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2023 Vol. 44, No. 6
Published: 2023-12-28
699
Research progress on dynamic behavior of medium/high entropy alloys
Medium/high entropy alloys are a class of multi-principal alloys proposed in the last two decades, which are totally different from the traditional alloy design idea with only 1-2 principal elements. Medium/high entropy alloys show excellent mechanical properties under both quasi-static and dynamic conditions due to their unique composition design, as compared to the traditional metals such as aluminum alloys, titanium alloys and steels. In this review, research progress on dynamic properties, including dynamic shear properties, Charpy impact properties, dynamic spalling strength, and self-sharpening during penetration) of medium/high entropy alloys, is first introduced. Then, the microstructural deformation mechanisms on the dynamic response of medium/high entropy alloy are presented. Moreover, research progress on temperature effects and shear banding in medium/high entropy alloy is introduced. Finally, the future perspective on the application of medium/high entropy alloys in the fields of impact dynamics is presented.
2023 Vol. 44 (6): 699-717 [
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718
Research Progress in Mechanical Properties Characterization and Mesoscopic Optimal Design of Additively-Manufactured 3D Microlattice Materials
Three-dimensional microlattice material is a kind of ultra-lightweight structural material composed of complex topological cells arranged periodically, which combines extremely low density, superior mechanical properties and excellent energy absorption capacity. Accordingly, it becomes an important novel strategic material to meet the requirements of lightweight, impact resistance and multifunctional integration. The rapid development of additive manufacturing technology has brought convenient conditions for the fabrication and optimal design of three-dimensional microlattice materials. The combination of microlattice design and additive manufacturing provides new ideas for the realization of lightweight and multifunctional integration of protective structures in aerospace, rail transit, weapons and other fields. In order to clarify the dynamic mechanical properties and deformation mechanism of additively-manufactured 3D microlattice materials, further carry out multi-scale optimization design of these materials, and expand their application in the field of impact protection, the research results of mechanical behavior and design of additively-manufactured 3D microlattice materials were systematically reviewed and prospected. According to the multi-scale structure characteristics of additively-manufactured 3D microlattice materials, comments on the macroscopic dynamic response and collapse mechanism, mesoscopic properties characterization and structural optimization design, microscopic structural characteristics as well as deformation mechanisms of different microlattice materials were presented. Some prospects on the future problems and challenges of additively-manufactured 3D microlattice materials in the field of impact protection were pointed out.
2023 Vol. 44 (6): 718-754 [
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Evolution mechanisms of deformation microstructure in CoCrNiSi0.3C0.048 medium entropy alloy under high velocity Taylor impact
Taylor impact test was carried out for CoCrNiSi0.3C0.048 medium entropy alloy (MEA), and a wide range of strain and strain rates with gradient distribution in the alloy was introduced. The strain and strain rate-dependent gradient microstructure distribution characteristics and evolution mechanism were investigated. With the increase of strain and strain rate, the evolution process of the primary Cr23C6 carbides is mainly the increase of cracks, crack branching and crack width. For the secondary Type-Ⅰ SiC precipitates, the evolution process is mainly the formation and propagation of cracks. However, the tertiary Type-Ⅱ SiC precipitates are mainly gradual intensification of the dislocation - bypass mechanism. In the FCC matrix, the interaction among dislocation, twins, and three-level hierarchical precipitates is intensified with the increase of strain and strain rate.
