Chapter6FractureofMetals金属的断裂货船cargoship问题的提出：构件失效、灾难性的后果bridgebridge桥桥梁梁挤压制品的周期裂纹塑性成形塑性成形plasticdeformationplasticdeformation加工材料出现表面加工材料出现表面//内部裂纹→整内部裂纹→整体破断体破断surface/internalcracksinworkingsurface/internalcracksinworkingmaterials→integralfailure.materials→integralfailure.轧制轧制rolling,rolling,挤压挤压extrusion,extrusion,拉拔拉拔drawing,drawing,锻造锻造forging.forging.成品率成品率//生产率↓生产率↓..therateoffinishedproductsandtherateoffinishedproductsandproductionrateproductionrateWeconcernaboutfractureforWeconcernaboutfracturefortworeasons.Oneiscrack’stworeasons.Oneiscrack’sdestructiveeffectdestructiveeffect,theotheroneis,theotheroneisthatfractureisrelatedtothatfractureisrelatedtomaterial’smaterial’sformabilityformability..(1)(1)破坏；破坏；(2)(2)成形性。成形性。Inthischapter,wewillInthischapter,wewillanalyzetheanalyzethephysicalessencephysicalessenceandlawsoffracture.andlawsoffracture.断裂的断裂的物理本质物理本质//规律规律Definitionoffracture断裂－金属材料在变形超过其塑性极限—完全分开.原子间结合力遭受破坏。Whenmetallicmaterialdeformationforereachitsplasticlimit,itwilldividecompletely.Thentheinteratomicforceisdamaged.relatedsubjects断裂力学fracturemechanics-macroscopic•Stressfield应力场•Strainfield应变场•Fracturecriterion断裂判据断裂物理断裂物理fracturephysics-fracturephysics-micromicroscopicscopic•FracturemechanismFracturemechanism断裂机制断裂机制•MicrostructureMicrostructure组织组织6.1断裂的基本类型Basictypesoffracture根据断裂前金属是否有明显的塑性变形可分为Accordingtowhetherthemetalhasobviousplasticdeformationbeforefracture,itcanbesortedasfollowing:brittlefracture脆性断裂ψ<5%ductilefracture韧性断裂ψ>5%按断裂面相对作用力的取向关系可分为按断裂面相对作用力的取向关系可分为AccordingtotheorientationAccordingtotheorientationrelationshipbetweenfractureandrelationshipbetweenfractureandactingforceactingforce正断正断normalfailureagainsttonormalfailureagai...
