Dynamic Peak Strain Research Articles

The 2022–2023 seismic sequence onshore South Evia, central Greece: evidence for activation of a left-lateral strike-slip fault and regional triggering of seismicity

On 29 November 2022, an earthquake of ML 5.0 (Mw 4.8) occurred onshore South Evia Island (central Greece) preceded by a ML 4.7 (Mw 4.6) event. The pattern of relocated aftershocks indicates the activation of a single, near-vertical fault segment, oriented NW-SE at shallow crustal depths (6–11 km). We suggest that both events ruptured a blind, left-lateral strike-slip fault, about 5 km southeast of village Almyropotamos. We observed that a clear foreshock activity (N=55 events) existed before the two moderate events. The impact of the static stress loading on neighboring fault planes diminishes after a distance of 7 km from the November 2022 epicenters, where the static stress falls below +0.1 bar. We further explore triggering relationships between the 29 November events and the late December 2022 moderate events (ML 4.9) that occurred about 60 km toward NW in the Psachna and Vlahia regions of central Evia. We present evidence of possible delayed dynamic triggering of the late December 2022 central Evia sequence, based on marked changes in seismicity rates and on measured peak ground velocities (PGVs) and peak dynamic strains, both exhibiting local maxima in their map distributions. The causes of the delayed triggering may be related to the well-known geothermal field in central/north Evia and the NW-SE strike of the seismic fault.

Investigation of dynamic compression properties of lightweight engineered geopolymer composites containing different ceramsites (LW-EGC)

Lightweight engineering geopolymer composites (LW-EGC) can contribute to green building materials products by taking advantage of the advantages of man-made ceramsite and geopolymers. In this paper, an active "sacrifice" method was proposed, which is based on the idea that low elastic modulus ceramsites are preferentially damaged or ruptured during the impact loading process, thus absorbing and dissipating the impact energy. LW-EGC was enhanced by PVA fiber with volume fraction of 2% and multi-walled carbon nanotubes with mass fraction of 0.15%. The dynamic compression properties of LW-EGC containing different ceramsites were studied by using Φ100 mm split Hopkinson pressure bar (SHPB) test device. The compression characteristics of the LW-EGC under an impact load were evaluated, including the strain rate, dynamic stress–strain relationship, elastic modulus, dynamic increase factor (DIF), energy absorption, and failure patterns. The results showed that the dynamic peak stress, dynamic peak strain, DIF, energy absorption and damage degree of LW-EGC all increased with the increase of strain rate, showing obvious strain-rate sensitivity. At high strain rate, the dynamic elastic modulus mainly showed softening effect. At the same strain rate, the impact resistance of LW-EGC-1 containing fly ash ceramsite was the best, and the damage degree of LW-EGC-3 containing shale ceramsite was the lowest. Empirical DIF formulas of the LW-EGC was proposed; the DIF increased approximately linearly with the strain rate in a logarithmic manner.

Ross Ice Shelf Displacement and Elastic Plate Waves Induced by Whillans Ice Stream Slip Events

AbstractIce shelves are assumed to flow steadily from their grounding lines to the ice front. We report the detection of ice‐propagating extensional Lamb (plate) waves accompanied by pulses of permanent ice shelf displacement observed by co‐located Global Navigation Satellite System receivers and seismographs on the Ross Ice Shelf. The extensional waves and associated ice shelf displacement are produced by tidally triggered basal slip events of the Whillans Ice Stream, which flows into the ice shelf. The propagation velocity of 2,800 m/s is intermediate between shear and compressional ice velocities, with velocity and particle motions consistent with predictions for extensional Lamb waves. During the passage of the Lamb waves the entire ice shelf is displaced about 60 mm with a velocity more than an order of magnitude above its long‐term flow rate. Observed displacements indicate a peak dynamic strain of 10−7, comparable to that of earthquake surface waves that trigger ice quakes.

