Instrumented Ball Research Articles

Use of a modified critical fracture strain model for fracture toughness estimation of high strength rail steels

This paper explores the feasibility of estimating fracture toughness (KIC,pred) for nine high-strength rail steels using data from smooth tensile and instrumented ball indentation test methods via a modified critical fracture strain model. The modification focuses on determining the equivalent plastic fracture strain and equivalent plastic strain from tensile and indentation tests, respectively, as well as the characteristic distance needed for estimation of fracture initiation. It shows that stress triaxiality plays a vital role by decreasing the ductility required to initiate fracture, based on the kinetic damage evolution law for a multiaxial stress state. A void growth index model was established from average grain sizes, and then used as the characteristic distance for fracture initiation. At the end, the KIC,pred defined based on equivalent plastic strain from tensile tests showed a strong correlation with KIC determined from ASTM standard method. KIC,pred from indentation also offers the opportunity for ascertaining the possibility of estimating the fracture toughness of high strength rail steels, non-destructively by focusing on the equivalent plastic strain and pressure at the tip of the indenter.

A multi-scale analysis of basketball throw in virtual reality for tracking perceptual-motor expertise.

To benefit from virtual reality (VR) as a complementary tool for training, coaches must determine the proper tools and variables for tracking sports performance. We explored the basketball shooting at several scales (basket-ball, ball-player, and player systems) by monitoring success-rate, and ball and body kinematics. We measured how these scales of analysis allowed tracking players' expertise and perceptual sensitivity to basket distance. Experienced and novice players were instructed to naturally throw and swish an instrumented ball in a stereoscopically rendered virtual basket. We challenged their perceptual-motor systems by manipulating the distance of the virtual basket while keeping the surrounding environment unchanged. The success-rate accounted for the players' shooting adjustments to the manipulation of basket distance and allowed tracking their expertise. Ball kinematics also reflected the manipulation of distance and allowed detecting gender, but did not reflect the players' expertise. Finally, body kinematics variables did not echo players' adjustments to the distance manipulation but reflected their expertise and gender. The results gained at each scale of analysis are discussed with regard to the simulator's construct, biomechanical, and psychological fidelity.

Identification Method for Material Constants in Johnson–Cook Model Associated With Strain-Rate and Temperature Sensitivities Using Ball Impact and Indentation Tests

Abstract The Johnson–Cook (JC) flow stress model can simply express the strain-rate and temperature dependencies of the flow stress. We previously proposed a concept of a simple identification method for material constants in the JC model associated with the strain-rate and temperature sensitivities (JC parameters C and m) at high-strain rates. However, several issues still exist in our method for practical use. In this study, we modified our method to identify both the JC parameters C and m. The fundamental concept was formulated based on the requirement that the normalized indentation depths obtained from the ball impact and instrumented ball indentation tests are equal to each other. In addition, the conversion factor was derived to transfer from the impact velocity to the strain rate. The ball indentation and impact analyses based on a finite element method were conducted to verify the established method. The analysis results obtained under idealized conditions demonstrated that C and m can be accurately identified using the established method, even at exceeding 104 s−1. Changes in the radius of the impactor are more effective in obtaining different strain rates than changes in the impact velocity because the identification accuracy can be ensured at lower than 200 m/s.

Assessing load in ball mill using instrumented grinding media

Monitoring mill load is vital for the optimization and control of grinding process. This study proposed the use of an instrumented grinding media to assess solid loading inside a ball mill, with size and density of the instrumented ball comparable to that of the ordinary grinding media. The acceleration signal was captured by an embedded triaxial accelerometer. The signal was first detrended by a complete ensemble empirical mode decomposition and then reconstructed using a correlation coefficient method. The filling ratio, particle to ball ratio, time domain features and sample entropy are features extracted from the signal, providing input to a support vector machine (SVM) learning model. Grinding experiments with different loads were conducted. The typical loading level was classified according to grinding efficiency index and associated power consumption. Different methods were adopted to determine the optimal values of parameters in the SVM model, including particle swarm optimizer (PSO), genetic algorithm (GA), and grid search (GS). The results showed that the accuracy of particle swarm optimizer can reach 96.67%. This study demonstrates the potential of using instrumented grinding media for real-time characterization of mill feed and operation monitoring.

