Dynamic Material Properties Research Articles

Taylor Impact Tests with Copper Cylinders: Experiments, Microstructural Analysis and 3D SPH Modeling with Dislocation Plasticity and MD-Informed Artificial Neural Network as Equation of State

Taylor impact tests involving the collision of a cylindrical sample with an anvil are widely used to study the dynamic properties of materials and to test numerical methods. We apply a combined experimental-numerical approach to study the dynamic plasticity of cold-rolled oxygen-free high thermal conductivity OFHC copper. In the experimental part, impact velocities up to 113.6 m/s provide a strain up to 0.3 and strain rates up to 1.7 × 104 s−1 at the edge of the sample. Microstructural analysis allows us to find out pore-like structures with a size of about 15–30 µm and significant refinement of the grain structure in the deformed parts of the sample. In terms of modeling, the dislocation plasticity model, which was previously tested for the problem of a shock wave upon impact of a plate, is implemented in the 3D case using the numerical scheme of smoothed particle hydrodynamics (SPH). The model includes an equation of state implemented in the form of an artificial neural network (ANN) and trained according to molecular dynamics (MD) simulations of uniform isothermal stretching/compression of representative volumes of copper. The dislocation friction coefficient is taken from previous MD simulations. These two efforts are aimed at building a fully MD-based material model. Comparison of the final shape of the projectile, the reduction of the sample length and increase in the diameter of the impacted edge of the sample confirm the applicability of the developed model and allow us to optimize the model parameters for the case of cold-rolled OFHC copper.

Molecule Dynamics Simulation of the Effect of Oxidative Aging on Properties of Nitrile Rubber.

The effects of oxidative aging on the static and dynamic properties of nitrile rubber at the molecular scale were investigated by molecular dynamics simulation. The aged nitrile rubber models were constructed by introducing hydroxyl groups and carbonyl groups into rubber molecular chains to mimic oxidative aging. The static and dynamic properties of the unaged and aged nitrile rubber under different conditions were evaluated by mean square displacement, self-diffusion coefficients, hydrogen bond, fractional free volume, radial distribution function, cohesive energy density and solubility parameter. The results show that the elevated temperature intensified significantly the mobility of rubber molecular chains and fractional free volume, while the compressive strain displayed the opposite effect resulting in packing and rearrangement of rubber chains. The introduction of hydroxyl groups and carbonyl groups enhanced the polarity, intermolecular interactions, the volume and rigidity of molecular chains, implying weaker mobility of molecular chains as compared to unaged models. The compressive strain and oxidative aging both decreased the fractional free volume, which inhibited gaseous and liquid diffusion into the rubber materials, and slowed down the oxidative aging rate. This study provides insights to better understand the effect of molecular changes due to oxidative aging on the structural and dynamic properties of rubber materials at the molecular level.

Wavelet transform based method of measuring multi-frequency electrostatic force microscopy dynamic process

Electrostatic force microscopy (EFM) has high sensitivity and lateral resolution, and it is widely used to measure the electrostatic properties of new energy materials. The time-resolved electrostatic force microscope technology is used to measure the dynamic electrical properties of materials, pump detection method commonly used in this technology has problems such as complex equipment, high cost, and uncertainty in the measurement. In this work the method of directly measuring the time domain is adopted. This method reduces the complexity of measurement. By using the multi-frequency or high-frequency excitation method, the simultaneous measurement of multiple EFM parameters and the improvement of time resolution can be achieved, reaching a time resolution of microseconds, and by applying wavelet transform to the tip signal obtained by the measurement the dynamic electrical properties of the materials can be extracted. Applying this technology to simulation experiments, it is possible to measure the dynamic potential changes and the characteristic time parameter of ion movement in the microsecond-level electrical dynamic process of the simulated battery materials.

