Split Hopkinson Pressure Bar Tests Research Articles

Experimental study on the dynamic mechanical and progressive fracture behavior of multi-jointed rock mass under repetitive impact loading

The failure of rock masses is often controlled by structural planes, and the study on the dynamic mechanical behavior of multi-jointed rock masses under repetitive dynamic loading is still few. A series of repetitive impact tests on multi-jointed gabbro (MJG) are conducted with the split Hopkinson pressure bar (SHPB) testing apparatus. The effects of repetitive impact and joint inclination angles (α) on the dynamic mechanical behavior of MJG from the perspectives of impact number, stress equilibrium, dynamic mechanical properties, energy evolution, and macro and micro failure modes are deeply investigated. The results show that the joint inclination angle affects the impact resistance of the MJG. Under repetitive impact loadings, the mechanical behavior of the MJG is consistent, with tensile wing cracks initiating from the joint tips and propagating along the loading direction until specimen failure. During this process, cracks propagate along the weakest paths, thereby consuming the energy generated by the impact and preventing the activation of other minor defects. The macroscopic failure of the MJG undergoes four stages: the appearance of white patch, crack coalescence, crack penetration, and fracture, with the final failure mode being splitting. The microscopic formation stage of white patch is divided into microcrack activation and microcrack widening.

Axial Impact Resistance of High-Strength Engineering Geopolymer Composites: Effect of Polyethylene Fiber Content and Strain Rate

High-strength engineered geopolymer composite (EGC) materials exhibit excellent mechanical properties under quasistatic loading, thus showing great potential in military and civilian facilities subjected to impact or explosive loading. However, its dynamic mechanical response under high-speed loading is not fully understood. In this study, dynamic compressive test was performed on EGC with PE fiber contents of 0%, 0.5%, 1.0%, 1.5%, and 2.0% using the Split Hopkinson Pressure Bar (SHPB) test. The results indicated that EGC reinforced with 1.5% fiber exhibited optimal static and dynamic mechanical performance. In the strain rate range of 181 s−1 to 201 s−1, when the fiber content increased from 1.0% to 1.5% and 2.0%, the dynamic compressive strength of the EGC increased by 24.3%, 28.8%, and 44.0%, respectively, compared to the matrix without fiber. Dynamic parameters of the EGC, including dynamic compressive strength, dynamic increase factor, and impact toughness, showed sensitivity to strain rates and increased with strain rate. A modified model, incorporating the fiber bridging effect, was proposed based on the CEB-FIP model, providing important guidance for practical engineering applications.

Experimental study on dynamic and static mechanical properties of polyvinyl alcohol fiber cement soil under salt freezing cycle

A universal testing machine and a 50 mm split Hopkinson pressure bar (SHPB) were used to conduct salt erosion and freeze-thaw (F-T) cycle coupling tests on cement soil specimens with 0.5% polyvinyl alcohol (PVA) fiber and without fiber in order to study the effects of salt solution and F-T cycles on the dynamic and static mechanical properties of cement soil. In four distinct solution settings (clear water, 9 g/L sodium sulphate solution, 9 g/L sodium chloride solution, and 9 g/L sodium sulphate and sodium chloride mixed solution). After F-T cycles, the cement soil specimens underwent the unconfined compressive strength (UCS) test, SHPB test, and SEM test. The findings indicate that as the number of F-T cycles increases, the dynamic and static mechanical properties of cement soil specimens decrease, and the rate of decline is rapid followed by slow. After five F-T cycles, the combined solution's unconfined compressive strength dropped to 15.91% (without fiber) and 29.41% (with fiber), respectively. After five F-T cycles, the dynamic compressive strength in sodium sulphate solution fell by 95.17% (without fiber) and 93.86% (with fiber). Fibers help to some degree by preventing salt erosion and F-T cycles. With more F-T cycles, the absorbed energy declines exponentially, and the order of the solutions' effects on the absorbed energy is: mixed sodium chloride and sodium sulphate solution > sodium chloride solution > sodium sulphate solution > clear water.

