嵌板受近距離水下爆炸衝擊的損壞分析

The Damage Analysis of Plate Panel Subjected to Near Field Underwater Explosion

本文旨在探討水下背面為空氣的嵌板，受到不同藥量在近距離水下爆炸衝擊產生的彈塑性暫態反應與破損狀態。爆炸點到平板中心距離在爆炸最大氣泡範圍內，在不同爆震因子（shock factor）條件下，爆炸衝擊平板產生塑性大變形以致破裂很壞的狀況。嵌板周圍，流場與爆震波受到氣泡影響，衝擊嵌板之瀑震波歷不易以估算式或近似理論推算，需採用全有限元素分析模型進行分析。本文先檢討近距離水下爆炸FE分析的炸藥模型與水域網格分割的合理性。水域與炸藥以六面體元素與處理，作藥、氣泡與水域共存之空間，以多物質模型與ALE（Arbitary Lagrangian-Eulerian）網格處理。其次以Ramajecyathilagam & Vendha（2004）（簡稱為R＆V 2004）的試驗模型為探討對象，試驗目標板的長×寬×厚＝0.55m×0.45m×0.002m，四周以4cm厚板支撐並以螺栓鎖定於中空的厚鋼板箱，彼末被厚板加強的範圍長與寬分別為0.30m與0.25m。爆炸過程嵌板結構在高速衝擊下急速進入塑性範圍，需考慮應變率對板結構之材料非線性變形的影響。本文嵌板採用非線性材料板殼元素，並考慮邊界螺栓支撐狀況對分析結果之影響。本文數值分析工具採用LS/DYNA，比較主爆震波衝擊與後續氣泡脈衝不同階段，結構的彈塑性暫態反應興破損狀況。分析結果與R&V（2004）試驗結果比較。檢討採用簡化爆震波衝擊壓估算模型與有限元素分析近距離水下爆炸過程之衝擊負荷以及FEM模型的合理性。 In this paper, the elasto-plastic transient dynamic responses and the damage states of an air-backed plate panel subjected to near field underwater explosion (UNDLX) has been examined. Various shuck factors with standoff distance smaller than half of the radius of the first explosive babble were investigated, and the damaged states covered three damage stages: the permanent deformation of plate panel, the tensile tearing damage at support edges or plate center, and the shearing damage at support edges. The distribution of shock pressure on the plate surface predicated by conventional empirical formula is not available for near field of UNDEX. In this paper, a full FE-analysis to predicate the pressure distribution was performed first, to examine effects of the explosive model and the mesh distribution on the calculated results for near held UNDEX. And then the analysis of impact response of plate panel under different weight of charges was carried out by the LS/DYNA code. The multi-material space combined ALE (Arbitary Lagrangian-Eulerian) mesh technology was used to simulate the water, air and explosive held for analysis of shock pressure. The experimental model of Ramajecyathilagam & Vendha (2004) teas adopted as study ease. The target plate has the dimension of length × width × thiekness=0.55 m×0.45 m 0.002 m, whose four edges are supported by thick plates and mounted on a strong steel castings with bolt, the unsupported area of the target plate is 0.30 m×0.25 m. The dynamic responses of the target plate reached to plastic range at extremely high speed under high speed impact of UNDEX, the non-linear material model with stain rate effect should be taken into consideration. The effects of bolted connection on the analyzed results were also investigated. The FE-analyzed results were compared with the experiment accomplished by Ramajecyathilagam & Vendha (2004). The shock loading predicated by approximate method and by full model of finite element analysis were compared and discussed.