Size Effect in the Split Hopkinson Pressure Bar Experiment

For many structures, their service environment is very strict, and the requirements for the impact resistance of materials are very high. Therefore, the dynamic testing method has important scientific significance and application value for practical engineering. Split Hopkinson pressure bar (SHPB) is one of the most common experimental methods for obtaining dynamic mechanical properties of materials. However, there is no uniform standard for the size of the bars and specimens used in the test. Theoretically, the size has little influence on the experimental results, but it has not been proved by experiments. This paper mainly studies the influence of device/specimen sizes of split Hopkinson pressure bar through experiments, it is demonstrated that the sizes of bars and specimen have little effect on experimental results.

Design of Asymmetric Parallel Manipulator for Axial-Bending Dynamic Stiffness Analysis

This paper presents an asymmetric 5-bar parallel manipulator capable of characterizing the dynamic stiffness properties of materials used in robotic joints in 2 degrees of freedom, axial and bending, simultaneously. The end effector is actuated by two stepper motors with linear rails. Two force sensors were added to estimate axial force and moment. Experiments were performed in axial compression, bending, and a mixed axial-bending motion. A spring-mass-spring system was constructed to evaluate the fabricated apparatus for frequency analysis up to 20Hz. The frequency analysis result was accurate when compared to the theoretical response of the system. Axial stiffness estimation had an error of 1.5%, bending stiffness had an error of 3.4%, and mixed-mode had a total error of 1.8%. Future experiments will showcase the versatility of the apparatus and test nonlinear samples.

Mechanical and dynamic responses of unidirectional/woven carbon fiber reinforced thermoset and thermoplastic composites after low velocity impact

It is highly important to determine how mechanical and dynamic properties of composite materials will change after impact loads considering the coupled effects of composite design parameters. For these reasons, three-point bending and vibration tests have been carried out for the carbon fiber reinforced thermoset and thermoplastic composites with various stacking sequences before and after low velocity impact, and it is expected that these results achieved from the current study will be beneficial for applications where high damping and impact resistance are demanded together. In this context, vibration tests were carried out under free-free boundary conditions, and their natural frequencies, flexural moduli and structural damping were obtained. Furthermore, three-point tests were conducted in the elastic region with 1 mm/min crosshead speed using a universal test machine, and thus flexural moduli of the composite specimens were obtained. The results were validated by comparing the flexural moduli obtained from the both vibration and three-point bending tests, found to be reliable and comparable. As a result of the current study, it was concluded that woven fabric reinforced composite specimens exhibited 50% higher specific damping capacity (SDC) but 70% lower flexural modulus than unidirectional specimens thanks to biaxially fiber alignment. On the other hand, specific damping capacities of the thermoset and thermoplastic composites with different stacking sequences have been examined, and it was observed that thermoset specimens exhibited unexpectedly 192% higher SDC compared to the thermoplastics. This was interpreted as even though thermoplastics are normally expected to exhibit more damping than thermosets, stacking sequence being more effective on damping responses. Apart from that, although there were slight changes in material properties due to degradation in structural integrity after 2 m/s and 3 m/s low-velocity impacts, it was not found to be significantly effective due to the limited damage areas.

Velocity characteristics of fracture fragments of mica-crystal materials under high-speed impact

Determination of the velocity of individual fragments of a fragmented matter following an impact is necessary for studying the dynamic mechanical properties of materials. Various models descriptive of specific collision cases are used to predict the fragmentation parameters including the velocity of fragments. The models have been mostly designed to describe metallic materials. The research aims at experimental determination of the fragments destruction velocity following an impact against hard-melting non-metallic silicate material (potassium fluorphlogopite). Potassium fluorphlogopite targets have been shaped as flat plates sized 280x160x15 mm. The 23 mm steel ball (Steel 20) was used as a projectile. Four impact tests have been conducted with the following parameters: ball velocity 230 m/s and collision angle 90°; ball velocity 120 m/s and collision angle 90°; ball velocity 230 m/s and collision angle 30°; ball velocity 120 m/s and collision angle 30°. Velocity of burst fragments was determined on the basis of a video recording with Photron Fastcam SA5 high-speed camera. The video has been processed using frame-by-frame image analysis in ImageJ-FiJi software (TrackMate module). The experiment determined the velocities of individual burst fragments following an impact against hard-melting non-metallic silicate material, specifically potassium fluorphlogopite. It has been established that the change in the velocity of fragments in time corresponds to the hyperbolic function; a coefficient has been proposed to calculate the change in the velocity of potassium fluorphlogopite fragments break-off in time.

