Critical Impact Energy Research Articles

Preparation and Decomposition of Spherical CL-20 Composites with Enhanced Laser Absorbance and Decreased Mechanical Sensitivity.

Direct initiation of secondary explosives by a semiconductor laser is highly demanded, but it is challenging to exclude the use of sensitive primers. Most laser-sensitive energetic materials are usually mechanically sensitive. In order to reduce the mechanical sensitivity (MS) of 2,4,6,8,10,12-hexanitro-2,4,6,8,10,12-hexaazaisowurtzitane (CL-20) while improving laser absorbance in the near-infrared band, spherical CL-20 composites (SCCs) embedded with nano aluminum (Al) powder and graphene-based catalyst (GO-CHZ-Co) were prepared by a spray drying method. These SCCs have been characterized comprehensively in terms of their morphologies, particle size distribution, laser absorbance, thermal decomposition behaviors, MS, and laser ignition properties. Results show that the maximum critical impact energy of SCCs was 3.8 J, which is 2.8 J higher than that of pristine ε-CL-20. The critical friction load was increased by at most 108 N compared to pristine CL-20. The absorbance has also been significantly increased up to almost 70% in the wavelength between 400 and 1400 nm, where the peak absorption is located in the region of 800-900 nm. In addition, the initial decomposition temperature (Ti) of SCCs is lower than that of pure CL-20, especially in the presence of GO-CHZ-Co. The apparent activation energy (Ea) for the decomposition of SCCs was largely dependent on the particle size of Al. Preliminary ignition tests indicate that the SCCs can be ignited successfully by a small-power laser.

Testing the shock protection performance of Type I construction helmets using impactors of different masses.

Wearing protective helmets is an important prevention strategy to reduce work-related traumatic brain injuries. The existing standardized testing systems are used for quality control and do not provide a quantitative measure of the helmet performance. To analyze the failure characterizations of Type I industrial helmets and develop a generalized approach to quantify the shock absorption performance of Type I industrial helmets based on the existing standardized setups. A representative basic Type I construction helmet model was selected for the study. Top impact tests were performed on the helmets at different drop heights using two different impactor masses (3.6 and 5.0 kg). When the helmets were impacted with potential impact energies smaller than the critical potential impact energy values, there was a consistent relationship between the peak impact force and the potential impact energy. When the helmets were impacted under potential impact energies greater than the critical potential impact energy values, the peak impact forces increased steeply with increasing potential impact energy. A concept of safety margin for construction helmets based on potential impact energy was introduced to quantify the helmets' shock absorption performance. The proposed method will help helmet manufacturers improve their product quality.

Determination of critical energy for coal impact fracture under coupled static-dynamic loading

Deep coal is constantly subjected to high static loading, and the accompanying mining disturbances will exacerbate the energy changes in the coal specimen. This study utilized the Split Hopkinson Pressure Bar (SHPB) system to examine the critical energy required for coal impact fracture under one-dimensional (1D) and three-dimensional (3D) coupled static-dynamic loading. The results revealed that a sufficiently large impact disturbance was required to cause deformation of the coal specimen when the initial static energy storage was low. Additionally, the coal with higher initial static energy storage was more likely to fracture under minor impact. Compared to the 1D loading, the 3D loading resulted in a higher critical impact energy and velocity for intact coal to fracture. Additionally, a model was developed to demonstrate the inherent energy evolution of coal specimen breakage under coupled static-dynamic loading, based on the relationship between energy and coal specimen deformation. Reducing the initial energy storage, weakening the dynamic absorbed energy, and increasing the critical instability energy of the coal matrix were the primary recommendations for disaster prevention. And corresponding prevention and control measures are suggested. This research can provide a scientific foundation and guidance for predicting dynamic disasters in order to ensure safe and efficient mining engineering.

