Dynamic Compressive Mechanical Properties Research Articles

Dynamic Compressive Mechanical Properties of UR50 Ultra-Early-Strength Cement-Based Concrete Material under High Strain Rate on SHPB Test

UR50 ultra-early-strength cement-based self-compacting high-strength material is a special cement-based material. Compared with traditional high-strength concrete, its ultra-high strength, ultra-high toughness, ultra-impact resistance, and ultra-high durability have received great attention in the field of protection engineering, but the dynamic mechanical properties of impact compression at high strain rates are not well known, and the dynamic compressive properties of materials are the basis for related numerical simulation studies. In order to study its dynamic compressive mechanical properties, three sets of specimens with a size of Φ100 × 50 mm were designed and produced, and a large-diameter split Hopkinson pressure bar (SHPB) with a diameter of 100 mm was used to carry out impact tests at different speeds. The specimens were mainly brittle failures. With the increase in impact speed, the failure mode of the specimens gradually transits from larger fragments to small fragments and a large amount of powder. The experimental results show that the ultra-early-strength cement-based material has a greater impact compression brittleness, and overall rupture occurs at low strain rates. Its dynamic compressive strength increases with the increase of strain rates and has an obvious strain rate strengthening effect. According to the test results, the relationship curve between the dynamic enhancement factor and the strain rate is fitted. As the impact speed increases, the peak stress rises, the energy absorption density increases, and its growth rate accelerates. Afterward, based on the stress–strain curve, the damage variables under different strain rates were fitted, and the results show that the increase of strain rate has a hindering effect on the increase of damage variables and the increase rate.

Experimental Study of the Dynamic and Static Compression Mechanical Properties of Closed-Cell PVC Foams.

Closed-cell polyvinyl chloride foam (PVC) possesses many advantages, including its light weight, moisture protection, high specific strength, high specific stiffness, and low thermal conductivity, and is widely used as the core material in composite sandwich structures. It is increasingly used in fields with light weight requirements, such as shipbuilding and aerospace. Some of these structures can be affected by the action of dynamic loads during their lifespan, such as accidental or hostile blast loads as well as wind-loaded debris shocks. Examining the material properties of PVC foams under dynamic load is essential to predict the performance of foam sandwich designs. In this study, the compressive responses of a group of PVC foams with different densities were investigated under a broad range of quasi-static conditions and high strain rates using a universal testing machine and a lengthened Split Hopkinson press bar (SHPB) fabricated from titanium alloy. The results show that the mechanical properties of foam materials are related to their density and are strain rate-sensitive. The compressive strength and plateau stress of the foams were augmented with increased foam density. In the quasi-static strain rate range, the compressive strength of PVC foams at 10−1 s−1 was 27% higher than that at 10−4 s−1. With a strain rate of 1700 s−1, the strength was 107% higher than the quasi-static value at 10−4 s−1.

Experimental study on compression mechanical characteristics of filled rock joints after multiple pre-impacts

The prefabricated artificial filled jointed rock specimens are impacted by a self-made drop hammer impact device for many times, and the specimens with different degrees of cumulative damage characteristics are obtained. Then, the static and dynamic compression mechanical properties are studied by using universal testing machine and SHPB device. Through the static compression test, the strength and deformation characteristics of jointed rock specimens after multiple impacts are obtained, and the influence of the damage degree of jointed rock specimens characterized by wave velocity on the compressive strength of filled joints is analysed. Based on the results of SHPB impact test, the dynamic strength and deformation evolution, wave propagation law and energy dissipation law of filled joints after multiple impacts are analysed. During the SHPB test, the impact failure process of rock specimens is recorded by a high-speed camera. The experimental results show that the damage degree of jointed rock samples increases nonlinearly after multiple impacts. The attenuation laws of static strength and dynamic strength of rock samples under the same damage evolution conditions are different. With the increase of impact times, the failure mode of jointed rock samples after damage is simpler and tends to compression failure.

