Microstructure and mechanical properties of laser beam welded Al–Li alloy 2060 with Al–Mg filler wire

Alloy 2060-T8 is a newly developed high-strength Al–Li alloy for applications in aircraft industry. Crack-free welds were obtained in laser beam welding with 5087 filler wire under optimized welding conditions. In this paper, fusion zone microstructure and joint mechanical properties were investigated. Microstructure typical for the weld metal consists of α-Al matrix with a few nanoscale precipitates inside and a coarse icosahedral quasicrystalline T₂ phase at the dendritic and grain boundaries. The quasicrystalline occurred normally in Al–Li–Cu alloys with higher Li contents. Our investigations show that the icosahedral quasicrystalline phase T₂ phase forms in the laser-welded Al–Li alloy 2060 with lower Li content as a result of segregation and replacement of Mg element. The joint tensile strength in as-welded condition is around 317 MPa, about 63% of that of the base metal, and fracture occurs within the fusion zone.     

Crystallographic structure- and texture-dependent fracture behavior of polycrystalline lead zirconate titanate ceramics

Journal of Electroceramics - The effect of crystallographic structure and texture on the fracture behavior of lead zirconate titanate (PZT) ceramics was investigated. PZT ceramics with Zr/Ti ratio...     

Ash-related issues during biomass combustion: Alkali-induced slagging,silicate melt-induced slagging (ash fusion), agglomeration,corrosion, ash utilization,and related countermeasures

Biomass is available from many sources or can be mass-produced. Moreover, biomass has a high energy-generation potential, produces less toxic emissions than some other fuels, is mostly carbon neutrality, and burns easily. Biomass has been widely utilized as a raw material in thermal chemical conversion, replacing coal and oil, including power generation. Biomass firing and co-firing in pulverized coal boilers, fluidized bed boilers, and grate furnaces or stokerfed boilers have been developed around the world because of the worsening environmental problems and developing energy crisis. However, many issues hinder the efficient and clean utilization of biomass in energy applications. They include preparation, firing and co-firing, and ash-related issues during and after combustion. In particular, ash-related issues, including alkali-induced slagging, silicate melt-induced slagging (ash fusion), agglomeration, corrosion, and ash utilization, are among the most challenging problems. The current review provides a summary of knowledge and research developments concerning these ash-related issues. It also gives an in-depth analysis and discussion on the formation mechanisms, urgent requirements, and potential countermeasures including the use of additives, co-firing, leaching, and alloying.Alkali species, particularly alkali chlorides and sulfates, cause alkali-induced slagging during biomass combustion. Thus, the mechanisms of generation, transformation, and sequestration of alkali species and the formation and growth of alkali-induced slagging, formed as an alternating overlapping multi-layered structure, are discussed in detail. For silicate melt-induced slagging (ash fusion), the evolutions of chemical composition of both the elements and minerals in the ash during combustion and existing problems in testing are overviewed. Pseudo-4D phase diagrams of (Ma₂O)-MaeO-P₂O₅-Al₂O₃ and (Ma₂O)-MaeO-SiO₂-Al₂O₃ are proposed as effective tools to predict ash fusion characteristics and the properties of melt-induced slagging. Concerning agglomeration that typically occurs in fluidized bed furnaces, melt-induced and coating-induced agglomeration and coating-forming mechanisms are highlighted. Concerning corrosion, seven corrosion mechanisms associated with Cl₂, gaseous, solid/deposited, and molten alkali chlorides, molten alkali sulfates and carbonates, and the sulfation/silication of alkali chlorides are comprehensively reviewed. The effects of alloying, salt state (solid, molten, or gaseous), combustion atmosphere, and temperature are also discussed systematically. For ash utilization, potential approaches to the use of fly ash, bottom ash, and biomass/coal co-fired ash as construction and agricultural materials are explored.Several criteria or evaluation indexes are introduced for alkali-induced slagging and agglomeration, and chemical equilibrium calculation and multicomponent phase diagrams of silicate melt-induced slagging and agglomeration. Meanwhile, remedies, including the use of additives, co-firing, leaching, alloying, and the establishment of regulations, are discussed.It is suggested that considerable attention should be focused on an understanding of the kinetics of alkali chemistry, which is essential for the transformation and sequestration of alkali species. A combination of heterogeneous chemical kinetics and multiphase equilibrium modeling is critical to estimating the speciation, saturation levels, and the presence of melt of the ash-forming matter. Further practical evaluation and improvement of the existing criterion numbers of alkali-induced slagging and agglomeration should be improved. The pseudo-4D phase diagrams of (Ma₂O)-MaeO-P₂O₅-Al₂O₃ and (Ma₂O)-MaeO-SiO₂-Al₂O₃ should be constructed from the data derived from real biomass ashes rather than those of simulated ashes in order to provide the capability to predict the properties of silicate melt-induced slagging. Apart from Cr, research should be conducted to understand the effects of Si, Al, and Co, which exhibit high corrosion resistance, and heavy metals such as Zn and Pb, which may form low-melting chlorides that accelerate corrosion. Regulations, cooperation among biomass-fired power plants and other industries, potential technical research, and logistics should be strengthened to enable the extensive utilization of biomass ash. Finally, alkali-induced slagging, silicate melt-induced slagging, agglomeration, and corrosion occur concurrently, and thus, these issues should be investigated jointly rather than separately.     

