Al基和Al-6Si基闭孔泡沫铝的动态压缩性能

利用熔体转移发泡法制备了不同密度的Al基和Al-6Si基闭孔泡沫铝(CCAF),探讨了CCAF基体的微观形貌及物相组成,对其动态压缩性能进行了研究。结果表明:Al基CCAF基体微观形貌较单一,基本上是小块状(Al20CaTi2);而Al-6Si基CCAF基体微观形貌复杂,主要呈大片状(Al3.21Si0.47和CaAl2Si3)、长针状(Al3Ti)和小白点(Al2O3)。动态压缩结果显示:Al基CCAF压缩应力—应变曲线较平缓,断裂层有明显的材料撕裂痕迹;而Al-6Si基CCAF压缩应力—应变曲线不光滑,个别曲线波动较大,断裂层出现显著的脆性材料断裂特征;随着相对密度的增加,Al基和Al-6Si基CCAF屈服强度(σpl)和表观弹性模量(E0.2)整体趋势都在增加。     

泡沫填充铝合金多胞防爬器的吸能机理

提出了一类新型防爬器—泡沫填充铝合金多胞防爬器，并通过数值仿真结合试验验证的方法研究了其在轴向荷载作用下的能量吸收机理。结果表明，填充闭孔泡沫铝并提高其密度可以在峰值压溃力几乎不变的前提下有效提高铝合金多胞防爬器的能量吸收能力，且能够进一步提升蒙皮材料的吸能潜力。此外，当壁厚较小时，该防爬器极易产生不利于能量吸收的整体失稳；而壁厚增大时，防爬器的变形模式趋于稳定，总能量吸收增加，且蒙皮材料的能量吸收占比逐渐增加。     

开孔泡沫铝压坑变形的力学行为

分别采用圆柱体的平压头应力(FEP)、球面压头(SEP)和圆锥面压头(CEP)3种不同形状的压头对不同参数泡沫纯铝和泡沫Al Si12合金进行了准静态压坑实验,研究了泡沫铝压坑变形的应力随压入深度变化的响应特征,以及相对密度对压坑应力及吸能性的影响。结果表明:平压头压坑的应力-压深曲线由弹性段和应力持续上升的塑性段组成,有明显的屈服点,屈服强度和压坑应力均随密度增加而升高,球面压头和圆锥面压头压坑应力-压深曲线上没有明显的弹性段,只有应力先缓慢上升然后快速升高的塑性段。随相对密度增加和基体强度提高,泡沫铝的压坑应力和吸能性均显著上升。     

小孔径泡沫铝的制备及压缩性能研究

在常规熔体发泡法基础上,采用添加0.5%Mg(质量分数,下同)以降低表面张力;发泡剂400 ℃,6 h+500℃,1 h氧化预处理以协调发泡剂分散均匀性与发泡过程关系;发泡搅拌60s以破碎初始气泡等措施,成功制备出了平均孔径1.3 mm、孔隙率70.5%、结构均匀的小孔径泡沫铝.泡沫铝及Al-9Si泡沫的压缩性能分析表明,随平均孔径减小,泡沫铝的屈服强度、致密化应变和能量吸收能力均明显提高,泡沫铝压缩性能随孔径减小而提高,与泡沫铝的孔结构因素及孔结构均匀性有关.     

真空渗流法制备泡沫铝及其动态力学性能的研究

以真空渗流法制备陶瓷中空球泡沫铝,研究了应变率对吸能量和吸能效率的影响、相对密度对屈服强度的影响,并与普通泡沫铝进行比较。结果表明,工艺简单可行,所制备的泡沫铝的动态压缩应力-应变曲线只有弹性变形区和塑性变形区;随应变率的增大,屈服强度和吸能效率变化规律不明显,吸能量增大;随相对密度的增大,屈服强度增大,吸能量增大,吸能效率也增大;动态压缩时两种泡沫铝的吸能效率均较高,最大吸能效率大于0.9,是良好的吸能材料。     

含Sc、Zr泡沫铝合金的压缩和能量吸收性能

以孔隙率为71.5%~72.5%的泡沫Al-0.16Sc-0.08Zr合金为研究对象(熔体发泡法),研究了等时时效对泡沫铝压缩力学性能和能量吸收性能的影响。结果表明,泡沫铝合金孔多呈球形,孔径约为0.9mm;由于Zr添加量较少,基体中并未发现初生Al3(Zr,Sc)相析出;试样经200~600℃等时时效,随时效温度升高,其压缩强度先增加后降低,时效至400℃的试样压缩屈服强度和能量吸收能力最强;时效处理会导致胞壁塑性下降,影响试样屈服平台过程,其能量吸收效率得到显著提高,且高效阶段更持久。TEM结果表明,等时时效至400℃的试样胞壁中弥散分布着大量纳米级共格Al_3(Sc,Zr,Ti)相,粒径为2.9~4.8nm。这些纳米相能钉扎晶界,阻碍位错运动,改善其压缩和吸能性能。     

泡沫Al合金的压缩性能及其能量吸收

研究了泡沫纯铝和泡沫ＡｌＳｉ７Ｍｇ０．４５在单向压缩条件下的应力－应变（σ－ε）曲线,分析了它们的变形行为,并讨论了其能量吸收和能量吸收效率,结果表明：泡沫纯铝与泡沫Ａｌ合金的σ－ε曲线均由弹性变形段、平缓段和紧实段组成;在压缩过程中,泡沫纯铝的骨架变形以弯曲为主,泡沫ＡｌＳｉ７Ｍｇ０．４５的骨架变形主要由局部断裂产生;在相同孔隙率下,泡沫ＡｌＳｉ７Ｍｇ０．４５的能量吸收大于泡沫纯铝;能量吸收效率     

