Study On The Mechanical Behavior Of EPS Foams And Their Sandwich Structures Under Ball Loading

Porous foam materials are widely applied in aerospace,automotive,construction and other engineering fields because of their good mechanical properties and multifunctional features such as heat resistance,cushioning and sound insulation.Foams have plateau stages where the stress almost keeps constant,so they have good energy absorption capacity and impact resistance.They are often used as packaging and energy absorption materials in the fields of structural safety protection and passive safety.Foam materials have a wide range of application prospects,but the studies on their large deformation mechanical response are not well developed,which to a certain extent limits their applications.By performing experimental study,numerical simulation,and theoretical analysis,the purpose of this work is to investigate the large deformation mechanical behavior and to establish prediction method on the response of foams and sandwich structures,which are subjected to static and dynamic ball loading.The main content and conclusions are as follows:1)The mechanical properties of expanded polystyrene(EPS)foam materials with different densities were measured through tensile and load/unload compression tests.The dependency of the mechanical properties of the foam material on the loading rate and foam density is analyzed based on the test results.Then,the indentation deformation and mechanical response of EPS foam blocks under static and dynamic ball loading are studied.2)The low-density foam constitutive model in the non-linear finite element software LS-DYNA is used to simulate the ball loading process of EPS foam blocks,and the simulation results are compared with experimental results to verify the finite element model.Parametric studies are then carried out to analyze the effect of the radius of the ball by using the validated numerical models.3)Based on experimental and numerical simulation observations,a theoretical analysis model is proposed on deformation of foams under ball indentation,which can predict the load response of the foams.In the theoretical model,the load pressure _nP is set as a function of the indenter.This improvement enables the theoretical model to give more accurate prediction results during the densification region of the foam.Comparisons show that the predicted results of the proposed theoretical model compare well with the experimental and numerical results.4)Experimental and numerical methods are used to study the deformation mechanism and mechanical response of the sandwich structures with EPS foams core during the ball loading.Research shows that,for foams with three different densities,the face sheets result in a mass increase of 70.5%,43.7%,and 35.3%,while the energy absorption increase by 124%,113%and 176%,respectively.