In this paper, an explosive loading technique is applied to study the uniform expansion of smooth
wall cylinder specimen (low-carbon steel and 304 stainless steel;Do-t-L: 34-3-100 mm) at high strain rate.
A column of high explosive PETN is installed coaxially inside a cylinder specimen and initiated at the central
axis by exploding fine copper wires using an impulsive discharge current from a capacitor bank.
The streak and framing camera photos indicate radially symmetrical and axially almost uniform expansion of
cylinders with the average strain rate of over 104s-1 and the wall velocity of
3-7x102m·s-1, representing rather earlier fracture for 304SS cylinders.
The initial time-histories of surface velocity are measured to monitor the spall damage of cylinder wall,
and the experimental average wall velocities are compared with those calculated using the simple equation on
energy consumption. Hydro codes have been applied to simulate the experimental behavior of the cylinders,
examining the constitutive equations and the fracture criteria. A steel chamber filled with wasted clothe-pieces for
cushioning is provided inside the explosion pit,
and 84 - 99 % of the fragments of the exploded cylinder installed at
the center are recovered successfully. The sizes of every fragment are measured, and in this study the circumferential
fracture spacing is investigated using the Grady's fragmentation model.
本論文では,爆薬の特異な起爆技術を用いて平滑な金属円筒 (炭素鋼, SUS304ステンレス鋼 : Do × t × L / 34 × 3 × 100 mm) を超高速で膨張させている｡すなわち金属円筒内部にPETN爆薬を同軸円柱状(完全充填または空気層設置)に装填し, 中心軸に設置した銅細線をコンデンサーからの衝撃電流で一斉爆発･起爆させて円筒状発散爆轟波を生成した｡ 高速度カメラの流し写真とコマ撮り写真から円筒は軸対称, 軸方向一様に高速膨張(円筒壁速度:3-7×102m･s-1)し, 周方向の平均ひずみ速度は10-4s-1に達すること, SUS304鋼における早期の分裂破壊などが分かった｡ また表面剥離計測やエネルギーの釣合いに基づく変形速度についても検討した｡ 変形観測結果は流体解析コードによる数値解析結果と比較し, 高速域での構成式や破壊則(限界応力･ひずみ)について考察した｡ さらに円筒の破壊挙動や破断ひずみについて検討するために緩衝材を充填した鋼鉄チャンバーをピット内に設置し, その中心部で同様の爆発実験を行った｡ その結果84 - 99 %の回収率で破片回収ができ, 各条件下における金属円筒の分裂形態について把握することができた｡ 本報では主要な短冊状破片に着目し周方向破断間隔を表すGradyの分裂モデルを用いた検討を行った｡