粉煤灰聚氨酯复合泡沫静动态力学特性实验研究

以大尺寸粉煤灰漂珠为主要组分,以硬质聚氨酯泡沫为黏结剂制备了一种具有多尺度胞孔形态的复合泡沫,对其准静态压缩和动态冲击下的力学性能和变形机制进行研究。结果表明:①该复合泡沫应力应变曲线具有典型的线弹性、塑性平台和致密化三个特征阶段且具有相对稳定的平台应力;在密度0.45~0.6 g/cm^3,复合泡沫平台应力(6.5~18 MPa)和到压实应变处吸收的能量(3.42~8.9 MJ/m 3)随密度增大而提高,且平台应力与相对密度之间满足幂函数关系;②采用铝蜂窝为增强相可使同密度下复合泡沫抗压强度和平台应力分别提升约20%~45%和10%~25%,准静态下复合泡沫主要发生剪切失效,增强泡沫的主要失效形式则转变为轴向压缩失效。③在0.001~1500 s^-1应变率范围内,复合泡沫抗压强度有明显的应变率效应但平台应力并未随应变率的增大而提高。增强复合泡沫的强度和平台应力均呈现出明显的应变率效应,采用铝蜂窝不仅能提高复合泡沫力学性能,还能够改善其力学行为,使材料具有更优异的动力学特性;研究为工业固废粉煤灰的综合利用提供新思路。     

轻质泡沫混凝土的物理性能试验研究

轻质泡沫混凝土有自重小、极好的隔音和隔热性能,是一种有前途的结构材料。为了研究轻质泡沫混凝土的物理性能,该文对不加粉煤灰和掺加粉煤灰泡沫混凝土的力学性能进行一系列试验研究,还研究25次冻融循环对混凝土抗压强度的影响。试验结果如下：1）硬化泡沫混凝土的密度与混合料中的泡沫含量密切相关。2）随着泡沫混凝土密度增大,其抗弯强度降低。3）在相同密度下,含粉煤灰混合料的抗压强度比不含粉煤灰的试样低20%左右。研究结果可为轻质泡沫混凝土开发提供参考。     

泡沫铝-聚氨酯复合材料力学及吸能性能分析

目的 研究泡沫铝相对密度、孔径对泡沫铝-聚氨酯复合材料准静态压缩力学性能、吸能性能、吸能效率和理想吸能效率的影响。方法 将制备的泡沫铝-聚氨酯复合材料试样在万能材料试验机上进行准静态压缩试验,得出对应的应力-应变曲线,由应力-应变曲线分析材料的吸能性能、吸能效率、理想吸能效率。结果 当泡沫铝孔径一定,泡沫铝相对密度由0.350提升至0.384时,泡沫铝-聚氨酯复合材料屈服强度提升了4.38 MPa,而最大吸能效率由0.29下降至0.27,准静态压缩性能有所提高。当泡沫铝相对密度一定,泡沫铝孔径由5 mm增加至9 mm时,泡沫铝-聚氨酯复合材料屈服强度提升了6.16 MPa,而最大吸能效率由0.25升高到0.27,准静态压缩性能有所提高。结论 当进行准静态压缩时,泡沫铝-聚氨酯复合材料压缩性能随相对密度的增大而增大,随孔径的增大而增大;泡沫铝-聚氨酯复合材料的吸能性能随相对密度的增大而增大,随孔径的增大而增大;泡沫铝-聚氨酯复合材料的最大吸能效率随相对密度的增大而减小,随孔径的增大变化微小。     

搅拌法制备漂珠增强铝基复合材料的熔体分层与控制

采用液态搅拌法制备漂珠增强铝基复合材料过程中, 当颗粒含量较低时, 熔体容易分层。为了了解颗粒在铝熔体中的分布情况, 对试样的不同位置进行扫描电镜分析。结果表明, 在试样的底部有明显的纯铝层,而漂珠在上部的铝熔体中分布均匀。漂珠向熔体上部移动的速度主要取决于漂珠颗粒与铝熔体的密度差、颗粒直径、颗粒体积分数及铝熔体粘度。原料确定后, 只能通过增加铝熔体的粘度或减少浇铸过程的时间来减少纯铝层的产生。因此, 可以采用下浇铸式方法和快速冷却装置, 使颗粒来不及向上运动而被凝固在铝熔体中, 形成漂珠在铝熔体中均匀分布的复合材料。      

