ポリエチレン丸棒材の引張―ねじり複合負荷変形によるミクロボイドの抑制効果
Restraint Effect of Microvoid Creation by the Tension-torsion Combined Stress in Polyethylene Cylindrical Rod
片桐武司・中西英二・日比貞雄
Katagiri, Takeshi / Nakanishi, Eiji / Hibi, Sadao
To investigate the effects of external forces on microvoid creation, polyethylene cylindrical rods were loaded under seven conditions of combined tension-torsion stress. Neck formation and whitening were examined, and structural changes were investigated using scanning electron microscopy (SEM), differential scanning calorimetry (DSC) and density measurements.
Necking formed under all of the seven conditions and fibrillar structure was observed on the cracked surfaces. However, whitening was not observed for conditions which twisting is strong. It is believed that compression in the sample radial direction exists because a neck is formed in a simple torsional test. For conditions which twisting is strong, compression toward the center axis of the specimen initiates necking and suppresses the creation of microvoids. For conditions which drawing is strong, a neck is formed by local drawing and creation of microvoids increases. It is suggested that necking is formed by means of either local drawing or compression toward the center axis. Twisting of the fibrillar structure generates a compression force which controls microvoid creation.
Key words: Polyethylene / Tension-torsion combined stress / Necking / Fibrillar structure / Microvoid