text: relationships 
  structures. 
  
  for aircraft  and powerplant 
  
  CREEP CONSIDERATIONS. By definition, 
  creep is the structural deformation which oc- 
  curs as a function of time. 
  If a part is subjected 
  to a constant stress of sufficient magnitude, the 
  part will continue to develop plastic strain and 
  deform with 
  failure can 
  time. Eventually, 
  occur from the accumulation of creep damage. 
  Creep conditions are most critical at high 
  stress and high temperature since both factors 
  increase the rate of creep damage. Of course, 
  any structure subject to creep conditions should 
  not encounter excessive deformation or failure 
  within  the anticipated service life. 
  
  The high operating temperatures of gas tur- 
  bine components furnish a critical environment 
  for creep conditions. The normal operating 
  temperatures and stresses of gas turbine com- 
  ponents create considerable problems in design 
  for service life. Thus, operating limitations 
  deserve very serious respect since excessive 
  engine speed or excessive turbine temperatures 
  will cause a large increase in the rate of creep 
  damage and lead to premature failure of com- 
  ponents. Gas turbines require high operating 
  temperatures to achieve high performance and 
  efficiency and short periods of excessive tem- 
  peratures can incur highly damaging creep 
  rates. 