Obvious Strain Rate Effect Research Articles

Mesoscale Modeling of Microcapsule-Based Self-Healing Cementitious Composites under Dynamic Splitting Tension

Microcapsule-based self-healing cementitious composite (MSCC) offers autonomous damage repair, extending the service life of structures. However, most of the existing studies focus on static behavior and healing effectiveness but rarely explore dynamic responses. This study developed the mesoscale modeling approach to investigate MSCC behavior under dynamic split tensile loading. At the mesoscale, MSCC can be treated as a four-phase composite consisting of coarse aggregates, interfacial transition zones, cement mortar, and microcapsules. Alternatively, it can be simplified as a two-phase composite comprising a homogeneous mortar matrix and microcapsules. Four-phase and two-phase mesoscale MSCC models were developed for 2D simulations, while a two-phase 3D model was also developed for comparison. Mesoscale numerical simulations were conducted based on Split-Hopkinson Pressure Bar Brazilian disk-splitting tests, considering various strain rates. Simulation results of different mesoscale models were compared with experimental results. All of the models accurately predicted the tensile strength of MSCC, with the 2D four-phase model providing the best representation of failure modes and crack propagation. Both experimental and numerical data exhibited obvious strain rate effects, indicating that MSCC’s mechanical properties were sensitive to the loading rate. Dynamic increase factors were obtained, quantifying rate sensitivity. The obtained dynamic mechanical properties of MSCC provide insights for designing MSCC components and structures that can better withstand collisions or explosions.

Research on damage behavior of silicone rubber under dynamic impact

Viscoelastic rubber materials are widely used in various vibration reduction structures of military and construction machinery. The complex driving and working conditions make the mechanical structure suffer severe impact, which leading to the damage or lose efficacy of the important viscoelastic elements. In order to reveal the dynamic mechanical properties of silicone rubber after impact, the Uniaxial compression tests of silicone rubber under different high strain rates were carried out with the separated Hopkinson pressure bar (SHPB) dynamic impact experiment, and the original Zhu-Wang-Tang (ZWT) constitutive model was modified by combining logarithmic law and power function law. The dynamic impact simulation model of silicone rubber was established using the modified ZWT-rate-dependent constitutive model, and the dynamic impact damage behavior of silicone rubber was studied under the condition of high strain rate, and the microscopic damage analysis was carried out on the experimental silicone rubber samples by scanning electron microscopy (SEM). The results show that the silicone rubber has obvious strain rate effect and strong deformation resistance at high strain rate. The modified ZWT-rate-dependent constitutive model can be used to obtain the constitutive expression of unified parameters, which can better describe the dynamic mechanical properties of silicone rubber at high strain rates. After dynamic impact compression, a damage line zone appears in the silicone rubber sample. There is a certain rule between the position of the line zone and the loading strain rate and the friction coefficient of the end face, and the silicone rubber is significantly affected by the friction effect of the end face.

Strengthening effect of monolayer graphene oxide on the impact mechanical properties of concrete and the mechanism analysis based on fractal theory

Graphene oxide (GO), a new nanomaterial with excellent properties, having the prospect of improving the performance of cementitious composites. Graphene oxide reinforced concrete (GORC) was prepared and the impact tests were performed through a φ100 mm SHPB test apparatus, to investigate the effects of impact velocity and GO content on the impact mechanical properties of concrete. The effects of GO on the pore structure and microscopic morphology of concrete were analyzed by MIP and SEM tests. Furthermore, the pore structure fractal dimension and fragment fractal dimension were calculated to quantitatively relate the microscopic pore structure to the macroscopic impact mechanical properties, and the enhancement mechanism of GO was investigated from microstructure optimization and stress dispersion mechanism. The results show that GO promotes the growth and aggregation of cement hydration products, and significantly improves the quasi-static and impact mechanical properties of concrete through filling-compacting effect and anticracking-unloading effect. When the GO content is 0.06 wt %, GO shows the best improvement effect. Compared with plain concrete (PC), the quasi-static compressive strength, dynamic compressive strength, elastic modulus, DIF, peak strain, ultimate strain and impact toughness are increased by a maximum of 29.95 %, 52.27 %, 9.79 %, 75 %, 51.54 %, 59.6 % and 86.2 % respectively. GORC has an obvious strain rate effect in the impact velocity range of 5.5 m/s-9.5 m/s, and the average particle size of specimen fragments satisfies a logarithmic relationship with the impact velocity. In addition, the pore structure fractal dimension and fragment fractal dimension satisfy a positive correlation. Larger pore structure fractal dimension indicates more defects in concrete and worse mechanical properties of it.

