The shaped charge jet formation of a Zr-based amorphous alloy and the applicability of different numerical algorithms to describe the jet formed were experimentally and numerically investigated. ...X-ray experiments were performed to study jet characteristics. The numerical results for the Zr-based amorphous alloy jet formed via the Euler and smooth particle hydrodynamics (SPH) algorithms were compared and analyzed using the Autodyn hydrocode. Particle motion was examined based on material properties. The Zr-based amorphous alloy formed a noncohesive jet driven by an 8701 explosive. Both the Euler and SPH algorithms achieved high accuracy for the determination of jet velocity. When the improved Johnson-Holmquist constitutive model (JH-2) was used, numerical results confirmed the model's suitability for the Zr-based amorphous alloy. The Euler algorithm effectively reflected jet shape within a short computing time, whereas the SPH algorithm was highly suitable for showing the shape of the jet tail within a long computing time. In the 3D Euler model, the flared jet mouth indicated radial particle dispersion; however, in the 2D model, particle dispersion in the head was directly observed by using the JH-2 material model. The brittle fracture of the material reduced the proportion of particles near the liner apex forming a jet. Furthermore, a new method in which stagnation pressure was used to predict jet formation and its coherence was proposed since the collapse angle was difficult to obtain.
The flow stress of face-centered cubic (FCC) metals exhibits a rapid increase near a strain rate of 104 s−1 under fixed-strain conditions. However, many existing constitutive models either fail to ...capture the mechanical characteristics of this plastic deformation or use piecewise strain-rate hardening models to describe this phenomenon. Unfortunately, these piecewise models may suffer from issues such as discontinuity of physical quantities and difficulties in determining segment markers, and struggle to reflect the underlying physical mechanisms that give rise to this mutation phenomenon. In light of this, this paper proposes that the abrupt change in flow stress sensitivity to strain rate in FCC metals can be attributed to microstructural evolution characteristics. To address this, a continuous semiempirical physical constitutive model for FCC metals is established based on the microstructural size evolution proposed by Molinari and Ravichandran and the dislocation motion slip mechanism. This model effectively describes the mutation behavior of strain-rate sensitivity under fixed strain, particularly evident in an annealed OFHC. The predicted results of the model across a wide range of strain rates (10−4–106 s−1) and temperatures (77–1096 K) demonstrate relative errors generally within ±10% of the experimental values. Furthermore, the model is compared with five other models, including the mechanical threshold stress (MTS), Nemat-Nasser–Li (NNL), Preston–Tonks–Wallace (PTW), Johnson–Cook (JC), and Molinari–Ravichandran (MR) models. A comprehensive illustration of errors reveals that the proposed model outperforms the other five models in describing the plastic deformation behavior of OFHC. The error results offer valuable insights for selecting appropriate models for engineering applications and provide significant contributions to the field.
•This paper verifies the applicability of BSMPM, GIMP, and CPDI in mesoscale simulating the SCJs.•BSMPM based on cubic and quartic splines is most suitable for mesoscale simulating, whose SCJs are in ...great continuity with little cavity and small surface roughness.•For SCJs material, the strain evolution is hierarchical and the particle trajectories can be classified as a laminar layer, transition layer, and turbulent layer from outer to the axis, consistent with the grain size evolution.
