Previous studies have found that the nano-polycrystalline diamond (NPD) is harder than single crystal diamond, consequently NPD prepared from graphite has been widely studied. Previous experiments revealed that the NPD originated from graphite contains both homogeneous fine structure and lamellar structure, while the mechanism has not been fully understood. In this work, molecular dynamics simulation was carried out, in which graphite models with different interlayer spacings were built up and compressed. The results showed that the graphite under different compression conditions exhibit different phase transition behaviors, namely, lamellar diamond is obtained under martensite transformation, and fine nanodiamonds without a specific orientation are obtained under diffusive transformation. Under hydrostatic pressure, or, if the slip of the graphite layer is not limited and [002] is the maximum pressure direction, the graphite converts into lamellar cubic diamond; if the maximum pressure is in [210] or [010] direction, the phase transition product is the polycrystalline diamond; if the maximum pressure is in [002] direction, the slip of graphite layers is hindered, the product is a mixture of polycrystalline hexagonal and cubic diamond. The microscopic analysis of atomic motion reveals the formation mechanism of NPD transformed from graphite with homogeneous fine structure and lamellar structure, which is expected to provide insights for large-scale synthesis of superhard NPD.

The effects of pressure on the crystal structure, elasticity, electronic and thermodynamic properties of the new MAX phases Zr₂SeC and Hf₂SeC were investigated by employing the first principle of density generalized function theory. Elastic constants and phonon calculations show that both compounds have stable structure in the pressure range of 0–40 GPa. Unlike most MAX phases, Zr₂SeC and Hf₂SeC are more easily compressed along the a-axis than along the c-axis, and the effect of external pressure on the crystal structure of Zr₂SeC is more significant than Hf₂SeC. Electronic structure calculations show that Zr₂SeC and Hf₂SeC have metallic properties, and the electronic density of states at the Fermi energy level decrease gradually with increasing pressure, thus improving the stability of Zr₂SeC and Hf₂SeC. In addition, the elastic modulus, the Poisson’s ratio and the anisotropy index show an enhancement with increasing pressure. In the pressure range of 0–40 GPa, the elastic modulus of Hf₂SeC is greater than that of Zr₂SeC at the same pressure, indicating that Hf₂SeC has stronger resistance to fracture and deformation than Zr₂SeC at high pressure. Thermodynamic property calculations show that Zr₂SeC and Hf₂SeC have higher melting temperatures in the pressure range of 0–40 GPa.

It is very important that new preparation method of nano-lanthanum oxide is explored in view of the current problems of low purity, poor sinterability, and large molecular gaps. Detonation method was employed to prepare rare earth nano-La₂O₃ powder in this study. La(NO₃)₃·6H₂O was added to the emulsion explosive as a lanthanum source, and the high temperature and high pressure conditions for the synthesis of La₂O₃ were provided by the detonation reaction of the emulsion explosive in a 0.5 kg TNT equivalent vacuum explosion container. The physical phases, morphologies and ingredients of the purified and forged products were characterized by X-ray diffraction (XRD), scanning electron microscope (SEM), Fourier transform infrared spectroscopy (FT-IR), and the powder performances were determined by ultraviolet-visible spectroscopy (UV-Vis), Brunauer Emmett Teller (BET), CO₂-temperature programmed desorption (CO₂-TPD) and O₂-temperature programmed desorption (O₂-TPD). The results show that the forging temperature has a significant effect on the crystalline growth of La₂O₃ powder. Nano-La₂O₃ powder with high ultraviolet light absorption, high purity and good dispersion was successfully produced at a forging temperature of 800 ℃ and a forging time of 3 h. The particle size is in the range of 50－175 nm, and the crystal has a hexagonal structure. The specific surface area of the nano-La₂O₃ is 17.46 m²/g, with a good pore order and concentrated pore size distribution. The nano-La₂O₃ has good adsorption of acid gas and oxygen migration performance. The detonation method applied to the preparation process of nano-La₂O₃ powder provides a new reference for the industrial preparation of nano-La₂O₃.

