Dynamic Mechanical Response Research Articles

Self-heating and dynamic mechanical behavior of silicone rubber composite filled with carbonyl iron particles under cyclic compressive loading

Self-heating and dynamic mechanical behavior of isotropic silicone rubber composite (SRC) filled with micro-sized carbonyl iron particles (CIPs) subjected to cyclic compressive loading have been studied. Effects of pre-strains from 5 to 20%, strain amplitudes from 1 to 5%, and excitation frequencies from 10 to 50 Hz on the self-heating and dynamic mechanical response of the isotropic SRC were investigated. The self-heating temperatures were measured on the surface and at the center of cylindrical SRC specimens. The self-heating temperatures of the isotropic SRC samples showed a fast increase in an initial transient stage and the following isothermal stage. The temperature distribution in the isotropic SRC specimens was non-homogeneous and the temperature decreased from the center to sample edges. The self-heating temperatures of the isotropic SRC increased gradually with raising the strain amplitude and frequency. However, the difference between the internal and surface temperatures was slight for low strain amplitudes and frequencies, while it was significant for high strain amplitudes and frequencies. The temperatures of the isotropic SRC boosted rapidly with increasing the pre-strain to 10% and thereafter gained slightly. Although the isotropic SRC dynamic moduli reduced with the rise of the strain amplitude, they enhanced with increasing the pre-strain and frequency. Besides, the storage modulus of the isotropic SRC varied slightly with time, while the loss modulus reduced markedly especially at the initial period. The decrease in the loss modulus of the isotropic SRC under cyclic compressive loading is attributed to its self-heating temperature rise. A finite element simulation of the heat transfer in the SRC cylinder was conducted. The calculated temperatures in the SRC cylinder were in good agreement with the measured ones at different strain amplitudes and frequencies.

Simulation of convective combustion reactions in PBX based on DEM–CPM

Convective combustion is a characteristic process in the violent evolution of polymer-bonded explosives (PBX), which increases the reaction and causes rapid pressurization, high reaction violent explosion, or deflagration to detonation. Thus, simulations of convective combustion reactions are necessary to predict the risks associated with violence properly. There is rapid pressurization in the crack and flame penetration that are the main characteristics of convective combustion. Traditional numerical simulation methods are not applicable to simulate PBX convective combustion reactions. Therefore, in this paper, a discrete element method coupled with the corpuscular method was proposed, combined with the Ward-Son-Brewster (WSB) burn model. By using this method, the dynamic mechanical responses of PBX, the reaction products, and the combustion of PBX are modeled by the discrete element, gas particle, and WSB combustion mode, respectively. This coupled method has been validated by the simulation of the slot-pressurization experiment. Furthermore, the reaction evolution after ignition in PBX was simulated, as well as the process of flame penetration into charge. The analysis of flame penetration into the charge contributes to a deeper understanding of the violent event of PBX.

Tuning of Static and Dynamic Mechanical Response of Laser Powder Bed Fused AlSi10Mg Lattice Structures through Heat Treatments

The use of additive manufacturing allows the production of complex designs, including metallic lattice structures, which combine lightness and good mechanical properties. Herein, the production of AlSi10Mg lattice structures by laser powder bed fusion is explored and consistent processing parameters are selected. Thereafter, it is demonstrated that heat treatments, specifically designed on the basis of the alloy's metallurgy, can be used to selectively induce different microstructural modifications and, consequently, finely tune the static and dynamic mechanical behavior of the aluminum lattice structures. In particular, removal of residual stresses results to be the dominant factor in allowing a smooth quasistatic compressive behavior and improving the structure's ability to absorb energy during collapse. On the contrary, the increase in ductility connected to the spheroidization of the Si network is shown to be of paramount importance in improving the structure's dynamic damping ability by allowing local plasticization.

Influence of Filler Surface Modification on Static and Dynamic Mechanical Responses of Rice Husk Reinforced Linear Low-Density Polyethylene Composites

Influence of Filler Surface Modification on Static and Dynamic Mechanical Responses of Rice Husk Reinforced Linear Low-Density Polyethylene Composites

Dynamic fracture behavior of piezoelectric ceramics under impact: Force-electric response and electrical breakdown

The brittle fracture may occur in the application of piezoelectric ceramics, but the traditional research is still limited to the static fracture of the materials. Based on the improved Hopkinson pressure bar loading system and high-speed photography technology, the experimental study on the fracture behavior of piezoelectric ceramics under impact loading was carried out. The dynamic mechanical and electrical response of lead zirconate titanate (PZT) and the possible electric breakdown phenomenon were analyzed. The experimental results show that the output voltage is stable and the maximum output voltage is 889 V when the impact load does not cause the material to fracture. When the material breaks, its macroscopic output voltage fluctuates due to electric breakdown. Combined with the finite element simulation of the impact fracture process, the distribution characteristics of the stress field and electric field near the crack during the fracture process were analyzed. The results show that the sliding between grains formed the crack cavity parallel to the electric field during the impact process. Furthermore, based on the theory of dielectric breakdown, the possibility of electric breakdown in the initial defect and the elliptical cavity formed by the impact is analyzed.

