Significant Strain Rate Sensitivity Research Articles

Effect of strain rate and temperature on dynamic compressive behavior of HfBeTiZrCuNi high entropy bulk metallic glass

This study investigated the high-temperature dynamic mechanical properties of Hf-based high entropy bulk metallic glass (HE-BMG). Uniaxial dynamic compressive tests of Hf-based HE-BMG were conducted at elevated temperatures (from 298 to 800 K) under a high strain rate (from 1000 to 5000 s−1) by a split Hopkinson pressure bar (SHPB) device with a high-temperature system, and the failed specimens were analyzed in terms of microstructures and fracture modes. The dynamic test results show that the maximum compressive stress and the total strain decrease with increasing strain rate and temperature, exhibiting significant strain rate and temperature sensitivity. Three different fracture modes were observed with increasing strain rates, while heating the temperature could promote the transition process of the fracture modes. When the adiabatic or heating temperature reaches above the crystallization temperature, the embrittlement caused by metallic glass crystallization makes the fracture mode change. The mechanical behavior of Hf-based HE-BMG at high temperatures and high strain rates could be attributed to the combination of adiabatic heating and embrittlement.

Synergistic effect of microfibers and oriented steel fibers on mechanical properties of UHPC

The study introduces a novel approach to enhance the properties of Ultra-High Performance Concrete (UHPC) through multi-scale synergistic reinforcement using microfibers (0.66 mm) and oriented steel fibers (13 mm). Various aspects were investigated, including rheological properties, fiber orientation, and fiber pull-out characteristics. Besides, quasi-static mechanical properties and dynamic compressive properties of UHPC were tested and the bending failure was monitored by acoustic emission technique. Experimental results showed that microfiber improved mechanical properties of UHPC matrix and enhanced the fiber-matrix interface. Compressive strength, flexural strength, and toughness of specimens were increased by as high as 25 %, 78 %, and 55 %, respectively, when microfiber was mixed with oriented steel fibers. In terms of dynamic impact performance, UHPC exhibited significant strain rate sensitivity, and microfibers blended with oriented steel fibers resulted in complete damage pattern when subjected to impact loading, and dynamic compressive strength and energy absorption increased by 48.5 % and 54.8 %, respectively. Therefore, oriented steel fibers coupled with microfibers provide an effective method to enhance the mechanical performance of UHPC.

Dynamic splitting behavior of microcapsule-based self-healing cementitious composites under SHPB impact loading

This study presents an experimental study on the dynamic splitting tensile performance of microcapsule-based self-healing cementitious composites and fiber-reinforced microcapsule cementitious composites. The research aims to determine the effect of microcapsule dosages, fiber types, and strain rates on the dynamic splitting tensile behavior of materials. A total of 99 specimens were subjected to the split Hopkinson pressure bar (SHPB) impact loading within the strain rates of 0.85–17.12 s−1. A high-speed camera was employed to capture the crack propagation process, and scanning electron microscopy (SEM) was used to characterize the corresponding microstructure. The results indicated that the splitting tensile performance of materials exhibits significant strain rate sensitivity. The addition of microcapsules increases the dynamic splitting tensile strength of the material, and the highest energy absorption capacity can be achieved with a 5 % microcapsule dosage. The incorporation of polyvinyl alcohol (PVA) and polyethylene (PE) fibers effectively enhances dynamic splitting tensile strength and energy absorption capacity, achieving optimal performance with the incorporation of PVA-PE hybrid fibers. Furthermore, the investigation of the dynamic increase factor (DIF) of the material indicates that fibers heighten the strain rate sensitivity of the material.

