仪器压痕法断裂韧性检测方法.ppt
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1、Fast&Precise SolutionsFast&Precise Solutions for Quality&Reliability for Quality&ReliabilityEvaluation of Fracture Toughness of MaterialsUsing Instrumented Indentation Technique:Ductile/Brittle Fracture Models2013.08.30.Won Je JoContents Introduction Indentation Fracture Toughness Models-Brittle fra
2、cture 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 toughnessFast&Precise SolutionsFast&Precise Solutions for Quality&Reliability for Quality&ReliabilityFracture t
3、estCrack propagation and fractureIndenterIITNo crack and no fractureIssue of indentation fracture toughnessWhat is a correlation between fracture test and IIT?In the case of metals,2Fast&Precise SolutionsFast&Precise Solutions for Quality&Reliability for Quality&ReliabilityConstraint effectahead of
4、a crack tipPlastic region constrained by elastic regionbeneath an indenterSimilar constraint effectSimilar constraint effect3Fast&Precise SolutionsFast&Precise Solutions for Quality&Reliability for Quality&ReliabilityR=250mIndenterMaterial:API X70loadingConstraint effect2.1 3.22.3 3.0Triaxiality of
5、crack tip Triaxiality of indentationSENBSENBIndentationIndentation4Fast&Precise SolutionsFast&Precise Solutions for Quality&Reliability for Quality&ReliabilityIndentation fracture toughnessAnalogous situation5Fast&Precise SolutionsFast&Precise Solutions for Quality&Reliability for Quality&Reliabilit
6、yEnergy concept=Required energy for crack propagationEquivalent fracture energy in IndentationAnalysis of indentation process6Fast&Precise SolutionsFast&Precise Solutions for Quality&Reliability for Quality&ReliabilityIndentation processFormation of a plastic zone to the surface7Fast&Precise Solutio
7、nsFast&Precise Solutions for Quality&Reliability for Quality&ReliabilityFormation of a fully-developed plastic zone (c/a is constant)Expansion of plastic zone(c/a increase)cacaAssumptionOnset of formation of a fully-developed plastic zone=Maximum strain energy beneath the indenter Formation of equiv
8、alent fracture energyh*8c/ahh*Fast&Precise SolutionsFast&Precise Solutions for Quality&Reliability for Quality&ReliabilityBrittle materialsDuctile materialsFracturesurfaceDeformationRelatively little or no deformationLarge plastic deformationCriterionStress controlledcritical fracture stress at the
9、crack tip(sf)Strain controlledcritical fracture strain at the crack tip(ef)Formation offracture energyWhen stress reached critical fracture stressWhen strain reached critical fracture strainFracture Behavior9Brittle Fracture ModelDuctile Fracture ModelFast&Precise SolutionsFast&Precise Solutions for
10、 Quality&Reliability for Quality&ReliabilityBrittle Fracture Model10Fast&Precise SolutionsFast&Precise Solutions for Quality&Reliability for Quality&ReliabilityCriterion11Critical indentation depth(h*)rrCritical stress(pressure)at h*CriterionFast&Precise SolutionsFast&Precise Solutions for Quality&R
11、eliability for Quality&ReliabilityAssumptionOnset of formation to a fully-developed plastic zone=Formation of Equivalent fracture energy12Fast&Precise SolutionsFast&Precise Solutions for Quality&Reliability for Quality&ReliabilityApplication of indentation theoriesStep 1 Yielding right outside the c
12、ontact areaFormation of a plastic zone to the surfaceStep 2Expansion of the plastic zoneFormation of fully-developed plastic zonecah*13Fast&Precise SolutionsFast&Precise Solutions for Quality&Reliability for Quality&ReliabilityHertz elastic contact theoryStress outside the contact area(r a)vWhen a r
13、adial stress at the edge of the contact area(r=a)satisfied yielding criterion By Von Mises yield criterion14Fast&Precise SolutionsFast&Precise Solutions for Quality&Reliability for Quality&ReliabilityExpanding cavity model(E-P theory)Stress within plastic zone(a r c)vChange of the core pressure(r=a)
14、until forming the fully-developed plastic zoneby K.E.Puttick(1977)15coreFast&Precise SolutionsFast&Precise Solutions for Quality&Reliability for Quality&ReliabilityCriterion of equivalent fracture energyStep 1The total pressure required for equivalent fracture energy,Step 216Fast&Precise SolutionsFa
15、st&Precise Solutions for Quality&Reliability for Quality&ReliabilityFracture toughness for brittle materiall Pm-h curvel Indentation load-depth curve-Mean contact pressure at each unloading depth(1)Indentation testing(6)Indentation fracture toughness(KJC)(2)Measuring ys&Determining Pmc-ys from analy
16、zing L-h curve(3)Fitting Pm-h curve-(4)Determining h*-Inserting determined Pmc into Pm-h curve(5)Equivalent fracture energy until h*17Fast&Precise SolutionsFast&Precise Solutions for Quality&Reliability for Quality&ReliabilityDuctile Fracture Model18Fast&Precise SolutionsFast&Precise Solutions for Q
17、uality&Reliability for Quality&ReliabilityCriterion19Critical indentation depth(h*)rrCritical strain at h*CriterionFast&Precise SolutionsFast&Precise Solutions for Quality&Reliability for Quality&Reliability20Critical strain at h*CriterionAbsorbed strain energy until fracture strain=Toughness(tensil
18、e energy)Fast&Precise SolutionsFast&Precise Solutions for Quality&Reliability for Quality&ReliabilityAssumptionElastic energy released due to the crack growth is equal to the amount of plastic work ahead of the crack tip.Peel and Frosyth,1973Plastic work done per unit areaPlastic work done per unit
19、arear:the radius of the plastic zoneUT:plastic work done per unit volumeFor small scale yielding,Elastic energy released per unit areaElastic energy released per unit area21Fast&Precise SolutionsFast&Precise Solutions for Quality&Reliability for Quality&ReliabilityPlastic workMechanical metallurgy,G
20、E.DieterPlastic work done =Area Under the Stress-Strain CurvesR:flow stressef :engineering fracture strain22Fast&Precise SolutionsFast&Precise Solutions for Quality&Reliability for Quality&ReliabilityMechanical parametersEstimation from indentation parametersPlastic zone sizeFracture strainMeasured
21、 parametersElastic propertiesvs.Plastic propertiesFunction of uniform strain Yield strength Ultimate tensile strength Elastic modulus Poissons ratio,n=0.3Fracture toughnessrcefMeasured by indentation test23Fast&Precise SolutionsFast&Precise Solutions for Quality&Reliability for Quality&ReliabilityPl
22、astic zone size,rcPPlastic flowElastic constraintPlastic zoneA balance between plastic flowand elastic constraintDominant elastic constraintDominant plastic flow Small PZSLarge PZSResilienceResilienceFracture strain,efExperimental relation betweentrue uniform strain and engineering fracture strain,2
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- 仪器 压痕 断裂韧性 检测 方法
