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There are an immense number of discontinuous structural surfaces represented by tensile joints in natural rock mass, in which the thickness of tensile joints determines the form how stress wave interacts with joint surface, which has a significant influence on the fracture behavior of jointed rock mass under blast loading. Open joint specimens were prepared using 3D printing technology, an indoor 3D blasting experiment was carried out with respect to different open joint thicknesses. Through CT scanning and three-dimensional reconstruction, the rupture and the distribution patterns of three-dimensional cracks of the post-blasting specimens were compared, and the rupture characteristics of the rock masses with different open joint thicknesses under blast loading were analyzed. The blasting process of the rock masses with open joints was inverted by AUTODYN numerical simulation software, the effects of open joint thickness on the propagation of stress wave and the three-dimensional damage characteristics of rock mass were revealed. Results showed that under the blast load, the wing cracks derived from the end of the open joints are greatly affected by the thickness of the joints and as the joint thickness increases, the annular derived cracks formed on the right outer surface of the specimen gradually decrease. In case of a change in the open joint thickness, the intensity at which the stress wave diffracts and transmits through the end of the joint will be directly affected. This makes it hard for the wing cracks at the end to initiate, the distribution density of the radial tension cracks traversing through the open joint surface attenuates obviously, resulting in the decrease of the fractal dimension and the damage extent of the specimen. As the thickness of open joints increases, the blast stress wave running through the joint surface will endure a time delay and reduced intensity, the closure of the joint surface gradually reduces, and the degree of stress concentration at the end gets weak. In the course of stress wave propagation, the rock mass on the back-blast side of the joint endures the combined actions of compressive stress field, tensile and tangential stress field and compressive and tangential stress field. As the thickness of open joint increases, the time point for the back-blast side to reach the peak stress is delayed, the intensity of the composite stress field subjected to compressive and tangential stress field decreases, and the normal displacements on the near-blast side and the back-blast side of the joint follow the opposite trend. [ABSTRACT FROM AUTHOR]

Honeycombs are widely used in engineering protection, while the gap between peak and mean stresses remains to be narrowed, and the interaction effects among walls are weak. To break these limits, gradient curved‐walled honeycombs have been proposed recently. However, their in‐plane crashworthiness has never been studied, which restricts the actual applications in complex load environment. For this purpose, this article adopts experiments, finite‐element simulations, and theoretical analysis to reveal in‐plane crash performance of gradient curved‐walled honeycombs. Quasistatic and dynamic experiments are carried out for 3D‐printed honeycomb specimens made of 316L stainless steel, and numerical simulations are conducted by ABAQUS/Explicit. Compared to traditional straight‐ and curved‐walled honeycombs, gradient curved‐walled honeycombs display stabler deformation mode and more efficient mechanical response. Their EA and SEA are respectively 25.5% and 6.4% larger than straight‐walled honeycombs, and their energy absorption and force efficiencies are nearly 2.4 and 5.3 times larger, respectively. On this basis, plastic hinge model with high accuracy has been established, to derive the analytical solutions of their force–displacement relations. This work extends the comprehensive properties and application prospects of gradient curved‐walled honeycombs and sets an example to develop plastic hinge analysis with effective simplification and desirable accuracy on complex‐shaped structures. [ABSTRACT FROM AUTHOR]

The safety assessment and control of large-diameter pipelines under tunnel blasting at ultrasmall clear distances is a significant problem faced in construction. However, there has been no reference case for the quantitative comparison of the disturbance degree of surrounding rock by using two blasting schemes of non-electric detonator design and electronic detonator design under a similar total blasting charge consumption. In this study, the blasting test was carried out based on the engineering background of drilling and blasting methods to excavate the tunnel under the water pipeline at a close distance. The peak particle velocity (PPV), stress, and deformation responses of the pipeline under the two construction methods of non-electric and electronic detonators were comparatively analyzed. The PPV can be remarkably reduced by 64.2% using the hole-by-hole initiation of the electronic detonators. For the large-diameter pipeline, the PPV on the blasting side was much larger than that on the opposite side because the blasting seismic wave propagated a longer distance and attenuated more rapidly, owing to its greater cavity vibration reduction effect. The PPV of the electronic detonators decayed more slowly than that of the non-electric detonators. The cumulative damage caused by consecutive hole-by-hole blasting using electronic detonators was less than that caused by simultaneous multi-hole initiation using non-electric detonators, with a reduction of about 50.5%. When the nearest peripheral holes away from the pipeline are detonated, the cumulative damage variable D and damage range increase rapidly. The PPV, dynamic tensile strength, and cumulative damage variables were used to evaluate the safety of the pipelines. [ABSTRACT FROM AUTHOR]

This paper studies the effect of schistosity on the dynamic mechanical properties and failure pattern of thin-layered schist. Wudang Group schist with thin layers is selected as the research object, and the influence of the dynamic mechanical properties and failure pattern of schist under different angles and spacing is studied by combining an SHPB test and numerical simulation. The results indicate that under dynamic loading, the stress–strain curve demonstrates elastic compression, plastic deformation, and strain softening stages. Moreover, it is observed that the dynamic critical failure strength of schist exhibits typical "U"-type strength anisotropy. Specimens with a schistosity angle of 0° or 90° exhibit higher dynamic compressive strength under dynamic loading, with axial splitting and schistosity splitting as predominant failure modes. Conversely, when the schistosity angles are 30°, 45° or 60°, there is a noticeable decrease in compressive strength accompanied predominantly by shear failure along with local compressive shear failure. We additionally noted that as the spacing between schists decreases from 22 mm to 7 mm, there is a gradual reduction in dynamic compressive strength by approximately 20.3%. [ABSTRACT FROM AUTHOR]

The impact-resistant capacity of the subway tunnel lining is significant to prevent the subway tunnels from the serious damage under the blast impact loading. In this paper, the light gas gun experiment of the shield tunnel segment is carried out. The impact loading generated by light gas gun is used to simulate the blast impact loading. The strain variation characteristics and the damage crater of the shield tunnel segment are analyzed based on the experimental results. Three-dimensional finite element simulations of the specimens under the impacts of bullets with different velocities are also performed using the dynamic finite element program LS-DYNA, and their reliability are verified by the experimental data. Based on the numerical simulation results, the stress states of the elements of the shield tunnel segment are investigated to understand the damage mechanism. The damage levels of the shield tunnel segment under different blast impact loading are also studied. The relationship model between the impact velocities of the bullets and the impact loading is established. The damage depths of the shield tunnel segments under different blast impact loadings are quantified. Finally, the effect of concrete strength on the damage of shield tunnel segment is studied. [ABSTRACT FROM AUTHOR]