (r a)m2 2r pr2 a)21( ss 0 z sv When a radial stress at the edge of the contact area (r = a) satisfied yielding criterion mr p 221 s By Von Mises yield criterion ysym Cp s 1 14 Expanding cavity model (E-P theory)Stress within plastic zone (a r c) rip s 31)ln(2 rcyy ssss 32)ln(2 rcyrssysiysr pac sss ln232v Change of the core pressure (r = a) until forming the fully-developed plastic zone1ac 2Cac by K.E. Puttick (1977)im pp ysi acp s ln23215 core Criterion of equivalent fracture energyStep 1 ysfcm Cp s mymcm ppp cmpThe total pressure required for equivalent fracture energy, Step 2iym pp 16 Fracture toughness for brittle material 0 20 40 60 800500 10001500 Pcm Indentation depth (m)h*Indentation mean pre ssure(kgf/m2 ) )1( 2 EwK fJC l Pm - h curve 0 20 40 60 80 100 120 140 160010203040 5060L (kgf) hmax (m) l Indentation load-depth curve 2cmaxm aLp - Mean contact pressure at each unloading depth *0h cf dhALw (1) Indentation testing (6) Indentation fracture toughness (K JC) (2) Measuring ys RT and -29oCApplications at low temperature 32 Applications at low temperature - Master Curve : KJC from IIT : KJC from J-Test Specimen information and testing conditions Chemical composition (wt.%) C Si Mn P S Ni 0.21 0.24 1.36 0.007 0.002 0.92 Cr Mo Al Cu V 0.21 0.49 0.022 0.03 0.005 Chemical composition of specimen Material SA508-3, ID:GS880Specimen Compact tension and precracked CVNUse Nuclear reactor pressure vesselTemperature range(about10 Interval) -110-20Fracture toughness testing ASTM E1920 33-200 -150 -100 -50 0 50050100 150200 250 FMCG, KAERI GS880, PCVN K JC,1T (MPa-m 0.5 ) Temperature (oC) T0 = -63.5oC Median 5, 95% Tolerance bound Applications at low temperature - Master Curve : KJC from IIT : KJC from J-Test Reference : Bong-Sang Lee, Min-Chul Kim, Maan-Won Kim, Ji-Hyun Yoon, Jun-Hwa Hong, “Master curve techniques to evaluate an irradiation embrittlement of nuclear reactor pressure vessels for a long-term operation”, International Journal of Pressure Vessels and Piping 85 (2008) 593599 Specimen information and testing conditions Chemical composition (wt.%) C Si Mn P S Ni 0.21 0.24 1.36 0.007 0.002 0.92 Cr Mo Al Cu V 0.21 0.49 0.022 0.03 0.005 Chemical composition of specimen Material SA508-3, ID:CS50Specimen Compact tension and precracked CVNUse Nuclear reactor pressure vesselTemperature range(about10 Interval) -110-20Fracture toughness testing ASTM E1920 34-200 -150 -100 -50 0 50050100 150200 250 FMCG, KAERI CS50, PCVN K JC,1T (MPa-m 0.5 ) Temperature (oC) T0 = -26.5oC Median 5, 95% Tolerance bound