闭孔泡沫铝压缩力学性能的实验和三维有限元模拟

基于X射线电子计算机断层扫描技术,建立了反映闭孔泡沫铝真实结构的三维有限元模型.对闭孔泡沫铝准静态和动态压缩力学性能进行了实验和数值模拟,分析了闭孔泡沫铝的变形特性及力学性能,验证了模型的可靠性.结果表明,准静态压缩下,试件主要沿加载轴45°方向产生塑性变形.压缩速率为低速时,其变形模式与准静态相同.闭孔泡沫铝试件截面上结构薄弱处首先出现应力集中,材料达到塑性屈服.在高速压缩下,试件加载端首先达到塑性屈服.比较闭孔泡沫铝不同应变率下的屈服强度,动态压缩下的屈服强度远高于准静态压缩下的.应变率280~700 s-1下,其屈服强度变化不明显,应变率继续升高至2 000 s-1,屈服强度略微提高.      

Shape formation of closed-cell aluminum foam in solid–liquid–gas coexisting state

The mold pressing process was applied to investigate the formability of closed-cell aluminum foam in solid–liquid–gas coexisting state. Results show that the shape formation of closed-cell aluminum foam in the solid–liquid–gas coexisting state was realized through cell wall deformation and cell movement caused by primary α-Al grains that slid, rotated, deformed, and ripened within cell walls. During formation, characteristic parameters of closed-cell aluminum foam were almost unchanged. Under proper forming conditions, shaped products of closed-cell aluminum foam could be fabricated through mold pressing.     

Al-Si闭孔泡沫铝材料的压缩行为

对熔体转移发泡法制备的不同密度Al-Si闭孔泡沫铝材料进行了准静态压缩实验,研究了Al-Si闭孔泡沫铝材料的准静态压缩力学行为及变形机制,并从微观上分析了相对密度对Al-Si闭孔泡沫铝材料的力学性能影响.结果表明,Al-Si闭孔泡沫铝材料的压缩过程具有明显的脆性材料压缩变形特征,即经历三个阶段线弹性阶段、脆性崩溃阶段、致密化阶段.相对密度对Al-Si闭孔泡沫铝材料的力学性能影响显著,随着相对密度的增加,压缩强度和弹性模量逐渐增大,且理论结果与试验结果比较吻合.     

高温对活性粉末混凝土抗压强度和热膨胀性能的影响

研究了不同钢纤维掺量的活性粉末混凝土(RPC)高温后的抗压强度和20~800℃温度段内的线膨胀系数,借助TGDSC测试手段对RPC热膨胀性能变化规律进行机理分析。结果表明:随温度升高,RPC抗压强度呈下降趋势,在200℃内下降缓慢;200℃以上下降较快;钢纤维掺量越高,剩余抗压强度越高;线膨胀系数总体呈现先升高后下降的趋势,钢纤维掺量为1%时较素RPC大,钢纤维掺量大于等于2%时较素RPC小。     

闭孔泡沫铝材料吸声性能分析

为更全面地反映闭孔泡沫铝材料的吸声降噪能力,从密度、厚度、背后空腔深度、打孔率几个方面,对闭孔泡沫铝材料的吸声性能进行研究.改变以往单纯用吸声系数的峰值表征的方法,而是用吸声系数的峰值、降噪系数、半峰宽3个指标来评价闭孔泡沫铝材料的吸声性能.通过驻波管法测试吸声系数,用Origin软件进行吸声曲线的分析,建立一次函数....     

轧制制度对闭孔泡沫铝材料塑性的影响

研究了采用熔体发泡法制备的闭孔泡沫铝材料的轧制过程,分析了不同道次压下量条件下泡沫铝的变形特点与破坏方式,探讨了影响泡沫铝轧制能力的主要因素.结果表明:闭孔泡沫铝的轧制应遵循多道次、小变形的原则.道次压下量为0.1 mm时,Si质量分数为12%的泡沫铝(厚度约11 mm)经10道次变形后可实现1 mm的总变形量.道次压下量过大时泡沫铝的破坏方式为典型的脆性断裂,适宜的压下量则有利于发挥泡沫铝良好的吸能性,但小变形时易出现弯曲而使材料最终发生剪切破坏.提高泡沫铝轧制能力的具体方法为降低基体中的Si含量,提高材料组织性能的均一性,轧制工艺中采用适宜的道次压下量和较低的轧制速度.     

