In this paper, the microcellular silicone rubber foams, strengthened with tetrapod-like Zinc Oxide whisker（T-ZnOw） are prepared. Through further characterization, it can be seen that the average cell diameter size o...In this paper, the microcellular silicone rubber foams, strengthened with tetrapod-like Zinc Oxide whisker（T-ZnOw） are prepared. Through further characterization, it can be seen that the average cell diameter size of the filled with T-ZnOw is reduced. The distribution uniformity of microcellulars is improved obviously with increasing T-ZnOw filler. The reason that introduction of T-ZnOw can greatly enhance mechanical properties of the microcellular silicone rubber foams is its good interfacial adhesion with the matrix contributes. It is also found that the reducing effects of T-ZnOw on the compressive stress relaxation ratio of microcellular silicone rubber foams, and the improvement is obvious with increasing T-ZnOw filler.展开更多
Silicon carbide （SIC） foams with a continuously connected open-cell structure were prepared and characterized for their mechanical performance. The apparent densities of SiC foams were controlled between about 0.4 a...Silicon carbide （SIC） foams with a continuously connected open-cell structure were prepared and characterized for their mechanical performance. The apparent densities of SiC foams were controlled between about 0.4 and 2.3 g/cm^3, with corresponding compressive strengths ranging from about 23 to 60 MPa and flexural strengths from about 8 to 30 MPa. Compressive testing of the SiC foams yielded stress-strain curves with only one linear-elastic region, which is different from those reported on ceramic foams in literature. This can possibly be attributed to the existence of filaments with fine, dense and high strength microstructures. The SiC and the filaments respond homogeneously to applied loading.展开更多
Aluminum foam is a light weight material with good mechanical and energy absorption properties. In this study, aluminum foam composite was fabricated using aluminum powder 6061 and silicon carbide (SiC) powder. Titani...Aluminum foam is a light weight material with good mechanical and energy absorption properties. In this study, aluminum foam composite was fabricated using aluminum powder 6061 and silicon carbide (SiC) powder. Titanium hydride (TiH2) was used as the foaming agent. Cold compact followed by hot pressing (sintering) was used to produce the composite precursor. Foaming was carried out, following the sintering process, by heating the aluminum composite precursor to a temperature above the melting point of aluminum (Al). The linear expansion of the foam and the percent porosity were found to increase as the SiC percentage decreased from 10 to 4%, whereas the density got lower. The percent porosity and linear expansion were both found to increase as the percentage of the foaming agent was increased from 0.5 to 1.5%. Compression stress was evaluated for two different porosity values (40% and 47%), and found to be higher for the samples with lower percent porosity at the same strain value. Effect of shape memory alloy fiber, made of nickel and titanium (NiTi), on the mechanical properties was also investigated. The compression stress was higher, in the densification region, for the samples in which NiTi was used.展开更多
Geopolymers are three-dimensional aluminosilicates formed in a short time at low temperature by geopolymerization. In this pa-per, alkali-activated foam geopolymers were fabricated from circulating fluidized bed fly a...Geopolymers are three-dimensional aluminosilicates formed in a short time at low temperature by geopolymerization. In this pa-per, alkali-activated foam geopolymers were fabricated from circulating fluidized bed fly ash （CFA）, and the effect of SiO2/Na2O mole ratio （0.91-1.68） on their properties was studied. Geopolymerization products were characterized by mechanical testing, scanning electron mi-croscopy （SEM）, energy-dispersive X-ray spectroscopy （EDX）, and X-ray diffraction （XRD）. The results show that SiO2/Na2O mole ratio plays an important role in the mechanical and morphological characteristics of geopolymers. Foam samples prepared in 28 d with a SiO2/Na2O mole ratio of 1.42 exhibit the greatest compressive strength of 2.52 MPa. Morphological analysis reveals that these foam geo-polymers appear the relatively optimized pore structure and distribution, which are beneficial to the structure stability. Moreover, a combina-tion of the Si/Al atomic ratio ranging between 1.47 and 1.94 with the Na/Al atomic ratio of about 1 produces the samples with high strength.展开更多
The damping properties of an Mg alloy foam and its composite foams were investigated using a dynamic mechanical thermal analyzer. The results show that the loss factors of both the Mg alloy and its composite foams are...The damping properties of an Mg alloy foam and its composite foams were investigated using a dynamic mechanical thermal analyzer. The results show that the loss factors of both the Mg alloy and its composite foams are insensitive to temperature and loading frequency when the temperature is less than a critical temperature Tcrit. However, it increases when the temperature exceeds the Tcrit values, which are 200 and 250°C for the Mg alloy foam and the Mg alloy/SiCp composite foams, respectively. The Mg alloy/SiCp composite foams exhibit a higher damping capacity than the Mg alloy foam when the temperature is below 200°C. By contrast, the Mg alloy foam exhibits a better damping capacity when the temperature exceeds 250°C. The variation in the damping capacity is attributed to differences in the internal friction sources, such as the characteristics of the matrix material, abundant interfaces, and interfacial slipping caused by SiC particles, as well as to macrodefects in the Mg alloy and its composite foams.展开更多
