This　paper　calibrates　micromechanical　fracture　models　for　duplex　stainless　steel　in　order　to　study　its　fracture　behaviour　under　seismic　loading,　characterized　by　large　strain　ultra　low　cyclic　conditions.　In　this　investigation,　smooth　round　bars　and　notched　round　bars　were　subject　to　monotonic　and　cyclic　loading.　Monotonic　and　cyclic　loading　constitutive　models　were　calibrated　against　smooth　round　bar　test　tests.　The　fracture　toughness　parameters　of　the　void　growth　model　(VGM),　the　stress　modified　critical　strain　(SMCS)　model　and　the　cyclic　void　growth　model　(CVGM)　were　calibrated　against　the　notched　round　bar　tests.　Furthermore,　the　skeleton　curve,　hysteresis　loop　and　characteristic　length　of　duplex　stainless　steel　were　also　investigated.　The　test　results　indicate　that　duplex　stainless　steel　exhibits　cyclic　hardening　behaviour　under　cyclic　loading,　and　the　subsequent　numerical　simulation　successfully　captured　this　behaviour.　The　toughness　parameters　of　duplex　stainless　steel　are　generally　higher　than　those　for　carbon　steel　grades　Q345B　and　Q460,　which　demonstrates　that　duplex　stainless　steel　has　better　toughness.　All　the　experimental　results　provide　useful　data　for　the　prediction　of　ultra　low　cycle　fatigue　(ULCF)　fracture　of　duplex　stainless　steel.　(C)　2018　Elsevier　Ltd.　All　rights　reserved.