﻿720 
  Prof. 
  E. 
  L. 
  Hancock 
  : 
  Results 
  of 
  Tests 
  of 
  

  

  No 
  attempt 
  has 
  as 
  yet 
  been 
  made 
  to 
  check 
  the 
  results 
  by 
  

   theory 
  with 
  great 
  accuracy, 
  nor 
  does 
  it 
  seem 
  probable 
  that 
  

   this 
  will 
  be 
  of 
  much 
  value, 
  as 
  the 
  presence 
  of 
  such 
  a 
  large 
  

   number 
  of 
  vacuum-tubes 
  alters 
  the 
  capacity 
  and 
  introduces 
  

   leakance 
  into 
  the 
  helix. 
  But 
  the 
  general 
  effects 
  observed 
  are 
  

   of 
  value 
  in 
  illustrating 
  the 
  theory 
  of 
  wave-propagation. 
  

  

  The 
  author's 
  thanks 
  are 
  tendered 
  to 
  Mr. 
  C. 
  M. 
  Dowse 
  who 
  

   has 
  taken 
  considerable 
  trouble 
  in 
  arranging 
  the 
  apparatus 
  and 
  

   experiments, 
  and 
  to 
  Mr. 
  A. 
  C. 
  Cossor 
  for 
  the 
  construction 
  of 
  

   the 
  vacuum-tubes, 
  whicli 
  were 
  only 
  obtained 
  sufficiently 
  

   uniform 
  after 
  a 
  considerable 
  amount 
  of 
  trouble. 
  

  

  LXI. 
  Results 
  of 
  Tests 
  of 
  Materials 
  subjected 
  to 
  Combined 
  

   Stresses. 
  By 
  E. 
  L. 
  Hancock, 
  Assistant 
  Professor 
  of 
  

   Applied 
  Mechanics, 
  Purdue 
  I 
  uirersity 
  * 
  . 
  

  

  DURING 
  the 
  past 
  four 
  years 
  the 
  writer 
  has 
  conducted 
  

   tests 
  of 
  steel 
  under 
  combined 
  stresses. 
  These 
  have 
  

   been 
  carried 
  out 
  in 
  such 
  a 
  way 
  as 
  to 
  combine 
  torsion 
  with 
  

   tension, 
  flexure, 
  and 
  compression. 
  It 
  is 
  the 
  writer's 
  purpose 
  

   in 
  this 
  brief 
  report 
  to 
  make 
  a 
  summary 
  of 
  these 
  tests, 
  as 
  well 
  

   as 
  other 
  tests 
  that 
  have 
  been 
  made 
  along 
  the 
  same 
  lines, 
  and 
  

   to 
  present 
  these 
  results 
  in 
  such 
  form 
  that 
  they 
  may 
  be 
  readily 
  

   available 
  for 
  the 
  purposes 
  of 
  the 
  engineer. 
  

  

  Among 
  designers 
  of 
  structures 
  subjected 
  to 
  combined 
  

   stresses 
  three 
  theories 
  have 
  found 
  favour, 
  namely 
  : 
  — 
  

  

  (1) 
  The 
  Maximum 
  Stress 
  Theory. 
  — 
  This 
  theory 
  assumes 
  

   that 
  the 
  material 
  yields 
  when 
  the 
  tensile 
  (or 
  com- 
  

   pressive) 
  stress 
  on 
  any 
  element 
  reaches 
  a 
  certain 
  

   maximum. 
  It 
  leads 
  to 
  the 
  following 
  relation 
  : 
  

  

  <7=l/2(i>± 
  Sf+M), 
  . 
  . 
  . 
  . 
  (1) 
  

  

  where 
  q 
  is 
  the 
  greatest 
  unit-tension 
  (or 
  compression) 
  

   on 
  any 
  element 
  and 
  p 
  and 
  p 
  s 
  are 
  the 
  unit-tension 
  (or 
  

   compression) 
  and 
  unit-shear, 
  found 
  by 
  testing 
  the 
  

   material 
  in 
  simple 
  tension 
  or 
  compression 
  and 
  simple 
  

   shear. 
  This 
  theory 
  has 
  been 
  used 
  almost 
  exclusively 
  

   by 
  American 
  and 
  English 
  engineers. 
  

  

  (2) 
  The 
  Maximum 
  Strain 
  Theory. 
  — 
  This 
  theory 
  holds 
  that 
  

   the 
  material 
  yields 
  when 
  the 
  deformation 
  in 
  tension 
  

   or 
  compression 
  of 
  any 
  element 
  reaches 
  a 
  certain 
  

  

  * 
  Communicated 
  by 
  the 
  Author. 
  Read 
  before 
  the 
  American 
  Society 
  

   for 
  Testing 
  Materials, 
  June 
  1908. 
  

  

  