Impact toughness and dynamic constitutive model of geopolymer concrete after water saturation

The dynamic compression test of geopolymer concrete (GC) before and after water saturation was carried out by the split Hopkinson pressure bar (SHPB). And the effects of water saturation and strain rate on impact toughness of GC were studied. Based on Weibull statistical damage distribution theory, the dynamic constitutive model of GC after water saturation was constructed. The results show that the dynamic peak strain and specific energy absorption of GC have strain rate strengthening effect before or after water saturation. The impact toughness of GC decreases after water saturation. The size distribution of GC fragments has fractal characteristics, and the fractal dimension of GC fragments after water saturation is smaller than that before water saturation. The dynamic constitutive model based on Weibull statistical damage distribution theory can accurately describe the impact mechanical behavior of GC after water saturation, and the model fitting curves are in good agreement with the experimental stress–strain curves.

Dynamic and Energy Consumption Characteristics of Sandstone Ring Specimens under Dry and Wet Cycling

The aim of this study was to examine the effects of sandstone ring specimens with different inner diameters on dynamic compression mechanical characteristics after dry and wet circulation. To carry out our study, we subjected a sandstone ring specimen with a 50 mm outer diameter and a 0~25 mm inner diameter to 10 cycles of dry and wet circulation. Afterward, we recorded the specimen’s basic physical parameters and used a split-Hopkinson pressure bar (SHPB) test device to perform an impact compression test. Following dry and wet circulation, our results showed that the mass loss rate increased and the volume expansion rates and density decreased with the increase in the inner diameter of the sandstone ring sample. Simultaneously, with the increase in the inner diameter of the specimen ring, the dynamic compressive strength of the specimen presented an exponential negative correlation, the dynamic elastic modulus presented a quadratic negative correlation, and the dynamic peak strain presented a quadratic positive correlation. Concurrently, the average particle size of the specimen decreased, and the degree of breakage increased with the increase in the sandstone sample’s inner diameter. Regarding the energy analysis performed in this study, the sandstone ring sample’s energy dissipation increased, and its kinetic performance evidently weakened with the increase in the ring sample’s inner diameter. The results of this study have certain reference values for the construction and maintenance of natural cavity rock and underground hard rock roadways.

Dynamic mechanical behavior of sandstone with filled joints at varying angles under coupled triaxial static and dynamic loading

Natural or artificially formed rock composite structures with consecutively filled joints at varying angles are frequently disturbed by coupled static and dynamic loads. Understanding the impacts of the confining pressure and joint angle on the dynamic mechanical behavior of rocks is important for the stability of rock mass engineering structures. In this study, seven joint angles and four confining pressures were considered. Dynamic triaxial compressive tests of sandstone with consecutively filled joints were conducted using a split Hopkinson bar (SHPB) apparatus. The test results showed that varying degrees of “strain rebound” phenomena were observed in the stress–strain curves, implying that the jointed samples in the failure stage could still store more elastic energy, which may trigger rock burst accidents in practical engineering. Moreover, the dynamic compressive strength and elastic deformation modulus were proportional to the confining pressure, but showed a trend of slight decrease followed by a noticeable increase with an increase in the joint angle from 0° to 90°. The combined effects of axial pre-stress and confining pressure resulted in different trends in the dynamic peak strain. The plastic deformation moduli of samples with smaller joint angles were insensitive to changes in the confining pressure and smaller joint angles, whereas those of samples with larger joint angles were sensitive to changes in the confining pressure and larger joint angles. In addition, the experimental tendency of the dynamic compressive strength under coupled triaxial static and dynamic loading was in good agreement with the theoretical derivation.

