Evolution of molecular structure of TATB under shock loading from transient Raman spectroscopic technique

By combination of the transient Raman spectroscopic measurement and the density functional theoretical calculations,the structural evolution and stability of TATB under shock compression was investigated.Due to the improvement in synchronization control between two-stage light gas gun and the transient Raman spectra acquisition,as well as the sample preparation,the Raman peak of the N-O mode of TATB was firstly observed under shock pressure up to 13.6 GPa,noticeably higher than the upper limit of 8.5 GPa reported in available literatures.By taking into account of the continuous shift of the main peak and other observed Raman peaks,we did not distinguish any structural transition or any new species.Moreover,both the present Raman spectra and the time-resolved radiation of TATB during shock loading showed that TATB exhibits higher chemical stability than previous declaration.To reveal the detailed structural response and evolution of TATB under compression,the density functional theoretical calculations were conducted,and it was found that the pressure make N-O bond lengths shorter,nitro bond angles larger,and intermolecular and intra-molecular hydrogen bond interactions enhanced.The observed red shift of Raman peak was ascribed to the abnormal enhancement of H-bound effect on the scissor vibration mode of the nitro group.

Performance of a double-layer BAF using zeolite and ceramic as media under ammonium shock load condition

An experiment was carried out to investigate the anti-ammonium shock load capacity of a biological aerated filter （BAF） composed of a double-layer bed. This bed was made up of a top layer of ceramic and a bottom layer of zeolite. The experiment shows that the anti-ammonium shock load process can be divided into two processes： adsorption and release. In the adsorption process, the total removal efficiency of ammonia nitrogen by zeolite and ceramic was 94%. In the release process, the ammonia nitrogen concentration increased significantly and then gradually returned to the normal level four hours after the shock load. The results indicated that the double-layer BAF had a high level of adaptability to the short-term ammonium shock load and long-term operation. The main factors influencing the dynamic process of ammonia nitrogen adsorption were the filter bed height, ammonia nitrogen concentration of influent, and flow rate. The bed depth service time （BDST） model was used to predict the relationship between the filter bed height and breakthrough time at different flow rates, and the results are reliable.

Simplified design of rock cavern concrete lining to resist shock loading

A simplified method was proposed for the design of concrete lining in underground rock cavern/tunnel against shock loading. The loading may result from the detonation of explosives on ground surface or ground penetration projectiles exploding adjacent to the cavern/tunnel. The resulting problem necessitates the solution of the dynamics of a beam loaded by a transient pressure uniformly distributed over the span. According to mechanical characteristics of the system with rock bolt and shotcrete, a dynamic support design method based on equivalent single degree of freedom （SDOF） was put forward. The SDOF method was applied to obtaining the maximum displacement at the mid-span of the beam, which is often the controlling factor in the blast-resistant design. In the formulation of the problem, the proposed method combines the phenomena of spalling and structural dynamics theory. An example is provided to demonstrate the applicability of this simplified method.

Spall in Aluminium with Helium Bubbles under Laser Shock Loading

The spallation behaviors of Al＋0.2wt% ^10B targets and neutron irradiated Al＋0.2wt% ^10B targets with 5nm radius helium bubble subjected to direct laser ablation are presented. It is found that the spall strength increases significantly with the tensile strain rate, and the helium bubble or boron inclusions in aluminum reduces the spall strength of materials by 34%. However, slight difference is observed in the spall strength of unirradiated samples compared with the irradiated sample with helium bubbles.

Phase Transformations in ZrO_2 after Shock Loading

The effects of shock loading on the morphology,grain growth during heating and phase transforma- tion of ZrO_2 have been investigated.It is shown that shock loading may be efficiently used to modify submicron ceramic powders with nanocrystalline structure.After shock loading,the critical diameter of ZrO_2 particles transformed from tetragonal to monoclinic decreased due to stored strain energy. Annealing of powders resulted in reversible transformation to the tetragonal without considerable grain growth up to 1200℃.

Dynamic strength behavior of a Zr-based bulk metallic glass under shock loading

Dynamic strength behavior of Zr51Ti5NiloCu25A19 bulk metallic glass （BMG） up to 66 GPa was investigated in a series of plate impact shock-release and shock-reload experiments. Particle velocity profiles measured at the sample/LiF window interface were used to estimate the shear stress, shear modulus, and yield stress in shocked BMG. Beyond confirm- ing the previously reported strain-softening of shear stress during the shock loading process for BMGs, it is also shown that the softened Zr-BMG still has a high shear modulus and can support large yield stress when released or reloaded from the shocked state, and both the shear modulus and the yield stress appear as strain-hardening behaviors. The work provides a much clearer picture of the strength behavior of BMGs under shock loading, which is useful to comprehensively understand the plastic deformation mechanisms of BMGs.

