589 



(d) A test of Hopklnson's scaling rule . Hopkinson's scaling nile 

 (Section V, 3,d) was tested using Lot 5 steel diaphragms in half-scale and 

 full-scale UERL damage gauges suid was found to apply, within the precision 

 of measurement, \inder these conditions. 



Two thicknesses of steel diaphragms (average thickness 0.079 and 

 0.038 in.) were rolled from the same melt of steel so as to have as nearly- 

 identical properties as possible. By the man\ifacturer's test, the ultimate 

 tensile strength was about 68,000 lbs/in? for the thicker and about 

 63,000 lbs/in? for the thinner diaphragms. The full-scale gauges were 

 regular UERL dama ge gauges and the half-scale gauges were accurately 

 scaled in all dimensions. The gauges were mounted on steel rings with 

 the charges in the center. 



The loose tetryl charges were scaled in their linear dimensions 

 (within 5/^) and the weights were in the ratio 8 to 1. Both tin cans and 

 cardboard containers were used and no difference was observed due to 

 container . 



The resxilts are given in Table XXV. It will be noted that, on the 

 average, Hopkinson's nile is followed to within 35^. 



Table XXV - Results of scaling tests with diaphragm gauges 



a/ Standard deviation of the mean. 



b/ Corrections based upon Kirkwood's theory (See. V,k,a.) 



(e) Static calibration of steel diaphragms . In an attempt to 

 determine whether or not the variations in the physical properties of the 

 steel diaphragms used in the UERL damage ga\iges were sviff iciently large to 

 cause significajit variations in damage, a number of 1 in. diameter steel 

 disks were deformed by static pressure. These disks were cut from the 

 regular diaphragms used in the damage gauges; as majay as four could be cut 

 from the area outside the damage portion in the case of a diaphragm which 

 had already been damaged. Otherwise, disks were cut from undamaged dia- 

 phragms. The disks were cut to fit into Modi:igno32/ gauges; they were 

 placed in the gauges and clamped in position as in the customary use of 

 these gauges. Illxistrations of a Modugno gauge apart and assembled are 

 given in Figure 31 • 



30/ Preliminary Design Branch (Ship Protection Group), BuShips Underwater 

 Explosion Report I9U2-3, October 19^2. 