Study on high temperature dynamic characteristics and mesoscopic simulation of HFRC under dynamic and static combined loading

The Φ50mm SHPB system was used to carry out three-dimensional dynamic and static combined loading tests on hybrid fiber reinforced concrete (HFRC) treated at different temperatures (25 °C, 200 °C, 400 °C) under different confining pressure ratios (0, 0.1, 0.2, 0.3). The temperature effect, confining pressure effect and failure characteristics of HFRC under impact load were studied. The effect of fiber was equivalently treated in mortar, and the meso-aggregate model of HFRC considering aggregate, mortar and interfacial transition zone (ITZ) was established. The simulation results were compared with the experimental results. The results showed that the higher the confining pressure ratio, the more significant the temperature effect of peak stress is. The higher the temperature is, the less obvious the enhancement effect of confining pressure on peak stress is. Compared with the influence of confining pressure on dynamic peak strain, the influence of temperature effect on dynamic peak strain is higher. The established three-dimensional meso-aggregate model and calculation method can accurately reflect the dynamic response characteristics of HFRC at different temperatures and confining pressure ratios. Prestress will affect the internal stress distribution of the specimen, thus affecting the compression failure characteristics of the specimen. The confining pressure can constrain the damage course of the specimen and has a good protective effect on the specimen.

Study on the Influence of Sample Size on the Mechanical and Integrity Characteristics of Coal Measure Sandstone under High Strain Rate

In order to explore the size effect of the mechanical and damage characteristics of coal measure sand stones under dynamic load, uniaxial impact compression tests were carried out on coal-bearing sand stones with a diameter of 50 mm and a length–diameter ratio of L/R = 0.5, 0.8, 1, 1.2, 1.5, 1.8, and 2 by using the Hopkinson pressure bar test system. The size effect law of the mechanical properties and energy dissipation of coal-bearing sandstone under a high strain rate were investigated. Then, the mercury injection test was carried out on the fragments at different positions, and the electron microscope scanning test was carried out on the fragments near the end of the transmission rod. Based on the area damage definition method and normalization treatment, the integrity model of coal measure sandstone, considering the influence of the length–diameter ratio, was established. The results showed that the peak strength and dynamic elastic modulus of coal measure sandstone increased first and then decreased with the increase in length–diameter ratio under impact compression load, and they reached the maximum when the length–diameter ratio was 1.2. The dynamic peak strain increased gradually with the increase in length–diameter ratio. The energy of coal-bearing sandstone showed strong size effect, that is, the total absorbed energy, elastic energy, and dissipated energy increased with the increase in length–diameter ratio, and the size effect of total absorbed energy was the most obvious. Under the same impact pressure, the porosity of coal-bearing sand stones with seven kinds of length–diameter ratios near the incident end was roughly the same. But when the length–diameter ratio was greater than 0.5, the porosity decreased gradually with the increase in the distance from the incident end. And the larger the length–diameter ratio, the more obvious the decreasing trend. When the length–diameter ratio was smaller, the size of the holes and cracks and the cluster density were larger. The integrity model of coal measure sandstone, considering the influence of the length–diameter ratio, showed that the larger the length–diameter ratio, the better the relative integrity of coal-bearing sandstone.

The chemical damage of sandstone after sulfuric acid-rock reactions with different duration times and its influence on the impact mechanical behaviour

The low-permeability characteristic of sandstone-type uranium deposits has become the key geological bottleneck during the in-situ leaching mining, seriously restricting the development and utilization of uranium resources in China. At present, the blasting-enhanced permeability (BEP) and acidizing-enhanced permeability (AEP) are confirmed to be mainstream approaches to enhance the reservoir permeability of low-permeability sandstone-type uranium deposit (LPSUD). To clarify the synergistic effect of BEP and AEP, the acid-rock reaction and dynamic impact experiments were conducted, aiming to study the effect of chemical reactions on pore structure, dynamic mechanical properties and failure pattern of sandstone. Results show that with the increasing acid-rock reaction time, the total pore volume of samples is promoted largely and exhibits obvious chemical damage. The change of pore volume depends on the pore size, the 100–1000 nm and 1000–10000 nm pores are more susceptible to acid-rock reactions. The dynamic peak strength and the dynamic elastic modulus are decreased and the dynamic peak strain and strain rate are increased when lengthening the acid-rock reaction time, whose evolution laws can be fitted by the logistic expression, the linear expression and the exponential expression, respectively. The acid-rock reactions also have an influence on the fracture development of samples after the dynamic impact. The damaged fractures on the end faces of samples grow from the isolated short fracture, the isolated long fracture to the fracture network, and the damaged fractures on the sides of samples develop from the non-penetration fractures, penetration fractures to the multi-branch fractures. This study clarifies the physical and chemical combined damage mechanism, demonstrates the potential of reservoir stimulation by uniting the BEP and the AEP, and provides a theoretical reference for the reservoir stimulation of LPSUD.

