Antonio Virga

Investigation on the load-displacement curves of a human healthy heel pad: In vivo compression data compared to numerical results

The aims of the present work were to build a 3D subject-specific heel pad model based on the anatomy revealed by MR imaging of a subjects heel pad, and to compare the load-displacement responses obtained from this model with those obtained from a compression device used on the subjects heel pad. A 30 year-old European healthy female (mass=54kg, height=165cm) was enrolled in this study. Her left foot underwent both MRI and compression tests. A numerical model of the heel region was developed based on a 3D CAD solid model obtained by MR images. The calcaneal fat pad tissue was described with a visco-hyperelastic model, while a fiber-reinforced hyperelastic model was formulated for the skin. Numerical analyses were performed to interpret the mechanical response of heel tissues. Different loading conditions were assumed according to experimental tests. The heel tissues showed a non-linear visco-elastic behavior and the load-displacement curves followed a characteristic hysteresis form. The energy dissipation ratios measured by experimental tests (0.25±0.02 at low strain rate and 0.26±0.03 at high strain rate) were comparable with those evaluated by finite element analyses (0.23±0.01 at low strain rate and 0.25±0.01 at high strain rate). The validity and efficacy of the investigation performed was confirmed by the interpretation of the mechanical response of the heel tissues under different strain rates. The mean absolute percentage error between experimental data and model results was 0.39% at low strain rate and 0.28% at high strain rate.

Evaluation of energy-saving driving styles for bus drivers

Abstract A procedure is presented for evaluating the performance in terms of driving style of public transport bus drivers, within the context of a programme for energy savings in urban public transportation. The purpose of this evaluation is that of providing suitable tools for training of personnel with the objective of attaining more energy-efficient driving styles and improving driving quality. Quality can be defined as the combination of an energy saving driving style with a behaviour that is respectful of the environment (noise, pollution and safety) and of the vehicle and is comfortable for the passengers as well. Economical driving provides direct savings in fuel of up to 25 per cent as well as indirect savings deriving from general improvements in quality; a more controlled driving style can also be accompanied by reductions in air pollution and noise emission. The procedure utilizes a fuzzy logic approach and can be implemented aboard vehicles in an automatic monitoring system, the sole requirement being that of measuring the instantaneous road speed of the vehicle and its current load. The procedure has been developed and validated on the basis of data coming from a test campaign carried out on vehicles equipped with automatic and manual transmission, operating over both urban and intercity itineraries in three different cities, and adopting different driving styles with different drivers. By analysing the results, in relation to the itinerary and conditions of traffic, stops, load, etc., it can be determined which conditions, for each driver, lead to either good or poor performance. Such specific information, together with assessment of the overall driving style, provides useful indications for training drivers, both through training programmes with specific itineraries and trials, and through self-learning processes with the procedure implemented using an on-board monitoring system.

Evaluation of emergency braking deceleration for accident reconstruction

Tire–road coefficient of friction is often used to estimate stopping distances and other aspects of accident reconstruction. The actual value that must be used in the calculations is often obtained from published data and sometimes measured on-site. While it depends mainly on tires, road surface, ambient conditions and speed, the effective stopping capability of a vehicle is influenced also by other parameters (car, driver, ABS, etc.). This paper presents a methodology that, exploiting data obtained with on-site measurements and/or published by technical press, allows the evaluation of the coefficient of friction and the stopping capability of a car. This is done by means of a computer program, based on a fuzzy logic approach.

