On flexible protection and stiff protection for structure safety under explosive/impact loading

This study investigates the influence of tunnel span on the dynamic response of rock masses with high integrity under intense dynamic load, analyzing an unlined circular tunnel excavated in intact surrounding rock with a uniaxial compressive strength of fr=57 MPa. Using a combined approach of physical model testing and numerical simulation, the influence mechanism of span on tunnel stability under different intense dynamic loads is systematically analyzed. The research results indicate the following: (1) When the peak intense Dynamic load is below 0.51fr, the surrounding rock mass remains in an elastic state. (2) When the peak load ranges between 0.51fr and 0.54fr, plastic zones emerge at the tunnel wall. (3) Once the peak load exceeds 0.70fr, the influence of the tunnel span on stability becomes significantly more pronounced with increasing load intensity. In small-span tunnels, plastic zones primarily distribute along the wall sides, whereas in large-span tunnels, they extend further upward and downward. (4) At a peak load of 0.70fr, the ratio of the maximum extent of the plastic zone in a 20 m span tunnel to that in a 5 m span tunnel is 10.70, and the ratio of the maximum relative displacement between the vault and invert is 4.67. When the peak load increases to 1.40fr, the plastic zone extent ratio rises to 13.94, and the vault–invert displacement ratio increases to 6.17. The conclusions of this study provide theoretical foundations for the design of tunnels with varying spans under intense dynamic load.

A simple model to assess the effect of soil shear resistance on the response of soil-buried structures under dynamic loads

This paper presents a physical and mathematical model that has been developed in the framework of the approach used in the computational mechanics of materials. The model is designed to enable the study of the patterns of deformation and fracture of ceramic composites with a transformation-hardened matrix at the mesoscopic and macroscopic levels under intense dynamic loading. The influence of the loading rate on the formation of the fracture and energy dissipation fronts for composite materials based on the Al2O3-20%ZrO2 system is shown. Nonlinear effects in the considered composites under intense dynamic loading are associated with the processes of the self-organization of structural fragments at the mesoscopic level, as well as with the occurrence of martensitic phase transformations in the volumes of the strengthening particles. In this paper, specific destruction work is used as the main parameter that determines the contribution of each composite component to the destruction work.

The effect of stress wave propagation on dynamic response of square tube was investigated by the experimental and numerical simulation methods in the present paper. The square tubes were subjected to the axial impact by split Hopkinson pressure bar. And the deformation process of each square tube was recorded by a high speed camera. Typical dynamic plastic buckling phenomena were observed in the experiments. And the numerical calculation of the experimental load case was conducted to analyze the effect of the stress wave propagation on the initial buckling of the square tube. The results show that there is obvious stress wave propagation in the square tube before the buckling of the square tube. And the initial buckling starts from the rear end of the tube due to the propagation of the stress wave. The relation between the stress wave propagation and initial buckling of the square tube was also discussed.

At the earliest timescale after projectile impact on woven composites, stress waves propagate out from the area of impact both radially and through the thickness. At a later timescale, momentum transfer leads to the formation of a deformation cone. Studies of wave propagation in composites typically consider the radial stress wave propagation and the formation of the transverse deformation cone but neglect through-thickness stress waves. This chapter investigates the effects of through-thickness stress wave propagation on damage and delamination under a projectile in a woven composite. This investigation uses a mesoscale model of plain weave composite, validated using 1D stress wave theory. This model uses a cohesive traction-separation law to simulate delamination cracking, inelastic progressive damage composite tows, and rate-dependent matrix. The 1D stress wave theory is generalized for any number of layers. A finite element modeling approach is validated using the generalized 1D theory.

Experimental and numerical investigation of dynamic progressive collapse of reinforced concrete beam-column assemblies under a middle-column removal scenario

Shear failures in reinforced concrete structures under intense dynamic loads are brittle and limit the structure's energy‐absorbing capabilities. This paper comprises a review of the literature dealing with the problem of dynamic shear of reinforced concrete elements, with a focus on parameters that control flexural shear and direct shear. In this context, dynamic loads refer to intense events due to explosions and impacts. For this reason, the initial response is also highlighted. Experimental investigations and calculations show that shear force and bending moment distributions in dynamic events are initially significantly different from the distributions under slowly applied loads. Therefore, structural wave propagation, geometrical properties of elements, strain rate effects and dynamic load characteristics need to be considered when analysing shear. The review also indicates that arch action in the shear span soon after the load has been applied has a large influence on the shear capacity of an element. This action is of particular importance in intense loading events. Finally, suggestions for further research are identified.

Explosion accidents and terrorist attacks seriously threaten the safety of concrete structures. To study the anti-explosion performance of concrete structures, a rate-dependent peridynamic model of concrete suitable for explosive load is established by introducing the strain rate effect of materials into the original peridynamic theoretical framework. In this model, the relationships between the stretch rate and the dynamic critical stretches of concrete are established. In addition, the strainsoftening effect of concrete and different fracture characteristics under tension and compression are considered in the model. To verify the correctness of the proposed model, the dynamic failure of concrete slabs under contact explosion is investigated, and the failure mode and crack propagation path consistent with the experimental results are obtained.