Research on Dynamic Response and Fracture Properties of Metal Materials for Vehicle

Research on Dynamic Response and Fracture Properties of Metal Materials for Vehicle

Laser-plasma jet driven sub-millimeter diameter aluminum flyer and its gesture diagnosis

Laser-driven flyer has been studied for decades as it promises to possess many applications such as in measuring the equation of state (EOS) under ultrahigh pressure, investigating the material dynamic properties under high strain rate, simulating the high-speed impact for aircraft protection, and igniting explosives. However, the planarity and integrity of flyers are determined by indirect velocity lnterferometer system for any reflector (VISAR) or witness slab results due to its high speed and small dimension. For further and wide applications, it is very important to obtain direct experimental proof of the flyer gesture and configuration. Thus, the acceleration and gesture investigation of aluminum flyer driven by laser plasma are studied on Xingguang-III laser facility. The X-ray radiography is achieved by a picosecond laser irradiating the copper wire target. The shadowgraph of flyer and plasma are realized by the incidence of a bunch of infrared laser through the flyer flight path. In additon, photon Doppler velocimetry is employed to measure the flyer velocity simultaneously. The radiography, shadowgraph and velocity of typical small aluminum flyer are obtained. By optimizing the thickness of both CH ablation layer and vacuum gap, the flyer is slowly accelerated via consecutive stress wave produced by plasma colliding. The aluminum flyer has a thickness of 20 μm and diameter of about 500 μm. The whole flyer remains the integrated shape after a great angle of rotation due to uneven plasma loading. The flight distance is about 400 μm, giving an average velocity of 2.2 km/s. The planarity of the flyer is good except a little bend on the two sides due to side rarefaction of plasma. The study verifies that the laser plasma collision can generate a sub-millimeter-diameter metal flyer with integrated shape and a velocity of several kilo-meters per second, showing that it possesses the promising applications in measuring the EOS and igniting explosive .

Investigation of mechanical characteristics of braided carbon fiber

The use of composite materials in various branches of modern industry is rapidly increasing due to their high strength properties, low weight and good manufacturability. A wide variety of materials used, types of reinforcement and internal structures creates a need for studies of the static and dynamic properties of composite materials. Due to the latest advances in technology, composite materials are widely used in a variety of industrial applications. As a result, there is considerable interest in studying and understanding the behavior of composite structures. Analysis of composite structures, study of resonance frequencies, damping factors and modal shapes played an important role in determining the dynamic characteristics of the structure, detecting damage and monitoring the state of the composite structure. In this paper, the results of computational and experimental researches of the Young’s modulus, natural frequencies and modes of vibration, damping properties of the composite material are presented. The researches were carried out on samples of the woven ten-layer carbon fiber reinforced plastic. The investigated carbon fiber reinforced plastic has a plain weave. Samples were cut in three directions: warp (0 °), weft (90 °) and 45 °. Nine samples were prepared for each direction. To study the Young’s modulus, a tensile testing machine was used, and a vibration stand was used to determine the natural frequencies and modes of vibration. Damping properties are calculated by the Oberst method, based on the amplitude-frequency characteristics of the samples. Statistical processing of the experimental results was carried out and the values ​​of the mathematical expectation and variance were obtained. Geometric and finite element models of сarbon fiber reinforced plastic samples were built, their natural frequencies and vibration modes were determined. Comparison of the computational and experimental data with numerous calculations using the finite element method is carried out.