Simultaneous influence of strain rate and moisture on the anisotropic mechanical behavior of direct compounded compression molded PA6/Glass LFTs

Fibre-reinforced polymer composites are an increasingly critical long-term solution for lightweighting the transportation sector, therefore, a comprehensive understanding of their mechanical behavior under varying environmental conditions and loading rates is critical. This study investigated the tensile properties and behavior of a direct-compounded compression-molded Polyamide6 (PA6)/glass long fibre thermoplastic (LFT-D) material, specifically examining the influence of moisture content and intermediate tensile loading rates, up to 150 s−1. This range is of significance to the transportation industry and is highly desirable for engineering design since data in the current literature is limited. Dried and undried samples were also examined at four distinct material orientations: 0°, +45°, ˗45°, and 90°. The results confirmed that moisture presence significantly altered the mechanical properties of PA6/Glass LFT material under quasi-static loading rates; in contrast, its effects were negligible under dynamic loadings. Notably, the material exhibited significant strain rate sensitivity within the range of 0.0001 s−1 to 150 s−1. In the 0° material direction, with higher fibre orientation distribution, the undried materials demonstrated a substantial increase of 93% in Young's modulus and 172% in ultimate tensile strength while the complementary dried samples displayed increases of 76% and 97%, respectively. Tensile strength reached 293.8 MPa and 276.7 MPa for undried and dried samples, respectively, in this particular material direction. However, the strain at failure remained consistent at approximately 4% for undried samples and 3% for dried samples, resulting in an increase in tensile toughness by 292% (up to 6.9 MPa) for undried samples and 114% (up to 4.7 MPa) for dried samples.

Microstructure and Mechanical Behavior Comparison between Cast and Additive Friction Stir-Deposited High-Entropy Alloy Al0.35CoCrFeNi.

High-entropy alloys (HEAs) are new alloy systems that leverage solid solution strengthening to develop high-strength structural materials. However, HEAs are typically cast alloys, which may suffer from large as-cast grains and entrapped porosity, allowing for opportunities to further refine the microstructure in a non-melting near-net shape solid-state additive manufacturing process, additive friction stir deposition (AFSD). The present research compares the microstructure and mechanical behavior of the as-deposited AFSD Al0.35CoCrFeNi to the cast heat-treated properties to assess its viability for structural applications for the first time. Scanning electron microscopy (SEM) revealed the development of fine particles along the layer interfaces of the deposit. Quasi-static and intermediate-rate compression testing of the deposited material revealed a significant strain-rate sensitivity with a difference in yield strength of ~400 MPa. Overall, the AFSD process greatly reduced the grain size for the Al0.35CoCrFeNi alloy and approximately doubled the strength at both quasi-static and intermediate strain rates.

Impact Resistance of Rubberized Alkali-Activated Concrete Incorporating Recycled Aggregate and Recycled Steel Fiber

Alkali-activated concrete (AAC) features excellent mechanical properties and sustainability. The incorporation of crumb rubber (CR), recycled concrete aggregates (RCAs), and recycled steel fibers (RSFs) can further enhance environmental sustainability. This paper mainly investigated the dynamic behaviors of a novel rubberized AAC incorporating RCAs and RSFs (RuAAC) through Split-Hopkinson Pressure Bar (SHPB) tests. The variables included three types of RSF content (1%, 2% and 3%), five types of rubber content (0%, 5%, 20%, 35% and 50%) and five impact pressures (0.5 MPa, 0.6 MPa, 0.7 MPa, 0.8 MPa and 0.9 MPa). Dynamic stress–strain curves, dynamic strength, the dynamic increase factor (DIF), impact toughness and the synergistic effects of RSF and CR were discussed. The results show that increasing RSF and CR contents could improve the impact resistance of RuAAC under impact loading. The RuAAC exhibited significant strain rate sensitivity, and the sensitivity increased with larger contents of RSF and CR. The increase in strain rate sensitivity was more pronounced with higher CR contents, which was reflected in larger dynamic increase factor (DIF) values. Under high impact pressure, the impact toughness was obviously enhanced with higher RSF contents, while the contribution of increased CR content to impact toughness was not apparent, which may be attributed to the fact that this study only calculated the integral under the dynamic stress–strain curve before the peak stress to determine impact toughness, neglecting the potential contribution of CR particles after the peak point. The obvious strain sensitivity exhibited by the RuAAC in the SHPB tests indicated superior impact performance, making it particularly suitable for architectural structures prone to seismic or explosive impacts.