Experimental and numerical study on the dynamic mode III fracture behaviors of rock using an axially notched flattened Brazilian disc in SHPB tests

The dynamic mode I and mode II fracture of rock have been widely investigated over the past decades. However, the lack of dynamic mode III fracture testing method and the rare understanding of mode III fracture mechanism of rock remain a significant knowledge gap in the realm of rock mechanics. In this work, an innovative axially notched flattened Brazilian disc (ANFBD) sample is proposed for the mode III fracture tests of rocks using the split Hopkinson pressure bar (SHPB). Firstly, the optimal geometrical dimension of the ANFBD sample for achieving true mode III fracture of rocks is comprehensively discussed using finite element method (FEM) analysis. Then, the reliability of ANFBD-SHPB method is experimentally verified through dynamic mode III fracture experiments on the Fangshan marble (FM). Laboratory experimental results show that the mode III fracture toughness (KIIId) values of FM are approximately 2.8 times of the mode I fracture toughness (KId) values at similar dynamic loading rates. Post-mortem examinations on the fracture surfaces show that the famous facet coarsening mechanism in mode III fracture is suppressed under high loading rates. Furthermore, insightful assessments regarding the inner progressive fracturing behaviors of the ANFBD sample are given by virtue of three-dimensional discrete element method (DEM) simulation. Moment tensor (MT) analysis indicates that the shear fracture mechanism mainly dominates the whole failure process of the ANFBD sample, while the tensile fracture mechanism slightly increases during the facet coarsening process. These results are of significant importance for revealing the failure mechanism of rock under dynamic mode III loading and give some beneficial implications for natural strike-slip fault structures.

Dynamic mechanical properties of selective laser-melted AlSi10Mg lattice structures: experimental and numerical analysis with emphasis on Johnson-Cook model parameters

Additively manufactured lattice structures are extensively utilized because of their unique characteristics, including lightweight design, high energy absorption capabilities, and exceptional specific strength. This study focuses on accurately simulating the dynamic mechanical behavior of AlSi10Mg lattice structures produced using selective laser melting (SLM). A series of experimental studies has been conducted to establish the parameters of the J–C hardening and damage model for additively manufactured AlSi10Mg alloys. The lattice structures, featuring face-centered cubic (FCC) and diamond topologies with a 25% designed relative density, underwent scanning electron microscopy (SEM) for geometrical precision assessment. Dynamic compressive behavior was investigated via split Hopkinson pressure bar (SHPB) tests. Numerical simulations in Ls-Dyna, utilizing the identified J–C parameters, were employed to replicate SHPB tests. Findings indicate that the specific strength and the specific energy absorption values of FCC lattice samples have higher than those of diamond samples at strain rates of 750 and 1100 s−1. While the overall strains and deformation modes were well predicted by numerical analyzes, a deeper insight into local stress concentrations under dynamic loads was achieved. Consequently, the obtained J–C model parameters offer valuable insight into characterizing the dynamic behavior of AlSi10Mg lattice structures produced by SLM.

Comparative study on dynamic mechanical properties of additive manufacturing high strength steel and wrought high strength steel under high strain rate

Additive manufacturing high-strength steel has a unique manufacturing process and has broad application prospects in military equipment, aerospace, and other fields, but it is often threatened by dynamic loads such as explosion and high-speed impact during use, which has attracted wide attention. In this paper, the dynamic impact of additive manufacturing high-strength steel LMD-BK and wrought high-strength steel BK was carried out at strain rates of 1000 s−1–5000 s−1 by the Split-Hopkinson pressure bar (SHPB) test, respectively, and the differences in the dynamic mechanical properties of the two were investigated under the impact of different strain rates. Using scanning electron microscope (SEM) and electron backscatter diffraction (EBSD) micro-observation techniques, the microstructure morphologies of LMD-BK and BK before and after dynamic impact were characterized, and the microstructure evolution mechanism of the two was investigated. The results show that both LMD-BK and BK are strain rate sensitive, and the dynamic compressive strength increases and then decreases with the increase of strain rate, with a maximum at 2000 s−1 and a minimum at 1000 s−1. The maximum and minimum values of dynamic compressive strength for LMD-BK are 1978 MPa and 1757 MPa, respectively; for BK, the maximum and minimum values of dynamic compressive strength are 1389 MPa and 1329 MPa, respectively. The final strain of the material increases as the strain rate increases. At the same strain rate, the final strain of BK is always larger than that of LMD-BK. With the increase in strain rate, the impact work absorbed by the material increases, and at the same strain rate, LMD-BK can absorb more impact work than BK. Microscopic observations show that after dynamic impact, LMD-BK undergoes fragmentation of the columnar structure and compression of the cellular structure to form a deformation localization zone. These results are of great significance for the study of dynamic mechanical properties and microstructure evolution mechanism of high-strength steel made by additive manufacturing under extreme environments such as explosion and high-speed impact.