Static pressure and dynamic impact characteristics of filled jointed rock after frozen-thaw cycle damage

In the construction project, rock mass is often destroyed from the joint plane, and the jointed rock mass is easy to be eroded by freeze-thaw environment. Therefore, the damage mechanical properties of filled jointed rock mass under freeze-thaw action are very important for construction disaster prevention, engineering safety evaluation and reinforcement. In order to research the effect of the freeze-thaw cycle on the mechanical deterioration properties and damage characteristics of filled jointed rocks, prefabricated filled jointed rock samples are tested with different numbers of freeze-thaw cycles under the temperature range of -20°C~20°C. Then the wave velocity test, static compression test and SHPB impact test are conducted on the rock samples after freeze-thaw. Based on the test results, the change regularity of wave velocity degradation, static compression mechanical properties and dynamic compression mechanical properties of filled jointed rocks under the effect of freeze-thaw cycles were analyzed. The results show that the wave velocity, static compressive strength and dynamic compressive strength of the filled jointed rocks all show a downtrend with the increase of the number of freeze-thaw cycles, and each parameter is positively correlated with the strength of the filling materials. Among them, the decrease in the wave velocity of the rock sample after 30 freeze-thaw cycles is greater than 30%, and the strength loss of the static peak compressive strength exceeds half of its initial strength. The static peak strain rises exponentially with the increase of the number of freeze-thaw cycles while the dynamic peak strain does not show a clear trend. The dynamic peak strain is about 1/10 to 1/5 of the static peak strain. Under the same freeze-thaw action, the lower the strength of filling material, the more serious the damage.

Determination of Blast Vibration Safety Criteria for Buried Polyethylene Pipelines Adjacent to Blast Areas, Using Vibration Velocity and Strain Data.

In order to ensure the safe operation of buried polyethylene pipelines adjacent to blasting excavations, controlling the effects of blasting vibration loads on the pipelines is a key concern. Model tests on buried polyethylene pipelines under blasting loads were designed and implemented, the vibration velocity and dynamic strain response of the pipelines were obtained using a TC-4850 blast vibrometer and a UT-3408 dynamic strain tester, and the distribution characteristics of blast vibration velocity and dynamic strain were analyzed based on the experimental data. The results show that the blast load has the greatest effect on the circumferential strain of the polyethylene pipe, and the dynamic strain response is greatest at the section of the pipe nearest to the blast source. Pipe peak vibration velocity (PPVV), ground peak particle velocity (GPPV), and the peak dynamic strain of the pipe were highly positively correlated, which verifies the feasibility of using GPPV to characterize pipeline vibration and strain level. According to the failure criteria and relevant codes, combined with the analysis of experimental results, the safety threshold of additional circumferential stress on the pipeline is 1.52 MPa, and the safety control vibration speed of the ground surface is 21.6 cm/s.

