3D direct writing and micro detonation of CL-20 based explosive ink containing O/W emulsion binder

The booming development of DIW technology present an unprecedented prospect in energetic materials field and has attracted great interest due to its relative simplicity and high flexibility of manufacturing.Herein,a novel CL-20 based explosive ink formulation have been developed successfully for MEMS initiation systems via DIW technology.We designed PVA/GAP into an oil-in-water(O/W)emulsion,in the way that the aqueous solution of PVA as water phase,the ethyl acetate solution of GAP as oil phase,the combination of Tween 80 and SDS as emulsifier,BPS as a curing agent of GAP.The ideal formulation with good shear-thinning rheology properties and clear gel point was prepared using only 10 wt%emulsion.The dual-cured network formed during the curing process made the printed sample have good mechanical properties.The printed samples had satisfactory molding effect without cracks or fractures,the crystal form of CL-20 not changed and the thermal stability have improved.Deposition of explosive inks via DIW in micro-scale grooves had excellent detonation performances,which critical detonation size was 1×0.045 mm,detonation velocity was 7129 m/s and when the corner reaching 150°can still detonated stably.This study may open new avenues for developing binder systems in explosive ink formulations.

Quasi-static and Dynamic Compressive Fracture Behavior of SiC_f/SiC Composites

To understand the quasi-static and dynamic compressive mechanical behavior of two- dimensional SiC fiber-reinforced SiC composites （2D-SiC1/SiC）, their compressive behavior at room temperature was investigated at a strain rate from 10-4 to 104/s, and the fracture surfaces and damage morphology were observed. The results show that the dynamic failure strength of 2D-SiC1/SiC obeys the Weibull distribution, and the Weibull modulus is 5,66. Meanwhile, 2D-SiC1/SiC presents a transition from brittle to tough with a decrease of strain rate, and 2D-SiC1/SiC has a more significant strain rate sensitivity compared to the 2D-C/SiC composites. The failure mode of 2D-SiC1/SiC depends upon the strain rate.

Two types of coaxial self-balancing robots

Two types of coaxial self-balancing robots(CSBR)were proposed,one can be used as a mobile robot platform for parts transporting in unmanned factory or as an inspector in dangerous areas,and the other can be used as a personal transporter ridden in cities.Mechanical designing and control structures as well as control strategies were described and compared in order to get a general way to develop such robots.A state feedback controller and a fuzzy controller were designed for the robot using DC servo motors and the robot using torque motors,respectively.The experiments indicate that the robots can realize various desired operations smoothly and agilely at the velocity of 0.6 m/s with an operator of 65 kg.Furthermore,the robustness of the controllers is revealed since these controllers can stabilize the robot even with unknown external disturbances.

Reaction Mechanism and Microstructure Evolution of Reaction Sintered h-BN

Hexagonal boron nitride ceramic（h-BN） based on the nitridation of B powders was obtained by reaction sintering method. The effects of sintering temperature on the mechanical properties and microstructure of the resultant products were investigated and the reaction mechanism was discussed. Results showed that the reaction between B and N2 occurred vigorously at temperatures ranging from 1 000 ℃ to 1 300 ℃, which resulted in the generation of t-BN. When the temperature exceeded 1 450 ℃, transformation from t-BN to h-BN began to occur. As the sintering temperature increased, the spherical particles of t-BN gradually transformed into fine sheet particles of h-BN. These particles subsequently displayed a compact arrangement to achieve a more uniform microstructure, thereby increasing the strength.

Effect of pH, milling time, and Isobam content on porous silicon nitride ceramics prepared by gel casting

As a non-toxic copolymer of isobutylene and maleic anhydride,Isobam is successfully used as a dispersant and a gelling agent for fabricating porous Si_(3)N_(4) ceramics by gel casting.The dispersity and rheological properties of the Si_(3)N_(4) slurry are influenced by the pH,milling time,and Isobam content which varies from 0.1 wt.%to 0.6 wt.%,and these factors are investigated.The slurry with 40 vol.%solid content and milled for 4 h has a high zeta potential at pH 12(adjusted by Tetramethyl ammonium hydroxide(TMAH)),which means that the particles are well dispersed.The mechanisms of TMAH are electrostatic repulsion and steric hindrance.The viscosity of the slurry increases with the increase of Isobam content.After pressureless sintering at 1700℃ for 2 h,a uniform unique interlocking microstructure of rod-like β-Si_(3)N_(4) grains is observed,which may improve the flexural strength of the ceramics by intergranular fracture and particle pullout of β-Si_(3)N_(4) grains.The density and porosity of the samples fluctuate negligibly with the increase of Isobam content,and the Si_(3)N_(4) ceramic with 0.1 wt.% Isobam exhibits the highest bending strength of 251.6 MPa among all samples.

Research on Maintenance Information Management System for Distributed Manufacture System

An architecture and design of a maintenance information management system for distributed manufacture system is presented in this paper, and its related key technologies are studied and implemented also. A frame of the maintenance information management system oriented human-machine monitoring is designed, and using object-oriented method, a general maintenance information management system based on SQL server engineering database and adopted client/server/database three-layer mode can be established. Then, discussions on control technologies of maintenance information management system and remote distributed diagnostics and maintenance system are emphasized. The system is not only able to identify and diagnose faults of distributed manufacture system quickly, improve system stability, but also has intelligent maintenance functions.