Plasticity and melting characteristics of metal Al with Ti-cluster under shock loading

Impurity agglomeration has a significant influence on shock response of metal materials.In this paper,the mechanism of Ti-clusters in metal Al under shock loading is investigated by non-equilibrium molecular dynamics simulations.Our results show that the Ti-cluster has obvious effects on the dislocation initiation and melting of bulk Al.First,the Ti clusters induces the strain concentrate and leads the dislocations to be initiated from the interface of Ti cluster.Second,dislocation distribution from the Ti-cluster model results in a formation of a grid-like structure,while the dislocation density is reduced compared with that from the perfect Al model.Third,the critical shock velocity of dislocation from the Ti-cluster model is lower than from perfect Al model.Furthermore,it is also found that the temperature near the interface of Ti-cluster is100 K–150 K higher than in the other areas,which means that Ti-cluster interface melts earlier than the bulk area.

Stress Analysis of Printed Circuit Board with Different Thickness and Composite Materials Under Shock Loading

In this study,the deformation and stress distribution of printed circuit board(PCB)with different thickness and composite materials under a shock loading were analyzed by the finite element analysis.The standard 8-layer PCB subjected to a shock loading 1500 g was evaluated first.Moreover,the finite element models of the PCB with different thickness by stacking various number of layers were discussed.In addition to changing thickness,the core material of PCB was replaced from woven E-glass/epoxy to woven carbon fiber/epoxy for structural enhancement.The non-linear material property of copper foil was considered in the analysis.The results indicated that a thicker PCB has lower stress in the copper foil in PCBs under the shock loading.The stress difference between the thicker PCB(2.6 mm)and thinner PCB(0.6 mm)is around 5%.Using woven carbon fiber/epoxy as core material could lower the stress of copper foil around 6.6%under the shock loading 1500 g for the PCB with 0.6 mm thickness.On the other hand,the stress level is under the failure strength of PCBs with carbon fiber/epoxy core layers and thickness 2.6 mm when the peak acceleration changes from 1500 g to 5000 g.This study could provide a reference for the design and proper applications of the PCB with different thickness and composite materials.

Enhancement of seal life through carbon composite back-up rings under shock loading conditions in defence applications

The life of Nitrile Butadiene Rubber(NBR) O-ring seal having shore hardness of A70 and A90 under shock loading conditions was investigated by a specially designed pneumo-hydraulic shock test rig. Shock tests have been carried out on bare seals, seal with conventional polytetrafluoroethylene(PTFE) back-up rings and seal with newly developed carbon composite back-up rings to study its behaviour under different operating conditions until failure. Experiments were conducted by varying annular gap ranging from 0.3 to 0.5 mm, oil temperature from 30 ℃ to 70 ℃ and rate of pressure rise from 600 to 2400 MPa/s. Significant enhancement in seal life was observed with carbon composite back-up ring at reduced annular clearances compared to seal life with conventional PTFE back-up ring and without back-up rings.

Robustness of anammox granular sludge treating low-strength sewage under various shock loadings:Microbial mechanism and little N2O emission

With the increasing application of anammox for the treatment of high-strength industrial wastewater,application of anammox in municipal sewage has been gaining more attention.Sludge granulation in particular enhances the enrichment and retention of anammox bacteria in municipal sewage treatment systems.However,the performance of granular sludge under continuous and varying hydraulic loading shock remains little understood.In this study,the robustness of anammox granular sludge in treating lowstrength municipal sewage under various shock loadings was investigated.Results showed that an upflow anaerobic sludge blanket(UASB)reactor with anammox granules performed well,with anammox specific activity up to 0.28 kg N/kg VSS/day and anti-loading shock capability up to 187.2 L/day during the 8-month testing period.The accumulation rate of N2O(<0.01 kg N/kg VSS/day)in the liquid phase was seven times higher than that of the gas phase,which could be mainly attributed to the incomplete denitrification and insufficient carbon source.However,only a small part of the produced N2O escaped into the atmosphere.High-throughput sequencing and molecular ecological network analyses also identified the bacterial diversity and community structure,indicating the potential resistance against loading shock.The composition and structural analyses showed that polysaccharides were an important functional component in the tightly bound extracellular polymeric substances(TB-EPS),which was the major EPS layer of anammox granules.Scanning electron microscopy(SEM)also showed that the gaps in between the anammoxclusters in the granules inhibit the flotation of the sludge and ensure efficient settling and retention of anammox granules.

