Shock Loading Conditions Research Articles

Modeling and numerical investigation of mechanical twinning in β-HMX crystals subjected to shock loading

This manuscript establishes a crystal plasticity finite element (CPFE) model with large volumetric deformation for β-HMX (1,3,5,7-tetranitro-1,3,5,7-tetrazocane) energetic crystals with emphasis on the deformation twinning behavior under shock loading conditions. The CPFE model captures the nonlinear response of the monoclinic crystal through the application of large volumetric change under shock condition, dislocation slip at low and high moving speeds and mechanical twinning idealized by the twin volume fraction evolution. The twinning behavior is distinguished from dislocation slip through the decomposition of the plastic velocity gradient in which dislocation slip, twinning and slip in the twinned region are separately considered. Third-order Birch Murnaghan EOS is incorporated in the CPFE framework to describe the volumetric deformation under extreme pressure induced by explosion or impact. The results of the numerical investigations show that the twinning behavior exhibits strong orientation dependency, which becomes more evident at higher loading regime. Particle shape significantly affects the twin concentration. Peak twin volume fraction in HMX polycrystalline with regularized particle shapes is lower compared with mesostructure with realistic particle morphologies.

Comparison between a single unit bioreactor and an integrated bioreactor for nutrient removal from domestic wastewater

The simultaneous nitrogen and phosphorous removal efficiency of Bacillus cereus GS-5 immobilized single unit packed bed bioreactors was compared with that of integrated bioreactors. Both the single unit and integrated bioreactors were fed with domestic wastewater (NH4+-N 70 mg/L, NO3–-N 70 mg/L and PO43--P 15 mg/L) under 300–1000 mg/L carbon loading and 7.2–28.8 L/d hydraulic loading rates. The removal efficiencies of NH4+-N, NO3–-N and PO43--P in the integrated bioreactor were 94.2%, 92.3%, and 97.6%, respectively, which are slightly better than the single unit bioreactor. The specific oxygen utilization rate (SOUR) showed that the integrated bioreactor (17.06 mg-O2/g-MLSS/h) has a higher microbial activity than the single unit bioreactor (15.2 mg-O2/g-MLSS/h). Both the single unit and integrated bioreactors successfully resisted the organic as well as hydraulic shock loading conditions. This work established promising application prospects of both single unit fixed bed and integrated bioreactor for nutrient removal from domestic wastewater.

Carbon clusters formed from shocked benzene

Benzene (C6H6), while stable under ambient conditions, can become chemically reactive at high pressures and temperatures, such as under shock loading conditions. Here, we report in situ x-ray diffraction and small angle x-ray scattering measurements of liquid benzene shocked to 55 GPa, capturing the morphology and crystalline structure of the shock-driven reaction products at nanosecond timescales. The shock-driven chemical reactions in benzene observed using coherent XFEL x-rays were a complex mixture of products composed of carbon and hydrocarbon allotropes. In contrast to the conventional description of diamond, methane and hydrogen formation, our present results indicate that benzene’s shock-driven reaction products consist of layered sheet-like hydrocarbon structures and nanosized carbon clusters with mixed sp2-sp3 hybridized bonding. Implications of these findings range from guiding shock synthesis of novel compounds to the fundamentals of carbon transport in planetary physics.

Hydraulic characteristics of integrated settler based biofilm reactor as onsite sanitation system

Abstract The present study identifies the hydraulic efficiency of a novel onsite sanitation system at variable hydraulic shock loading conditions. The system consisted of three chambers, each working as an up-flow anaerobic bioreactor, accommodated within a single unit. The hydraulic characteristics were identified with the help of residence time distribution (RTD) analysis by step feeding of lithium chloride (LiCl) solution into the system. The experiments were run at variable hydraulic loading conditions at different peak flow factors (PFF) of 1, 2, 4 and 6 while maintaining 24-h hydraulic retention time. As revealed in the RTD analysis, the biofilm reactor achieved a very good hydraulic efficiency that varied from 0.76 to 0.81 at PFF 1, 2 and 4. Although in the case of PFF6, it was comparatively low. It was noted that the dispersion number was always below 0.2 at variable hydraulic shock loading conditions under different PFFs, which indicated that the reactor behaved perfectly between mixed-flow and plug-flow reactor. The system was also able to achieve good pollutant removal efficiency for chemical oxygen demand (COD) and total suspended solids (TSS) under all PFFs, which was more than 68 and 75%, respectively.

