High-speed Test Research Articles

Characteristics of contact force for normal collision of rubber sphere with rigid plate

This paper examines the contact force dynamics during a normal collision involving a rubber sphere and a rigid plate. A high-speed camera test system is utilized to capture the key parameters of the sphere. Through image processing, these parameters are extracted. To complement the experimental data, an equivalent finite element model is constructed by using LS-DYNA. The visco-hyperelastic constitutive model parameters are determined by validating against the coefficient of restitution. By comparing the results of the finite element simulation with the experimental outcomes, the model’s accuracy is established. Through simulations, the relationships between the contact force and pertinent variables are explored, deriving an analytical expression for the contact force, which is subsequently verified. Our findings demonstrate that the proposed contact force formulation offers a more precise calculation of the contact force in a normal collision between a rubber sphere and a rigid plate.

Research on biaxial tensile fracture prediction of 5052 aluminum alloy on electromagnetic sheet bulging

High-speed deformation fracture prediction of aluminum sheet, especially for biaxial tension state deformation, was a major problem in the development of electromagnetic bulging process. In this study, the biaxial tension failure limit of the AA5052 sheet was tested by the electromagnetic high-speed biaxial tensile testing equipment and quasi-static Nakazima experiment. A Digital Image Correlation (DIC) system was used to measure failure strain. Based on the tested data, a failure model considered stress state and strain rate coupling effect was established, which available for electromagnetic bulging failure prediction. Electromagnetic free bulging experiments were conducted to verify the failure criteria effectiveness. Results showed that the strain rate effects of the failure strain were influenced by the loading path. The strain rate effect of the sheet failure strain under plain strain state was higher than the loading stress triaxiality of uniaxial and biaxial tension state. Compared with the fracture prediction criterion ignored stress state effect on strain rate influence factor, the modified fracture model considered stress state and strain rate coupling effect could well predict the failure of electromagnetic bulging, which would exhibit different failure models at the rounded corner or the top under different discharge energies.

Frequency-scanning burst-mode filtered Rayleigh scattering for kHz-rate, multi-parameter, gas-phase measurements.

Molecular Rayleigh scattering (RS) is sensitive to the pressure, temperature, velocity, and number density of the gaseous flow. Filtered Rayleigh scattering (FRS) utilizes a narrowband molecular filter to remove stray scattering and deconvolve the effect of flow conditions on the signal intensity. As single-frequency, intensity-based FRS techniques can typically only deconvolve a single parameter per detector angle, frequency-scanning (FS) FRS has been used to semi-spectrally resolve the signal and quantify multiple parameters using a single detector. In this work, the FS-FRS data rate was increased by a factor of 105 using a rapid wavelength-tunable burst-mode laser operated at 20 kHz. The technique is demonstrated for simultaneous, spatially resolved temperature, pressure, and radial velocity measurements time-averaged across 1 ms in an underexpanded jet, yielding a measurement rate of 1 kHz for potential use in high-speed flow test facilities.

Dynamic Tensile Response of Basalt Fibre Grids for Textile-Reinforced Mortar (TRM) Strengthening Systems.

The present work constitutes the initial experimental effort to characterise the dynamic tensile performance of basalt fibre grids employed in TRM systems. The tensile behaviour of a bi-directional basalt fibre grid was explored using a high-speed servo-hydraulic testing machine with specialised grips. Deformation and failure modes were captured using a high-speed camera. Tensile strain values were extracted from the recorded images using the MATLAB computer vision tool, 'vision.PointTracker'. The specimens, consisting of one and four rovings, were tested at intermediate (1-8/s) and quasi-static (10-3/s) strain rates. After the tensile tests, scanning electron microscopy (SEM) analyses were performed to examine the microscopic failure of the material. Linear and non-linear stress-strain behaviours were observed in the range of 10-3 to 1/s and 4 to 8/s, respectively. Tensile strength, ultimate strain, toughness, and elastic modulus increased at intermediate strain rates. Overall, the dynamic increase factors for these properties, except for the latter, were between 1.4 and 2.3. At the macroscopic level, the grid failed in a brittle manner. However, microscopic analyses revealed that the failure modes of the fibre and polymer coating were strain-rate sensitive. The enhanced tensile performance of the grid under dynamic loading conditions rendered it suitable for retrofitting structures prone to extreme loading conditions.

