高孔隙率、小孔径泡沫铝的制备及压缩性能

以纯铝为基体材料、钙为增黏剂、TiH2为发泡剂制备了高孔隙率(80%)不同孔径的泡沫铝;研究了对发泡剂进行表面氧化处理、增黏搅拌时间、发泡剂加入量和发泡时间对泡沫铝孔结构的影响,并对不同孔径的泡沫铝进行了压缩试验。结果表明:对发泡剂进行氧化处理可以减缓其释放氢的速度,经过相同时间发泡后可获得孔径更小的泡沫铝,但要获得相同孔隙率的泡沫铝,则经氧化处理发泡剂的加入量应比未经氧化处理的大;延长增黏搅拌时间有利于获得小孔径泡沫铝;其他条件相同时,泡沫铝的孔径和孔隙率随着发泡时间的延长而增大;孔隙率相近时,孔径小的泡沫铝,单向压缩应力应变屈服平台较高,吸能能力也较大。     

闭孔泡沫铝的表面积与耐腐蚀性能

通过建立闭孔泡沫铝表面积模型,并进行相应的腐蚀试验,研究了泡沫铝孔结构参数与表面积和耐腐蚀性能的关系.结果表明:平均孔径一定时,材料孔隙率越大,实际表面积越大;孔隙率一定时,平均孔径越小,实际表面积越大;闭孔泡沫铝的耐腐蚀性远低于实体金属,在孔径相近情况下,随孔隙率的增大,耐腐蚀性能下降;孔隙率增加,使材料耐腐蚀性能下降的根本原因是表面积的增大.     

基于PolyMAX模态分析法研究闭孔泡沫铝的阻尼特性

采用Image-Pro Plus软件表征闭孔泡沫铝的孔结构,在此基础上采用PolyMAX模态分析法研究了闭孔泡沫铝的模态阻尼比与孔隙率、平均孔径和固有频率之间的关系,并通过模态置信度矩阵验证各阶试验模态的独立性。结果表明:各阶模态之间具有较高的独立性,泡沫铝的阻尼比随孔隙率的提高以及平均孔径的降低而呈增加的趋势,且各阶固有频率随孔隙率的增加而降低。     

泡沫铝结构的吸能特性影响参数试验分析

闭孔泡沫铝是一种轻质吸能金属材料,在低密度下具有良好的比刚度和比强度、宽而平坦的屈服平台区、良好的抗冲击性和能量吸收特性。在进行了大量试验的基础上,研究了泡沫铝裸材及其填充薄壁管的吸能特性,验证了闭孔泡沫铝结构的各向同性,研究了泡沫铝的孔隙率、孔径等对其力学性能的影响。给出了泡沫铝及其填充结构吸能能力的评价指标,指出了泡沫铝与薄壁管在轴向压缩吸能中的相互作用效应,并得出填充结构能够提高承载能力43%、提高吸能能力87%的结论。     

孔结构参数对闭孔泡沫铝合金超声衰减性能的影响

研究了闭孔泡沫铝合金孔结构参数对其超声衰减性能的影响。结果表明：闭孔泡沫铝合金在1～10MHz范围内是一种具有良好超声衰减性能的轻质材料。其超声衰减系数α随孔径d的减小、孔隙率Ps的增加和比表面积Sv的增加而增大。     

多孔铝的低压成形工艺及其影响因素

以纯铝粉和氯化钠为原料,经混合、低压成形、烧结、溶出造孔剂的方法制备多孔铝,分析了影响多孔铝的孔隙率、孔隙结构、渗透性能、冲击变形量的各种因素。结果表明:含氯化钠45%的混合粉体于120 MPa下成形,在655℃烧结3 h后于水浴中将氯化钠溶出,制备出孔隙率为53.4%及渗透流量为0.128 mL.s-1的多孔铝。成形压力对多孔铝的性能影响最为显著,成形压力增大使开孔孔隙率、渗透流量降低,冲击变形量降低,使闭孔孔隙率增大。     

Bezier曲线优化Voronoi泡沫铝几何模型研究

闭孔泡沫铝材料因其轻质、比强度和比刚度高、抗冲击和吸能特性好等优点在汽车制造等领域应用广泛。然而,目前用于仿真计算的泡沫铝材料几何建模研究仍有不足,广泛使用的Voronoi模型无法模拟真实泡沫铝材料内部圆弧状的胞孔结构。在传统Voronoi模型基础上,建立具有周期性边界的二维Bezier曲线优化模型。通过引入填充度概念,并建立孔隙率关于填充度的一元幂函数方程,可以生成71%～93%指定孔隙率二维泡沫铝几何优化模型,能够还原真实泡沫铝内部结构。利用优化模型进行泡沫铝材料单轴压缩仿真计算,结果相较于传统Voronoi模型更接近试验值。分析优化模型仿真计算过程中随机剪切带的演化,从细观变形角度验证了优化模型的准确性。Bezier曲线优化模型的开发为泡沫铝材料高仿真几何建模研究提供了理论基础。     