Nanoindentation in cyclotetramethylene tetranitramine (β-HMX) single crystals: the effect of pressure-sensitivity

Cyclotetramethylene tetranitramine (HMX) is a molecular crystal used as explosive in a broad range of civilian and military application. Its mechanical behavior is important as it relates to the initiation of the decomposition reaction though the formation of hot spots. However, the mechanics of the HMX crystal is complex and insufficiently understood. In particular, the pressure sensitivity of the mechanical behavior was largely ignored in the past, despite indications that material properties are strongly dependent on pressure. In this work we develop a pressure-sensitive crystal plasticity model for single crystals of β-HMX which accounts for the dependence on pressure of both the elastic constants and the yield surface, and calibrate it based on results from molecular simulations reported in the literature. The model is implemented in a finite element solver and is used to represent nanoindentation in β-HMX single crystals using a Berkovich tip. It is observed that accounting for pressure sensitivity is required if predictions close to experimental indentation results are to be obtained. The pressure sensitivity of the yield surface has a larger impact on predictions than that of the elastic constants. While these effects are demonstrated here in the context of quasi-static indentation, it is suggested that they become essential under shock loading conditions when stress states with large pressure components result.

Polymorphism of gold under laser-based ramp compression to 690 GPa

The high-pressure behavior and polymorphism of gold have attracted strong recent interest from theory as well as from both static and dynamic experiments. In this study, gold was dynamically ramp-compressed to 690 GPa via laser ablation using the Omega Laser Facility (University of Rochester) in order to investigate the stability regions of this noble metal's polymorphs. Stresses were determined from measurements of surface or interface velocities by laser interferometry. In situ x-ray diffraction was carried out to constrain the structure and density. The ambient face-centered-cubic (fcc) phase was observed at 162 GPa, followed by a mixed-phase region consisting of the fcc and body-centered-cubic (bcc) phases. The presence of only the bcc phase was observed between 377 and 690 GPa. Our results are consistent with recent shock-compression experiments and demonstrate that gold transforms to the bcc phase under conditions of both ramp and shock loading.

Anaerobic semi-fixed bed biofilm reactor (An-SFB-BR) for treatment of high concentration p-nitrophenol wastewater under shock loading conditions.

P-nitrophenol (PNP or 4-NP) has been widely used as a biorefractory raw material in chemical industry, whereas been highly concerned for its characteristics of mutagenic/carcinogenic activity and food chain bioaccumulation. In this study, an anaerobic semi-fixed bed biofilm reactor (An-SFB-BR) was constructed and used to treat PNP wastewater which discharged from chemical industries. Experimental results revealed that the An-SFB-BR was successfully cultivated with the gradually increasing of influent PNP from 0 to 540mg/L (gradually increased 10mg/L every time in stage II and 30-50mg/L for stage III), with the observation of an average removal efficiency of 98% for PNP and 80% for chemical oxygen demand (COD), also a biogas production and biogas production rate of 2.1 L/(L·d) and 0.57 m3/kg-COD, respectively. Finally, the conversion rate of P-aminophenol (PAP), the primary intermediate of PNP reached 80% after An-SFB-BR biodegradation. A relatively stable pH was maintained throughout the entire process, and insignificant VFA accumulation. The reactor exhibited a strong toxic shock resistance, and 16S rRNA sequencing results demonstrated that the dominant microbial community changed slightly with the gradually increasing of PNP concentration, which guaranteed the PNP removal efficiency.

