Cushion Package System Design and Numerical Simulation of Expanded Polypropylene（EPP）
Date Issued
2011
Date
2011
Author(s)
Hoi, Kou-Pang
Abstract
Products bear a lot of risks of getting damaged because of falling, getting compressed, etc. during transportation of logistics. In order to preserve products shape and quality, we can reduce the impact force during the logistics using packaging system. In general, we consider that packaging materials would not exhibit the strain rate effect while we predict free drop test results. In other words, the quasi-static compression stress-strain curve is used to simulate the results. But some packaging materials probably have the strain rate effect. Therefore, the foam packaging system of free drop test in this research considers the strain rate effect, that is the packaging materials are strain rate dependent. The energy loss is also considered into account when using numerical simulation methods to predict the maximum acceleration.
The aim of this research is to understand the behavior of foam packaging materials during free drop by numerical simulation methods. Most of the literature on relevant research of foam packaging system neglects the strain rate effect to simplify the numerical simulation. But in this research it is shown that the strain rate effect would influence the maximum strain captured by high speed camera, even if there is no difference between free drop test and numerical simulation on maximum acceleration if the strain rate effect is not considered. So this research generalizes some experimental results to coordinate the relationship between the strain rate effect and the energy loss. Later, both energy method and single degree-of-freedom of nonlinear spring system are used to predict the results from free drop test.
The constitutive law of foam packaging materials used in this research, for example expanded polypropylene (EPP), is constructed by series of quasi-static compression test and high-rate dynamic impact test. A numerical material constitutive law model considering the strain rate effect is also published to simulate the strain rate dependent property about EPP. We can accomplish the aim, considering the strain rate effect is used in this model when we are simulating the results, and to develop the numerical simulation which can predict maximum strain more accurately. In addition, for verifying that EPP has the strain rate effect, the high speed camera cooperated with the accelerometer through free drop test is used to derive the actual stress-strain curve of EPP packaging system. Finally, the fact that EPP is strain rate depenedent material has been proved. The microstructure photos of EPP by both optical electron microscope (OEM) and scanning electron microscope (SEM) were captured. This research also attempts to understand the relationship between strain rate effect and the microstructure of EPP.
Furthermore, for designing EPP packaging system of real products, the appropriate range of strain energy density of EPP was chosen. The maximum acceleration, maximum strain and actual stress-strain curve of free drop test are predicted by numerical simulation methods considering the strain rate effect or not. To conclude, the results by several numerical simulation methods and free drop test are compared to explain that these methods which considers strain rate effect are feasible and accurate.
Subjects
expanded polypropylene
constitutive law
free drop test
strain rate effect
constitutive law model considering strain rate effect
microstructure
energy loss
foam packaging system design
Type
thesis
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