Mechanical properties and constitutive relation of hydrotalcite-carbon nanotube concrete

Co-Fe-Mg-Al quaternary hydrotalcite-carbon nanotube composites (LDH-CNT composites) were prepared by co-precipitation method and blended into concrete. Universal testing machine and SHPB testing device were used to carry out static and dynamic tests on LDH-CNT concrete specimens with different LDH-CNT additions (0, 0.25 wt.%, 0.5 wt.%), and the dynamic constitutive equation was obtained according to the dynamic stress-strain curve. Results show that compared with ordinary concrete, the compressive strength and toughness of LDH-CNT concrete have been greatly improved. When the LDH-CNT composites content is 0.5 wt.%, the strength and toughness are increased by 10.8% and 16.3%, respectively; The dynamic compression mechanical properties of LDH-CNT concrete show a significant strain rate effect, and the impact compression mechanical parameters increase with the increase of the maximum strain rate. In the strain rate range of 10°∼102s−1, the theoretical curve and the measured curve fit better, and the constitutive equation can describe the dynamic mechanical response of LDH-CNT concrete.

Research on Dynamic Cumulative Damage Effect of Metal Rubber and Stress Wave Propagation Characteristics of Layered Composite Structure

The development of protective materials and structures is of great significance for improving the impact resistance, penetration resistance and spalling resistance of military equipment. At present, the layered composite structure has been widely used due to its good protective performance. In this paper, a special elastic porous material-metal rubber (MR) with excellent cushioning and damping properties was used to prepare high-performance layered composite structures. To begin with, the dynamic mechanical response and the dynamic cumulative damage effect of MR were studied through Split-Hopkinson Pressure Bar (SHPB) tests. Then, the failure form and stress wave propagation characteristics of the layered composite structures were investigated through SHPB tests and finite element method. The results show that repeated impacts can enhance the compactness of MR, thereby increasing the ultimate bearing capacity and energy absorption capacity, which is beneficial for MR to resist repeated impacts. The MR in composite structures can reduce ceramic damage, attenuate stress wave and smooth stress distribution. The titanium alloy on the back of the ceramic will aggravate the damage of the ceramic, and ultra-high molecular weight polyethylene on the back of the ceramic provides cushioning for the ceramic. Therefore, the impact resistance of the composite structure can be improved by adding MR and the reasonable arrangement of materials, and the SiC/UHMWPE/MR/TC4 composite structure has relatively reasonable stress distribution and better protection performance.

Influence of temperature on the electrical characteristic parameters and dynamic electro-mechanical behaviour of PZT-5H

In the field of ammunition, piezoelectric ceramics are increasingly used as part of impact fuze systems. It is an urgent problem to improve the low-temperature storage and low-temperature environment adaptability of piezoelectric ceramic power supply. In order to study the dynamic mechanical and electrical response characteristics of PZT-5H at − 40 to 25 °C, the static electrical parameters of PZT-5H at different temperatures were measured, and the Hopkinson bar experiments at different temperatures and impact velocities were carried out by using the self-established low-temperature mechanical and electrical test system. The variation of resistivity and relative permittivity of PZT-5H from − 40 to 25 °C is obtained by experiment, and the relaxation time of PZT-5H is obtained according to Debye’s theory. Combined with the observation of scanning electron microscope (SEM), the influence mechanism of porosity and crack on the electrical output characteristics of piezoelectric ceramics was obtained. The mechanism of the freezing effect of piezoelectric ceramics at low temperatures is obtained through space charge theory analysis. The variation of the dynamic piezoelectric voltage constant with temperature and time in the elastic region measured by the experiment is clarified.