Micro-macro fracture mechanism of heterogeneous granite in percussive drilling

The conventional rotary rock breaking method faces a technical bottleneck in improving the rate of penetration (ROP) in deep hard formations. Percussive drilling is the most potential approach to increase rock-breaking efficiency and ROP. However, the rock-breaking mechanism of percussive drilling is still unclear enough, especially the micro-fracture mechanism of rock under confining pressure (under lateral pressure and hydraulic pressure). In this paper, the impact rock breaking experiments by four kinds of Polycrystalline Diamond Compact (PDC) cutters are carried out using a drop-weight impact testing machine and an acoustic emission (AE) recording system, the influence of parameters such as cutter shape, rake angle, and impact energy on rock-breaking are systematically analyzed. This study includes a numerical simulation to examine the process of crack initiation, propagation, and cuttings formation during the impact process with the consideration of confining pressure. The results show the conical-shaped cutter is the most aggressive with high breaking efficiency. The penetration depth of the cutter is mainly influenced by the impact energy and cutter shape than the rake angle of the cutter. There exists critical impact energy makes the rock breaking efficiency the highest. The critical impact energy is about 40 J when using the conical-shaped cutter with a rake angle of 15°. The rock mainly failed in tensile mode, and the inter-grain crack is the main crack. Hydraulic pressure can inhibit the formation of horizontal cracks, while lateral pressure can inhibit the formation of vertical cracks and reduce the proportion of tensile cracks. The research results can provide some reference and basis for improving the rock-breaking efficiency in deep hard formations.

An investigation on the microscale detonation transmission performance of HMX-based explosive ink

ABSTRACT To investigate the effect of Octogen (HMX) in the application of microscale explosive transfer sequence charges. In this paper, we designed and formulated four kinds of explosive inks with different solid contents using submicron HMX as the main explosive and polyvinyl alcohol (PVA) aqueous solution / fluorocarbon resin (FEVE) ethyl acetate solution emulsion as the binder system, studied the effect of solid content on the rheological properties of explosive inks, conducted micro loading studies using a direct ink writing molding platform, The morphology, safety performance and explosion transmission performance of the microscale printed molding samples were tested and analyzed. The results show that the ink containing 90 wt.% HMX explosive has the largest n value, has good printability, smooth surface of the molded sample, consistent, uniform particle dispersion inside the line; HMX crystalline type is still β type; critical impact energy and critical friction of the printed sample compared to the raw HMX increased by 114% and 100% respectively, critical impact energy compared to CL-20-based explosive ink printed sample increased by 67%, indicating that the printed samples have a high safety under the Mechanical Sensitivity. The detonation velocity of the printed sample is 6902 m·s−1 at a charge cross-section size of 1 mm × 1 mm. The critical detonation thickness of the printed sample is 1 × 0.095 mm, Can be stable under the corner of not more than 120 ° detonation.The results of the study show that HMX as the main charge can improve the wide applicability of direct-written explosive ink.

Material similarity law of blunt projectiles penetrating scaled steel target plates

This study aims to enable the use of target plates composed of different materials in the penetration problem through the H-method similarity framework. Since different fracture toughness can lead to imperfect similarity between models, the concepts of Volume-failure strain and Volume-yield stress are introduced, which can well describe the high-velocity penetration problem involving fracture toughness. To ensure that the initial velocity of the projectile does not change, the similarity distortion among scaled models composed of different materials and the prototype is compensated by changing the target plate thickness. The feasibility of the proposed method is preliminarily proven based on the analysis model of the dimensionless critical impact energy of the target plate and the residual velocity of the projectile during penetration. Moreover, numerical simulations of blunt projectiles penetrating steel plates are performed. By changing the target plate thickness, the similarity differences among scaled models composed of different materials are effectively resolved. The errors of the residual velocity and peak force are in a completely reasonable range.

