考慮應變率效應之發泡式緩衝包裝系統試驗與數值模擬

Experiment and Numerical Simulation of Foam Packaging System Considering Strain Rate Effect

吳冠毅(Quan-Yi Wu)

指導教授 ： 呂良正

國立臺灣大學/工學院/土木工程學研究所/碩士(2010年)

https://doi.org/10.6342/NTU.2010.01840

摘要

產品物流運送過程中，都必須承受搬運輸送的風險，例如摔落、擠壓等，透過包裝系統可以減少物流期間外界輸入產品之衝擊力，避免損壞產品以保持原有的品質。由於在包裝系統各項評估試驗中，以落下所造成的衝擊最為劇烈，又一般傳統在預測分析時，皆將以準靜態應力－應變曲線模擬，未考慮當材料具應變率效應時之影響，故本研究以發泡式緩衝包裝系統的自由落下試驗，考慮應變率效應以及加入能量損失的考量來進行數值模擬，用以評估緩衝包材之功效，取代傳統試誤法的包裝系統設計方式。

本文旨在透過試驗和數值模擬了解發泡式緩衝包材在掉落測試實驗中的行為，並用以評估其包裝效果；同時考慮應變率效應對緩衝包材行為的影響，考量應變率效應與能量損失的關係，以利於更貼近於真實落下過程中碰撞之數值模擬。文獻上對於包裝系統設計的相關研究大多忽略緩衝包裝材料之應變率效應，以簡化數值分析，但本研究在試驗中發現材料應變率效應對於落下過程中所受的最大加速度值無論是實驗或是數值模擬其差異不大，但於模擬時可較以往未考慮應變率效應之數值模擬更加貼近於真實的力學行為，即對於應變之估計可更加貼近於真實的碰撞行為，更加準確。故本研究先將試驗結果整理歸納出考慮應變率效應與、否之能量損失，以此搭配考慮應變率效應與，否的單自由度非線性彈簧系統以及靜態評估曲線法預測落下之碰撞結果。

本研究所使用之材料組成律為分別對材料進行一系列的準靜態壓縮試驗與高速動態衝擊試驗，並提出一應變率相依之材料組成律模型來將材料的應變率相依特性並表示成數學解析式，以於數值模擬乃至於真實產品之緩衝包裝系統設計上可以預估的更加貼近於真實落下碰撞的力學行為。此外，本研究運用高速攝影機拍攝觀察真實落下行為，配合加速度規量測之加速度歷時反推出真實行為下的應力－應變曲線，並另以高速衝擊試驗驗證反推的結果，最後證實發泡式緩衝包裝材料是有應變率效應的，歸納出考慮應變率效應下的能量損失。於材料微結構方面，亦使用掃描式電子顯微鏡觀察發泡式緩衝包裝材料之微結構，了解其微結構形式，以嘗試將材料具應變率效應與、否的因素歸咎於材料微結構上之差異。

另一方面，對於實際產品設計而言，本文先將緩衝包裝系統的應變能密度設計於材料之適用範圍，再透過本研究考慮應變率效應與、否之數值模擬方法，來預測實際產品在落下時的最大加速度值、最大應變乃至於真實應力－應變曲線，進而與真實落下試驗的結果作比較。最後以有限元素商業軟體LS-DYNA對於真實產品之設計實例同樣考慮應變率效應與、否進行模擬，驗證本文考慮應變率效應的數值模擬方法之準確性與可行性。

關鍵字

發泡式緩衝包裝材料 ； 材料組成律 ； 應變率效應 ； 落下試驗 ； 應變率相依之材料組成律模型 ； 微觀結構 ； 能量損失 ； 緩衝包裝系統設計

並列摘要

The products are bearing a lot of risks during transportation of logistics. For example drop, compression etc., in order to keep product’s quality packaging system can reduce the impact force during the logistics. In general, we consider packaing materials don’t have strain rate effect while we predict drop test result. In other words, we using quasi-static compression stress-strain curve to simulate. But sometimes, packaging materials probably have strain rate effect. Therefor the foam packaging system of drop test in this research takes strain rate effect, namely packaging materials are strain rate dependent. And energy loss into account when using numerical simulation methods to predict the result.

The purpose of this research is to understand the behavior of foam packaging materials during dropping by numerical simulation methods. Most literature on relevant research of foam packaging system neglect strain rate effect to simplify analysis. But in this research it is saying that strain rate effect has influence on maximum strain captured by high speed camera, even there isn’t difference between drop test and numerical simulation about maximum acceleration if we considering strain rate effect. So this research gerneralizes experiment’s result to coordinate the relationship between strain rate effect and energy loss first. Second, use energy method, single degree of freedom of nonlinear spring system to predict the result of drop test.

The constitutive law of foam packaging materials this research use are caught by series of quasi-static compression test and high rate dynamic impact test, and a material constitutive law model considering strain rate effect is published to simulate strain rate dependent property about the foam packaging materials. Using this model we can accomplish the aim that considering strain rate effect when we are simulating, and to develop the numerical simulation which can predict maximum strain much better. In addition, to verify foam packaging system has strain rate effect, this research makes use of high speed camera cooperated with accelerometer through drop test to derive actual stress-strain curve of foam packaging system. Finaly, the results prove that foam packaging materials have strain rate effect. We also have some effort to capture the microstructure photos of foam packaging materials by scanning electron microscope. We attempt to understand the relationship between strain rate effect and microstructure.

Furthermore, about foam packaging system design of reality products, we design it’s strain energy density in appropriate range of the foam packaging material that we choose first. To predict the maximum acceleration, maximum strain and actual stress-strain curve of drop test by numerical simulation method considering strain rate effect or not second. Finally, using finite element method softeware LS-DYNA to simulate, and try to compare the results by several simulation methods and drop test to explain the numerical simulation methods considering strain rate effect are accurate and feasible.

並列關鍵字

foam packaging material ； constitutive law ； strain rate effect ； drop test ； constitutive law model considering strain rate effect ； microstructure ； energy loss ； foam packaging system design

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