Evaluating the influence of residual stresses and surface damage on fatigue life of Nickel superalloys

The effect of surface damage, such as dents caused due to the low velocity impact of hard blunt objects, on the fatigue life of mechanical components are investigated in this paper. A twodimensional dislocation density approach is used to obtain the stress intensity factors of a crack propagating under dents. Both the contributions of the geometrical stress concentrator (notch), due to the presence of the dent, and the residual stress field, generated during the impact, on the stress intensity factor of the crack are obtained. A short crack growth model is then used to predict the fatigue life of nickel superalloys in the presence of two dent depths. The effect of the residual stress field has been shown to be the main contributor to the difference observed in predicted fatigue life between the two dent depths analysed

Evaluating the influence of residual stresses and surface damage on fatigue life of Nickel superalloys

The effect of surface damage, such as dents caused due to the low velocity impact of hard blunt objects, on the fatigue life of mechanical components are investigated in this paper. A twodimensional dislocation density approach is used to obtain the stress intensity factors of a crack propagating under dents. Both the contributions of the geometrical stress concentrator (notch), due to the presence of the dent, and the residual stress field, generated during the impact, on the stress intensity factor of the crack are obtained. A short crack growth model is then used to predict the fatigue life of nickel superalloys in the presence of two dent depths. The effect of the residual stress field has been shown to be the main contributor to the difference observed in predicted fatigue life between the two dent depths analysed

The influence of contacting Ni-based single-crystal superalloys on fretting fatigue of Ni-based polycrystalline superalloys at high temperature

Fretting fatigue tests at high temperature were carried out with single-crystal and polycrystalline alloys. The influence of the crystallographic orientation of contacting single-crystal pads on the lives of polycrystalline specimens is investigated. An analytical formulation of the contact problem between two anisotropic cylinders is used to study the changes in peak stress and contact width due to the orientation of the single-crystal. Finite element analysis is also used to study the variation of stress near the contact edge due to crystallographic orientation. An area averaging method is suggested to correlate fretting fatigue and plain fatigue curves. Using finite element analysis combined with the area averaging method, a better correlation was found between fretting fatigue results and plain fatigue. © 2014 Elsevier Ltd. All rights reserved

The influence of contacting Ni-based single-crystal superalloys on fretting fatigue of Ni-based polycrystalline superalloys at high temperature

Fretting fatigue tests at high temperature were carried out with single-crystal and polycrystalline alloys. The influence of the crystallographic orientation of contacting single-crystal pads on the lives of polycrystalline specimens is investigated. An analytical formulation of the contact problem between two anisotropic cylinders is used to study the changes in peak stress and contact width due to the orientation of the single-crystal. Finite element analysis is also used to study the variation of stress near the contact edge due to crystallographic orientation. An area averaging method is suggested to correlate fretting fatigue and plain fatigue curves. Using finite element analysis combined with the area averaging method, a better correlation was found between fretting fatigue results and plain fatigue. © 2014 Elsevier Ltd. All rights reserved

Estimation of the coefficient of friction in partial slip contacts between contacting Nickel superalloys

Standard methods for measuring the coefficient of friction between two objects are not appropriate for partial slip contacts, since less damage occurs at the interface. A discussion on the different methods for measuring the coefficient of friction in partial slip contacts is carried out. Results of the coefficient of friction between Nickel superalloys, measured by a non-sliding technique, are presented. The effect of crystal orientation of single-crystals on the friction coefficient was found to be small. A study for using the energy dissipated in two-dimensional partial slip contacts is also presented. An approach for measuring the friction coefficient using the dissipated energy is proposed and the challenges and difficulties in measuring friction through the dissipated energy at the contact are discussed

Estimation of the coefficient of friction in partial slip contacts between contacting Nickel superalloys

Standard methods for measuring the coefficient of friction between two objects are not appropriate for partial slip contacts, since less damage occurs at the interface. A discussion on the different methods for measuring the coefficient of friction in partial slip contacts is carried out. Results of the coefficient of friction between Nickel superalloys, measured by a non-sliding technique, are presented. The effect of crystal orientation of single-crystals on the friction coefficient was found to be small. A study for using the energy dissipated in two-dimensional partial slip contacts is also presented. An approach for measuring the friction coefficient using the dissipated energy is proposed and the challenges and difficulties in measuring friction through the dissipated energy at the contact are discussed

Incomplete contacts in partial slip subject to varying normal and shear loading, and their representation by asymptotes

We develop a method for the solution of partial slip contact problems suffering complex loading cycles where, generally, the normal load, shear force and, potentially, differential bulk tensions are all functions of time, using an edge-asymptote approach. The size of the slip zone and local shear traction distribution are revealed as functions of time. The results are then re-worked in asymptotic form, so that they do not hinge on inherent symmetry and anti-symmetry conditions for the contact overall, and are of general applicability. The multipliers on the local solutions (generalised stress intensity factors) are also appropriate as a means of taking laboratory tests quantifying fretting fatigue and employing them to wholly different prototypical problems

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

A methodology for evaluating the effect of surface damage in the fatigue life of nickel superalloys is presented in this paper. Dents generated due to low velocity impacts of hard objects were simulated using a finite element (FE) model. The residual stress distribution underneath the dent root obtained numerically was compared with the measurements on experimentally simulated damaged specimens using ring-core milling at the micron scale through a combined Focused-Ion Beam and Digital Image Correlation technique (FIB-DIC). The numerical and experimental results for the residual stress show good agreement in terms of residual stress trends and magnitudes. The residual stress distribution obtained via the FE model was subsequently used in a fatigue short crack growth model for an estimation of the fatigue life of dented specimens. The fatigue life predictions were then compared with experimental fatigue results for the nickel superalloy at high temperatures. The comparison shows a significant improvement in the prediction of fatigue life of parts with superficial damage due to careful consideration of the residual stresses around the damage