Influence of strain amplitude on damping property of aluminum foams reinforced with copper-coated carbon fibers

Aluminum foams containing 0.35, 1.0, 1.7 vol.% copper-coated carbon fibers were fabricated by a melt route. The room temperature damping property of Al/C_f foam was studied at different strain amplitude in two directions. The experimental results show that the critical strain amplitude decreases and the damping capacity of Al/C_f foam increases with the copper-coated carbon fibers contents. It can be attributed to the interfacial micro-slip increasing with the C_f contents and the microplasticity deformation arises from the micro-crack among the C_f–Al interface. Moreover, the damping property in the transverse direction is higher than that in the longitudinal direction. The ratio of longitudinal loss factor to transverse loss factor is almost independent of the C_f contents and strain amplitude.     

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.     

Anisotropic damping behavior of closed-cell aluminum foam

Closed-cell aluminum foams were prepared by molten body transitional foaming process. The anisotropic damping property of closed-cell aluminum foam was measured in two directions using the forced vibration method. The measured results show that the loss factors of the TD specimens are higher than that of the LD specimens. The loss factors ratio β_L/β_T depends linearly on the shape-anisotropy ratio R. Anisotropic damping behavior is due to the variation of Young’s modulus resulting from anisotropic cell morphology.     

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.     

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。     

Electromagnetic shielding effectiveness of aluminum alloy–fly ash composites

The cenosphere and precipitator fly ash particulates were used to produce two kinds of aluminum matrix composites with the density of 1.4–1.6 g cm⁻³ and 2.2–2.4 g cm⁻³ separately. The electromagnetic interference shielding effectiveness (EMSE) properties of the composites were measured in the frequency range of 30.0 kHz–1.5 GHz. The results indicated the EMSE properties of the two types of composites were nearly the same. By using the fly ash particles, the shielding effectiveness properties of the matrix aluminum have been improved in the frequency ranges 30.0 kHz–600.0 MHz and the increment varied with increasing frequency. The EMSE properties of 2024Al are in the range −36.1 ± 0.2 to −46.3 ± 0.3 dB while the composites are in the range −40.0 ± 0.8 to −102.5 ± 0.1 dB in the frequency range 1.0–600.0 MHz. At higher frequency, the EMSE properties of the composites are similar to that of the matrix. The tensile strength of the matrix aluminum has been decreased by addition of the fly ash particulate and the tensile strength of the composites were 110.2 MPa and 180.6 MPa separately. The fractography showed that one composite fractured brittly and the other fractured in a microductile manner.     

Microstructure and some mechanical properties of fly ash particulate reinforced AA6061 aluminum alloy composites prepared by compocasting

Fly ash has gathered widespread attention as a potential reinforcement for aluminum matrix composites (AMCs) to enhance the properties and reduce the cost of production. Aluminum alloy AA6061 reinforced with various amounts (0, 4, 8 and 12 wt.%) of fly ash particles were prepared by compocasting method. Fly ash particles were incorporated into the semi solid aluminum melt. X-ray diffraction patterns of the prepared AMCs revealed the presence of fly ash particles without the formation of any other intermetallic compounds. The microstructures of the AMCs were analyzed using scanning electron microscopy. The AMCs were characterized with the homogeneous dispersion of fly ash particles having clear interface and good bonding to the aluminum matrix. The incorporation of fly ash particles improved the microhardness and ultimate tensile strength (UTS) of the AMCs.     

粉煤灰漂珠粒径对粉煤灰漂珠/AZ91D镁合金复合材料阻尼性能的影响

通过搅拌铸造法向半固态AZ91D镁合金中添加粉煤灰漂珠（FAC）制备了FAC/AZ91D镁合金复合材料,研究了FAC粒径对该复合材料阻尼性能的影响。结果表明:FAC/AZ91D镁合金复合材料的阻尼性能明显优于基体材料,在FAC含量相同时,FAC的粒径越大,其阻尼性能越好。室温下FAC对提高FAC/AZ91D镁合金复合材料的阻尼性能起重要作用,FAC附近的基体产生了高密度的位错,形成了塑性区。室温下FAC粒径越大,在其附近产生的塑性区越大,阻尼性能越好。随温度的升高,FAC/AZ91D镁合金复合材料的阻尼性能迅速提高。位错、晶界以及FAC和基体之间的界面运动是提高阻尼性能的关键。      

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.     

Compressive behaviour of closed-cell aluminium foams at high strain rates

It has been well established that ALPORAS® foams is a strain rate sensitive material. However, the strain rate effect is not well quantified as it is not unusual for strain rate to vary during high speed compression. Moreover, according to previous research, aluminium foams, especially ALPORAS® foams, behave differently at low and high strain rates. Therefore, different plastic deformation mechanisms are expected for low and high strain rate loadings as a result of micro-inertia of cell walls. In this paper, the strain rate effect on the energy dissipation capacity of ALPORAS® foam was investigated experimentally by using a High Rate Instron Test System, with cross-head speed up to 10 m/s. The compressive tests were conducted over strain rates in the range of 1 × 10^?3 to 2.2 × 10² s^?1, with each test being at a fairly constant strain rate. An energy efficiency method was adopted to obtain the densification strain and plateau stress. The effect of strain rate and the foam density was well presented by empirical constitutive models. The experimental data were also discussed with reference to the recent results by other researchers but with different range of strain rates. An attempt has been made to qualitatively explain the observed decrease of densification strain with strain rate.     

