ANSYSExplicitDynamicsPPT学习教案

1、会计学1ANSYSExplicitDynamicsgeological materials, concrete)nChemical energy deposition (e.g. explosives)nTensile failurenPhase changes (solid-liquid-gas)nNo single material model incorporates all of these effectsnEngineering Data offers a selection of models from which you can choose based on the mater

2、ial(s) present in your simulation第1页/共54页第2页/共54页Change in VolumeChange in Shape第3页/共54页第4页/共54页 For linear elasticity, stresses are given by Hookes law : where l and G are the Lame constants (G is also known as the Shear Modulus) The principal stresses can be decomposed into a hydrostatic anda devi

3、atoric component : where P is the pressure and si are the stress deviators Then :第5页/共54页Hookes LawGeneralized Non-Linear ResponseEquation of StateStrength Model Many applications involve stresses considerably beyond the elastic limit and so require more complex material modelsFailure Modeli (max,mi

4、n) = f 第6页/共54页第7页/共54页Shear Modulus GYoungsModulus EPoissonsRatio nBulk Modulus KShear ModulusYoungs ModulusShear ModulusPoissons RatioShear ModulusBulk ModulusYoungs ModulusPoissons RatioYoungs ModulusBulk ModulusPoissons RatioBulk ModulusE - 2G2GGE3 (3G - E)2G (1 + n)2G (1 + n)3 (1 - 2n)9KG3K + G

5、3K - 2G2 (3K + G)E2 (1+ n)E3 (1 - 2n)3EK9K - E3K - E6K3K (1 - 2n)2 (1 + n)3K (1 - 2n)第8页/共54页第9页/共54页modulus are derived for use in the material solutions.nTemperature dependence of the linear elastic properties is not available for explicit dynamics 第10页/共54页properties is not available for explicit

6、 dynamics 第11页/共54页第12页/共54页StressTimeStrainTimes = Constante = ConstantStress RelaxationCreep第13页/共54页nNeed to verify the applicability of the model chosen prior to use.nCurrently hyperelastic materials may only be used for solid elements0.001.002.003.004.005.006.00012345678Eng. StrainEng. Stress (

7、MPa)Mooney-RivlinArruda-BoyceOgdenTreloar ExperimentsTensile tests on vulcanised rubber第14页/共54页Examples of Hyperelasticity第15页/共54页第16页/共54页第17页/共54页第18页/共54页1212Initial Yield surfaceCurrent Yield surfaceIsentropic Hardening (3 = 0) Kinematic Hardening (3 = 0) 第19页/共54页nProperties defined nUp to te

8、n stress-strain pairsnIsotropic HardeningnTotal stress range is twice the maximum yield stress, YnKinematic HardeningnCan only be used with solid elements 第20页/共54页第21页/共54页Normal impact of tungsten sphere on thick steel plate at 10 kms-1Lagrange Parts used with erosionJohnson-Cook strength model us

9、ed to model effects of strain hardening, strain-rate hardening and thermal softening including meltingEffects of Strain Hardening (Johnson-Cook Model)Hypervelocity Impact第22页/共54页第23页/共54页第24页/共54页bccfcc第25页/共54页limiting value of the yield stress.nThree formsnLinearnOriginal Drucker-Prager modelnSta

10、ssinConstructed from yield strengthsin uniaxial compresion and tensionnPiecewisenYield stress is a piecewise linear function of pressure第26页/共54页instead of dislocation movement (metallic plasticity)nFully cracked material still retains some strength in compression due to frictional effects in crushe

11、d grainsnYield reduced from intact value to fractured value via a Damage functionnDamage accumulates due to effective plastic strain第27页/共54页strain over a pressure-dependant fracture strainnTwo methods for application of damagenGradual (default)nDamage is incrementally applied as it accumulatesnInst

12、antaneousnDamage accumulates over time, but is only applied to failure when it reaches 1.0nCan be used with a Linear or Polynomial Equation of State第28页/共54页nCan be used with a Linear or Polynomial Equation of StatenThe gradual softening in the more recent continuous model (JH2) has not been support

13、ed by experimental data, so this earlier variant is still commonly used第29页/共54页Johnson-Holmquist Strength SegmentedExample: Penetrator dwell第30页/共54页第31页/共54页Impact onto plain concreteImpact onto reinforced concrete RHT Concrete Strength Examples第32页/共54页第33页/共54页modulus property, this material def

14、inition is equivalent to using an Isotropic Linear Elastic, modelnShear Modulus nA shear modulus must be used when a solid or porous equation of state are selected.nnTo represent fluids, specify a small value.第34页/共54页nThe shock HugoniotnA standard adiabat nThe 0 K isotherm nThe isobar p = 0nThe cur

15、ve e = 0nThe saturation curve第35页/共54页第36页/共54页第37页/共54页第38页/共54页第39页/共54页第40页/共54页nThe Bulk Modulus of the material is calculated from nModel can be combined with a variety of strength and failure models第41页/共54页nFor non-linear unloading, if the current pressure is less than the current compaction

16、pressure, the pressure is obtained from the bulk modulus using:第42页/共54页第43页/共54页depending on the type of failure modelnInstantaneous FailurenDeviatoric stresses are immediately set to zero and remain sonOnly compressive pressures are supportednGradual Failure (Damage)nStresses are limited by a dama

17、ge evolution lawnGradual reduction in capability to carry deviatoric and / or tensile stresses第44页/共54页with a plasticity or brittle strength model第45页/共54页第46页/共54页第47页/共54页第48页/共54页Pressure (Pmin), failure occursnMaterial instantaneously fails.nIf Material also uses damage evolution, the Maximum Tensile Pressure is scaled down as the damage, D, i