本論文主要目的是利用CAE技術探討四輪小貨車結構設計,包括結構模態與碰撞強度。在執行整車結構分析前必須先確定整車主結構之有限元素模型之等效性,然後再進行整車碰撞模擬才能獲得精確的分析結果。首先建立整車車架主結構之有限元素模型,經由有限元素分析軟體 ANSYS 進行模態分析,其有限元素模型之材料機械性質是利用拉伸試驗取得。主結構之有限元素模型的等效性可以經由量測重量、重心與質量慣性矩及實驗所得模態參數進行驗證比對,實驗所得模態參數主要驗證有限元素模型結構質量與剛性的分佈。整車主結構模型比對完成並確認有限元素模型之等效性後,即可建立整車碰撞分析模型。整車碰撞分析模型包含車體主結構與動力系統、懸吊系統及其他相關配件(包括:保險桿、座椅載物箱、水箱、油箱、引擎、前、後差速器、前、後懸吊系統、輪胎),動力系統、懸吊系統及其他相關配件之有限元素模型亦須確保其重量與材料剛性等效於實體。結構材料彈塑性模型是採用Piecewise Linear Plasticity Model,此模型考慮應變率對於材料變形行為的影響,適用於金屬等向性材料的塑性變形分析,其中之應變率參數 (C, p)是經由衝擊試驗比對驗證所獲得的數值。最後進行整車碰撞模擬分析,分析軟體採用ANSYS LS-DYNA,探討整車空車(空車+正副駕駛)重量,以時速30英哩之前碰撞與時速35英哩之後碰撞分析條件,碰撞後所產生之車體結構變形是否侵入乘客安全空間以及油箱,最後與美國聯邦道路安全法規之前後碰撞標準(FMVSS208、FMVSS301)做比較。
This research presents the structural design and analysis, including normal mode and impact strength, for a pick-up truck by using computer-aided engineering (CAE) technology. The finite element model of the full vehicle structure is established by using the software ANSYS. The CAE model includes body structure, bumper, seat, water tank, fuel tank, engine, transmission, container, suspensions, differential gears, tires, etc. Static tests are first conducted on the main body structure to obtain the weight and center of gravity in order to validate the finite element models. The mechanical properties of body structures are obtained from the tensile tests. Normal mode analysis was performed to obtain the natural frequencies and associated mode shapes of the body structures. Experimental modal analytical (EMA) are conducted on the body structures to validate the analysis results. An impact hammer with force transducer is used to excite the structures and accelerometer is used to obtain the modal parameters. The FEA results are validated in comparison with the EMA results. Model updating is then performed to modify the FE model based on the correlation of natural frequencies and the associated mode shapes. Finally, the equivalent FE mode is used to perform the frontal and rear impact analyses by using software LS_DYNA and based on the FMVSS (Federal Motor Vehicle Safety Standard). Piecewise Linear Plasticity Model is used to simulate the dynamic behavior of structural materials. The material constants of this model are obtained from the bending impact tests of the body structures. The significant results provide the designer the guidance of reinforcement design of the body structure.
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