孔结构对通孔泡沫铝水声吸声性能的影响

测试了不同孔结构通孔泡沫铝样品在 3～ 2 4kHz频段内的水声吸声系数。试验结果表明 :不同孔结构的通孔泡沫铝都具有较好的水声吸声性能 ,其水声吸声性能与其孔结构密切相关。当孔径减小 ,孔隙率和厚度增大时 ,水声吸声性能增高     

真空渗流法制备的通孔泡沫铝的吸声性能

研究了真空渗流法制备的通孔泡沫铝的吸声性能、通孔泡沫铝的孔结构参数及厚度对通孔泡沫铝吸声性能的影响。试验结果表明 ,真空渗流法制备的通孔泡沫铝具有较大的吸声系数 ,而且随孔径减小或孔隙率、厚度增加 ,所制备通孔泡沫铝的吸声性能提高     

防锈闭孔泡沫Al-Mg-Re基合金的制备与性能

在熔体发泡法制备工艺基础上,引入合金化阻燃技术,制备了Al-Mg-Re基防锈闭孔泡沫铝合金.实验结果表明,熔体发泡前同时加入Mg、Ca和稀土制备的防锈闭孔泡沫Al-Mg-Re基合金孔结构均匀,由于Mg和稀土元素的双重作用,Al-Mg-Re基防锈闭孔泡沫铝合金具有优异的耐腐蚀性能.     

CFRP中孔隙几何形貌与超声衰减系数关系的研究

通过金相和超声衰减系数表征CFRP层压板中的孔隙,研究孔隙形貌对超声衰减的影响。结果表明:超声衰减系数随孔隙几何形貌参数(平均长、宽、面积)的增大而增大;平均孔隙长度随孔隙率的增加程度大于平均孔隙宽度随孔隙率的增加程度;超声衰减系数随主要尺寸区域内的孔隙所占比例的增加,总体趋势减小;同一孔隙率下,大尺寸孔隙所占的比例越多,其超声衰减系数越大。总之,本试验中孔隙形貌对超声衰减有一定的影响且不能忽略。     

聚甲醛/泡沫铝合金互穿复合材料导热性能的研究

使用硅烷偶联剂KH570对孔隙率不同的泡沫铝合金进行表面改性后,通过注塑成型法制备了聚甲醛/泡沫铝合金互穿复合材料。采用傅立叶变换红外光谱仪(FT-IR)、扫描电子显微镜(SEM)和导热系数测试仪分别研究了改性后的泡沫铝合金的表面的红外结构、复合材料的界面结合问题以及所制备复合材料的导热性能。结果表明,硅烷偶联剂KH570成功接枝到了泡沫铝合金的表面;泡沫铝合金与聚甲醛两相界面结合良好;泡沫铝合金的充填提高了复合材料的导热性能。当泡沫铝合金孔隙率为60.48%~75.41%时,聚甲醛/泡沫铝合金互穿复合材料的导热系数随孔隙率(λ)的增大而降低,其导热系数在10.2945~17.6471 W/(m·K)之间。     

泡沫铝/环氧树脂复合材料电磁屏蔽及力学性能实验

以环氧树脂填充泡沫铝.制备了具有一定结构性能及电磁屏蔽功能的结构和功能一体化复合材料试件,泡沫铝的孔径设计为1.0 mm和2.0 mm,厚度为5.0mm、10.0 mm和15.0 mm.通过法兰同轴测试法,分别测试了这6组试件的电磁屏蔽效能,研究发现:泡沫铝厚度一定,频率为10～300 MHz时,随着孔径的增大屏蔽效能增强;频率为300 MHz～1.5 GHz时,孔径对屏蔽效能的影响不明显.泡沫铝孔径一定,频率为10～300 MHz时,随着厚度的增大屏蔽效能增强;频率为300 MHz～1.5 GHz时,厚度对屏蔽效能影响不大.同时,通过拉伸和弯曲实验测试了复合材料中泡沫铝孔径不同的试件的强度和弹性模量等力学性能.结果表明,泡沫铝孔径小的复合材料的抗拉和抗弯性能比孔径大的更好.     