To explore the flexible measurement technology under low-intensity shock wave, the shock tube calibration experiment was carried out for the polyvinylidene difluoride (PVDF) sensor based on the flexible substrate with an aperture of 8 mm. According to the experimental results, different bonding modes are used to add different thicknesses of damping layer for the PVDF sensor, and the reliability of the sensor was evaluated in terms of the signal pulse width, the sensitivity coefficient and the amplitude of overshoot signal after loading shock waves with different intensities. Then the narrow pulse width shock wave was loaded to verify that the designed sensor can adapt to the measurement of different pulse width shock waves. The experimental results show that adding damping layer can greatly reduce the amplitude of overshot signal and improve the pulse width and frequency response of sensor measurement. STS-400 (single-side thickened sensor-400) under two types of pulse width signal loading obtained better test results, and the relative measurement error is not greater than ±12%. At the same time, it is concluded that PVDF film sensor is more suitable for testing signals with a pulse width of 10 ms or less. The new PVDF sensor designed can provide ideas for measuring explosive shock wave signals.

In order to investigate the tensile mechanical behavior and failure mechanism of polycarbonate (PC) composite reinforced by short glass fibers in different orientations at a wide range of strain rates, the tensile experiments of PC composites with 20% glass fiber content and fiber orientations of 0°, 45° and 90° were carried out at a strain rate range of 0.001－1000 s⁻¹ by using a material test machine, a medium strain rate test machine, and a split Hopkinson tensile bar device. The fractured surface morphologies of the three types of specimens under the stain rate range of 0.001－1000 s⁻¹ were analyzed with scanning electron microscopy. The experimental results showed that PC composites have significant strain rate effects on tensile propertie and failure mechanism. When the loading strain rate increases from 0.001 s⁻¹ to 1000 s⁻¹, the tensile strengths of the specimens contained 0°, 45° and 90° glass fibers are increased by 57.5%, 58.2% and 49.4%, respectively, while the failure strains are increased by 74.1%, 125.1% and 129.1%, respectively. The tensile strength of specimen with glass fiber orientation of 0° is higher than that of the other two types of specimen, while the failure strain is lower than that of the other two types of specimen. Under the strain rate of 0.001 s⁻¹ in quasi-static loading, there are four failure modes of the glass fiber reinforced PC composites: fiber pull-out, fiber fracture, matrix brittle fracture and fiber/matrix debonding. At the high strain rate of 1000 s⁻¹, there are five failure modes: fiber pull-out, fiber fracture, matrix plastic deformation, matrix plastic fracture, and fiber/matrix debonding. The adiabatic temperature rise effect under high strain rate loading leads to a softening of the PC matrix in the glass fiber reinforced PC composite, resulting in a plastic deformation and an increase of matrix/fiber interface adhesion force, which is the main mechanism of the significant increase of the failure strength and failure strain compared with that under quasi-static loading.

In natural evolution, numerous biomaterials exhibit astonishing mechanical properties due to the exquisite coordination of their internal structures at all levels. Carbon fiber, as an excellent artificial material, provides an important raw material support for the design of biomimetic materials. This study uses short carbon fibers and polyurethane as raw materials, combined with a syringe extrusion and thermal evaporation methods to prepare short carbon fiber reinforced polyurethane composite film with specific fiber orientation. Then, a spiral layered structure material resembling mantis shrimp with different interlayer angles was prepared using laminated assembly method. In addition, the mechanical strengthening mechanism of the material was studied by observing its morphology characteristics before and after stretching and measuring its tensile strength. The results show that short carbon fibers have good orientation consistency in thin film materials. When the fiber orientation angle is 45°, the tensile strength of the thin film material is the highest; when the interlayer angle is 30°, the tensile strength of short carbon fiber reinforced polyurethane biomimetic spiral structure material is the highest. The results of this study are of guiding significance for the design and preparation of high-performance short fiber reinforced composite materials, and for achieving their performance biomimetic optimization.