纸木复合蜂窝夹心包装材料物理力学性质研究

纸质蜂窝材料作为包装材料,正被广泛的应用着.现利用木质单板和纸质蜂窝材料复合,该复合材料不但保留了原蜂窝材料的优点,而且还大大提高了力学强度.本文就纸木复合蜂窝夹心材料的力学性质进行了研究,并和原蜂窝纸板进行了比较;同时还研究了环境湿度对纸木复合蜂窝材料力学性能的影响.结果表明:木质单板与纸芯及纸板复合后,除平压强度略有所降低外,其余力学强度较原纸板大大增强;环境湿度对纸板及复合材料的力学性能影响较大,且随着环境湿度的加大,复合材料及纸板的强度有所下降;考虑材料和环境湿度的综合作用,对平压强度环境而言,湿度的影响大于材料,对其余力学强度而言,材料的影响大于环境湿度.     

纳米纤维增强闭孔泡沫材料的力学性能

为研究纳米纤维增强闭孔泡沫材料的力学性能,采用Voronoi随机泡沫模型对闭孔泡沫材料的细观几何结构进行模拟,并将纳米纤维随机分布在泡沫材料的胞壁中,利用改进的自动搜索耦合（ASC）技术将纤维单元与基体单元进行耦合,建立了能够反映纳米纤维增强闭孔泡沫材料细观结构的数值模型。在此基础上,进一步研究了泡沫模型随机度、相对密度以及纳米纤维长径比和质量分数对纳米纤维增强闭孔泡沫材料弹性模量与屈服强度的影响规律。结果表明:由所建立的数值模型得到的纳米纤维增强闭孔泡沫材料的弹性模量和屈服强度与实验值吻合较好;提高泡沫模型的随机度会使复合泡沫材料的弹性模量和屈服强度增加,而当随机度达到0.450以后,材料的弹性模量和屈服强度几乎不再发生变化;当相对密度在0.05~0.30范围内变化时,复合泡沫材料的弹性模量与屈服强度几乎随相对密度的增加呈线性增长;提高纳米纤维长径比和质量分数也会使材料的弹性模量和屈服强度得到提高,但当纤维长径比达到500以后,纤维长径比的增强作用逐渐减弱。所得结论对纳米纤维增强闭孔泡沫材料的制备具有重要意义。      

相对密度对泡沫铝力学性能和能量吸收性能的影响

对不同相对密度的两种胞孔结构--开孔和闭孔泡沫铝进行了单轴压缩试验,研究了相对密度对泡沫铝力学性能和能量吸收性能的影响.结果表明:随着相对密度的增大,泡沫铝的屈服强度与流动应力也相应增加,通过对本实验结果进行拟合,得出泡沫铝的屈服强度与相对密度的关系式.泡沫铝材料吸收的能量随着应变量的增大而增加,在相同应变量下,高密度开孔泡沫铝的吸收能比低密度闭孔材料多.吸能效率反映材料本身的一种属性,高的理想吸能效率表明泡沫铝是一种优良的吸能材料.     