Modulation structure stability of heat-treated Co/C and CoN/CN soft X-ray multilayers

Modulation structure stability of Co/C and CoN/CN soft X ray multilayers has been investigated by X ray diffraction and Raman spectroscopy. The graphitization of the amorphous carbon layers in Co/C multilayers causes a period expansion of 12% at annealing temperatures below 400℃. An enormous period expansion (～40%) induced by the crystallization and agglomeration of Co layers has been observed at 500℃. While the period expansion of CoN/CN multilayers is only 4% at 400℃. The interface pattern of the CoN/CN multilayers still exists even if they were annealed at 700℃. The relatively good thermal stability of CoN/CN multilayers can be attributed to the suppression of the formation of the sp 3 bonding and, at annealing temperatures higher than the phase transition temperature of 420℃ (from hcp to fcc), the coexistence of hcp and fcc Co structures through doping nitrogen.     

皮层对皮-芯结构木塑复合材料性能的影响

【目的】研究在两种不同芯层材料的复合体系下,增强材料含量与皮层厚度对共挤出(皮-芯结构)木塑复合材料弯曲与热膨胀性能的影响。【方法】以共挤出技术为加工工艺,选取短玻璃纤维(SGF)为皮层的增强材料,制备共挤出型(皮-芯结构)木塑复合材料(WPC)。分析了在芯层1与芯层2两种复合体系下,不同皮层厚度(1.0、1.2及1.6 mm )和皮层填料含量(0%、10%、20%、30%和40%)对共挤出型皮-芯结构WPC的弯曲性能和热膨胀性能的影响。【结果】当表面为纯的高密度聚乙烯(HDPE)时,在芯层1和芯层2两个复合体系中,皮层越厚则复合材料的热膨胀系数(LTEC)越高,其热膨胀性能越差; 当SGF的加入量恒定时,其LTEC随着皮层厚度的增加而降低。当皮层的弯曲模量比芯层低时,共挤出木塑复合材料的弯曲模量随着皮层厚度的升高逐渐降低; 当芯层的弯曲模量比皮层低时,共挤出木塑复合材料的弯曲模量随皮层厚度的升高而升高。皮层为SGF/HDPE材料时,在芯层1和芯层2两个复合体系中,随着皮层SGF的含量从0%增加到40%时,其弯曲性能显著性提高,LTEC显著降低。当皮层的 LTEC 值比芯层大时,皮层厚度的降低可以降低共挤出木塑复合材料的LTEC; 当皮层的 LTEC 值小于芯层时,共挤出木塑复合材料的 LTEC 随皮层厚度的增加而减少。【结论】通过改性芯层可以提高皮-芯结构木塑复合材料的整体性能,其增强趋势与表层的增强趋势相似。     

养护温度对LiNO3抑制碱硅酸反应及其膨胀的影响

研究了38℃和60℃下石英玻璃在掺LiNO_3的Na OH溶液中碱硅酸反应过程,采用酸化处理法确定体系中SiO_2分布,采用等离子发射光谱(ICP)分析溶液中Na、Si和Li元素浓度变化,采用X射线衍射(XRD)和扫描电子显微镜(SEM)表征反应产物的组成和形貌;并检测了38℃和80℃湿气养护下掺LiNO_3的沸石化珍珠岩混凝土微柱的膨胀性。结果表明:加入LiNO_3降低了溶液中石英玻璃的溶蚀率和SiO_2的溶解度,减缓了ASR的反应速率;不同养护温度下形成的含锂产物不同,提高温度有利于Li_2SiO_3晶体的形成。对于混凝土微柱,掺锂试件早期抑制效果良好,后期仍膨胀;相同锂掺量下80℃湿气养护的试件膨胀率却明显低于38℃时的膨胀率。可见,高温养护下LiNO_3抑制ASR膨胀的效果不能很好地评价在低温下的作用效果。     

闭孔泡沫铝声屏障的降噪效果研究

用闭孔泡沫铝板作为高速公路声屏障材料,以沈阳市东西快速干道珠林桥附近安装的几段声屏障为例,对高速公路安装声屏障前后噪声的声压级进行了实地测量,计算得出声屏障的插入损失,以此考察闭孔泡沫铝板声屏障的降噪效果.通过对闭孔泡沫铝声屏障和普通百叶声屏障降噪效果的对比分析,发现闭孔泡沫铝声屏障整体降噪效果优于普通百叶声屏障,在高...     

