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.     

单轴压缩载荷下闭孔泡沫铝的变形机制

基于X射线计算机断层扫描技术,重构了能够反映闭孔泡沫铝真实细观结构的三维有限元模型。采用数值模拟与试验测试相结合的方法,研究了泡沫铝在准静态单轴压缩载荷作用下的力学响应及其变形机制,重点关注了平台阶段及致密化阶段的变形模式。结果表明:试件中变形带的出现是压缩过程进入平台阶段的一个标志,此时棱杆和孔壁的变形以塑性弯曲为主;平台阶段,棱杆及孔壁的变形逐渐向塑性起皱与塑性屈曲转变;伴随致密化阶段的发生,变形带内部的胞孔严重坍塌,呈‘双凹圆盘’状。闭孔泡沫铝细观结构变形模式的数值模拟与试验结果相符,验证了该模型的有效性,为进一步研究各相关物理量(相对密度、加载速率等)及变形机制对其宏观吸能性能的影响奠定了基础。     

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.     

Fatigue damage of closed-cell aluminum alloy foam: Modeling and mechanisms

The objective of this work is to experimentally investigate the damage evolution and damage mechanism in closed-cell aluminum alloy foam under tension–tension fatigue loading. Constant amplitude fatigue tests are performed for the aluminum alloy foam, and experimental results indicate the large scatter of the fatigue damage in the aluminum alloy foam. To describe the fatigue damage with large scatter, a statistical fatigue damage model is developed on the basis of continuum damage mechanics. It is seen that the statistical damage model can describe the fatigue damage of the foam. Scanning electron microscopy (SEM) observation on the fracture surface of the tested specimen is carried out to understand the damage mechanisms of the foam. Four major categories of fatigue damage mechanism are concluded, i.e. damage initiates from the material surface, damage initiates on the cell wall, damage initiates at the intersection of several cell walls and damage initiates from the edge of cell. The high-resolution SEM images reveal that the fatigue mechanisms of the foam are mainly governed by the cell structure.     

Prediction of compressive properties of closed-cell aluminum foam using artificial neural network

The design of artificial neural network (ANN) is motivated by analogy of highly complex, non-linear and parallel computing power of the brain. Once a neural network is significantly trained it can predict the output results in the same knowledge domain. In the present work, ANN models are developed for the simulation of compressive properties of closed-cell aluminum foam: plateau stress, Young’s modulus and energy absorption capacity. The input variables for these models are relative density, average pore diameter and cell anisotropy ratio. Database of these properties are the results of the compression tests carried out on aluminum foams at a constant strain rate of 1 × 10⁻³ s⁻¹. The prediction accuracy of all the three models is found to be satisfactory. This work has shown the excellent capability of artificial neural network approach for the simulation of the compressive properties of closed-cell aluminum foam.     

Depth of penetration prediction for closed-cell aluminum foam experiencing impact of different shape projectiles

In this study, we combined dynamic cavity expansion theory and the Poncelet resistance formula to investigate varying penetration depth of closed-cell aluminum foam impacted by ogival-nose, truncated-ogive nose, and hemispherical-nose projectiles. We employed the explicit finite element program LS-DYNA to predict the penetration depth of projectiles at normal impact. A high-pressure air gun was also used to propel the projectiles. Finally, we compared the results of the theoretical model, experiments, and numerical simulation.     

Compressive behavior of closed-cell aluminum alloy foams at medium strain rates

Compressive behavior of closed-cell aluminum alloy foams at strain rates of 10⁻³-450 s⁻¹ has been studied experimentally. The fully stress-strain curves of specimens at medium strain rates were obtained using the High Rate Instron Test System, which can maintain a constant loading rate. The experimental results show that plateau stress and energy absorption capacity are remarkable dependent on strain rate, while the densification strain has a negligible dependence.     

The dependence of damping property of fly ash reinforced closed-cell aluminum alloy foams on strain amplitude

Closed-cell aluminum alloy foams with 1.5, 3.0 wt.% fly ash particles have been manufactured by molten body transitional foaming process. The room temperature damping properties of fly ash reinforced aluminum alloy foams were measured at different strain amplitude in two directions using the forced vibration mode. The results show that the damping properties of fly ash reinforced aluminum alloy foams increase with FA content. A critical strain amplitude ε_crit was observed and ε_crit decreases with increasing FA content. Moreover, the damping property in the transverse direction is higher than that in the longitudinal direction. The related mechanism has been discussed.     