2023 Vol. 44 (6): 755-770 [
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771
Dynamic mechanical responses and microstructural evolution of DZ2 axle steel under medium strain-rate tension loading
Impacts at low velocity is one of the typical operation conditions that the domestic axle for high-speed trains always suffers. Understanding the mechanical response and deformation-damage behavior of the axle under this condition is of significant importance for the designing and maintenance of the axle. This paper analyzed the tensile mechanical properties and microstructural evolution of the DZ2 axle steel within the medium strain rate range (0.1~100 s-1) at room temperature. The plastic deformation and fracture mechanisms of the DZ2 axle steel had been revealed, and the Zerilli-Armstron constitutive model which could accurately describe the dynamic response behavior of the axle steel was proposed. The experimental results showed that the dislocation motion and ductile fracture were the plastic deformation and failure mechanisms of the DZ2 axle steel under the tensile deformation process. However, the dependence of the strength on the strain rate varied with the increasing strain rate. When the strain rate was below 10 s-1, a small number of the dislocations were generated. The resistance to dislocation movement was low, and in consequence, the strength of DZ2 axle steel would not be apparently enhanced with the increase of strain rates. The DZ2 axle steel exhibited low strain rate sensitivity. When the tensile deformation was carried out at the strain rate extended 10 s-1, the mobile dislocation density in the axle steel increased substantially. Because the velocity of dislocation slipping was very fast, the short-range interaction of dislocations was enhanced significantly. In this case, the tensile deformation resistance of DZ2 axle steel became more and more stronger with the increasing strain rate, leading to a remarkable strength dependence of DZ2 axle steel on the strain rates. Its strain rate sensitivity became pronounced. Compared the experimental one, it was found that the simulation date by the proposed Zerilli-Armstron constitutive relation had high related coefficient and low average absolute relative error, indicating the applicability in predicting the dynamic mechanical properties of DZ2 axle in the intermediate tensile strain rate range. All abovementioned results could provide support for the operational safety assessment of the domestic DZ2 axle.
2023 Vol. 44 (6): 771-781 [
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782
Johnson-Cook Constitutive Model and Failure Parameters of Al-based energetic structural material
The static and dynamic mechanical properties of Al-based energetic structural material at different temperatures were obtained by universal testing machine and Hopkinson bar. The validity of the dynamic experiment is verified by using the stress balance factor. Results show that the alloy is a brittle material with tension-compression symmetry. By analyzing the compression experimental results, the effects of temperature and strain rates on the mechanical properties were discussed, and the Johnson-Cook constitutive model of the alloy were established. The specimens with different notch sizes were designed, and the relationship of failure plastic strain with stress triaxiality were obtained by the two-dimensional digital image correlation (DIC) method. Based on the tensile experimental results and fracture morphology analysis, the parameters describing the relationship of failure plastic strain with strain rate and temperature in Johnson-Cook failure model were obtained. The empirical linear relationship between particle velocity and stress wave velocity of the material was acquired by planar impact experiments. Based on the constitutive model and the equation of state (EOS) of the alloy, impacts of the Al-based energetic structural material on multilayered thin steel targets were analyzed numerically. When the projectile made of Al-based energetic structural material impacts a multilayer steel target with 1800m/s, the central perforation diameter of the first, second and third target is 7.9mm, 24.5mm and 10mm, the error between numerical simulations and experiments is 1.3%, 5.8% and 5.3% respectively. The diameter of the spreading area of the crater on the second target is about 61mm, and the maximum dispersion diameter of fragments on the third target is 50mm, the error between numerical simulations and experiments is 7.0% and 8.7% respectively. The shallow pits with an average size of 8mm on the fourth target can be observed by numerical simulations, which is consistent with the experimental results. When the impact velocity increased to 2200m/s, the damage of the target in numerical simulation is similar to the experimental results. The Johnson-Cook constitutive model and failure parameters could be used in numerical simulation to study the hypervelocity impact mechanism of the Al-based energetic structural material.