Strengthening mechanisms and microstructural evolution of medium manganese steel under dynamic and static loading

The study analyzes the deformation strengthening mechanisms of medium manganese steel under dynamic and static loading conditions. Different austenite volume fractions (7.4 %, 19.1 %, 30.9 %, 37.7 %) were obtained by varying the heat treatment temperatures (640 °C, 660°C, 680 °C, 700 °C). Results show a linear increase in austenite volume fraction with higher annealing temperature, while carbon content in austenite decreases. Yield strength initially decreases and then increases with annealing temperature. The mechanical properties of all four temperature-tested steels show a clear strain rate dependence in the high strain rate range, with strength increasing with strain rate. Quasi-static conditions no significant strain rate sensitivity. 680 °C test steel's quasi-static deformation is mainly governed by the transformation-induced plasticity (TRIP) effect and dislocation slip in body-centered cubic (bcc) crystals. Dynamic deformation after a strain of 0.14 shows a weakened TRIP effect, and dislocation strengthening in bcc crystals becomes dominant despite a large amount of untransformed austenite. During quasi-static deformation, 700 ℃ test steel exhibits strain hardening due to the TRIP effect at low strains and significant dislocation strengthening in bcc crystals at high strains. Although the TIRP effect is initially suppressed during dynamic deformation, it lasts for a long time. The combined effects of the TRIP effect and martensite dislocation strengthening determine the deformation strengthening mechanisms. Additionally, an optimized Voce model with strain rate strengthening term is proposed. It can well describe the mechanical behavior under dynamic strain rate.

Dynamic compressive behavior of high-strength engineered geopolymer composites

As a low-carbon geopolymer material, Engineered Geopolymer Composite (EGC) possesses high tensile ductility, holding tremendous potential for structural construction and reinforcement. However, the dynamic behavior of EGC has not been fully explored. In this study, the effect of various fiber lengths (6 mm, 12 mm, 18 mm) on the dynamic compressive response of EGC was investigated by Split Hopkinson Pressure Bar (SHPB) test. The findings indicated that as the fiber length increases, the workability and compressive strength of EGC decrease, while the tensile strength improves. In comparison to geopolymer matrix, EGC specimens exhibited a more significant strain rate sensitivity under impact loading, and fiber length had a notable effect on strain rate sensitivity. By adjusting the length of incorporated fibers, it was observed that EGC with 12 mm fibers demonstrated the highest dynamic compressive strength and dynamic increase factor (DIF), along with superior energy absorption capability. A modified CEB-FIP model was proposed to describe the dynamic behavior of high-strength EGC. The proposed model for DIF provides valuable guidance for optimizing EGC design and application.

Effect of B4C particle size and TiB2 content on the mechanical properties of B4C composites and their dynamic mechanical properties

AbstractB4C–MAS and B4C–TiB2–MAS ceramic composites were prepared by hot pressed sintering. The effects of particle size of B4C and TiB2 content on the microstructure and general mechanical properties of the ceramic composites were investigated by using X‐ray diffractometer, scanning electron microscope, and universal testing machine. The strengthening and toughening mechanism of ceramic composites is mainly attributed to the addition of magnesium–aluminosilicate (MAS) and thermal mismatch effect of TiB2. When the TiB2 content was 20 wt.%, the bending strength, fracture toughness, and Vickers hardness of B4C–TiB2–MAS ceramic composites were 375 MPa, 4.42 MPa·m1/2, and 23.9 GPa, respectively, and its relative density could reach 99.7%. The dynamic mechanical properties of B4C–TiB2–MAS ceramic composites were investigated at strain rates of 2000–6000 s−1 using a Separate Hopkinson Pressure Bar (SHPB) device. The results showed that the B4C–TiB2–MAS ceramic composites exhibited significant strain rate sensitivity. The dynamic compressive strength of the ceramic composites increased from 4634 to 5734 MPa with increasing strain rate in the tested strain rate range.

