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Three-Dimensional Crack Growth: Numerical Evaluations and Experimental  Tests   355


          Part-through crack  propagation.  Even  if  the  notch  introduced  on  the  specimen  hole  is
          triangular, for the simulation a quarter circular comer crack has been modelled (because already
          available in the BEASY database) but checking that, after the pre-cracking phase, two identical
          initial conditions were obtained between the numerical and experimental crack front. Starting
          from  this  point  the  comparisons  between  numerical  and  experimental  crack  shapes  and
          propagation times are presented (Fig.  14):  the simulated propagation proceed faster than the
          experimental one and this turns out to be conservative even if not strongly accurate. The SIF’s
          effective along the crack front for each propagation step are presented in Fig. 15.


                                   Total Number of Cycles vs Crack Size
                    5.00
                    4.50
                    4.00                         .......
                  7 3.50
                  E 3.00
                  2 2.50   .................                   ........
                  5  2.00   ........                   ...............
                   e!
                    1.50                            ..................
                    1 .oo                   .......................
                    OSO 0.00 2

                       0    5000   loo00   15000   2oooO   25000   30000   35000   40000
                                           Number of Cycles

         Fig.  14. Crack propagation data (C is the break point inside the hole, whilst A is on the visible
          surface): an exponential regression line was drawn through the experimental data.


                    3,6E+02
                    3,4E+02           +STEPS   +STEP6   +STEP7   *STEP8

                  ,.  3.ZEi02
                  -2 3.0E+02


                   Y
                   a
                  2 2,6E+02
                  ;;                                  .   _L  .’  ’- -   -b
                    2,4E+02
                                           _ _ _ _ _ ~
                    2,2E+02
                    2.OEi02
                        0.0   0,I   0,2   0,3   0,4   0.5   0,6   0,7   0,8   0,9   1.0
                                      Local Position on Crack Front
               Fig. 15. SIF’s effective along the crack front for the elliptical part-through crack.
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