Published: Jan 2005
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THE SPECIMENS USED TO DETERMINE TRANSITION RANGE DATA ARE shown in Figs. 7 and 8. Three compact specimen designs are shown in Fig. 7, all of which have fixed height to width ratios, 2H/W of 1.2. Thickness B = W/2. The one specimen on the left has a machined-in slot that is too narrow for inserting a displacement-measuring clip-gage at the load line. J-integral calculations require the measurement of work done on the specimen (area under the load versus load point displacement test record), so that load-line displacement measurement is necessary. However, the displacement gage can be placed on the front face of the specimen at a position 0.25W in front of the load-line. Front face displacement, Vff, is nominally a factor of 1.37 times the load-line displacement, VLL , hence the area under a load versus Vff plot will be 1.37 times the area under a load versus VLL plot, enabling J-integral calculations to be based on either type of test record. An alternative would be to use the caliper-type “over-the-top gage” shown in Fig. 9. Use of this gage should be limited to materials of low fracture toughness, since specimens that fracture with high stored elastic strain energy may damage such gages. The other two compact specimen designs shown in Fig. 7 provide recesses for clip gages that are placed on the load-line. Both have small vertical faces onto which razor blade knife-edges can be spot welded. Razor blade steel is easily trimmed to the size and shape needed with ordinary sheet-metal shears.