Modeling and Measurement of Residual Stresses along the Process Chain of Autofrettaged Components by Using FEA and Hole-Drilling Method with ESPI

Abstract

The incremental hole-drilling method is a well-known mechanical measurement procedure for the analysis of residual stresses. The newly developed PRISM® technology by Stresstech Group measures stress relaxation optically using electronic speckle pattern interferometry (ESPI). In case of autofrettaged components, the large amount of compressive residual stresses and the radius of the pressurized bores can be challenging for the measurement system. This research discusses the applicability of the measurement principle for autofrettaged cylinders made of steel AISI 4140. The residual stresses are measured after AF and after subsequent boring and reaming. The experimental residual stress depth profiles are compared to numerically acquired results from a finite element analysis (FEA) with the software code ABAQUS. Sample preparation will be considered as the parts have to be sectioned in half in order to access the measurement position. Following this, the influence of the boring and reaming operation on the final residual stress distribution as well as the accuracy of the presented measurement setup will be discussed. Finally, the usability of the FEA method in early design stages is discussed in order to predict the final residual stress distribution after AF and a following post-machining operation.

Effect of Different Manufacturing Process Steps on the Final Residual Stress Depth Profile along the Process Chain of Autofrettaged Thick-Walled-Cylinders

“…Until the elements are finally deleted from the mesh, they remain in contact with the underlying elements and introduce a mechanical stress which then leads to the generation of residual stresses. The principal applicability of the model and all its relevant boundary conditions have been presented in [5,6].…”

“…Necessary process steps like forming, machining or heat treatment additionally induce residual stresses to an unknown extent and depth [4]. This leads to complex and superimposed final residual stress states [5].…”

“…A challenging task is the prediction of the superposition of residual stresses along the process chain. Brünnet et al [5,6] have proposed a finite element approach which is capable to model the autofrettage process as well as a subsequent post-machining process with boring and reaming. However, the measurement of the residual stress depth profiles especially for internally pressurized components is difficult to perform when considering conventional measurement methods such as hole-drilling or X-ray diffraction.…”

“…This leads to a significant redistribution of the residual stress depth profile [7]. Appropriate finite element models can be used to account for the redistribution effects [8,9,10]. However, the original residual stress state before cutting the components cannot be measured destructively.…”

X-Ray Diffraction Measurements and Investigation of the Stress Relaxation in Autofrettaged AISI 4140 Steel Thick Walled Cylinders

“…It leads to a beneficial and pronounced compressive RS vs. depth profile [1,2] and several authors report an extension in fatigue life for components treated with this process [3,4]. Its principle can be explained as follows [5]: when applying AF, a low-viscosity hydraulic medium is used to rapidly over-pressurize the treated component. If the resulting stresses exceed the yield strength of the material, then elasto-plastic deformation will result.…”