International Journal of Impact Engineering最新文献

This paper introduces a framework specifically designed to simulate hypervelocity impact scenarios precisely. The framework utilizes the multiscale shock technique (MSST) from molecular dynamics (MD) to accurately model material states under extreme impact loading conditions, focusing on calculating the equation of state (EOS). A vital aspect of this work is the acquisition and application of the Mie-Grüneisen EOS, which is highly relevant in impact analysis research. The framework employs the material point method (MPM) to conduct analyses of hypervelocity impacts using the derived EOS. This method offers a detailed insight into the dynamic responses of materials subjected to hypervelocity impacts, underscoring the integration of molecular dynamics with the MPM.

This study fills a challenging gap in the field of structural dynamics. A potential rule is theoretically proved: The peak displacements of undamped single-degree-of-freedom (SDOF) systems subjected to nonnegative but symmetric pulse loads necessarily occur within the pulse loading duration if the frequency ratio $\beta <$1, and after the pulse loading duration if the frequency ratio $\beta$>1. As a special case, the first peak displacements accurately take place at the end of the pulse loading when $\beta$=1. Also, the occurrence time of the first peak displacements has a theoretic value of $t_{\varphi }$=$t_p$/2+$T$/4 in the case of $\beta$>1. Although this potential rule can be easily verified in certain cases, it has not been theoretically and systematically proved so far. A rigorous and complete proof is presented and featured by the proposed analysis based on Duhamel's integral. The analyzation circumvents the difficulties in analytically solving dynamic responses to different pulse loads in different shapes, but still reaches theoretical conclusions and yields a general law of structural dynamics. The proved law can be used to predict the occurrence phase of the first peak displacements when undamped SDOF systems subjected to nonnegative but symmetric pulse loads.

This paper investigates overpressure attenuation capacity and failure mechanism of the polyurea-coated aramid fabric (PCAF) subjected to air-blast loading experimentally. The peak overpressure, arrival time and positive pressure duration of shock waves on the blast and back side of PCAFs were obtained in tests and analyzed. In addition, the failure mode and mechanism were revealed with the electron scanning microscope (SEM), meanwhile the effect of polyurea type, coating position and thickness ratio on the blast resistance were discussed. The results show that in the cases of scaled distances of 1.84 and 2.32 m/kg^1/3, PCAFs, one-layer polyurea coated on three-layer aramid woven fabrics, can attenuate the peak overpressure by about 70 %, delay the arrival time by about 0.7 ms, and shorten the positive pressure duration by 10 %-50 %. This is due to the increased out-of plane stiffness and closure of interweaving apertures of the aramid fabric. Furthermore, perforation is the main failure mode of aramid fabrics, in which the tensile breakage in weft yarn and the frictional slip in warp yarn, while the failure modes of PCAF mainly include fracture and exfoliation, with both weft and warp yarns breakage and polyurea failure. It was concluded that the degree of infiltration between the polyurea and fabric affects mechanical properties of the fiber, changing the failure mode of PCAF. In terms of the extent of damage, the PCAF exhibits a superior blast resistance when the polyurea coated on the back side. The blast resistance of PCAF increases first then decreases with an increase in the thickness of the polyurea layer under the same areal density.

Porous material (PM) has excellent energy absorption performance and is widely used as an impact-energy absorber. However, the PM may provide little utility when the impact conditions change. Shear stiffening gel (SSG) with an extremely strong viscosity effect can be as a dynamic responding fortifier to overcome the limitation of PMs. In this paper, a rate-dependent, smart energy-absorbing material (SSG/PM) is fabricated by incorporating SSG that is reinforced with CaCO₃ particles onto the PM. Aided by the dynamic compression experiments at the strain rate range of 0.001 to 100 s⁻¹, both SSG/PM and neat PM are assessed and compared for crushing performance. Results reveal that the SSG/PM exhibits a pronounced dynamic stiffening characteristic in response to various strain rates owing to the rate-dependent phase transition of embedded SSG, thereby contributing to enhancing the PM skeleton's ability to withstand deformation. The SSG/PM displays a noteworthy boost in energy absorption (up to 831.98 %). Moreover, the influence of loading rate, particle mass fraction, and PM aperture size are also examined. The findings indicate that its crushing resistance and energy absorption capability are enhanced with the increase in strain rate, demonstrating the ability to adapt to various dynamic scenarios. The use of a higher particle mass fraction and smaller aperture size helps to improve the energy absorption capability of the SSG/PM. Additionally, quantitative energy analysis is implemented in which the energy dissipation mechanisms of the SSG/PM are attributed to the synergistic interaction of skeleton deformation, shear stiffening effects, and particle enhancement. It is ascertained that as the loading rate increases, the shear stiffening effect continues to strengthen; the particle content effect exhibits a rising-falling trend; while the skeleton deformation shows a rate-independent feature. This study sheds light on the crushing behaviors and corresponding energy dissipation mechanisms of SSG-based composites, thereby providing valuable insights for the design of SSG-based composites.

The freeze recovery method (FRM) is a crucial approach for investigating the high-speed fracture process of metal cylindrical shells under explosive loading. However, the precise impacts of the recovery process on the deformation and fracture behavior of such shells remain unclear, significantly constraining the widespread application of this method in high-speed fracture studies. This paper quantitatively evaluates the effects of the expansion contour, fracture mode, and damage state of intermediate shells at different stages of fracture development using a crack evolution simulation method and nondestructive crack detection technique. The recovered shell contour can effectively represent the free expansion contour of the shell at the equivalent moment, with an error of less than 4%. Impact induces tensile cracks on the outer wall of the shell, which leads to changes in the local fracture mode. A method of crack elimination and equivalence in the damage statistics of the recovered shell is proposed to address this effect. The recovered shell can characterize the damage evolution during free expansion at the equivalent moment after eliminating the influence of excess tensile cracks. Based on the principle of stress analysis and energy conservation, the formation mechanism of tensile cracks in the outer wall of the shell is explored, and the correlation between tensile cracks and recovery time is elucidated. The study shows that the impact of fracture damage caused by freezing recovery is gradually reduced over time. The improved freezing recovery method based on the hard recovery principle is successfully used to recover the multistage intermediate shell, meeting the demand for obtaining the transient physical model in the high-speed fracture field.

Cellular solids are interesting materials for blast energy absorption because of their high porosity, cell structure, and unique mechanical properties. Also, it will undergo graded compression over the same foam density. Hence, in this study, an experimental investigation of blast pressure impact on the trilayered sequences made of three different polyurethane (PU) foam densities of equal thickness, such as D1-29.201 kg/m${}^3$, D2-59.692 kg/m${}^3$, and D3-107.720 kg/m${}^3$ is carried out. The force transmitted $\left(F_T\right)$ on the reaction plate and incident force on the blast impact face are recorded. The maximum force amplification $\left(F_{amp}\right)$ of the 63.79% was observed in the S5 and the minimum of 6.19% in S4. Thus the reduction in $F_{amp}$ in S4 compared to S5 is 90.3%. Similarly, the energy absorbed $\left(E_{abs}\right)$ by the trilayer is a maximum of 24.80 J in S2 and a minimum of 3.60 J in S3. The $E_{abs}$ increased to 85.48% in S2 solely by altering the layer sequences in S3. Hence, the location of the density in the layer sequences plays a key role in effective blast mitigation on different response measures.