Solving the problems of strength and destruction of materials and structural elements using a complex experimental-theoretical approach

The paper considers a complex experimental and theoretical approach to studying high-speed deformation of structural materials including a system of basic dynamic experiments aimed at determining the strength and deformation properties of materials under various types of stresses, a program for direct parametric identification of models of deformation and fracture, as well as a system of special verification experiments in the natural and numerical realizations, which makes it possible to assess the adequacy of the model obtained and its performance in conditions other than those in which it was received. To obtain a set of mechanical strength and deformation properties of materials under compression, tension or shear, a series of basic experiments was carried out on an installation that implements the Kolsky method using sets of split Hopkinson bar of various configurations. According to the results of these experiments, together with the data of static deformation, the parameters of the Johnson-Cook model of plasticity with various versions of the model factor responsible for the influence of the strain rate were identified. To test the adequacy of the model (verification), special test experiments have been developed that are simple enough, on the one hand, and allow an unambiguous interpretation of the results and numerical reproduction without simplifications, whilst, on the other hand, the stress state in these types of tests, as well as the history of changes in the loading parameters, differs from that in basic experiments. The chain of obtaining an adequate (verified) model of deformation and fracture used in software complexes for calculating the stress-strain state and the strength of critical structures under shock loading conditions is considered in the example of steel 3.

Coupled Fluid–Structure Interaction based Numerical Investigation on the Large Deformation Behavior of Thin Plates Subjected to under Water Explosion

Coupled fluid structure interaction based numerical investigation on rectangular mild steel plates subjected to underwater explosion is tested using Explosion Bulge Testing (EBT) is presented in this paper. The test plate along with the EBT box model fixture immersed in water domain subjected to small explosive charges of PEK I at a standoff distance of 0.15 m from centre of the plate is considered for the analysis using LSDYNA code. For the analysis, explosive charge is modelled using high explosive burn with JWL equation of state. The fluid is using null material model with Gruinesian equation of state, the EBT setup is using Lagrangian solid element with rigid material model and the test plate is modelled using Belytschko-Tsay shell element with piece-wise linear plasticity material model. The numerical analysis aims to predict the permanent deformation of the plate under various shock loading conditions. The results are then compared with experimental results available in the literature and numerical results based on Taylor’s plate theory. Parametric investigations on the large deformation behaviour of different plate thickness of various shock loading conditions are presented.

Nitrous oxide (N2O) emissions from a pilot-scale oxidation ditch under different COD/N ratios, aeration rates and two shock-load conditions

Nitrous oxide (N2O) generated from wastewater treatment plants (WWTPs) has drawn attention due to its high emission load and significant greenhouse effect. In the present study, N2O emissions from a pilot-scale Carrousel oxidation ditch under various chemical oxygen demand (COD) to nitrogen ratio (COD/N) and aeration rates were systematically investigated. The highest N2O emission factor was 0.142 ± 0.013%, at COD/N of 5 and aeration rate of 1.8 m3 h−1, which was much lower than the majority of previous studies. The results could be attributed to the high internal recycle ratio of the oxidation ditch process which lightened the burden of influent load to the system. The profiles of N2O emissions and dissolved N2O concentration along the channels showed a distinct spatial variation that N2O emissions primarily occurred in the aeration zones due to the air stripping effect. However, both the aeration and anoxic zones contributed to N2O generation due to autotrophic nitrification (AN), which was considered to be the main N2O generation process. In addition, two simulated shock-load conditions, ammonia overload shock and aeration failure shock, were carried out to explore the response of the biological nitrogen removal (BNR) system. The results indicated that both shock-loads lead to excessive N2O emissions, especially at higher aeration rates, which could be explained by the improved N2O generation by AN process during the shock-load period. This study offered new insights into the role of operational parameters to N2O emission and the alternative approach for N2O mitigation during both the steady-state operation and shock-load conditions in the oxidation ditch process.