Stress overshoot and its evolution of ceramsite concrete with freeze–thaw cycles under impact loading

In the present study, the impact characteristics of ceramsite concrete after freeze–thaw cycles are studied. The split Hopkinson pressure bar (SHPB) device is applied to conduct impact compression tests on ceramsite concrete samples with different volume fractions and freeze–thaw cycles under different strain rates. The performed analyses show that there is an obvious stress overshoot evolution after the peak stress of the stress–strain curve. The obtained results show that the stress and damage evolution of the stress overshoot platform has an obvious strain rate effect. It is found that with an increase in freeze–thaw cycles, freeze–thaw damage increases, while the magnitude of platform stress and overshoot stress decreases. The volume fraction of ceramsite affects the evolution of the stress overshoot platform. It is pointed out that the physical nature of the plateau trend originates from the competition between the effects of damage softening and secondary strain strengthening. The dynamic constitutive relationship of ceramsite concrete considering the influence of freeze–thaw cycles and damage evolution is established. The performed analyses demonstrate that the theoretical model can be applied to accurately analyze the stress–strain characteristic curve of ceramsite concrete. The results demonstrate that the impact failure images obtained from the finite element method are good consistent with the experimental results.

Investigation of dynamic compression properties of basalt fibre reactive powder concrete

Basalt fibre reactive powder concrete (BFRPC) was prepared by incorporating basalt fibres (BFs) instead of steel fibre into reactive powder concrete. In this study, the impact resistance of BFRPC was experimentally and numerically analysed at different strain rates (101–102 s−1). The 75 mm dia. split-Hopkinson pressure bar was used for impact compression tests and the finite-element software LS- Dyna was used for numerical simulation analysis. The results showed that the high-strength BFRPC has an obvious strain rate effect and the dynamic increase factor (DIF) of compressive strength increases logarithmically with strain rate. Meanwhile, the parameters of the Comité Euro-international du Béton (CEB) model were refitted and the relationship between strain rate and DIF was established. By using the Holmquist−Johnson−Cook material constitutive model (HJC model), the stress−strain curves and failure patterns obtained were consistent with the experimental results. The incorporation of BFs significantly improves the deformation properties of BFRPC.

Investigations of Dynamic Mechanical Performance of Rubber Concrete under Freeze-Thaw Cycle Damage

In order to study the effect of the freeze-thaw cycle on the integrity and dynamic mechanical performance of rubber concrete, the wave speed of rubber concrete specimens with 10% rubber volume was measured by a nonmetallic ultrasonic detector. The impact tests were also performed on rubber concrete specimens with different numbers of freeze-thaw cycles (0, 25, 50, 75, 100, and 125) at different impact air pressures (0.3, 0.4, 0.5, and 0.6 MPa) using a 74 mm diameter split Hopkinson pressure bar (SHPB) device, peak stress, ultimate strain dynamic intensity enhancement factor (DIF), and energy absorption effect. The results show that with the increase of freeze-thaw cycles, the wave speed decreases, and the freeze-thaw action will damage the rubber concrete and reduce the longitudinal wave velocity. Under the same freeze-thaw cycles, with the rise of strain rate, the peak stress, limit strain, DIF, and absorbed energy increase, and there is an obvious strain rate effect; under the pressure of 0.6 MPa, the peak stress of 25, 50, 75, 100, and 125 freeze-thaw cycles decreases by 25.1%, 37.1%, 46%, 52.5%, and 54.8%. With the increase of the freeze-thaw cycles, the peak stress of the specimen decreases, and the decrease gradually decreases. After the number of cycles exceeds 100, the stress decrease of the specimen is no longer obvious, the limit strain increases, and the absorbed energy decreases. The freeze-thaw environment significantly reduces the strength and integrity of rubber concrete specimens.

