LECTURE #29 :3.11 MECHANICS OF MATERIALS F03INSTRUCTOR : Professor Christine OrtizOFFICE : 13-4022 PHONE : 452-3084WWW : http://web.mit.edu/cortiz/www• PLASTICITY IN POLYMERS ISUMMARY : LAST LECTUREII. Deformation Energiesσεfailure•Εεp =εresidual•UplasticUelasticσεσYεY0.002failure••••UMORσfailureUMOT•εf•Yf022YYMOR0MOT0PLASTICUdEUd22UdUMechanical or Deformational Energy : Modulus of Resilience or Elastic Strain Energy : Modulus of Toughness :Plastic Work of Fracture : Elastic Energεεεσεεσσεσε=====∫∫∫ELASTICUy Released on Fracture : II. Molecular Origins of Plasticity in Metals• edge and screw dislocations• 2-D and 3-D movement of dislocations• slip systems, planes, directions• critical resolved shear stress• polycrystalline plastic deformationPLASTIC DEFORMATION IN SINGLE CRYSTALSFFslip planesedge dislocationsslip directionPolycrystalline Plastic Deformationhttp://www.jwave.vt.edu/crcd/farkas/lectures/dislocations/tsld022.htmStress versus Strain Curve For Various Types of PolymersσεI.II.III.IV.Structure of Semicrystalline PolymerslamellaeStructure of Semicrystalline Polymers IIhttp://web.utk.edu/~kit/201/Transmitted, polarized-light micrograph of polypropylene spherulites (167 X)Stress versus Strain Curve For Semicrystalline PolymersσεσmaxLoεfI.II.III.IV. V.VI.VII.•σYVIII.Stress versus Strain Curve For Semicrystalline Polymersσε•Plastic Deformation of Semicrystalline PolymersPlastic Deformation of Amorphous, Glassy Polymers (T<Tg)σεCrazing in Amorphous, Glassy Polymers (T<Tg)σ,εσ,εCrazing in Amorphous, Glassy Polymers (T<Tg)σ,εσ,εentanglementoriented polymerchainsfibrilCRAZE NANOSTRUCTUREmain fibrilcross-tie fibrilcraze-bulk interface crazebulkbulkCrazing in Amorphous, Glassy Polymers (T<Tg)σ,εσ,εShear DZ’s in Amorphous, Glassy Polymers (T<Tg)σ,εσ,εMacroscopic sample~ neckingMicroscopic structureCRAZING OR SHEAR
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