Investigating the Dynamic Compressive and Tensile Properties of Polymer Binder Explosive Based on the Split-Hopkinson Bar Technique

Split Hopkinson bar technique was often used to measure the dynamic mechanical properties of engineering materials. In this paper, the dynamic tensile and compression mechanical properties of polymer explosive bonded (PBX) under different strain rates were obtained by using split Hopkinson pressure/tension bar. The thickness of the specimen and the shape of the incident wave are designed to ensure the rationality of the experimental results. By comparing the experimental results, it was found that the PBX had different dynamic tensile and compression properties. The PBXs have been tested and shown tensile and compressive strengths ratios that range between 5 and 7. A constitutive relation is developed for modeling the dynamic mechanical response of PBX-I by using the Boltzmann superposition principle with a Prony series representation. The parameters of the PBX-I were fitted by using least square method. A finite element model was used to simulate the dynamic compressive and tensile behavior of PBX-I, and the numerical simulation results were in good agreement with the experimental results, which proved that the linear viscoelastic constitutive relation can be applied to the PBX-I.

Experimental Study on Dynamic Mechanical Properties of Sandstone Corroded by Strong Alkali

In order to analyze the effect of different corrosion times on the dynamic compression mechanical properties of sandstone, the coal mine sandstone specimens are subjected to corrosion in NaOH solution with pH 11 for 0 d, 1 d, 3 d, 7 d, 14 d, and 28 d, and then, the impact compression tests and Brazilian splitting test are conducted using a split Hopkinson pressure bar apparatus. The study results show that sandstone specimen mass and the average density growth rate increases, with the corrosion time first rapidly increasing and then tending to level off the trend. The impact of the compression specimens on the dynamic stress–strain curve change law is basically the same, but the time gradient curve shape is different, and the line elastic deformation stage and plastic deformation stage curve difference gradually decreases. The specimen dynamic compressive strength and the dynamic elastic modulus with corrosion time are quadratic, and the exponential function declines the relationship. After corrosion of 28 d sandstone specimens, the dynamic compressive strength and dynamic elastic modulus are much lower than the uncorroded specimens. The average strain rate and the dynamic peak strain with the corrosion time extension are a quadratic function of the increasing relationship after the corrosion effect of the sandstone dynamic peak strain, and the average strain rate is significantly greater than the uncorroded specimens. With the corrosion time extension of sandstone specimens by the impact of damage degree being increased, the 14 d and 28 d specimen ruptures’ degree is much greater than other time gradients. The dynamic tensile strength of the split specimens decreases with increasing corrosion time; the dynamic peak strain increases quadratically; and the transmitted energy also decreases with increasing corrosion time.

Mechanical Properties and Constitutive Model of Selective Laser Melting 316L Stainless Steel at Different Scanning Speeds

To investigate the effects of different scanning speeds on the mechanical properties of selective laser melting 316L stainless steel (SLM 316L SS), process specimens with scanning speeds at 350 mm/s, 650 mm/s, 950 mm/s, and 1250 mm/s were prepared using the SLM technique in this paper. The quasistatic and dynamic compressive mechanical properties of the four specimens were tested by electrohydraulic servo experimental machine and Hopkinson compression bar experimental device, and the mechanical differences of the specimens were analyzed by microscopic observation. Finally, the modified Johnson-Cook (J-C) model was adopted to describe the dynamic mechanical properties of SLM 316L SS. Results showed that the four process steel specimens exhibited typical viscoplastic characteristics and significant strain rate strengthening effects in the mechanical property tests. Moreover, the scanning speed significantly affects the internal defects and melt pool characteristics of the SLM 316L specimens, and the yield strength decreases significantly with the disappearance of the melt pool characteristics. Finally, the modified J-C model can better describe the mechanical behavior of SLM 316L SS material more accurately. This study can provide theoretical references for improving the fabrication process of SLM 316L SS to broaden the practical application of this material.