Net sheet-flow sediment transport rate: Additivity of wave propagation and nonlinear waveshape effects

Inconel 718, which is a nickel-based superalloy material used in aero engines, may be subjected to intense dynamic loading in an accidental engine failure. However, the material models for Inconel 718 employed in existing studies can not describe the mechanical behaviors under complex stress states, high strain rates and elevated temperatures satisfactorily. In this paper, various parameters of a previously proposed dynamic constitutive model for Inconel 718 are determined and verified. First, the parameters of strength, strain rate effect, temperature effect and failure for precipitation hardened Inconel 718 are calibrated against various material tests. Then, the parameters are verified by comparing the numerical results obtained from the dynamic constitutive model with the corresponding ballistic test data. It transpires that the numerical results agree well with the test data, which demonstrates the accuracy and effectiveness of the dynamic constitutive model for Inconel 718. It can also be concluded that the consideration of Lode angle effect and precise descriptions of strain rate and temperature effects are significant for the reproduction of mechanical responses of Inconel 718 plates under intense dynamic loadings in numerical simulations.

Crystalline silicon has a complicated phase transition mechanism, which has received extensive attention in the research field of phase diagram, and the deformation mechanism of silicon crystals under dynamic loading is the current research hotspot. In order to reveal its deformation and phase transition behaviors under intensive dynamic loading, molecular dynamics method was used to simulate the shock compression behavior of single crystal silicon along the crystal directions [001], [110] and [111] at an initial ambient temperature of 300 K, respectively. All simulations were carried out basing on the classical open-source codes LAMMPS and a Tersoff interatomic potential was adopted to describe the material responses of silicon under dynamic compression. Before shock loading, periodic boundary conditions were applied along the three independent directions, and an NPT ensemble was used to equilibrate the systems; then shock compression was applied by using the piston method, where a virtual piston wall impinges the sample such that the particle velocity in the sample is the same as the piston speed after the shock reaches a steady state. The shock particle velocities varied from 0.3 km/s to 3.2 km/s, and a timestep of 0.001 ps was adopted. During the stress wave formation and propagation, the simulation system was in the NVE ensemble with the absence of temperature control. The loading method and effect are similar to typical plane impact experiments. The results show that with the increase of shock particle velocity, the shear stress of single crystal silicon increases gradually and then decreases sharply due to the structural phase change. Both the phase transition threshold and the phase transition mechanism are anisotropic. Among them, a variety of solid-solid phase transitions and solid-liquid phase transitions are observed under shock compression along the [001] crystal direction. The phenomenon of solid-liquid coexistence is highly consistent with the recent international experiments. The research results provides new nano-scale results to support the study of phase transition of crystalline silicon under dynamic loading.

Structural phase transition and amorphization in hexagonal SiC subjected to dynamic loading

One of the biggest challenge for acoustic emission (AE) signal classification on real constructions is transfer from laboratory measurement on specimens to full scale. Detected AE responses are (among other factors) strongly influenced by propagation of waves in material and transfer function of sensor used. Propagation of elastic stress waves in plate of AISI 304 stainless steel was investigated in this work. Two types of wave excitation were used: broad band HSU-Nielsen source and artificial narrow band source via Vallen VS150-M transducer. AE responses were detected with use of 3 different AE transducers to take into account the effect of sensor transfer function on detected response. Attenuation curves were constructed from extracted amplitudes and digitalized signal was recorded for subsequent advanced analysis. Description of detected wave modes and separation of reflected waves was successfully done with use of combination of voltage-time dependency, wavelet transform (WT) and dispersion curves. Effect of wave propagation and transfer function of a sensor on signal maximum amplitude was discussed.

The dynamic responses of two-dimensional granular material subjected to the oblique impact and side impact of a spherical projectile are investigated experimentally and also numerically by using discrete element method. The granular material is modeled by the 329 nylon spheres arranged regularly and two-dimensionally in a rectangular container. The numerical simulations are carried out at the impact velocities less than 10 m/s. The numerical simulations are compared with the results of measurements using high-speed video camera. It is ascertained that the motion of each particle can be well simulated by discrete element method. The dynamic response of the particulate aggregation is elucidated by probing the distribution of velocity vectors of individual particle and normal direction component of contact forces between particles in detail. The effect of wave propagation on the shattering behavior of granular materials is manifested. It is found that the dynamic arching in granular material is formed just under impact point.

Design and calculation of steel concrete beams on yielding supports under dynamic loading requires considering the development of the thrust reaction that can lead to a significant increase in the bearing capacity and crack resistance of beams with yielding supports, which reduce the intensity of dynamic loading. Purpose : The aim of the work is to analyze the positive effectiveness of installing yielding supports in thrust conditionally flexible beams under intense dynamic loading. Methodology: The strength analysis of steel concrete beams at conditionally elastic deformation with thrust on yielding supports under the dynamic load. Numerical results are based on this method. Research findings : It is confirmed that the strength of flexible steel concrete beams with thrust directly depends on flexibility in the vertical direction. Value: The effectiveness is shown for yielding supports in flexible steel concrete structures with thrust under short-term dynamic loading.