FINITE ELEMENT PARAMETRIC INVESTIGATION ON THE RESIDUAL STRESSES INDUCED BY SPLIT SLEEVE COLD EXPANSION PROCESS

Mithun Kumar Kumar Dey

Residual Stress distribution and different parametric influence was studied for the split sleeve cold expanded holes in Al 2024 T351 alloy, by developing a three-dimensional finite element model of the process. Aluminum 2024 T351 alloy is very popular in the aviation industry. Fastener holes in the aerospace structures are necessary for the manufacturing process but create potential areas for stress concentration, which eventually leads to fatigue under cyclic loading. Beneficial compressive residual stress distribution induced by split sleeve cold expansion process provides retardation against crack initiation and propagation at the critical zones near hole edges. This retardation significantly increases the fatigue life of the structure. There are many experimental procedures to quantify the compressive residual stress as a result of this process. Experimental or visual validation is quite expensive and time-dependent but provides less reliability for the measurement of residual stress. So better numerical prediction with the transparency of the analysis design can provide critical information on the process.Many parameters are affecting the residual stress distribution. For better understanding, these parameters are divided into two separate groups, such as process parameters and analysis parameters. Process parameters include friction, mandrel design, split sleeve design, mandrel velocity, geometric configurations, expansion percentages, material properties, etc. Analysis parameters are analysis decisions and assumptions to get as close as possible to the realistic process. This includes analysis type decision, contact analysis between the assembled parts, boundary conditions, meshing techniques, mesh sensitivity, mesh element quality, interaction properties, etc. This study can provide the necessary data to change the traditional view on finite element analysis. Previous literature reviews reveal many assumptions that can result in poor prediction of residual stress. Those assumptions are in place to make the simulation less complicated and efficiently reducing the computational cost. In this thesis, the finite element analysis reached the effectiveness along with these complexities and assumptions that mirror the realistic approach. This numerical study is involved with contact analysis between assembled parts, contact friction properties, split sleeve, and mandrel elastic behavior consideration, and non-linear geometric deformations to present a more realistic approach.

FINITE ELEMENT PARAMETRIC INVESTIGATION ON THE RESIDUAL STRESSES INDUCED BY SPLIT SLEEVE COLD EXPANSION PROCESS

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