Resistance to Wear of Four Matrices with Ball Attachments for Implant Overdentures: A Fatigue Study

PURPOSE The study evaluated in vitro the retention force and the wear resistance over simulated function of four matrix components of ball attachments for implant-retained overdentures. MATERIALS AND METHODS Four types of matrices for ball attachments were evaluated in a fatigue study simulating 5500 cycles of insertion and removal. The matrices used were (1) a Teflon matrix supported by a metal housing, (2) a titanium matrix, (3) a gold alloy matrix, (4) an O-ring matrix using the red color ring for medium retention. Dimensional changes of the ball attachments were investigated with a profilometer. RESULTS The Teflon matrices showed an increase of 27% in retention at 5500 cycles while the gold alloy matrices showed an increase of 50% in retention in the first 500 cycles and remained relatively stable up to 5500 cycles. On the other hand, titanium matrices and O-ring matrices exhibited progressive loss of retention ending with 68% and 75% of retention loss, respectively, at 5500 cycles. Dimensional analysis by profilometer revealed significant wear on the ball attachment only for titanium matrixes. CONCLUSIONS Gold alloy and Teflon matrices showed the highest retention values without retention loss after 3 years of simulated function. Titanium and O-ring matrices presented a continuous loss of retention with the highest wear on the ball attachments when combined with the titanium matrix.

Influence of the lighting system on the driver's behavior in road tunnels: A driving simulator study

ABSTRACT The tunnel lighting system is an important factor affecting driving safety, but it also represents the most expensive operative cost of a tunnel. Conventional tunnel lighting systems have been progressively replaced by LED lighting systems. This technology is spreading fast because of its low energy consumption and the high durability combined with low maintenance requirement. Aim of this research was to assess, by means of driving simulator experimentation, the impact of the LED lighting system on traffic safety. The driver performance approaching inside and exiting LED lighted tunnels was analyzed and compared to the behavior maintained in tunnels illuminated with a traditional system, in normal and in critical conditions. Thirty-one young participants drove through two different virtual scenarios while data on their speed, lateral position, and reaction in front of a sudden obstacle in the carriageway were collected. A statistically significant difference was revealed as a function of the type of lighting; simulated LED lights often induced a better driving behavior under some aspects. The motorists were able to perceive in advance the critical situation and the consequent maneuvers were carried out in a more effective way. Moreover, drivers kept better their lateral trajectory control in transition areas.

Investigations on the viscoelastic behaviour of a human healthy heel pad: In vivo compression tests and numerical analysis

The aim of this study was to investigate the viscoelastic behaviour of the human heel pad by comparing the stress–relaxation curves obtained from a compression device used on an in vivo heel pad with those obtained from a three-dimensional computer-based subject-specific heel pad model subjected to external compression. The three-dimensional model was based on the anatomy revealed by magnetic resonance imaging of a 31-year-old healthy female. The calcaneal fat pad tissue was described with a viscohyperelastic model, while a fibre-reinforced hyperelastic model was formulated for the skin. All numerical analyses were performed to interpret the mechanical response of heel tissues, with loading conditions and displacement rate in agreement with experimental tests. The heel tissues showed a non-linear, viscoelastic behaviour described by characteristic hysteretic curves, stress–relaxation and viscous recovery phenomena. The reliability of the investigations was validated by the interpretation of the mechanical response of heel tissues under the application of three pistons with diameter of 15, 20 and 40 mm, at the same displacement rate of about 1.7 mm/s. The maximum and minimum relative errors were found to be less than 0.95 and 0.064, respectively.

Investigation into the elastic properties of ex vivo porcine corneas subjected to inflation test after cross-linking treatment

Background The aim of this work was to evaluate the effect of cross-linking (CXL) on ex vivo porcine corneal elastic properties, using an inflation procedure. Methods Twelve corneas were subjected to standard CXL (370 nm, 3 mW/cm2, 30 minutes), while 12 were used as controls. Corneal thickness was measured by Visante optical coherence tomography, before and immediately after treatment, and before inflation test. Both intraocular pressure and radial apical cornea displacement were measured during inflation. Stress-strain curves were obtained by applying the linear shell theory. The elastic modulus was evaluated by calculating the slope of the stress-strain curves. Results Results showed a statistically significant increase in elastic modulus (p<0.0001), with a mean of 3,868 ± 502 kPa for cross-linked corneas and 2,727 ± 238 kPa for untreated corneas, when subjected to high pressure (40-60 kPa). CXL significantly increased porcine cornea stiffness by about 42%. Findings did not show any significant difference within the physiological range of pressure (2-4 kPa). Conclusions The inflation test has been proven to be a valuable tool for the investigation of corneal biomechanics, maintaining both integrity and geometry of corneal tissue.

