168 ANNUAL REPORT SMITHSONIAN INSTITUTION, 194 5 



stainless steel at 23,600. Chrome-moly steel comes in at 22,900, alu- 

 minum alloy at 22,100, and then a terrible drop to paper laminate at 

 9,400, canvas laminate at 7,100, and wood-flour-phenolic, molded, at 

 0,200^ 



This comparison shows that if the competition be confined to sheet 

 materials, the plastics stand up fairly well in tensile strength by 

 weight, but the moment it centers about really shapeable forms by 

 bringing in the moldable group, the plastics lose position rapidly. 



Table 1. — Some plastics and metals compared as to light weight (lightest at the top 



of the list) 



Specific grav- 

 Materials'and characteristics ities 



Formica Pregood No. 100. Impregnated compressed wood 1. 30 



All laminations parallel. Classed as a high-strength product. 



Water absorption 6 percent maximum. 

 Formica canvas laminate-phenolic. Grade C 1. 33 



Cotton fabric, 4 ounces per yard. Tough. 



Water absorption 0.3 percent. 

 Formica paper base laminate-phenolic. Grade X 1.33 



Primarily for mechanical applications. 



Water absorption 4 percent. 

 Bakelite wood-flour-phenolic BM-120. Best all-around molding 



composition 1. 36 



Water absorption 0.3 percent. 

 Bakelite macerated canvas phenolic BM-3510 1. 38 



High-production, high-impact molding. 



Water absorption 1 percent. 

 Formica glass mat base phenolic. Grade MF 1. 50 



Basically for electrical purposes. 



Water absorption 0.35 percent. 

 Formica asbestos fabric base laminate. Grade AA 1. 80 



Strength, toughness, minimum dimensional changes. 



Water absorption 1.5 percent. 



Magnesium allov ( AM-585) 1. 81 



Aluminum alloy (24 ST) 2, 80 



Stainless steel 7. 85 



Chrome-moly steel 7. 85 



With respect to compressive strength the steels are strongest; with 

 some of the plastics better than some of the other metals, as can be 

 seen in table 3. When the specific gravity correction is applied, how- 

 ever, all the plastics (except Pregwood, now) rate higher than the 

 metals. Therefore if compressive strength is the determining factor 

 in a specific design, plastics (some form of thermosetting phenolic or 

 urea) will serve the purpose best pound for pound. 



Similar data on modulus of elasticity in tension, which is a measure 

 of a material's rigidity, are given in table 4 and show clearly that the 

 metals are outstanding in this respect, even on a per-pound basis. 

 And beyond that, on shear strength, impact strength, and flexural 

 strength there is just no point in presenting tables, no matter how they 

 might be corrected for comparative weights, for the plastics are 

 woefully inferior to metals in these respects. 