Research on the dynamic mechanical properties and constitutive model of metal rubber under impact loading

The development of lightweight, impact-resistant and high energy dissipation materials is of great significance to reduce the hazards of explosions and impacts. Metal rubber (MR) has the characteristics of low density, high damping performance and high elasticity, which shows great potential in the field of protection. However, there are few studies on the dynamic mechanical response of MR under high-speed impact. A series of experiments were carried out to study the mechanical properties of MR. It is found that the deformation mechanism of the metal wire inside the MR determines the mechanical properties. Under quasi-static conditions, the stress-strain of MR includes an elastic stage, a softening stage and a hardening stage, and the stress-strain under high-speed impact includes an elastic stage, a softening stage and a failure stage. In addition, the smaller the wire diameter, the higher the load-bearing capacity of the MR. The damage characteristics of MR under high-speed impact are divided into expansion failure and compaction failure, which will affect mechanical performance in the failure stage. The calculated energy absorption and ideal energy absorption efficiency show that MR is a material with excellent energy absorption properties. The dynamic elastic modulus and dynamic peak stress of MR have strain rate effect and density effect. A constitutive model based on Sherwood-frost equation was established, which can precisely forecast the dynamic mechanical properties.

A- or X-site mixture on mechanical properties of APbX3 perovskite single crystals

Organic–inorganic halide perovskites (OIHPs) have the typical composition of APbX3, in which A is a cation such as methlyamine (MA) and formamidine (FA) and X is a halide anion such as Cl, Br, or I. The mixture at the A or X site in OIHPs provides greatly improved versatility in their compositions and therefore allows the enhancement of their performance in LEDs and solar cells. In real application circumstances and deformable devices, the mechanical properties of OIHPs are of great importance. In this work, the mechanical properties of three series of mixed OIHP single crystals, MAPbIxBr3−x, MAPbBrxCl3−x, and FAyMA1−yPbBr3, are studied by nanoindentation. The results are summarized according to the composition of these mixtures. With the increase in the FA content at the A site, the average Young’s modulus (E) of FAyMA1−yPbBr3 decreases greatly from 19.2 GPa to 11.5 GPa, which indicates that the influence of organic cations on the mechanical properties of OIHPs is as important as that of Pb-X bonds. The mixture at the A or X site could also increase the hardness (H) and the wear resistance (H/E ratio). The average values of hardness and wear resistance of MAPbI0.1Br2.9 are almost double (0.63 GPa, 0.033) the values for undoped MAPbBr3 (0.32 GPa, 0.017). The dynamic mechanical responses of the OIHP single crystals show reduced creep stress exponents and thus increased strain rate sensitivities in the mixture at the X site, thereby improving the ductility. The nanoindentation sites are characterized using a scanning electron microscope and slip bands are observed, suggesting the plastic deformation mechanism governed by the activation of dislocations.

Dynamic mechanical response and a constitutive model of 42CrMo steel that incorporates the effects of high strain rates

<p indent=0mm>To study the dynamic mechanical properties and constitutive relationship of 42CrMo steel, which is primarily used in high-speed train axles, a dynamic compression test and a metallographic observation were conducted. The material exhibited strong strain-rate dependence, and the adiabatic shear behavior under dynamic loadings was found to be the dominant cause of the different mechanical properties resulting from different strain rates. The thermal activation theory, which separately considers the thermal and athermal stresses to explain the deformation mechanism, was employed to obtain the descriptions of the strain-rate effects. Accordingly, a physically based constitutive model was proposed that incorporated the effects of the high strain rates. A criterion for adiabatic shear, which was coupled to the model, was proposed to determine the onset of instability. The model was confirmed to sufficiently describe the quasi-static and dynamic mechanical behavior of the 42CrMo steel, especially the effects of strain hardening and strain rates on the yield stress.

Microstructure evolution and constitutive relation establishment of Mg–7Gd–5Y–1.2Nd–0.5Zr alloy under high strain rate after severe multi-directional deformation

At room temperature, dynamic mechanical response of Mg–7Gd–5Y–1.2Nd–0.5Zr alloy under high strain rate after severe multi-directional deformation were measured by a Split-Hopkinson pressure bar equipped with a set of limited strain rings under the strain rates of 0.001, 1800, and 2300 s−1 along the extrusion direction (ED). An electron back-scattering diffraction and a transmission electron microscopy were used to characterize the microstructure evolution of the alloy. When compressed along ED direction at the strain rate of 2300 s-1, prismatic and pyramidal < a > slip mechanisms first occurred in the ultra-fine grain band, and then tensile twins, basal slip, prismatic slip, pyramidal slip, dynamic recovery, and recrystallization occurred in the equiaxed fine-grained region. At the same strain rate (7% strain), various deformation mechanisms in the ultra-fine grain region and equiaxed fine-grained region, as well as the dynamic recovery and recrystallization mechanisms in the equiaxed fine-grained region were strengthened with the increase of strain rate. Based on the phenomenological Johnson–Cook relationship and the microstructure evolution analysis during deformation, a new constitutive relation was constructed by inserting a softening term with strain into the formula to calculate the stress–strain curve, which was in good agreement with the experimental data.