Science and technology of polymeric ablative materials for thermal protection systems and propulsion devices: A review

Ablative materials are at the base of entire aerospace industry; these sacrificial materials are used to manage the heat shielding of propulsion devices (such as liquid and Solid Rocket Motors (SRMs)) or to protect vehicles and probes during the hypersonic flight through a planetary atmosphere. Accordingly they are also known as Thermal Protection System (TPS) materials. Some non-polymeric materials have been successfully used as ablatives; however, due to their versatility, Polymeric Ablatives (PAs) represent the widest family of sacrificial TPS materials. In fact, when compared to non-polymeric ablatives such as high melting point metals, inorganic polymers (or metal oxides or carbides), PAs have some intrinsic advantages such as: tunable density, lower cost, and higher heat shock resistance. This review covers all main topics related to the science and technology of ablative materials with current and potential applications in the aerospace industry. After a short, yet comprehensive, introduction on non-ablative materials, this review paper summarizes fifty years of research efforts on polymeric ablatives, starting from the state of the art solutions currently used as TPS, up to covering the most recent efforts for nanostructuring their formulations.     

爆炸螺栓捕获器设计及捕获可靠性研究

针对大质量机动再入飞行器和高载荷条件,提出一种爆炸螺栓捕获器设计方案,并对爆炸螺栓的分离捕获过程进行了仿真计算;设计了可捕获可靠性试验,利用空气炮模拟爆炸螺栓分离冲击;通过高速、低速边界捕获试验,对捕获可靠性进行了评估.结果表明:捕获器设计方案及仿真计算正确,单个捕获器的捕获可靠度达到0.9999.     

3D printed ceramic phosphor and the photoluminescence property under blue laser excitation

An Al₂O₃/YAG: Ce³⁺ ceramic phosphor was fabricated for high-flux laser lighting using the digital lighting process (DLP)-based 3D printing method for the first time. The photocurable ceramic suspension for 3D printing was prepared by blending well-treated Al₂O₃/YAG: Ce³⁺ composite powders with photosensitive resin monomers and photo-initiators. The printing parameters, debinding and sintering processes were designed delicately to fabricated the dense sub-millimeter-sized cylinder ceramic with high dimensional accuracy. The ceramic showed excellent luminescence property under blue laser excitation with a threshold of 20.7 W/mm², higher than that prepared via dry-pressing followed by vacuum sintering. The luminescence properties and the microstructures of both ceramics were further comparatively investigated to find the possible interpretations for improvement of laser flux for the 3D-printed ceramic. The present work indicated that the new developed 3D printing method was promising for preparing luminescent ceramics for high-flux laser lighting in a rapid, effective, low-cost and precision-controlled manner.     

三维加速度测试横向灵敏度交叉影响消除方法

针对传感器横向灵敏度较大,容易影响径向加速度测试结果的问题,提出了一种消除三维加速度测试传感器横向灵敏度交叉影响的方法。该方法首先利用冲击台静态标定加速度传感器,得出加速度横向灵敏度校正矩阵,再对测得的加速度进行校正便可得出引信安全系统部位内弹道中间段三维加速度。分析与试验表明:将加速度横向灵敏度作为三向加速度校正因子,能够确保三维加速度测试曲线准确,从而有助于分析和判断引信瞎火甚至早炸故障。     

弹体非正撞击/侵彻载荷响应的一种半经验分析方法

针对非正撞击/侵彻情况下的弹体结构动响应预示问题,将球形腔膨胀理论与经验方法结合,提出了一种弹体非正撞击/侵彻动载荷计算的半经验方法.基于本文半经验方法,沿终点弹道计算侵彻弹体的动载荷时间历程,进一步运用模态叠加法求解弹体结构动响应,对多个弹体算例的侵彻过载和应力进行预示并与数值仿真结果对比表明本文方法具有较强适应性,...     

大锥角药型罩聚能装药结构对混凝土介质侵彻研究

采用脉冲X光照相、威力效应实验及数值模拟方法,对两种不同形状的大锥角药型罩聚能装药结构对混凝土的侵彻能力进行了研究,实验测试获得了大锥角截顶药型罩装药结构形成的爆炸成型杆式侵彻体的形状、头尾速度及对混凝土靶的侵彻参量;采用AUTODYN-2D程序对两种结构药型罩聚能装药的成形过程和侵彻过程进行了数值模拟.结果表明,相比于大锥角截顶药型罩,大锥角球缺型药型罩所形成的爆炸成型杆式侵彻体在混凝土靶中形成的孔道更能满足复合侵彻战斗部对一级侵彻的要求.     

聚能切割索切割能力仿真及试验研究

为深入研究聚能切割索的切割能力,采用数值仿真和试验的手段研究了聚能切割索（Flexible Linear Shaped Charge,FLSC）切割不同材料铝板的切割效果。仿真和试验结果表明：材料的屈服强度对侵彻性能影响最大,随着被切割对象屈服强度的增大,侵彻深度降低。