钪锆元素增强泡沫铝合金的压缩和吸能性能

采用熔体发泡法制备孔隙率为71.5%~72.5%、孔结构均匀的泡沫Al-0.2Sc-0.17Zr合金。研究孔结构、胞壁显微组织以及等时时效对其压缩和能量吸收性能的影响。结果表明:泡沫铝合金的孔径约为1 mm,且多呈球形;初生Al3(Zr,Sc,Ti)相具有层状结构,并能有效细化铸态晶粒(尺寸约为50μm);在200~600℃等时时效过程中,泡沫试样的压缩性能随温度升高呈现先升高后下降的趋势,325和425℃分别表现出由Sc和Zr大量析出引起的两个明显的强度峰;时效至425℃时试样的能量吸收能力最强,且峰值时效附近的试样能量吸收效率均得到提高,高效阶段更持久;TEM实验结果表明,时效至425℃的泡沫铝试样胞壁中弥散分布着大量细小、共格的二次Al3(Sc,Zr,Ti)相,其粒径为2.1~4.1 nm,这些相能钉扎晶界,阻碍位错运动,因而能显著提高泡沫铝合金的压缩和吸能性能。     

采用改进的SHPB方法对闭孔泡沫铝的动态压缩性能的研究

采用改进的分离式霍普金森压杆,分别对长度为10、16mm的闭孔泡沫铝试件在不同应变率下进行了动态压缩试验,得出了相应的应力-应变曲线,分析了应变率对闭孔泡沫铝的变形、应力以及能量吸收性能的影响.结果表明:在340～1350s-1下,两组试件均未能完全压实,动态压缩应力-应变曲线只存在弹性区和屈服平台区,缺少致密区;闭孔泡沫铝的变形、应力以及能量吸收性能均有明显的应变率效应.     

热处理对多孔铝合金压缩吸能性能的影响

采用渗流铸造工艺 ,制备了Al Si系多孔铝合金 ,讨论了其压缩变形特征及能量吸收性能 ,分别对ZL10 1、ZL111两种多孔铝合金进行T6热处理 ,研究了热处理对这两种多孔铝合金压缩吸能性能的影响。研究结果表明 ,热处理能够提高多孔铝合金的能量吸收能力 ,对屈服强度及能量吸收效率也有显著的影响 ,为提高多孔铝合金的压缩性能 ,应尽可能施行热处理     

The first matrix cracking behavior of fiber-reinforced ceramic matrix composites

First matrix cracking stress in fiber reinforced ceramic composites is an important design parameter as it signifies the onset of mechanical damage and subsequent degradation of fiber and interface properties due to oxidation and corrosion. In this study, the influence of variation in the matrix crack length and fiber volume fraction on the first matrix cracking stress of ceramic matrix composites is investigated. To this end, zircon matrix composites uniaxially reinforced with silicon carbide fibers and monolithic zircon were fabricated. The monolithic and composite samples were microindented to create flaws of controlled size on the surface, and were then tested in 3-point flexure to obtain the matrix cracking stress. The results obtained from this study clearly indicated the non-steady state (short crack) and steady state (long crack) matrix cracking behaviors in ceramic matrix composites. The experimental results are compared with the theoretical results based on the fracture mechanics analyses published previously.     

原位合成金属基复合材料

综述了原位合成金属基复合材料的研究现状、制备方法。     

Ductile Ti-based nanocrystalline matrix composites

High-strength Ti–Nb–Cu–Ni–Al in situ cast composites were prepared via arc-melting and injection casting into a copper mold. The microstructure of the Ti-based alloys consists of a bcc β-Ti type main phase and minor amounts of several nanocrystalline interdendritic phases. The optimization of the Ti-based alloy composition is performed to achieve both high strength and high ductility. The best combination of strength and ductility was found for a copper mold cast (TiNb)₇₉(CuNiAl)₂₁ alloy, which exhibits a fracture strength of more than 2000 MPa coupled with a plastic strain of 30%. Also the arc-melted ingot of this alloy exhibits similar mechanical properties compared to its mold cast counterpart. These features significantly improve the mechanical behavior of such composites and open the possibility of obtaining tailored mechanical properties by controlling composition and solidification conditions.     

A numerical strength analysis of metal matrix composites considering the interface and matrix damage evolution

A numerical micromechanical method is adopted here to investigate the tensile strength of metal matrix composites (MMC) by considering interface and matrix damage evolution. A cohesive zone model is employed to simulate the fiber/matrix interface damage. The damage in the matrix, which characterizes microvoid nucleation, growth and coalescence, is described in term of the Gurson-Tvergaard material model. These damage models are performed to a boundary value problem that involves a double periodic array of elastic continuous fibers in the elastic-plastic matrix subjected to transverse loads. The main attempt is made to investigate effects of interface strength and toughness on tensile strength of MMC.     

镶拼式冲裁模CAD

介绍了镶拼式冲裁模ＣＡＤ系统的概念,论述了镶拼式凸、凹模的分块原则、拼合点的交互式设计及凸、凹模拼块图的自动绘制。