Study on dynamic mechanical properties and meso-damage mechanism of carbon fibers recycled aggregate concrete under freeze-thaw environment

The uniaxial compression mechanical properties tests of carbon fibers recycled aggregate concrete (CFRAC) were carried out in order to investigate the effect law of coupling freeze-thaw cycles (FTCs) and dynamic strain rates on the mechanical properties of CFRAC. Two cases of carbon fibers (CFs) doping of 0% and 0.3% were considered. The full CFRAC uniaxial compressive stress-strain curves at different strain rates (10−5/s, 10−4/s, 10−3/s, 10−2/s) after different FTCs (0, 50, 100) were obtained. The microscopic characteristics and microcrack propagation process of the specimens were analyzed by means of nuclear magnetic resonance (NMR), scanning electron microscope (SEM) and acoustic emission (AE). The results showed that the specimens still had significant strain rate sensitivity after FTCs. With the same amount of CFs doping and strain rate, the strength and elastic mode (E) of the specimens kept decreasing as the number of freeze-thaw cycles (N) increased. With the same N, the strength and E of the specimens increased and the deformation capacity decreased as strain rate increased. With the addition of 0.3% CFs, the frost resistance and crack resistance of the specimens were significantly enhanced. Combined with the statistical damage constitutive model, the influence of FTCs and dynamic strain rates coupling on the meso-damage mechanism of CFRAC was analyzed. The meso damage evolution process was characterized by five characteristic parameters E0, εa, εh, εb and H. The results showed that there was an obvious regularity between the change of characteristic parameters and CFs content, dynamic strain rate and the N. An effective link between the fine-scale damage mechanism and the macroscopic nonlinear intrinsic behavior was established. The phenomenon of AE signal lag in uniaxial compression was explained from the perspective of effective stress.

Dynamic deformation behaviors and mechanisms of CoCrFeNi high-entropy alloys

Due to their unique microstructures and chemical compositions, high-entropy alloys (HEAs) exhibit remarkable mechanical properties, such as high strength, excellent ductility and good thermal stability. However, to date, there have been limited studies on the dynamic behaviors of HEAs. Here, we systemically investigated the mechanical behaviors and deformation mechanisms of CoCrFeNi HEAs and their connections under dynamic loading by combining mechanical tests and molecular dynamics simulations. Compressive testing on polycrystalline CoCrFeNi HEA samples at different strain rates showed that both yield and flow stresses increase with strain rate and exhibit a significant strain rate sensitivity due to solid solution strengthening and lattice distortion of the HEA. The strain rate sensitivity of the CoCrFeNi HEA transitions from 0.010 at low strain rates (5.0×10−5–2.5×103 s−1) to 0.333 at high strain rates (2.5×103–6.5×103 s−1). Large-scale molecular dynamics simulations further revealed that this transition is related to the plastic deformation mechanism transition from dislocation nucleation and slip at low strain rates to massive dislocation nucleation and drag at high strain rates. Furthermore, the CoCrFeNi HEA exhibited a remarkable strain-hardening capability at high strain rates, which originated from the formation of primary and secondary nanoscale twins and twin-twin and twin-dislocation interactions. Our current study sheds light on the plastic deformation mechanisms of HEAs under dynamic loading, providing guidance for the design and fabrication of HEAs with excellent dynamic mechanical properties.

