Theoretical analysis on initiation of covered high explosive with different thickness plates by shaped charge jets

This study investigated how mild steel cover plates of various thicknesses affected the collapse of re-entrant auxetic structures under penetration at 500 m/s by ø16 mm spherical projectiles. A combination of experimental and numerical methods was used to capture this effect with auxetic structures made from 3D printed titanium alloy (Ti6Al4V) and ABS plastic (acrylonitrile butadiene styrene), and wire cut 304 stainless steel (SS304). Experimentally, structures were tested with a 2.90 mm cover plate and without the cover plate. Numerically, the effect of the cover plate thickness on the auxetic response of the structure was tested with 0.95 mm, 1.50 mm, and 2.90 mm cover plates (as well as no cover plate). The auxetic densification was found to be greatest under the thickest cover. Material characterisation tests were conducted to develop strength and failure models for the mild steel cover and back plates in this study, which produced simulated correlation to the ballistic experiments. Although the simulated auxetic effect generally increased with cover plate thickness, similar to the experiments, the structure material significantly affected the range of this dependence. For the ductile SS304 structures, a thin (0.95 mm) cover plate showed a small improvement in the auxetic response, with a marked improvement with a 1.50 mm cover plate. Whereas the Ti6Al4V structures showed a steady improvement in auxetic densification as the cover plate thickness was increased. Overall densification of the ABS structures was significantly improved by adding cover plates, however collapse was delayed compared to the other materials. These findings therefore indicate that the thickness of cover plates in auxetic sandwiches can be specifically engineered to maximise auxetic effect while considering the ranges of this dependence with different auxetic materials.

Influence of sewage culvert cover plate thickness on dynamic response and damage of the cover plate under gas explosion

The interface defeat and dwell can effectively improve the ballistic performance of ceramic armors under high velocity impact of long rod projectiles. Confinement conditions along both axial and radial directions of ceramic armors can affect these behaviors. With the aim of giving an insight into the effect of cover plate thickness and connection mode of cover plates with confining tubes on these behaviors, numerical simulations were performed in which the confined silicon carbide (SiC) targets with cover plates were impacted by tungsten rods. The pressure on the surfaces of SiC targets with fixed cover plates are compared to that with free cover plates, showing that the plates fixed with the confining tubes can produce higher pressure by way of wedging. With the increase in cover plate thickness, the dwell duration of the tungsten rods on the ceramic interface gradually grows. In addition, the upper and lower limits of transition impact velocities for the SiC targets with cover plates in different connection modes (i.e., free or fixed) were obtained and analyzed. The results show that the increase rate of the transition velocity region for the cover plate with the fixed-mode is relatively stable and lower than with the free-mode. On this basis, the fixed cover plate contributes higher ballistic performances to the SiC target than the free cover plate. It is also noteworthy that the size of transition velocity region does not enlarge linearly with the increase in cover plate thickness due to the slow growth of the upper limit. Accordingly, thickness thresholds exist, which are 5 mm and 6 mm for the fixed and free cover plates, respectively. Considering the ballistic performance and economy, the cover plate with the thickness ranging from 3 mm to 5 mm, i.e., 1.5~2.5 times of the tungsten rod diameter, is ideal for the structural dimensions in this paper.

The recent progress on the study of deflagration to detonation transition (DDT) is remarkable in terms of numerical analysis. The lecture summarizes the history of DDT study from experimental and numerical point of view. Then the recent findings from DDT study will be presented that the numerical study can explain the details of the experimental results obtained in the past years; Urtiew and Oppenheim experiments. The key words of DDT is flame acceleration and bow shock wave as well as Navier-Stokes equations, boundary layer and a precursor shock wave.

The shock-to-detonation transition (SDT) in gaseous n-heptane/oxygen/argon mixtures has been experimentally studied, using a shock tube, at low initial pressure (2–4 kPa) for a better understanding of the deflagration-to-detonation transition process. The detonation is generated by a precursory shock wave (PSW), with a Mach number smaller than that of the self-sustained detonation. Pressure (P2) and temperature (T2) behind incident shock waves have been accurately determined from the PSW velocity. The transition occurs in the measurement zone located between 3.20 m and 3.65 m from the shock tube diaphragm. The auto-ignition of mixture behind PSW is immediately followed by the onset of a combustion wave, which propagates at near Chapman–Jouguet (CJ) detonation velocity in the mixture carried at P2, T2 conditions. Consequently, the pressure peak can reach 350 times the initial pressure during the transition. The combustion wave merges with the PSW to form an overdriven detonation propagating in the initial mixture at velocity that progressively decreases to a value close to CJ value, of the order of 2 000 m.s−1. The experimental particles heating times are compared with the computed ignition delay times, τI,2, by using a detailed kinetic model of n-heptane oxidation. For stoichiometric n-heptane/oxygen mixtures diluted by 50% Ar, the experimental delay times are compatible with those computed. In this case, τi,2 is governed by the so-called “high temperature mechanism” (T2 > 1000 K) and varies exponentially with temperature. For undiluted mixtures, the particle heating times is much shorter than τi, 2. Then, the chemistry is governed by the “low temperature mechanism” (T2 < 950 K). Between 750 K and 950 K, τi, 2 decreases or small changes with temperature decrease but is sensitive to pressure. Turbulence in boundary layer could also promote the SDT.