弹载加速度记录仪抗冲击防护结构设计

针对弹体侵彻混凝土环境,提出一种中薄型防护外壳嵌套内壳体,两壳体间填充泡沫铝缓冲材料的记录仪抗冲击防护结构。针对应力波作用下防护外壳的屈曲和泡沫铝缓冲性能不足导致内部电路模块冲击断裂的典型失效模式,通过对记录仪抗冲击防护结构在应力波作用下的结构响应分析,提出一套以壳体厚度h、泡沫铝密度ρ、泡沫铝厚度h_b为主要设计指标的弹载加速度记录仪抗冲击防护结构设计方法。设计出防护外壳半径为29 mm,壁厚3 mm,泡沫铝密度1.1g/cm~3,泡沫铝厚度23 mm的抗冲击防护结构,经计算该结构理论抗冲击能力为63 300 g。在实弹侵彻混凝土试验中,测得冲击加速度峰值为56 300 g,在此冲击下记录仪壳体结构稳定,内部电路工作正常,验证了此抗冲击防护结构具有较高的可靠性。     

闭孔泡沫铝压缩性能研究

闭孔泡沫铝作为一种新型多孔金属材料,被应用于各个领域,但其压缩力学性能受到孔隙率、孔洞结构参数、相对密度及材料基本力学性能等的影响,因此针对某闭孔泡沫铝企业研究出的一款新型产品,在确定其相关参数后进行10组试样的压缩力学试验,确定其应力-应变曲线,分析各段曲线意义和产生机理,并针对其特有的压缩力学性能,研究在外力作用下...     

电磁改性谐振水泥基复合材料的吸波性能研究

利用涂挂法,分别在粉煤灰漂珠和闭孔珍珠岩表面涂挂石墨和铁氧体,通过扫描电镜对比改性前后漂珠和珍珠岩表面的微观变化.研究表明石墨和铁氧体在连续釉化面与特殊蜂窝结构的相间的珍珠岩颗粒表面分布均匀,形成了谐振腔吸波体.改性漂珠和珍珠岩分别与水泥基材料复合,形成吸波水泥基复合材料.采用RCS法测量各复合水泥基材料对S～C波段和X～Ku波段的电磁波反射率,研究复合水泥基材料的吸波效能.研究表明与涂挂法改性漂珠相比,涂挂法改性闭孔珍珠岩能有效提高水泥基材料的吸波效能,拓宽了一10dB带宽,具有进一步实际应用研究的意义.     

Compressive and ultrasonic properties of polyester/fly ash composites

The addition of hollow fillers having appropriate mechanical properties can decrease the density of the resulting composite, called syntactic foams, while concurrently improving its mechanical properties. In this study, hollow fly ash particles, called cenospheres, are used as fillers in polyester matrix material. Cenospheres are a waste by-product of coal combustion and, as such, are available at very low cost. In this study, the composites were synthesized by settling cenospheres in a glass tube filled with liquid polyester resin and subsequently curing the resin. This process resulted in a functionally graded structure containing a gradient in the cenosphere volume fraction along the sample height. Uniform radial sections were cut from each composite and were characterized to observe the relationship between cenosphere volume fraction and compressive properties of the composite. The composite was also tested using ultrasonic non-destructive evaluation method. Results show that the modulus of the composites increases with increasing cenosphere volume fraction. The modulus of composites containing more than 4.9 vol% cenosphere was found to be higher than the matrix resin. In general, the modulus of composites increased from 1.33 to 2.1 GPa for composites containing from 4.9–29.5 vol% cenospheres. The specific strength of the composite was found to be as high as 2.03 MPa/(kg/m³) compared to 0.96 MPa/(kg/m³) for the neat resin. Numerous defects present in fly ash particles caused a reduction in the strength of the composite. However, the reduction in the strength was found to be only up to 22%. Increase of over 110% in the specific modulus and only a slight decrease in the strength indicates the possibility of significant saving of weight in the structures using polyester/fly ash syntactic foams.     

