Thermal And Mechanical Properties Of Ultralight Composite Materials

In the past decades,China's society,economy,science and technology had been well developed.More attention has been paid to designing various composites for engineering applications.Among them,ultralight composite materials or structures are especially interesting,due to their featured physical properties of low density,high stiffness and strength,so that they can be used for the purpose of energy saving.On the one hand,hollow glass microsphere(HGM)based ultralight cement material is accounted for.HGM is a white tiny bubble with the micron-scaled diameter and wall thickness.Such hollow structure and fine spherical shape makes HGM have some distinctive properties,such as high compressive strength,low density,low water absorption,low heat conduction,and high chemical resistance,which are important to develop new structural materials,such as multilayer sandwich composites,syntactic foams,and lightweight concretes,for engineering applications in civil,deep-sea exploration,and hydrogen storage,et.al.Besides,due to its low thermal conductivity,HGM can be applied as an insulating material to meet the increasing requirement of energy saving.In this study,the characterization of physical properties of HGMs is firstly performed by experimental and computational approaches,then the effects of constituent properties as well as the volume fraction of hollow glass microsphere to the thermal properties of the cement composite are investigated.Subsequently,the random array of HGMs in the cement matrix is introduced to approximate their real distribution in the cement matrix,then numerical simulation of established random micromechanical model is carried out with ABAQUS to reveal the influence of distribution of HGMs.On the other hand,as one type of ultralight cellular materials,foam structure contains a high fraction of air pores and thus has high porosity.In this study,a two-dimensional closed-cell foam model involving randomly distributed air pore phase and solid wall phase is rebuilt by shrinking Voronoi tessellation technique to approximately represent the real foam structure.The porosity,pore size and solid wall thickness of the established random foam structure can be easily and precisely controlled by the introduced shrinking ratio.In the analysis,the effects of the porosity size,the number of pores and the thermal conductivity of solid wall material on the foam structures are investigated respectively.Based on the investigation,the geometric physical parameters,such as geometrical parameters of micropores,thickness of wall and thermal conductivity of matrix,of foam structure have great influence to the effective thermal conductivity of the whole system.