Dario Vangi

Data Management for the Evaluation of Residual Stresses by the Incremental Hole-Drilling Method

The semidestructive incremental hole drilling method commonly used to evaluate residual stresses is exceedingly sensitive to experimental errors, with sensitivity increasing as hole depth increases. To determine stress variations through the engine thickness, it is necessary to use accurate drilling methods, as well as suitable mathematical models and procedures to minimize the errors associated with residual stress measurement. This work examines he effects of measurement errors on the evaluation of residual stresses with the integral method

Simplified method for evaluating energy loss in vehicle collisions

A method is proposed for the evaluation of energy loss in road vehicle collisions. The energy loss evaluation is an essential task to reconstruct the dynamics of a road accident. The proposed method combines the simplicity of visual evaluation, typical of the method based on EES (equivalent energy speed), with flexibility, in order to evaluate the energy loss on any kind of vehicle deformation profile, of the methods based on measuring residual crush. The method is based on linearizing the damage profile, so that it is possible to predetermine the analytical expression of the kinetic energy loss in relation to only two parameters that characterise the shape of the damage. The stiffness of the vehicle is determined by estimating the geometric parameters of the damage starting from a photograph of generic damage, with documented EES, on a vehicle of the same model as the one under investigation. The proposed method was validated performing crash tests and using data from crash tests found in the literature. The method estimate with sufficient accuracy the kinetic energy loss in deformation on vehicles. The method, thanks to its simplicity and versatility, can constitute a valid alternative to the classic procedures for evaluating energy loss commonly utilised.

Influence of braking force in low-speed vehicle collisions

Abstract The aim of this research is to find out the influence of braking force on the impact dynamics in low-speed rear-end collisions. The method used to simulate the crash is a step-by-step impulsive model including tyre friction and the rolling resistance effect. The simulation allows a separate analysis of the compression and restitution phases. The first is based upon experimental data of the crash test between the vehicles, the latter leads to two different choices of reconstruction, considering the bumper rebound or neglecting it. The coefficient of restitution is calculated by the force reached at compression ending, thus including the influence of external forces (as friction). The results show a great accuracy and matching with experimental data. The main changes in the impact dynamics due to the rise in braking force are the enlargement of the crush with a delay of the restitution start and a lowering of the coefficient of restitution, the increase of the impact duration and the decrease of the velocities at the collision end. These effects depend on the closing velocity and are more marked at low speed. This study therefore demonstrates that the braking force is not negligible in a good reconstruction of impact dynamics at low speed.

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.

Stress evaluation by pulse-echo ultrasonic longitudinal wave

In this paper, an activity aimed at developing an ultrasonic technique for evaluation of states of stress, and in the presence of gradients deriving from local effects of concentrated stress, is presented. The approach is based on the acoustoelastic effect in which ultrasonic wave propagation speed is linked to the magnitude of the stresses present. The technique developed calls for the use of longitudinal waves in pulse-echo technique that propagate in a direction perpendicular to the surface of the work piece. The technique has been applied in different experimental configurations on test specimens with concentration of stresses deriving from notches and fatigue cracks and has furnished encouraging results that highlight the potentiality of the method.

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.

Methodology for minimizing effects of temperature in monitoring with the acousto-ultrasonic technique

The acousto-ultrasonic (AU) technique can be a useful methodology for monitoring structures or mechanical components during endurance tests, fatigue tests or, in general, during the life of the components. To obtain reliable information about the failure and fatigue cracks at their earliest initiation stages and to follow their evolution regardless of any disturbance effects, refined experimental procedures and signal processing are needed. In particular, the effects of temperature variation cannot be entirely suppressed and are difficult to evaluate. This means that the results of the AU technique are not immediately interpretable and usable for monitoring structures. This paper describes some procedures aimed at minimizing the effects of disturbance on AU signals caused by temperature variation, allowing use of AU for monitoring over extensive periods of time or when the component is subjected to heating.

Residual Stress Evaluation by the Hole-Drilling Method With Off-Center Hole: An Extension of the Integral Method

With the incremental hole-drilling method, it is possible to evaluate residual stress variations with depth, acquiring strain values for each step by strain gages. These data can be processed by the integral method. Usually strain gages are not spaced equidistant from the hole center nor arranged in the radial direction, due to practical difficulties in drilling a centered hole. In this study the author presents a development of the integral method for evaluating stress variations with depth in the specimen for eccentric blind hole cases. The results can be extended and adopted for use with a nonconventional strain gage array.

Performance of triangle method for evaluating energy loss in vehicle collisions

The present study is aimed at the validation of the triangle method for evaluating energy loss in vehicle collisions. The validation of the method is performed under two different points of view: first, the ability of the method to provide correct energy loss values; this was done by comparing the method results to experimental and numerical crash tests; and second, the ability of the method to produce results with a low scatter, due to the uncertainty in input data; this was done by performing a sensitivity analysis. It is clearly demonstrated that the triangle method can be used to evaluating energy losses involved in car crashes.

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.