Helically Intersected Conductive Network Design for Wearable Electronic Devices: From Theory to Application.

Flexible and stretchable strain sensors are crucial components for wearable electronics that can detect and quantify the stimuli from the environment and thus realize the rapid feedback and control of smart devices. However, reconciliation of the conflict between resourceful design of conductive networks and large-scale production in the industry still faces a huge challenge. Herein, we present a new flow-manipulated strategy to prepare a wearable strain sensor featuring a helically intersected conductive network, which exhibited easy integration, multidimensional sensibility, and robust mechanical properties. From visualization of simulation and verification of experimental results, the helically intersected conductive network formed in an elastomer ring can simultaneously reflect the static and dynamic mechanical responses with a tunable gauge factor (10.41-31.12), wide linear region (0-40o), mechanical robustness (σs = ∼7 MPa, ε = ∼1400%), and rapid response time (∼300 ms). We further constructed a control system based on smart rings and demonstrated its application in controlling industrial robotic arms and remote-controlled cars. Looking ahead, this kind of a smart ring will be more widely used in space and underwater exploration, intelligent robotics, and human-machine interface technologies.

Experimental Study of Dynamic Mechanical Response and Energy Dissipation of Rock Having a Circular Opening Under Impact Loading

Experimental Study of Dynamic Mechanical Response and Energy Dissipation of Rock Having a Circular Opening Under Impact Loading

A progressive damage model of composite laminates under low-velocity impact

In this paper, a progressive damage model for studying the dynamic mechanical response and damage development of composite laminates under low-velocity impact was established. The model applied the Hashin and Hou failure criteria to predict the initiation of intra-laminar damage (fiber and matrix damage); a linear degradation scheme combined with the equivalent displacement method was adopted to simulate the damage development; a cohesive zone model with the bilinear traction-separation relationship was used to predict delamination. A user material subroutine VUMAT was coded, and the simulation analysis of carbon fiber reinforcement composite laminates subjected to 25 J impact was performed via commercial software ABAQUS. The predicted impact force-time curve, impact force-displacement curve, and damage distribution contours among the layers were in a good agreement with the experimental, which verified the proposed model. According to the simulation results, the fiber damage and matrix damage were analyzed, and the expansion of delamination was discussed.

Experimental and numerical investigations on dynamic mechanical responses and failure process of gas-bearing coal under impact load

With mining depth increasing, the mining structure becomes more and more complex. It is easy to cause dynamic disaster during coal mining. To reveal the failure process of gas-bearing coal at complex mining environment, the dynamics experiments were conducted through Split Hopkinson Pressure Bar of gas-bearing coal (SHPB-GAS) experimental system. The results showed that the filtered stress waveform presented to be sine-like. With the impact load increasing, the amplitude of incident wave, reflected wave and transmission wave also increased. After calculation of stress wave data, the stress-strain curves were obtained, which included linear elastic stage, step stage, yield and rupture stage. The dynamic mechanical strength increased with the increase of impact load, and the specimen developed from stratiform rupture with macro cracks to crush rupture in fragments. To verify the experimental results, COMSOL Multiphysics software was adopted to conduct numerical simulation. The simulation results indicated that the high stress area was formed at the end faces of specimen firstly and expanded to interior of specimen gradually under different impact load. High stress induced the plastic deformation in coal specimen, which also developed from end faces to specimen inside. These results were consistent with the phenomenon of experiments, which explained the causes of failure process of gas-bearing coal. Based on the experimental and simulation achievements, the formed mechanism of dynamic disaster induced by impact load were discussed.

The Out-of-Plane Compression Response of Woven Thermoplastic Composites: Effects of Strain Rates and Temperature.

The dynamic mechanical response of high-performance thermoplastic composites over a wide range of strain rates is a challenging research topic for extreme environmental survivability in the field of aerospace engineering. This paper investigates the evolution of the dynamic properties of woven thermoplastic composites with strain rate and damage process at elevated temperatures. Out-of-plane dynamic-compression tests of glass-fiber (GF)- and carbon-fiber (CF)-reinforced polyphenylene sulfide (PPS) composites were performed using a split Hopkinson pressure bar (SHPB). Results showed that thermoplastic composites possess strain-rate strengthening effects and high-temperature weakening dependence. GF/PPS and CF/PPS composites had the same strain-rate sensitivity (SRS) below the threshold strain rate. The softening of the matrix at elevated temperatures decreased the modulus but had little effect on strength. Some empirical formulations, including strain-rate and temperature effects, are proposed for more accurately predicting the out-of-plane dynamic-compression behavior of thermoplastic composites. Lastly, the final failure of the specimens was examined by scanning electron microscopy (SEM) to explore potential failure mechanisms, such as fiber-bundle shear fracture at high strain rates and stretch break at elevated temperatures.