Role of Microstructure on the Shock-Induced Strengthening Behavior of Ti–6Al–4V Alloy

The influence of microstructure on the shock-induced strengthening behavior of Ti–6Al–4V (Ti-64) alloy was systematically investigated through plate impact experiments and quasi-static reload compression tests. Ti-64 displays no enhanced shock-induced strengthening effect at equivalent strain, regardless of the microstructure and shock stress amplitude. However, the shock-induced enhancement ratio is higher in the alloy having the bimodal microstructure with high equiaxed primary α-phase ($$\alpha_{P}$$) volume fraction or the lamellar microstructure with wide α-platelets. The microstructure analyses show that the substructures of the postshock Ti-64 with both bimodal and lamellar microstructures are dominated by planar slip. Dislocations are easier to nucleate, move and tangle in those large-sized α phases, such as equiaxed $$\alpha_{P}$$ and wide α-platelet, leading to the formation of reticular substructures and slip bands. However, the dislocation density is relatively low in the small α plate of the transformed β regions and in the narrow α-platelet, which is attributed to the relaxation of shock stress and consequently to the suppression of dislocation nucleation caused by the obvious grain/phase boundary damping effect. Only a small number of twins were formed in the lamellar microstructure with wide α-platelet, indicating that grain size and interface damping also affect the twinning behavior of Ti-64 under shock loading conditions.

Обоснование правил подобия разрывной нагрузки рыболовных крученых изделий

The article focuses on the problem of physical modeling of the physical and mechanical properties of fishing twisted filamentary materials, in particular, the most important one – the breaking load. The problems arise because of conducting full-scale experiments, particularly when the ropes of large diameter are used to build the rope parts of fishing gear. The solution to the problem of determining the breaking load on filamentary parts can be found by using specialized tensile testing machines and modern software, which is an effective tool for predicting the reliability and a resource of a gear part operating in difficult conditions of dynamic and shock loads. However, de-signing of fishing gear must begin with large-scale modeling, which will help to correctly calculate the physical and mechanical properties of the designed object using the well-known parameters of the full-scale material. The similarity rules of breaking load of fishing twisted filamentary gear used for the construction of industrial fishing tools will make it possible to model new elements of these tools without conducting full-scale experiments. At the same time, they will already contain solutions to problems associated with studying the dynamic processes, deformation, fracture, as well as the prediction of reliability and resource of the material. The technique proposed based on determining the scale of similarity of filamentary gear made of polyamide fibers, will help to simu-late various net and rope elements from filaments gear of various sizes and structures, instead of conducting energy-intensive experimental studies on ropes of large diameter.

Effect of stacking fault tetrahedron on spallation of irradiated Cu via molecular dynamics study

Stacking fault tetrahedron (SFT) is a common type of three-dimensional vacancy clustered defect in irradiated FCC metals and alloys, which has a great influence on the mechanical properties of the materials. Previous researches mostly concentrated on the effect of SFT on the mechanical response of material under quasi-static or constant strain rate loading condition, while very few studies focused on its influence on mechanical properties under the shock loading condition. Spallation is a typical failure mode of ductile metal material under shock loading, and the initial defects in the material have a great influence on the spallation behavior. In this study, molecular dynamics simulation is carried out to investigate the influence of SFT on spallation behavior of irradiated copper single crystal under different shock intensities. Copper single crystal with a perfect structural model is also investigated under the same simulation condition for comparison. The model is divided into two parts: the flyer and the target. The shock wave is generated by moving the flyer at a velocity in a range of 1.0–2.5 km/s along the [111] crystallographic orientation to achieve the desired shock-state particle velocity <i>U</i><sub>p</sub> in a range of 0.5–1.25 km/s. The time evolution of pressure, free surface velocity and corresponding microstructure, are analyzed in detail to illuminate the spallation behavior of the Cu with SFT. It is revealed that the SFT collapses during shock compression and induces the generation of dislocations and stacking faults in the material. Subsequently, spallation happens when the voids nucleate and grow in the region of dislocations and stacking faults. Moreover, the materials show different spallation behaviors at different shock intensities. When <i>U</i><sub>p</sub> ≤ 1.0 km/s, only elastic deformation occurs in perfect single crystal copper under shock compression, but in the copper with SFT, local defects appear and plastic deformation occurs due to the collapse of SFT under shock compression. The influence of SFT on spallation is most pronounced at a medium shock intensity. When <i>U</i><sub>p</sub> = 0.75 km/s, the local defects caused by the collapse of SFT provide a wider nucleation area for the voids and promote the heterogeneous nucleation of the voids, resulting in the decreasing of the spall strength. The void nucleation of single crystal copper with SFT is found to be much later than the perfect one and the rate of spall damage evolution also decreases due to energy dissipation during SFT’s collapse and plastic deformation. When <i>U</i><sub>p</sub> increases to 1.25 km/s, shock compression induces many defected atoms in both samples, so the SFT has little influence on the spall strength and spall damage of the materials.