Optimizing woodcutting with zirconia-toughened alumina: Processing, performance, and industrial insights.

Since the 1950s, the woodcutting industry has relied heavily on tungsten carbide (WC) cutting tools to overcome the challenges posed by the complex structure of wood, including hard knots and abrasive elements such as sand and tannic acids. These demands require cutting tools with superior thermal conductivity and mechanical properties. However, the rising cost of WC materials has prompted the search for alternative solutions. As a result, zirconia-toughened alumina (ZTA) ceramic materials with varying amounts of in situ formed SrAl12O19 have been introduced as potential substitutes. This study focuses on the processing, microstructural characterization, and mechanical behavior of these ceramic cutting tools with the goal of matching or exceeding the cutting performance and tool life of conventional WC tools. The study demonstrates the effectiveness of the improved ceramic tools through numerical evidence obtained from short-term trials and subsequent extended high-speed tests conducted on industrial cutting machines. In particular, comparable wood surface quality and wear resistance were achieved along with a significant improvement in cutting speed, resulting in a threefold reduction in machining time. These results underscore the potential of ceramic cutting tools as a cost-effective and efficient alternative in the woodcutting industry.

Blade Vibration Difference-Based Circumferential Fourier Fitting Algorithm for Synchronous Vibration Parameter Identification of Rotation Blades.

Blades are the core components of rotating machinery, and the blade vibration status directly impacts the working efficiency and safe operation of the equipment. The blade tip timing (BTT) technique provides a solution for blade vibration monitoring and is currently a prominent topic in research on blade vibration issues. Nevertheless, the non-stationary factors present in actual engineering applications introduce inaccuracies in the BTT technique, resulting in blade vibration measurement errors. The theory of blade vibration difference offers a new perspective for high-precision BTT techniques. This paper optimizes the traditional circumferential Fourier fitting (CFF) algorithm. According to the blade departure time measurement mechanism, four sets of BTT signals are obtained by two probes, six sets of blade vibration differences are established, and, then, a blade vibration difference-based circumferential Fourier fitting (BVD-CFF) algorithm for blade synchronous vibration parameter identification is proposed. Simulation studies demonstrate that the BVD-CFF algorithm exhibits superior anti-noise performance. Moreover, experimental investigations on a high-speed rotation blade vibration test rig and a large-scale centrifugal compressor test rig display that the engine order of blade synchronous vibrations obtained by the BVD-CFF algorithm are essentially the same as those obtained by the strain gauge method.

Optimized Design and Test of Geometrically Nonlinear Static Aeroelasticity Model for High-Speed High-Aspect-Ratio Wing

Large transport aircraft tend to adopt a wing layout with a high aspect ratio and swept-back angle due to the requirement of a high lift-to-drag ratio. Composite material is typically employed to ensure the light weight of the structure, causing serious static aeroelasticity problems to the aircraft. When the airplane is flying in the transonic region, its aerodynamic load is very complex, and the large load leads to large deformation of the wing, triggering geometric nonlinear effects, which further affects the static aerodynamic elasticity characteristics of the wing. In this study, in order to study the static aeroelastic characteristics of the transonic flow of a high-aspect-ratio airfoil, a new design method of the scaled similar optimization model is described, and the change in the model lift coefficient due to geometrically nonlinear static aeroelasticity effects when the angle of attack is changed was investigated by using simulation and wind tunnel test methods. In order to ensure the accuracy of the wing shape when the model was deformed greatly, this study employed the structural design scheme of the wing with the skin as the main stiffness component, and the thicknesses of different regions of the skin were used as the design variables for the stiffness optimization design. The engineering algorithm of nonlinear finite elements was used in this study to calculate the curve of lift with the angle of attack considering the geometric nonlinear static aeroelasticity effect. The results show that the similarity optimization process employed in this study can be used to complete the design of the high-speed aerostatic wing test model, and the wind tunnel test results show that geometric nonlinearity has a large impact on the lift coefficient of the wing.