Dynamic response of sandwich beam with star-shaped reentrant honeycomb core subjected to local impulsive loading

The star-shaped reentrant honeycomb produces lateral shrinkage but also rotation under compression. With the consideration of such interesting deformation characteristics, the dynamic deformation evolution of the sandwich beam with star-shaped reentrant honeycomb core (SSRHC) was carried out for the first time. In this experiment, the aluminum foam projectile was used to produce local impulsive loading on the sandwich beam to research failure/deformation modes and deformation evolution of the SSRHC. The experimental results demonstrated the simultaneous shrinking and rotating deformations in the core. Finite element model (FEM) was employed to capture the dynamic mechanical response of panels and SSRHC on account of experimental results. Numerical results illustrated that the face panel moved toward the loading area in the early stage of impact, and local shrinkage or expansion was found within different regions of the star honeycomb cores during the entire compression process. In addition, it was found that the rotational deformation of the star honeycomb cells mainly occurred in the local indentation stage of the sandwich beam.

Phase Field Study of the Microstructural Dynamic Evolution and Mechanical Response of NiTi Shape Memory Alloy under Mechanical Loading.

For the purpose of investigating the microstructural evolution and the mechanical response under applied loads, a new phase field model based on the Ginzburg-Landau theory is developed by designing a free energy function with six potential wells that represent six martensite variants. Two-dimensional phase field simulations show that, in the process of a shape memory effect induced by temperature-stress, the reduction-disappearance of cubic austenite phase and nucleation-growth of monoclinic martensite multi-variants result in a poly-twined martensitic microstructure. The microstructure of martensitic de-twinning consists of different martensite multi-variants in the tension and compression, which reveals the microstructural asymmetry of nickel-titanium (NiTi) alloy in the tension and compression. Furthermore, in the process of super-elasticity induced by tensile or compressive stress, all martensite variants nucleate and expand as the applied stress gradually increases from zero. Whereas, when the applied stress reaches critical stress, only the martensite variants of applied stress-accommodating continue to expand and others fade gradually. Moreover, the twinned martensite microstructures formed in the tension and compression contain different martensite multi-variants. The study of the microstructural dynamic evolution in the phase transformation can provide a significant reference in improving properties of shape memory alloys that researchers have been exploring in recent years.

Molecular origin of viscoelasticity in mineralized collagen fibrils.

Bone is mineralized tissue constituting the skeletal system, supporting and protecting the body's organs and tissues. In addition to such fundamental mechanical functions, bone also plays a remarkable role in sound conduction. From a mechanical standpoint, bone is a composite material consisting of minerals and collagen arranged in multiple hierarchical structures, with a complex anisotropic viscoelastic response, capable of transmitting and dissipating energy. At the molecular level, mineralized collagen fibrils are the basic building blocks of bone tissue, and hence, understanding bone properties down to fundamental tissue structures enables better identification of the mechanisms of structural failures and damage. While efforts have focused on the study of micro- and macro-scale viscoelasticity related to bone damage and healing based on creep, mineralized collagen has not been explored at the molecular level. We report a study that aims at systematically exploring the viscoelasticity of collagenous fibrils with different mineralization levels. We investigate the dynamic mechanical response upon cyclic and impulsive loads to observe the viscoelastic phenomena from either shear or extensional strains via molecular dynamics. We perform a sensitivity analysis with several key benchmarks: intrafibrillar mineralization percentage, hydration state, and external load amplitude. Our results show an increase of the dynamic moduli with an increase of the mineral percentage, pronounced at low strains. When intrafibrillar water is present, the material softens the elastic component, but considerably increases its viscosity, especially at high frequencies. This behavior is confirmed from the material response upon impulsive loads, in which water drastically reduces the relaxation times throughout the input velocity range by one order of magnitude, with respect to the dehydrated counterparts. We find that, upon transient loads, water has a major impact on the mechanics of mineralized fibrillar collagen, being able to improve the capability of the tissue to passively and effectively dissipate energy, especially after fast and high-amplitude external loads. Our study provides knowledge of bone mechanics in relation to pathologies deriving from dehydration or traumas. Moreover, these findings show the potential for being used in designing new bioinspired materials not limited to tissue engineering applications, in which passive mechanisms for dissipating energy can prevent structural failures.