Probing the Dynamic Progression of Erosion–Corrosion of X65 Pipeline Steel Using the Electrical Resistance Method in Conjunction with Galvanostatic Polarization

The initiation of erosion and the coupled damage of erosion and corrosion on the surface of X65 pipeline steel with varying applied anodic currents were online monitored using the electrical resistance (ER) method. Results show that ER method in conjunction with anodic polarization was a highly effective approach for the investigation of the interaction effect between erosion and corrosion, which can be used to quickly and conveniently obtain the synchronously changed erosion and corrosion rates. The critical impact energy is a key parameter of sand particles to induce erosion damage on the steel surface, which can remove the flaky cementite at the edge of the pits. The threshold anodic current density that can cause a synergic effect between erosion and corrosion of X65 pipeline steel can be quantitatively fitted based on the erosion rates under varying anodic currents.

A new similarity law for penetration of steel plates by blunt projectiles

ABSTRACT The structural impact similarity laws have corrected the distortion caused by the strain-rate effect and the material property differences mostly by changing the impact velocity. However, in many practical environments, the velocity of the projectile cannot be used as an initial condition for modification. This paper develops a new similarity framework that takes into account the material property differences in the penetration problem and corrects the similarity distortion between scaled models and prototypes by changing the plate thickness. The method is preliminarily proved feasible by an analytical model of dimensionless critical impact energy under penetration. In addition, a series of numerical simulations of blunt projectiles striking steel plates are carried out. The results show that differences in similar distortions between different scaled models with different materials can all be compensated by a dimensionless number based on the thickness of the target plate.

Microstructure and mechanical properties of 122 mm welded joints of low-carbon microalloyed heavy plate steel after TM+ACC

The relevance of investigating the quality of thick-walled welded joints is explained by the increased technological complexity of manufacturing and the consistent increase in the requirements for reliability and operational durability of welded structures for critical purposes. Microstructure and mechanical properties of 122 mm thick-walled welded joints after submerged arc welding (SAW) with heat inputs of 15 and 50 kJ/cm are under investigations. The microstructural condition of critical heat-affected zones, hardness, impact energy and resistance to fatigue strength are identified, described and tested. The microalloyed steel with СEQ ≤ 0.33% used for the welded joint and produced by thermomechanical controlled process with accelerated cooling, is showing a high level of resistance to static and dynamic loads in the welded joint and is recommended for use when manufacturing critical structures with high level of reliability. The results of the study were used in the course of certification testing of VL E36 / S420ML heavy plates according to the international rules DNV-OS-B101 and TUV 305/2011/EU: System 2+ and ABS Rules Materials and Welding.

Forming iron-rich planets with giant impacts

ABSTRACT We investigate mantle stripping giant impacts (GI) between super-Earths with masses between 1 and $20\, {\rm M}_{\oplus }$. We infer new scaling laws for the mass of the largest fragment and its iron mass fraction, as well as updated fitting coefficients for the critical specific impact energy for catastrophic disruption, $Q_{{\rm RD}}^{*}$. With these scaling laws, we derive equations that relate the impact conditions, i.e. target mass, impact velocity, and impactor-to-target mass ratio, to the mass and iron mass fraction of the largest fragment. This allows one to predict collision outcomes without performing a large suite of simulations. Using these equations we present the maximum and minimum planetary iron mass fraction as a result of collisional stripping of its mantle for a given range of impact conditions. We also infer the radius for a given mass and composition using interior structure models and compare our results to observations of metal-rich exoplanets. We find good agreement between the data and the simulated planets suggesting that GI could have played a key role in their formation. Furthermore, using our scaling laws we can further constrain the impact conditions that favour their masses and compositions. Finally, we present a flexible and easy-to-use tool that allows one to predict mass and composition of a planet after a GI for an arbitrary range of impact conditions, which, in turn, allows to assess the role of GI in observed planetary systems.

