Experimental and numerical study of pneumatic needle peening effects on Aluminium Alloy 2024-T3

Pneumatic needle peening process was experimentally calibrated using high speed camera and numerically simulated using previous developed shot peening and peen forming finite element (FE) models. High speed photography was applied to record the images of peening needles and digital image treatment program was developed to calculate needle peening velocities for the FE simulation. A single impact simulation was performed for convergence study and indentation comparison to validate the impact model. Good accordance between the simulated and experimental indentation diameters was obtained. Then multiple needle impact models were applied to simulate the induced stress profiles for different peening conditions. Finally, the induced stress profiles were input into a peen forming FE model to predict the specimen deflections (or arc heights). Similar to Almen intensity definition, saturation point was determined by defining certain peening time, when double peening time, the produced arc height increases equal to 10%. The residual stress profile at saturation time for one of the scenarios was calculated and compared against the X-ray diffraction (XRD) measured results at the same operating pressure. In addition, the residual stress profile calculated from the induced stress profile using analytical equations was compared with XRD measurements. Compared to experimental measurements, both the model simulated and analytical calculated residual stress profiles were able to predict the surface compressive residual stress and maximum compressive residual stress very well. The simulated deflection results for the studied peening pressures were then compared against the deflection measurements using the coordinate measuring machine (CMM). The difference between experimental and predicted results ranges between 0.3% and 13.2% for the four higher peening pressures. However, for the lowest peening pressure, larger error of 50% was obtained, which can be explained as the overestimation of the peening velocity at the lowest peening pressure. In conclusion, the presented methodologies are able to calibrate the peening velocities, to predict the induced stresses and further to calculate sample deflections of thin specimen by pneumatic needle peening.