徑向梯度特性對竹材機械及柔韌性質之影響

Effects of radial gradient characteristics on the mechanical properties and fl exibility of bamboo materials

本研究利用四點抗彎強度試驗及循環彎曲載重試驗，以評估徑向梯度特性對台灣桂竹與孟宗竹機械性質及柔韌性質之影響。試驗結果得知，在抗彎性質方面，桂竹OC試片（Outer in compression，OC）最大彎矩應力約為227.2 MPa，此值高於OT試片（Outer in tension，OT）的199.1 MPa。而OT試片抗彎強度下之曲率值（（1/r）max）為16.8 m-1，此值高於OC試片之11.0 m-1。該結果顯示 OT試片顯示高延展性，而OC試片則顯示高最大彎矩應力。然而，孟宗竹OC試片最大彎曲值與OT 試片於統計上無顯著的差異。對於彈性模數方面，無論OT試片與OC試片，桂竹與孟宗竹之彈性模數分別約20 GPa與15 GPa，此結果顯示試片承載方向對於彈性模數無顯著的影響。而有關抗循環彎曲載重性質方面，桂竹OT試片之全循環次數的最大彎矩應力（（σmax）c），其（σmax）c保留率比OC試片高。此外，桂竹OT試片相較OC試片表現低永久應變值，此結果顯示OT試片具有高抗循環彎曲性質。而孟宗竹方面，與桂竹呈現相似的趨勢，顯示OT試片相較OC試片具有高抗循環彎曲性質。 In this study, effects of radial gradient characteristics on the mechanical properties and flexibility of Makino bamboo (Phyllostachys makinoi) and Moso bamboo (Phyllostachys edulis) were estimated by using 4-point bending test and cyclic bending test. In flexural properties, the maximum bending stress (σmax) of the outer of Makino bamboo in compression (OCma) showed 227.2 MPa, which was higher than its outer in tension (OTma). The maximum curvature value ((1/r)max) in OTma was 16.8 m-1, which was higher than one in OCma (11.0 m-1). These results indicated that the OTma exhibited higher ductility, while the OCma showed higher bending stress. However, the outer in compression and tension of Moso (OTmo and OCmo) showed no signifi cant difference for their fl exural properties. Additionally, regardless of OT and OC, the elastic modulus for Makino and Moso bamboo exhibited 20 GPa and 15 GPa, respectively.The result illustrated that the elastic modulus was not infl uenced by the loading orientation on the specimen. Furthermore, according to the (σmax)c that is σmax at the whole cycle number after cyclic 4-point bending test, its retention ratio for OTma exhibited higher than the OCma. On the other hands, the OTma exhibited lower permanent strain with compared to the OCma, indicating that the OTma was higher cyclic bending resistance. As for Moso bamboo, the (σmax)c retention ratio showed the same tendency with Makino bamboo, indicating that the cyclic bending resistance for OTmo was superior to that for OCmo.