Automatic Control Model of Power Information System Access Based on Artificial Intelligence Technology

Looking at the issues of low efficiency, poor control performance, and difficult access control of the traditional role-based access control model, an artificial intelligence technique-based power information system access control model has been designed. The detector is designed by artificial intelligence technology, combining artificial neural network, and artificial immune algorithm, which provide the basis for checking the access request module. It has been proved that the design model can effectively support the access and modification of legitimate users and prevent illegal users from accessing, and the control accuracy is high. The use of artificial intelligence (AI) in the power sector is now reaching emerging markets, where it may have a critical impact, as clean, cheap, and reliable energy is essential to development. Artificial intelligence can be proven very efficient for resolving the control and decision-making issues in high complex systems.

The EOS/resolution conspiracy: convergence in proto-planetary collision simulations

ABSTRACT We investigate how the choice of equation of state (EOS) and resolution conspire to affect the outcomes of giant impact (GI) simulations. We focus on the simple case of equal-mass collisions of two Earth-like 0.5-M⊕ proto-planets showing that the choice of EOS has a profound impact on the outcome of such collisions as well as on the numerical convergence with resolution. In simulations where the Tillotson EOS is used, impacts generate an excess amount of vapour due to the lack of a thermodynamically consistent treatment of phase transitions and mixtures. In oblique collisions this enhances the artificial angular momentum (AM) transport from the planet to the circum-planetary disc reducing the planet’s rotation period over time. Even at a resolution of 1.3 × 106 particles, the result is not converged. In head-on collisions, the lack of a proper treatment of the solid/liquid-vapour phase transition allows the bound material to expand to very low densities, which, in turn, results in very slow numerical convergence of the critical specific impact energy for catastrophic disruption $Q_{\rm {RD}}^{*}$ with increasing resolution as reported in prior work. The simulations where ANalytic Equation Of State (ANEOS) is used for oblique impacts are already converged at a modest resolution of 105 particles, while head-on collisions converge when they evidence the post-shock formation of a dense iron-rich ring, which promotes gravitational re-accumulation of material. Once sufficient resolution is reached to resolve the liquid-vapour phase transition of iron in the ANEOS case, and this ring is resolved, the value of $Q_{\rm {RD}}^{*}$ has then converged.

The sliding instability of rock roof block induced by vertical dynamic disturbance: An experimental study

The dynamic disturbance is one of the major reasons to trigger rock block sliding along the discontinuities of roof rock mass during the mining excavation. A self-developed test machine was used in this study to investigate the sliding instability of an isosceles trapezoid rock block triggered by dynamic disturbance. The sliding displacement, strain, and impact energy were monitored during the hammer impact under different lateral clamping load conditions. The experimental results show that the typical vertical displacement of key blocks can be divided into three modes post-disturbance depending on the clamping load and impact energy. Two distinct instability processes were observed once the key block began to lose stability and fall: Immediate falling and delayed falling. The difference between them involves the instantaneous slide distance and pendulum-type wave propagating on the sliding interface. The critical impact energy causing the key block to fall shows a nearly logarithmical increment with the gradually ascending lateral clamping load. Based on the energy analysis, an analytical solution to key block sliding displacement under dynamic disturbance is proposed, which accounts for the influence of clamping load, disturbance energy, interface friction coefficient, and key block incline angle. By comparison with the experimental results, the theoretical calculation is shown to effectively estimate the sliding distance of the key block under dynamic disturbance. This work may provide some sound guidance for the real-time assessment of key rock block stability via displacement monitoring.

Numerical Investigation of the Damage Mechanism of Offshore Pipeline Impacted by the Lump-Shaped Falling Object

AbstractDamage mechanism analysis of the exposed offshore pipeline impacted by lump-shaped falling objects plays a significant role in offshore pipeline design, inspection, maintenance, and protection. A series of three-dimensional (3D) coupling models are established and simulated to investigate mechanical behaviors and responses of exposed offshore pipelines impacted by lump-shaped falling objects. The effects of both offshore pipeline parameters and lump-shaped falling object parameters were discussed under the joint action of internal pressure and external seawater pressure. The results demonstrate that seabed soil could absorb partial impact energy and act as a cushion. Indentation on the pipeline top and stress concentrations on the pipeline bottom starts to appear when the impact velocity is larger than 10 m/s and 14 m/s, respectively. The critical impact energy before pipeline failure is around 9733.339 J. A variation in contact area has a noticeable influence on the dent depth, but a slight influence on the global deformation. An increase in pressure difference mitigates the impact damage. The depression rate increases with the rise of the radius-thickness ratio, and the most severe plastic deformation occurs when the radius-thickness ratio is 40. Besides, the eccentric distance is an essential factor influencing the damage mechanism of the offshore pipeline.