Elastic and electric properties of closed-cell aluminum foams: Cross-property connection

Foamed aluminum (AlMg1Si0.6) in the porosity range 0.45–0.85 produced by the powder metallurgy method is analyzed with regard to its elastic and electric properties. Various predictive models for the electrical conductivity and Young's modulus of closed-cell metal foam are assessed based on the experimental measurements. It is shown that the differential scheme provides the best predictions of the electrical conductivity in the porosity range 0.7–0.85, while Mori–Tanaka's scheme gives the best results for the Young's modulus. Comparing the two sets of the experimental data, cross-property coefficient that connects changes in the Young's modulus and electrical conductivity of a material due to pores was determined. A non-trivial finding is that the best prediction of the cross-property coefficient is obtained in the framework of non-interaction approximation.     

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.     

Compressive properties of closed-cell aluminum foams with different contents of ceramic microspheres

In this paper, closed-cell aluminum foams with different kinds and contents of ceramic microspheres are obtained using melt-foaming method. The distribution and the effects of the ceramic microspheres on the mechanical properties of aluminum foams are investigated. The results show that both kinds of ceramic microspheres distribute in the foams uniformly with part in the cell wall matrix, some in adhere to the cell wall surface and part embed in the cell wall with portion surface exposed to the pores. Ceramic microspheres have an important effect on the yield strength, mean plateau stress, densification strain and energy absorption capacities of aluminum foams. Meanwhile, the content of ceramic microsphere in aluminum foams should be controlled in order to obtain good combination of compressive strength and energy absorption capacity. The reasons are discussed.     

Strain rate effects on the compressive property and the energy-absorbing capacity of aluminum alloy foams

The strain rate sensitivity of various relative densities, open-cell aluminum alloy foams fabricated by a powder metallurgical method is investigated under compression loading. Their response to strain rate has been tested over a wide range of strain rates, from 10⁻³ to 2600 s⁻¹ at room temperature. Within this range, the experimental results show that the yield strength and the energy absorbed increase with an increase of strain rate. However, the yield strength of higher relative density foams increases bilinearly with the logarithm of strain rate, and the yield strength of lower relative density foams shows only a linear increase. The compaction strain slightly decreases with an increase of strain rate. The higher relative density aluminum alloy foams are more sensitive to strain rate than the lower relative density foams.     

Effect of homogenizing heat treatment on the compressive properties of closed-cell Mg alloy foams

Closed-cell AZ31 Mg alloy foams were successfully prepared by melt-foaming method. Homogenizing heat treatment was applied on the foams and the effects of heat treatment on compressive properties of closed-cell Mg alloy foams were investigated systematically. The results showed that homogenizing heat treatment enhanced the compressive properties in terms of yield strength, mean plateau strength, available energy absorption capacity and ideality energy absorption efficiency of the foams. In addition, homogenizing heat treatment greatly reduced the stress drop rates of the foams. Specimens homogenized at the temperature of 753 K for 24 h possessed good combination of yield strength, compressive stability, available energy absorption capacity and ideality energy absorption efficiency under the present experiment conditions. And the reasons were discussed.     

The durability properties of polypropylene fiber reinforced fly ash concrete

This paper reports of a comprehensive study on the durability properties of concrete containing polypropylene fiber and fly ash. Properties studied include unit weight and workability of fresh concrete, and compressive strength, modulus of elasticity, porosity, water absorption, sorptivity coefficient, drying shrinkage and freeze–thaw resistance of hardened concrete. Fly ash content used in concrete mixture was 0%, 15% and 30% in mass basis, and fiber volume fraction was 0%, 0.05%, 0.10% and 0.20% in volume basis.     

Fabrication and characterization of closed-cell aluminum foams with different contents of multi-walled carbon nanotubes

Closed-cell aluminum foams with different contents of multi-walled carbon nanotubes (MWCNTs) were fabricated by using modified melt foaming method. In order to effectively disperse MWCNTs, orthogonal tests were utilized to determine the optimal ball-milling parameters. The existence forms of MWCNTs in aluminum foams and the compressive properties of the foams were investigated. Considered from the dispersion degree and structural changes of MWCNTs, the optimal parameters were obtained, the parameters mainly referred to weight ratio of MWCNTs to aluminum powder, weight ratio of ball to powder, milling rate and milling time, respectively. The results showed that MWCNTs mainly existed in three forms: totally embedded in cell wall, partly embedded in cell wall and totally exposed on cell wall surface, respectively. The reasons were mainly due to the existence of defects and amorphous carbon on the surface of MWCNTs, which promoted the wettability between the aluminum matrix and MWCNTs. In addition, with the MWCNT content increasing, the yield strength, structural stiffness and energy absorption capacity of the foams increased first and then decreased. Meanwhile, under the present conditions the foams with MWCNT content of 0.5% possessed the optimal comprehensive mechanical properties and the reasons were discussed.