50 



137 



1.50 



1.25 



1.00 



0.75 



0.50 



0.25 



0.1 



0.2 



0.3 



0.4 



0.5 



0.6 



Proportionote Deflection 



Figure 42 - Pressure-Deflection Curves for Two STS Plates 



a = 10.25 inches a^ = 125,000 pounds per square inch 



appears that there is also a possibility of size effects; thinner materials 

 require proportionately more pressure. However, with the exception of the 

 curves for furniture steel in Figure 39. the differences are relatively small; 

 the deviations from the average are generally less than 5 per cent. For a 

 given material, accordingly, it may be concluded that for approximate analy- 

 ses variations caused by differences in relative thickness or manufacture can 

 frequently be ignored. 



The deviations in the composite curves of Figure 43 are larger, TO 

 per cent or more from the average in some instances. In this case the differ- 

 ences in the plastic stress-strain properties of the materials are an impor- 

 tant factor. The biaxial stress-strain characteristics of the materials are 

 not directly given, but it is of some interest to examine the curves in the 

 light of the uniaxial stress-strain curves of Figure 37- If proportionate 

 deflection is taken to be related to strain, and proportionate pressure is 

 related to stress, then the sequence from top to bottom of the two sets of 

 curves might be expected to be the same In this respect Figure U3 partially 

 agrees with Figure 37 Special treatment steel is highest and medium steel 

 lowest over much of the range. Copper starts at high values in Figure Hj, but 

 ultimately assumes the lowest values plotted High tensile and furniture 

 steels occupy an Intermediate position in agreement with Figure 37- However, 