Al-Si闭孔泡沫铝电磁屏蔽效能

通过调整发泡温度、发泡时间、保温时间及发泡剂加入量等工艺参数,采用熔体转移发泡法制备不同相对密度的Al-Si闭孔泡沫铝.利用法蓝同轴法测试其电磁屏蔽效能,结果表明:电磁干扰频率对其屏蔽效能影响显著,在10～600MHz范围内,随着干扰频率增加,泡沫铝屏蔽效能逐渐减小,在600～1500MHz范围内,屏蔽效能又逐渐增加.相对密度对Al-Si闭孔泡沫铝材料电磁屏蔽效能影响不大.     

高温处理后闭孔泡沫铝压缩性能及变形机理

目的 探究温度和孔隙率对闭孔泡沫铝材料压缩力学性能和变形机理的影响。方法 将孔隙率为84.3%～87.3%的泡沫铝试件在温度25～700 ℃内进行加热处理,对处理后的试样开展准静态压缩实验。结果 在准静态压缩条件下,闭孔泡沫铝材料在不同温度加热处理后的压缩应力–应变曲线均经历了3个阶段:弹性阶段、塑性平台阶段和密实阶段。孔隙率从87.3%减小到84.3%时,其弹性模量增大了44.4 MPa,屈服强度增大了0.39 MPa,平台应力增大了0.94 MPa。孔隙率为84.3%的泡沫铝,在25 ℃时,其弹性模量为141.4 MPa、屈服强度为4.25 MPa、平台应力为4.75 MPa;当加热温度为500 ℃时,弹性模量减小到了128.0 MPa、屈服强度减小到了4.22 MPa、平台应力减小到了4.51 MPa。结论 泡沫铝的弹性模量、抗压屈服强度和平台应力均随孔隙率的增加而减小;加热温度低于500 ℃以下时,泡沫铝材料力学性能变化很小,但屈服强度和弹性模量均小幅度降低;在压缩载荷下,泡沫铝的变形破坏模式呈现出先从试件铝基体较薄弱部分产生孔壁塑性变形、孔洞坍塌,并逐渐出现断裂压缩带,直至泡沫铝孔洞完全坍塌密实。     

铝硅闭孔泡沫铝吸声性能研究

利用熔体转移发泡法制备了不同孔隙率(厚度为20mm;孔隙率为67.3%、77.7%、80.4%、88.1%)和不同厚度(孔隙率为79.6%;厚度为10、20、30mm)的铝硅闭孔泡沫铝,运用驻波管法对其吸声性能进行了测试,对其吸声机理进行了探讨,并研究了孔隙率和厚度对其吸声性能的影响.结果发现铝硅闭孔泡沫铝吸声主要是通过亥姆霍兹共振器结构和孔壁微孔以及裂缝等来实现的,实验进一步证实其吸声特性曲线符合理论分析.铝硅闭孔泡沫铝的孔隙率和厚度对其吸声性能影响显著:吸声系数随孔隙率增加而增加;低频阶段,吸声系数随厚度的增加而提高,高频阶段,吸声系数随厚度的增加而下降,但整体吸声性能受厚度影响较小,只出现了最高吸声系数向低频处迁移的现象.     