Microstructure and mechanical behavior of die casting AZ91D-Fly ash cenosphere composites

The feasibility of incorporating fly ash cenospheres in die cast magnesium alloy has been demonstrated. The effects of fly ash cenosphere additions on the microstructure and some of the salient physical and mechanical properties of magnesium alloy (AZ91D) metal matrix composites were investigated. The control AZ91D alloy and associated composites, containing 5, 10, and 15 wt.% of fly ash cenospheres (added), were synthesized using a die casting technique. A microstructural comparison showed that microstructural refinement – occurred due to the fly ash additions and became more pronounced with an increase in the percentage of the fly ash added. The metal matrix areas nearer to the fly ash particles exhibited a greater degree of refinement than was observed in the areas further away from these particles. Both filled and unfilled fly ash cenospheres, and porosity were observed in the composite microstructures. The composite specimen densities decreased and the coefficient of thermal expansion did not change significantly as the volume percent of fly ash was increased within the range investigated. The hardness values of the composite specimens exhibited an increase in proportion to the increase in percentage of added fly ash. The tensile strength of the composites also increased as the concentration of fly ash cenospheres was increased. In contrast, the Young’s modulus of these composite samples, as measured by non-destructive pulse-echo method, decreased as the percentage of fly ash in the composite was increased. SEM micrographs of the tensile fracture surfaces showed broken cenospheres on the fracture surface and evidence of ‘pull outs’, where fly ash particles were previously embedded in the matrix. Compression testing results showed that the presence of 5 wt.% cenospheres decreased the compressive strength and compressive yield strength of the composite relative to that of the AZ91D matrix alloy. Surprisingly, a significant change in compression strength was not observed for the composites with 10 and 15 wt.% cenospheres in comparison to the AZ91D matrix alloy. In contrast to the tensile tests, no cenosphere remnants were observed on the compressive test fracture surface of the composites. This observation suggests that the fracture of the composite was initiated within the AZ91D matrix by normal void nucleation and growth, followed by crack propagation through the matrix, avoiding any of the cenospheres, leading to composite fracture of the matrix.     

Effect of particle surface treatment and blending method on flexural properties of injection-molded cenosphere/HDPE syntactic foams

The present work on cenosphere/high-density polyethylene (HDPE) syntactic foams aims at understanding the effect of surface treatment of cenospheres and functionalization of HDPE on flexural properties. Cenospheres are treated with silane, and HDPE is functionalized with 10 % dibutyl maleate. Effects of mechanical and Brabender mixing methods are also studied. Flexural test specimens are cast with 20, 40, and 60 wt% of cenospheres using injection molding. The flexural modulus and strength are found to increase with increasing cenosphere content. Particle breakage increases with the cenosphere content, and the measured properties show increased dependence on processing method. Brabender mixing resulted in 70 and 41 % higher modulus and strength for 60 wt% cenospheres than HDPE. Modulus of syntactic foams is predicted by two theoretical models. Bardella–Genna model provides close estimates for syntactic foams having 20 and 40 wt% cenospheres, while predictions are higher for higher cenosphere content, likely due to particle breakage during processing. The uncertainty in the properties of cenospheres due to defects contributes to the variation in the predicted values.     

粉煤灰微珠-TiO_2复合颗粒制备与性能表征

以粉煤灰微珠为基体,利用TiOSO_4水解法,制备TiO_2包覆微珠复合颗拉。通过扫描电镜、X射线衍射、比表面积、超声振荡和光电子能谱等检测手段,对复合微珠的表面形貌、包覆层相组成、比表面积、包覆层与基体结合强度与结合方式进行了研究和探讨。检测与分析表明:得到的复合微珠表面包覆层为均匀非连续包覆,包覆层主要为金红石相,包覆后微珠比表面积比未包覆前提高了超过600倍,且包覆层颗粒与基体结合强度较高,二者间存在化学键的联结。     

Performance and application study of silane coupling agent (KH550) modified wood fiber-fly ash cenosphere/epoxy resin composites

In this paper, the epoxy resin composite filled with wood fiber and fly ash cenosphere was prepared. In order to improve the bonding properties between wooden fiber/fly ash cenosphere and epoxy resin, the grafting treatment of wooden fiber and fly ash cenosphere surfaces was carried out here using KH550 type silane coupling agent. The effects of different process parameters on the surface modification effect of wooden fiber and fly ash cenosphere were investigated, the mechanical properties and energy absorption characteristics of the materials before and after the filler modification were tested, and the microscopic interfacial structures of the matrix with wooden fiber and fly ash cenosphere were investigated by scanning electron microscopy. Meanwhile, based on LS-DYNA simulation software, the energy-absorbing performance of energy-absorbing boxes prepared from AA6061 aluminum alloy and modified wooden fiber-fly ash cenosphere/epoxy resin composites were compared in low-velocity collisions.     

