- 3 - 487 



In addition to Figure 2, the other rndin result of the theory Is equation (109) of the 

 Appendix, namely: 



T-T W^ 9 W^ 



-2 i = K -L = — K -2- (109) 



T^j Uab 32 tab 



where from eqoations (l3l) and (132) we should take K = 25 as a reasonable probable value and 

 K = UO as a probable overestination of K. 



Experimental data . 



The Box Model, described in an earlier report, consists essentially of a rectangular steel 

 box open at one side which is covered during the trial by 9 target plate held in position between 

 the box and a stout flat frame by twc rcws of -g' 8.S. bolts passing through the frame and through 

 an angle bar fastened round the edge of the box (Figure l) . The external dimensions of the 

 target plate were 7 feet by 5 feet, while those of the large plate frame were 9 feet by 8 feet. 

 In two shots (206 and 209) the large plate frame was repb ced by a small frame of 7 feet by 5 feet 

 external dimensions. 



Due to minor repairs after damaging shots, the unsupported area of target plate was not 

 exactly constant, but for the present purpose it is sufficient to note that its area was 

 70 X «6 = 3220 square inches correct to 5» for all shots. 



Shots involving rupture at the edge fixings are not amenable to analysis, and all shots 

 considered are thus non-rupture shots. In all cases the target plate was mild steel and was 

 suspended vertically with charge and centre of target plate it a depth of 7 feet. Details of 

 charge conditions and plate thicknesses do not enter into the present analysis but are include:? in 

 Table 1 for sake of completeness. 



In order to measure the si,- fu! 1 in, a line ras scribed on the target plate at the inside 

 edge of the clamping frame before the shot and the displacements of this line relative to the frame 

 measured after the shot. The final values for total area of pull-in are given in Table 1 and, 

 except for Shots 206 and 209, it is considered that thty are correct to an experimental error of 

 about 5» or less. 



For shots 206 and 209, the very rigid large plate frane was replaced by a small frame for 

 a reason not concerned with the present analysis, and, as a result, the fraror and box suffered 

 slight distortion, the total pull-in of the target plate being appreciably greater than that 

 measured relative to the frame. Unfortunately, the subsidiary role of the pull-in measurements 

 led to this distortion of the frame renaining unnoticed until after the second shot so that it is 

 not possible to give any accurate correction for frame distortion for each shot separately. 



Hcwever, the final total pull-in of tne frame for the two shots was approximately equal to 

 the combined pull-in relative t: the frame in the two shots and the values of the latter were 

 accordingly multiplied by a factor of two to give the corrsctef values of S'^^ shown in Table 1. 

 These corrected values for Shots 206 and 209 may be up to about 25% In error. 



Compart son of th e ory a nd ex peri men t . 



(1) Preparation of data for analysis . 



In order to analyse the experimental dat? hv means of the theory, it Is necessary firsi to 

 estimate the total Increase of area S due to both Rjll-if, _-; p'.^te stretching. This can b3 

 calculated from: 



where W is the final mean deflection and A, is given by equation (9) of the Appendix if f • (x,y) 

 is the final shape. The mean de^'cction W_^ is calculated from the observed deflections ty a cub'.ture 

 formula as described in a previous report and Is tabulated in Table 1. In paragraph A, in of the 

 Appendix it is shown that for smooth shapes the value of A varies but little with exact shape 



of 



