Under　progressive　normal　load,　a　spherical　indenter　(radius　of　500　mu　m)　made　of　zirconia　ceramic　was　used　to　explore　the　elastic-plastic　deformation　of　ductile　materials　including　three　polymers　and　twenty　metals　during　instrumented　scratch　tests.　The　results　of　instrumented　scratch　tests　show　that　as　the　normal　load　increases,　the　elastic　recovery　ratio,　residual　scratch　hardness,　geometric　scratch　hardness,　and　lateral　scratch　hardness　of　metals　can　approach　constant　levels.　However,　the　elastic　recovery　ratio　and　geometric　scratch　hardness　of　polymers　decrease　monotonically,　possibly　due　to　the　occurrence　of　damage　or　failure.　The　fracture　toughness　values　of　polymers　estimated　at　the　largest　normal　load　based　on　linear　elastic　fracture　mechanics　are　consistent　with　the　results　in　the　literature.　Under　large　loads,　both　residual　scratch　hardness　and　lateral　scratch　hardness　of　polymers　can　be　approximated　as　being　constant.　Residual　scratch　hardness　is　found　to　be　larger　than　geometric　scratch　hardness.　The　geometry　of　a　spherical　indenter　helps　explain　the　nonlinear　increase　in　friction　coefficient　with　increasing　applied　normal　force　(the　constant　levels　of　friction　coefficients　for　gray　and　nodular　cast　irons　are　mainly　caused　by　the　influence　of　graphite).　Most　materials＇　scratch　responses　are　closely　related　to　their　mechanical　properties:　the　critical　scratch　strain　(the　initial　strain　of　the　steady　state　of　elastic　recovery　ratio)　is　proportional　to　yield　strain;　there　is　a　linear　relationship　between　yield　strength　and　the　steady-state　residual　scratch　hardness,　which　is　proportional　to　Knoop　hardness.