Lightweight cellular I-beams have excellent energy absorption characteristics under external loads. This paper proposes to use cell web instead of solid web to design the I-beam structure of cell web. Based on the combination of square cell, honeycomb cell, concave cell and round cell, and square, honeycomb, concave and circular web openings, the configuration of this paper was designed. The effects of different sibling type and web opening type on compression performance and energy absorption of I-beam were studied by experiments and finite element analysis. The results show that cell types and web hole types have significant effects on the compression performance of I-beam. The ultimate bearing capacity of square cell I-beam is larger, while honeycomb cell I-beam has the best energy absorption characteristics, while circular cell I-beam has poor bearing capacity and energy absorption performance. The negative Poisson’s ratio cell can significantly change the deformation mode of thin-walled I-beam, and the concave cell can effectively inhibit the dislocation extrusion instability trend of I-beam on both sides of the web.

Combining hierarchy with nested, two kinds of circular nested hierarchical multi-cell tubes with different nested methods were designed innovatively. The energy absorption characteristics under axial impact were studied by numerical simulation. The results show that the high-level multi-cell tubes have better energy absorption capacity than the low-level multi-cell tubes, regardless of the same wall thickness or the same mass. Under the same wall thickness, the specific energy absorption and crush force efficiency of high-level multi-cell tubes increased by 22.49% and 16.55%, respectively. Compared with the traditional circular tube, the specific energy absorption and impact efficiency of the multicellular tube were 43.16% and 36.45% higher, respectively. Under the same mass condition, the specific energy absorption and crush force efficiency of high-level multi-cell tubes were increased by 21.04% and 24.47%, respectively. Finally, the crashworthiness of circular nested hierarchical multi-cell tubes was studied systematically by the by used structural parameters such as layer number and wall thickness.

Al₃Ti is characterized by low density and high hardness, however, due to its brittleness, it is prone to fracture under smaller deformation. To improve the application range of Al₃Ti, inspired by biological structures, a biomimetic finite element model was established based on the geometry of shell pearl layer, conch shell and fish scale, and the influences of hard phase shape, as well as impact velocity, were investigated to analyze the fracture resistance mechanism of bionic composites in terms of fracture behavior, crack propagation process and energy absorption effect. A shape coefficient was defined to optimize the structure design. The results show that the shape of the hard phase has a significant effect on the fracture behavior of the bioinspired pearl-like layer specimens under quasi-static condition. The rectangular hard phase can better hinder the crack growth toward the load end, thus improving the load-bearing capacity of the specimen. The specimen with shape factor around 5.0 shows the optimal fracture resistance and energy absorption. Under dynamic impact conditions, the soft phase has increased ability to hinder crack growth, which further improves the fracture resistance and energy absorption effect of the rectangular specimen.

​The dynamic response of aluminum foam-filled sandwich tubes subjected to lateral blast loading was investigated numerically using the dynamic explicit finite element method. Based on numerical simulation, the structural blast resistance was optimized with the core energy absorption and outer tube stiffness as the optimization objectives. The effects of structural geometric parameters, the relative density of the aluminum foam core layer, and blast loading conditions on the deformation patterns and energy absorption properties of aluminum foam-filled sandwich tube have been systematically investigated. The study results indicate that the deformation region of the aluminum foam-filled sandwich tube under lateral blast loading is mainly concentrated in the middle span. Energy absorption occurs through plastic deformation in the middle of the span and bending deformation at the left and right ends of the deformed region for both the inner and outer tubes. In contrast, the energy absorption of the aluminum foam core layer relies primarily on core compression. Reducing of the thickness of the outer tube or the relative density of the aluminum foam core layer can effectively improve the specific energy absorption of the structure and increase the deformation of the inner and outer tubes. The effect of the geometry parameters of the outer tube on the energy absorption properties of the structure and the deformation of the inner and outer tubes is much larger than that of the inner tube. A response surface model is constructed based on the numerical simulation results of aluminum foam-filled sandwich tube. Subsequently, multi-objective optimization is performed and the resulting Pareto front graph is provided. The determination of the wall thickness of the inner and outer tubes, together with the relative density of the aluminum foam core layers in the aluminum foam-filled sandwich tube, can be based on the specific engineering application requirements.

