Thermal stress ratcheting

Thermal stresses are secondary stresses because they are self-limiting. That is, yielding or deformation of the part relaxes the stress (except thermal stress ratcheting). Thermal stresses will not cause failure by rupture in ductile materials except by fatigue over repeated applications. They can, however, cause failure due to excessive deformations. 

Thermal stress ratcheting is progressive incremental inelastic deformation or strain that occurs in a component that is subjected to variations of mechanical and thermal stress. Cyclic strain accumulation ultimately can lead to incremental collapse. Thermal stress ratcheting is the result of a sustained load and a cyclically applied temperature distribution. 

Elastic Stress Analysis - Simplified Elastic-Plastic Method. This method may be used in the case where the method indicated above shows the Pr + Pb + Q stress limits are not satisfied, but indicates that the Pl + Pb + Q range and excluding thermal effects must be less than Sps- Additionally, the effective alternating equivalent stress amplitude must include the fatigue penalty factor, ICej, which is based off of the simplified elastic-plastic criteria from the pre-2007 Section VIII, Division 2. Finally, a thermal stress ratcheting assessment must be made. 

Elastic Stress Analysis - Thermal Stress Ratcheting Assessment. This section will evaluate the allowable limit on the secondary stress range from cyclic thermal loading. 

A ratchet mechanism is proposed to account for growth, in which the stresses generated by anisotropic thermal expansion of TNT are... 

The walls of outdoor metal silos can expand during the day and contract at night as the temperature drops. If there is no discharge taking place and the matoial inside die silo is fiee fiowing, it will settle as the silo expands. However it cannot be pushed back up when the silo walls contract, so it resists the contraction which in turn causes increased tensile stresses in the wall. This phenomenon, which is repeated each day the material sits at rest, is called thermal ratcheting. [19-23]... 

Unlike lead, tin exhibits anisotropy, e.g., coefficient of thermal expansion that varies by a factor of 2 in different crystallographic directions. As discussed in Sec. III.C, this condition can lead to large internal stresses and thermal ratcheting in tin alloys that does not occur in lead-based solders. These effects are anticipated during normal thermal and power cycling tests with no... 

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