高速衝撃荷重をうける金属の力学的挙動を研究するために,火薬爆圧を利用した定速型の高速引張り試験装置が建設された.この装置は火薬により発射される質量により試験片に高速引張りを与えるもので,弾速は210m/s,試片の実際の引張り速度は120m/sに達している.この装置を用いて,5種の金属材料:2S-Oアルミニウム,2024C-O超ジュラルミン,SPC-1軟鋼,18-8ステンレス鋼,およびST-60チタニウムの薄板試片の高速単軸引張り実験が行なわれ,伸び率～引張り速度の関係が0～120m/sの範囲内で測定された.この結果によると,アルミニウムとその合金では,高速伸び率の方が静的のそれよりも大きく,ステンレス鋼についてはほとんど引張り速度により変化せず,軟鋼とチタニウムについては高速の方が静的より小さい.従って,この範囲内では,面心立方格子の金属では高速で伸び率が増大するが少くとも減少しないこと,体心立方および稠密六方格子の金属では,高速で伸び率が減少するように思われる.静的な公称応力-ひずみ線図にもとづいて計算された限界衝撃速度以上においても,急激な伸び率の減少は認められなかった.Karman-Duwezの理論については更に検討の必要があると思われる.ひずみと硬さの分布についても,二三の測定がなされた.また実験技術上の問題として,荷重導入用の質量の移動速度と真の試片引張り速度との差異に注意すべきことが明かにされた.

For the investigation of the behaviours of metals under high speed impact loading, a high speed impact testing machine of a constant speed type applying the explosion pressure of low explosives, is constructed. In the testing machine, a high speed tension is given to the test specimen through a striking jaw from the projectile ejected by explosion pressure of explosive. In the present state, the speed of the projectile reaches up to 210m/sec, and the actual tensile speed of specimens up to 120m/sec. Using the machine, high speed uniaxial tensile tests of materials of five kinds: 2S-0 aluminium, 2024C-0 super duralumin, SPC-1 mild steel, 18-8 stainless steel and ST-60 titanium, are carried out, and the relations of percent elongations versus tensile speed in the range from 0 to 120m/sec are determined. The percentage elongations in high speed tension are larger than the static ones for aluminium and its alloy, but are smaller for mild steel and titanium than their own static ones. For stainless steel, the percentage elongation seems to show little change with tensile speed. Basing upon these results, it seems that high speed elongation is larger or nearly equal for metals of face centered cubic lattice, but is smaller for metals of body-centered cubic and of hexagonal close packed lattice, than their own static elongations in the speed range above mentioned. The reasoning should be studied further for many other metals. The critical impact volocities proposed by Karman in 1950 are caluculated basing upon the statical nominal stress-strain diagram, and compared with the experimental results. Drastic decreasing of percentage elongation at velocities beyond the calculated critical impact velocities are not found in the range of this experiment. Strain and hardness distributions in mild steel, stainless steel and titanium are shown. It is shown that there are some difference between the speed of load introducing mass and the actual tensile speed of specimen, and it is important to consider the difference in high speed tension.

資料番号: SA4135044000