Shaped charge (SC) generates a fluid-like high-speed jet (SCJ) undergoing extremely large ductile stretching without fracture. It is a formidable challenge to accurately track and monitor the mesoscale deformation characteristics of materials using fluid simulation algorithms. To address this issue, the Material Point Method (MPM) is introduced as an efficient particle-based method that discretizes the continuum into Lagrangian particles moving through a fixed Eulerian grid. By possessing all material properties, these particles facilitate tracking throughout the deformation process and enable the implementation of history-dependent constitutive models. Regrettably, the utilization of MPM in the study of SCJ formation is restricted. The objective of this study is to assess the capability of 2D-axisymmetric MPMs in modeling SCJ formation and free flight at the mesoscale, thereby providing valuable guidelines for their application in SCJs. The MPMs employed in this study are based on the B-spline (BSMPM) and domain interpolations (generalized and convected particle domain interpolations in MPM). The numerical results indicate that BSMPM with cubic and quartic splines is the most suitable method for calculating SCJs due to its exceptional continuity and alignment with the experimental data. The mesoscale evolution of particles reveals that the material undergoes impact crushing and tensile tearing, transforming into a low-speed slug and a high-speed jet. The equivalent plastic strain (EPS) in SCJs exhibits a radial expansion from the exterior to the axis in a layered manner. Particles in the outer layer with a thickness of approximately 1/2 exhibit a 'laminar' distribution, while particles near the axis exhibit 'turbulent' distribution and undergo severe deformation. The hierarchical progression of EPS and particle motion traces provides insight into the underlying causes of mesoscale experimental phenomena, such as the axial elongation of voids in the SCJ slug and the radial distribution of the material in three concentric circles.
How to effectively reduce the damage of frequent accidental explosions and explosion attacks to existing walls is an important concern of the blast resistance field. In the present study, the ...influence of the foamed concrete (density 820 kg/m3, water-cement ratio 0.4) coating thickness on the blast resistance of a 120 mm RC (reinforced concrete) wall was studied through blast experiments, numerical simulations, and shock wave theory. Results show that the influences of foamed concrete on the blast resistance of RC walls are jointly decided by the stress drop caused by impedance effect and exponential attenuation and the stress rise caused by high-speed impact compression. The coating thickness mainly affects the foam concrete’s fragmentation degree and stress attenuation. A lower critical coating thickness exists in foamed concrete-coated RC walls. The blast resistance of the RC wall will decrease when the coating thickness is less than that value. The lower critical coating thickness is related to the intensity of blast load and the energy absorption capacity of foamed concrete, and it can be predicted by monitoring the explosive stress and energy incident to the RC wall.
The effect of liquid parameters on the defense capability of the liquid-filled compartment structure (LFCS) of a shaped charge jet (SCJ) is quantified using dimension analysis of experiments on the ...reduced depth of SCJ penetration, which is disturbed via the LFCS with different liquids. The effects of three parameters, namely, liquid density, sound velocity and dynamic viscosity, on LFCS defense for SCJ are discussed quantitatively. Dynamic viscosity exerts the most important effect on LFCS disturbance of SCJ penetration, followed by liquid density. Meanwhile, sound velocity causes a negligible effect on LFCS disturbance of SCJ when the hole diameter in LFCSs are short. LFCSs offer excellent protection as they can significantly reduce the penetration capability of SCJ. Thus, LFCSs can be used as a new kind of armor for defense against SCJ.
In this study, electromagnetic interference testing of microcontroller units (MCUs) under different electromagnetic pulse (EMP) amplitudes, full width at half maximum (FWHM), and at different angles ...was carried out on an EMP cell. The coupling path of the radiation-type EMP experiment on the circuit board is random. However, in several experiments with two pins specific to a certain integrated circuit, by measuring the interference voltage of MCU pins, the statistical results indicate that as the pressure of the air gap switch of the power source increased, both the breakdown voltage and the electric field in the transverse electromagnetic (TEM) cell increased, resulting in higher electromagnetic interference (EMI) received by these two pins. As the capacitance of the storage capacitor increased, the EMI also increased. In addition, the results showed that the interference of EMP on the MCU had strong directionality; i.e., path selectivity, which was related to the structure of the MCU. X-ray imaging of the destroyed MCU showed that when the internal wiring direction of the pin is consistent with the propagation direction of the interference pulse, the EMI was minimal or even unnoticeable.
The formation characteristics of the shaped charge jet (SCJ) from the shaped charge with a trapezoid cross-section is analyzed in this work. A theoretical model was developed to analyze the ...collapsing mechanism of the liner driven by the charge with a trapezoid cross-section. Based on the theoretical model, the axial and radial velocities of the SCJ from different trapezoid cross-section charges. The pressure model was employed to calculate the velocity for the subcaliber shaped charge, which was verified through numerical simulation. The results show that the influence of the angle of the trapezoidal charge (acute angle) on the axial velocity of the SCJ is not distinct, whereas the variation of the radial velocity of the shaped charge jet is obvious as the change in the angle of the trapezoidal charge. In addition, the related X-ray experiments were conducted to verify the theory. The theoretical results correlate with the experimental results reasonably well.