Investigation of mechanical behavior, constitutive modeling, and fracture criteria for as-cast Al0.3CoCrFeNi high entropy alloy

High entropy alloys (HEAs) have garnered significant attention in recent years, primarily focusing on alloying design and thermal processing. The objective of this study was to investigate the mechanical response of Al0.3CoCrFeNi, a representative HEA, under various stress states, temperatures, and strain rates, aiming to establish its constitutive equation and fracture criteria. Employing a hybrid FEM/EX approach, the constitutive behaviour of the alloy was characterized using the modified Johnson-Cook (MJC) model, while the fracture properties were assessed using the Hosford-Coulomb (HC) equation. Experimental findings highlighted the remarkable tensile strength (578.1 MPa) and ductility (69%) of the as-cast Al0.3CoCrFeNi at room temperature. However, at elevated temperatures ranging from 400 °C to 650 °C, a reduction in ductility was observed, accompanied by serration behaviour. Notably, precipitation hardening was detected at 800 °C, indicative of strengthening through precipitate formation. Additionally, Al0.3CoCrFeNi exhibited significant strain rate sensitivity and a positive strain rate effect, emphasizing its dynamic response under different loading conditions. The accuracy of the constitutive model and fracture criteria was validated through the examination of deformation and fracture modes in Taylor impact tests. The MJC model demonstrated predictions within a 10% deviation from experimental data, while the HC fracture criterion, accounting for stress triaxiality and Lode parameters, effectively predicted shear fracture in the projectiles. Crack formation in the projectiles resulted from a combination of tension and shear, followed by propagation at a 45° angle under combined compression and shear loading. This comprehensive study enhances understanding of the mechanical properties of Al0.3CoCrFeNi, providing valuable insights for its application in engineering, particularly in impact protection.

Effect of temperature and strain rate on quasi-static and dynamic compressive behavior of forged CrMnFeCoNi high entropy alloy

The equiatomic CrMnFeCoNi high entropy alloy (HEA) has attracted much attention due to the superior ductility. However, as a face-centered cubic (FCC) single-phase solid solution, the as-cast CrMnFeCoNi HEA is limited in many applications because of the low strength. The aim of this work is to improve the mechanical properties of CrMnFeCoNi HEA by forging. The forged CrMnFeCoNi HEA was prepared and the effect of temperature and strain rate on the deformation behavior and mechanism under quasi-static and dynamic compression was investigated. After hot forging, CrMnFeCoNi HEA still maintained FCC single-phase structure, the average grain size reduced to ∼40 μm, the distribution of elements was more uniform, and some defects were introduced into the material. The quasi-static (1 × 10−3 s−1) and dynamic (2 × 103, 7 × 103 and 1 × 104 s−1) compression tests of forged CrMnFeCoNi HEA were performed at temperatures ranging from −196 °C to 950 °C. The material exhibited excellent compressive strength and great plasticity, and showed significant temperature sensitivity and strain rate sensitivity of the yield strength. When the strain rate was up to 1 × 104 s−1, the yield strength was ∼1076 MPa at −100 °C and ∼80% higher than that under quasi-static compression. The strain hardening rate increased with the decrease of temperature under both quasi-static and dynamic conditions, while strain rate sensitivity was exhibited only at high temperatures. Discontinuous dynamic recrystallization (DDRX), continuous dynamic recrystallization (CDRX) and twinning-induced dynamic recrystallization (TDRX) were activated during hot compressions. DDRX was activated when the strain rate was low, and CDRX and TDRX were strengthened with the increase of strain rate. The influence of strain rate and temperature on the deformation mechanism was investigated. Low temperature and high strain rate were conducive to the formation of deformed twins.

Effect of shear thickening gel on microstructure and impact resistance of ethylene–vinyl acetate foam

To satisfy the ever-increasing demand for better anti-impact performance of personal protective equipment, a composite foam by incorporating shear thickening gel (STG) with ethylene–vinyl acetate (EVA) was developed. The superiorities of EVA foam in softness, lightness and flexibility were maintained in the novel material. The microstructure of STG/EVA composite foam was characterized using Scanning Electron Microscope. A series of experimental approaches including Dynamic Mechanical Analysis test, compression test, Split Hopkinson Pressure Bar test and drop hammer test were applied to study the material properties at different strain rates. Attributed to the shear thickening property of STG, STG/EVA exhibited significant strain rate sensitivity. The results showed that STG/EVA foam possessed better mechanical performance than plain EVA foam. In the ballistic test, the body armor consisting of the STG/EVA buffer layer possessed better protective performance than the regular one. The improvement mechanism was interpreted with micromorphological changes before and after tests. The introduced STG reinforced the integrity and continuity of microstructure to enhance the capability of the composite material in absorbing and dissipating impact energy. Therefore, the application prospect of the developed STG/EVA foam in personal protective equipment is promising.

