The effects of surface elasticity and surface tension on the tra

The effects of surface elasticity and surface tension on the transverse overall elastic behavior of unidirectional nano-composites

Sofia G. Mogilevskaya^{a, ,} , Steven L. Crouch^a, Alessandro La Grotta^b and Henryk K. Stolarski^a

^a Department of Civil Engineering, University of Minnesota, 500 Pillsbury Drive S.E., Minneapolis, MN 55455, USA

^b Facoltà di Ingegneria, Università di Bologna, Viale Risorgimento 2, 40136 Bologna, Italy

Received 14 August 2009; 

revised 4 November 2009; 

accepted 11 November 2009. 

Available online 16 November 2009.

Abstract

The effects of surface elasticity and surface tension on the transverse overall behavior of unidirectional nano-scale fiber-reinforced composites are studied. The interfaces between the nano-fibers and the matrix are regarded as material surfaces described by the Gurtin and Murdoch model. The analysis is based on the equivalent inhomogeneity technique. In this technique, the effective elastic properties of the material are deduced from the analysis of a small cluster of fibers embedded into an infinite plane. All interactions between the inhomogeneities in the cluster are precisely accounted for. The results related to the effects of surface elasticity are compared with those provided by the modified generalized self-consistent method, which only indirectly accounts for the interactions between the inhomogeneities. New results related to the effects of surface tension are presented. Although the approach employed is applicable to all transversely isotropic composites, in this paper we consider only a hexagonal arrangement of circular cylindrical fibers.

Keywords: A. Nano-composites; A. Fibers; B. Mechanical properties; C. Elastic properties

Pore structure and chloride permeability of concrete containing

Pore structure and chloride permeability of concrete containing nano-particles for pavement

Mao-hua Zhang^{a, b, ,} and Hui Li^b

^a School of Civil Engineering, Northeast Forestry University, 150040 Harbin, China

^b School of Civil Engineering, Harbin Institute of Technology, 150090 Harbin, China

Received 21 March 2010; 

revised 26 July 2010; 

accepted 28 July 2010. 

Available online 31 August 2010.

Abstract

Pore structure and chloride permeability of concrete containing nano-particles (TiO₂ and SiO₂) for pavement are experimentally studied and compared with that of plain concrete, concrete containing polypropylene (PP) fibers and concrete containing both nano-TiO₂ and PP fibers. The test results indicate that the addition of nano-particles refines the pore structure of concrete and enhances the resistance to chloride penetration of concrete. The refined extent of pore structure and the enhanced extent of the resistance to chloride penetration of concrete are increased with the decreasing content of nano-particles. The pore structure and the resistance to chloride penetration of concrete containing nano-TiO₂ are superior to that of concrete containing the same amount of nano-SiO₂. However, for the concrete containing PP fibers, the pore structure is coarsened and the resistance to chloride penetration is reduced. The larger the content of PP fibers, the coarser the pore structure of concrete, and the lower the resistance to chloride penetration. For the concrete containing both nano-TiO₂ and PP fibers, the pore structure is coarser and the resistance to chloride penetration is lower than that of concrete containing the same amount of PP fibers only. A hyperbolic relationship between chloride permeability and compressive strength of concrete is exhibited. There is an obvious linear relationship between chloride permeability and pore structure of concrete.

Keywords: Nano-particles; Pore structure; Chloride permeability; Polypropylene (PP) fibers; Pavement concrete

Measuring mechanical properties of micro- and nano-fibersnext te

Measuring mechanical properties of micro- and nano-fibers embedded in an elastic substrate: Theoretical framework and experiment

Guoxin Cao^a, Xi Chen^{a, ,} , Zhi-Hui Xu^b and Xiaodong Li^b

^a Nanomechanics Research Center, School of Engineering and Applied Sciences, Mail Code 4709, Columbia University, New York, NY 10027-6699, USA

^b Department of Mechanical Engineering, University of South Carolina, 300 Main Street, Columbia, SC 29208, USA

Received 12 February 2009; 

accepted 7 March 2009. 

Available online 17 March 2009.

Abstract

We propose to measure the elastoplastic properties of micro- and nano-fibers by a normal indentation technique in which the vertically aligned fibers are embedded in an elastic matrix. Measurements are taken at two different indentation depths, which represent different levels of the matrix effects and lead to the establishment of two independent equations that correlate the fiber/matrix properties with the indentation responses. Effective reverse analysis algorithms are proposed, and by following which the desired fiber properties can be determined from a sharp indentation test. Comprehensive analysis is also carried out to verify the effectiveness and error sensitivity of the presented method. The extracted material properties agree well with those measured from the parallel experiments on human hair and glass fibers.

Keywords: A. Fibres; D. Nanoindentation; B. Mechanical properties; C. Computational modeling

Effects of nanonext term-SiO2 on morphology, thermal energy stor

Effects of nano-SiO₂ on morphology, thermal energy storage, thermal stability, and combustion properties of electrospun lauric acid/PET ultrafine composite fibers as form-stable phase change materials

Yibing Cai^{a, b, c}, Huizhen Ke^a, Ju Dong^a, Qufu Wei^{a, ,} , Jiulong Lin^a, Yong Zhao^c, Lei Song^b, Yuan Hu^b, Fenglin Huang^{a, ,} , Weidong Gao^a and Hao Fong^c

^a Key Laboratory of Eco-Textiles, Ministry of Education, Jiangnan University, Wuxi, Jiangsu 214122, PR China

^b State Key Laboratory of Fire Science, University of Science and Technology of China, Hefei, Anhui 230027, PR China

^c Department of Chemistry, South Dakota School of Mines and Technology, Rapid City, SD 57701, USA

Received 3 August 2010; 

revised 2 December 2010; 

accepted 24 December 2010. 

Available online 15 January 2011.

Abstract

The ultrafine composite fibers consisting of lauric acid (LA), polyethylene terephthalate (PET), and silica nanoparticles (nano-SiO₂) were prepared through the materials processing technique of electrospinning as an innovative type of form-stable phase change materials (PCMs). The effects of nano-SiO₂ on morphology, thermal energy storage, thermal stability, and combustion properties of electrospun LA/PET/SiO₂ composite fibers were studied. SEM images revealed that the LA/PET/SiO₂ composite fibers with nano-SiO₂ possessed desired morphologies with reduced average fiber diameters as compared to the LA/PET fibers without nano-SiO₂. DSC measurements indicated that the amount of nano-SiO₂ in the fibers had an influence on the crystallization of LA, and played an important role on the heat enthalpies of the composite fibers; while it had no appreciable effect on the phase change temperatures. TGA results suggested that the incorporation of nano-SiO₂ increased the onset thermal degradation temperature, maximum weight loss temperature, and charred residue at 700 °C of the composite fibers, indicating the improved thermal stability of the fibers. MCC tests showed that the heat resistance effect and/or barrier property generated by nano-SiO₂ resulted in an increase of initial combustion temperature and a decrease of the heat release rate for the electrospun ultrafine composite fibers.

Keywords: Form-stable phase change materials; Electrospinning; LA/PET composite fibers; Nano-SiO₂; Morphology; Thermal energy storage