Limitations　of　finite　element　analysis　(FEA)　in　providing　accurate　localized　stress　and　strain　information　in　superelastic　nltinol　are　well　recognized.　Understanding　the　parent　texture　and　the　crystallography　of　stress-induced　martensitlc　transformation　holds　the　key　to　bridge　the　gap　between　continuum　mechanics　and　the　microscopic　stress-strain　condition　Imposed　by　the　phase　transformation　In　understanding　the　deformation　mechanism　of　this　complex　material.　A　scanning　electron　microscope　equipped　with　an　electron　beam　back　scatter　diffraction　detector　is　a　powerful　tool　that　can　extract　microscopic　crystallography　Information　from　bulk　specimens.　The　technique　has　been　employed　to　study　the　crystallography　of　stress-Induced　martensitic　transformation　during　tensile　and　bend　deformations　of　superelastic　nitinol.　The　results　suggest　that　for　tensile　deformation,　the　transformation　variants　of　stress-induced　martensite　(SIM)　inside　the　Lüders　band　follow　maximum　shear　stress　along　the　martensite　shape　change　direction.　The　observation　also　confirms　that　the　SIM　transformation　is　Incomplete,　leaving　a　significant　amount　of　retained　B2　parent　phase　inside　the　Lüders　band.　As　tensile　deformation　proceeds,　the　Lüders　band　propagates　by　nucleating　new　martensite　plates　instead　of　by　thickening　of　the　existing　martensite　variants.　For　bend　deformation,　SIM　appears　to　transform　much　easier　in　the　tension　side　than　in　the　compression　side,　confirming　previous　studies　on　the　asymmetrical　tension-compression　property　in　superelastic　nitinol　materials.　Lastly,　the　local　stress　field　at　the　tip　of　martensite　plate　has　been　computed　by　finite　element　(FEA)　simulation　based　on　the　observed　martensite　morphology.　The　implication　on　local　stress　field　and　plasticity　provides　a　rationalization　in　explaining　why　nitinol　fatigue　life　appears　to　be　insensitive　to　the　mean　strain　effect.　Copyright　©　2009　by　ASTM　International.