Controlling process parameters of lost foam casting （LFC） enables this process to produce defect-free complex shape castings. An experimental investigation on lost foam casting of an A1-Si-Cu cast alloy was carried ...Controlling process parameters of lost foam casting （LFC） enables this process to produce defect-free complex shape castings. An experimental investigation on lost foam casting of an A1-Si-Cu cast alloy was carried out. The effects of pouting temperature, slurry viscosity, vibration time and sand size on surface finish, shrinkage porosity and eutectic silicon spacing of thin-wall casting were investigated. A full two-level factorial design of experimental technique was used to identify the significant manufacturing factors affecting the properties of casting. Pouring temperature was found as the most significant factor affecting A1-Si-Cu lost foam casting quality. It was shown that flask vibration time interacted with pouring temperature influenced euteetic silicon spacing and porosity percentage significantly. The results also revealed that the surface quality of the samples cast in fine sand moulds at higher pouring temperatures was almost unchanged, while those cast in coarse sand moulds possessed lower surface qualities. Furthermore, variation in slurry viscosity showed no significant effect on the evaluated properties compared to other parameters.展开更多
In this study, a constitutive model based on microscopic physical mechanism of silicone rubber foams was established. A theoretical statistical model of rubber elasticity considering the effect of dangling chains was ...In this study, a constitutive model based on microscopic physical mechanism of silicone rubber foams was established. A theoretical statistical model of rubber elasticity considering the effect of dangling chains was modified to build this model. When a strain amplification factor （X） was introduced, the theoretical model could fit the tensile stress-strain data of mono- and bi-modal foam matrix well （Adj. R-Square = 0.9989, 0.9983）. Parameters related to the polymer network, namely, average molecular weight （Me） and volume fraction （Ф） of chain segments between adjacent cross-linking points （network strands）, were calculated by probabilistic method from the number-average molecular weight （Mn）, vinyl content （wvi） of the primary polysiloxanes and percent conversion （q） of vinyl groups. The primary and infinite strain amplification factors （X0, X∞） and decay exponent （z）, introduced by X and related to the nanoparticles, were obtained by fitting. Inspired by the fact that the actual strain of matrix was lower than that of the foams＇, we introduced another item, strain hysteresis item （H, related with the foam porosity and cell structure）, into the statistical model as well. With the same above values of Mc, Ф, X0 and X∞, the model could also fit the compressive stress-strain data of mono- and bi-modal foams well （Adj. R-Square = 0.9948, 0.9985）. Interestingly, the strain hysteresis items of the mono- and bi-modal foams almost completely coincided under all experimental strains, which may be attributed to the almost equal porosity and similar cell structure of the two foams. This constitutive model may connect the macroscopic stress-strain behaviour to the parameters of microscopic molecular structures, promisingly providing a basis for the performance improvement and optimization of silicone rubber foams.展开更多
文摘In this paper, the microcellular silicone rubber foams, strengthened with tetrapod-like Zinc Oxide whisker（T-ZnOw） are prepared. Through further characterization, it can be seen that the average cell diameter size of the filled with T-ZnOw is reduced. The distribution uniformity of microcellulars is improved obviously with increasing T-ZnOw filler. The reason that introduction of T-ZnOw can greatly enhance mechanical properties of the microcellular silicone rubber foams is its good interfacial adhesion with the matrix contributes. It is also found that the reducing effects of T-ZnOw on the compressive stress relaxation ratio of microcellular silicone rubber foams, and the improvement is obvious with increasing T-ZnOw filler.
文摘Silicon carbide （SIC） foams with a continuously connected open-cell structure were prepared and characterized for their mechanical performance. The apparent densities of SiC foams were controlled between about 0.4 and 2.3 g/cm^3, with corresponding compressive strengths ranging from about 23 to 60 MPa and flexural strengths from about 8 to 30 MPa. Compressive testing of the SiC foams yielded stress-strain curves with only one linear-elastic region, which is different from those reported on ceramic foams in literature. This can possibly be attributed to the existence of filaments with fine, dense and high strength microstructures. The SiC and the filaments respond homogeneously to applied loading.
文摘Aluminum foam is a light weight material with good mechanical and energy absorption properties. In this study, aluminum foam composite was fabricated using aluminum powder 6061 and silicon carbide (SiC) powder. Titanium hydride (TiH2) was used as the foaming agent. Cold compact followed by hot pressing (sintering) was used to produce the composite precursor. Foaming was carried out, following the sintering process, by heating the aluminum composite precursor to a temperature above the melting point of aluminum (Al). The linear expansion of the foam and the percent porosity were found to increase as the SiC percentage decreased from 10 to 4%, whereas the density got lower. The percent porosity and linear expansion were both found to increase as the percentage of the foaming agent was increased from 0.5 to 1.5%. Compression stress was evaluated for two different porosity values (40% and 47%), and found to be higher for the samples with lower percent porosity at the same strain value. Effect of shape memory alloy fiber, made of nickel and titanium (NiTi), on the mechanical properties was also investigated. The compression stress was higher, in the densification region, for the samples in which NiTi was used.
