Auteliano Antunes dos Santos

Ultrasonic stress measurement using PC based and commercial flaw detectors

The determination of the stress field inside metallic parts is one of the most important challenges to the designer. Although the prediction of the stress distribution can be done by several numerical and empirical methods, the real stress value is almost always unknown. Several destructive and nondestructive techniques have been tested to accomplish this task, including the application of x rays, saw cut, neutron diffraction and so on, but none of them seems to have a suitable correlation between cost and applicability. Ultrasonic techniques have been used for flaw detection since the 1950s. The main application was in the identification of cracks and voids. In this work we present the application of ultrasound in the evaluation of a one-dimensional stress field using the longitudinal critically refracted waves (LCR). A new ultrasonic LCR probe is presented and its performance is evaluated using PC based instrumentation. Also, the LCR waves’ sensitivity is verified using a low cost commercial flaw detect...

Stress analysis in carbon/epoxy composites using Lcr waves:

This work presents the application of an ultrasonic method to measure stresses in unidirectional carbon fiber composites with epoxy matrix (HexTow® AS4/Hexply® 8552). This kind of composite is largely employed as a structural material in the aeronautical industry. The ultrasonic method is based on the acoustoelastic principle, a principle that holds that wave speed is affected by variations in strain in the material. We employ critically refracted longitudinal waves (Lcr waves) and relate their time-of-flight with applied strains and stresses. We first performed tests on a polygonal specimen evaluating the influencing factors on the results, that is, temperature and transducer positions, as well as their effects on each fiber direction: 0°, 45°, and 90°. Tensile tests were next performed on rectangular specimens, as we sought, for each fiber direction, the relation between stress and wave speed variation, otherwise known as the acoustoelastic coefficient. The results showed that the wave speed was sensitive to the stress variation along the fiber direction (0°) and nearly insensitive to any other direction. Also, temperature (between 20℃ and 27℃) was not a relevant factor for waves propagating along the fiber. These findings support the notion that the method holds promise as an alternative to measuring stresses in multidirectional composite materials.

Combined regenerative and mechanical braking in electric vehicle

Regenerative braking in electric vehicles involves a storage element, such as supercapacitor, which can store energy peaks generated by braking. This article describes the development of an experimental prototype of a system that simulates an electric vehicle induction motor using a supercapacitor bank for supplying and storing energy. The system allows carrying out the study of power supplied to the vehicle, causing acceleration, and recovered from it during the deceleration. Tests were performed to find best ways to recover the kinetic energy in regenerative braking, aiming more efficiency. The proposed system can work together with mechanical braking for low speeds, high deceleration or emergencies, keeping the braking performance.

Effect of Mean Grain Size in the Time of Flight for Lcr Waves

The ultrasonic methods are widely used for evaluation of materials for its inexpensive and practical features. Among the largely used ultrasonic methods is the Critically Refracted Longitudinal Waves (Lcr), which applies longitudinal bulk waves travelling right below the surface, parallel to it. The method can be used to measure stresses near the surface through acoustoelasticity. However, the materials microstructure directly influences the propagation of these waves. The mean grain size is one of the factors that affect the wave speed. The purpose of this paper is to evaluate the effect of mean austenitic grain size in the time of flight (TOF) of Lcr wave. Samples (CDPs) of ASTM A36 steel were manufactured with dimensions of 5/8″ × 6″ × 12″. These were submitted to heat treating at the different temperatures ranges and cooled in air to generate different grain sizes. The results were compared to the grain size estimated in the literature and obtained from optical microscopy. The study showed a clear dependence of TOF on mean austenitic grain size for ASTM A36 steel. Such effect has to be studied to allow stress measurements with Lcr waves.Copyright

Proposal of an energy management architecture applied into a regenerative braking system

Regenerative Braking in vehicles is projected as an intelligent and simple technique to improve the energy replenishment and autonomy in them, due to the fact that it is based on the concurrent process of deceleration. It is smart because takes advantage of the capability of the electric machine to behave as a generator. So, it is possible to recover the kinetic energy store in the rotating inertias by using regenerative braking during the deceleration and restore it into batteries. Some authors are focused on maximizing the energy regenerated, applying techniques as independent factors of the process, like storage elements, control of speed, acceleration, current, etc. In this work we exposes the regenerative braking process and its main parts in a holistic model, where discrete and continuous states and events are related, also linked into the dynamic behavior, bringing the possibility not only to have a general model that commands all the process, but also improve and monitor each stage as a whole. Thus our management architecture pretends to maximize the gain energy in every deceleration, and minimize the energy consumed.

