V型槽對薄鋼板之動態挫曲特性之影響

Abstract

首先，本實驗研究將對一個使用1至3個V形凹槽來增加其勁度且二端被夾緊的金屬薄板做動態挫曲探討。此長方形板片的長度和厚度均為固定值，分別為300 mm和1.0 mm，寬度則分別為70、140和210 mm。V形凹槽的深度分別為4、 7和10 mm。在靜態和動態試驗中，結果顯示，薄板抵抗挫曲和吸收變形能量的能力，因為此V形凹槽而明顯的提升了。210 mm寬度，具有1或2個凹槽的薄板，凹槽深度較淺的比深度較深的板片在動態挫曲抵抗能力方面有比較大的抵抗力。ㄧ般而言，增加凹槽的深度和數量可增加金屬薄板的能量吸收能力。因此，金屬薄板的抵抗挫曲能力和吸收變形能量的能力不能被視為僅和剖斷面的面積二次矩有關，因為薄板足夠寬並且拘束以任何數量的凹槽，動態實驗，在挫曲以前的塑性變形期間，由於凹槽較深者在相鄰兩凹槽面彼此間的交互作用，也同樣的提升吸收能量的能力。 其次，針對具凹槽金屬薄板之塑性挫曲問題，以田口法規劃實驗，探討金屬薄板分別在不同凹槽間距、不同板片厚度､具不同凹槽數量和不同凹槽深度四種條件下，經不同挫曲速度作用時，對於臨界負載與塑性挫曲變形所吸收之能量的影響做最佳化設計分析。此結果顯示：在近似靜態的速度進行挫曲作用時，以凹槽深度為此四項參數中影響最大的關鍵因素；以高速度進行挫曲作用時，薄板厚度與凹槽深度分別為此四項參數中對於臨界作用力與塑性挫曲變形所吸收之能量的最大影響因素。綜合此田口法實驗分析結果，具凹槽金屬薄板受軸向負載之挫曲變形的最佳化設計條件為凹槽間距55 mm、厚度 1 mm、具3個凹槽數量且凹槽深度10 mm，此分析結果和實驗值符合。以上結果顯示田口法適用於減少傳統實驗設計次數，協助探討挫曲變形的問題。 最後，採用顯性動態有限元素法程式LS-DYNA模擬分析具V形槽之金屬薄板，承受衝擊負荷時之挫曲負載與吸收能量之變化過程。應用質量因子與接觸判斷解析技巧，探討金屬薄板承受不同的速度衝擊負荷之挫曲抵抗現象與負荷之關係。結果顯示，具有V形凹槽的金屬薄板較無V形凹槽之金屬薄板遇到軸向衝擊負荷時，前者可承受之挫曲抵抗臨界負載較之後者超過12倍，並且，此數值分析結果與實驗結果相當吻合。因此，本文採用之解析模式和技巧，對於設計一個需要相當大的挫曲抵抗能力之金屬薄板應用方面，頗有助益。以上結果可提供航太或其他工程設計產業，作為提昇結構的比強度的最佳化設計參考，對於取代質量較大的機構甚或交通工具的安全設計均有很大的裨益。

Firstly, experimental study was made for the dynamic buckling of thin plates stiffened by stamping with 1 to 3 parallel V-grooves in a clamped-end condition. The length of the blanks was set at the same value of 300 mm, while the width was of 70, 140 and 210 mm at a thickness of 1 mm, otherwise specified. The depth of V-grooves was set at values of 4, 7 and 10 mm. In both static and dynamic tests, the results show that the ability of the plates to resist buckling and to absorb deformation energy was substantially enhanced by stamping with V-grooves. Stamped with 1 or 2 grooves of smaller values in depth, the plates 210 mm wide had larger resistance to dynamic buckling than those of greater values in depth did. In general, increases in number and depth of grooves caused an increase in the plates’ capacity of energy absorption. However, the ability of the plates to resist buckling and to absorb deformation energy cannot be determined only in accordance with the second moment of area of cross section, because the plates sufficiently wide stamped with any number of grooves deformed plastically before buckled in dynamic tests and, the interaction between deep grooves during deformation also enhanced the capacity of energy absorption. Secondly, by using the Taguchi method, this article studies the strongly influent parameters on buckling-resistant properties of thin steel plates stamped with V-grooves of various numbers and dimensions. The parameters include the distance between any two neighbouring V-grooves, the thickness of the plates, the number and the depth of the V-grooves. The Taguchi method with orthogonal arrays was used to determine the optimal combination of manufacturing parameters and reduce the variation in quality, but using a minimal number of experiments. The experimental results indicate that the depth of V-grooves, one of the four parameters of interest strongly influenced buckling properties under quasi-static loads. However, the thickness of the plates and the depth of grooves strongly affected the critical buckling loads and the capacity to absorb energy under high-speed impact loads. This investigation also demonstrates that the buckling-resistant properties of thin steel plates can be increased to reasonable required values by using a minimum number of trials in stamping various numbers and dimensions of V-grooves. At last, this part numerically investigates the buckling loads and the absorbed energy of thin metallic plates stamped with V-grooves. By using the dynamic-explicit FEM Code, LS-DYNA together with the mass scaling technique and contact algorithm, the collapse processes of the plates subjected to various impact velocities were simulated. The results show that the buckling-resistant properties of plates stamped with V-grooves can be more than 12-times larger than those of plates without V-grooves. Also, the results from numerical modeling show good agreement with the experiments. Therefore, the suggested model and technique are helpful in the design of thin metallic plates requiring considerable buckling resistance.