Evaluation of the Elastic Compliance of the Hardness Tester in Instrumented Indentation Tests

The elastic compliance of the instrument (hardness tester) should be taken into account when determining the mechanical properties of materials by means of instrumented indentation with registration of indentation diagrams. The values of Young’s modulus of the tested materials significantly depend on the method for evaluating and accounting for elastic compliance. Therefore, the methods should be verified during instrumented indentation of materials with known but very different Young’s moduli. Successful experience in evaluating and accounting for elastic compliance of the instrument during the instrumented indentation of materials with a diamond pyramid has already been accumulated to date. This is reflected in the relevant standards. However, this experience cannot be applied to instrumented indentation with a steel ball or hard-metal ball without additional research and experimental verification. We propose a method for evaluating the elastic compliance of the hardness tester using the instrumented diagram of ball indentation based on the Hertz equation in the case of elastic contact of the ball with the plane. It is found that additional elastic deformations of the links of instrument are directly proportional to the indentation load; this dependence is typical of each instrument and the diameter of the ball does not affect it. This dependence allows one to take into account the elastic compliance of the instrument using software when registering and processing diagrams of ball indentation. Experiments to determine Young’s modulus and hardness by instrumented ball indentation of various materials (steel, aluminum alloy, magnesium alloy, and titanium alloy) using the known and proposed methods to account for the elastic compliance of the instrument are performed. The main criterion confirming the reliability of the method is the coincidence or proximity of the values ​​of Young’s modulus of the same material determined from the diagram of ball indentation and the diagram of tension of the sample. The advantages and disadvantages of the known and proposed methods are described. Practical recommendations for use of these methods are given.

Effect of mill speed and slurry filling on the charge dynamics by an instrumented ball

In the ball mill, the motion of charge is a complex system, especially under wet grinding. It is difficult to measure the charge physical quantities and hard to validate the correctness of charge motion simulation. To this end, an instrumented ball which is capable of measuring the charge physical quantities was designed. The laboratory ball mill was lined with 12 pieces of trapezium lifters and filled with Jb = 25% grinding balls. An iron ore was used to prepare the slurry at 50% solid concentration by mass. A series of tests were carried out to investigate the charge dynamics at different mill speeds and slurry filling. The average rotational kinetic energy, average applied force and mill power were measured and analyzed. The results showed that the average rotational kinetic energy increases with mill speed, whereas the average applied force first increases and then decreases. The average rotational kinetic energy and applied force first increases and then decreases by the increase in slurry filling. Furthermore, there exists a slurry filling U = U* that the mill power has a maximum value.

Fracture toughness estimation for high-strength rail steels using indentation test

In this paper, tensile properties and mode I critical stress intensity factor (KIc) are measured on the railhead of six types of high-strength rail steels using standard testing methods. An instrumented ball indentation testing method is then developed to estimate fracture toughness for the six rail steels based on continuum damage mechanics. Critical damage parameter, determined by combining repeated loading-unloading tensile tests and a ductile damage model, is used to characterize a critical contact depth under indentation that is used to calculate the specific indentation energy, and thus the fracture toughness for indentation (KInd). Comparison between KInd and KIc for the six high-strength rail steels suggests that the current indentation testing method can successfully rank the six high-strength rail steels for their fracture toughness.

A Method for Accurate Measurement of the Non-linear Rolling Friction Coefficient between an Instrumented Ball and a Surface

The non-linear velocity-dependent rolling friction coefficient between a rigid ball and soft surface was determined by instrumenting the ball with a triaxial gyroscope and converting the spin rate to translational velocity. The latter was differentiated numerically and the resulting translational acceleration was normalised to the gravitational acceleration in order to obtain the rolling friction coefficient. The rolling friction coefficient between a rigid sphere and a foam surface increased with velocity and consisted of three components: a sharp increase in friction coefficient at slow velocities, starting at the static rolling friction coefficient; a constant coefficient at medium velocities; and a coefficient increasing with velocity squared at higher velocities.

Simulating Sport Ball Impact Through Material Characterization

In finite element models of sport ball impacts, modeling the ball has been much more challenging than modeling equipment. Clubs, racquets, and bats tend to be largely linear-elastic, while sport balls are often non-linear, inelastic, and rate dependent. Obtaining ball material properties is further complicated by the difficulty in achieving the high deformation rates representative of impact. The following describes the implementation of a dynamic impact test apparatus that was designed to characterize sport ball materials. The apparatus was used to construct a loading and unloading stress-strain curve of polyurethane foam at deformation rates and magnitudes representative of play. The stress-strain response was used in explicit finite element simulations of ball impacts. The simulated impacts were compared with instrumented ball impacts. The foam material model provided closer agreement with experiment over a range of impact speeds and surfaces than viscoelastic material models that are commonly used.

