異方性降伏関数を用いた6000系アルミニウム合金板の液圧バルジシミュレーションと実験検証

摘要

自動車の軽量化はCO_2排出量の削減に有効であり，地球環境保全の上で極めて重要な技術課題である。アルミニウム合金板は軟鋼板に比べて比重が小さく，さらに耐食性にも優れており，軽量化を実現する材料として注目されている。しかし，アルミニウム合金板は軟鋼板に比べて，延性に劣り破断しやすい，弾性率が小さいために弾性回復（スプリングバック）が大きいなど，プレス成形が難しい材料である。%Biaxial tensile tests of 6000 series aluminum alloy sheets with different density cube textures were carried out using cruciform specimens. The specimens were loaded under linear stress paths in a servo-controlled biaxial tensile testing machine. Plastic orthotropy remained coaxial with the principal stresses throughout every experiment. Successive contours of plastic work in stress space and the directions of plastic strain rates were precisely measured and compared with those calcu lated using selected yield functions ; the von Mises, Hill's quadratic and Yld2000- 2d. The Yld2000-2d yield functions with exponents of 12 and 6 are capable of reproducing the general trends of the work contours and the directions of plastic strain rates observed for test materials with high and low cube textures, respectively. Hydraulic bulge tests were also conducted and the variations of the thickness strain along the meridian directions of the bulged samples were compared with that cal culated using finite element analysis (FEA) based on the Yld2000- 2d yield functions with expo nents of 12 and 6. The differences of cube texture density cause significant differences in the strain distributions of the bulged specimens, and the FEA results calculated using the Yld2000- 2d yield functions show good agreement with the measurement results.