Shaking table test of the dynamic response of a tunnel across a main sliding surface

A shaking table test was conducted to study the dynamic response of a tunnel across a main-sliding surface under seismic action for the first time, and acceleration and dynamic strain data were obtained. A strain-time domain analysis method was implemented to reveal the distribution of the strain field strength factors in the tunnel lining. The plastic effect coefficient (PEC) was proposed to describe the extent of plastic deformation of the tunnel lining, and the applicability of the seismic cumulative failure effect (SCFE) in the stress strength analysis was assessed. The acceleration field of the tunnel lining was also analyzed in the time–frequency domain. The magnification of the Arias intensity (MIa) was applied to characterize the whole-local deformation damage of the tunnel lining, which was considered from the aspects of deformation characteristics, frequency domain, and energy. The results suggest that the residual strain (RS) and PEC are more sufficient to describe the plastic deformation characteristics of the tunnel lining than the increment of the peak dynamic strain (ΔPDS). In addition, PEC has a more definite physical meaning than RS; thus, it is capable of defining the SCFE of the tunnel lining, which describes the stages of deformation effects, including the elastic deformation effect stage (<0.15 g), elastic–plastic deformation effect stage (0.15–0.3 g), and plastic deformation effect stage (0.3–0.6 g). In addition, according to MIa energy and different frequency-domain incremental displacement analyses, the low-frequency component of seismic waves results in global deformation of the lining section, whereas the high-frequency component causes vault and arch waist-H local deformation. The results of MIa and PEC values can provide a scientific basis for identifying the seismic failure state of the tunnel lining and appropriate seismic reinforcement.

Experimental study of shear behavior of rock–shotcrete interface under dynamic shearing: insights from interface roughness and strain rate

Rock–shotcrete structures are often suffered from dynamic shearing. However, the understanding of the dynamic shear response of rock–shotcrete structures is still at its infancy. To investigate the effects of strain rate and interface roughness on the dynamic shear response of rock–shotcrete structure, laboratory tests were carried out on the modified double notched sandstone–concrete specimen. Testing results show that the dynamic shear strength and dynamic peak strain of sandstone–concrete specimens are both far less than those of sandstone and concrete specimens. With increasing strain rate, the dynamic shear strength of sandstone–concrete specimen increases and the failure mode changes from interfacial shear failure to the mixed failure, i.e., the interfacial, concrete and sandstone shear failure. With the increase in interface roughness, the failure mode changes from sliding fracture to shear-off fracture, leading to an increase in dynamic shear strength and shear peak strain of sandstone–concrete specimens. In addition, it is the smallest sawtooth angle at the sandstone–concrete interface that dominates the dynamic shear strength of sandstone–concrete specimens. The findings in the present study could facilitate understanding the shear behavior and failure mechanism of the rock–shotcrete structure subjected to dynamic loading and be helpful in the efficient design, reinforcement and stability of rock–shotcrete engineering.

Experimental study on compressive behavior of PE-ECC under impact load

Compared with polyvinyl alcohol-engineered cementitious composites (PVA-ECC), engineered cementitious composites containing polyethylene fibers (PE-ECC) has captured the attention of researchers because of lower cost. Nevertheless, there is a limited amount of research that focuses on their dynamic behavior. Thus, specimens with different water binder ratios were tested by split Hopkinson pressure bar (SHPB) to unveil the dynamic compressive behavior of PE-ECC. The dynamic behaviors were analyzed based on the tests, including dynamic failure modes, dynamic stress-strain curves, dynamic compressive strength, dynamic peak strain, and dynamic toughness. The result shows the PE-ECC has excellent compressive ductility, and a long post-peak descending part in the stress-strain relations. Furthermore, the sensitivity analysis reveals that the strain rate is the most crucial factor that directly affects the dynamic compressive strength, dynamic peak strain, and dynamic toughness in a monotonic fashion.

