This　paper　presents　a　novel　two-step　procedure　for　measuring　the　critical　current　(I　c)　properties　as　a　function　of　tensile　stress.　The　proposed　method　completely　eliminates　the　possible　negative　effect　of　the　voltage　tap　used　during　the　tensile　procedure,　allowing　the　actual　I　c　irreversible　degradation　stress　to　be　clearly　determined.　Six　different　commercial　REBCO　tapes　from　five　manufacturers　were　tested.　The　I　c　value　does　not　degrade　until　the　stress　reaches　the　＇inflection　area＇　in　the　tensile　curve,　which　corresponds　to　the　most　pronounced　transformation　step　from　elastic　to　plastic　deformation.　This　allows　easy　estimation　of　the　stress　corresponding　to　I　c　irreversible　degradation　by　a　simple　and　accurate　cryogenic　tensile　curve　instead　of　complicated　in-situ　I　c　tensile　measurement.　A　feasible　composite-material　tensile　model　is　established　to　explain　the　phenomenon.　In　addition,　fatigue　measurements　on　a　commercial　REBCO　tape　from　Shanghai　Superconductor　technology　show　that　the　tape　can　withstand　10　000　cycles　under　580　MPa　and　over　5000　cycles　under　695　MPa,　which　also　is　consistent　with　the　proposed　composite-materials　tensile　model　and　is　confirmed　by　the　EBSD　experiments　on　the　Hastelloy　substrate.　This　research　provides　better　insight　and　tools　for　designing　and　fabricating　extremely　high-field　magnets.