Dynamic compression mechanical properties of eco-friendly ultra-high performance concrete produced with aeolian sand: Experimental and three-dimensional mesoscopic investigation

The dynamic mechanical properties of ultra-high performance concrete (UHPC) containing aeolian sand was studied via the split Hopkinson pressure bar technique and three-dimensional mesoscopic numerical simulation. A novel method for three-dimensional modeling of end-hook steel fibers was proposed. Employing the 3D mesoscale model, the dynamic compressive responses of aeolian sand-based UHPC were simulated and analyzed. Simulation results exhibited constitutive relationships and failure patterns that agree well with the impact test results, which verified that the established three-dimensional mesoscopic model enables effective analysis of the dynamic mechanical properties of aeolian sand-based UHPC. Then the effects of strain rate, fiber content and matrix strength on the stress-strain relation and energy evolution process were quantitatively discussed, which provide a basis for the application of aeolian sand-based UHPC.

Study on dynamic compressive mechanical properties of freeze-thaw concrete

In this paper, the split Hopkinson pressure bar (SHPB) equipment was adopted to investigate the dynamic compressive mechanical properties of C40 concrete under various loading speeds after freeze–thaw cycles. The range of freeze–thaw times was 0 to 125 times. The range of loading speed was 4 to 10 m/s, and the tested peak strain rate ranged from 39.87 to 163.35 s−1. During the experiment, pulse shaper and lubricating oil were applied to make the test results more accurate. Based on the obtained results, this paper discussed two fundamental assumptions of one-dimensional wave propagation and dynamic stress equilibrium. A general equation was developed to express the dynamic compressive strength in dependency of the freeze–thaw times. The test results showed that the dynamic compressive strength of concrete increased first and then decreased with the increase of freeze–thaw times. The dynamic compressive strength also increased gradually with the increase of loading velocity. In addition, this paper discussed the difference and relationship between failure patterns of specimens and revealed the changing rules of stress versus strain curve, dynamic compressive strength, and dynamic impact factor (DIF). Two influence coefficients were introduced to quantify the effects of freeze–thaw damage and hydration on the dynamic compressive strength. Theory of statistical damage and Weibull distribution were employed to establish a constitutive model of freeze–thaw concrete. The results showed that the model can effectively describe the dynamic compressive mechanical responses of freeze–thaw concrete under impact loading, and gave some suggestions to concrete structural design, structural health detection, structural performance evaluation and so on in cold areas.

Effects of Heat Treatment on the Microstructure and Mechanical Properties of Selective Laser Melting 316L Stainless Steel

316L stainless steel materials are widely used in impact-resistant structures. Heat treatments could affect the mechanical properties of 316L stainless steel parts formed by selective laser melting (SLM), which is vital for ensuring service safety. This study aimed to analyze the mechanical behavior of SLM 316L stainless steel under different heat treatment methods. Therefore, test specimens were prepared using the SLM technique and then annealed at 400°C for 1 h. The solution was treated at 1050°C for 20 min. The dynamic compressive mechanical properties of the deposited, annealed, and solution-treated specimens were tested at high strain rates by using a split Hopkinson pressure bar (SHPB) experimental apparatus. Moreover, the microstructures of the previously mentioned samples were analyzed by optical microscopy and scanning electron microscopy. The experimental results showed that the three-state samples exhibited strain rate sensitivity in the dynamic mechanical tests and that solution treatment could alter their mechanical properties significantly. In addition, the microstructure of the deposited specimens presented cylindrical cellular crystal features, which have a higher dislocation density. Hence, the yield strength of deposited specimens is higher than that of the solution-treated ones. After annealing, the microstructures of the samples did not change obviously, and their dynamic yield strength remained almost unchanged. After solution treatment, its cellular crystal disappeared and dislocation density dropped dramatically, resulting in a sharp decrease in yield strength. Finally, this research can provide a theoretical reference for broadening the practical application of SLM 316L material parts.

