471 



PRELIMINARY STATIC TEST OF A BOX MODEL TARGET PLATE 



E. N. Fox. 

 May 1943 



Ciummary . 



(1) Results are given of a static test on a Box Model target plate subjected to 

 uniformly distriButed lateral pressure, 



(2) The shape of the deflected plate is in reasonable agreement with that expected 

 theoretically on the assumption, as made by Professor G. I. Taylor in the report 

 ■The distortion under pressure of a diaphragm which is clamped along its edge 

 and stressed beyond the elastic limit" (hereafter called report a), of uniform 

 stress in the plate. The load-deflection curve is also iri reasonable agreement 

 with the theory of report A if, due to strain hardening, the uniform stress in 

 the plate is assumed to increase as the deflection increases with pressure. 



(3) Permanent strains, as measured along the centre lines, were greater near the 

 edges than at the centre. This result is attributed mainly to the influence of 

 strain hardening. 



Introductory Note . 



The test described in this report was of an exploratory nature carried out with restricted 

 facilities and both tne accuracy and scope of the measurements were necessarily limited. 



Since it has not yet been possible to carry out a more comprehensive trial it is thought 

 that the results obtained in this preliminary test are of sufficient interest to warrant the present 

 report. 



Arrang e ments for trial . 



The 8o< Model used for the test was of welded construction built by M.C.D. Portsmouth 

 immediately p: jr to the test and since used for explosion trials in conjunction with the older 

 Models of similar design but of riveted construction. 



The Model is essentially a rectangular box open at one face around which an external angle 

 section forms a flange to which the mila steel target plate (5 lbs. /square feet nominal poundage) 

 was fastened by bolts passing through a flat clamping plate of the same width (6 inches) as the 

 flange. views of the model, taken after the test, are shown in Plates 1 to ". 



The yodel was rested on its back with target plate horizontal and is shown in Plate 1 without 

 clamping frame but with the arrangement devised by M.C.D. Portsmouth for measuring deflections 

 during the trial. This arrangement consists of nine wooden rods, of square section with pointed 

 lower end, constrained to move vertically by guldinj holes in the channel frames seen In Plate 1. 

 These rods wr-re marked off on one face with scales to -jTjth inch, readings of which were taken where 

 they were crossed, for each group of three rods, by a thin thread stretched horizontally Between 

 the vertical angle sections supporting the overhead channels. These threads (not shown in Plate l) 

 were not quite touching the rods to ensure their not moving with the rods and th'> scales were read 

 during the t?st By the usf of binoculars at a short distance from the Model. This latter arrangement 

 was adopted as a safety precaution since It was not known prior to the test at what pressure or in 

 what manner the plate would fail. No difficulty was experienced in reading the scales 

 to the nearest marking. I.e. to Tjjth inch, by this method. 



The 