Fatigue Performance Test and Finite-Element Analysis of Concrete-Filled Steel-Tube K-Joints

To avoid fatigue cracking of K-joints in concrete-filled steel-tube (CFST) truss arch bridges, fatigue performance tests and finite-element analysis were conducted to investigate the hot spot stress distribution, fatigue performance evolution, and final fatigue failure pattern of the CFST K-joints. The results of a CFST K-joint were compared with those of a steel tube (ST) K-joint, to reveal the influence of concrete filled in a chord on the fatigue performance of the CFST K-joint. The results show that the hot spot stress of a CFST K-joint can be obtained by quadratic extrapolation. The stress concentration factor (SCF) on the chord side of the intersecting weld of CFST K-joints is larger than those on the brace side, and the maximum SCF is located at the crown point on the chord side of the intersecting weld connecting the tensioned brace to the chord. Because the constraint action of the core concrete improves the radial stiffness of the chord, making the section radial deformation of the CFST K-joint much smaller than that of the ST K-joint, the in-chord concrete could relieve the SCF of CFST K-joints by 19.5%–49.7%. Since the existing SCF calculation methods of ST K-joints and CFST K-joints do not consider the effect of in-chord concrete or the coupling effect of geometric parameters, they are not applicable to the SCF calculation of CFST K-joints. The fatigue crack growth process of a CFST K-joint can be divided into four stages: crack initiation, slow propagation, rapid propagation, and sharp fracture. The fatigue crack propagation speed of the CFST K-joint is obviously slower than that of the ST K-joint due to the effect of the in-chord concrete. The number of cycles corresponding to the 15% change of the peak dynamic strain is recommended as the fatigue life of the CFST K-joint. An S-N curve for fatigue life evaluation of CFST K-joints is proposed. Comparing with the fatigue test in this paper and existing fatigue test of other CFST joints, the proposed S-N curve for CFST K-joints has high precision and safety.

Dynamic compressive properties of lightweight engineered geopolymer composites containing ceramsite (LW-EGC)

In this paper, polyvinyl alcohol (PVA) fiber and multi-walled carbon nanotubes (MWCNTs) reinforced lightweight engineered geopolymer composites containing ceramsite (LW-EGC) were presented. The dynamic compressive response and microstructures of these LW-EGC under different steel fiber contents (0, 0.5, 1.0, and 1.5%) and strain rates (91.06 s−1–255.79 s−1) were investigated. The dynamic compressive behavior of the LW-EGC was tested using a split Hopkinson pressure bar with a diameter of 100 mm. The microstructures of the LW-EGC and the failure modes of the hybrid fibers were analyzed. Compared with LW-EGC-C, when the steel fiber content was 1.0%, its quasi-static compressive strength and elastic modulus were increased by 39.28% and 15.32%, respectively. Under similar strain rates, the dynamic peak strain and dynamic compressive strength increased initially and subsequently decreased with an increase in the steel fiber content. The optimal content of steel fibers was 0.5%, and the peak strain and dynamic compressive strength were 0.77% and 94.54 MPa, respectively. Moreover, the dynamic mechanical properties of the LW-EGC indicated a significant strain rate enhancement effect. A negative correlation was noted between the steel fiber content and the dynamic increase factor. The DIF predicted by DIFPre was quite consistent with the experimental results, and can be used in the dynamic design of LW-EGC. Additionally, microscopy observations showed that steel fibers, PVA fibers, and functionalized MWCNTs bridged cracks at different scales and improved the impact resistance of the LW-EGC.

Dynamic mechanical properties and energy dissipation analysis of frozen sandstone with initial damage

Damaged rock masses on the slopes of open pit coal mines are prone to geological disasters such as landslides under low temperatures and dynamic loads such as blasting impacts. Based on the Low Temperature Split Hopkinson Pressure Bar (LT-SHPB) system, dynamic compressive tests were done on sandstone specimens, which were damaged by uniaxial loading and unloading test. Dynamic stress–strain curves and dynamic mechanical properties of frozen sandstone with initial damage were analyzed as well as the energy dissipation characteristics. The results indicate that both compressive state and plastic deformation state of the dynamic stress-strain curves increase with the increase of the damage value. Dynamic peak stress and dynamic elastic modulus exhibit an evident damage weakening effect while the dynamic peak strain, in contrast, exhibits a damage enhancement effect. In addition, all three dynamic mechanical properties of the damaged frozen sandstone exhibit an impact effect. The dissipation energy ratio and reflection energy ratio of frozen sandstone increase with the increase of initial damage value while the transmission energy ratio decreases. With the increase of initial damage value and strain rate, the energy utilization rate during the sandstone failure process increases, resulting in more small fragments and powders.