Dynamic compressive behavior of polyethylene fiber reinforced high strength and high ductility concrete over wide ranges of strain rate

High strength and high ductility concrete (HSHDC) possesses extraordinary mechanical properties, including high compressive strength (123.3 MPa), high tensile strength (9.1 MPa), and ideal tensile strain capacity (6.6%), and exhibits promising application prospects in structures against dynamic loadings. This study systematically explored the dynamic compressive behavior of Polyethylene (PE) fiber reinforced HSHDC over wide ranges of strain rates (10−5–102 s−1) using the hydraulic servo-controlled testing machine and split Hopkinson pressure bar device. The dynamic stress-strain relations and failure patterns of HSHDC were obtained, based on which the dynamic compressive strength, peak compressive strain, and specific energy absorption (SEA) were analyzed in detail. It indicated that the compressive strength increased moderately at low strain rates (2.4 × 10−5–2.4 × 10−2 s−1) and obviously at high strain rates (105.8–258.8 s−1) with the increase of strain rate. To describe the dynamic compressive strength, several dynamic increase factor (DIF) formulae in the literature were evaluated, and an experimentally fitted DIF formula was proposed. The peak compressive strain remained almost constant at low strain rates, while it decreased significantly with the increase of strain rate at high strain rates. Besides, the dynamic SEA shows a bilinear growth law with the increasing strain rate and has a more obvious strain rate effect than the dynamic compressive strength. Finally, a nonlinear viscoelastic constitutive model was established, which satisfactorily predicts the compressive stress-strain relationship of HSHDC at different strain rates.

The Mechanical Properties of Silicone Rubber Composites with Shear Thickening Fluid Microcapsules.

In this study, Sylgard 184 silicone rubber (SylSR) matrix composites with shear thickening fluid (STF) microcapsules (SylSR/STF) were fabricated. Their mechanical behaviors were characterized by dynamic thermo-mechanical analysis (DMA) and quasi-static compression. Their damping properties increased with the addition ofSTF into the SR in DMA tests and the SylSR/STF composites presented decreased stiffness and an obvious positive strain rate effect in the quasi-static compression test. Moreover, the impact resistance behavior of the SylSR/STF composites was tested by the drop hammer impact test. The addition of STF enhanced the impact protective performance of silicone rubber, and the impact resistance increased with the increase of STF content, which should be ascribed to the shear thickening and energy absorption of STF microcapsules in the composites. Meanwhile, in another matrix, hot vulcanized silicone rubber (HTVSR) with a mechanical strength higher than Sylgard 184, the impact resistance capacity of its composite with STF (HTVSR/STF) was also examined by the drop hammer impact test. It is interesting to note that the strength of the SR matrix obviously influenced the enhancement effect of STF on the impact resistance of SR. The stronger the strength of SR, the better the effect of STF on improving the impact protective performance of SR. This study not only provides a new method for packaging STF and improving the impact resistance behavior of SR, but is also beneficial for the design of STF-related protective functional materials and structures.

Comparative study on toughness evaluation indicators of nano-concrete under impact load

In order to determine the evaluation indicator of toughness of nano-concrete under impact load, 7 kinds of nano-concrete were prepared by using inorganic nanoparticles (nano-SiO2, nano-CaCO3) and metal oxide nanoparticles (nano-Al2O3, nano-Fe2O3). The impact compression test was carried out by using the Φ 100 mm separated Hopkinson pressure bar (SHPB) test device on inorganic nanoparticle modified concrete, metal oxide nanoparticle modified concrete and composite nanoparticles modified concrete. The impact toughness of nano-concrete was studied based on two evaluation indicators (peak toughness and specific energy absorption), and the comparative analysis and mechanistic exploration were also conducted. The results show that the development trend reflected by the two evaluation indicators of impact toughness is consistent. One is that the impact toughness indicators have obvious strain rate effect, and the other is that nanoparticles have a certain toughening effect on concrete. When evaluating the impact toughness of nano-concrete, it is more effective and reasonable to use the indicator of specific energy absorption. The strain rate sensitivity of peak toughness and specific energy absorption of concrete is improved by adding nanoparticles. Among composite nanoparticles modified concrete, co-doping inorganic nanoparticles has the best toughening effect on concrete.

