Stresses  on  the  Elastic  Properties  of  Steel.  281 
the  loads  in  tension  were  being  applied — and  this  notwith- 
standing the  increased  friction  ofthe  heads — showed  a  decided 
weakening  of  the  material  in  torsion  due  to  the  combined 
stresses.  However,  sufficient  data  have  not  been  taken  to  give 
a  satisfactory  report  on  this  point. 
35 
32 
28 
24 
20 
16 
12 
Fig.  4. 
Carbon-Steel. — Tension  part  only  of  Torsion-Tension  Test? 
Series  C. 
1 
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Fig.  5  shows  two  torsion  curves  A  and  B,  the  former 
representing  an  average  of  two  tests  of  the  material  made 
while  the  specimen  was  under  a  tensile  load  of  4000  lbs. 
per  sq.  in.,  and  the  latter  an  average  of  two  simple  torsion 
tests  of  the  same  material.  The  curves  show  the  expected 
lower  elastic  limit  in  the  case  of  the  specimens  subjected  to 
combined  stresses.  In  the  case  of  this  plate  the  ordinate's 
represent  the  shearing  stress  on  the  outer  fibre,  and  the 
abscissae  the  angle  of  twist  measured  at  the  centre  o£  the 
specimen. 
When  the  tests  have  been  more  completely  worked  out,  it 
is  planned  to  compare  the  values  obtained  from  the  tests  under 