Experimental and numerical investigation of a novel inlet for boundary layer ingesting propulsion systems

Boundary Layer Ingestion (BLI) propulsion systems have the potential to significantly enhance aircraft performance, particularly by improving fuel efficiency and reducing emissions. However, the high total pressure losses and distortions at the outlet of the BLI inlet normally restricts the development of BLI propulsion systems. This paper introduces and investigates a high-performance dual-sided BLI inlet configuration suitable for a large amount of boundary layer ingesting through a combination of computational and experimental methods. The dual-sided BLI inlet has two air entrances located at the top and bottom of the aircraft's rear fuselage, with the two ducts from the upper and lower inlets deflecting towards each other and converging at the same annular outlet. Simulation results indicate that the dual-sided BLI inlet prevents the concentration of low-energy flow observed with single-sided inlets, thereby reducing outlet distortion. Additionally, high-speed wind tunnel tests were conducted to validate the design's feasibility. The test results indicate that the dual-sided BLI inlet demonstrates good performance at the design point (Mfar=0.75, MAIP=0.50, δ/h≈45 %). The total pressure recovery coefficient σfar=0.907 and σin=0.995, the outlet total pressure distortion index DC60=0.24, and the outlet swirl intensity is minor. In conclusion, the novel BLI inlet maintains robust performance under designed conditions, fulfilling the engine's stability requirements.

Assessing the retrieval procedure of complex-valued forces from airborne pressure fields by means of DIC-based full-field receptances in simplified pseudo-inverse vibro-acoustics

Lightweight structural components in many engineering fields can be severely excited by airborne pressure fields, becoming a concern for their structural dynamics and reliability. Nowadays, the quality reached by optical measurements, in contactlessly estimating - as maps of displacements over force - complex-valued full-field receptances, allows an accurate description of the structural dynamics in a broad frequency domain, without any numerical structural model. This is even more relevant for lightweight components, otherwise affected by potential distortions, coming from the inertia of more traditional transducers. High-speed DIC structural testing is here combined with acoustic propagation in direct and pseudo-invertable vibro-acoustic FRFs, obtained by the simple Rayleigh integral approximation, here re-formulated to take advantage of the experiment-based full-field receptances, when a force excites a vibrating surface, which radiates sound pressure into air and vice-versa. Starting from airborne pressure fields, known in their spectra, the pseudo-inverse vibro-acoustics aims at identifying the force, with a broad frequency band, which can be transmitted to the excitation locations, previously used in defining the vibro-acoustic FRFs in the direct problem. Extended details and considerations on this full-field receptance-based vibro-acoustic approximation are thoroughly provided, with special attention to its complex-valued nature, to numerical precision and to broad dynamics' excitation signature, thanks to the accurate DIC-based testing of a real thin plate.

Experimental and numerical study on cavitation flow characteristics of refrigerants with different thermophysical properties in confined micro-clearance

In high-speed hydraulic machinery, its efficiency and reliability are affected by the cavitation in the bearing. Due to the confined effect of the bearing clearance, cavitation bubbles grow in a two-dimensional way. To uncover the cavitation process with confined and high speed shearing effect, the high-speed cavitation flowing of different refrigerants is researched experimentally based on the high-speed shearing test rig with micro-clearance. The influence of thermophysical properties on growth of cavitation bubble is evaluated and analyzed. The confined effect of micro-clearance and high-speed shearing effect has a significant influence on the cavitation bubbles evolution. The high-speed camera is used to record the morphology of cavitation bubbles for various refrigerants with different thermalphysical properties. Furthermore, the thermal-sensitive cavitation model is used to analyze the bubble-foam alternation from cavitation flow inside micro-clearance. For different refrigerants, the growth process of cavitation bubble area is exponential. Inside the micro-clearance, the cavitation inducing pressure drops of different refrigerants are analogous due to the similar thermodynamic properties. According to pressure drop during cavitation, different refrigerants are classified by introducing dimensionless numbers, σ·Re (Jie et al., 2009) [2] and σ·We. The pressure and temperature drop increase with the dimensionless numbers. The refrigerants with similar thermodynamic properties have a similar relationship between dimensionless number and supercooling degree.