Coupling Effect of Strain Rate and Freeze-Thaw Temperature on Dynamic Mechanical Properties and Fractal Characteristic of Saturated Yellow Sandstone

Strain rate is not only an important influence factor for deformation property but also an important parameter for analyzing the dynamic mechanical behavior of rock material. In this study, the dynamic compressive mechanical properties of saturated yellow sandstone at four strain rates and six freeze-thaw temperatures are investigated by using the SHPB test system. The coupling effect of strain rate and freeze-thaw temperatures on the mechanical parameters of rock material are discussed in detail, and the relationship formula of peak strain and dissipated energy with strain rate and freeze-thaw temperature are also established. Finally, the fractal dimension characteristic of fracture specimens with the strain rate and temperature are analyzed by using the fractal dimension method. The research results indicate that (1) with the increase of strain rate, the increase speed of peak strain, peak strength, and dissipated energy at medium strain rate level was obviously higher than that at high strain rate level, indicating that the strain rate effect weakened at high strain rate. (2) Freeze-thaw temperature can improve the brittleness-ductile transformation rate of saturated specimens. (3) According to the strain rate sensitivity coefficient, at room temperature, the strain rate effects on peak strain and peak strength are weakest, while at -20°C ~ -30°C, they are most significant. In addition, the strain rate effect on dissipated energy is significant at room temperature, while weakest at -30°C. (4) The fractal dimension gradually increases with strain rate increasing or freeze-thaw temperature decreasing, indicating that the freeze-thaw environment has a positive function for increasing the damage and fracture degree of specimens for saturated specimen. Our research results can provide an extremely important theoretical basis for the dynamic disaster prevention and structural design of rock engineering in cold regions.

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.

Dynamic compressive behavior of concrete confined with unidirectional natural flax FRP based on SHPB tests

This paper presents an experimental study on the dynamic compressive behaviors of concrete confined with unidirectional natural flax fiber reinforced polymers (FFRPs) under an axial impact load. A total of 80 specimens were prepared and tested using a 75 mm diameter split Hopkinson pressure bar (SHPB) at different strain rates varying from 50 to 200 s−1. The experimental results showed that the failure modes and dynamic compressive mechanical properties (i.e., dynamic compressive strength, critical compressive strain, and energy absorption capacity) of FFRP-confined concrete were sensitive to the strain rate. The unconfined concrete specimens were crushed into small pieces at relatively low strain rates, whereas the FFRP-confined concrete specimens failed with FRP rupture and partial damage to the core concrete at relatively high strain rates. This indicates that the confinement of FFRP jackets can alleviate concrete damage and improve impact resistance. Compared with unconfined concrete, the application of the FFRP jacket remarkably improves the compressive strength, critical strain, and toughness, which indicates outstanding impact resistance. Increasing the confinement stiffness of the FFRP contributed to increasing the compressive strength, critical strain, and toughness. Based on the experimental results, the confinement mechanism of external flax FRP jackets on concrete was discussed, and a new dynamic strength model was proposed to predict the dynamic compressive strength of FFRP-confined concrete within the investigated strain rate range.

Microstructure, mechanical properties, and corrosion resistance of friction stir welded Mg-Al-Zn alloy thick plate joints

Mg-Al-Zn (AZ31) of 10-mm thick plates were subjected to friction stir welding (FSW) using a conventional tool (CT) and bobbin tool (BT), respectively. The microstructure, room temperature tensile properties, dynamic compressive mechanical properties, and corrosion resistance of the base metal (BM) and various regions of the friction stir welded joints were investigated systematically. The mean grain size, dislocation density, and precipitate distribution in the various regions of the friction stir welded joints were various due to different thermal cycle and plastic deformation. Compared with the CT, a relatively more homogeneous microstructure, a larger number of high-density dislocations and precipitates were produced in the various regions of the joint prepared by the BT due to higher thermal cycle and strain rate. As a result, the friction stir welded joint prepared by the BT exhibits excellent tensile properties and dynamic compressive mechanical properties, and outstanding corrosion resistances compared to those of the CT. In addition to slight changes in tensile properties and dynamic compressive mechanical properties, the corrosion resistance of the joint prepared by the BT was significantly improved compared to the BM. FSW with BT was suggested to be the optimal method to weld AZ31 alloy thick plate.