Challenges to model the role of heterogeneities on the shock response and spall failure of metallic materials at the mesoscales

The predictive modeling of the experimentally observed behavior of metallic materials under shock loading conditions (wave structures, spall strengths) is a critical challenge toward the design of next-generation structural materials. This challenge is due to the lack of computational methods that can predict microstructural evolution at the mesoscales under dynamic loading conditions. While classical molecular dynamics simulations have been able to provide atomic-scale insights in the defect and damage nucleation/evolution mechanisms, the capability to have a direct comparison with experimental data at the same time and length scales is still a challenge. The current computational approaches require that several approximations be made either for the loading conditions or for the micromechanisms related to defect evolution and interaction at the mesoscales. This viewpoint discusses the insights obtained from molecular dynamics simulations of shock deformation and spall failure of heterogeneous metallic microstructures. An example Al–Ni microstructure is used to identify the critical atomic-scale phenomena that need to be addressed by the mesoscale methods when considering shock deformation and failure (spallation) at the mesoscales.

Shock Experimentation of a Direct Oil Heater Used In Ships

Mechanical shock and vibrations are the major problems, which affects the machinery or equipment. In the present scenario, when exposed to the specified shock analysis, the equipment continues to work satisfactorily without time restrictions. Mechanical shock covers the transient mechanical response .In marine environment, an underwater explosion impart to the hull a force which causes rapid local movement both to the hull structure and machinery or equipment attach to it. This work is mainly focused on the shock analysis of a direct oil heater used in ships. It includes the following analysis are as follows: Shock analysis process & procedure, stress analysis and permissible proof stress analysis and finite element analysis of different parts namely shell, saddle support, plate flange, heating element. The analysis is made to check the shock strength of the equipment, which has been analyzed to operate under severe conditions of shock loading due to underwater explosion. The finite element analysis is an indirect method of stress analysis to analyze the different parts of a heater with considering the shock forces. The values of stresses obtained are compared with the permissible values of the stresses. The permissible stresses are found for different time durations (viz < 5ms, 48ms, >50ms). Factor of safety is found for shocks in different directions.

Shock deformation and spallation of Cu bicrystals with (1 1 1) twist grain boundaries

The shock deformation and spallation of Cu bicrystals with (111) twist grain boundary (GB) of different misorientation angles are investigated by using molecular dynamics simulations. The selected GBs include low angle (LAGB), near twin (NTGB) and intermediate angle (IAGB) twist GBs, and the shock direction is along the GB normal. It is demonstrated that the bicrystals are of lower Hugoniot elastic limit than single crystal, as the twist GBs provide dislocation sources for deformation. At the shock compression stage, GB plasticity at the LAGBs and NTGBs is initiated via reaction and dissociation of GB dislocations, and can be triggered by elastic shock wave more readily than that at the IAGBs, on which dislocation emission is homogeneous and irrelevant to initial GB dislocations. At the tension stage, the incipient spall for different twist GBs occurs at an identical shock strength, but is of different details in dislocation and void evolutions. With varying shock strength and misorientation angle, spall strength of the Cu bicrystals depends on whether GB plasticity is produced at the compression stage, and the values are consistent with that of Cu single crystal under similar shock loading conditions.

Fracture behavior of magnesia refractory materials under combined cyclic thermal shock and mechanical loading conditions

AbstractTo investigate the effect of cyclic thermal shock and mechanical loading on the fracture behavior of magnesia refractories showing different brittleness, the as‐received and cyclic thermally shocked specimens are subjected to monotonic and cyclic wedge splitting test. The whole duration of test is monitored by digital image correlation and acoustic emission. Both thermal and mechanical fatigue resistance increase with the reduction of brittleness. Repetitive thermal shock results in pronounced reduction of strength. However, the specific fracture energy and nonlinearity increase after exposure to thermal shock due to the expanded micro‐crack network inducing the development of a significant fracture process zone. Periodic loading mainly leads to the decrease of strain bearing capacity, as the fatigue loads favor the extension of crack tip instead of fracture process zone expansion. The combined application of periodic thermal shock and mechanical loads gives a new insight into the progressive damage behavior of refractory under critical conditions.