Comprehensive modification of emulsified asphalt on improving mechanical properties of crumb rubber concrete

The surface modification of crumb rubber concrete (CRC) by the emulsified asphalt (EA) is presented in this paper. The effect of different EA contents on the mechanical properties of CRC (the fine aggregate was replaced with 5%, 10% and 15% rubber by volume) was studied. Several tests, including the static mechanical experiments of compression, bending, splitting tensile and three-point bending, the dynamic mechanical experiments of the split Hopkinson pressure bar (SHPB) and the micro-analysis of the digital image correlation (DIC) test and SEM image, were carried out to compare with CRC modified by NaOH. The tests depict that CRC modified by EA demonstrates better mechanical properties, such as the higher compressive strength, the higher splitting tensile strength, the more significant strain rate sensitivity at high strain rates, the lower the elastic modulus (Ec) and the bending modulus (Eb). The better modified effects can be attributed to the better interfacial bonding surface between the cement matrix and the rubber particles and the fewer stress concentrations than that of NaOH modification. The modification of CRC by EA can be regarded as a better synergistic method to bring advantages of CRC into full play.

High strain rate compressive behaviour of 6000-series aluminium alloy sheet under SHPB impact loading

High velocity forming technologies are widely used in manufacturing industries to improve the formability of the aluminum alloy sheets. In order to better control the high velocity forming technologies through numerical simulation, the dynamic compression properties of the thin 6000-series aluminum alloy sheet were investigated by SHPB experiments. The influence of strain rate on the mechanical properties is analyzed in detail. Results show the elastic modulus is independent of the strain rate. However, under high strain rate condition, the yield stress, ultimate compression strength and ductility enhance with the increased high strain rate. So this 6000-series aluminum alloy sheet has significant strain rate sensitivity. As a reference, the quasi-static uniaxial tension test is also carried out and the uniaxial compressive stress-strain data in the literature is also listed. However, it is found the quasi-static uniaxial tensile yield stress is larger than the uniaxial compressive yield stress, and the quasi-static uniaxial compressive yield stress is lower than that under dynamic compressive condition. Results prove the aluminum alloy has obvious tension-compression anisotropy. For the high velocity forming technologies that take stretching as the main deformation mode, the dynamic tensile behaviour, instead of the dynamic compressive behaviour, should be used for accurate simulation.

Silicone rubber matrix composites with shear thickening fluid microcapsules realizing intelligent adaptation to impact loadings

In this paper, silicone rubber matrix composites with shear thickening fluid microcapsules (SR-STF) with intelligent adaptation to impact loadings are fabricated for advanced impact protective structure. The composites exhibit more flexibility at low strain rates but higher stiffness at high loading rates, indicating significant strain-rate sensitivity. In addition, the initial flexibility and the strain-rate sensitivity of the composite increase with increasing the mass fraction of the STF microcapsules, which should be ascribed to the shear thickening and compressive jamming of the STF microcapsules in the composite during impulse loadings. Based on experimental results, a hyper-viscoelastic constitutive model is developed, in which the influence of the mass fraction of STF microcapsules, the strain-rate sensitivity, and the strain-hardening effect are taken into account. The paper develops a practical strategy for applications of STF in soft protective structures and provides a reliable prediction of the dynamic mechanical behavior of the SR-STF composites.

