环氧树脂基复合泡沫材料的研究

以环氧树脂为基体,空心玻璃微珠为填充材料制备了具有高强度、低密度的复合泡沫材料。系统研究了固化剂用量,空心玻璃微珠的填充量、偶联剂的用量等对复合泡沫材料的力学性能的影响,并采用扫描电镜分析了复合泡沫材料的断口形貌。研究表明:随着空心玻璃微珠填充量的增大,复合泡沫材料的压缩强度和密度逐渐降低;偶联剂的加入能有效地改善环氧树脂与空心玻璃微珠之间的界面作用,从而提高力学性能。     

玻璃微珠/环氧树脂复合泡沫材料的力学性能及其理论分析

以环氧树脂(EP)为基体,空心玻璃微珠(HGM)为填料制备复合泡沫,并对其开展压缩、拉伸和低速冲击试验,探究不同微珠体积分数和冲击能量对微珠泡沫复合材料破坏形态、强度、模量和冲击吸能效应的影响.结果表明:当微珠体积含量从50％增加到75％时,微珠泡沫的抗压强度和模量分别降低了65％和55％,抗拉强度和模量分别降低了39％和30％,材料得到很大程度的轻量化.在43 J和49 J的冲击能量作用下,复合泡沫吸收的能量随着微珠体积分数的增大而增加,而当冲击能量进一步增大,微珠体积比为70％的复合泡沫比吸能(SEA)最高.过多微珠导致的团聚以及材料之间界面作用减弱对复合泡沫力学性能产生较大影响.基于复合材料细观力学理论,通过夹杂方法计算出微珠泡沫复合材料的有效模量,其理论值与试验值吻合较好.     

Si元素对碳纳米管增强铝基复合泡沫组织与性能的影响

针对金属基复合材料,添加合金元素是提升其综合性能的有效途径.本文通过高能球磨和填加造孔剂法,制备了添加Si元素的碳纳米管(CNTs)增强铝基(CNTs/Al-Si)复合泡沫,通过准静态压缩实验测试其压缩性能和吸能性能,进一步研究烧结温度和不同Si元素含量对CNTs/Al-Si复合泡沫微观组织、压缩性能和吸能性能的影响,...     

空心球/铝基复合泡沫材料制备及性能研究

采用粉末冶金技术制备了不同孔隙率的空心球/铝基复合泡沫材料,对其进行T7热处理,并开展了不同孔隙率材料压缩性能及隔声性能的测试。结果表明,制备的泡沫材料中空心球均匀分布于基体内,且空心球与基体之间形成明显的过渡层;空心球/铝合金基复合泡沫材料的压缩应力-应变曲线呈现线弹性、应力平台、致密化3个阶段。随着孔隙率的增加,空心球/铝合金基复合泡沫材料的压缩峰值应力、平台应力及能量吸收能力均呈先上升后下降的变化趋势;随着孔隙率的增加,复合泡沫材料隔声性能逐渐下降。     

模压成型高微珠含量复合泡沫材料的制备及性能研究

以牌号为HGS8000X的空心玻璃微珠为填充材料,以环氧树脂为基体,采用真空辅助模压成型法制备了空心玻璃微珠体积添加量为65%—70%的复合泡沫材料。研究了空心玻璃微珠的体积分数对材料的密度、压缩强度、吸水率以及耐静水压性能的影响。结果表明,当空心玻璃微珠体积分数为67%—69%时,材料综合性能性能最佳,可以保持50 MPa、24 h的吸水率小于1%和压缩强度大于80 MPa的情况下使材料的密度由0.65 g/cm3降低到0.60 g/cm3。分析指出,高微珠含量的复合泡沫材料的性能更大程度上依赖于由于环氧树脂缺失而导致的材料的显微结构和空心玻璃微珠受力状态的改变。     