Effects of scale and strain rate on the tensile behaviors of large-rupture-strain fiber-reinforced polymers (LRS-FRP)

A comprehensive understanding of the dynamic material properties of LRS-FRP/epoxy laminates at high strain rates is urgently needed for guiding the design and performance evaluation of LRS-FRP strengthening structures under dynamic loadings. In this study, quasi-static tensile tests of LRS-FRP at different scales (single filament, fiber bundle, FRPs with single and five bundles) were first conducted and the experiment results showed that size effect and existence of resin matrix had marked influences on tensile behaviors of LRS-FRP. Then, LRS-FRP sheets whose scale were close to engineering applications, were tested with a high-speed hydraulic servo system to investigate their tensile behaviors at varying stain rates. The variation tendencies of key mechanical parameters, such as tensile strength, elastic and secondary tangent moduli, and toughness, were analyzed based on the experimental results. The dynamic tensile behaviors of PEN-FRP/PET-FRP showed obvious strain rate effects at the strain rate ranging from 0.0001 s−1 to 100 s−1. The strengths at the turning point of PEN/PET-FRP at a strain rate of 100 s−1 reached more than twice the values at quasi-static loading, while the amplification of ultimate strengths with strain rate increasing from 0.0001 s−1 to 100 s−1 was about 20 %. Empirical formulas of dynamic increase factor for LRS-FRPs are derived and a dynamic tensile constitutive model of LRS-FRP is finally established.

Strain rate effect on the fracture parameters of concrete three-point bending beam with a small span-to-height ratio

The fracture properties of concrete are greatly affected by strain rate, and changes in fracture parameters can reflect the crack resistance and failure mechanism of concrete. In this study, fracture tests were carried out on samples of concrete three-point bending beam (TPB) by considering 3 small span-to-height ratios (2, 2.5 and 3) and 4 strain rate grades (10−5/s, 10−4/s, 10−3/s and 10−2/s), in order to examine the strain rate effect on the fracture parameters of TPB. From the test data, the crack propagation rate, fracture toughness, length of fracture process zone (FPZ) and determination of damage scale were calculated. The results showed that the fracture parameters of TPB with a small span-to-height ratio were subjected to an obvious strain rate effect. With the increase of span-to-height ratio, the strain rate effect on the crack propagation rate, fracture toughness and determination of damage scale was gradually weakened, while that on the length of fracture process zone (FPZ) was gradually strengthened. Overall, changes in strain rate can significantly affect the fracture parameters of TPB with a small span-to-height ratio. This paper provides a reference for further research on the strain rate effect and failure mechanism of TPB with a small span-to-height ratio.

Dynamic response characteristics and damage rule of graphite ore rock under different strain rates

In the process of mining graphite mine, rock mass is often subjected to dynamic loads such as blasting or mechanical crushing, which involves dynamic responses of different strain rates, and blasting and crushing effect are affected by the rock dynamic properties and damage specials. The dynamic response characteristics and damage rule of graphite ore rock under different strain rates are very important but rarely studied in the past. To study these issues and provide support for graphite ore rock mining, the dynamic compression tests of graphite ore rock under five kinds of impact pressures were designed and carried out by using the Split Hopkinson Pressure Bar (SHPB) test system, combining with the high-speed photography system and crushing screening tests. The dynamic characteristics, crushing process, crushing mode, crushing form and fragmentation distribution of the graphite ore rock under different strain rates were analyzed. The results show that the dynamic characteristics of the graphite ore rock have obvious strain rate effect. The hardening coefficient (DIF) is positively correlated with the cubic root of strain rate, and the softening factor (K) is negatively correlated with the cubic root of strain rate. Shear failure mainly occurs in the graphite ore rock under impact load, and the crushing process can be divided into five stages, they are compaction, crack initiation, crack expansion and penetration, fragmentation collision and fragmentation fall. In addition, the crushed blocks are mainly triangular pyramid (or cone-like) fine granular and powder. The broken fragments of the graphite ore rock are in accord with the fractal geometry characteristics. That is, the average broken particle size (dS) decreases linearly with the increase of strain rate, and the fractal dimension (Da) increases weakly with the increase of strain rate. Based on D-P fracture criterion and Weibull distribution model, the dynamic damage constitutive model of the graphite ore rock was established, and the correlation between strain rate and Weibull distribution parameters (m and F0) was used to reasonably modify the damage constitutive model. The modified damage constitutive model curve is in good agreement with the experimental curve, which can basically reflect the strain rate effect of the dynamic characteristics of the graphite ore rock and the evolution characteristics of the dynamic stress–strain curve at different stage.