泡沫混凝土的负泊松比设计与静载力学特性研究

拉胀材料因其特殊性能在材料领域备受重视.将负泊松比效应应用在泡沫混凝土中,可使其具备良好的力学性能与吸能效果.本试验利用化学发泡法制备了三种不同孔隙形态的泡沫混凝土,分别为闭孔泡沫混凝土、连通孔泡沫混凝土、内凹孔泡沫混凝土.利用图像法对泡沫混凝土的干密度和孔隙结构参数进行表征,通过万能试验机测试了泡沫混凝土的静态压缩强度、抗折强度,通过工业相机及数字散斑相关方法(DSCM)研究了泡沫混凝土的区域形变行为以及泊松比值.结果表明:泡沫混凝土的孔隙率、孔径及干密度与发泡剂的添加量有关,添加量越多,干密度越小,孔隙率和孔径增大;泡沫混凝土的抗压、抗折强度也与发泡剂的添加量有关,其强度随着添加量的增多而减小,但孔隙呈内凹状的泡沫混凝土具有较高的抗压强度和抗折强度,内凹孔泡沫混凝土的压缩断裂能为33.9×103 J/m3,相比闭孔泡沫混凝土提高44.9％.DSCM表明内凹孔泡沫混凝土在压缩过程中会出现明显的收缩效应,其收缩率为闭孔泡沫混凝土的37.5％,压缩期间负泊松比值最大可达-3.7.     

球形孔泡沫铝合金三明治梁的三点弯曲变形

研究了球形孔泡沫铝合金的单轴压缩性能,得到了抗压强度与相对密度的关系;与多边形孔泡沫铝合金和泡沫纯铝作了对比,发现球形孔使力学性能有了较大的提高.根据球形孔泡沫铝合金三明治梁三点弯曲的载荷(P)位移(δ)曲线研究了四种常见破坏模式并建立了破坏模式图.用极限载荷公式得到的计算值与极限载荷的实验值吻合良好.球形孔泡沫铝合金力学性能高于多边形孔泡沫铝合金及泡沫纯铝,因而其三明治梁的力学性能最好.     

高比强多孔铝合金的压缩变形性能

采用渗流法制备了新型多组元、高比强多孔铝合金，研究了合金的单向压缩变形特征和能量吸收性能，讨论了孔壁厚度均匀性、孔隙率和强化热处理对性能的影响．结果表明：提高多孔铝合金的孔壁厚度的均匀度和强化热处理都显著提高多孔铝合金的压缩吸能性能；随着孔隙率的降低多孔铝合金的压缩强度增加。     

创新构型泡沫TiAl的制备及其力学响应特征

兼有金属和陶瓷特性的TiAl金属间化合物泡沫材料具有明确的性能优势和目标需求,在高温隔热材料、酸碱环境下的过滤材料、催化剂载体等领域有广阔的应用前景。本文首先采用Ti/Al元素粉末反应烧结制备了TiAl合金粉体,然后采用脱溶-烧结工艺制备了孔隙分布均匀、通孔型单孔结构的泡沫TiAl,该工艺可实现孔隙率、孔径、孔形等可控。准静态压缩测试表明,TiAl属于脆性泡沫材料,超过弹性区到达上屈服点时,材料瞬时坍塌失效。同时,随孔隙率的增大,TiAl的屈服强度、杨氏模量和弹性区域均减小,屈服强度与孔隙率的响应关系满足Gibson-Ashby模型。     

闭孔泡沫铝的力学性能和吸能能力

在闭孔泡沫铝准静态压缩试验的基础上,研究了其力学性能、吸能能力。结果表明,闭孔泡沫铝单轴压缩应力-应变曲线呈现线弹性变形、塑性平台阶段、致密化阶段3个阶段;闭孔泡沫铝的压缩强度、吸能能力随着孔隙率的增大而减小,采用Gibson-Ashby模型分析闭孔泡沫铝的压缩屈服强度,吻合良好。并在此基础上,提出可供工程使用的多孔泡沫金属吸能能力公式,为其工程应用提供理论支持。     

玻璃纤维复合材料孔隙率对超声衰减系数及力学性能的影响

在0.1~0.6 MPa热压压力条件下, 制备了不同孔隙率含量的玻璃纤维布/618环氧树脂层压板试件。采用超声C扫描及烧蚀密度法测定了试件的超声衰减系数与平均孔隙率, 并通过金相显微分析对孔隙的分布、 形状及尺寸进行了表征。讨论了孔隙率对层压板拉伸、 弯曲和层间剪切性能及超声衰减系数的影响规律, 获得了使力学性能下降的临界孔隙率及衰减系数值。结果表明, 随着固化压力减小, 孔隙率从0.976%增加到5.268%, 抗拉强度、 弯曲强度和层间剪切强度均下降, 衰减系数由1.460 dB·mm^-1增加到2.150 dB·mm^-1, 使力学性能下降的临界衰减系数约为1.5 dB·mm^-1。     