2023 Vol. 44 (6): 782-794 [
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795
Failure Modes and Damage Mechanisms of Lithium Batteries under Repeated Impact
Lithium-ion batteries are widely used in electric vehicles due to their superiority of high energy density. However, the number of fire and explosion accidents of electric vehicles equipped with lithium-ion batteries has increased sharply in recent years because of the structural damages of the batteries in crashes. And repeated impact is a common scenario for lithium-ion batteries in service. Such cumulative damage may ultimately lead to short-circuit failure of the batteries or pose a potential long-term safety risk. To investigate the influence of repeated impact on the failure of lithium-ion batteries, dynamic tests with different energy levels were designed. By combining electrochemical characterization and inspection of the macro and micro damage to the internal structures of the impaired batteries, two failure modes (delayed failure and immediate failure) were discovered and the corresponding failure mechanisms were analyzed, which is revealed to be related to the impact energy. The relationship between battery failure and impact energy, as well as the number of impacts was discussed in detail. And the electrical performance degradation of non-failed batteries was evaluated. The results indicate that the failure of the battery is due to the cumulative damage of the separator, where the extent of separator damage is determined by the energy of single impact loads, corresponding to different failure modes of the battery. Repeated impacts with low energy led to delayed failure, while high energy impacts cause immediate failure. Additionally, the post-test performance decay of the batteries is also revealed to be related to the degree of electrode damage under different impact energy levels. The electrical performance of the battery can significantly deteriorate with the fracture of electrodes. By observing the disassembled battery, we also found that the positive and negative electrodes of the battery exhibit different behaviors after impact, where the negative electrode is more susceptible to the impact damage. These findings provide new perspectives for the reuse and safety assessment of impaired batteries and propose some new insights for the safety design of batteries.
2023 Vol. 44 (6): 795-804 [
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Study on the dispersion law of waveform in an elliptical cylindrical shell chain
2023 Vol. 44 (6): 805-814 [
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Longitudinal Stress Wave Propagations in an Elastic SHPB Specimen and the Resulted Transverse Additional Stress
Using the Rayleigh-Love bar theory which considers the lateral inertia effect, the elastic wave propagations in an elastic specimen under the split Hopkinson pressure bar (SHPB) loading was analyzed. By using the Laplace transform and inverse transform technique, the analytical solutions for deformation, velocity, strain, and stress inside the specimen were obtained. Through numerical calculation, the time histories of the longitudinal stress and the transversal additional stress (TAS) were evaluated for different loading parameters. Calculations show that: near the specimen/incident bar interface, TAS generated by the initial wave loading is the largest, which can reach 12% of the incident wave height; in a majority specimen length, TAS caused by the longitudinal stress wave propagation is 4~6% of the incident wave height; Larger Poisson’s ratio or lower bar/specimen impedance ratio results in higher TAS; the rise time of the incident wave and the aspect ratio of the specimen has little effect on TAS.
2023 Vol. 44 (6): 815-830 [
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831
Characterization of Rate-Dependent Shear Behavior of Electronic Interconnection Conductive Adhesive
The mismatch of force/thermal performance between the chip and packaging substrate during the electronic packaging interconnection, as well as the vibration, drop and impact suffered by the electronic products during the service are easy to cause the shear deformation of conductive adhesive interconnection layer to different degrees and even the adhesive interconnection failure. Effective characterization of the rate-dependent shear behavior of electronic interconnection conductive adhesive is an important foundation of the reliability research on adhesive interconnection packaging structure. The effective acquisition of rate-dependent shear behavior of conductive adhesive interconnection layer is different from that of the traditional metal/alloy materials. In this study, research on the shear test and characterization under different loading rates of the double-shear overlapping copper specimen interconnected with conductive adhesive (50wt.% Ag, 60wt.% Ag) were carried out by the Instron universal material testing machine and split Hopkinson pressure bar device (SHPB), the waveform shaping of SHPB incident wave were performed to ensure the stress equilibrium and uniform deformation state of specimen at constant strain rate within a certain time frame before and after shear failure of adhesive interconnection layer. The shear failure mode of conductive adhesive interconnection specimen under different working conditions and the acquisition method of adhesive interconnection shear strain/strain rate eliminating the elastic deformation effect of overlapping copper were provided. The effects of loading rate and conducting particles on adhesive interconnection shear deformation behavior and shear strength were analyzed. The adhesive interconnection shear strain/strain rate after eliminating the elastic deformation of overlapping copper is relatively small, and the adhesive interconnection shear under different working conditions mainly shows adhesive failure mode. The adhesive interconnection shear strength with lower silver content is relatively higher under quasi-static loading, while opposite under dynamic loading. Research results are of great significance to the efficient application of conductive adhesive in electronic industry and the effective characterization of shear behavior of adhesive interconnection structures.
2023 Vol. 44 (6): 831-842 [
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