微弧氧化闭孔泡沫铝的准静态力学性能

采用微弧氧化法对闭孔泡沫铝进行了不同时间的微弧氧化处理,得到了具有不同厚度陶瓷膜的闭孔泡沫铝,研究了微弧氧化对泡沫铝压缩、弯曲性能的影响。结果表明:不同时间的微弧氧化处理对泡沫铝的准静态压缩性能没有明显的影响,但对其弯曲性能有显著的改善;陶瓷膜厚约为7.4μm时,泡沫铝的抗弯强度最大,为3.554MPa。     

无需增黏熔体发泡法制备泡沫铝及其压缩性能

以CaCO3为发泡剂,加入基体质量1.0%~3.0%的镁,在不使用增黏剂的情况下采用熔体发泡法制备出了孔结构均匀、孔隙率在62.4%~84.0%的泡沫铝,研究了镁的添加对铝熔体发泡效果的影响,最后考察了泡沫铝的压缩性能。结果表明:在铝熔体中添加适量的镁有利于形成孔结构均匀的泡沫铝,CaCO3与熔体发生产气反应后,产生的金属氧化物颗粒对铝熔体有增黏作用,可以提高熔体黏度,并可以存在于胞壁中,有利于小孔径胞孔的形成;但泡沫铝胞壁中存在的大量微孔会导致泡沫铝压缩性能降低。     

泡沫金属基相变蓄热单元管蓄热性能研究

用LB方法研究了相变蓄热单元管内融化过程,以蓄热量及融化速率为评价标准分析了不同操作参数及泡沫金属结构对相变蓄热单元管的强化蓄热作用。填充泡沫金属有利于提高管内的融化速率,是一种可行、高效的方法。泡沫金属的结构对融化速率影响较大,孔隙率越小融化速率越高,但孔隙率的减小使得单管内相变材料装载量急剧下降;泡沫金属体积热容越大,温度变化越慢,不利于融化速度的提升;导热系数对融化速率的影响较大,导热系数越高相变材料融化越快,同一时间段内,管内整体温度相对较高,蓄热量大。     

A novel approach to manufacturing and experimental investigation of closed-cell Al foams

This investigation proposes a modified technique for manufacturing closed-cell aluminum foams to reduce the cost of production of foaming agents during the casting and foaming process. The addition of foaming agents promotes the uniformity of cell sizes and controls the viscosity of the melting aluminum alloy. Moreover, this work elucidates the mechanical characteristics of closed-cell aluminum foams under compressive loading. Discussions cover the compressive stress-strain curve, densification strain and energy absorption effects of various specimens with various porosities. Furthermore, the thermal conductivity of the aluminum foams is determined, and the results compared with some theoretical predictions. The optimum parameters for meeting some tendentious and practical design requirements, such as those of impact absorption and thermal insulation design applications, are discussed. Finally, an empirical correlation between normalized yield strength and relative densities is obtained .     

A novel approach to the manufacturing and experimental investigation of closed-cell Al foams

This investigation proposes a modified technique for manufacturing closed-cell aluminum (Al) foams to reduce the cost of the foaming agents during the casting and foaming processes. The addition of foaming agents promotes the uniformity of cell sizes and controls the viscosity of the melting aluminum alloy. This work elucidates the mechanical characteristics of closed-cell aluminum foams under compressive loading. The discussions in this paper cover the compressive stress–strain curve and the densification strain and energy absorption effects of various specimens with various porosities. The thermal conductivity of the aluminum foams is determined, and the results are compared with some theoretical predictions. The optimum parameters for meeting some practical design requirements, such as impact absorption and thermal insulation design applications, are discussed. Finally, an empirical correlation between the normalized yield strength and the relative densities is obtained.     

Thermal characteristics of graphite foam thermosyphon for electronics cooling

Graphite foams consist of a network of interconnected graphite ligaments and are beginning to be applied to thermal management of electronics. The thermal conductivity of the bulk graphite foam is similar to aluminum, but graphite foam has one-fifth the density of aluminum. This combination of high thermal conductivity and low density results in a specific thermal conductivity about five times higher than that of aluminum, allowing heat to rapidly propagate into the foam. This heat is spread out over the very large surface area within the foam, enabling large amounts of energy to be transferred with relatively low temperature difference. For the purpose of graphite foam thermosyphon design in electronics cooling, various effects such as graphite foam geometry, sub-cooling, working fluid effect, and liquid level were investigated in this study. The best thermal performance was achieved with the large graphite foam, working fluid with the lowest boiling point, a liquid level with the exact height of the graphite foam, and at the lowest sub-cooling temperature.     

Experimental study of cure process of foam rubber: observation of cell structure

Experimental study has been made during cure process of SBR/NR foam rubber. Rubber sample with 30 mm thick, made up by stacking thin rubber sheets in layers, was packed in a metal mold, and peroxide cure was performed by transient heat conduction. Rubber heating time was changed in several steps in order to study the effects of the cure time on the blowing characteristics. Also swelling test was conducted in order to study the relation between the cell structure and the crosslink density. Typical temperature field of one-dimensional, transient heat conduction was observed, and results of the observation studies showed that the cell structure changed depending on both the position from the heating surface and the heating time, and two extreme cell structure, open-cell foam, and closed-cell foam, was clearly observed. Image analyses of the cell structure showed that the porosity distribution increased with the increase of the distance from the heating surface, and the porosity was lower for longer heating time at a same position. Average area of the foam almost took similar results for the result of the porosity, and these various quantities were correlated to the crosslink density.     

