在纖維強化塑膠射出製程中不同纖維長度引導其微結構變化與巨觀特性變異相關性之研究

The Effects of Fiber Length on Micro-structure and Macro-properties of Fiber Reinforced Injection Molded Parts

朱家豪(Jia-Hau Chu)

指導教授 ： 黃招財

淡江大學/工學院/化學工程與材料工程學系碩士班/碩士(2020年)

https://doi.org/10.6846/TKU.2020.00742

摘要

論文提要內容:
隨著環保意識的興起，節能減碳已經成為各國的主要發展政策之一，由於纖維強化熱塑性塑膠(fiber reinforced thermoplastics, FRT)具有非常優異的特性，近年來已成為產業中主要的輕量化技術之一，尤其是在汽車及航太產業中。然而，因為纖維在塑膠內部的微結構非常複雜且很難掌握，更無法有效定量其對成品之巨觀翹曲變形以及機械性質的影響。為此，本研究利用三種不同澆口型態的(Model I為側邊入料、Model II為直接入料、Model III為雙邊入料)標準拉伸試片(ASTM D638)的複合幾何模型，並同時利用四種不同之材料，包含純聚丙烯(PP)、3 mm之短纖維(SF)、12 mm之中纖維(MF)以及25 mm之長纖維(LF)材料，藉此複合幾何改變以及不同材料之纖維長度差異來探索纖維微結構之變化以及其對成品巨觀性質之影響。具體來說，本研究同時利用CAE模擬分析來探討微結構與巨觀性質之變化，並利用實際射出實驗來加以驗證。結果顯示，在射出成品之巨觀翹曲變形中，CAE模擬與實驗趨勢十分吻合，以SF材料之翹曲變形為例，從Model I和Model III長邊翹曲皆是呈現哭臉(中間高，兩邊低)的趨勢，而且比較PP和SF成品後可明顯看出當纖維加入後可以有效降低整體之翹曲量值。在機械性質上，也可以觀察到SF複合試片之強度明顯提升。更進一步探討後發現，因為成品幾何設計所引導之入口效應改變了纖維排向，使Model I之強度大於Model II。特別是我們可從CAE模擬結果中看到Model I之A11纖維排向比例大於Model II，此等纖維特性也經電腦斷層掃描及影像重建驗證。再者，我們比較SF、MF以及LF纖維長度變化後發現，CAE模擬分析纖維排向幾乎沒有差異(此部份可能起因於CAE內部纖維排向理論還不夠完善)；纖維長度則隨著初始長度越長，其成品保留之纖維長度越長，但其斷裂長度也越長；再則，在纖維濃度分布上，比較相同初始纖維含量之MF和LF發現，其成品纖維濃度差異都介於5 wt %之內，沒有因為纖維長度不同而有太大變化。從巨觀性質上比較，當纖維長度越長，對於翹曲變形的抵抗能力越好，此部分模擬和實驗皆十分吻合；至於在機械性質上，纖維長度及濃度之提升對於拉伸強度都有補強效果。然而，當纖維長度增加到一定長度後，拉伸強度卻沒有等量提升，此部份推測是因LF複合材料經射出成品後，許多長纖維可能聚集形成纖維束、產生氣泡，或者長纖維可能彎曲變形，導致強化之功能降低。

關鍵字

射出成型 ； 纖維強化塑膠 ； 纖維微結構 ； 纖維長度分布 ； 機械性質

並列摘要

Energy saving and carbon reduction have become an important objective for the world. Thanks to the excellent properties of the fiber reinforced thermoplastics (FRTs), it has been applied into industry as one of the major lightweight technologies for the automobile and aerospace industry. However, the micro-structures of fiber inside the plastic matrix are very complicated, which makes it difficult to understand the influence of micro-structures on the warpage and mechanical properties. We used a benchmark system with three standard specimens based on ASTM D638 where those specimens have different gate designs. We also applied four materials including pure polypropylene(PP), short fiber of 3 mm(SF), medium fiber of 12 mm(MF) and long fiber of 25 mm(LF). This system is used to study the fiber microstructures and associated macro-properties using numerical simulation and experimental studies. Results showed that the simulation data of full model warpage is consistent with the experimental observation. Specifically, the warpage can be improved significantly in the appearance of the fibers. Moreover, the mechanical properties were also improved when using the SF material. Moreover, the different gate design of Model I and Model II caused the entrance effect which changed the fiber orientation distribution. The change in fiber orientation would further enhance the mechanical properties of Model I. To confirm the observation, the fiber orientation distribution is predicted using CAE simulation, and verified using micro-CT scan and image analysis. Moreover, we compare the product of SF, MF and LF reinforced plastics to find out the effect of fiber lengthes. The fiber orientation distribution of SF, MF and LF by CAE simulation only have slightly different. As for the fiber length distribution, increasing the initial fiber length would increase the fiber length in the final product. However, increasing the intial fiber length would also accompany by the more fiber breakage. The fiber density distribution was slightly affected by the fiber length as we compared the MF and LF products. The fiber density difference between MF and LF parts is under 5 wt %. As we compared the macro-properties of the three fiber materials. We found that the longer fiber length is introduced, the better full model warpage behavior can be. The mechanical properties are also proportional to the fiber length. However, the mechanical improvement was not seen in the LF product. It is possible due to the fiber bending or entanglement of fibers.

並列關鍵字

Injection molding ； fiber reinforced thermoplastics(FRT) ； fiber microstructure ； fiber length distribution ； mechanical properties

參考文獻

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