Experimental and simulated instrumented ball in a tumbling mill—A comparison

Tumbling mills play an essential role in modern mineral processing. Because of the nature of the mill, the internal forces make instrumentation of the mill interior difficult. One solution to this problem is the use of an instrumented ball. An instrumented ball, equipped with an accelerometer, rotation rate sensors and a temperature sensor has been built. The instrumented ball and a camera system are used to measure the state of the charge within a laboratory mill. In parallel, a discrete element model (DEM) of the laboratory mill is developed. Using the distributions and moments of the energy terms of the charge, the simulation and experimental results are analyzed and compared. The moments are used to tune the DEM, such that the simulation results are in agreement with the experimental results. The comparison also identifies which aspects require further improvement.

Pitcher training aided by instrumented baseball

Proper pitching mechanics are imperative for developing different types of pitches (e.g., fastball vs. breaking ball) and for preventing injury. Different pitch types are distinguished by the path (i.e. break) and speed of the ball which, in turn, are dictated by the angular velocity of the ball and the velocity of the ball center at the instant of release from the pitcher's hand. While radar guns effectively measure ball speed, they provide no information about the direction of the velocity of the ball center, the angular velocity of the ball, or the way in which these quantities change during the throw. These quantities can, in principle, be calculated using high-speed video-based motion capture (mocap), but doing so requires measurements in a controlled lab environment taken by a skilled technician. Moreover, mocap is unlikely to accurately resolve the angular velocity of the ball which is crucial to understanding pitching. This paper addresses these shortcomings by presenting an instrumented ball containing a miniature, wireless inertial measurement unit (IMU) to measure ball dynamics on the field of play. Measurements reveal that this technology can deduce the magnitude and direction of the ball's velocity at release to within 4% when benchmarked against mocap. Moreover, the IMU directly measures the angular velocity of the ball for pitches that remain within the measurement range of the associated angular rate gyros.

INSTRUMENTED BALL DESIGN AND DEVELOPMENT

In the mineral processing industry, tumbling mills are used in the size reduction or comminution of ore to a target size distribution. As the tumbling mill environment is quite violent it is difficult to monitor mill charge motion let alone single ball or particle motion. An effort was initiated to investigate the development of an instrumented ball that includes data collection capabilities. A variety of sensors, including accelerometers and gyros, form the instrument package. The data collected by the instruments allow the calculation of a number of dynamic and kinematic quantities as a function of time. Using instrumented ball data, the error model of the instrument can be found. Finally, the importance of the data with respect to ball mills is discussed along with the relationship between the instrumented ball data and charge motion simulation results is discussed.

Impact response of sports materials

Sports equipment exposed to impact loading often involves polymeric materials. The impact response tends to be time dependent with large stress-strain hysteresis. Replicating impact loading in a controlled laboratory environment for material characterization is challenging, but necessary if models are to accurately describe impact behaviour. This study considers ball impacts for which mechanical properties are typically phenomenologically developed where numerical models simulate instrumented ball impacts. The following describes a split Hopkinson pressure bar apparatus to induce uniform stress at controlled magnitudes and rates in polyurethane foam test samples (the principle constituent of a softball). The apparatus was able to describe the loading phase of the stress-strain response of the polyurethane at strain rates representative of softball impacts. Test samples were taken from balls of varying coefficient of restitution and stiffness. The uniaxial impact properties were consistent with the expected response of the balls (i.e. stiffer balls exhibited higher modulus). Results from numerical simulations using the laboratory mechanical properties did not agree with experimental measurements, however. The large energy absorption of the polyurethane limited the range in strain rates over which material characterization could be performed, which is apparently needed to describe the material response throughout the ball.

