538 



Increasing the veight of the gauge by 50 lbs. (total weight 8o lbs.) 

 did not further increase the damage. It was concluded, therefore, that 

 increasing the inertia of the gauges considerably did not materially 

 change the damage results. 



Early in the siamner of 19^3, however, a new shipment of lumber used 

 for constructing the frames was received which produced msirkedly different 

 damage results. This led to the investigation of several types of support- 

 ing frames. 



The usual type of frame, Figure 11, made of 3 x 3A ^^' furring, was 

 vsa-ied by "quartering" each member to decrease the strength of the frame, 

 and by "doubling" to increase the strength. The doubled frame was con- 

 structed simply by nailing together two members for the side pieces of 

 the frame shown in Figure 11 so that the dimensions of these sections 

 were 3 x 1-1/2 in. It should be noted that for this type frame the 

 closest edge of the wooden frame was closer to the charge than the gauge 

 diaphragms. Figure 12 shows a partially doubled frame in which the 

 sections between C and D, and B smd D have been doubled in the same 

 fashion. Figure 13 shows a frame constructed so that aJ.1 parts of the 

 wooden frame were farther from the charge than the diaphragms in the 

 gauges. Weakened and doubled frames were investigated for this style 

 frame as well. Finally, tests were made with the gauges mounted rigidly 

 on a steel ring (Figure 1^;) . The ring was made of 1-1/2 in. solid 

 round stock and the gauges were mounted (l) on spruce blocks, (2) on 

 osik blocks, and (3) on moimts made of 1-1/2 in. angle iron. The results 

 varied with each type of mounting. The ring was not significantly 

 affected by the shots. 



Our conclusions from these experiments were as follows. The data 

 are listed in Tables TV to VII. 



(a) The regular frames (Figure 11) produced a definite decrease 

 In damage when strengthened by means of the doubled sides, and an 

 increase in damage when weakened by use of the quartered sides. An 

 increase in damage was also shown when the frame members were decreased 

 from 3 X S/k in. to 2 x 3/^ in. The data for these shots are shown in 

 Table IV. Here it may be seen that strengthening the frame by doubling 

 may decrease the damage as much as If^ and weakening the frame by 

 quartering the frame increase it as much as U9/6. This was also shown 

 in shots in which frames were tuisymmetrically strengthened as shown in 

 Figure 12. The data in Table V indicate that less damage occurred for 

 those gauges moimted on the doubled sections of the frame. 



(b) The use of the "outside" frames (Figure 13) for which all 

 charge-to-frame distances were greater than the charge -to -gauge distance 

 resulted in a damage greater than with the frames of Figure 11. The 

 increases in damage were as much as 16%, as indicated in Table VI. The 

 weakening of this type of frame by changing from 3 x 3/^ in, members to 

 the 2 X 3/14- size and the dovibling of the frame had comparatively little 

 effect. Increasing the distance d of the gauge from the frame tended to 

 increase the damage. 