Considering the real irregular geometrical characteristics of ballast and strain rate effect and failure behavior of material, finite element models of ballast impact on equipment cabin bottom plate of high-speed trains was established, and the deflection history response of transverse and longitudinal centerline nodes of equipment cabin front face sheet was analyzed. The history evolution regulation of contact force between equipment cabin bottom plate and ballast was investigated, and the effects of impact velocity, impact angle and ballast shape on impact response and damage behavior of equipment cabin bottom plate were also discussed, the failure mode and damage morphology characteristics of equipment cabin bottom plate under different conditions were analyzed, the relationship between the maximum transient deformation displacement as well as pit depth and impact velocity were quantified. The results show that, under the same impact condition, the maximum transient deformation displacement and pit depth of equipment cabin bottom plate increase with the increase of impact velocity and impact angle separately; the shape and size of maximum deformation zone of front face sheet of equipment cabin, and the area and distribution characteristics of front face sheet damage failure region are closely related to ballast shapes, the most severe damage failure occurs in ellipsoid ballast conditions; equipment cabin bottom plate under different impact conditions shows different degrees of ductile damage, and the larger ballast mass and impact velocity conditions also show tensile tear damage or even slight punching plug phenomenon.

In order to investigate the mesoscale development in the dynamic fracture damage of heterogeneous rocks at the mineral crystal scale, a heterogeneous rock model that can reflect the microstructure characteristics was constructed based on the particle flow code-grain based model (PFC-GBM) method. By establishing the split Hopkinson pressure bar (SHPB) system using finite difference method FLAC^2D and discrete element method PFC^2D, the dynamic impact failure process of heterogeneous rock under different impact loading was simulated and studied. Through the self-compiled Fish language, the number of intragranular and intergranular microcracks in different minerals during the dynamic failure process was grouped and counted. The microscopic evolution process of dynamic fracture damage of heterogeneous rocks was deeply analyzed from a mesoscopic perspective. The research results show that intergranular failure is an important reason for the failure of the dominant heterogeneous rock under the static uniaxial compression condition. Under impact loading condition, the growth process of microcracks within and between crystals of each mineral had four stages: initiation, rapid growth, slow growth and stop growth. Similar to the growth pattern of the number of microcracks under static uniaxial compression condition, the number of intergranular cracks at the initial stage of dynamic failure was significantly higher than the number of intragranular cracks in each mineral. The rock mainly suffered intergranular damage. As the degree increases, the number of intragranular cracks in dynamic failure gradually exceeds the number of intergranular cracks. In addition, the peak strain rate and the corresponding maximum pressure as well as the dynamic peak strength and the corresponding maximum pressure under different impact loads in the simulation show good linear relationships, which provides a simple method to quickly determine the relevant dynamic mechanical parameters of the rock.

It is very important for semiconductor manufacturing and small particle protection to study the dynamic impact response of nano-scale multi-layer composite structures. Molecular dynamics simulation was used to investigate the impact resistance of Ag-PMMA composite films supported with Si substrates in this paper. The energy dissipation mechanism of the metal polymer composite film supported on the substrate was explored through contact force response, kinetic energy loss, stress wave propagation, dislocation and damage evolution, and penetration depth. The results show that the impact process includes local compression stage and global deformation stage. During the local compression stage, the atoms in the contact region of Ag surface directly transform into amorphous structures due to the stress concentration effect under high-speed impact, so the contact force reaches the peak of the whole penetration process. The thickness of the film mainly affects the global deformation stage. The thinner composite film is obviously limited by the action of the substrate, and the penetrating damage occurs directly under the high-speed impact. However, the thicker composite film dissipates the kinetic energy of the bullet through a large number of Ag dislocations and PMMA elastic deformation, which can give full play to the material performance of each layer.