Dynamic and Damage Characteristics of Mortar Composite under Impact Load

In the process of underground construction, it is common to spray concrete on the working surface, which will form a concrete-rock composite structure, to achieve the expected reinforcement effect. Compared with pure concrete or rock structures, composite structures have different mechanical properties, energy evolution and damage characteristics. Understanding the dynamic mechanics and damage characteristics of composite structures under impact loads is important to the safety of underground engineering construction. First, dynamic compression tests on different grades of mortar-sandstone composite specimens were carried out by using a Hopkinson pressure bar system to discuss the effect of impact velocities on the mechanical properties and failure modes of composite specimens. The results show that the dynamic peak stress, strain energy density and fragmentation block of the mortar-sandstone composite have an obvious strain rate effect. With an increase in impact velocity, the internal cracks of the sample do not have sufficient time to expand, and the energy absorbed by the sample leads to the continuous initiation of new cracks in the sample, resulting in an increasing damage degree of composite specimens. The increase in mortar strength can significantly increase the peak stress, improve the load-bearing capacity of the sample, and reduce the degree of sample damage. At the same impact velocity, the fragmentation degree of the mortar sample is more severe than that of sandstone, and the mortar sample is broken into powder debris, while the sandstone is broken into fragments. In addition, according to the failure properties of the composite sample, the mortar and sandstone samples are described by different damage models, and the dynamic damage constitutive model of the mortar-sandstone composite is established based on the overlay principle. The dynamic test results were fitted. The research shows that the fitting curves of the model are well fitted with the test curves and that the model accurately reflects the changes in the mechanical parameters of the composite specimens.

Experimental and numerical simulation study of fiber-reinforced high strength concrete at high strain rates

With the widespread use of fiber-reinforced high strength concrete (FRHSC) in military and civil fields, it is necessary to have an accurate understanding of the mechanical properties and failure modes of FRHSC under impact. The dynamic compression experiments were performed on FRHSC using the large-size split Hopkinson pressure bar (SHPB) apparatus. The experimental results were analyzed to determine the reasonable strain rate range of FRHSC under large-size SHPB loading conditions. The strain rate effect, critical strain, and failure mode of FRHSC under dynamic impact were studied. The strain rate and strength parameters in the Holmquist-Johnson-Cook (HJC) model were determined based on the experimental results, and the numerical simulation of SHPB was completed by LS-DYNA. The results revealed that the reasonable strain rate of FRHSC under large-size SHPB loading did not exceed 100 s−1. The material presented an obvious strain rate effect, and the critical strain was almost unchanged with the increased strain rate. Steel fiber improves the toughness of FRHSC. Under quasi-static loading, the tensile-compression ratio of the material was 0.13, and there was no apparent damage under impact. The rationality of the strain rate and strength parameters in the HJC model was verified by comparing the stress wave curve of the pressure bar, the stress-strain curve, and the failure mode of the specimen obtained by experiment and simulation.

Experimental and theoretical study of dynamic mechanical behavior of concrete subjected to triaxial confining and impact loads

Confining stress is a key factor affecting the dynamic mechanical behaviour of concrete. To explore the mechanism of triaxial confining stress on the dynamic compressive properties of concrete, a series of static–dynamic combined compression experiments were performed using three–dimensional Split Hopkinson Pressure Bar equipment. The results show that there is an obvious strain rate effect of concrete under triaxial confining conditions, which is closely associated with the static triaxial confining stress and strain rate of impact loads. The confining stress significantly affects the dynamic response stress (strain) and dynamic stress (strain) along the loading direction. Moreover, the effects would decrease with an increase in the dynamic loading strain rate. Obvious fractures will occur on the concrete surface when the effective dissipated energy ratio exceeds 2.56 J/cm3, which proves that it is suitable to describe the fracture features of concrete under triaxial static–dynamic loads. In this study, a dynamic strength criterion of concrete was proposed for concrete under triaxial dynamic loads. The testing data and reference results matched well with suggested value of the proposed dynamic strength criterion. This can provide the theoretical guidance for concrete engineering construction.

Research on the anisotropy of plastic behavior and deformation mechanism of textured pure titanium

The anisotropy of the plastic behavior and the associated deformation mechanism of textured pure titanium were studied using uniaxial tensile tests with different strain rates along the rolling direction (RD), 45° direction (BD), and tangential direction (TD), and combined with crystal orientation observation and Schmid law analysis. The experimental results show that the yield and hardening behaviors of textured pure titanium exhibit an obvious strain rate effect and anisotropy, with TD exhibiting a three stage characteristic, RD exhibiting continuous variation, and BD falling somewhere in between. According to the Schmid law and critical shear stress (CRSS) analysis, the RD tensile yield mechanism is prismatic <a > slip, whereas the BD and TD tensile yield mechanisms are the result of the combined action of two or more slip systems. Twinning polarity and Schmid law both have an effect on twinning activation, and the new texture component 〈0001〉//RD generated by {10−12} extension twinning is beneficial to prismatic <a > slip and pyramidal <a > slip activation. The combined effects of twinning-induced grain refinement strengthening, texture softening, and strain softening jointly affect the material hardening and softening behavior.