Effect of aluminium evaporation loss on pore characteristics of porous FeAl alloys produced by vacuum sintering

This study investigated the effect of aluminium evaporation loss on the pore characteristics of a porous Fe–Al alloy. The porous Fe–Al alloy samples were produced through pressureless reaction synthesis from powder compacts of elemental Fe and Al powder mixture under vacuum. Cellular characteristics were analysed by X-ray diffraction, scanning electron microscopy and energy dispersive spectrometry. The maximum open-cell pore size, open-cell porosity and permeability increased with increasing sintering temperature. Based on the Miedema model and Langmuir equation, the evaporation weight losses were calculated and in good agreement with the experimental measurements. The relationship between the evaporation weight losses and the cellular morphology and physical properties of the porous Fe–Al samples is also discussed.     

Ultrasonic attenuation and backscatter from flowing whole blood are dependent on shear rate and hematocrit between 10 and 50 MHz

Ultrasonic backscatter has recently been used extensively to investigate erythrocyte aggregation, which is an inherent hematological phenomenon in the blood circulation system. The size of rouleaux can be estimated by measuring certain parameters of signals backscattered from flowing blood. However, most measurements of backscatter from blood use a constant value for the attenuation coefficient to compensate for the loss of ultrasound energy. This correction may be inaccurate because the attenuation varies with the blood properties, which prompted us to explore the effects of hemodynamic properties on ultrasonic attenuation and backscatter to better understand the blood rheological behaviors. Experiments were performed on porcine whole blood in a Couette flow apparatus. Ultrasonic attenuation and the backscattering coefficient of blood were measured at various frequencies (from 10 to 50 MHz), hematocrits (from 0 to 60%), and shear rates (from 0.1 to 200 s?1). The results indicated that the attenuation and backscattering coefficients of blood are highly variable, depending in a complex manner on shear rate, hematocrit, and the measurement ultrasound frequency. The attenuation of blood decreased rapidly with increasing shear rates, eventually reaching a steady state asymptotically, and increased linearly with the hematocrit from 10 to 50 MHz at various shear rates, and also with the ultrasound frequency. The effect of erythrocyte aggregation means that the change in ultrasonic attenuation in blood with shear rate may be attributed to the absorption mechanism, which is enhanced by the increased blood viscosity at lower shear rates. Compensating the measured backscattering coefficients of blood for the shear-rate-dependent attenuation coefficient increased the accuracy of erythrocyte aggregation assessments. Together, the experimental results suggest that the shear-rate-dependent attenuation coefficient should be considered in future developments of ultrasonic technologies for characterizing blood rheology when the ultrasound frequency is higher than 20 MHz.     

Investigation on compressive behavior of Cu-35Ni-15Al alloy at high temperatures

Microstructures and mechanical properties of Cu-35Ni-15Al alloy in cast and porous states were studied by scanning electron microscopy and compression tests. The influence of porosity, deformation temperature and loading rate on mechanical properties of the two kinds of alloys was investigated. The results show that the as cast alloy and porous alloys have almost the same phase constitution: Cu rich phase, Ni rich phase and K intermetallics. The yield strength of porous alloys increases continuously with decreasing porosity, the relationship between porosity and yield stress follows Gibson-Ashby equation. With decreasing deformation temperature, the yield strength of as cast alloy and porous alloy increase. With the increase of loading rate, the yield strength of these alloys shows an increasing trend. After compression, the microstructure of as cast alloy is more uniform, and porous alloys are more prone to have localized deformations.