球磨对碳纳米管增强泡沫铝基复合材料压缩与吸能性能的影响

因碳纳米管（CNTs）具有优异的性能,被认为是金属基复合材料理想的增强体,因此如何制备得到CNTs增强体均匀分散的金属基复合材料一直是本领域的研究热点。本文通过原位化学气相沉积（CVD）、短时球磨和填加造孔剂的工艺成功制备了CNTs增强的泡沫铝基复合材料,着重研究了球磨过程对复合泡沫铝的微观形貌、压缩性能和吸能性能的影响规律。结果表明,随着球磨时间的延长,CNTs的分散性提高并逐步嵌入铝基体中,使复合泡沫铝的组织均匀性得到改善。相对于未球磨的含CNTs 3.0wt%的复合泡沫材料,当球磨时间增加至90 min时,复合泡沫铝的孔壁硬度、屈服强度和吸能能力分别提高了67%、126%和343%。     

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。      

GFRP约束微珠泡沫柱准静态受压性能

本研究对2根微珠泡沫柱及5根玻璃纤维复合材料(GFRP)约束微珠泡沫组合柱开展准静态轴压试验,探讨了GFRP层数、横向纤维与纵向纤维比例、泡沫密度等参数对组合柱极限承载力和吸能效应的影响,并与静态试验结果进行对比,研究不同加载速率对构件受压性能的影响规律.结果表明:准静态压缩作用下GFRP层数和泡沫密度的增加均提高了构...     

玻璃空心微球/铝基多孔复合材料的制备及其准静态压缩特性和吸能性能

铝基多孔复合材料由铝基体和空心微球复合而成，兼具轻质与吸能特性。本文采用放电等离子烧结(SPS)方法制备玻璃空心微球/铝基多孔复合材料，通过光学显微镜、SEM、准静态压缩原位观察和数字图像相关技术表征，分析了空心微球含量及尺寸对复合材料准静态压缩变形行为和吸能性能的影响。结果表明：两步升温SPS烧结制备所得的铝基多孔复合材料，其微球弥散均匀嵌于铝基体中，铝基体熔合致密。随空心微球含量增加，复合材料压缩应力整体降低，屈服平台区扩大但由平滑转变为锯齿状，压缩变形行为从较均匀的鼓状形变逐渐发展为脆性剪切，微球体积分数为50vol%的多孔复合材料吸能能力为23.6 J·cm^-3，高于体积分数为30vol%和70vol%的多孔复合材料，复合材料吸能能力与微球含量间存在最优对应关系。小尺寸微球具有更好的抗压能力，随小尺寸微球占比的提高，复合材料微观上可承受更高的应力-应变集中，宏观上剪切形变的压缩应变增大，本文中小尺寸微球多孔复合材料的峰值应力和吸能能力分别为89.4 MPa和29.0 J·cm^-3，与大尺寸微球多孔复合材料相比分别提高23.5%和22....     

木粉/聚丙烯木塑复合泡沫材料吸能特性

采用模压法制备木粉/聚丙烯复合泡沫材料,并对不同木粉含量的泡沫材料进行静态压缩、循环压缩、压缩蠕变、动态热机械分析的测试,探讨了不同木粉含量的木粉/聚丙烯复合泡沫材料的能量吸收效果。结果表明: 随着木粉含量的增加,木粉/聚丙烯木塑复合泡沫材料的能量吸收量、能量吸收效率参数、松弛率、循环损耗量、动态力学性能等均呈先升后降的趋势,在木粉质量比为30%时泡沫材料吸能性能达到最佳。     

Hygrothermal studies on syntactic foams and compressive strength determination

Syntactic foams are commonly used as core materials in composite sandwich structures for weight sensitive applications such as aircraft and spacecraft structures and boat hulls. Moisture absorption is highly undesirable in these applications. The present study evaluates the hygrothermal properties of two types of syntactic foams. Distribution of outer diameter of cenospheres (hollow particles) incorporated in both types of syntactic foams is the same but there is variation in the internal diameter causing difference in the density of syntactic foams. Epoxy resin is used as matrix material and the volume fractions of matrix and cenospheres are kept at 0.35 and 0.65 by volume, respectively. Moisture absorption experiments are conducted at two different temperatures, 25 and 70 °C and in deionized and salt waters. Non-destructive ultrasonic imaging technique is used to find the extent of moisture penetration and damage to the specimens. Syntactic foam samples are tested for compressive strength after moisture absorption and the results are compared with the compression test results of dry syntactic foam samples.     