Impact of initial braking temperature on thermal-induced brake fade during long-downhill operations

The advancement of high-speed railways and the widespread application of complex terrains have highlighted the issue of performance degradation in braking friction pairs during long-downhill braking, especially under high-temperature conditions. This study addressed this problem using a self-developed high-speed train braking simulation test rig to investigate the effects of varying initial braking temperatures (IBTs) on the performance degradation of braking friction pairs. A combination of thermal imaging, energy dispersive spectroscopy (EDS), high-temperature hardness testing, and X-ray diffraction (XRD) was employed to assess performance changes under different temperature conditions. By controlling the IBT of the brake disc, a detailed analysis of the coefficient of friction (COF), frictional heat distribution, wear morphology, hardness variation, and residual stress were conducted to uncover the brake fade mechanisms. The findings reveal that as IBT increases, COF decreases with greater fluctuations, resulting in significantly extended braking times and distances. At elevated IBTs, the brake disc and friction block materials experience reduced hardness, increased tangential residual stress, decreased radial residual stress, and accelerated wear, leading to unstable COFs and extended braking distances. This work provides valuable insights into the mechanisms of thermal-induced brake fade during long-downhill braking, offering crucial technical guidance for enhancing the safety and reliability of high-speed train braking systems under extreme conditions.

Design, simulation and testing of U-type actuator-based single-coil active-magnetic-bearing

This work represents an experimental investigation using testing and modeling for a single-axis U-type Active-Magnetic-Bearing (AMB). To obtain the inductance profile and resistance value respectively, the AC and DC tests are conducted. A load cell test is performed to measure the magnetic attraction force. Further, the U-type actuator’s inductance and force are estimated using finite element analysis software. Using a variety of controllers in MATLAB-Simulink, the control system architecture is demonstrated and contrasted. According to the design data, the hardware system is configured. Finally, the high-speed test is performed satisfactorily for the proposed system at 16656 rpm.

Investigation of the Inhibition Mechanism of Process Porosity in Laser-MIG Hybrid-Welded Joints for an Aluminum Alloy

In this paper, 4 mm thick 7075 aluminum alloy was utilized for conducting laser-MIG hybrid welding tests to investigate the correlation between the dynamic behavior of keyholes and process-induced porosity. Additionally, the generation and inhibition mechanisms of process porosity were elucidated. Utilizing a high-speed camera test system of our own design, the formation position and movement characteristics of keyholes in the molten pool under different welding parameters were captured using a “sandwich” method. The dynamic behavior of keyholes during the hybrid welding process was analyzed, and the porosity of each welded joint was quantified, revealing an intrinsic relationship between keyhole dynamics and aluminum alloy laser-MIG hybrid welding porosity. The findings indicate that variations in the defocusing amount can influence both the morphology and stability of keyholes in the molten pool, consequently impacting welding porosity. The dynamic behavior of keyholes under different defocusing amounts can be categorized into five types: no keyhole formation, collapse of the keyhole root, complete instability of the keyhole, instability of the keyhole root, and stability of the keyhole. At a defocus of +12 mm, stable keyholes were observed, and no defects in the welded joints were identified.

Research on safety control technology of high-speed railway combined test based on threatening event analysis

PurposeSafety management is a key point and poses a challenge in joint testing. To detect and address potential accidents' hidden dangers early, this paper conducts research on the safety control technology for high-speed railway joint tests by incorporating the concept of hazardous events.Design/methodology/approachAiming at ensuring the safety of high-speed railway combined inspections and trials, this paper starts from the dual prevention mechanism. It introduces the concept of threatening events, defines them and analyzes the differences between threatening events and railway accidents. The paper also proposes a cause model for threatening events in high-speed railway combined inspections and trials, based on three types of hazard sources. Furthermore, it conducts research on the control strategies for these threatening events.FindingsThe research on safety control technology for high-speed railway combined operation and testing, based on the analysis of threatened events, offers a new perspective for safety management in these operations. It also provides theoretical and practical support for the transition from passive prevention to active risk pre-control, which holds significant theoretical and practical value.Originality/valueThe innovation mainly includes the following three aspects: (1) Building on the traditional dual prevention mechanism, which includes risk hierarchical management and control as well as hidden danger investigation and management, a triple prevention mechanism is proposed. This new mechanism adds the management of threatening events as the third line of defense. The aim is to more comprehensively identify and address potential security risks, thereby enhancing the efficiency and effectiveness of security management. (2) In this paper, the definition of a railway threatening event is clarified, and the causative model of a high-speed railway threatening event based on three kinds of danger sources is proposed. (3) This paper puts forward the control strategy of the high-speed railway combined operation and trial, which includes five key links: identification, reporting, analysis, rectification and feedback, which provides a new perspective for the safety management of the high-speed railway combined operation and trial and has important theoretical and application value.

