Characterization Of Crack Growth Behavior Under Multiple Cracks Interaction Of High Temperature Components

It is common for high temperature ageing engineering components containing multiple crack-like defects,which is often divided into surface and embedded cracks.During the operation of components,the interaction between multiple cracks would accelerate the crack growth rate and largely reduce the life of components.Two coplanar dissimilar embedded and surface cracks subjected to remote tensile load were investigated.The damage model was implemented into USDFLD user subroutine of commercial ABAQUS code to simulate the crack growth.The influence of crack configurations and residual stress on crack growth behavior in the presence of multiple cracks were studied through the variation of crack growth rate.Moreover,the experiment of multiple surface cracks was also conducted at elevated temperature to validate the finite element analysis.The finite element analysis reveal that the crack depth rate（a/t）has little influence on the embedded cracks growth direction,while the crack shape（a/c）,crack relative length（c₂/c₁）,crack distance（s/c）affect the embedded cracks crack growth direction.The surface cracks have little relationship with s/c and c₂/c₁.The crack depth rate（a/t）and crack shape（a/c）change the crack growth direction.With the relative crack sizes（a/t,a/c）become larger and the distance between two cracks（s/c）becomes close,the interaction between two cracks were enhanced and the crack growth rate was improved.The highest value of the magnified rate of crack growth rate for embedded cracks is 4.28（a/t=0.5）and for surface cracks is 12.49（a/t=0.8）.At the same crack configuration,the interaction intensity of surface cracks is twice as that of embedded cracks.The existence of residual stress will intensify the interaction of two cracks.With the increase of residual stress,the level of multiple cracks interference will increase obviously.According to the change of crack growth rates,the combination rule of multiple creep cracks was proposed.Asγ_creep≥1.15（embedded cracks）orγ_creep≥1.27（surface cracks）two interacting cracks should be considered to combine into a new big crack otherwise they can be treated as isolated cracks,respectively.And the new single big crack sizes were decided by the following formula:2c=?_creep*max（2c₁,2c₂）2a=max（2a₁,2a₂）,which can reduce the conservatism of predicted results.