Dynamic mechanical behavior of composite materials reinforced by graphene and huntite minerals

Abstract The aim of this study is to investigate the dynamic mechanical properties of composite materials reinforced by mineral experimentally. Graphene and huntite minerals were added to epoxy resin at different weight ratios (wt.-%) as 0.5 weight percent, 1 weight percent and 3 weight percent, to examine the effect of mineral types and percentages on the resulting dynamic mechanical properties. In addition, the effect of non-layered huntite unlike graphene, with a nano-sized grain structure, was investigated. Thus, glass transition temperature (Tg), storage modulus (E’), loss modulus (E”) and damping ratio (tan δ) values were determined and compared. Moreover, a tensile test was performed in order to explain the relation between stress and strain. It was seen that adding different minerals caused different results according to types and proportions. In general, adding minerals to the pure resin increased the storage modulus and loss modulus, whereas the damping ratio (tan δ) decreased compared to the pure resin.

Observation of 4- and 6-Magnon Bound States in the Spin-Anisotropic Frustrated Antiferromagnet FeI2

Spin-waves e.g. magnons are the conventional elementary excitations of ordered magnets. However, other possibilities exist. For instance, magnon bound-states can arise due to attractive magnon-magnon interactions and drastically impact the static and dynamic properties of materials. Here, we demonstrate a zoo of distinct multi-magnon quasiparticles in the frustrated spin-1 triangular antiferromagnet FeI$_2$ using time-domain terahertz spectroscopy. The energy-magnetic field excitation spectrum contains signatures of one-, two-, four- and six-magnon bound-states, which we analyze using an exact diagonalization approach for a dilute gas of interacting magnons. The two-magnon single-ion bound states occur due to strong anisotropy and the preponderance of even higher order excitations arises from the tendency of the single-ion bound states to themselves form bound states due to their very flat dispersion. This menagerie of tunable interacting quasiparticles provides a unique platform in a condensed matter setting that is reminiscent of the few-body quantum phenomena central to cold-atom, nuclear, and particle physics experiments.

Machine learning prediction of structural response of steel fiber-reinforced concrete beams subjected to far-field blast loading

Owing to its superior mechanical properties, enhanced energy absorption, and improved blast resistance, steel fiber-reinforced cementitious composites are a prime choice for the development of resilient structures. Sizable advancements have recently been made in assessing the blast performance of steel fiber-reinforced concrete (SFRC), high-strength steel fiber-reinforced concrete (HSFRC), and ultra-high-performance steel fiber-reinforced concrete (UHPFRC). However, there is still need for concerted research to explore the effects of fiber parameters under blast loading and to develop simple and robust predictive models. Thus, the present study develops a machine learning model to predict the maximum displacement of SFRC, HSFRC, and UHPFRC beams subjected to far field blast loading. Using Gaussian Process (GP) regression and Conditional Tabular Generative Adversarial Networks, a novel model was developed considering 117 experimental and 300 synthetic datasets. The proposed model was appraised through several statistical performance metrics and compared to existing analytical and numerical methods. The model imparts noteworthy reduction in modeling complexity in terms of static and dynamic material properties. A parametric analysis was conducted using the developed model to investigate the effects of fiber properties for diverse beam configurations. The proposed simplified model achieved highly favorable predictive performance with MAE of 2.75, R2 of 90.32%, and MAPE of 13.8%.

Inverse parameter estimation to predict material parameters of the\xa0Cowper\u2013Symonds constitutive equation in electrohydraulic forming process

The development of a reliable numerical simulation is essential for understanding high-speed forming processes such as electrohydraulic forming (EHF). This numerical model should be created based on the accurate material properties. However, dynamic material properties at strain rates exceeding 1000 s^{-1} cannot be easily obtained through an experimental approach. Thus, this study predicted two material parameters in the Cowper–Symonds constitutive equation based on inverse parameter estimation, such that the parameters predicted using the numerical simulation corresponded well with those obtained from the experimental results. The target material was a 1-mm-thick Al 5052-H32 sheet. The comparison target included the final deformation shape of the sheet in the EHF-free bulging test at three input voltages of 6, 7, and 8 kV. For the inverse parameter estimation, the posterior distribution for the two parameters included a likelihood and a prior distribution. For the likelihood construction, a reduced-order surrogate model was developed in advance to substitute the numerical simulation based on ordinary Kriging and principal component analysis. Moreover, the error distribution of the bulge height between the experiment and reduced-order surrogate model was obtained. The prior distribution at 7 kV was defined as a uniform distribution, and the posterior distribution at 7 kV was employed as a prior distribution at 6, 7, and 8 kV. Furthermore, Markov chain Monte Carlo sampling was employed and the Metropolis–Hastings algorithm was adopted to obtain the samples following the posterior distribution. After the autocorrelation calculation for sample independence, the lag with an autocorrelation of pm ,0.02 interval was selected and every lag^{mathrm {th}} sample was obtained. The total number of acquired samples was 10^{5}, and the mean values were calculated from the obtained samples. Consequently, the numerical simulation with mean values displayed good agreement with the experimental results.