基金financially supported by the Research Fund for the Doctoral Program of Higher Education of China(No.20120023110011)the Fundamental Research Funds for the Central Universities of China(Nos.2009KH09 and 2009QH02)
文摘Geopolymers are three-dimensional aluminosilicates formed in a short time at low temperature by geopolymerization. In this pa-per, alkali-activated foam geopolymers were fabricated from circulating fluidized bed fly ash （CFA）, and the effect of SiO2/Na2O mole ratio （0.91-1.68） on their properties was studied. Geopolymerization products were characterized by mechanical testing, scanning electron mi-croscopy （SEM）, energy-dispersive X-ray spectroscopy （EDX）, and X-ray diffraction （XRD）. The results show that SiO2/Na2O mole ratio plays an important role in the mechanical and morphological characteristics of geopolymers. Foam samples prepared in 28 d with a SiO2/Na2O mole ratio of 1.42 exhibit the greatest compressive strength of 2.52 MPa. Morphological analysis reveals that these foam geo-polymers appear the relatively optimized pore structure and distribution, which are beneficial to the structure stability. Moreover, a combina-tion of the Si/Al atomic ratio ranging between 1.47 and 1.94 with the Na/Al atomic ratio of about 1 produces the samples with high strength.
基金financially supported by the National Natural Science Foundation of China (Nos. 51174060 and 51301109)the Science and Technology Department of Liaoning Province of China (No. 2013223004)the Fundamental Research Funds for the Central Universities (No. 140203004)
文摘The damping properties of an Mg alloy foam and its composite foams were investigated using a dynamic mechanical thermal analyzer. The results show that the loss factors of both the Mg alloy and its composite foams are insensitive to temperature and loading frequency when the temperature is less than a critical temperature Tcrit. However, it increases when the temperature exceeds the Tcrit values, which are 200 and 250°C for the Mg alloy foam and the Mg alloy/SiCp composite foams, respectively. The Mg alloy/SiCp composite foams exhibit a higher damping capacity than the Mg alloy foam when the temperature is below 200°C. By contrast, the Mg alloy foam exhibits a better damping capacity when the temperature exceeds 250°C. The variation in the damping capacity is attributed to differences in the internal friction sources, such as the characteristics of the matrix material, abundant interfaces, and interfacial slipping caused by SiC particles, as well as to macrodefects in the Mg alloy and its composite foams.
基金the Ministry of Higher Education of Malaysia (MOHE) for the financial support under the vote GUP-Q.J130000.2501.04H18
文摘Controlling process parameters of lost foam casting （LFC） enables this process to produce defect-free complex shape castings. An experimental investigation on lost foam casting of an A1-Si-Cu cast alloy was carried out. The effects of pouting temperature, slurry viscosity, vibration time and sand size on surface finish, shrinkage porosity and eutectic silicon spacing of thin-wall casting were investigated. A full two-level factorial design of experimental technique was used to identify the significant manufacturing factors affecting the properties of casting. Pouring temperature was found as the most significant factor affecting A1-Si-Cu lost foam casting quality. It was shown that flask vibration time interacted with pouring temperature influenced euteetic silicon spacing and porosity percentage significantly. The results also revealed that the surface quality of the samples cast in fine sand moulds at higher pouring temperatures was almost unchanged, while those cast in coarse sand moulds possessed lower surface qualities. Furthermore, variation in slurry viscosity showed no significant effect on the evaluated properties compared to other parameters.
基金financially supported by the National Natural Science Foundation of China(Nos.51473151 and 51703210)
文摘In this study, a constitutive model based on microscopic physical mechanism of silicone rubber foams was established. A theoretical statistical model of rubber elasticity considering the effect of dangling chains was modified to build this model. When a strain amplification factor （X） was introduced, the theoretical model could fit the tensile stress-strain data of mono- and bi-modal foam matrix well （Adj. R-Square = 0.9989, 0.9983）. Parameters related to the polymer network, namely, average molecular weight （Me） and volume fraction （Ф） of chain segments between adjacent cross-linking points （network strands）, were calculated by probabilistic method from the number-average molecular weight （Mn）, vinyl content （wvi） of the primary polysiloxanes and percent conversion （q） of vinyl groups. The primary and infinite strain amplification factors （X0, X∞） and decay exponent （z）, introduced by X and related to the nanoparticles, were obtained by fitting. Inspired by the fact that the actual strain of matrix was lower than that of the foams＇, we introduced another item, strain hysteresis item （H, related with the foam porosity and cell structure）, into the statistical model as well. With the same above values of Mc, Ф, X0 and X∞, the model could also fit the compressive stress-strain data of mono- and bi-modal foams well （Adj. R-Square = 0.9948, 0.9985）. Interestingly, the strain hysteresis items of the mono- and bi-modal foams almost completely coincided under all experimental strains, which may be attributed to the almost equal porosity and similar cell structure of the two foams. This constitutive model may connect the macroscopic stress-strain behaviour to the parameters of microscopic molecular structures, promisingly providing a basis for the performance improvement and optimization of silicone rubber foams.