Mechanical Performance Degradation of Glass Fiber-reinforced Polyurethane Foam Subjected to Repetitive Low-energy Impact

Polyurethane foam (PUF) has excellent thermal insulation performance owing to its closed cellular solid structure. Additionally, this microstructural characteristic provides outstanding impact absorption performance. Owing to these advantages, PUF is widely adopted in transportation applications. From the viewpoint of use in practical applications, it is necessary to evaluate the residual strength after repetitive low-energy impacts on the structure. Thus, in the present study, we investigated the effects of repetitive low-energy impact on mechanical behavior of glass fiber-reinforced PUF. After the free-falling type repetitive impact test, a series of compressive tests were performed to investigate the effect of impact conditions on the compressive performance. As a result, the critical impact energy causing degradation of the impact and compressive performance of RPUF was 1,092 - 1,228 J/m2. In the impact performance, the peak stress, impact duration, and peak strain decreased by 13.5%, increased by 28.5%, and increased by 35.2%, respectively, after 80 repetitions of a 1,500 J/m2 impact. Moreover, under the same impact condition, the elastic modulus decreased by 44.5% compared to that of the intact specimen.

Glacial ice impacts: Part II: Damage assessment and ice-structure interactions in accidental limit states (ALS)

Floating glacial ice features of various sizes pose a substantial threat to the structural integrity of offshore structures in ice-prone regions. Relatively small ice feathers, e.g., bergy bits and growlers, are a major concern because they are more difficult to detect by marine radars and perform concurrent ice management operations, especially in extreme sea states.This two-part companion paper aims to assess potential loads of accidental ice actions that are exerted on an offshore semi-submersible platform and the consequences of these actions. Paper I investigates the probability distributions of glacial ice impact velocities and the associated impact heights under different sea states. Given the critical impact energy identified from Paper I, Paper II investigates ice crushing and structural damage during glacial ice impacts in accidental limit states (ALS) and ice-structure interactions. Three different approaches, i.e., the integrated approach, weakly coupled approach and fully coupled approach, are employed. The methods are based on different coupling strategies between ice and the structure and are used to identify the critical local ice sharpness for stiffened panels of the platform column, which causes maximum structural damage given an energy demand. The accuracy of the simulation results, calculation efficiency and scope of application using the three approaches are compared and discussed.With the identified critical sharpness of the ice model, numerical simulations are performed to impact various locations of the platform column. Apart from scenarios with head-on ice impacts, several oblique impact scenarios are simulated, where the glacial ice feature slides along the contact plane with different initial indentations of the panel. The results are discussed with respect to the resistance and energy absorption of the ice and structure and ice-structure interactions.

A smart Kevlar-based triboelectric nanogenerator with enhanced anti-impact and self-powered sensing properties

A novel single electrode triboelectric nanogenerator (TENG) with high energy-harvesting performance and safeguarding behavior has been developed by integrating carbon nanotubes (CNTs) and shear stiffening gel (SSG) on Kevlar fabric. The output voltage and power of the three layer structure SSG/CNTs/Kevlar-based TENG (S-TENG) reaches to as high as 41.27 V and 212.90 μW, respectively. Due to the good triboelectric property, S-TENG also acts as a wearable self-powered device to harvest as well as monitor various human motions. More importantly, when impacted by a 1.26 kg impactor dropping from 30 cm, S-TENG with enhancing stiffness can not only resist the impact force, but also gather dynamic impact energy by producing an output voltage of 1.50 V. Finally, the mechanical and the electric properties of the S-TENG under the heavy hammer impact and quasi-static piercing has simultaneously investigated. In comparison to the neat Kevlar (7.66 J), the critical impact energy resisted by S-TENG is as high as 19.16 J, indicating a better anti-impacted property. Because of the excellent triboelectric and anti-impact properties, the smart S-TENG with self-power sensing, energy-gathering and safeguarding performance possesses high potential in next generation of body armor materials, robots, wearable electronics and human-machine interactions.

