陳復國臺灣大學：機械工程學研究所洪廷芳Hung, Ting-FangTing-FangHung2007-11-282018-06-282007-11-282018-06-282006http://ntur.lib.ntu.edu.tw//handle/246246/61213由於安全考量與法規的要求，汽車結構強度必須通過一連串的測試。然而，原形車的製造與實驗的進行均需要花費相當多的時間，在節省時間與成本的考量下，通常會在進行實驗前利用有限元素法模擬車身的結構強度，然而，模擬分析的精確度，尤其是動態撞擊分析，仍然需要加以改進。 本論文選擇某車型的引擎室作為研究載具，利用有限元素法軟體LS-DYNA模擬引擎蓋自由落下撞擊散熱器支架之行為，並在模型建立的過程中，討論在模型建立時所必須考量的重點，例如元素的連結性，焊點的模擬以及材料模型的選擇等。 在模型建立方面，必須特別注意CAD圖檔的品質，以免發生不連續的元素外，本文亦針對修補CAD圖檔提出了可行的方法。此外，本文亦比較了兩種建立旋轉機構的方式，分別為直接建立旋轉接頭與利用剛接連結旋轉接頭，並在所建立的模型中採用了適當的模擬方式。 在焊點方面，本文比較了拘束式焊點與接觸式焊點兩種模擬焊點方式之效果，並且發現拘束式焊點往往會產生較高的應力，此外，本研究比較了不同的焊點排列方式對於模型與模擬分析的影響性。針對運算速度方面，本研究將引擎蓋旋轉至撞擊瞬間之高度，並利用本文所推導之引擎蓋落下之質心角速度公式，建立可節省模擬分析時間的簡化模型。 最後利用實際的引擎室，進行引擎蓋自由落下撞擊散熱器支架之應變與受力實驗，而模擬結果亦確認了模擬模型的正確性。本論文所探討的動態有限元素模型建立方式，亦可應用於整車結構件之模擬分析。The structural strength of an automobile must pass through a series of tests due to safety concerns and regulations. However, it often takes a long time to manufacture a prototype and conduct a series tests. In order to save time and cost, the finite element simulations are usually performed to evaluate the strength of the designed car-body structure before the actual tests are conducted. However, the accuracy of finite element simulation for the strength analysis of a car-body structure, especially the dynamic impact analysis, is still being improved by researchers. In this thesis, the strength of a radiator support frame impacted by a free-falling engine hood was examined with the use finite element code, LS-DYNA. The entire engine room of a recreational vehicle was modeled for the analysis. Key points of building a reliable model, such as connectivity of elements, modeling of spot welds and selection of material models, were determined first. In the construction of a finite element model, disconnected elements were found due to poor quality of CAD files imported. An appropriate approach to remedy the CAD files was developed for the subsequent mesh generation. In order to model the hinge connecting the hood to the engine room, two different elements, such as revolute joints with rigid elements and revolute joints with rigid links, were thoroughly examined and the suitable element type was selected to represent the hinge in the finite element model. In modeling spot welds, the efficiency in using the constrained spot weld approach and contact spot weld approach was compared. Constrained spot weld was found resulting in higher stress. In addition, the effects of different arrangements of constrained spot welds in the finite element model on the simulation accuracy were also examined. In order to further reduce the computation time, a theoretical model was also proposed in the present study to calculate the instantaneous angular velocity of the free-falling engine hood at the incipient impact to the radiator support frame, which was used to replace the simulation of the free falling of engine hood. A series of experiments were also conducted in the present study to measure the strains and impact forces during the impact of the engine hood to the radiator support frame. The experimental data were found consistent with those obtained from the finite element simulation results. The accuracy of the finite element model built for the dynamic analysis for the impact of an engine hood to the radiator support was then validated. The approaches developed in the present study for the dynamic finite element model of impact analysis could be extended to the whole car-body structure. Keywords: dynamic finite element analysis, impact analysis, engine hood, hinge and spot-weld models, experiments.目錄 Ⅰ 圖目錄 Ⅳ 表目錄 Ⅷ 第一章 緒論 1.1 前言 1 1.2 研究動機與目的 2 1.3 文獻回顧 4 1.4 研究方法與步驟 7 1.5 論文總覽 9 第二章 研究載具及分析軟體簡介 2.1研究載具介紹 11 2.2有限元素模擬軟體簡介 17 2.3顯性積分法 20 第三章 結構模型之建立與研究 3.1利用前處理器讀取CAD圖檔 24 3.2各零件之組合 28 3.3引擎蓋轉軸機構模擬模型 32 3.4橡膠模型 43 3.5邊界條件 44 3.6材料性質 47 3.7已完成之有限元素模型 48 第四章 模擬分析結果之探討 4.1焊點模擬方式之比較 49 4.2點焊與三角形元素的連接 56 4.3焊點元素旋轉自由度問題 59 4.3.1焊點元素旋轉自由度問題之驗證 64 4.3.2焊點試驗的規劃 64 4.4引擎蓋轉軸機構之摩擦模擬 68 4.5簡化模型之研究 70 4.6橡膠之模擬 73 4.6.1橡膠材料測試原理 74 4.6.2橡膠材料之單軸壓縮試驗 75 4.6.3橡膠材料之單軸壓縮試驗結果 77 4.6.4 Mooney-Rivlin材料模型的模擬 78 4.6.5橡膠墊片的模擬 82 第五章 實驗規劃與實驗驗證 5.1模擬結果之實驗驗證規劃 85 5.1.1量測項目 85 5.1.2實驗儀器 86 5.1.3應變量測 87 5.1.4荷重量測 96 5.2實驗結果 97 5.2.1應變量測結果 98 5.2.2荷重計量測結果 102 第六章 結論 6.1研究之結論 104 6.2建議 105 參考文獻 107 附錄 1133208652 bytesapplication/pdfen-US動態有限元素法分析撞擊分析引擎蓋旋轉機構與焊點模型實驗dynamic finite element analysisimpact analysisengine hoodhinge and spot-weld modelsexperimentsthesishttp://ntur.lib.ntu.edu.tw/bitstream/246246/61213/1/ntu-95-R93522514-1.pdf