粉煤灰空心球/Al复合泡沫材料准静态力学性能及本构模型

为研究粉煤灰空心球/Al(Fly ash cenosphere/aluminum syntactic foam,FAC/Al)复合泡沫材料静力性能,采用万能试验机对铝基复合泡沫材料进行了准静态轴向压缩性能试验,考察了不同空心球平均粒径(分别为150、200和300 μm)对铝基复合泡沫材料变形失效模式及力学性能的影响,并获取了具有不同空心球粒径的复合材料在准静态下的应力-应变曲线,在此基础上分析了空心球粒径大小对复合材料能量吸收性能的影响。试验结果表明,在准静态荷载作用下,随着空心球粒径的增大,复合材料的压缩屈服强度、吸能能力及理想吸能效率有着明显的降低。此外,在获得的应力-应变曲线基础上,采用最小二乘法拟合得到了铝基复合泡沫在准静态荷载作用下的本构方程,并对其进行了验证,结果表明该方程具有较好的拟合度。      

Synthesis and properties of light weight magnesium–cenosphere composite

Significantly light weight magnesium composite foams are synthesised by addition of fly ash cenosphere particles (waste from coal-fired power plants) in biocompatible pure magnesium using solidification-based disintegrated melt deposition technique. The density of the composite foams synthesised in this study approaches that of plastics- and polymer-based composites. Microstructure development of Mg/cenosphere composite foams was favourable as they exhibited better dimensional stability (reduced coefficient of thermal expansion) and remarkable improvements in tensile strengths, compressive strengths, compressive total strain and microhardness. The present study highlights the processing, microstructure and mechanical properties of Mg/cenosphere composite foams which hold great potential as light weight metal-based green materials for diverse weight critical applications spanning from engineering to biomedical sector.     

Mechanical behavior of pure Al and Al–Mg syntactic foam composites containing glass cenospheres

Glass cenospheres were used as space holders for making aluminum matrix syntactic foams by pressure infiltration technique. The mechanical properties and failure behavior of cenospheres/Al syntactic foams with pure Al and Al–Mg alloys were investigated in the present work. The failure behavior of cenospheres in two syntactic foams was similar. However, the mechanical behavior of these two syntactic foams was different. Under compression process, the cenospheres/pure Al showed discontinuous shear band and drum shape, while cenospheres/Al–Mg exhibited continuous shear band and was divided by main shear zone. At the tensile state, the cenospheres in pure Al matrix syntactic foam debonded from the matrix, while the cenospheres in Al–Mg matrix syntactic foam was well-bonded and appeared to lamellar tearing. It is suggested that the difference of mechanical deformation behavior could be attributed to the matrix ductility and the forming of interfacial reaction product MgAl₂O₄ coatings.     

Method to determine mixture proportions of workable ultra lightweight cement composites to achieve target unit weights

Ultra lightweight cement composite (ULCC) is a type of composite characterized by low unit weights <1500 kg/m³ and high compressive strengths of up to about 65 MPa. The low unit weight is achieved by incorporating cenospheres as micro-lightweight aggregates in cement paste. As the cenospheres are by-products from coal burning power plants, their properties may vary greatly. This results in great difficulty in determining the mixture proportions of the ULCC. In this research, a new design method is developed and proposed that can be used to effectively determine the mixture proportions of workable ULCC to achieve a desired target unit weight with minimal laboratory trials. The relationship between the spacing among spherical cenospheres and the water-to-cementitious materials ratio (w/cm) needed to achieve the target workability is the basis of this design method. For a given cenosphere sample, if its particle size distribution and particle density are determined, it is possible to design a mixture of ULCC using this method.