Experimental Study on the Dynamic Mechanical Properties of a Jointed Rock Mass under Impact Loading

The propagation law of blast stress waves in jointed rock masses is closely related to the characteristics of the joint filling medium. The water content and thickness of the filling medium affect the propagation characteristics of the blast stress wave in the joint surface. Based on similarity theory, mortar-red clay-mortar composite specimens with different moisture contents (36%, 39%, 42%, and 45%) and medium thicknesses (3 mm, 6 mm, and 9 mm) were prepared with red clay as the filling medium. The dynamic uniaxial compression test of the specimen under different strain rates was carried out by using a variable cross-section split Hopkinson compression bar with a diameter of 50 mm. The effects of strain rate, moisture content, and medium thickness on the stress wave propagation characteristics, dynamic stress-strain curve, peak stress, crushing energy consumption density, and crushing characteristics of mortar-red clay-mortar composite specimens were analyzed. The results show that the blocking effect of joints on stress waves increases significantly with increasing filling medium thickness and water content. With increasing strain rate, the peak stress and energy of the composite specimen increase and there is an obvious strain rate effect. With the increase in the thickness and moisture content of the filling medium, the peak stress, dynamic elastic modulus, energy consumption density per unit volume, and crushing degree of the specimen gradually decrease and the nonlinear deformation is more obvious. There is a good linear relationship between the peak stress and the thickness and moisture content of the filling medium. The existence of joints greatly weakens the damage effect of stress waves on the specimens behind the joints, and with the increase in the thickness and water content of the filling medium, the degree of damage to the specimens behind the joint surface decreases under the same impact pressure and the weakening effect becomes increasingly significant.

Static and Dynamic Mechanical Properties of Recycled Concrete under Microwave Irradiation

The application of recycled concrete can alleviate environmental pollution and has great practical value. In this study, microwave irradiation technology is used to treat recycled concrete in order to obtain reinforced recycled coarse aggregate. Then, the quasi-static and dynamic mechanical properties of concrete (C), recycled concrete (RC), and recycled concrete irradiated by microwave (MRC) were studied, and the effect of the replacement rate of coarse aggregates on its mechanical properties was also studied. The results showed that the quasi-static compressive strength of MCR is higher than that of CR at all replacement rates. With the increase in the replacement rate, the quasi-static compressive strength of MCR decreases gradually, while the quasi-static compressive strength of CR decreases first and then increases, reaching the minimum value at 60%. The dynamic mechanical properties of CR and MCR all have an obvious strain rate effect. The dynamic increase factor (DIF) has an exponential relationship with the natural logarithm of the strain rate. The dynamic constitutive model of RC was established based on composite material mechanics and viscoelastic theory. The research content can provide guidance and basis for the study of mechanical properties and constitutive relationship of RC.

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.

Study on Mechanical Properties and Mesoscopic Numerical Simulation of Recycled Concrete

To obtain the mechanical properties of recycled concrete (RC) under different replacement rates (RRs) of recycled coarse aggregate (RCA), a quasi-static uniaxial compression test, a uniaxial splitting tension test and a uniaxial dynamic compression test of RC with replacement rates (RRs) of 0%, 20%, 40%, 60%, 80% and 100% were carried out. ABAQUS was used to investigate the cracking and failure of RC. The results showed that, when the RR was less than 60%, the uniaxial compressive and tensile strengths of RC decreased with the increase in RR, but slightly increased when RR was greater than 80%. Under impact load, the dynamic compressive strength of RC increased linearly with the increase in the strain rate, showing an obvious strain rate effect. With the increase in RR, the strain rate sensitivity of RC gradually decreased. The concrete damage plastic (CDP) model can describe the mechanical behavior of RC well. The damage and failure of RC occurred first at the old interface transition zone (ITZ) and old mortar. As the strain rate increases, the damage and failure rate of the specimens is intensified. Research on the mechanical properties of RC can provide a basis for the application and promotion of RC technology.