Modification of extended Oxley’s predictive machining theory and determination of Johnson-Cook material model constants by inverse approach

The Johnson-Cook (J-C) flow stress model, renowned for its consideration of the combined effect of strain, strain-rate, and temperature on material property, forms the cornerstone of this research. Its simplicity and applicability in numerical simulation render it widely popular. The study addresses two primary objectives: first, to modify extended Oxley’s predictive machining theory by eliminating the iterative loop for calculating the tool-chip interface temperature, and second, to utilize an inverse approach for determining J-C material model constants specific to medium carbon steel. The modified approach successfully eliminates the iterative loop, thereby streamlining the determination process and effectively reducing calculation time by 25%–40%, thereby enhancing overall efficiency. Concurrently, the study employs an inverse approach to accurately determine the J-C constants (A, B, n, C, and m). Notably, the research avoids the need for expensive and time-consuming Split Hopkinson Pressure Bar (SHPB) tests, instead opting for low-cost axial tensile tests and numerical optimization techniques to obtain the J-C constants. Thus, this study provides a practical method for determining J-C constants, pivotal for accurate material representation in numerical simulations and metal cutting applications. Standard materials and machines are employed, ensuring ease of understanding for a wider audience. The predicted values for the J-C constants are in proximity to the experimental values obtained by using SHPB test. Validated findings, achieved with precision under specified metal cutting conditions, highlight the effectiveness and applicability of the proposed approach, providing valuable insights for optimizing machining processes and improving efficiency.

Anisotropic dynamic compression response of an ultra-high strength steel fabricated by laser hybrid additive manufacturing

Directed energy deposition (DED) is a technological innovation revolutionizing in-situ repair, hybrid manufacturing, and multi-material integration manufacturing, characterized by microstructural heterogeneity on a macro-scale. However, the overall performance of these DED-fabricated components under dynamic loading, particularly along different directions, remains uncharted. This work explores the anisotropic dynamic compression response of an ultra-high strength steel, namely 35CrMnSiA steel, fabricated using DED on a wrought substrate. The laser hybrid additive manufactured samples were subjected to split Hopkinson pressure bar testing along different directions. The results show the following: 1) hybrid manufactured 35CrMnSiA steel has an anisotropic dynamic compression response due to the mismatched properties of each subzone induced by microstructural heterogeneity, 2) low-strength DED part shows higher strain under compression along the build direction but behaves similarly to the wrought material when compressed along the transverse direction, 3) intergranular void/crack is the primary damage mechanism, cracks preferred formed in wrought substrate due to the martensite with poor plastic dissipation ability, 4) when the interface is subjected to parallel directional impact loads, the strain mismatch between the two side subzones leads to interface separation. This study provides comprehensive understanding of the dynamic behavior of DED-fabricated components with heterogenous microstructure, and new insight into demanding tailored strategies to ensure consistent and predictable behavior under various loading conditions.

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.

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 response and deformation mechanism of poly (ε-caprolactone) (PCL) / epoxy resin(EP) shape memory polymer composites

The dynamic mechanical response and deformation mechanism of poly (ε-caprolactone) (PCL) and epoxy resins shape memory polymer (SMP) composites were investigated in this paper. The SMP composites were a blend of PCL and epoxy resins by using the facile melt-mixing method. The distribution of PCL in the composites was observed by SEM, which was in from microparticle morphology to continuous morphology with the increasing PCL content. And the dynamic mechanical analyzer (DMA) tests were performed to demonstrate the viscoelastic properties and shape memory effect of the PCL/EP composites. Based on the above characterization of PCL/EP composites, the split Hopkinson pressure bar (SHPB) tests were performed to study the dynamic mechanical properties at the strain rates of 4000/s to 7000/s. The results showed that the flow stress increased with the increasing strain rate, which exhibited an obvious sensitivity to strain rate. However, the flow stress of PCL/EP decreases with the increasing PCL content due to the low strength of PCL. And PCL/EP composites failed in a typical ductile failure mode under quasi-static loading, whereas an excellent plastic deformation ability was observed at high strain rates, which was attributed to the heat generated by the plastic work during the adiabatic compression. Combining with the experimental results, the corresponding deformation mechanism was also discussed.