Electrochemical characteristics of the dynamic progression of erosion-corrosion under different flow conditions and their effects on corrosion rate calculation

The erosion-corrosion performance of X65 carbon steel at different flow conditions was electrochemically studied. Results show that the anodic polarization branch would have a significant distortion in the flowing electrolytes, leading to an overestimation of the Stern-Geary coefficient using the traditional Tafel extrapolation. It is found that the critical impact energy for the initiation of erosion-corrosion is around 0.016 μJ. Surface morphology was obviously changed from “flow mark” appearance to continuous craters with the initiation of erosion-corrosion. The results indicate that the synergy of erosion and corrosion is the main factor contributing to the erosion-corrosion damage under active corrosion. The dynamic progression of erosion-corrosion is associated with the propagation of impingement pits at anodic sites and the wear of the corrosion product film at cathodic sites.

Impact protection of borosilicate glass plates with elastomeric coatings in drop tower tests

Drop tower testing was performed on borosilicate glass plates to determine the effectiveness of an elastomeric polyurethane/urea coating against impact and to improve our understanding of how the coating could be used to protect high voltage (HV) porcelain bushings against rifle damage [1,2]. Drop tower testing was found to be a very useful and practical tool for the prediction of failures of very brittle materials subjected to low energy impact as a function of coating thickness. The testing also improved our understanding of the impact behavior of the coatings and how to relate their low energy impact performance in drop tower tests to much higher energy impact situations, such as rifle bullet impact. By performing a series of drop tower tests on the plates with the coating thickness ranging from 1.3 to 5.6 mm, the effectiveness of the coating was determined from the critical contact force and from the critical impulse. These critical parameters were determined at the onset of catastrophic fractures of the uncoated and coated glass specimens. It was found that the coating protected the glass samples by a factor of 5.25 times with respect to the critical maximum contact force, and 9.31 times with respect to the critical impulse. Therefore, the overall coating effectiveness was estimated to be 7.28. It was also shown that the high effectiveness of the elastomeric coating can be achieved for a coating thickness as small as 1.3 mm, for a range of critical impact energies between 8.7 J and 22.7 J. Since the same coating with a thickness of 3 mm efficiently protected HV porcelain bushings against rifle impact at energies as high as 3.1 kJ [2], the very high effectiveness of the protection for small coating thicknesses could be independent of the impact energy within the range of energies considered. This therefore could be the main observation from the comprehensive work performed in this study and in [1,2].

Shattering impact fragmentation of slender nanoprojectiles

Molecular dynamics simulations of the rigid-anvil collision test are performed to achieve the complete pulverization of slender nanoprojectiles. The simulation setup mimics the traditional Taylor test (the flat-ended nanoscale bars collide with a rough rigid wall) at striking velocities that reach an awesome range from 20 km/s to 120 km/s. The objective is to investigate, so called, shattering fragmentation, defined by the complete disintegration (pulverization) of the slender monocrystalline nanoprojectile into the cloud of monatomic debris (mmax = mmax1 ≡ 1). The critical impact energy associated with this transition from the stochastic to the deterministic fragment distribution is investigated at two widely different initial temperatures of the slender nanoprojectile while scaling its size in a self-similar manner by varying their widths (diameters) at a fixed aspect ratio. For all but the smallest nanoprojectiles, the minimum achievable mmax ≫ mmax1 is discussed based on the physically-limiting striking velocity range.