The Mechanic Properties And Impact Energy Absorption Of Foam-made Loosefill Materials Under Dynamic Load

As a packaging material, the foam-made loosefill materials play an important role in filling packaging, especially in the packing of products which are strange shaped and have small quantities such as the rare heritage and so on. With the development of logistics industry, the packages for small quantity products are more and more needed, so the uses of loosefill materials are increased. As a result, it has important applications to study the mechanic properties and energy absorption of these filling materials. However, studies on the packaging materials and the foam materials have been focused on the material itself; there are hardly researches on the loosefill materials as a whole. Only individual scholars have reported some experiment results on some special loosefill materials.In this study, the EPS foam spheres loosefill materials are studied. At first, the compression tests at different loading rates of the EPS material itself, a single EPS foam sphere and an assembly of many EPS spheres were carried out respectively, and the drop hammer tests were done on the assembly of many EPS spheres too. The constitutive model of the EPS material which includes the contribution of the pressure in the material and the effect of the strain rate was established according to the experiment results. Then the constitutive model of the assembly of many EPS spheres for application was given. Based on this model, the drop impact response of the products which were packed by these loosefill materials were analyzed and the results were compared with the drop hammer tests results. At last, the FEA method was used to study the factors that affect the mechanic behavior of the assembly of many EPS spheres.The results show that the EPS material itself is a typical closed-cell cellular material, the effect of the pressure in the material on the material's stress-strain relationship can be expressed by the gas model proposed by Ashby etal. And it shows obvious strain rate effect as many polymer materials. The force-displacement curve of the assembly of many EPS spheres is similar to the wood chips', foam rubber's, cotton's and shredded paper's which shows nonlinear elastic characteristics. And this kind of force-displacement curve can be fitted well with the tangent-type function. The crushable foam model in ABAQUS 6.9 with hardening data from the uniaxial compressive stress strain curve can simulate the compressive stress strain properties of the low-density, closed-cell EPS foam well, and the foam harden data in the crushable foam model can be substituted by the data of gas contribution . The primary reason that affects the compressive properties of the assembly of many enclosed EPS particles is the contact and interaction between the spheres. The effect of the gas between the spheres is very small.