421 research outputs found
Non-Destructive Characterization and Dynamic Destructive Characterization of an Historical Bell- Tower
No full textAn accurate knowledge about the dynamics of structures is definitely useful for seismic assessment and design of risk mitigation interventions. In this paper, the opportunities provided by dynamic identification techniques for the non-destructive evaluation of heritage structures are discussed with focus on the bell tower of Announziata, a masonry tower, which shows a high damaged scenario and, consequently, a high vulnerability to dynamic and seismic forces. A Finite Element (FE) numerical model has been built for research into the structural behaviour, deformation and stress distribution of the tower under static and dynamic loading. The model has been updated considering the modal parameters obtained by experimental tests carried out on the tower. The experimental measurements were difficult because of the compromised state of the building. The dynamical identification and the model updating required several assumptions of the material behaviour and properties that are not accurately available
Dynamic identification and finite model updating of Trani Cathedral's bell tower
No full textThe aim of the paper is to present the dynamical identification of the bell tower of the Cathedral of Trani (Bari, Italy). The tower, built in 1200, is about 60 meters high and has a square plan with a side of about 7.50 meters; moreover it is connected to the church through a step supported by a pointed arch. The tower vibrations due to ambient actions have been recorded and analyzed with different modern algorithms in such a way as to estimate the modal parameters of the tower. The identified modal parameters were utilized to evaluate the dynamic interaction between the tower and the church and some mechanical properties of the structural elements
Evaluation of the NSIFs on the basis of the averaged strain energy density under mixed mode
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How the Releasing Moment of Conical Steel Couplings is Influenced by the Combined Effect of Adhesive and Interference
No full textThe purpose of the present work is to carry out a research started some years ago and concerning the evaluation of the releasing moments in conical couplings realized with the simultaneous presence of interference and anaerobic adhesive (LOCTITE 638); the investigation was particularly focused on the effects due to the adhesive defect density and the interference level.
The releasing tests have been performed in accordance with the DOE (Design of Experiment) methodology. Therefore, a factorial experiment with two parameters (interference and adhesive defect density) on different levels, was designed with the goals to evaluate the significance of the main and the interaction effects and to determine the mathematical model of the failure load
Experimental evaluation of the damping properties and optimal modeling of coatings made by plasma-deposition techniques
No full textCoating layers, applied by means of different deposition technologies, can be used to produce composites with high damping properties. This is well known in literature and it is also verified by some experimental results reported in this work. The constitutive equivalent material model of coated specimens is identified and optimized by means of a generalized Kelvin model of n-th order, defined by means of the ratio of polynomials in the frequency domain. Dynamical measurements data obtained from coated single-layered and multi-layered samples obtained with different deposition techniques, are used to identify the optimal material model order and parameters. A robust identification technique that makes use of Forsythe orthogonal polynomials is employed for the numerical identification of the model parameters and a specific technique is introduced to eliminate the model non-physical components generated by measurement and model noise
EFFECTS OF SCREW SURFACE TREATMENTS AND OF DIFFERENT LUBRICATIONS ON THE FRICTIONAL PROPERTIES OF BOLTS
No full textThermo-mechanical Behaviour of Turbine Disc Assembly in the Presence of Residual Stresses
No full textA comprehensive three dimensional coupled thermo-mechanical finite element study is performed on turbine blade attachments in gas turbine engines. The effects of the self-generated centrifugal forces of the disc and the associated blades, thermal loads, and shot peening residual are all considered in this thesis. Three aspects of the work were accordingly examined. The first was concerned with the coupled thermo-mechanical stress analysis and load sharing between the teeth of the fir-tree root. The second was devoted to the development of a complete model incorporating the effect of shot peening residual stresses upon the developed stress state. The effectiveness of shot peening treatment in response to cyclic thermo-mechanical loadings at the contact interface has also been studied. The third was concerned with the validation of some aspects of the developed models analytically using closed form solutions and experimentally using photoelasticity.MAS
Effect of Perfectly Aligned CNTS Under Cohesive Crack Bridging in Adhesive Joint
No full textRecent advances in nano-engineering have prompted the use of nanofillers to strengthen composites and adhesive joints. This is because of the phenomenal mechanical properties that these nanotubes possess. For example, carbon nanotubes have elastic modulus ~1 TPa, and tensile strengths of ~100 GPa, which are more than 300 times those of a polymeric material. It is the purpose of this project to quantify the exceptional effect of nanofillers in cohesive crack bridging in structural adhesive bonds (SABs) for the aircraft industry. In this study, we assume that the high aspect ratio nanotubes are perfectly aligned in a thermoset epoxy adhesive. We carried out finite element modeling of the nano-reinforced SABs taking into account the constitutive law of the nanofillers by using the atomistic-based continuum finite element model. A crack in the nanocomposite is propagated using the virtual crack closure technique and the resulting fracture toughness is calculated. The analysis was conducted using atomic-based continuum finite element in which the constitutive laws for the different phases were carefully selected. Specifically, the Lennard-Jones inter-atomic potentials were used to treat the nanotubes and continuum constitutive laws were used for the SABs. The model represents nanofillers pullout with nonlinear springs and the epoxy is modeled with 2D plane stress elements. Our work reveals that the introduction of perfectly aligned CNTs results in improvements in fracture toughness of the composite of up to 195% at 0.5 wt%. Increasing the weight percentage of carbon nanotube fillers was found to increase the fracture toughness almost linearly. The effect of alignment on the bridging phenomena yields significantly higher toughness values than those typically found experimentally, but this correlates well with studies regarding the effect of nanotube alignment
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