On the Mechanical Properties of Aluminum Matrix Syntactic Foams

Metal matrix syntactic foams (MMSFs, often referred as composite metal foams (CMFs)) are lightweight materials with high specific strength. MMSFs are on the borderline between metal matrix composites and metal foams. On one hand MMSFs are composites, because they are filled by hollow particles and the particles may add strength to the material. On the other hand, they are foams, because the hollow particles ensure porosity to the material. Among metallic foams, MMSFs exhibit outstanding specific mechanical properties due to the hollow inclusions that are typically made from ceramics or high strength alloys, therefore they can be applied as structural materials. The goal of this paper is to summarize the available data on the mechanical properties of MMSFs with aluminum matrix in order to give a strong support to the design engineers. Since the foams are most frequently loaded in compression, the main part of this paper is organized around the available standard related to the compressive properties of porous materials and metallic foams. The quasi‐static results are complemented by properties measured at higher strain rates. Besides this, some insight into the basic fatigue properties as well as into the toughness of MMSFs is also provided.

     

Determination of Dynamic Modulus of Syntactic and Particulate Foams by a Non‐Destructive Approach

Abstract: Developments in aviation posed requirement of lightweight, high strength and highly damage‐tolerant materials. Sandwich‐structured composites fulfilling these requirements have become the first choice for many aerospace applications as well as structural components for ground transport and marine vessels. Sandwich composites are a special class of composite materials which are widely used because of their high specific strength and high bending stiffness. Syntactic foams, which are hollow particle‐filled core materials used in sandwich composites, have recently emerged as attractive material for applications requiring low weight, low moisture absorption and high insulation properties. Quasi‐static and dynamic properties of these syntactic foams are commonly determined though various destructive techniques such as quasi‐static compression and split Hopkinson pressure bar testing. However, there is a need for characterising these materials non‐destructively in the field. The present study focuses on the prediction of dynamic Young's modulus using ultrasonic testing in various types of hollow particle‐reinforced syntactic foam and solid particulate composites. Hollow particle‐filled syntactic foams and solid particulate composites are fabricated with three different volume fractions of 10%, 30% and 60%. Longitudinal and shear wave velocities are used for calculating the dynamic modulus. Effect of longitudinal attenuation behaviour along with longitudinal and shear wave velocities on the varying density and volume fraction of syntactic foams is also discussed.     

Electrical properties of hollow glass particle filled vinyl ester matrix syntactic foams

Low dielectric constant materials play a key role in modern electronics. In this regard, hollow particle reinforced polymer matrix composites called syntactic foams may be useful due to their low and tailored dielectric constant. In the current study, vinyl ester matrix/glass hollow particle syntactic foams are analyzed to understand the effect of hollow particle wall thickness and volume fraction on the dielectric constant of syntactic foams. The dielectric constant is found to decrease with increase in the hollow particle volume fraction and decrease in the wall thickness. Theoretical estimates are obtained for the dielectric constant of syntactic foams. Parametric studies are conducted using the theoretical model. It is found that a wide range of syntactic foam compositions can be tailored to have the same dielectric constant, which provides possibility of independently tailoring density and other properties based on the requirement of the application.     

空心微球/环氧树脂复合泡沫塑料的抗压性能与破坏机制

以环氧树脂为基体, 不同粒径空心玻璃微球为填充体, 制备了轻质高强复合泡沫塑料。通过单轴准静态压缩试验研究了空心微球的粒径大小对复合泡沫塑料的抗压性能的影响, 并采用SEM对复合泡沫塑料的微观结构进行观测。通过随机空间分布法建立了空心玻璃微球/环氧树脂复合泡沫塑料的实体模型, 并且使用有限元分析软件对复合泡沫塑料在1 kPa载荷下的应力分布进行了分析。结果表明, 在相同体积含量下, 当空心微球的粒径从30 μm增大到120 μm时, 复合泡沫塑料的抗压强度无明显变化。有限元分析的结果表明, 在复合泡沫塑料中主要承载部分为空心微球, 空心微球上的应力大于树脂基体上的应力。最大应力分布在空心微球的内壁, 结合SEM图像可推测, 空心微球在破裂之前受到充分的挤压, 并且从内壁产生裂纹。     