Effects of Nonlinear Friction Wedge Damping on Freight Train Dynamics

Engineers pay great attention to comfort and performance issues, which are related to passenger trains suspension systems. Complex active shock-absorbing devices are developed and modern simulation tools are employed to determine car body vibrations and ride behavior. Freight train suspensions, however, were not given the same focus, presenting the same basic design for about 70 years now. Recent increases in pay-loads and train lines speed, and growing pressures to decrease maintenance costs, are slowly changing this scenario in such a way that numerical simulation methods are being more and more used. Most commercially available simulation software used by train manufacturers to address full vehicle behavior treats the friction wedge — the main damping element in the three-piecetruck suspension — as a weightless unidirectional force element like springs and dampers, which connects the wheel frames to the bolster that supports carbody load. This paper uses an improved friction wedge model to emphasize the importance of considering nonlinear characteristics of friction damping to vertical and longitudinal dynamics of a freight truck wagon modeled with multi-body dynamics.Copyright

A comparison of the use of critically refracted longitudinal waves and magnetic Barkhausen noise for stress measurement in API 5L X70 steel

According to acoustoelastic theory, ultrasonic wave velocity varies as a function of the state of stress in a body. In ferromagnetic materials, stress alters magnetic domain walls created by cyclic magnetic excitation and affects the amplitude of magnetic Barkhausen noise signals. In this work, both these properties are used to measure different levels of stress in specimens of API 5L X70 steel. Time of flight of ultrasonic critically refracted longitudinal (Lcr) waves and magnetic Barkhausen noise are measured and compared using three parameters: sensitivity, linearity, and dispersion. The results show that while magnetic Barkhausen noise is much more sensitive to variations in stress, the time of flight values fit a linear curve better. Also, for the ultrasonic technique, dispersion between the curves for the different specimens is lower. For both techniques, measurement dispersion in the specimens when no stress is applied is high. The findings of this study can be used to indicate the limits within which each technique can be used and to help decide when it is more appropriate to use one technique rather than the other.

A Multibody System Approach to the Wedge Damper Friction Formulation

Secondary suspension of railway three-piece-trucks hasn’t changed much in the past century. Despite this, its most common damping element, the friction wedge, is not yet fully understood. The frictional damping is a known source of non-linearity and non-smoothness that imposes chaotic behaviors to the system, making the mathematical modeling of such devices a difficult task. The present paper presents a multi-body model of a three-piece-truck’s secondary suspension and the results of its simulations with three types of commonly used friction models.Copyright

Stress Relaxation in Aluminum Welding Using Ultrasonic Method

Stress relaxation of welded joints can increase the safety of structures. Although it is not absolutely clear why it happens, several researches have proved the phenomenon. This work presents the application of the ultrasonic technique to evaluate the stress relaxation in welds of 5052 aluminum. A special geometry was developed, so each welded plate had uni-axial stresses in the measurement region. Twenty-two plates were tested, eleven in the rolling direction and the remaining in the perpendicular direction. The plates were stress relief using a heat treatment to set an initial stress free reference state. After that, they were welded to create the stress field in the area of investigation. A final step was to cut each of the samples after different periods of time from the welding. The stress was measured in the uni-axial stress region. A calendar of the process was established to record precisely the time for each step. Longitudinal critically refracted waves were used to measure the stresses. The results showed a clear effect of relaxation. The magnitude was not as pronounced as in steel, but kept the same relation with the ultimate strength of material.Copyright

Evaluation of the Rolling Direction Effect in the Acoustoelastic Properties for API 5L X70 Steel Used in Pipelines

Ultrasonic evaluation of stresses has experienced great development in the last decade, mostly because of the new electronic instruments and high-speed data acquisition systems now available. Past applications have been applied mostly using shear waves and the birefringence technique. Longitudinal critically refracted (skimming) waves have proved to be more sensitive to stress variation, and have been applied recently to oil steel pipelines. Oil pipe failures have caused a lot of environmental damage in Brazil. The environmental and economical costs are very high. This work describes part of a research effort to further apply longitudinal critically refracted waves to inspect the welded region in pipes in Brazil through a study of the acoustoelastic constants. Twenty-eight samples were cut from a flat plate of the oil industry class steel (API 5L X70) which would be typically formed into pipe. The samples were prepared for tensile testing. Half of those were cut from what would be the longitudinal direction of the pipe, and the other half from the perpendicular direction. The samples are bars of 760×70×10.8-mm3 . Some bars were stress relieved before the test. The results show that there are significant differences between the acoustoelastic constants for the rolling direction and the perpendicular direction. It is clearly important to have the correct value for the acoustoelastic coefficient when applying the technique to stress measurement. There is a minor, but important influence of the stress relief process.Copyright