Experimental Study on the Dynamic Mechanical Properties of Reinforced Concrete under Shock Loading

A simple experimental method was introduced to study the mechanical properties of reinforced concrete under shock loading. The one-stage light gas gun was used to test the me- chanical properties of reinforced concrete with different reinforcement ratios under various impact velocities. Three Mn-Cu piezoresistive pressure gauges embedded in the target were used to record the voltage-time signals, from which the stress-strain curves of reinforced concrete were obtained using Lagrangian analysis. Experimental results indicated that the load-bearing capacities of re- inforced concrete increased greatly with the impact velocity and the reinforcement ratio. The peak stress of the shock wave decreased exponentially with the propagation distance.

Performance of biotrickling filters for hydrogen sulfide removal under starvation and shock loads conditions

In the industrial operation of biotrickling filters for hydrogen sulfide(H2S) removal,shock loads or starvation was common due to process variations or equipment malfunctions.In this study,effects of starvation and shock loads on the performance of biotrickling filters for H2S removal were investigated.Four experiments were conducted to evaluate the changes of biomass and viable bacteria numbers in the biotrickling filters during a 24-d starvation.Compared to biomass,viable bacteria numbers decreased significantly during the starvation,especially when airflow was maintained in the absence of spray liquid.During the subsequent re-acclimation,all the bioreactors could resume high removal efficiencies within 4 d regardless of the previous starvation conditions.The results show that the re-acclimation time,in the case of biotrickling filters for H2S removal,is mainly controlled by viable H2S oxidizing bacteria numbers.On the other hand,the biotrickling filters can protect against shock loads in inlet fluctuating H2S concentration after resuming normal operation.When the biotrickling filters were supplied with H2S at an input of lower than 1700 mg/m3,their removal efficiencies were nearly 98% regardless of previous H2S input.

Reliability Analysis of Filtering Reducers Considering Temperature Correction and Shock Load of Space

Owing to some excellent properties(such as large transmission ratio, high reliability, high precision,large stiffness, small volume and long service life), filtering reducers are suitable for occasions with high requirements(e.g. space equipment). However, the tough working condition in space(including frequent changes of temperature, and large temperature difference combined with shock loads) may significantly affect the reliability.In this paper, the expressions of the minimal and maximal instantaneous transmission ratios(ITRs) considering temperature correction are developed. The minimal and maximal ITRs from simulation are used to verify the accuracy. Moreover, the reliability of a filtering reducer under different temperatures and the shock load are calculated, respectively. The research is beneficial to the design of spacecraft mechanism.

Dynamic response and damage evolution of Zr-based bulk metallic glass under shock loading

Dynamic response and damage evolution of Zr_(70)Cu_(13)Ni_(9.8)Al_(3.6)Nb_(3.4)Y_(0.2) bulk metallic glass(Zr-based BMG)under impact pressure ranging from 4.03 GPa to 27.22 GPa were studied.The Hugoniot Elastic Limit(HEL)and the spalling Strength(σ_(sp))were measured as 7.09 GPa and 2.28 GPa,and the curve of impact velocity(D)and particle velocity(u)were also obtained.Under the strain rate of~10^(5)s^(-1),local crystallization phenomenon was observed.As increasing the impact pressure,the failure mode of Zr-based BMG changed from spallation to fragmentation caused by the combination of spalling cracks and longitudinal cracks.Cone-cup structures were also observed in the internal spalling zone via nano-CT characterization.When increasing the impact pressure,the thickness of Zr-based BMG increased after impact and the remelting and cladding layers were also observed on the fracture surfaces.The fragments of the specimen were welded after impact due to the high temperature remelting,which causes plastic deformation of Zr-based BMG under shock loading.

Influence of structural factors on the strength properties of aluminum alloys under shock wave loading

The results of measurements of the strength characteristics-Hugoniot elastic limit and spall strength of aluminum and aluminum alloys in different structural states under shock wave loading are presented.Single-crystals and polycrystalline technical grade aluminumА1013 and aluminum alloysА2024,АА6063Т6,А1421,A7,А7075,А3003,A5083,АА1070 in the initial coarse-grained state and ultrafine-grained or nanocrystalline structural state were investigated.The refinement of the grain structure was carried out by different methods of severe plastic deformation such as Equal Chanel Angular Pressing,Dynamic Channel Angular Pressing,High-Pressure Torsion and Accumulative Roll-Bonding.The strength characteristics of shock-loaded samples in different structural states were obtained from the analysis of the evolution of the free surface velocity histories recorded by means of laser Doppler velocimeter VISAR.The strain rates before spall fracture of the samples were in the range of 10^(4)-10^(5 )s^(-1),the maximum pressure of shock compression did not exceed 7 GPa.The results of these studies clearly demonstrate the influence of structural factors on the resistance to high-rate deformation and dynamic fracture,and it is much less than under the static and quasi-static loading.