On the use of a unified constitutive model for modelling slope large deformations with material point method

Landslides and debris flows can have devastating effects, particularly when movement involves a transition from solid-like to fluid-like process. The elastoplastic constitutive model has a limited ability to describe the entire movement process; thus, this paper establishes a unified constitutive model comprising a hypoplastic model and Bagnold model within a GPU-accelerated material point method (MPM) framework. The model is validated first through low-speed direct shear tests to demonstrate its ability to describe solid-state friction behaviour, then collision behaviour under rapid flow conditions is examined using high-speed annular shear tests. The validity of the unified model for geotechnical engineering large deformations is subsequently verified using column collapse, where the superiority of the unified model over the traditional constitutive model in describing the large deformation process is demonstrated. An index, the dynamic stress ratio, is comprehensively analysed over the whole column failure process and the dynamic stress ratio is found to correlate well with the second-order work conversion criterion, distinguishing the transition of movement from solid-like to fluid-like stage. Finally, the constitutive model is applied to a hazard assessment of the Qianjiangping and Tatopani landslides in which the applicability and stability of the model along with the MPM framework are further demonstrated.

High strain-rate fracture behavior of a hollow projectile

In this paper, a hollow projectile made of AISI4340 steel was fabricated based on an arbitrary warhead shape, and high-speed impact tests were performed according to various target encounter conditions including velocity and angle. In order to characterize the dynamic fracture behavior, tensile tests were performed on various notch specimens under three strain rates (10–3 s-1, 100 s-1, 103 s-1), and the stress state histories of the specimens were calibrated through a hybrid experimental-numerical analysis. In particular, for the intermediate (100 s-1) and high (103 s-1) strain rate conditions, the local temperature rose due to adiabatic heating until fracture was experimentally measured, and the thermal softening behavior determined from the inverse optimization technique was considered for the dynamic constitutive model. For the comparison with the high-speed impact test results, a rate-dependent ductile fracture model was utilized for numerical simulation. Considering that the model parameters were calibrated with the thermal softening effect, the proposed fracture model implicitly takes temperature into account. The deformation and fracture modes of the projectile from experimental and numerical study showed very good agreement under all impact conditions. It was confirmed that the softening of a material by adiabatic heating should be considered along with strain rate hardening in dynamic fracture simulation.

Deformation behavior of aluminum alloy rivets for aerospace applications

For many decades, solid rivets made of high-strength aluminum alloys have been used for mechanical joining of aircraft structures. For numerical modeling of riveting processes the detailed description of the deformation behavior of the rivets is of utmost importance; however, only very little reliable material data are available. Therefore, this study reviews and investigates the deformation behavior of commercial MS20426AD3-5 countersunk rivets made of aluminum alloy AA-2117-T4 as typically used in aerospace applications. The self-consistent procedure for determining the material-specific flow curve includes (i) the exact preparation of cylindrical samples, (ii) compression testing of the samples at testing speeds of 0.05 mm/s, 0.5 mm/s and 5 mm/s, and (iii) inverse numerical modeling of the testing procedure. In general, the compliance of the testing setup must be considered for obtaining reliable flow curves, especially when testing small samples. The determined flow curve of aluminum alloy AA-2117-T4 showed higher yield stress and more distinct initial strain hardening than most of the flow curves published in literature. Although the flow curve did not show any significant strain rate dependency, notable softening due to deformation-induced adiabatic heating of the compressed sample was observed at the highest testing speed. However, the fracture strain seems to be strain rate-dependent, because samples deformed at the low testing speed did not show any signs of macroscopic fracture, whereas local fracture occurred in samples deformed at the medium and high testing speeds.