Dynamic constitutive identification of concrete based on improved dung beetle algorithm to optimize long short-term memory model

In order to improve the accuracy of concrete dynamic principal identification, a concrete dynamic principal identification model based on Improved Dung Beetle Algorithm (IDBO) optimized Long Short-Term Memory (LSTM) network is proposed. Firstly, the apparent stress–strain curves of concrete containing damage evolution were measured by Split Hopkinson Pressure Bar (SHPB) test to decouple and separate the damage and rheology, and this system was modeled by using LSTM network. Secondly, for the problem of low convergence accuracy and easy to fall into local optimum of Dung Beetle Algorithm (DBO), the greedy lens imaging reverse learning initialization population strategy, the embedded curve adaptive weighting factor and the PID control optimal solution perturbation strategy are introduced, and the superiority of IDBO algorithm is proved through the comparison of optimization test with DBO, Harris Hawk Optimization Algorithm, Gray Wolf Algorithm, and Fruit Fly Algorithm and the combination of LSTM is built to construct the IDBO-LSTM dynamic homeostasis identification model. The final results show that the IDBO-LSTM model can recognize the concrete material damage without considering the damage; in the case of considering the damage, the IDBO-LSTM prediction curves basically match the SHPB test curves, which proves the feasibility and excellence of the proposed method.

Experimental Study on Dynamic Tensile Mechanical Behavior and Fracture Mechanical Characteristics of Sandstone with a Single Prefabricated Fissure

The structural stability of engineering rock mass under dynamic disturbance is directly associated with the fracture mechanics properties in engineering practice. Fully understanding the rock’s fracture mechanical behavior and crack evolution caused by stress concentration at the crack tip in engineering rock mass under dynamic load can offer useful insight into the rock’s dynamic fracture mechanism. A dynamic test using split-Hopkinson pressure bar (SHPB) test system was performed on a single prefabricated fissure sandstone centrally cracked Brazilian disk (CCBD) specimens. Based on the theory of fracture mechanics and one-dimensional stress wave theory, the dynamic crack initiation criterion of CCBD specimen is proposed, and the regression model of sandstone’s dynamic fracture toughness under the coupling effect of fissure angle and strain rate is established by using response surface methodology (RSM). The influence of strain rate and fissure angle on stress wave characteristics, dynamic tensile mechanical behavior, and fracture mechanics characteristic was investigated in this study. The findings demonstrate that: (1) The fissure angle plays a pivotal role in determining the failure mode of sandstone. As the fissure angle increases, three distinct failure modes emerge in the sandstone specimens, while variations in strain rate have minimal impact on the fracture mode of these specimens. (2) Alterations in the fissure angle result in changes to the waveform of transmitted waves. When the fissure angle is below 30°, the transmitted wave exhibits “double peak” characteristics; when it exceeds 30°, a “single peak” waveform is observed. This phenomenon can be attributed to diffraction principles governing incident waves. (3) When the impact pressure is 0.2 MPa, the peak load initially exhibits an increase followed by a decrease, with the peak load reaching its maximum at a fracture angle of 60°; when the impact pressures are 0.3 and 0.5 MPa, there exists a negative correlation between the peak load and the fissure angle. (4) The influence of strain rate on sandstone’s fracture resistance is predominant, with alterations in fissure angle exerting an auxiliary effect on this property. The research results can provide a theoretical and experimental basis for dynamic disaster prevention in urban underground space.

