Mechanical Properties And Elastoplastic Damage Constitutive Model For Foamed Concrete

As a member of lightweight concrete,the foamed concrete stands out in new building materials for its excellent performances,low cost and environmental friendly features.Recently,foamed concrete is widely used in many important fields,such as building energy conservation and protective structure.However,the present researches on the foamed concrete pay more attention to their functional characteristics,such as refractoriness,thermal conductivity and permeability;meanwhile,most of the mechanical studies are only focused on the compressive strength.It should be noted that,different from the traditional concrete,foamed concrete can be treated as a typical cellular materials due to the large amount of internal microscopic cell structures.Therefore,this paper comprehensively investigates the quasi-static uniaxial/multiaxial mechanical properties of foamed concrete by using the analytical method of cellular materials.In addition,based on the theoretical derivation,the different damage constitutive models have been established under different loading conditions.The main research contents and conclusions can be stated as follows:? The uniaxial tensile and compressive tests have been conducted on the foamed concrete with different densities.Results indicate that foamed concrete brittle damage,which is controlled by the tensile damage mechanism,can be obtained in the tensile tests.And the ductile damage is activated by the shear damage mechanism under the compressive load.Additionally,the uniaxial complete compression stress-strain curves of foamed concrete have obvious "three stages"(i.e.elastoplasticity,plateau and densification stages)characteristics.The elastic modulus,yield strength,plateau stress and energy absorption capacity of foamed concrete obviously increase with increasing the density.This phenomenon indicates that the density exhibits significant influences on the mechanical properties of foamed concrete.? The multiaxial yield behavior and failure mode of the foamed concrete under different confining pressures have been explored through the conventional triaxial compression tests.The related results indicate that the pressure dependence of yield behavior of foamed concrete can be attributed to their internal porosity.And the air voids also can offer sufficient space for the compression deformation,which lead to the volume contraction of foamed concrete in triaxial compression tests.Furthermore,confining pressures can provide lateral restraint to the specimen,which can inhibit the strain-softening of foamed concrete.In the current study,a phenomenological yield criterion(stress potential function)based on the uniaxial tensile,uniaxial compressive and hydrostatic compressive stress paths is established for foamed concrete.The above yield criterion can effectively reflect the effects of density,yield strength asymmetry and pressure-dependent.Moreover,the validity of the yield criterion is examined by comparing with the experimental yield surfaces.? Two damage constitutive models of foamed concrete have been established for different loading conditions.Firstly,based on the Weibull distribution function and "three stages" characteristics of cellular materials,a one-dimensional compressive damage model is proposed in this paper,which can accurately describe the compressive response and energy absorption of foamed concrete under high strain level.Secondly,starting from the theories of plasticity,continuum damage mechanics and thermodynamics,a phenomenological framework of the elastoplastic damage model is derived.Meanwhile,the yield criterion,damage criteria and the corresponding evolution laws are proposed to perfect the constitutive model.Finally,the calculation results of Matlab further consolidate the validity of the present constitutive model.