Papers by Keyword: Thermo-Mechanical Effect

Abstract: The crystallisation behaviour of Vitreloy 105 during different thermo-mechanical exposure conditions has been studied in a Gleeble 3500 thermo-mechanical simulator (TMS). Strains up to 0.1 applied at rates of 0.001 – 0.01 s^-1 in the supercooled liquid region (SLR) from 420 – 435 °C resulted in no change in the crystallisation kinetics compared with purely thermal exposure for the same times and temperatures. Separate deformation studies on the amorphous bulk metallic glass confirmed that the deformation conditions used corresponded to Newtonian flow conditions. It remains to be confirmed whether the lack of influence of permanent deformation persists for deformation at higher strain rates in the non-Newtonian regime.

Abstract: Laser shock processing (LSP) is consolidating as an effective technology for the improvement of metallic materials surface properties involving their fatigue life. The main acknowledged advantage of the LSP technique consists on its capability of inducing a relatively deep compression residual stresses field into metallic alloy pieces allowing an improved mechanical behaviour, explicitly the life improvement of the treated specimens against wear, crack growth and stress corrosion cracking. Progress accomplished by the authors in the line of practical development of the LSP technique at an experimental level, aiming its integral assessment from an interrelated theoretical and experimental point of view, is presented in this paper. Concretely, experimental results on the residual stress profiles and associated surface properties modification successfully reached in typical materials (especially Al and Ti alloys) under different LSP irradiation conditions are presented, a correlated analysis of the residual stress profiles obtained under different irradiation strategies and the evaluation of the corresponding induced surface properties as roughness and wear resistance being also presented. Through a coupled theoretical- experimental analysis the real possibilities of the LSP technique as a possible substitutive of related traditional surface modification techniques as, for example, shot peening.

Abstract: Due to the complex microstructure and phase transformations taking place in Shape Memory Alloys (SMA), the behaviour and properties of these materials are deeply influenced by their loading history in terms of stress, strain and temperature. Indeed, a thorough understanding of the effects of the loading history on SMA properties is fundamental for a correct modelling and design of SMA applications, in particular in the case of complex loading. An example are shape memory alloys embedded in composite systems, in which stress, strain and temperature vary simultaneously depending upon the properties of the SMA and composite. This work presents the first results of an experimental investigation on the effects of the loading history on SMA transformation temperatures. Nitinol wires of untrained material were considered. Specimens consisting of Martensite and R-phase were subjected to different loading histories, keeping in turn stress, strain or temperature at a constant value. Transformation temperatures at zero stress of these samples were measured via Differential Scanning Calorimetry. Contrarily to most constitutive models assumptions, the DSC results highlight a dependence of the transformation temperatures on the loading history, influencing in particular the Martensite to Austenite phase transformation.

Abstract: Molecular dynamics (MD) simulation and the experiment of adhesion force measurement were introduced to study the nanostructure formation process in the atomic force microscopy. The atomic level process of the nanostructure formation and the thermo-mechanical effect caused by the factors of the contact area, the adhesion force, and the temperature were clearly shown and discussed. The size of the forming nanostructures was found to be positively related to the contact area and temperature, but the adhesion force would decrease as the temperature increase. In the case of higher temperature with smaller adhesion force, however, the larger-size nanostructure could still be made.