Analysis of Dynamic Mechanical Properties and Energy Consumption of Fractured Sandstone under Dynamic–Static Combination Conditions

Under dynamic loads, such as blasting, excavation, or quarrying, rocks with fissures are the first to sustain damage, leading to instability in the engineering rock mass. To investigate the kinetic properties of fractured rocks, fractured coal mine sandstone specimens underwent impact compression tests using a dynamic–static combination SHPB (split Hopkinson pressure bar) test device at different loading rates under combined dynamic and static conditions. The damage characteristics of the specimens were analyzed from an energy point of view. The results show that under the dynamic and static combined condition, when five impact loading air pressures are used for loading at different impact rates, the trends of the dynamic stress–strain curves of prefabricated fissured rock samples under various impact pressures were discovered to be similar and were mainly categorized into three main stages of elasticity, yield, and destruction; the specimen’s dynamic compressive strength increases according to a power function relationship; as the average strain rate increases, the dynamic strain increases linearly and the dynamic modulus of elasticity increases in a quadratic relationship, all of which show a significant strain rate effect. The incident energy is a power function of the loading rate. The reflected, transmitted, and absorbed energies by the sample increase with the incident energy. The degree of the sandstone specimen fragmentation gradually grows with increasing impact loading rate and incident energy, as evidenced by a decrease in the scale of the fragments. The absorbed energy in the sample is mainly used for the deformation damage of the rock, and the more intense the fragmentation of the specimen, the more absorbed energy is required.

Dynamic fracture properties and criterion of cyclic freeze-thaw treated granite subjected to mixed-mode loading

Rock masses in high-elevation or cold regions are vulnerable to the combined effects of freeze-thaw (F-T) weathering and dynamic mixed-mode loading, posing a serious threaten to the safety and stability of geotechnical engineering. In this study, a series of dynamic fracture tests were conducted on notched semi-circular bend (NSCB) granite specimens subjected to different mixed-mode loading and F-T cycles using a split Hopkinson pressure bar (SHPB) test system. The effects of F-T treatment and dynamic mixed-mode loading on the fracture properties of granite, including effective fracture toughness, progressive fracture process, and macroscopic morphology of fracture surface, were comprehensively revealed. The experimental results suggest that the dynamic effective fracture toughness of NSCB specimens is dependent on the loading rate, particularly when the mode I loading is dominant. Additionally, the fracture toughness decreases as the number of F-T cycles increases, with an inflection point at 30 F-T cycles. All granite specimens subjected to mixed-mode loading exhibit a curved fracture path, with faster crack propagation speed and more fine cracks in specimens exposed to higher F-T cycles. Macroscopic morphology of fracture surface obtained using three-dimensional (3D) scanning indicates that the fractal dimension of the fracture surface increases with increasing F-T cycles, and the increment is more pronounced for specimens subjected to a higher mode II loading component. Moreover, this study compared the fracture resistance of F-T treated granite subjected to dynamic mixed loading using the maximum tangential stress (MTS) criterion and the generalized maximum tangential stress-based semi-analytical (SA-GMTS) criterion. Compared with the MTS criterion, the SA-GMTS criterion shows a more reasonable consistency with the experimental results, with a root mean square error within ±7%.

Analysis of the Fracture Characteristics and Crack Propagation Mechanism of Fractured Sandstone under Dynamic Loading

In order to study the impact of fracture thickness on the dynamic mechanical properties of rock specimens, impact compression tests on prefabricated sandstone specimens with different fracture thicknesses and intact specimens were carried out by using a split Hopkinson pressure bar (SHPB) test device, and the dynamic mechanical parameters of the fractured sandstone specimens were obtained. The results showed that the dynamic stress–strain curves of the prefabricated fractured sandstone specimens are similar to those of the intact sandstone specimens, which can be divided into three stages: elasticity, plasticity, and failure. With the increase in the thickness of prefabricated cracks, the dynamic compressive strength of the sandstone specimens decreases in a quadratic function, the dynamic strain decreases in a power exponential function, and the dynamic elastic modulus decreases linearly. Attempts were made to quantitatively analyze the crushing degree of sandstone specimens. The average particle size of the crushed specimens was negatively correlated with the thickness of prefabricated cracks, and the fractal dimension was linearly negatively correlated with the dynamic compressive strength. The 1.5–2.5 mm prefabricated fractured sandstone specimens produced airfoil cracks and secondary cracks; the 3–3.5 mm prefabricated fractured specimens produced airfoil cracks, coplanar secondary cracks, and secondary oblique cracks; and the complete specimens were subjected to axial failure to produce axial cracks.