Effect of cell shape anisotropy on the compressive behavior of closed-cell aluminum foams

The closed-cell Al–Si foams have been prepared by molten body transitional foaming process using TiH₂ foaming agent. The cell shape anisotropy ratio of specimens with various relative densities was measured. The quasi-static compressive behavior of Al–Si foams in both longitudinal and transverse directions were investigated. The results show that Al–Si foam loaded in the transverse direction exhibits a lower stress drop ratio. The relationship between plastic collapse stress ratio and cell shape anisotropy is in accordance with Gibson and Ashby model. The plastic collapse stress and the energy absorption property of Al–Si foams increase following power law relationship with relative density. Moreover, Al–Si foams exhibit higher plastic collapse stress and the energy absorption property in the longitudinal direction than that in the transverse direction.     

Cell structure and compressive behavior of an aluminum foam

The plastic collapse strength, energy absorption and elastic modulus of a closed cell aluminum foam are studied in relation to cell structures. The density, node size and the cell wall thickness of the aluminum foams decrease with increasing cell size. The failure of the foam cells under compressive load progresses successively from the top or/and bottom to the mid-layer of the compression specimens, and no initial rupture of the foam cells is observed in the mid-height of the foam samples. When foam density increases from 0.11 to 0.22 g/cm ³, the plastic collapse strength rises from 0.20 to 1.29 MPa, while the elastic modulus of the closed cell aluminum foam increases from 0.70 to 1.17 GPa. In contrast, the energy absorption of the foams decreases rapidly with increasing cell size. When cell size increases from 4.7 to 10.1 mm, the energy absorption drops from over unity to 0.3 J/cm ³. The normalized Yong’s modulus of the closed cell aluminum foam is E^*/E_s = 0.208 (ρ^*/ρ_s), while the normalized strength of the foams, σ */σ_s is expressed by σ */σ_s = c ⋅ ρ */ρ_s where c is a density-dependent parameter. Furthermore, the plastic collapse strength and energy absorption ability of the closed cell aluminum foams are significantly improved by reducing cell size of the aluminum foams having the same density.     

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.     

Effect of aluminum closed-cell foam filling on the quasi-static axial crush performance of glass fiber reinforced polyester composite and aluminum/composite hybrid tubes

The effect of Al closed-cell foam filling on the quasi-static crushing behavior of an E-glass woven fabric polyester composite tube and thin-walled Al/polyester composite hybrid tube was experimentally investigated. For comparison, empty Al, empty composite and empty hybrid tubes were also tested. Empty composite and empty hybrid tubes crushed predominantly in progressive crushing mode, without applying any triggering mechanism. Foam filling was found to be ineffective in increasing the crushing loads of the composite tubes over the sum of the crushing loads of empty composite tube and foam. However, foam filling stabilized the composite progressive crushing mode. In empty hybrid tubes, the deformation mode of the inner Al tube was found to be a more complex form of the diamond mode of deformation of empty Al tube, leading to higher crushing load values than the sum of the crushing load values of empty composite tube and empty metal tube. The foam filling of hybrid tubes however resulted in axial splitting of the outer composite tube due to the resistance imposed by the foam filler to Al tube inward folding and hence it was ineffective in increasing crushing load and SAE values over those of empty hybrid tubes.     

闭孔铝泡沫在静压痕下的力学响应

采用球形压头对闭孔铝泡沫材料进行了准静态压痕实验,研究了不同直径、铝泡沫相对密度及边界条件对铝泡沫的压痕硬度、吸能能力及能量吸收率的影响。研究表明,铝泡沫在球形压头作用下的响应曲线可采用幂函数形式进行描述,幂函数指数随相对密度的增大而线性增加。铝泡沫压痕处的断面显示铝泡沫变形被严格限制在压头之下,铝泡沫的压痕变形是局部的不均匀变形。铝泡沫的压痕硬度及吸能能力均随压头直径的增大而线性减小,但它们却均随铝泡沫相对密度的增大而线性增大;能量吸收率不随压头直径和铝泡沫相对密度而变化。在一定压痕深度范围内,刚性基础和简支条件对铝泡沫的压痕响应影响可以忽略不计。最后基于实验数据分别建立了压痕硬度和吸能能力与压头直径及铝泡沫相对密度的关系。      

Finite element analysis of closed-cell aluminium foam under quasi-static loading

Closed-cell aluminium foam was represented with a new type of repeating unit-cell (RUC) constructed from the tetrakaidecahedra structure. After that the thin shell geometrical parameters and material properties of aluminium foam were assigned to this unit-cell. Finite element studies were then conducted to evaluate the stiffness and mechanical response of this model under large strain. Our results are compared to cruciform-pyramidal and cubic-spherical unit-cell foam models that describe the load and global deformation response in-terms of unit-cell structure. We demonstrate that the plateau phase stress–strain characteristics of our model are more representative of real aluminium foam. It was also found that the crushing resistance and energy absorption capability of tetrakaidecahedral foam was higher than the cruciform-pyramidal and cubic-spherical foam models.     

