text: excess of the operational limits for these con- 
  increase the possibility of early 
  ditions will 
  failure of the turbine components. 
  
  the design service life with 
  trouble-free opera- 
  tion. The following items describe the critical 
  areas encountered during the operational use 
  of the turbojet engine: 
  
  While the turbine components are the most 
  critically stressed high temperature elements 
  they are not the only items. The combustion 
  chamber components may be critical at low 
  altitude where high combustion chamber pres- 
  sures exist. Also, the airframe structure and 
  equipment adjacent to the engine may be sub- 
  ject to quite high 
  temperatures and require 
  provision to prevent damage by excess time at 
  high temperature. 
  
  (1) The limiting exhaust gag tcmpcra;wcs pro- 
  vide the most important restrictions to the op- 
  eration of the turbojet engine. The turbine 
  components are subject to centrifugal loads of 
  impulse and reaction loads on the 
  rotation, 
  blades, and various vibratory loads which may 
  be inherent with the design. When the turbine 
  components are subject to this variety of stress 
  in the presence of high temperature, two types 
  of structural phenomena must be considered. 
  when a part is subject to a certain stress at some 
  high temperature, weep failure will 
  take place 
  after a period of time. Of course, an increase 
  in .tcmperature or stress will 
  increase the rate 
  at which creep damage is accumulated and 
  reduce the time required to cause failure. An- 
  other problem results when a part is subjected 
  to a repeated or cyclic stress. F&&e 
  failure 
  will occur after a number of cycles of a varying 
  stress. An increase in temperature or magni- 
  tude of cyclic stress will 
  increase the rate of 
  fatigue damage and reduce the number of cycles 
  It is important 
  necessary to produce failure. 
  to note that both fatigue and creep damage are 
  cumulative. 
  
  (2) The c~mprcs~or Jtall or surge has the pos- 
  sibility of producing damaging temperatures 
  in the turbine and combustion chamber or un- 
  usual transient loads in the compressor. While 
  the stall-surge phenomenon is possible with 
  the centrifugal compressor, the more common 
  the axial flow compressor. 
  .occurrence is with 
  Figure 2.13 depicts the pressure distribution 
  that may exist for steady state operation of 
  the engine. 
  In order to accelerate the engine 
  to a greater speed, more fuel must be added to 
  increase the turbine power above that required 
  to operate the compressor. 