闭孔泡沫铝在圆柱形平压头下的压痕性能

采用圆柱形平压头对闭孔泡沫铝进行了压痕试验,研究了压头直径、泡沫铝相对密度及边界条件对压痕响应、压痕硬度、吸能特性等的影响,并与单向压缩试验结果进行了对比.结果表明:闭孔泡沫铝压痕试验的应力-应变曲线与其单向压缩时的相似,但压痕试验时的屈服强度显著高于单向压缩时的;压痕试验时泡沫铝的变形被严格限制在压头之下,并且是局部的不均匀变形;压痕试验时泡沫铝的撕裂能和能量吸收效率不随压头直径和泡沫铝相对密度的变化而变化;压痕硬度随压头直径的增加而线性减小,随相对密度的增加而线性增大;其吸能能力分别随压头直径及相对密度的增加而线性增大;压痕深度在一定范围内(小于6 mm),刚性基础和筒支边界条件对泡沫铝在圆柱形平压头作用下压痕响应的影响可以忽略不计.     

闭孔泡沫铝力学特性及其在汽车碰撞吸能中的应用研究进展

汽车低能耗、安全和轻量化已经成为汽车领域研究的热点问题,闭孔泡沫铝作为一种轻质吸能金属材料,在低密度下具有良好的比刚度和比强度,同时具有良好的抗冲击性和能量吸收性,已逐渐引起汽车产业界地重视。简述泡沫铝单轴压缩试验中弹性模量、抗压强度、屈服强度、平台应力、致密化应变等参数的定义和试验标准;综述闭孔泡沫铝的本构方程的研究现状,重点讨论屈服面模型;总结泡沫铝的微观结构有限元建模方法,比较商业软件中集成的宏观材料模型。归纳吸能材料的特点,分析闭孔泡沫铝的吸能能力和抗冲击能力;综述应变率和冲击速度对泡沫铝吸能特性有无影响的研究进展,并对可能存在的影响进行解释。总结闭孔泡沫铝在汽车轻量化和碰撞安全性领域的应用,具体分析典型的案例。指出当前闭孔泡沫铝的力学特性及其在汽车结构中应用存在的问题与难点,总结并提出本研究领域可以借鉴的研究方向。     

基于十四面体模型的闭孔泡沫材料弹性性能的有限元分析

建立十四面体的单胞模型和多胞模型,采用有限元方法和周期性边界条件,研究胞体数目和相对密度对闭孔泡沫模型弹性性能的影响.同时,确定闭孔泡沫胞体在两种变形状态下的应力分布.文中还将数值结果与理论预测以及随机泡沫模型的计算结果进行比较.结果表明,十四面体模型可以较好地预测低密度闭孔泡沫的弹性性能.     

复合结构泡沫铝隔声性能的研究

采用自制的试验装置对泡沫铝与实体铝复合结构的隔声性能作了研究。结果表明：泡沫铝与实体铝的复合结构在声频范围内均具有较好的隔声作用且对频率敏感，在500-1000Hz内隔声效果最佳，综合降噪率为40％；隔声效果受两者复合方式的影响不大，但随泡沫铝孔结构的不同而异；孔径为1．0mm、孔隙率为60％的泡沫铝试样，隔声效果最优，可在实体铝隔声的基础上再降噪16％-23％。     

稀土对泡沫铝及泡沫铝合金耐腐蚀性能的影响

研究了稀土对泡沫铝及泡沫铝合金泡沫化和压缩性能的影响，讨论了稀土加入量和泡沫铝及泡沫铝合金耐腐蚀性能的关系。结果表明：稀土对铝合金泡沫化无异常影响；在泡沫铝和泡沫铝合金中添加适量稀土元素，可以提高泡沫铝和泡沫铝合金的耐腐蚀性能；相同腐蚀介质中，孔隙率高的泡沫铝合金腐蚀更严重；稀土对泡沫铝及其合金的力学性能影响不大。     

Effect of Porosity and Normal Load on Dry Sliding Friction of Polymer Foam Blocks

In this study, the effect of porosity on the dry sliding fiction of ethylene-vinyl acetate (EVA) foams was investigated under different normal load conditions. EVA foam blocks with varying porosities were slid against a smooth stainless steel plate under dry conditions. The friction coefficient increased with increasing porosity under all of the normal load conditions. In addition, the contact area was estimated using a contact model considering elastic buckling of the cell walls (elastic collapse). The elastic collapse area in the anterior portion of the EVA foam block increased with increasing normal load and porosity, which resulted in an increased contact area. Furthermore, the friction coefficient was positively correlated with the estimated contact area divided by the normal load, indicating that adhesion friction increases with increasing porosity of polymer foams. These results may contribute to the design of high-friction, lightweight shoe sole tread blocks prepared using polymer foam blocks.