Acoustic properties of closed-cell aluminum foams with different macrostructures

As structural materials, closed-cell aluminum foams possess obvious advantages in product dimension, strength and process economics compared with open cell aluminum foams. However, as a kind of structure-function integration materials, the application of closed-cell aluminum foams has been restricted greatly in acoustic fields due to the difficulty of sound wave penetration. It was reported that closed-cell foams with macrostructures have important effect on the propagation of sound waves. To date, the relationship between macrostructures and acoustic properties of commercially pure closedcell aluminum foams is ambiguous. In this work, different perforation and air gap types were designed for changing the macrostructures of the foam. Meanwhile, the effect of macrostructures on the sound absorption coefficient and sound reduction index were investigated. The results showed that the foams with half-hole exhibited excellent sound absorption and sound insulation behaviors in high frequency range(2500 Hz). In addition, specimens with air gaps showed good sound absorption properties in low frequency compared with the foams without air gaps. Based on the experiment results, propagation structural models of sound waves in commercially pure closed-cell aluminum foams with different macrostructures were built and the influence of macrostructures on acoustic properties was discussed.     

轻质微孔电磁屏蔽铝基复合材料研究

利用专利技术持压铸造法制备了空心微珠／2024Al复合材料，并对复合材料进行了力学性能以及电磁屏蔽性能的测试。形貌观察发现空心微珠基本完整．壳壁含有封闭微孔井且在复合材料中分散均匀。电磁屏蔽性能测试表明．在0．3MHz～1.5GHz的频率范围内．材料的电磁屏蔽性能与传统的屏蔽材料1J50相仿．当f=300KHz时，两者的屏蔽效能均达到106dB。     

轻质微孔电磁屏蔽铝基复合材料研究

利用专利技术挤压铸造法制备了空心微珠/2024Al复合材料,并对复合材料进行了力学性能以及电磁屏蔽性能的测试.形貌观察发现空心微珠基本完整,壳壁含有封闭微孔并且在复合材料中分散均匀.电磁屏蔽性能测试表明,在0.3MHz～1.5GHz的频率范围内,材料的电磁屏蔽性能与传统的屏蔽材料1J50相仿,当f=300KHz时,两者的屏蔽效能均达到106dB.     

不同温度下泡沫铝压缩行为与变形机制探讨

利用Hopkinson杆与MTS实验装置分别研究泡沫铝在不同温度下的动态与静态力学性能,实验结果表明,泡沫铝有很强的温度软化效应,坍塌应力与平台应力和“应力降”的大小均随温度的升高而降低。动态高温下应力应变曲线与静态低温下应力应变曲线类似,反映材料应变率与温度之间的等效关系。低温下泡沫金属强度较高,脆性较强,泡沫结构易脆性坍塌,并伴有脆性裂纹,随着温度的升高,基体材料逐渐软化,泡沫金属强度降低,胞孔结构在压缩过程中从低温下脆性失稳逐渐变成以胞壁屈曲与塑性变形为主,且在不同温度段,应变率敏感度不同。     

闭孔泡沫铝的动态压缩性能试验研究

为了研究闭孔泡沫铝动态压缩性能的应变率效应,采用改进的INSTRON高速动力加载系统,对不同应变率下闭孔泡沫铝试件进行动态压缩试验研究。首先利用正向试验和反向试验技术对不同厚度的闭孔泡沫铝试件在同一加载速率下的动态压缩性能进行了研究,得到了在一定速率下消除泡沫铝动态压缩试验中惯性效应的合理试件厚度。进一步开展了闭孔泡沫铝试件在不同加载速率下的高速压缩试验,研究了其动态压缩性能随应变率的变化规律。结果表明在高速压缩下,闭孔泡沫铝的应力-应变曲线与准静态条件相同,具有明显的弹性段、平台段及压实段的3阶段特征。闭孔泡沫铝的平台应力具有明显的应变率效应,而致密应变在不同的应变率下表现出了不同的变化趋势,初步解释为泡沫铝孔壁塑性变形机制的改变以及波动效应的相互影响。闭孔泡沫铝的吸能能力随应变率的增加而明显提升。