Viscosity of aluminum under shock-loading conditions

A reliable data treatment method is critical for viscosity measurements using the disturbance amplitude damping method of shock waves. In this paper the finite difference method is used to obtain the numerical solutions for the disturbance amplitude damping behaviour of the sinusoidal shock front in a flyer-impact experiment. The disturbance amplitude damping curves are used to depict the numerical solutions of viscous flow. By fitting the experimental data to the numerical solutions of different viscosities, we find that the effective shear viscosity coefficients of shocked aluminum at pressures of 42, 78 and 101 GPa are （1500±100） Pas, （2800±100） Pa.s and （3500±100） Pa.s respectively. It is clear that the shear viscosity of aluminum increases with an increase in shock pressure, so aluminum does not melt below a shock pressure of 101 GPa. This conclusion is consistent with the sound velocity measurement.

EFFECT OF STACKING－FAULT ENERGY ON RESIDUALSUBSTRUCTURE OF EXPLOSIVE SHOCK LOADED METALS

ＥＦＦＥＣＴＯＦＳＴＡＣＫＩＮＧ－ＦＡＵＬＴＥＮＥＲＧＹＯＮＲＥＳＩＤＵＡＬＳＵＢＳＴＲＵＣＴＵＲＥＯＦＥＸＰＬＯＳＩＶＥＳＨＯＣＫＬＯＡＤＥＤＭＥＴＡＬＳＹａｎｇＹａｎｇ；ＺｈａｎｇＸｉｎｍｉｎｇ（ＣｅｎｔｒａｌＳｏｕｔｈＵｎｉｖｅｒｓｉｔｙｏｆＴ...

Investigation on the Shock Response of Vitreous Carbon

The dynamic response of vitreous carbon to uniaxial strain loading has been investigated by means of the plate impact experiments. The two x cut shorted quartz gauges assembled with impactor and target were used to obtain the wave speeds in material and the stress histories at the sample gauge interface. The wave speed and stress histories were analyzed to determine the peak state in the sample. For compressive stress up to 4 0 GPa, the wave profiles were observed to be simple and steady, the uniaxial strain response is essentially nonlinear elastic, and no inelastic deformation has been found. All the experiment results indicate that the Hugoniot curve of vitreous carbon is concave downward just like that of fused silicon. There is no shock wave but the compressed wave propagating in the impacted samples.

冲击加载-卸载-再加载条件下Cr-Ni-Mo钢的层裂损伤

基于一级轻气炮加载技术,利用不同类型的多层复合飞片,实现了冲击加载-卸载-再加载路径,结合回收表征以及一维流体力学模拟,对Cr-Ni-Mo钢在冲击加载-卸载-再加载路径下的层裂损伤行为进行了深入研究。结果表明,在冲击加载-卸载-再加载路径下,层裂面会重新闭合并形成微损伤带,而孔洞位置仍然位于原奥氏体边界和板条群边界处,裂纹仍保持穿晶+沿晶的混合断裂模式。此外,第1层飞片与样品之间存在的较大阻抗差异会导致自由面速度中的再加载信号缺失。这些发现为深入理解Cr-Ni-Mo钢在复杂加载路径下的层裂行为提供了重要参考。

冲击载荷作用下钽电容的电压瞬变特性及微观机理

为探究钽电容在冲击载荷作用下的失效机制,设计并开展了5组不同强度的钽电容水下爆炸冲击实验,研究了冲击载荷作用下钽电容的电压瞬变特性,通过漏电、充电电流变化分析了钽电容的失效模式,利用扫描电镜观察钽电容的微观结构,讨论了冲击载荷作用下钽电容的失效机理。结果表明:钽电容受冲击后发生短路失效,电压大幅度降低,在自愈完成后电压缓慢上升。随着冲击波超压的增大,钽电容失效的概率增大,钽电容失效的临界超压约为32 MPa。不同类型的电压变化对应不同的失效模式,包括击穿后瞬间自愈、击穿后缓慢自愈和多次击穿自愈。不同类型电压变化的初始漏电电流峰值有较大差别,Ⅰ类电流峰值为2.5~5 A,Ⅱ类为1~2 A,Ⅲ类为8~9 A,且峰值越大,峰宽越小。冲击载荷作用下钽电容的微观失效机理与其氧化膜的瑕疵相关,机理包括氧化膜中微裂缝扩展使得局部电场强度超过击穿场强造成击穿、氧化膜较薄区域下方的杂质及晶态膜突出形成导电通道、贯穿型裂缝形成后气体电离导致的击穿。