A predictive model for fracture in human ribs based on in-vitro acoustic emission data

Purpose The aim of this paper is to propose a fracture model for human ribs based on acoustic emission (AE) data. The accumulation of microcracking until a macroscopic crack is produced can be monitored by AE. The macrocrack propagation causes the loss of the structural integrity of the rib. Methods The AE technique was used in in vitro bending tests of human ribs. The AE data obtained were used to construct a quantitative model that allows an estimation of the failure stress from the signals detected. The model predicts the ultimate stress with an error of less than 3.5% (even at stresses 15% lower than failure stress), which makes it possible to safely anticipate the failure of the rib. Results The percolation theory was used to model crack propagation. Moreover, a quantitative probability-based model for the expected number of AE signals has been constructed, incorporating some ideas of percolation theory. The model predicts that AE signals associated with micro-failures should exhibit a vertical asymptote when stress increases. The occurrence of this vertical asymptote was attested in our experimental observations. The total number of microfailures detected prior to the failure is urn:x-wiley:00942405:media:mp15082:mp15082-math-0001 and the ultimate stress is urn:x-wiley:00942405:media:mp15082:mp15082-math-0002 MPa. A significant correlation (p < 0.0001) between urn:x-wiley:00942405:media:mp15082:mp15082-math-0003 and the predicted value is found, using only the first N = 30 micro-failures (correlation improves for N higher). Conclusions The measurements and the shape of the curves predicted by the model fit well. In addition, the model parameters seem to explain quantitatively and qualitatively the distribution of the AE signals as the material approaches the macroscopic fracture. Moreover, some of these parameters correlate with anthropometric variables, such as age or Body Mass Index. The proposed model could be used to predict the structural failure of ribs subjected to bending.Peer ReviewedPostprint (author's final draft

Ultrasonic vibration-assisted ball burnishing tool for a lathe characterized by acoustic emission and vibratory measurements

Article number 5746This paper focuses on a resonant system used to induce a low-amplitude movement and ultrasonic frequency to complement a ball burnishing process on a lathe. The system was characterized through the combination of different techniques. A full vibratory characterization of this process was undertaken with the purpose of demonstrating that the mechanical system—composed of the tool and the machine—does not present resonance phenomena during the execution of the operation that could lead to eventual failure. This dynamic analysis validates the adequateness of the tool when attached to an NC lathe, which is important to guarantee its future implementation in actual manufacturing contexts. A further aim was to confirm that the system succeeds in transmitting an oscillating signal throughout the material lattice. To this end, different static and dynamic techniques that measure different vibration ranges—including impact tests, acoustic emission measurement, and vibration measurement—were combined. An operational deflection shape model was also constructed. Results demonstrate that the only high frequency appearing in the process originated in the tool. The process was not affected by the presence of vibration assistance, nor by the burnishing preload or feed levels. Furthermore, the frequency of the assisting ultrasonic vibration was characterized and no signal due to possible damage in the material of the specimens was detected. These results demonstrate the suitability of the new tool in the vibration-assisted ball burnishing process.Feder (UE) 001-P-001822Ministerio de Ciencia, Innovación y Universidades (España) RTI2018-101653-B-I0

Combination of acoustic emission and vibratory measure-ments to characterize an ultrasonic vibration assisted ball burnishing tool for a lathe

In this paper, a resonant system that produces a movement of low amplitude and ultrasonic frequency is used to achieve the vibration assistance in a ball-burnishing process. A full vibration characterization of this process performed in a lathe was done. It is carried out by a new tool designed in the research group of the authors. Its purpose is to demonstrate that the machine and the tool do not have any resonance problem during the process and to prevent possible failures. The analysis of this dynamic behaviour permits to validate the suitability of the tool when it is anchored to a numerical control lathe. This is very important for its future industrial implementation. It is also intended to confirm that the system adequately transmits vibrations through the material. To do this, a methodology to validate the dynamic tool behaviour was developed. Several techniques that combine the usual and ultrasonic vibration ranges through static and dynamic measurements were merged: vibration and acoustic emission measurements. An operational deflection shape (ODS) exercise has been also performed. Results show the suitability of the tool used to transmit the assistance vibrations, and that no damage is produced in the material in any case.Postprint (author's final draft

Advanced analysis of in-service movements of vehicle closures

Closures (doors, hood, tailgate, etc.) are attached to the vehicle body by means of articulated elements that allow a high level of mobility. This may cause the poor vibration performance of the closure when exposed to oscillating loads such as the ones produced by the engine, road irregularities and aerodyna mic forces. The poor vibration performance of a closure can cause squeak & rattle or lead to a high level of wind noise inside the ve hicle. The problems associated with small displacements of closures during driving conditions can be analysed in terms of the relative movement of these elements with respect to the vehicle body. This relative movement can be considered as a three-dimensional displacement and rotation, and its quantification allows us to detect the areas between the closures and the body that need special attention. This paper proposes an experimental method for decomposing the in-service relative movement of closures as the sum of two components, i.e., a rigid body motion contribution and the vibration motion part. It is shown that this approach is of particular interest in defining countermeasures to control closure displacements.Postprint (author's final draft

Investigation of ball burnishing process using vibration and acoustic emission sensors

In this paper, a ball burnishing tool mounted in a CNC lathe is characterized. This tool may work as vibration assisted ball-burnishing tool and in conventional way. The characterization consists of acoustic emission measurements in both burnishing processes, and vibration measurements with tri-axial accelerometers. The acoustic emission measurements permit to investigate if any kind of damage is produced in the material by the burnishing process. An operational deflexion shape exercise has been performed with the vibration measurements. This permits to investigate the movement of the tool during the burnishing process and to evaluate the rigidity of the tool.Peer ReviewedObjectius de Desenvolupament Sostenible::9 - Indústria, Innovació i InfraestructuraPostprint (published version