Deformation and fracture behavior in TRIP steels under static and dynamic tensile conditions

The present study sought to explore the deformation and fracture behavior of Quenching and Partitioning (Q&P) steel at five different strain rates (10−4 s−1, 1 s−1, 10 s−1, 100 s−1 and 1400 s−1). Tensile tests were carried out on Q&P steel at different strain rates, and the deformation and fracture behaviors were explored through digital image correlation (DIC) and scanning electron microscope (SEM). The results indicated that the strength and plasticity of Q&P steel had significant strain rate sensitivity. The yield strength and ultimate strength increases continuously, whereas the elongation first decreased and then increased with increase in strain rate. The dimples gradually became smaller and flatter with increase in strain rate. The dislocation density increased when strain rate was above 100 s−1, indicating that resistance to dislocation slip increases and the slip distance becomes shorter at high strain rates, which inhibits generation of large deformation. The local plastic strain at the fracture significantly decreased from 0.7 to 0.3, resulting in partial brittle fracture characteristics in fracture morphology. These findings provide a basis for further elucidating the deformability and fracture behavior of Q&P steel at different strain rates.

Characteristics of 3D-printing ultra-high performance fibre-reinforced concrete under impact loading

3D-printing concrete exhibits anisotropy under static loads, owing to its unique additive manufacturing process, while its dynamic performance study is still insufficient. In particular, the dynamic properties of 3D-printing ultra-high performance fibre reinforced concrete (3DP-UHPFRC) have not been studied yet. Therefore, this study explores the characteristics of 3DP-UHPFRC under impact loads using the SHPB tests. Three impact velocities of 3.886, 6.026, and 8.538 m/s were studied in the tests. The impact process was recorded by a high-speed camera. The dynamic mechanical characteristics of 3D-printing ultra-high performance concrete (3DP-UHPC) without fibre, 3DP-UHPFRC and reference specimens were investigated in terms of fibre type, fibre content, preparation method, loading direction, and impact velocity. The characteristics of strain rate, dynamic compressive stress, dynamic increase factor (DIF), energy absorption capacity and failure process were evaluated. The findings of this study indicated that the degree of failure of 3DP-UHPC was similar in all directions, while the degree of failure of 3DP-UHPFRC in all directions was different. The degree of failure in the X-direction was the worst, followed in decreasing order by the degrees of failure in the Y- and Z-directions. At the same impact velocity, the elastic modulus and strain rate effect of the 3D-printing specimens exhibited anisotropic characteristics, owing to the different elastic modulus of the 3D-printing specimens in each direction. Furthermore, the specimens were more susceptible to deformation in the X-direction than that in the Y- and Z-directions. As the impact velocity was increased, the dynamic peak stresses for 3DP-UHPFRC were isotropic at the same impact velocity, owing to the strain rate effect. Finally, the DIF of the 3D-printing specimens was observed to be anisotropic, and in the X-direction the specimens exhibited the most significant strain rate sensitivity.

Dynamic Mechanical Behavior and Microstructure of the Al0.1CoCrFeNiTix High‐Entropy Alloys

The effects of the microstructure and the strain rate on the compression behavior of the Al0.1CoCrFeNiTi x (x = 0.1, 0.3, and 0.5 in molar ratio) high‐entropy alloys (HEAs) are investigated. Compared with the Al0.1CoCrFeNiTi0.1 with the single‐phase face‐centered cubic (FCC) structure and the Al0.1CoCrFeNiTi0.3 HEAs, both the yield strength (YS) and the work hardening ability of the Al0.1CoCrFeNiTi0.5 HEA are enhanced significantly under the quasistatic condition. This is due to a combination of the solid‐solution strengthening and sigma‐phase precipitation hardening mechanisms. The strong work hardening of the Al0.1CoCrFeNiTi0.1 HEAs under quasistatic loading is attributed to the existence of the dislocation substructures (high‐density dislocation walls and dislocation cells) and the deformation twinning accompanying homogeneous deformation. A significant strain rate sensitivity on the YS is obtained as a result of the phonon drag effect under dynamic loading. Different from the quasistatic condition, the dynamic grain refinement and the nanoscale twins inside the grains are the main microstructure characteristics in the dynamic deformation process.