Plastic Theory And Large Deformation Analysis Of Graded Sandwich Beams

Owing to the excellent mechanical properties such as high specific stiffness and specific strength,good impact resistance and energy absorption performance,as well as many functions including heat dissipation,thermal insulation,sound insulation,electromagnetic shielding,etc.,lightweight sandwich structures have been the focus of lightweight research,and have been widely used in aerospace,high-speed trains,automobiles and ships,wind power generation,packaging protection and other fields.Considering the limitation of traditional symmetrical sandwich structure with single core,by introducing the graded core into the asymmetrical sandwich structure with varied face-sheets,and coordinating the physical and geometric characteristics of each face-sheet and the core layer,a novel sandwich structure that can meet more requirements of function and application can be realized,and the design space of sandwich structure can be further widened.Therefore,it is very important to investigate the plastic behavior of the asymmetrical sandwich structure with graded core.In this paper,theoretical analysis and numerical simulation are used to study the large plastic deformation of graded materials and their sandwich structures under transverse load.The influences of gradient parameters,core gradation and face-sheet asymmetry on the plastic yielding,load-carrying and energy absorption capacities of the graded materials and their sandwich structures are discussed in detail.The major elements and conclusions are as follows:1.The plastic deformation of the fully clamped graded material beam and its asymmetrical sandwich beam under transverse loading is studied.A layer-graded model of the graded material beam is proposed by discretizing the functionally graded material.The generalized yield criteria and large deformation governing equations of the graded material and its sandwich structure are established according to the gradient change law of yield strength,which are further applied to the surface-reinforced sandwich structure with a strengthening skin bonded on the impact surface of the traditional sandwich structure.After that,the theoretical analysis model is verified by the numerical simulation and the experimental results of the existing literature.The results indicate that the theoretical model can well predict the mid-span deflection,load-carrying and energy absorption capacities of the fully clamped graded material beam and its sandwich beam,the surface-reinforced sandwich beam and the traditional sandwich beam.Moreover,the larger the gradient variation ratio near the loading surface is,the more accurate the layer-graded beam model is.2.The influence of gradient profile and gradient intensity factor on the large deflection response of the graded material beam is studied.It is demonstrated that the gradient coefficient,gradient intensity factor and the strength ratios of the discrete layer have significant effects on the properties of the yield surface and the capacity of load-carrying and energy absorption of the graded material beams.Under the condition that the membrane force and thickness are constant,through an appropriate gradient design,the non-monotonic graded beam with the yield strength change from strong to weak and then to strong in the thickness direction shows better bending and tensile capacities,as well as excellent performance of load-carrying and energy absorption.Particularly,strengthen the surface material with large gradient variation ratio will be helpful to the load-carrying and energy absorption of the graded beam,especially when the other surface material is weaker.3.The effects of the gradient arrangement of the core layer and the asymmetrical configuration of the face-sheet on the plastic deformation of the sandwich structure with graded core are studied,and the mechanical properties improvements of different types of traditional sandwich beams with the help of the reinforced skin is clarified.The results show that the core gradation and the face-sheet asymmetry have obvious influence on the plastic deformation of the graded sandwich beam.Under the condition that the membrane force and thickness are constant,the load-bearing and energy absorption performances of the graded sandwich beam can be effectively improved by selecting a thinner and stronger top face-sheet,as well as a thicker and weaker back core,and arranging reasonable strength and thickness parameters of the core gradation and the face-sheet asymmetry.Moreover,the local denting,load-carrying and energy absorption characteristics of the traditional sandwich structure can be effectively improved by introducing a reinforced skin,especially when the top face-sheet is thinner and weaker than the bottom face-sheet.