text: The relationship between the stress-strain 
  diagram and operating strength limits should 
  If the aircraft is subjected to a 
  be obvious. 
  load greater than the limit, 
  the yield stress 
  may be exceeded and objectionable permanent 
  deformation may result. 
  is 
  subject to a load greater than the ultimate, 
  failure is imminent. 
  
  If  the aircraft 
  
  SERVICE LIFE 