Effect of hollow sphere size and size distribution on the quasi-static and high strain rate compressive properties of Al-A380–Al2O3 syntactic foams

Metal matrix syntactic foams are promising materials for energy absorption; however, few studies have examined the effects of hollow sphere dimensions and foam microstructure on the quasi-static and high strain rate properties of the resulting foam. Aluminum alloy A380 syntactic foams containing Al₂O₃ hollow spheres sorted by size and size range were synthesized by a sub-atmospheric pressure infiltration technique. The resulting samples were tested in compression at strain rates ranging from 10^?3 s^?1 using a conventional load frame to 1720 s^?1 using a Split Hopkinson Pressure-bar test apparatus. It is shown that the quasi-static compressive stress–strain curves exhibit distinct deformation events corresponding to initial failure of the foam at the critical resolved shear stress and subsequent failures and densification events until the foam is deformed to full density. The peak strength, plateau strength, and toughness of the foam increases with increasing hollow sphere wall thickness to diameter (t/D) ratio. Since t/D was found to increase with decreasing hollow sphere diameter, the foams produced with smaller spheres showed improved performance. The compressive properties did not show measurable strain rate dependence.     

Hydration-induced reinforcement of rigid polyurethane–cement foams: mechanical and functional properties

Mechanical and functional properties of a newly proposed hybrid foam based on rigid polyurethane foam and Portland cement for application in the building field are herein reported. The hybrid is characterized by the co-continuity of the two phases, hydrated cement and polyurethane, which cooperate in a synergistic way to the properties of the resulting material. Furthermore, the closed-cell foam structure gives the material properties typical of porous materials: in particular, the hybrid foam evidences thermal insulation, sound absorption and acoustic insulation, high impact energy and low density typical of polymeric foams. At the same time, the hybrid foam exhibits water vapor permeability, improvement of thermal stability, high compressive mechanical behavior, and adhesion to concrete and mortars typical of inorganic binders such as cement. The materials were obtained by mixing cement powder with polyurethane foam precursors, i.e., methylene di(phenyl-isocyanate), polyol polyether and catalysts, and silicone surfactants. Water was used as blowing reagent. The resulting compounds were foamed in flat closed molds. The cement phase was then allowed to hydrate in accelerated conditions, i.e., in water at 60?°C for 72?h. Mechanical, morphological, and functional characterization showed that the hydrated cement particles interacted with each other, forming an inorganic network within the polymeric matrix (co-continuity), thus “hydration-induced reinforcement of polymer–cement” hybrid foam, in contraposition with the term “composite foam.”     

Compressive fracture features of syntactic foams-microscopic examination

Syntactic foams made by mechanical mixing of polymeric binder and hollow spherical particles are used as core materials in sandwich structured materials. Low density of such materials makes them suitable for weight sensitive applications. The present study correlates various postcompression microscopic observations in syntactic foams to the localized events leading the material to fracture. Depending upon local stress conditions the fracture features of syntactic foam are identified for various modes of fracture such as compressive, shear and tensile. Microscopic observations were also taken at sandwich structures containing syntactic foam as core materials and also at reinforced syntactic foam containing glass fibers. These observations provide conclusive evidences for the fracture features generated under different failure modes. All the microscopic observations were taken using scanning electron microscope in secondary electron mode.     

Metal injection moulding of in-situ formed AlN hollow sphere reinforced Al matrix syntactic foam parts

In-situ formed AlN hollow sphere reinforced Al matrix syntactic foam parts have been fabricated by metal injection moulding, partial nitridation and a subsequent “open-closed pore transformation” without using pre-fabricated ceramic hollow spheres. The in-situ Al matrix systactic foams feature highly controllable pore size of <20 μm and exhibit high strength of ∼200 MPa, which is superior to conventional Al matrix syntactic foams having pre-fabricated ceramic hollow sphere reinforcements.