Experimental Investigation of Dynamic Compression Mechanical Properties of Frozen Fine Sandstone

Aiming at the dynamic mechanical properties of weakly cemented fine sandstone in the rich water-bearing strata in western China under dynamic loading, a 50 mm rod diameter separation Hopkinson pressure bar (SHPB) test was used to study the Paleogene fine sandstone in a coal mine in Ningxia. The system carried out the impact compression tests of −15°C, −20°C, and −30°C and the average strain rate of 28 s−1–83 s−1 and obtained the dynamic compressive strength of the frozen fine sandstone specimens under different test conditions. The strain curve and the fracture morphology were analyzed for the relationship between dynamic peak stress, peak strain, dynamic strength growth coefficient (DIF), and fracture morphology and strain rate. The results show that the peak stress of frozen fine sandstone increases from the decrease of freezing temperature under the same average strain rate. The peak stress of the specimen increases from the increase in the average strain rate of the same freezing temperature. The failure modes of specimen are mainly divided into axial splitting tensile failure and compression crushing failure. To the splitting tensile failure and the compression crushing failure, the main factors determining the two failure modes are the strain rate, while the temperature affects the severity of the impact damage. In the load strain rate and temperature range, the DIF of the frozen fine sandstone is linearly correlated with the strain rate, and the lower the temperature, the slower the growth rate of the DIF.

Dynamic compressive mechanical properties of carbon fiber-reinforced polymer concrete with different polymer-cement ratios at high strain rates

This study experimentally examined the effect of redispersible polymer emulsion powder on dynamic compressive properties of carbon fiber-reinforced polymer concrete (CFRPC). Impact experiments of CFRPC cylindrical specimens (100 mm diameter, 50 mm height) with 0.2% carbon fiber (volume ratio of carbon fiber to concrete) to 0%, 4%, 8% and 12% polymer-cement ratios (mass ratios) were done using a Φ100 mm Split Hopkinson pressure bar. The effects of emulsion powder on CFRPC were analyzed in terms of the dynamic compressive strength, deformation and toughness of the specimens. We find that at the same strain rate, the dynamic compressive strength of CFRPC initially increases and then falls with increasing polymer content. The dynamic compressive strength of the sample is highest when the polymer-cement ratio is 4%, and reaches up to 21.47–26.58%. The compressive strength and peak strain of CFRPC have obvious strain rate sensitivity. An appropriate amount of polymer can effectively improve the dynamic compression performance of CFRPC. Sample fragmentation and porosity analyses show that increasing the polymer-cement ratio reduces the number of pores in the concrete matrix, attaining a more optimal pore distribution and improved compactness.

Dynamic compressive mechanical properties of the spiral tungsten wire reinforced Zr-based bulk metallic glass composites

In this study, bulk metallic glass composite (BMGC) reinforced with a novel spiral structure of tungsten wires was prepared. The composite exhibits a high ultimate strength of 2830 MPa and a large plasticity of 26% under quasi-static compression. The dynamic compressive mechanical properties of this BMGC were also systematically investigated by split Hopkinson pressure bar technique. It is found that the yield stress of the composite under uniaxial compression increases firstly and then decreases with increasing the strain rate. To describe the strain-rate dependence of the yielding behavior of the composite, a constitutive model considering adiabatic shear localization was established. Furthermore, the deformation and fracture behaviors of the composite under quasi-static and dynamic compression were discussed in detail. Different from the tungsten fiber reinforced bulk metallic glass composites (BMGCs), the spiral tungsten wire reinforced BMGC fractured in a shear mode, which is distinctly favorable to the self-sharpening capability. These findings could deepen the understanding of deformation behaviors and failure modes of BMGCs and promote their applications.

Experimental and Constitutive Model on Dynamic Compressive Mechanical Properties of Entangled Metallic Wire Material under Low-Velocity Impact.

