Structural Analysis of Tirana’s Clock Tower in Albania

Preservation of the ancient heritage and old structures for future generations is considered as a fundamental issue in the cultural life of modern societies. The purpose of preserving old monuments is to protect them as enduring landmarks and as testimony of the Albanian’s unique, multi ethnic and rich cultural heritage. On the other hand, the repair and conservation of historical buildings and monuments is a complex and challenging discipline. Watch towers are common in Albania. In many cities these towers are often protected by law as part of the cultural heritage. The main focus of this paper is to investigate and to present a summary of the results of the structural response of the Clock tower of Tirana, including its response under gravity and seismic loads. The stress concentrations at the critical locations are investigated and the analysis results were discussed

Investigation of the martensitic transformation and the damping behavior of a superelastic Ti-Ta-Nb alloy

International audienceIn this study the α″ stress-induced martensitic transformation and damping behaviour of the superelastic β-Ti-25Ta-25Nb alloy are investigated by tensile tests at room temperature and by dynamic mechanical analysis (DMA) in tensile mode for different applied stresses. Tensile tests show a fully non-linear elastic domain and, consequently, a specific method is proposed to determine the elastic modulus. Due to the wide range of temperature over which the martensitic transformation occurs in this class of alloys, the martensitic start temperature, Ms, is not a relevant parameter to characterize the transformation and the temperature Mmax corresponding to the temperature of maximum transformation is used. The important gap between these two temperatures explains the fully non-linear elastic behaviour of this alloy during conventional tensile tests. It is observed that two main damping sources occur in this alloy: friction at austenite/martensite interfaces during the martensitic transformation and friction at martensite/martensite interfaces at lower temperature. However, a third unexpected damping peak is also observed at high stress. Its origin is discussed with respect to the orientation of the applied stress and with regard to the most favourably oriented martensite variants determined by Schmid factor analysis

Dislocation mobility in gum metal β-titanium alloy studied via in situ transmission electron microscopy

International audienceIn situ tensile tests in a transmission electron microscope were carried out on a "Gum Metal" β titanium alloy. Conventional dislocation slip was observed to be the only mechanism occurring during the plastic deformation. The low mobility of screw dislocations was shown to be due to their core structure configuration. Nanometer-sized obstacles were also present but have a weaker effect of the dislocation mobility. The density of these obstacles and the variation in energy due to the core structure of screw dislocations were measured and compared to theoretical data of literature

Mechanisms of deformation in gum metal TNTZ-O and TNTZ titanium alloys: A comparative study on the oxygen influence

International audienceIn this work, Ti-23Nb-0.7Ta-2Zr (TNTZ) and gum metal Ti-23Nb-0.7Ta-2Zr-1.2O (TNTZ-O) alloys were synthesized by cold crucible levitation melting with the objective of investigating the influence of oxygen on the deformation mechanisms. By tensile tests, electron backscatter diffraction, atomic force microscopy and transmission electron microscopy analyses, we showed that the deformation in the TNTZ-O alloy is only accommodated by dislocation slip. Thus, the addition of oxygen suppresses the formation of α″ martensite and prevents the twinning deformation mechanism, which were both observed in the TNTZ alloy. In addition, in situ tensile tests in a transmission electron microscope showed that conventional a/2〈1 1 1〉 dislocation slip occurs widely in the TNTZ-O alloy. Screw dislocations have a lower mobility than non-screw dislocations. Cross-slip is shown to be easy and multiplication of dislocations by a double cross-slip mechanism occurs extensively, leading to the formation of large slip bands

An alternative way to orient the parent phase in the cubic/orthorhombic martensitic transformation of titanium shape memory alloys

International audienceTitanium-based shape memory alloys undergo a cubic to orthorhombic martensitic transformation (β to α'' martensite). A new easy way operating as a reconstruction of the parent microstructure is used from electron backscattered diffraction. It is shown that the electron backscattered patterns of the martensitic microstructure can be directly indexed as the parent phase in order to obtain the correct orientation of the high temperature microstructure. This method is however specific to the cubic/orthorhombic martensitic transformation in titanium shape memory alloys

In situ TEM study of dislocation slip in a metastable β titanium alloy

International audienceDislocation slip is investigated in a metastable β titanium alloy with the Ti-23Nb-0.7Ta-2Zr-0.4Si composition (at. %) by in situ straining experiments in a transmission electron microscope (TEM). Moving dislocations have a/2 Burgers vectors and glide in {110}, {112} or {123} planes. The mobility of screw dislocations is lowered by punctual defects and the existence of a stable and sessile core configuration that has to recombine in order to allow dislocations to glide

Twinning system selection in a metastable β-titanium alloy by Schmid factor analysis

International audienceElectron backscattering diffraction and Schmid factor analysis were used to study the twinning variant selection in a Ti-25Ta-24Nb (mass%) metastable β-titanium alloy. The two twinning systems {1 1 2}〈1 1 1〉 and {3 3 2}〈1 1 3〉 were observed. For each system the Schmid factor was shown to be a relevant parameter to determine the activated variant. Moreover, selection between the two twinning systems depends on the crystallographic orientation of the grain with respect to the tensile direction

Deformation twinning in the full-α″ martensitic Ti–25Ta–20Nb shape memory alloy

International audienceDeformation twinning of the Ti–25Ta–20Nb (mass%) shape memory alloy is characterized using EBSD and TEM. The selfaccommodating α″ microstructure is shown to be first deformed using \111\α″ type I and <211>α″ type II reorientation twinning. Plastic deformation occurs further by plastic twinning with a new \130\<310>α″ twinning system. Maximum lattice deformation calculation is a relevant parameter to predict the variant of martensite that is favored during the reorientation process. Conversely, Schmid factor analysis can be used to predict the selection of \130\<310>α″ twinning variants during deformation. Analogy between \130\<310>α″ and \332\<113>β twinning systems is highlighte

Mechanical properties and corrosion resistance of some titanium alloys in marine environment.

International audienceTitanium alloys are used in several fields such as aerospace industry or biomedical. They are increasingly used in marine applications, a highly corrosive environment. We chose titanium alloys for their good properties such as high mech. strength, low d. and excellent corrosion resistance. This study is focused on titanium alloys potentially interesting to be used in marine transports, and mainly for the boats fittings such as a winch for example. [on SciFinder(R)

Effects of cold-rolling deformation on texture evolution and mechanical properties of Ti-29Nb-9Ta-10Zr alloy

International audienceThe crystallographic texture of Ti-29Nb-9Ta-10Zr alloy is studied after cold-rolling with different amounts of thickness reduction, up to 60%. The major texture components developed during cold-rolling were: γ-fibre components: {111}〈View the MathML source〉, {111}〈View the MathML source〉, {111}〈View the MathML source〉 and {111}〈View the MathML source〉; texture component: {112}〈View the MathML source〉 and texture components: {001}〈View the MathML source〉 and {010}〈001〉. Besides crystallographic texture the resulted mechanical properties were studied by nanoindentation. It was showed that the decrease in Young's modulus after different cold-rolling stages is mainly attributed to the stress-induced α″-Ti phase formation. At 60% cold-rolling thickness reduction obtained an elastic modulus close to 45.29±3.81 GPa, coupled with an average Vickers microhardness close to 279.83±4.28 HV