Quasi-Static, Dynamic Compressive Properties and Deformation Mechanisms of Ti-6Al-4V Alloy with Gradient Structure

Gradient structure metals have good comprehensive properties of strength and toughness and are expected to improve the dynamic mechanical properties of materials. However, there are few studies on the dynamic mechanical properties of gradient structured materials, especially titanium alloys. Therefore, in this study, ultrasonic surface rolling is used to prepare a gradient structure layer on the surface of Ti-6Al-4V, and the quasi-static and dynamic compressive properties of coarse-grained Ti-6Al-4V (CG Ti64) and gradient-structured Ti-6Al-4V (GS Ti64) are investigated. The results show that a GS with a thickness of 293 µm is formed. The quasi-static compressive strength of GS Ti64 is higher than that of CG Ti64. Both CG Ti64 and GS Ti64 exhibit weak strain hardening effects and strain rate insensitivity during dynamic compression, and the compressive strength is not significantly improved. The lateral expansion of CG Ti64 is more obvious, while the lateral side of GS Ti64 is relatively straight, indicating that uniform deformation occurs in GS Ti64. The α phase in the GS produces dislocation cells and local deformation bands, and the lamellar structure is transformed into ultrafine crystals after dynamic compression. Both of them produce an adiabatic shear band under 2700 s−1, a large crack forms in CG Ti64, while GS Ti64 forms a small crack, indicating that GS Ti64 has better resistance to damage. The synergistic deformation of GS and CG promotes Ti-6Al-4V to obtain good dynamic mechanical properties.

Development of a True-Biaxial Split Hopkinson Pressure Bar Device and Its Application.

Although highly desirable, the experimental technology of the dynamic mechanical properties of materials under multiaxial impact loading is rarely explored. In this study, a true-biaxial split Hopkinson pressure bar device is developed to achieve the biaxial synchronous impact loading of a specimen. A symmetrical wedge-shaped, dual-wave bar is designed to decompose a single stress wave into two independent and symmetric stress waves that eventually form an orthogonal system and load the specimen synchronously. Furthermore, a combination of ground gaskets and lubricant is employed to eliminate the shear stress wave and separate the coupling of the shear and axial stress waves propagating in bars. Some confirmatory and applied tests are carried out, and the results show not only the feasibility of this modified device but also the dynamic mechanical characteristics of specimens under biaxial impact loading. This novel technique is readily implementable and also has good application potential in material mechanics testing.

Band gap tuning through microscopic instabilities of compressively loaded lightened nacre-like composite metamaterials

Large deformation effects give the opportunity for tuning and manipulating the dynamic properties of periodic microstructured materials, including those related to vibration control and band gap phenomena. We investigate the wave propagation properties in bioinspired nacre-like composite metamaterials subjected to uniaxial loading processes, also considering the onset of instabilities at the microscopic and macroscopic scales. The dynamic response of a new 2D lightened brick-and-mortar microstructure containing periodically arranged cavities is investigated, by analyzing the propagation of elastic waves superimposed on a deformed state by means of a Bloch-wave analysis. The band gap properties of the proposed advanced metamaterial were investigated in terms of spectral quantities as a function of the main geometrical parameters and of the level of applied deformations. Numerical results have shown that the elastic wave propagation is strongly influenced by the prestress state inducing microscopic instability, thus providing new opportunities to design periodic bioinspired composite metamaterials characterized by wave absorption capabilities as a function of microstructural evolution.