Liver-expressed antimicrobial peptide 2 (LEAP-2), originally described as an antimicrobial peptide, has recently been recognized as an endogenous blocker of growth hormone secretagogue receptor 1a ...(GHS-R1a). GHS-R1a, also known as ghrelin receptor, is a G protein-coupled receptor (GPCR) widely distributed on the hypothalamus and pituitary gland where it exerts its major functions of regulating appetite and growth hormone (GH) secretion. The activity of GHS-R1a is controlled by two counter-regulatory endogenous ligands: Ghrelin (activation) and LEAP-2 (inhibition). Ghrelin activates GHS-R1a on the neuropeptide Y/Agouti-related protein (NPY/AgRP) neurons at the arcuate nucleus (ARC) to promote appetite, and on the pituitary somatotrophs to stimulate GH release. On the flip side, LEAP-2, acts both as an endogenous competitive antagonist of ghrelin and an inverse agonist of constitutive GHS-R1a activity. Such a biological property of LEAP-2 vigorously blocks ghrelin's effects on food intake and hormonal secretion. In circulation, LEAP-2 displays an inverse pattern as to ghrelin; it increases with food intake and obesity (positive energy balance), whereas decreases upon fasting and weight loss (negative energy balance). Thus, the LEAP-2/ghrelin molar ratio fluctuates in response to energy status and modulation of this ratio conversely influences energy intake. Inhibiting ghrelin's activity has shown beneficial effects on obesity in preclinical experiments, which sheds light on LEAP-2's anti-obesity potential. In this review, we will analyze LEAP-2's effects from a metabolic point of view with a focus on metabolic hormones (e.g., ghrelin, GH, and insulin), and discuss LEAP-2's potential as a promising therapeutic target for obesity.
The process of liquid radial reflux interference during jet penetration in a liquid-filled composite structure is divided in this study into three stages: bottom plate reflection interference, ...side-wall reflection interference, and side-wall secondary reflection interference. The calculation model of the velocity interval of the disturbed jet and the residual penetration depth of the jet has been established through theoretical analysis. Results show that the liquid-filled composite structure can interfere with the high-speed section of the shaped charge jet. The accuracy of the theoretical analysis in this paper has been verified through numerical simulation, X-ray, and depth-of-penetration experiments. Among the results, those of the X-ray experiment show that the liquid-filled composite structure has interference on the tip of the shaped charge jet, which provides a possibility for the application of the liquid-filled composite structure to ammunition safety and other extreme cases.
In the military field, determining how to increase the hole-expanding ability of shaped charge warheads is a key and difficult issue with respect to warhead development. Amorphous alloys have grains ...or grain boundaries, with unique mechanical properties. Zr41.2Ti13.8Cu12.5Ni10Be22.5 can be used as the liner material of shaped charges, resulting in high-speed particle flows that differ from those of traditionally shaped charges. In this paper, based on the analysis of the mechanical response characteristics of Zr41.2Ti13.8Cu12.5Ni10Be22.5 and its fracture morphology under impact, combined with the formation theory of shaped charge jets, a semi-empirical formula is derived to calculate the velocity of non-cohesive high-speed particle flow considering the elastic strain energy loss. Additionally, the reliability of the proposed theoretical model is verified through experiments. The penetration process of Zr-based amorphous alloy high-speed particle flow into a concrete target is theoretically analyzed, and the penetration stages of the high-speed particle flow into the target are clearly distinguished. Combined with the penetration theory of shaped charge particle jets, a high-speed particle flow penetration model is proposed, and a pore expansion model is established through an energy method. The experimentally obtained data on depth of penetration are in agreement with the theoretical calculation results.
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