National Key Laboratory of Advanced Functional Composite Material Technology

Beijing, China

National Key Laboratory of Advanced Functional Composite Material Technology

Beijing, China
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Zhang Y.,Beihang University | Lu Z.,Beihang University | Yang Z.,Beihang University | Zhang D.,National Key Laboratory of Advanced Functional Composite Material Technology | And 3 more authors.
Carbon | Year: 2017

Carbon-bonded carbon fiber composites (CBCFs) were widely used as thermal insulation materials due to their light weight and ultra-low thermal conductivity. The CBCFs with density of about 0.256 g/cm3 were tested in compression with the modulus and strength evaluated. The in-plane and out-of-plane tests revealed obvious anisotropic behavior of the material, which could be attributed to the fibers distribution. The unloading-reloading tests showed more evidence for the difference of the mechanical behaviors between in-plane and out-of-plane. In addition, we presented a finite element model to predict the mechanical properties of the CBCFs, and the deformation mechanisms as well. The numerical results showed the compressive modulus and strength increased with density following exponential functions. Moreover, the effects of fiber length and the fiber orientation on the mechanical properties were also discussed numerically. The results of this paper are helpful for the design and optimization of these materials for potential applications. © 2017 Elsevier Ltd


Liu Q.,Beihang University | Lu Z.,Beihang University | Zhu M.,Beihang University | Yang Z.,Beihang University | And 2 more authors.
Journal of Materials Science | Year: 2014

Three-dimensional (3D) random fibrous (RF) materials with bonded networks exhibit unique mechanical properties. In this paper, an inorganic RF material is fabricated and its compressive behavior is studied by experiment. Based on the experimental characterization, a 3D numerical model is constructed using a series of geometrical algorithms. Afterward, the statistical distribution of fiber segment aspect ratio is calculated using the numerical model, which is consistent with that measured from SEM photos. The compressive behavior of this RF material is simulated using finite element method (FEM). In the FEM model, the effect of fiber-fiber contact is realized by contact spring. The calculated results agree well with experimental data. Moreover, the predicted failure mechanism is verified by SEM observation. Finally, the FEM model is employed to investigate the influences of porosity on the elastic modulus and compressive strength of the RF material. © 2013 Springer Science+Business Media New York.


Lu Z.,Beihang University | Yuan Z.,Beihang University | Liu Q.,Beihang University | Hu Z.,National Key Laboratory of Advanced Functional Composite Material Technology | And 2 more authors.
Materials Science and Engineering A | Year: 2015

A new multi-scale model is proposed to investigate the relationship between the mechanical properties and microstructure of fiber-reinforced silica aerogel composites. The multi-scale model consists of the aerogel model in nanometers and the composite model in micrometers. The aerogel model is generated to represent the cluster structure of silica aerogels based on a modified diffusion-limited cluster aggregation (DLCA) algorithm, in which the size-dependent interactions between the primary particles are obtained from theoretical derivations. A continuum damage constitutive model is established to represent the behavior of the silica aerogel matrix in the composite by implementing the aerogel model with the discrete element method (DEM). After that, a modified embedded element technique (EET) is proposed to generate the finite element (FE) model of the silica aerogel composite with curve fibers. This multi-scale model is used to investigate the tensile behavior of fiber-reinforced silica aerogel composites, while a comparison with experimental results is presented. The numerical results show that the primary particle size has a significant effect on the Young[U+05F3]s modulus and the tensile strength of the composites. Moreover, our present model is employed to explore the relationship between the mechanical properties of the composite and the fiber characteristics, including the fiber volume fraction, length and curvature. The predictions indicate that the characteristics of the reinforcing fibers are significant for the mechanical properties of silica aerogel composites. The present multi-scale model can be extended to study the mechanical properties of other aerogel composites. © 2014.


Liu Q.,Beihang University | Lu Z.,Beihang University | Zhu M.,Beihang University | Yuan Z.,Beihang University | And 3 more authors.
Soft Matter | Year: 2014

A new two-level model is proposed to investigate the relationship between the mechanical properties and microstructure of silica aerogels. This two-level model consists of the particle-particle interaction model and the cluster structure model. The particle-particle interaction model is proposed to describe interactions between primary particles, in which the polymerization reaction between primary particles is considered. The cluster structure model represents the geometrical structure of silica aerogels, and it is established using a modified diffusion-limited colloid aggregation (DLCA) algorithm. This two-level model is used to investigate the tensile behavior of silica aerogels based on the discrete element method (DEM). The numerical results show that the primary particle size has significant effects on the elastic modulus and tensile strength of silica aerogels. Moreover, the power-law relationships between tensile properties and aerogel density are dependent on the variation of the primary particle radius with density. The present results can explain the difference among different experimental exponents to a certain extent. In comparison with experimental data within a wide density range, this two-level model provides good quantitative estimations of the elastic modulus and tensile strength of silica aerogels after the size effects of the primary particle are considered. This paper provides a fundamental understanding of the relationship between the mechanical properties and microstructure of silica aerogels. The two-level model can be extended to study the mechanical properties of other aerogels and aerogel composites. This journal is © the Partner Organisations 2014.


Liu Q.,Beihang University | Lu Z.,Beihang University | Hu Z.,National Key Laboratory of Advanced Functional Composite Material Technology | Li J.,National Key Laboratory of Advanced Functional Composite Material Technology
Materials Science and Engineering A | Year: 2013

Three-dimensional (3D) random fibrous materials exhibit extraordinary mechanical properties due to their complex morphological characteristic of bonded fibre networks on the meso-level. Based upon experimental characterisation, a simplified numerical model is presented that reveals the disordered features of bonded fibre networks and allows investigation of the tensile behaviour of 3D random fibrous (3DRF) materials. The calculated results' dependence on the quantity of numerical samples, mesh density and model size is analysed using finite element analysis (FEA); consequently, an optimised FEA model is obtained. The 3DRF materials' tensile behaviour is then predicted using the optimised FEA model. The calculated results agree well with the experimental data. Moreover, the predicted failure mechanism is consistent with SEM observations. The experimental data thus validate the FEA model. On this basis, we conduct a comprehensive investigation to understand the influences of the fibres' deformation mode, the bonding properties and the proportion of the constituent fibres on the macro-mechanical properties of 3DRF materials. These analyses provide insight into the mechanical behaviour of such materials. © 2013 Elsevier B.V.

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