Explosive full-field strain and crack dynamic fracture characteristics of a linear shaped charge
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摘要: 為了探究不同起爆位置下條形藥包全場應變以及裂紋動態斷裂特性，采用爆炸荷載動態焦散線實驗系統和數字圖像相關方法（DIC），開展了爆破模型實驗研究。研究結果表明：條形藥包一端起爆時，起爆點處翼裂紋擴展長度最小，隨著炸藥爆轟的傳播，翼裂紋擴展長度增長；中心起爆時，中心位置翼裂紋擴展長度小于兩端位置翼裂紋擴展長度，一端起爆時非起爆端翼裂紋擴展長度最長。無論中心起爆或一端起爆，條形藥包中心區域翼裂紋擴展主要為Ⅰ型裂紋，并且中心翼裂紋起裂韌度最大，端部翼裂紋為以Ⅱ型為主的Ⅰ?Ⅱ型復合裂紋。一端起爆時，拉壓應變作用范圍沿炸藥傳爆方向傳遞，且非起爆端拉壓應變作用區域大于起爆端，壓應變最大值為距起爆點約0.67 ~ 0.83倍的裝藥長度。中心起爆時，拉壓應變的作用過程沿起爆中心向兩端呈對稱形式傳播，中心點位置應變最大。兩種起爆方式下都出現端部壓應力集中現象。Abstract: This study explores the full-field strain and dynamic fracture characteristics of a linear shaped charge under different initiation positions. The explosion dynamic caustic line experiment system is employed to examine the characteristics of the blast crack propagation of the linear shaped charge at different initiation positions and capture the dynamic information of the crack tip propagation speed and stress intensity factor. Furthermore, the digital image correlation method was used to show the strain evolution law of the linear shaped charge at different initiation positions, as well as the medium strain response of the charge near the explosion zone caused due to detonation transmission. The results show that in end-initiation, the wing crack length at the initiation point is the smallest, and the wing crack propagation length increases with the detonation propagation of the explosive. Conversely, in center-initiation, the propagation length of the wing cracks at the center is less than those at both ends. The propagation length of the wing cracks in the noninitiation end is the longest for end-initiation, where the velocities of the wing crack initiation and propagation are minimum. For center-initiation, the wing crack initiation and propagation velocities are the smallest, i.e., irrespective of the initiation position, the wing crack initiation and propagation velocities at the initiation point are lower than that at other locations. Based on the dynamic stress intensity factor analysis, irrespective of the initiation position, the center wing cracks are type Ⅰ cracks with the largest crack toughness, the stress intensity factor value is the maximum, and the wing cracks at the ends are type Ⅰ?Ⅱ composite cracks dominated by type Ⅱ. Based on the full-field strain analysis of the linear shaped charge, at end-initiation, the range of tension and strain action is mainly along the direction of explosive transmission, and the tension and strain action area at the noninitiation end is larger than that at the initiation end. The corresponding position of the maximum compressive strain is 0.67–0.83 times the charge length from the initiation point. When the center detonates, the action process of tension and compression strain propagates symmetrically from the center to both ends of the initiation, and the strain at the center is the largest. The compressive stress concentration at the end occurs under both initiation modes because the explosive transmission is the process of energy accumulation; thus, the effect of the explosive explosion on the medium grows increasingly stronger along the direction of explosive transmission.
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圖 1 透射式焦散線試驗系統光路示意圖
Figure 1. Light path of the transmissive caustics experimental system
圖 2 模型加工示意（單位：mm）. (a) 中心起爆; (b) 一端起爆
Figure 2. Schematic of the model processing (unit: mm): (a) center-initiation; (b) end-initiation
圖 3 實驗結果. (a) 中心起爆; (b) 一端起爆
Figure 3. Test results: (a) center-initiation; (b) end-initiation
圖 4 焦散斑系列圖. (a) 中心起爆; (b) 一端起爆
Figure 4. Images of a series of dynamical caustics: (a) center-initiation; (b) end-initiation
圖 5 翼裂紋位移?速度隨時間的變化曲線. (a) 中心起爆; (b) 一端起爆
Figure 5. Curves of the pre-crack displacement–velocity variation with time: (a) center-initiation; (b) end-initiation
圖 6 翼裂紋應力強度因子隨時間的變化曲線. (a) 中心起爆; (b) 一端起爆
Figure 6. Curves of the pre-crack dynamic stress intensity factor variation with time:(a) center-initiation; (b) end-initiation
圖 7 DIC基本原理示意圖
Figure 7. Sketch maps of the DIC fundamental principle before and after the speckle deformation
圖 9 模型加工示意（單位：mm）. (a) 中心起爆; (b) 一端起爆
Figure 9. Schematic of the model processing (unit: mm): (a) center-initiation; (b) end-initiation
圖 10 全場應變演化過程. (a) 中心起爆; (b) 一端起爆
Figure 10. Full-field strain evolutionary process of the specimens: (a) center-initiation; (b) end-initiation
圖 11 測點位置示意圖. (a) 中心起爆; (b) 一端起爆
Figure 11. Sketch of the gage positions: (a) center-initiation; (b) end-initiation
圖 12 測點處應變時程曲線. (a) 中心起爆; (b) 一端起爆
Figure 12. Curves of strain vs time:(a) center-initiation; (b) end-initiation
圖 13 測點應變峰值曲線. (a) 中心起爆; (b) 一端起爆
Figure 13. Peak strain curve of the measuring points: (a) center-initiation; (b) end-initiation
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