A Practical Inverse Identification of Johnson–Cook Parameters at Intermediate Strain Rates Using Split Hopkinson Pressure Bar Test

AbstractA practical inverse method based on the hybrid experiment-finite element (FE) simulation is proposed for identifying strain rate sensitivity of a metal covering intermediate to dynamic loading conditions. The methodology uses the dynamic split Hopkinson pressure bar (SHPB) test for measuring mechanical responses at medium strain rates by optimizing temperature increase, non-uniform strain rate distributed in the non-standard notched SHPB specimens. From the standard dynamic SHPB test, the thermal softening index of the Johnson–Cook (JC) model is first determined by fitting the FE simulation to temperature changes in the specimen. The discrepancy between the measured and predicted flow stresses with the conventional JC model can be attributed to the assumption of constant strain rate sensitivity. Therefore, the new approach using the notched SHPB specimens under dynamic loadings is introduced to identify mechanical responses covering a broader range of strain rate. Finally, the strain rate sensitivity parameter in the JC model as a function of strain rate is evaluated through the inverse FE scheme, in which the sigmoidal function is determined to be optimum by predicting the flow stresses under wider range of strain rate, especially in the intermediate range of strain rate. The present study provides a new methodology based on hybrid experiment and numerical simulation to fill the gap in predicting mechanical responses between quasi-static and dynamic tests using commonly available tensile test and SHPB test. Graphical Abstract

Research on the reasonable sample dimension of woven composites in split Hopkinson pressure bar testing

AbstractAn experimental design method is proposed to guide the selection of specimen dimension and split Hopkinson pressure bar apparatus. This method is applicable to the woven composite with modulus independent of strain rate. This method can predict the maximum specimen dimension at the desired strain rate under the maximum strike velocity of the apparatus. Based on the proposed design method, the in‐plane dynamic compressive behavior of 2D plain weave carbon/aramid hybrid composite was obtained. The strength exhibited sensitive to strain rates. The nonlinear constitutive model described the dynamic constitutive relationship effectively. The distribution of delamination failure significantly influenced the final failure shape of the specimens through the high‐velocity camera. Microscopic observations indicated that carbon fiber yarns and aramid fiber yarns exhibited different fracture modes.Highlights An experimental design method applicable to woven composites in dynamic tests. Negative correlation between strength and strain rate of hybrid composites. The validity of the nonlinear constitutive model to dynamic property. The effect of hybridization and strain rates on damage modes.

Finite Element Modeling and Experimental Validation of AA 5052-H34 Machining: A Comprehensive Study on Chip Morphology and Temperature Analysis

An understanding of the dynamic behavior of materials plays a crucial role in machining improvement. According to the literature on this issue, one of the alloys whose dynamic behavior has been investigated less is AA 5052-H34, despite its numerous industrial applications. Using finite element (FE) modeling greatly reduces machining research costs. This research delved into the dynamic behavior modeling of AA 5052-H34 during dry-turning FE simulation. The dynamic behavior of AA 5052-H34 was achieved using the Johnson–Cook (J-C) constitutive equation, which was calculated using the uniaxial tensile and Split-Hopkinson pressure bar (SHPB) tests. To confirm the accuracy of the material model, these SHPB tests were then simulated in Abaqus. The J-C constitutive equation, paired with a J-C damage criterion, was employed in a chip formation and cutting temperature simulation. It was found that the feed rate significantly influences the dynamic behavior of AA 5052-H34. The thickness and morphology of the chip were investigated. The experimental and numerical chip thicknesses showed a direct relationship with the feed rate. The simulation temperature was also analyzed, and, as expected, it showed an upward trend with increasing cutting speed and feed rate. Then, the accuracy of the proposed FE simulation was confirmed by the agreement of the experimental and simulation results.

Strain rate effect of concrete based on split Hopkinson pressure bar (SHPB) test

Concrete is a strain rate sensitive material, which is widely used in protective structures, and its strain rate effect needs to be considered. This study aims to obtain the real strain rate effect of concrete material. Firstly, the dynamic compression test of concrete was carried out by using split Hopkinson pressure bar (SHPB). The classical Holmquist-Johnson-Cook (HJC) model of concrete is modified based on the test results and the test data of the static performance of concrete. Then the finite element model is established. The numerical simulation results and theoretical analysis show that the inertia effect leads to the error between the test value and the simulation value. To eliminate the influence of inertia effect, this study embeds the inertia effect term into the constitutive model for secondary modification. According to the results of numerical analysis, the specific form of this term and its related parameters are determined. The modified constitutive model can better predict the test results and reproduce the damage morphology of concrete under impact load.