Motorcycle-to-car impact: influence of the mass of the rider in the calculation of the relative impact velocity

In this paper an analysis method for a collision between a motorcycle and a car is presented, with the limitation that the frontal part of the motorcycle is involved, with wheelbase shortening. The velocities of the vehicles before the collision are usually the most important information for analysis of an accident and its causes, and therefore the methods to succeed in estimating these velocities are of great importance. The work focuses on finding an empirical formulation for the relative velocity between the motorcycle and the other vehicle, starting from the kinetic energy loss due to the collision and allowing for the mass of the motorcycle’s rider at the moment of collision. The equation was found by numerically simulating seven different impact configurations between a car and a motorcycle, with various impact velocities and masses in predefined ranges. Experimental crash tests conducted between a car and a motorcycle and the use of a high-speed video camera allowed the motion of the two-wheeler and its driver to be studied during the impact. A series of tests on crashes between a motorcycle with a rider and a vehicle was carried out, which also allowed validation of the formulation found.

Preliminary Study on the Acoustic Emission Wave Velocity on Filament Wound Glass Fiber Reinforced Polymer Pipes and its Correspondence with the Winding Angle

In this study, three types of filament wound glass fiber reinforced epoxy composite specimens were tested according to the ASTM standards to evaluate preliminary, the acoustic emission wave velocity. The pipe specimens had 300.0 mm of length, 50.5 mm of diameter and 3.5 mm of wall thickness. Ten points were marked over the imaginary central circle on the pipe middle, from zero degree up to 90º with nine divisions of 10º each one and an additional point representing the crossing of plies. Next, there are positioned two collinear acoustic emission (AE) sensors along the length, positioned at 35 mm from middle, axially. After the specimen preparation, took place the HSU-NIELSEN or pencil lead break (PLB) tests to analyze the signal wave time for both sensors, by means of the 0.3mm – 2H graphite lead brake. The results were compared to considering the angular variation and the velocity for each winding angle. It was evident that the procedure above can determine with good precision the variations occurred on the acoustic emission velocity on filament wound composite pipes, regarding the three angular variations compared. This study was the parameter of control to proceed with the acousticemission evaluation over tensile tests in further studies to predict the fatigue and the damage propagation on this typology of laminates.

Experimental measurement of forces during percutaneous dilatational tracheostomy

The measurement of mechanical effects associated with the dilatation phase of a percutaneous dilatational tracheostomy is of primary importance to identify the causes of major complications associated with this procedure, such as tracheal cartilage subluxation or fracture and bleeding. Such information can be very useful also for the design of better instruments and procedures. The aim of this study was to present a methodology to evaluate mechanical effects of the dilatation phase of a percutaneous dilatational tracheostomy on the tracheal rings and adjacent anatomical structures. Forces and moments were measured through a dilator instrumented with strain gauges. Two surgeons, with different levels of expertise, performed the percutaneous dilatational tracheostomy on a lifelike reproduction of an adult head, specifically designed for training professionals. The modified dilator was effective in measuring forces involved in the percutaneous dilatational tracheostomy without affecting the ability of the operator to perform the procedure. The main contribution to the insertion of the dilator was given by the axial force, defined as the force acting on the handle, compressing it (mean and peak force: 48.8 and 88.2 N for Surgeon 1, 31.3 and 82.8 N for Surgeon 2, respectively). The proposed method was effective in measuring differences between procedures performed by surgeons with different amounts of experience in terms of duration, forces applied and repeatability. In addition, it may have applications for use as a feedback for incorrect positioning or excessively variable pressure during the training of surgeons for the execution of percutaneous dilatational tracheostomy.