The influence of component thickness of ceramic armour performance against long rod projectile is a critical information for the process of armour design optimization. In this study, the correlation between dwell time and cover plate thickness and mechanism shift with different ceramic to backing plate thickness ratio were studied using hydrocode simulation software LS-Dyna. The projectile is a long rod projectile with a length to diameter ratio of 14 at a nominal velocity of 1.25 km/s. In this study the cover plate performance is studied based on a surrogate module configuration, where the backing thickness is 10 mm instead of the usual semi-infinite thickness backing which has minimal bending deformation. The parameters used in the simulation were calibrated against experimental data in previous studies. From the study, the cover plate needs a minimal thickness to establish dwell. For thicker cover plate, the dwell time starts to decrease due to the confinement provided by thickness of the cover, which limited the lateral flow of the cover plate. This restriction of lateral flow, resulted in pressure build-up at the ceramic surface, thus, reducing the dwell time.

The plate-column joint (PCJ) is a kind of typical semi-rigid joint improved from traditional plate joint and has larger bending stiffness. The influence of the geometric parameters of the joint on its bending stiffness and the stability of its semi-rigid reticulated shell has not been well-clarified. For this reason, this study first investigates the influence of the cover plate thickness and bolt diameter on the joint bending stiffness and then obtains the bending moment-rotation angle curves. Secondly, an improved bilinear model (i.e. bending moment-rotation angle) is proposed, and the fitting formulas of the stiffness coefficient, initial stiffness and yield bending moment of the bilinear model are formulated by a multiple regression analysis. Finally, the influence of the cover plate thickness on the bearing capacity of single-layer cylindrical reticulated shells with different spans and rise-to-span ratios is figured out. The results showed that the smaller the cover plate thickness, the smaller the bearing capacity of reticulated shell. When the thickness of the cover plate is less than 4 mm, the bending stiffness decreases significantly. Therefore, the cover plate thickness can be taken as 4‐6mm to save steel consumption. Furthermore, bending stiffness of the joint has a significant effect on the failure mode of the reticulated shell.

Fracture of aluminium foam core sacrificial cladding subjected to air-blast loading

The high-explosive channel effect is investigated to study the coupling dynamics of the precursor shock wave with the detonation. This is achieved experimentally by using porous pentaerythritol tetranitrate (PETN) powder in square channels. It is found that the precursor shock wave causes the detonation to accelerate to approximately 1.5 times the detonation velocity of the porous PETN. This phenomenon is found to be almost independent of the fill gas and the initial pressure in the channel. It is found that the precursor shock wave is insufficiently strong to initiate the PETN layer before the arrival of the main detonation front, and that the mechanism responsible for the observed acceleration is precompression of the explosive layer by the precursor shock wave. This mechanism is modeled analytically by generalizing an existing model for the precursor shock wave dynamics with boundary layers. The results agree well qualitatively and relatively well quantitatively considering the assumptions that are made.

Based on the idea of damage control, this article studied a new type of earthquake-resilient prefabricated sinusoidal corrugated web beam-column joints. First, the constitution and advantages of prefabricated sinusoidal corrugated web beam-column joints were introduced. Then, finite element models are developed based on the design theory, and the hysteretic behaviour of prefabricated sinusoidal corrugated web beam-column joints was investigated using the finite element method considering the effects of parameters such as the weakened form, thickness and unbolted length of the flange cover plate, the bolt hole form and the gap between the beams. Finally, cyclic loading test and repairing test were conducted on a basic specimen, and the rationality of the numerical analyses and the design theory were verified. It indicates that a properly designed prefabricated sinusoidal corrugated web beam-column joint has good bearing capacity and hysteretic behaviour with earthquake resilience. The thickness and unbolted length of the flange cover plate, the bolt hole form and the gap between the beams have significant effects on the seismic behaviour of the joint.

Steel rocking column bases with replaceable cover plates: Cyclic loading behaviour and practical design

Seismic behavior of assembled beam-column joints with C-shaped cantilever section

"A kind of assembled steel beam-column joint with C-shaped cantilever section was proposed. The influences of the lengths of cantilever sections and cover plates on seismic performance of the joints were discussed through low-cycle reciprocating loading tests and numerical simulations. Then the sensitivity analysis of key parameters such as thickness and width of flange plate ,bolt number and cover plate’s length were carried out. The results show that the joint consumed energy through warping deformations of end plate and the friction slippages between flange of beam, C-shaped cantilever section and cover plate. By reasonably increasing the lengths of C-shaped cantilevers section and cover plates, it can ensure that the joints have high bearing capacities, while significantly improving energy dissipation capacities of the joints. Parameter analysis showed that increasing thickness of the flange plate can effectively improve the stress concentration at root of the cantilever section. Reducing width of flange plate has a great impact on bearing capacity and initial stiffness of the joint with the maximum drop amplitude of 13.1% and 18.9%, respectively."

Seismic performance of bolted connection of H-beam to HSS-column with web end-plate

A hypervelocity projectile launcher for well perforation