Experiments, theoretical analysis, and numerical simulations were conducted to investigate the energy absorption characteristics of sunflower-like sandwich cylindrical shells under quasi-static axial loading. Firstly, quasi-static axial compression experiments and numerical simulations were conducted for sandwich cylindrical shells with three inner diameters and for their components. It was found that the specific energy absorptions and crushing force efficiencies of all sandwich cylindrical shells are greater than those of their individual components, and those of the sums of the individual components. The combination of cylindrical shell and corrugated core shell can effectively improve the energy absorption efficiency of thin-walled metal structure. Then, the theoretical formula of the axial average crushing force for the sandwich cylindrical shell was derived based on the simplified super folding element theory. The axial average crushing force predicted by the theoretical model was compared with the experimental and simulation results. It was found that the errors are within 10%. Finally, a multi-objective optimization design, with the objectives of maximum specific energy absorption and minimum peak crushing force for the sunflower-like sandwich cylindrical shell, was carried out. The Pareto front of specific energy absorption and peak crushing force of the sandwich cylindrical shell was obtained. The optimized sandwich cylindrical shell structure was improved in terms of specific energy absorption, average crushing force, and mass.

Concrete is a heterogeneous composite material composed of coarse aggregate, mortar and interfacial transition zone (ITZ). ITZ is the weakest phase inside the concrete and has a significant effect on the macroscopic fracture process of concrete. To respectively explore the effects of the distribution and value of ITZ strength on the crack propagation process in concrete under uniaxial compression, a discrete element model that reflects complex mesostructures of concrete aggregate, mortar and ITZ is established in PFC 2D by the use of FISH code. The numerical simulation results showed that cracks follow the propagation order from the centre of concrete to the loading end during the crack propagation process, and more than 80% of cracks appear in the softening stage after peak stress. The ITZ strength distribution has a weak effect on the crack propagation process in concrete, and the number of cracks in concrete is large when the ITZ strength shows a U shape distribution. The decrease in ITZ strength value leads to a gradual increase in the number and range of cracks. When the ratio of the minimum bond strength of ITZ to the bond strength of mortar p<0.5, the concrete strength is significantly reduced and the cracks expand around the centre of the concrete model to form a network macro-crack, resulting in scattered fracture failure. When p>0.6, the cracks expand from the centre of the concrete specimen to the loading end to form a macroscopic penetration crack, resulting in block fracture failure.

The paper takes the gas-liquid conveying pipe section in a 20 L spherical explosive device as the research object. The flow pattern structure and cross-section air voids characteristics of gas-liquid two-phase flow in the gas-liquid conveying pipe were studied by numerical simulation. The curvature radius and horizontal pipe length of the gas-liquid conveying pipe section were optimized and designed based on the simulation. The results show that C₆H₁₄, C₇H₁₆, C₈H₁₈, and C₁₀H₂₂ can form stable annular flow under at pressure of 0.6 MPa. The flow structure of C₆H₁₄ and C₇H₁₆ tends to become unstable with increasing pressure. Under the pressure conditions of 0.6–0.9 MPa, when the curvature radius of the gas-liquid conveying pipeline section is 34 mm and the length of the pipeline section is 200–300 mm, most of the liquid phase forms a film and moves along the pipeline wall, and the distribution of the liquid film is relatively homogeneous. The gas phase located in the center of the pipe section flows at high speed with a good gas core. It forms a more stable annular flow pattern structure. The optimization design of the gas-liquid conveying pipeline section can make the measurement of explosion characteristics more accurate, and provide a reference for the study of combustible liquid fuel explosion problems and engineering design.