保温砂浆外墙外保温系统在不利条件下温度变化规律

为得到保温砂浆外墙外保温系统耐候性保温效果及机理,对其进行耐候性试验,通过布点监测得到各构造层瞬态温度场,计算各层温度变化率及层间温度衰减系数,以对比不同结构层温度变化程度及保温能力。结果表明:在热雨循环15～70℃温度范围内,基层温度最大变化幅度仅为9.12℃,在热冷循环-20～50℃温度范围内,基层温度最大变化幅度仅为28.21℃,其温度改变幅度相较于另外两层明显平缓;基层与保温层层间温度衰减系数明显大于保温层与饰面层。可见系统保温性能优良,保温砂浆层是主要保温结构。     

Preparation and thermal stability of zirconia-doped mullite fibers via sol-gel method

The zirconia-doped mullite fibers were prepared via a sol-gel method from aluminum isopropoxide-aluminum nitrate-tetraethyl orthosilicate system.The effects of zirconia doping on the sol spinnability,mullitization,structure and thermal stability of mullite fibers were investigated by means of Fourier transform infrared(FT-IR) spectroscopy,scanning electron microscopy(SEM) and X-ray diffraction(XRD).The results showed that Zr—O—C bond was presented with the involvement of zirconium acetate,which accelerat...     

泡沫铝夹芯梁结构的高温3点弯曲力学性能研究

实验研究了泡沫铝夹芯梁结构在不同温度下的3点弯曲力学性能.通过引入Gibson模型构建夹芯梁架构在3点弯曲作用下的失效模式图,并将失效模式图扩展到高温情况下,得到泡沫铝夹芯梁的初始失效模式图随温度的变化趋势.结果发现,其他因素不变,随着温度的升高,夹芯梁结构更容易发生面板屈服失效模式,芯层剪切模式涉及的范围被大大压缩.根据修正的Gibson模型预测的夹芯梁结构的极限载荷和实验结果所得极限载荷比较发现,芯层剪切模式分析结果和实验数据很好地吻合,说明泡沫铝夹芯梁的最终失效破坏主要是由于芯层剪切引起的.     

Microstructure and oxidation resistance of SiC–MoSi2 multi-phase coating for SiC coated C/C composites

In order to improve the anti-oxidation of C/C composites, a SiC–MoSi2multi-phase coating for SiC coated carbon/carbon composites(C/C)was prepared by low pressure chemical vapor deposition(LPCVD) using methyltrichlorosilane(MTS) as precursor, combined with slurry painting from MoSi2 powder. The phase composition and morphology were analyzed by scanning electron microscope(SEM) and X-ray diffraction(XRD) methods, and the deposition mechanism was discussed. The isothermal oxidation and thermal shock resistance were investigated in a furnace containing air environment at 1500 1C. The results show that the as-prepared SiC–MoSi2coating consists of MoSi2 particles as a dispersing phase and CVD–SiC as a continuous phase. The weight loss of the coated samples is 1.51% after oxidation at 1500 1C for 90 h, and 4.79% after 30 thermal cycles between 1500 1C and room temperature. The penetrable cracks and cavities in the coating served as the diffusion channel of oxygen, resulted in the oxidation of C/C composites, and led to the weight loss in oxidation.     

In situ reaction mechanism of MgAlON in Al-Al2O3-MgO composites at 1700℃ under flowing N2

The Al-Al₂O₃-MgO composites with added aluminum contents of approximately 0wt%, 5wt%, and 10wt%, named as M₁, M₂, and M₃, respectively, were prepared at 1700℃ for 5 h under a flowing N₂ atmosphere using the reaction sintering method. After sintering, the Al-Al₂O₃-MgO composites were characterized and analyzed by X-ray diffraction, scanning electron microscopy, and energy-dispersive X-ray spectroscopy. The results show that specimen M₁ was composed of MgO and MgAl₂O₄. Compared with specimen M₁, specimens M₂ and M₃ possessed MgAlON, and its production increased with increasing aluminum addition. Under an N₂ atmosphere, MgO, Al₂O₃, and Al in the matrix of specimens M₂ and M₃ reacted to form MgAlON and AlN-polytypoids, which combined the particles and the matrix together and imparted the Al-Al₂O₃-MgO composites with a dense structure. The mechanism of MgAlON synthesis is described as follows. Under an N₂ atmosphere, the partial pressure of oxygen is quite low; thus, when the Al-Al₂O₃-MgO composites were soaked at 580℃ for an extended period, aluminum metal was transformed into AlN. With increasing temperature, Al₂O₃ diffused into AlN crystal lattices and formed AlN-polytypoids; however, MgO reacted with Al₂O₃ to form MgAl₂O₄. When the temperature was greater than (1640 ±10)℃, AlN diffused into Al₂O₃ and formed spinel-structured AlON. In situ MgAlON was acquired through a solid-solution reaction between AlON and MgAl₂O₄ at high temperatures because of their similar spinel structures.     

