▁the ▁in vention , ▁development ▁and ▁validation ▁of ▁the ▁non - contact ing , ▁image - based ▁de formation ▁measurement ▁methods ▁known ▁as ▁digital ▁image ▁correlation ▁methods , ▁or ▁D IC . ▁ ▁Career ▁ ▁In ▁the ▁early ▁ 1 9 8 0 s , ▁S utton ▁and ▁his ▁co - work ers ▁invent ed ▁the ▁first ▁D IC ▁method , ▁known ▁as ▁two - dimensional ▁D IC ▁or ▁ 2 D - D IC . ▁This ▁method ▁is ▁applicable ▁for ▁surface ▁measurements ▁on ▁plan ar ▁spec im ens ▁under going ▁nomin ally ▁in - plane ▁de formation . ▁ ▁While ▁working ▁with ▁NASA ▁research ers ▁as ▁part ▁of ▁the ▁US ▁A ging ▁A ircraft ▁Program , ▁S utton ▁showed ▁that ▁crack ▁tip ▁opening ▁disp lacement , ▁or ▁the ▁more ▁general ▁mixed ▁mode ▁form ▁using ▁three - dimensional ▁crack ▁tip ▁disp lac ements , ▁is ▁a ▁valid ▁crack ▁growth ▁predict or ▁for ▁the ▁thin ▁a eros pace ▁al umin um ▁al loy ▁components ▁such ▁as ▁ 2 0 2 4 - T 3 ▁and ▁ 2 4 2 4 - T 3 ▁commonly ▁used ▁in ▁commercial ▁av iation . ▁▁ ▁Their ▁research ▁led ▁to ▁the ▁establishment ▁of ▁an ▁A ST M ▁Standard ▁test ▁method ▁for ▁determ ining ▁resistance ▁to ▁stable ▁crack ▁extension ▁under ▁low - constraint ▁conditions . ▁This ▁test ▁is ▁used ▁to ▁demonstrate ▁the ▁f ract ure ▁resistance ▁of ▁thin ▁a eros pace ▁structures ▁when ▁subject ed ▁to ▁mechanical ▁loads . ▁▁ ▁During ▁the ▁mid - 1 9 9 0 s ,