Mechanical properties, damage evolution and energy dissipation of cemented tailings backfill under impact loading

In order to explore the influence of average strain rate(ASR) on mechanical properties, damage evolution and energy dissipation of cemented tailings backfill(CTB), the dynamic test of CTB was carried out in the laboratory. This study shows that dynamic peak stress and initial crack stress of CTB increase exponentially with the increase of ASR, indicating that the characteristic stress of CTB has a significant strain rate effect. The dynamic peak strain and initial crack strain of CTB also increase exponentially with the increase of ASR, and the CTB with lower cement content is more likely to produce deformation and failure. The increase of ASR can improve the energy indexes of CTB at the peak stress point, and the increase of cement content can also improve the energy parameters of CTB. The energy storage limit of CTB increases exponentially with the increase of ASR. In addition, a dynamic statistical damage constitutive model of CTB was established considering ASR, and the accuracy and reliability were verified. There are three stages for the damage failure of CTB: rapid growth stage of damage, slow growth stage of damage and stable growth stage of damage. In addition, the high strain rate has a certain retarding effect on the development of cracks inside the CTB, thus inhibiting the rapid growth of damage value. Under impact loading, the CTB samples are mainly axial macroscopic main crack tensile failure and crushing failure. When the average strain rate is higher than the critical strain rate, the failure pattern of CTB is mainly crushing failure. When the average strain rate is basically the same, the damage degree of CTB with higher cement content is smaller.

Study on Mechanical Properties of Ring Sandstone Specimen under Temperature and Water Coupling Dynamic Compression

The excavation of hard rock roadways in coal mines is often in the environment of underground water and high ground temperature, and it is easy to be affected by the dynamic load, which leads to roadway destruction and increases the difficulty of roadway support. The ring sandstone specimens with different inner diameters (0~25 mm) were treated with temperature and water coupled, and the dynamic compression test was produced by the Hopkinson pressure rod device (SHPB). The experimental results indicate that the coupling effect of temperature and water reduces the dynamic performance of sandstone specimens. XRD test results showed that the composition of sandstone specimens did not change before and after warm water coupling, and no new substances were found. Dynamic properties of ring sandstone specimens with different inner diameters weaken with the increase in inner diameters. With the increasing inner diameter of ring sandstone specimens, the energy dissipation per unit volume increases the dynamic compressive strength decreases, and the degree of breakage increases. Fracture morphology, average strain rate, and dynamic peak strain of ring sandstone specimens increase with inner diameter.

Effect of strength grade on mechanical properties of concrete under dynamic load

AbstractThe uniaxial compression test and dynamic compression test of C30, C50, and C80 concrete were carried out. The effects of strength grade and strain rate () on dynamic mechanical properties of concrete were analyzed in terms of dynamic compressive strength, dynamic increase factor (DIF), dynamic peak strain, and dynamic peak toughness. And the strain rate sensitivity of mechanical indexes and DIF fitting model of concrete with different strength grades were explored. The results show that the dynamic compressive strength, DIF and dynamic peak toughness of concrete with different strength grades all have obvious strain rate effects. With the increase of strength grade of concrete, the dynamic peak strain of concrete decreases continuously, and the strain rate sensitivity of dynamic compressive strength and dynamic peak toughness of concrete increases continuously. The mechanical indexes of C80 concrete have the strongest sensitivity to the strain rate. The DIF empirical formula of Comite Euro‐International du Beton (CEB) cannot fit the DIF of C30 and C80 concrete effectively. There is a critical strain rate beyond which the strain rate effect of DIF is significantly enhanced. With the increase of strength grade of concrete, the critical strain rate of concrete decreases continuously. The piecewise linear fitting of DIF and of concrete with different strength grades shows good results.