Design of an instrumented bowling ball and its application to performance analysis in tenpin bowling

An instrumented tenpin bowling ball was designed, by replacing the thumb and finger holes by tubes connected to 6D transducers, which in turn were connected to the shell of the ball. The transducers measured the forces and moments applied by the thumb and fingers to the tubes and thus to the ball. The ball was tested in weaker and better bowlers for each of the three basic types of shots (straight, hook, and spin). The performance parameters were identified based on the correlation with the average score. Better bowlers applied larger forces to the ball during the forward swing and thus moved and accelerated faster. Additionally, better bowlers had larger ratios of pinch force, period, and impulse of forward swing to backswing, and impart larger moments to the ball. The forces and moments were graphically represented in 4D vector diagrams. The moment vector shortly before release of the ball was predominantly horizontal in the straight shot, inclined left‐ and backwards in the hook shot, and predominantly...

Effect of aging on mechanical properties of 6063 Al-alloy using instrumented ball indentation technique

One of the most important issues of standard conventional test methods for determining mechanical properties of ductile materials is that the requirement of test materials should be adequate and it cannot be applied to in-service components. Therefore, in this study, an instrumented ball indentation technique has been applied to determine a few mechanical properties of a 6063 Al alloy in order to establish a correlation between microstructure and its mechanical properties. The as-received 6063 alloy sample was in cast and homogenized condition. It was solutionized at 520 °C with two aging treatments. It was found that solutionized material with subsequent aging at 220 °C for 3 h does not produce any noticeable variation in mechanical properties. Whereas, transmission electron microscopy (TEM) and scanning electron microscopy (SEM) on solutionized samples after 7 h aging at 220 °C of the same material revealed precipitation of sub-micron size (of the order of 60 nm) Mg 2Si phase and this subsequently resulted in variation in the mechanical properties of the alloy.

Validating the instrumented ball outputs with simple trajectories

An instrumented ball capable of measuring a number of physical quantities within a highly dynamic environment, such as a tumbling mill, has been designed, built and tested. To ensure that the instrumented ball is operating as designed, it is made to follow a number of known trajectories. The physical quantities measured by the instrumented ball are consistent with the expected results along the trajectories. An example of the use of a properly functioning instrument is also shown.

INVESTIGATING THE DIFFERENCES IN CHARGE DYNAMICS DUE TO A VARIATION OF THE INSTRUMENTED BALL PROPERTIES

The validation of charge mill motion simulations is limited by the lack of information from inside a tumbling mill. To this end, an electronic system capable of measuring a number of physical quantities within a highly dynamic environment has been designed, built and tested. Once protected, the system can be used to record physical quantities within a ball mill. Different types of protective shells may be used to protect the electronics. When comparing the measurements recorded using two different shells, some differences in the behaviour of the instrumented ball were observed.

Indirect Measurement Method for Laminar to Turbulent Airflow through Horticultural Produce Simulators

Sixty-four plastic balls were instrumented for use as horticultural produce simulators and strategically distributed in an orthogonal matrix along with 448 other plastic spheres to simulate precooling of column-stacked produce. This research tool was based on the correlation between the cooling rate of produce simulators and the air approach velocity. Since a range of airflow rates was already recognized as creating particular difficulties for indirect air velocity measurement, particular care was taken with the air velocity measurement of the theoretical range of each airflow pattern, namely, laminar, transient, and turbulent. Correlations were determined by measuring the half-cooling time of each instrumented ball positioned at a fixed location inside a ball matrix that was inserted into an open-ended ventilation tunnel and subjected to various airflows. The results obtained allowed the laminar flow pattern to be distinguished from the transient and turbulent patterns using a specific correlation relating the half-cooling time to the air velocity for this type of airflow pattern. However, a single equation was used to correlate half-cooling time to air velocity for transient and turbulent airflow patterns. The new calibration decreased the experimental error and standard deviation obtained with the indirect measurement method system previously developed.

Impact testing and simulation of composite sandwich structures for civil transportation

The impact response of sandwich panels with an improved structure to increase their impact resistance is investigated herein. In order to compare the impact performance of sandwich structures, a specific and instrumented ball drop tester was designed and developed. Two different sandwich structures are analyzed: the first type is a classical structure composed by a glass fiber-polyester matrix-composite skin and a foam core. The second one, specifically developed in this research, consists of skins made from a glass fiber-phenolic matrix composite laminate and a core formed by an internal corrugated structure of the same laminate used for the faces filled by a phenolic foam. The latter structure was specifically designed to improve crashworthiness for transport applications. The main results of this study are evaluation of the absorbing energy performance of the sandwich structures, subjected to a single impact, and the development of criteria useful for materials selection. The corrugate sandwich panels have shown a better performance in terms of impact energy absorbing properties and strength respect to traditional sandwich structures.