Abnormal thermal shock behavior in electrical conductivity of Ti2SnC

Some ternary carbide and nitride ceramics have been demonstrated to exhibit abnormal thermal shock behavior in mechanical properties. However, the influence of thermal shock on other properties is not clear. This work reports on the influence of thermal shock on electrical conductivity of Ti_2SnC as a representative member of ternary carbides. Abnormal change in electrical conductivity was first demonstrated during quenching Ti_2 SnC in water at 500-800 ℃. The residual electrical conductivity of the quenched Ti_2SnC gradually decreased with increasing temperature, but abnormally increased after quenching at 600 ℃. The microstructure of surface cracks was characterized. The main mechanism for the abnormal electrical conductivity recovery is that some narrow branching cracks are filled by metallic Sn precipitating from Ti_2SnC.     

Modification and investigation of silica particles as a foam stabilizer

As a solid foam stabilizer, spherical silica particles with diameters ranging from 150 to 190 nm were prepared via an improved Stöber method and were subsequently modified using three different silane coupling agents to attain the optimum surface hydrophobicity of the particles. Fourier transform infrared (FTIR) spectra and the measured contact angles were used to characterize the surface properties of the prepared particles. The foam stability was investigated by the foam drainage half-life and the expansion viscoelastic modulus of the liquid film. The results demonstrate that all of the modified silica nanoparticles effectively improve the foam stability. The surface hydrophobicity of the modified particles is found to be a key factor influencing the foam stability. The optimum contact angle of the particles lies in the approximate range from 50° to 55°. The modifier molecular structure used can also influence the stabilizing foam property of the solid particles. The foam system stabilized by (CH₃)₂SiCl₂-modified silica particles exhibits the highest stability; its drainage half-life at maximum increases by 27% compared to that of the blank foam system and is substantially greater than those of the foam systems stabilized by KH570- and KH550-modified particles.     

泡沫铝填充钢管横向压缩吸能特性试验

为了解填充泡沫铝对钢管吸收能量的影响及其能量吸收特性,通过试验方法研究了单个空钢管与泡沫铝填充钢管的准静态横向压缩性能及吸能特性。研究结果显示:空钢管在横向压缩作用下,其名义应力应变曲线关系与多孔金属材料比较相似。相同壁厚的钢管在横向压缩下,管径越大,其名义屈服应力越小,平台段越长。填充泡沫铝能改变其变形机制,提高钢管在横向压缩下的屈服应力值,较大地提高其能量吸收性能。泡沫铝密度对这种性能的提高影响较小,而钢管的直径对其影响较大。     

中-低温循环对2A14铝合金力学及疲劳性能的影响

国内对航天用2A14铝合金在中-低温循环条件下力学及疲劳性能的变化规律研究不足,为掌握该材料在上述工况下的力学表现及疲劳损伤情况,对2A14铝合金开展了室温—低温（-196 ℃×4 h）—室温,室温—中温（150 ℃/180 ℃×0.5 h）—室温两种工况循环条件下的力学、疲劳性能及组织变化规律研究。结果表明,在上述两种工况下循环5次,2A14铝合金的晶粒尺寸、粗大相形貌及分布均无显著变化,仍保持高强度及良好的塑韧性;随着应力幅值的降低,2A14铝合金的疲劳寿命逐渐延长;应力比为-1时,2A14铝合金的疲劳极限为150～175 MPa,上述两种工况下循环5次,不会改变2A14铝合金的韧性断裂机制。     

Kinetics and mechanism of titanium hydride powder and aluminum melt reaction

Based on the measurement of the released hydrogen gas pressure (P_H2), the reaction kinetics between TiH₂ powder and pure aluminum melt was studied at various temperatures. After cooling the samples, the interface of TiH₂ powder and aluminum melt was studied. The results show that the 2 H P_H2-time curves have three regions; in the first and second regions, the rate of reaction conforms zero and one order, respectively; in the third region, the hydrogen gas pressure remains constant and the rate of reaction reaches zero. The main factors that control the rate of reaction in the first and second regions are the penetration of hydrogen atoms in the titanium lattice and the chemical reaction between molten aluminum and titanium, respectively. According to the main factors that control the rate of reaction, three temperature ranges are considered for the reaction mechanism:(a) 700-750℃, (b) 750-800℃, and (c) 800-1000℃. In the first temperature range, the reaction is mostly under the control of chemical reaction; at the temperature range of 750 to 800℃, the reaction is controlled by the diffusion and chemical reaction; at the third temperature range (800-1000℃), the dominant controlling mechanism is diffusion.