Characterisation of handling and service surface damage on Nickel alloys caused by low velocity impacts of blunt hard objects

Abstract

This paper presents a characterisation of surface damage, more specifically dents, caused by low velocity impacts of blunt objects on RR1000 Nickel superalloys. These are representative of damage that may occur during handling and service of components during manufacturing or maintenance. The characterisation of dents produced in laboratory tests is carried out both in terms of their geometry and the residual stresses the damage. A finite element model is presented and the results are validated in terms of dent geometry produced for different impact velocities. The stress distribution predicted by the numerical model is also compared with experimentally measured stresses via X-ray diffraction for validation of the model. The residual stresses obtained from the finite element (FE) model and their implications to fatigue and crack propagation lives are also discussed here.

The effect of surface damage and residual stresses on the fatigue life of nickel superalloys at high temperature

“…The geometry of the damage is similar to that of the indenter, which has a hardened steel ellipsoidal tip with two principal radii of curvature (R 1 = 12.5 mm and R 2 = 1 mm). As described in [6], a calibration of the dent depth as a function of the reservoir pressure, and hence the impact velocity, was conducted. From the calibration consistent dent depths were obtained in each experimental damage simulation and different groups of dent depths were generated for the fatigue tests.…”

“…The first step for developing a model which incorporates the competing factors around the damage is to reproduce in laboratory similar surface dents and scratches as those found in real components. The challenge of simulating in laboratory the conditions in which handling damage may occur have been discussed by previous authors [6,7]. While the dent were created by indentation in [7] and previous work may be found suggesting that the residual stress field obtained by indentation is similar to that obtained by low velocity impacts [8], here, the experimental simulation of handling damage was carried by shooting onto the specimen a projectile with a blunt tip as to produce a dent similar to those observed in real engine components.…”

“…While the dent were created by indentation in [7] and previous work may be found suggesting that the residual stress field obtained by indentation is similar to that obtained by low velocity impacts [8], here, the experimental simulation of handling damage was carried by shooting onto the specimen a projectile with a blunt tip as to produce a dent similar to those observed in real engine components. This procedure is described in detail in [6] and the result is a more accurate representation of real engine occurrences of surface damage during manufacturing and maintenance of engines.…”

“…Recently, the authors have conducted a series of work on handling surface damage. First, the characterisation of surface damage due to the impact of hard blunt objects was studied [6]. The work focused on the geometry of the dent created, i.e.…”

“…Hence, the current paper aims to compare the fatigue life predictions with experimental results, for which is necessary to incorporate residual stress relaxation mechanisms into the fatigue life calculations. In order to validate the residual stresses obtained with the FE model along the crack path, the stresses along the crack path is needed, which in [6] was done only aver a large averaging area using XRD. Therefore, a point-wise comparison of the residual stresses obtained from the FE model with experimentally measured results is also carried out by using the micro ring-core method, which is a combination of Focused-Ion Beam and Digital Image Correlation techniques (FIB-DIC).…”