Modified Method for Dynamic Stress-Strain Curve Determination of Closed-Cell Foams

Abstract

The paper presents a modified method for the non‐linear dynamic stress‐strain curve determination with the use of cushion curves provided by the manufacturers of closed‐cell foams. This method consists of two main stages: stage 1 – the cushion curves transformation to the coordinate system of dynamic stress‐energy density, combined with the cubic b‐spline curve approximation, and stage 2 – development of the dynamic stress‐strain curve considering that the area under the curve is equal to the energy density of a collision. The stress‐strain curves are one of the basic parameters of the foam material models used to describe the collision process, in the modelling environments of finite element method (FEM), e.g. LS‐DYNA. Performed verification consisting in the reconstruction of cushion curves using LS‐DYNA showed that the proposed method of the dynamic stress‐strain curves determination is efficient and effective. Taking into account that access to the stress‐strain curves is hindered (cushioning material manufacturers do not publish them), and the access to charts of cushion curves is easier, the proposed method for determining the stress‐strain curves can relevantly shorten the process of preparing the input data, which are required during modelling of spatial structures using FEM. Copyright © 2016 John Wiley & Sons, Ltd.

Prediction of cushion curves of polymer foams using a nonlinear distributed parameter model

“…We have shown that the material behaviour can be adjusted to represent the impact response by calibrating the model using a viscous damping coefficient predicted from the shock pulse. This approach works well, since the dynamic stress strain relationship does not significantly deviate from the quasi‐static stress strain relationship in the polystyrene foam …”

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Acceleration Response First Passage Failure Probability Analysis Method for Nonlinear Package

“…erefore, the limit-state function of the system can be obtained by (21), and the FORM can be used to analyze the acceleration response reliability of the package. e reliability index is obtained by (13), the vector a(t) is obtained by (10), h(t) is obtained by (8), the vector s(t) can be obtained by (26), and the acceleration response rst passage probability of the package is obtained by (4). In this example, the rst passage failure probability of the package is calculated and shown in Figure 5.…”

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