Speaker
Description
The development of aeroengines with higher thermal efficiencies, has been facilitated by the advance in materials, notably the development of thermal barrier coatings and their testing techniques. The Small Punch Test (SPT) is a vastly used material test in industry, that is implemented to characterise mechanical behaviour of materials that are in a limited supply, such as thermal barrier coatings present on gas turbine blades.
However, after over 30 years of use in industry, the procedure still does not have a code of practice available and there remains dispute about the reliability of its results. This work therefore investigates the ability of the SPT to measure material mechanical properties. The material studied is CoNiCrAlY which is a bond coat in thermal barrier coatings. The work is undertaken by firstly conducting a sensitivity analysis of the Young’s Modulus (E) and Poisson Ratio (v) of CoNiCrAlY, to changes in the elastic properties of its β-NiAl phase. By creating a Representative Volume Element (RVE) of CoNiCrAlY, the impact of varying the elastic constant of its body-centred cubic β-NiAl phase on its E and v, is determined. Here the RVEs are used to model the polycrystalline microstructure of CoNiCrAlY whilst the elastic constants are responsible for defining the elasticity matrix of the cubic crystals present in the β-NiAl phase. Subsequently a finite element model of the SPT of CoNiCrAlY is constructed, using material properties obtained from the sensitivity analysis. The elastic and elastic-plastic results of the material are analysed based on the impact of several factors which are its yield stress, Young’s modulus and the friction between contacting surfaces in the SPT model. Finally, the results from the investigation are analysed to ascertain whether the SPT results are sensitive to changes in material properties of the material being tested or are more influenced by other factors such test parameters of the SPT.
| Speaker Country | United Kingdom |
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