Electrochemical Corrosion,Wear,and Tribocorrosion Behavior of Novel Ti-19Zr-10Nb-1Fe Alloy

The electrochemical corrosion,wear,and tribocorrosion behavior of the novel Ti-19Zr-10Nb-1Fe alloy were investigated.The electrochemical corrosion analysis results show that the corrosion resistance of the Ti-19Zr-10Nb-1Fe alloy is better than that of the Ti-6Al-4V alloy under the test conditions in this research.Compared with the static electrochemical corrosion,the corrosion resistance of Ti-19Zr-10Nb-1Fe alloy during tribocorrosion decreases significantly,because the wear accelerates corrosion.The wear volume of Ti-19Zr-10Nb-1Fe alloy is increased with the increase in applied load whether the electrochemical corrosion occurs or not.Due to the acceleration effect of electrochemical corrosion,the wear volume caused by electrochemical corrosion is larger than that without electrochemical corrosion.The results of Wa/Wc are much greater than 10,indicating that during the tribocorrosion process,the material loss caused by mechanical wear is much larger than that caused by electrochemical corrosion.Through SEM observation of the wear morphologies of Ti-19Zr-10Nb-1Fe alloy after tribocorrosion,it can be inferred that the micro-abrasion is the main wear mechanism.The above results show that during the tribocorrosion process,the corrosion accelerates wear,and the wear accelerates corrosion.

Investigation into the roles of interfacial H_(2)O structure in catalytic oxidation of HCHO and CO over CuMnO_(2) catalysts

The rapid deactivation of cost-effective MnO_(2)-based catalysts in humid air limits their application in practice,and the identification of the role of water in an oxidation process is significant for developing water-resistant MnO_(2)-based catalysts.Here,CuMnO_(2)showed a20.3%HCHO conversion in 10 hr at room temperature in humid air with relative humidity of 40%,but deactivated in 3 hr in dry air.The excellent activity and stability of HCHO oxidation in humid air were attributed to the positive effect of H_(2)O on HCHO oxidation to the H_(2)O-HOCH_(2)OH supermolecule assemblies via hydrogen bonds formed on CuMnO_(2).H_(2)O-HOCH_(2)OH supermolecule assemblies tend to be oxidized to carbonate,which is further oxidized to CO_(2).Furthermore,CuMnO_(2)exhibited a much poorer activity of CO oxidation in humid air,but the CO conversion was still 100%in 10 hr in dry air.H_(2)O showed a competitive adsorption effect to CO on CuMnO_(2).CuMnO_(2)could be applied in HCHO elimination in humid air and CO elimination in dry air.

Formation mechanisms of Ti_(3)(Si,Al)C_(2)/Al_(2)O_(3) composites from Ti_(3)AlC_(2) and SiO via low-temperature sintering

Ti_(3)SiC_(2)/Al_(2)O_(3) composites have attracted attention due to their excellent mechanical and electromagnetic properties,but the high temperatures(≥1400℃)required for the densification of aluminum oxide(Al_(2)O_(3))leads to the decomposition of Ti_(3)SiC_(2).To address this issue,Ti_(3)(Si_(x)Al_(1−x))C2/Al_(2)O_(3)(x represents the Si content)composites were synthesized for the first time via hot-pressing(HP)sintering and current-assisted sintering(CAS)of mixed Ti_(3)AlC_(2) and silicon monoxide(SiO)powders at 1300 and 1200℃,respectively.Both approaches produced composites with x values greater than 0.9,indicating that the compositions of the prepared composites were similar to those of Ti_(3)SiC_(2)/Al_(2)O_(3) composites.The synthetic mechanism involved substitution and continuous interdiffusion of Al and Si atoms.The composite prepared by CAS at 1200℃ was compacted,whereas the composite prepared by HP had a low density.The low-temperature densification mechanism is attributed to the combined effects of amorphous SiO,liquid Al,and the high heating rates for CAS.The flexural strength and hardness of the composite prepared by CAS were also comparable to those of compacted Ti_(3)SiC_(2)/Al_(2)O_(3) composites.

辐照缺陷装饰位错是否会导致硬化?

纳米尺寸的辐照缺陷常常会在位错线附近聚集,形成装饰效应.研究者通常采用级联诱导源硬化模型描述装饰效应引起的辐照硬化.本研究工作发现不可动辐照缺陷装饰位错会导致辐照硬化,硬化程度与理论模型预测一致.然而,当装饰辐照缺陷可动时,则不发生辐照硬化,甚至发生软化,这种硬化消失是由于位错环始终处于与位错线相互作用力近似为零的区域,并与位错线发生关联运动.该工作带来了对辐照缺陷装饰效应和辐照硬化的新理解.

Summarization on variable liquid thrust rocket engines

The technology actuality and development trend of variable thrust rocket engines at home and abroad are summarized. Key technologies of developing variable thrust rocket engines are analyzed. Development advices on developing variable thrust rocket engines that are adapted to the situation of our country are brought forward.

橡胶类材料有限变形黏-超弹性损伤模型:理论和数值实现

橡胶类材料存在着超弹性、时间相关性、率相关性和渐进损伤行为.作者之前的工作提出了一种超弹性损伤模型去描述软材料的应变软化行为(Lu et al.,2020).模型在单根分子链应变能函数中引入损伤变量D,然后将宏观变形和单链分子的伸长率联系在一起.本文改进了之前的模型,通过引入以Prony级数为基础的非线性黏弹性理论使得模型可以表征时间相关黏性效应.本文进一步将建立的有限变形黏-超弹性损伤本构模型在有限元软件ABAQUS中通过用户自定义子程序UMAT实现.本文利用文献中丙烯酸聚合物在单轴拉伸下的实验数据来校准本构模型的10个参数:包括4个弹性参数和6个黏性参数.利用ABAQUS模拟丙烯酸聚合物复杂几何形状试样的单轴拉伸和应力松弛,仿真结果与实验数据一致性较好.