Mechanically induced grain refinement, recovery and recrystallization of cold-sprayed iron aluminide coatings

FeAl coatings can be processed by cold spraying conditions only under the use of well-tuned parameter sets that guarantee shock-loading conditions, which provide sufficient ductility in iron aluminide intermetallic compounds and are capable to ensure sufficient heat creation and thus thermally softened interfaces for bonding. Original microstructures, present in the powder feedstock particles, locally change under the respectively applied loads and temperatures. Given the challenge due to the anomaly softening of such ordered alloys, the present study describes and discusses the differences of coating microstructures in terms of the effect of spraying parameters such as particle size, gas pressure, spraying distance and substrate heating. Electron backscatter diffraction analysis provides elucidation on the grain refinement mechanisms and internal particle strain upon particle impact. The microstructural characterization is complemented by the misorientation analysis within single grains, which is correlated with the spraying parameters and the respective thermal energy input. The misorientation analysis allows for analyzing grain refinement, internal grain bending and for elucidating associated stress relief mechanisms. The results show that the cold spray deposition of FeAl intermetallics can be explained by mechanically induced adiabatic shear instabilities as well as different recovery and recrystallization mechanisms causing a local stress relief.

X-ray radiography of microjetting from grooved surfaces in tin sample subjected to laser driven shock

When a triangular shock wave reflects from the free surface of a solid sample, microjetting may emit from the grooved surface, leading to high velocity approximately micrometer-size fragments. Microjetting is an important issue for material dynamic response under shock loading in both fundamental science and practical applications. In this paper, the dynamic process of microjetting is investigated in the laser-driven shock loading conditions, the experiments were performed at the ShenguangII-U (SGII-U) laser facility. Microjetting from the triangular grooves in the free surface of a tin sample is diagnosed with x-ray radiography, where the 40–200 keV high energy x-ray is created with the picosecond laser beam focused on a Au µ-wire target. The density distribution along the microjetting and cumulated mass can be inferred from the images radiographied by such ultrashot high energy x-ray. The density distribution shows two representative regions including the head region of microjetting with low density and high speed, and the root region with high density and low speed. The microjets from three continuous parallel grooves with 60° angle are significantly different from that of 120° angle, the effect of the groove angle was verified by numerical simulation and experimental results.

Fe0 inhibits bio-foam generating in anaerobic digestion reactor under conditions of organic shock loading and re-startup

Bio-foaming during the anaerobic digestion (AD) of the organic fraction of municipal solid waste (OFMSW) is a major cause of unstable reactor operations, especially under high organic loading rates (OLRs). Here, we used two 40-liter anaerobic reactors to deal with the actual organic fraction of municipal solid waste at OLRs of 5 and 7.5 kgVS/m3/d and tried to inhibit bio-foam generation by dosing with Fe0. One of reactors had 400 g of Fe0 added before operation and additional 200 g of Fe0 was added when the operating conditions changed; the other one was the control reactor with no Fe0 dosing. The results show that bio-foam was generated in the control reactor at an organic shock loading of 10 kgVS/m3/d and re-startup at 5 kgVS/m3/d, while the reactor containing Fe0 operated normally. Due to the surfactant attributes of volatile fatty acids (VFAs), the probability of bio-foam generation was positively correlated with the effluent’s degree of surface activity (SA) induced by VFAs, which is a parameter representing the foaming potential. Because VFA biodegradation was enhanced in the reactor with added Fe0, at the position of Fe0 accumulation, the SA was decreased by 49.7–59.2%. Furthermore, the effect of Fe0 dosing on inhibiting bio-foam was evaluated by comparison with traditional commercial anti-foam agents. The results suggest possible reasons for bio-foam generation in OFMSW AD and suggest the reasonable usage of Fe0 to inhibit bio-foam formation.