Experimental and analytical study on the compressive behavior of PMI foam with different densities and cell sizes under intermediate strain rates

Polymethacrylimide (PMI) foam materials have great potential for applications in the field of protective energy absorption owing to their superior compressive properties. Existing studies on the mechanical behavior of PMI foams are limited, particularly for loading at intermediate strain rates. This paper presents a comprehensive experimental study of PMI foam with four different densities under quasi-static and intermediate strain rate compression (0.001 s−1 to 100 s−1). Each density included three different cell sizes to determine their effects on the compressive performance. Loads parallel and perpendicular to the foam rise direction were considered to investigate the anisotropic behavior. Intermediate strain rate tests were conducted using a high-speed hydraulic servo testing machine, which achieved a stable strain rate while ensuring consistent specimen sizes in both quasi-static and dynamic tests. In all the experiments, the compression process was captured using a high-speed camera and the macroscopic deformation mode and microscopic deformation mechanism were analyzed by combining Digital Image Correlation (DIC) and Scanning Electron Microscopy (SEM). The PMI foam with finer cell sizes exhibited an enhanced compression performance. As the strain rate increased, the strain rate effect became more evident in the high-density specimens and an increase in cell size diminished this effect. A modified analytical model incorporating the cell-size correction term was developed based on Gibson and Ashby's model. The modified model exhibited an average error of 4.9 % in the predicted plateau stress of PMI foam with different cell sizes at the same density.

Event-Based Measurement of Aeroelastic Structure in High-Speed Flow

In high-speed aerodynamics research, point sensors are ideal for embedding in test models but lack spatial resolution, whereas high-speed cameras offer spatiotemporally resolved measurement but involve significant footprint, cost, and data size. To address these tradeoffs, this study explores the application of nascent event-based cameras for high-speed tests. Event-based cameras support continuous, data-sparse kilohertz-equivalent imaging at 720p resolution, on form factors as small as 36 mm and 40 grams in mass, combining the benefits of point sensors and high-speed cameras. However, these attributes come from asynchronous pixels that necessitate unique operating and postprocessing approaches. Here, the authors adapted event-based cameras for two-/three-dimensional photogrammetric tracking of aeroelastic structures, demonstrating an event-based workflow and two tracking algorithms (mean-shift filtering and circle fit). Bench-top validations achieved three-dimensional precision of 0.35 mm/s on 20 mm/s motion across a 259 mm field of view, while two-dimensional measurements of an aeroelastic titanium panel in Mach 0.76 transonic flow successfully identified millimeter-scale vibrations at 43.7, 120, and 270 Hz, validated against a laser displacement and high-speed camera. The transonic test’s raw data were 145.8 MB on the event-based camera, compared to 88.5 GB on the high-speed camera. The presented results demonstrated the viability of event-based techniques in high-speed aerodynamic testing, while highlighting challenges such as polarity switching and pixel latency.

Effects of temperature and loading rate on the shear performance of GFRP-steel single-lap joints

This research examines how the shear properties of glass fiber-reinforced polymer (GFRP) and steel single-lap joints react under various temperatures (−25, 0, 25, 50, and 100℃) and loading speeds (0.625, 1.25, 2.5, and 5.0 m/s). The GFRP sheets, aligned unidirectionally, were produced using vacuum-assisted resin transfer molding and were then adhesively attached to steel plates with epoxy resin. The assemblies were subjected to a high-speed servo-hydraulic testing apparatus for evaluation. The results indicate that the joint's performance is relatively unaffected by changes in the loading speed, but the overall toughness tends to decrease at higher speeds. However, the adhesive bond strength increases when temperatures are between −25 and 50℃ but diminishes as temperatures rise from 50 to 100℃. Most samples exhibited debonding at the steel-adhesive interface under varied speeds and colder temperatures, whereas debonding at the GFRP-adhesive interface was more prevalent at elevated temperatures. These insights are vital for both theoretical analyses and practical implementations of GFRP-steel single-lap joints in environments subject to extreme loading conditions and temperatures.