The numerical simulation of large diameter split Hopkinson pressure bar and Hopkinson bundle bar of concrete based on mesoscopic model

In the comparison of Hopkinson bundle bar (HBB) system and the large diameter split Hopkinson pressure bar (SHPB) system, the influence of bar diameter on the dispersion effect of the one-dimensional longitudinal wave is analyzed theoretically firstly. Three trapezoidal loads with different peak values are applied to the elastic bars with two types of sections to investigate the stress wave propagation. Then, based on the fractal characteristics of concrete aggregate, the 3D realistic mesoscopic model is constructed as numerical models. And the dynamic responses of concrete under two kinds of test systems have been compared and analyzed. The results show that, the HBB system can more effectively reduce the lateral dispersion in the stress wave propagation and is beneficial to maintain the waveform than the large diameter SHPB system. The large diameter SHPB simulated results based on the 3D realistic mesoscopic model are consistent with the experimental results, which verify the feasibility of the mesoscopic model. The HBB system can obtain the similar simulated results as the large diameter SHPB system, such as the similar waveform with the double peak phenomenon of the reflection wave. However, there is a significant difference in the failure pattern of the specimens under two test systems, which is caused by the boundary effect of the hexahedron specimen in the HBB system. In conclusion, the HBB system can also carry out the dynamic mechanical properties of concrete-like materials. Moreover, HBB system can obtain more detailed information, reflecting the difference of local mechanical properties of concrete. Although there are still some deficiencies, it can still provide additional ideas for related researchers.

Testing and Modelling of Elastomeric Element for an Embedded Rail System.

Modelling of elastomeric elements of railway components, able to represent stiffness and damping characteristics in a wide frequency range, is fundamental for simulating the train–track dynamic interaction, covering issues such as rail deflection as well as transmitted forces and higher frequency phenomena such as short pitch corrugation. In this paper, a modified non-linear Zener model is adopted to represent the dependences of stiffness and damping of the rail fastening, made of elastomeric material, of a reference Embedded Rail System (ERS) on the static preload and frequency of its deformation. In order to obtain a reliable model, a proper laboratory test set-up is built, considering sensitivity and frequency response issues. The equivalent stiffness and damping of the elastomeric element are experimentally characterised with force-controlled mono-harmonic tests at different frequencies and under various static preloads. The parameters of the non-linear Zener model are identified by the experimental equivalent stiffness and damping. The identified model correctly reproduces the frequency- and preload-dependent dynamic properties of the elastomeric material. The model is verified to be able to predict the dynamic behaviour of the elastomeric element through the comparison between the numerically simulated and the experimentally measured reaction force to a given deformation time history. Time domain simulations with the model of the reference ERS demonstrate that the modelled frequency- and preload-dependent stiffness and damping of the elastomeric material make a clear difference in the transient and steady-state response of the system when distant frequency contributions are involved.

Determination of mechanical properties from sharp dynamic indentation

In this study, a dynamic indentation test method based on the split Hopkinson pressure bar is proposed to obtain the dynamic parameters of Ludwik power law constitutive, namely, Young’s modulus E, strength coefficient K, and strain hardening index n by analyzing dynamic indentation load-indentation depth curve obtained from the theories relating to the Hopkinson pressure bar. The important parameters, namely, loading curvature C and transformation factor [Formula: see text], are invoked to examine the dynamic indentation response results in a wide range of target material parameters. Finite element calculation results are processed through simulation of dynamic indentation response with broad material parameters. Furthermore, the analytical method is used to fit simulation results to obtain the analytical equations for elastic–plastic parameters and curvature parameters for the subsequent analysis. The analytical equation of forward model to predict dynamic indentation response parameter–loading curvature C of a known material is proposed. Then, the elastic–plastic parameters of unknown materials (according to Ludwik power law) are obtained by substituting the dynamic indentation response parameters into an inverse analytical equation under the two types of half-cone angle indenters. The method is verified by other typical materials, which shows that the dynamic indentation test based on the split Hopkinson pressure bar can obtain sufficient conditions to obtain dynamic mechanical properties of target materials.