In this paper, the dynamic compressive mechanical properties of entangled metallic wire material (EMWM) under low-velocity impact were investigated and the constitutive model for EMWM under low-velocity impact was established. The research in this paper is based on a series of drop-hammer tests. The results show that the energy absorption rate of EMWM is in the range from 50% to 85%. Moreover, the EMWM with a higher relative density would not plastically deform macroscopically and has excellent characteristics of repetitive energy absorption. With the increase in relative density, the maximum deformation of EMWM decreases gradually, and the impact force of EMWM increases gradually. With the increase in impact-velocity, the phenomenon of stiffness softening before reaching the maximum deformation of EMWM becomes more significant. A constitutive model for EMWM based on the Sherwood–Frost model was established to predict the dynamic compressive mechanical properties of EMWM. The accuracy of the model was verified by comparing the calculated results with the experimental data of the EMWM with different relative densities under different impact-velocities. The comparison results show that the established model can properly predict the dynamic compressive mechanical characteristics of EMWM under low-velocity impact loading.

Experimental Study on Dynamic Compression Mechanical Properties of Aluminum Honeycomb Structures

In this paper, dynamic compression tests are developed to investigate the dynamic compression mechanical properties of the aluminum honeycomb structures at different strain rates, especially at the high strain rates. The difficulties at the high strain rates exist due to the large deformation, the low wave resistance and the size effect of the honeycomb structures. The Split Hopkinson Pressure Bar (SPHB) test method is carried out and special measures such as the adoption of waveform shaper, the size optimization of the impact bar and the specimen, and employment of the semiconductor strain gauge, etc. are taken to overcome the difficulties. It is discovered that the dynamic compression mechanical properties possess a stress hardening effect at a high strain rate from 1.3 × 103 s−1 to 2.0 × 103 s−1, but then a stress softening effect at a high strain rate of 4.6 × 103 s−1. It is also discovered that the yield strength and the average plateau stress at the strain rate of 2.0 × 103 s−1 is higher than that at the strain rate of 1.3 × 103 s−1. However, the yield strength and the average plateau stress at the strain rate of 4.6 × 103 s−1 is lower than that at the strain rate of 2.0 × 103 s−1 and 1.3 × 103 s−1, but higher than that at a quasi-static state. This indicates that the aluminum honeycomb structure is sensitive to the strain rate. Additionally, the damage mode of the aluminum honeycomb structure is plastic buckling, collapse and folding of the cell wall, which is carried out using dynamic compression tests. The folding length of the cell wall at a higher strain rate is found to be longer than that at a lower strain rate. The test results can also be used as the stress–strain curves of the honeycomb constitutive model at the high strain rates to carry out the numerical simulation of high-speed impact.

Experimental Study on Static and Dynamic Compression Mechanical Properties of Filled Rock Joints

The static and dynamic compression mechanical properties of the prefabricated artificial filled rock joints specimens with different fillings and different joint thicknesses are tested, respectively. Then, the strength, deformation, wave propagation and energy dissipation laws of the filled joints are analyzed. The experimental results show that the static and dynamic compression strength of filled joints increases with the strength of filling materials while decreases with the filling thickness. The deformation characteristics of filled joints under static and dynamic compression are positively correlated with the properties of filling materials and the thickness of filled joints. With the increasing of the filling thickness, the reflection coefficient increases while the transmission coefficient decreases. With the increase of the strength of the fillings, the reflection coefficient decreases while the transmission coefficient increases. The energy dissipation ratio decreases with the increase of the filliing thickness and increases with the increase of the strength of the filling material.

Compressive behavior and constitutive model of polyurea at high strain rates and high temperatures

To study the dynamic compressive mechanical properties of polyurea at strain rate range of 1400 s−1–5700 s−1 and high temperature range of 20 ℃–80 ℃, we conducted a dynamical mechanical experiment utilizing a split Hopkinson pressure bar (SHPB) system. The compressive stress-strain curves of polyurea under various strain rates and temperatures are analyzed and discussed. The experimental results indicated that the strain rate and high temperature can remarkably influence the mechanical behaviors of polyurea, compression behaviors increased with the increasing of strain rate and compression behaviors decreased with the increasing of temperature. In addition, a thermal-visco-hyperelastic constitutive model based on five-parameter Mooney-Rivlin model was proposed to describe the compression stress-strain behavior of polyurea over a wide range of strain rates and temperatures. The model parameters were obtained by fitting the experimental stress-strain curves. The model prediction results show good agreement with the experimental results.