The effects of machined topography on fatigue life of a nickel based superalloy

The surface topography of engineering components is known to affect fatigue behaviour. However, defining topography based on the average roughness (Ra) parameter is considered to be inadequate when correlating to fatigue performance. Alternative correlations utilising areal topographic parameters would therefore be valuable. This has been addressed through areal topographic measurements and fatigue testing of an advanced nickel based superalloy, Alloy720Li. Low cycle and high cycle … Continue reading The effects of machined topography on fatigue life of a nickel based superalloy

Titanium alloy developments for aeroengine fan systems

Recent research relating to two α+β processed titanium alloys, designed for specific employment in aeroengine fan disc and aerofoil components, is described. Timetal 575 (Ti575) and Timetal 639 (Ti639) are both novel compositions that provide relatively high strength compared to Ti–6Al–4V. Static and cyclic behaviour of the two developmental alloys were evaluated at room temperature. A dwell fatigue assessment of Ti575 is reported, while the … Continue reading Titanium alloy developments for aeroengine fan systems

Fatigue behaviour of geometric features subjected to laser shock peening: Experiments and modelling

Finite element models, using the eigenstrain approach, are described that predict the residual stress fields associated with laser shock peening (LSP) applied to aerospace grade aluminium alloys. The model was used to explain the results of laboratory fatigue experiments, containing different LSP patch geometries, supplementary stress raising features and different specimen thickness. It is shown that interactions between the LSP process and geometric features are … Continue reading Fatigue behaviour of geometric features subjected to laser shock peening: Experiments and modelling

Experimental and crystal plasticity studies of deformation and crack nucleation in a titanium alloy

This paper presents recent developments in crystal plasticity modelling to incorporate a non-local crack nucleation criterion and the comparison of experimental observations and model predictions for deformation and crack nucleation in a near-alpha titanium (Ti) alloy polycrystal. The model polycrystal was established so as to have grain morphology and crystallography nominally identical to that in the experiment, enabling direct interpretation and comparison of the results. … Continue reading Experimental and crystal plasticity studies of deformation and crack nucleation in a titanium alloy

Prediction of fatigue lives at stress raising features in a high strength steel

The fatigue properties of the high strength stainless steel CSS42L have been evaluated under strain and stress controlled conditions. The results have been used to derive a predictive approach based on the Walker strain equation. Accurate predictions are obtained for VCN and DEN specimens although the lower stress concentration RCN specimen is shown to compare more readily with plain specimen stress controlled data. The difference in fatigue life between … Continue reading Prediction of fatigue lives at stress raising features in a high strength steel

The Non-Proportional Behaviour of a Nickel-Based Superalloy at Room Temperature, and Characterisation of the Additional Hardening Response by a Modified Cyclic Hardening Curve

A study was carried out where tension-torsion deformation strain-controlled tests were completed at Swansea University, to characterise the non-proportional hardening response of a nickel-based superalloy across a range of strain ranges. The data generated was used to assess the validity of a non-proportional cyclic hardening curve correction proposed by Socie and Marquis to represent the material’s hardening response. This modification involves the linear translation of … Continue reading The Non-Proportional Behaviour of a Nickel-Based Superalloy at Room Temperature, and Characterisation of the Additional Hardening Response by a Modified Cyclic Hardening Curve

Prediction of fatigue lives at stress raising features in a high strength steel

The fatigue properties of the high strength stainless steel CSS42L have been evaluated under strain and stress controlled conditions. The results have been used to derive a predictive approach based on the Walker strain equation. Accurate predictions are obtained for VCN and DEN specimens although the lower stress concentration RCN specimen is shown to compare more readily with plain specimen stress controlled data. The difference in fatigue life between … Continue reading Prediction of fatigue lives at stress raising features in a high strength steel

A model for time dependent strain accumulation and damage at low temperatures in Ti–6Al–4V

Dwell fatigue effects at low temperatures in a range of titanium alloys have been well documented since the 1970s. However, attempts to model dwell fatigue phenomena are limited. The time dependent effects have been shown to be due to the inherent strain accumulation behaviour at ambient or low temperatures, loosely termed ‘cold creep’ in alloys such as Ti-6Al-4V. Periods of dwell in a fatigue cycle … Continue reading A model for time dependent strain accumulation and damage at low temperatures in Ti–6Al–4V

Considerations in fatigue lifing of stress concentrations in textured titanium 6-4

The effect of crystallographic texture has been considered in attempting to derive a total life prediction capability for the titanium alloy Ti6-4. Orientation effects due to texture are shown to be a result of stress relaxation in strain control specimens, and consequently occur in some cases of notched specimens. It is shown that these effects can be predicted using analytical methods such as the Modified Coffin–Manson and Walker strain … Continue reading Considerations in fatigue lifing of stress concentrations in textured titanium 6-4

Modelling the behaviour of titanium alloys at high temperature for gas turbine applications

Increased efficiency within the aero engine can be achieved through higher operating temperatures. In order to meet this requirement designers seek either to implement new alloys or show that existing alloys are capable of operating under more extreme conditions. At higher temperatures fatigue is no longer the sole damage mechanism and contributions from creep and environmental interactions must also be considered. This paper seeks to address some of these … Continue reading Modelling the behaviour of titanium alloys at high temperature for gas turbine applications