Antonio Culla

A method for evaluating the energy flow confidence level in vibrating systems with randomly perturbed parameters is presented. The energy flow is predicted in terms of the mobilities of resonant subsystems or by the solution of the velocity wave field for non-resonant subsystems. The statistical moments of the energy flow are calculated by a perturbation technique and a confidence factor

The purpose of this study was to evaluate cyclic fatigue fracture resistance of engine-driven nickel-titanium (K3XF) instruments under reciprocating movement in various angles. Fifty K3XF size 40 taper 0.06 nickel-titanium instruments were divided randomly into 5 groups of 10 each. All instruments were subjected to cyclic fatigue tests. Instruments in groups 1-4 were tested by using different reciprocating motions, whereas instruments of group 5 (control group) were used in continuous rotation. All instruments were rotated or reciprocated until fracture occurred. Time to fracture was recorded, and data were statistically analyzed by using one-way analysis of variance, followed by Tukey honestly significant difference test for comparison between different groups. All reciprocating groups (groups 1-4) showed a significant increase in time to failure when compared with group 5 (continuous rotation) (P < .05). Mean time was significantly higher in group 1, followed by group 2. No significant difference was found between groups 3 and 4 (P = .251). Increasing the clockwise angle of reciprocation and consequently increasing the angle of progression for each reciprocation cycle reduced the resistance to cyclic fatigue. Movement kinematics (reciprocating movements in various angles) had a significant influence on the cyclic fatigue life of the tested nickel-titanium instruments.

ABSTRACT This paper presents the results obtained from a 2D non linear finite element analysis under large transformations of the onset and evolution of sliding between two dissimilar isotropic elastic bodies separated by a frictional interface.The aim of this work is to investigate the time evolution of the global behaviour of the system, and relating it to the local phenomena occurring at the interface. Results from the numerical parameter space study show how the system parameters affect local dynamics. Consequently, local dynamics affect the macroscopic frictional behaviour of the system and excite the system dynamic response. The evolution of the tangential force changes from stick-slip like behaviour to continuous sliding as a function of local phenomena.

Two statistical techniques are developed to predict the statistical moments of the horizontal motion of a floating moored dock, known as catenary anchor leg mooring (CALM), loaded by hydrodynamic random forces. The dock is represented by a lumped mass, the mooring cables by equivalent nonlinear springs and the hydrodynamic forces are modelled by a modified Morison equation. The model of

ABSTRACT A limit of statistical energy analysis (SEA) is that of providing only the mean values of the mechanical energy of a vibrating system. In this paper, the variability of SEA solution under uncertain SEA parameters (coupling loss factors, internal loss factors and injected powers) is investigated by comparing a sensitivity approach and a design of experiment (DoE) approach. Uncertainties of the SEA parameters depend on uncertainties in the physical properties of the considered mechanical system. Numerical results are derived using a benchmark structure made by three aluminum plates with a common junction and a launcher fairing. The analysis of the effect of uncertainties of SEA parameters can be used for design purposes, i.e. to identify which are the most effective areas to modify in order to control the energy level of a given subsystem.

Friction drilling is a nontraditional hole-making process. A rotating conical tool is applied to penetrate a hole and create a bushing in a single step without generating chips. Friction drilling relies on the heat generated from the frictional force between the tool and sheet metal workpiece to soften, penetrate, and deform the work-material into a bushing shape. The mechanical and thermal aspects of friction drilling are studied in this research. Under the constant tool feed rate, the experimentally measured thrust force and torque were analyzed. An infrared camera is applied to measure the temperature of the tool and workpiece. Two models are developed for friction drilling. One is the thermal finite element model to predict the distance of tool travel before the workpiece reaches the 250°C threshold temperature that is detectable by an infrared camera. Another is a force model to predict the thrust force and torque in friction drilling based on the measured temperature, material...

In this paper a new approach is presented to reduce vibrations for one- and two-dimensional mechanical structures, as beam or thin plates, by means of several piezoelectric transducers shunted with a proper electric network system. The governing equations of the whole system are coupled to each other through the direct and converse piezoelectric effect. More in detail, the mechanical equations

In this paper an experimental analysis of the energy transmission in vibrating structures is considered. The classical discretization techniques (FEM, BEM) fail when one tries to solve high-frequency dynamic problems. At present, SEA is the most acknowledged theory for providing such kind of solution, giving information on the stored mechanical energy and on the dissipated mechanical power between the modal