Establshment of theory on fracture of wood and its application to RBD (Reliability Based Design)

(1)用有限区域断裂理论计算了带端部缺口的木梁的抗弯强度。理论计算结果与实验结果吻合较好。有限小区域的最佳尺寸为：晶向1.5 mm，径向或切向0.2 mm。并对螺栓连接进行了理论和试验研究，两者之间具有较好的相关性。用图像相关法观测了剪切过程中的应力-应变关系，发现剪切本构方程为非线性或近弹塑性(M.MASUDA)。引入线性断裂力学，特别是应力强度因子K，试图用简单实用的方法估计螺栓连接的失效或极限载荷，但需要更多的研究才能准确地估计(N.SOBUE)。(2)用蒙特卡罗方法估计杉木层板随层压的变异减小。考虑到粘结的增强效应和压缩过程中的弹塑性行为，可以更好地估计强度变化(H.MIHASHI)。(3)用扩展离散单元法对木材裂纹萌生后的扩展进行了理论研究。对于木材断裂过程的分析(M.OHTA)还需要进一步改进。通过扭转木材观察了木材在剪切过程中的塑性行为。结果表明，在混合模式应力(H.YOSHUHARA)条件下，Hill方程比Jenkin型方程更符合屈服行为。对I、II混合模式下的断裂进行了实验研究。没有一种断裂准则符合实验结果(K.SATO)。实验观察到，压缩拉伸法、三点弯曲法和单侧裂纹拉伸法测得的K_s值稍有不同。

(1) Bending strength of timber beams including end notches was calculated using finite area fracture theory. Theoretical results coincide well with experimental ones. The optimum sizes of the finite small area are 1.5mm for grain direction, 0.2mm for radial or tangential direction. Bolted joints were also investigated theoretically and experimentally, and good correlation was observed between them. Stress-strain relationship in shear was observed by image correlation method, and it makes clear that constitutive equation of shear is non-linear or nearly elasto-plastic (M.MASUDA) . Introduction of linear fracture mechanics especially stress intensity factor K was attemmpted for simple practical method in estimation of failure or ultimate load of bolted joints, but more investigation was needed for accurate estimation (N.SOBUE) .(2) Monte Carlo method was used to estimate decrease of variation with lamination of Sugi (Japanese cedar) laminae. Considering the reinforcement effect of adhesion and elastoplastic behavior in compression, better estimation of strength variation was observed (H.MIHASHI)(3) Propagation of crack in wood after crack initiation was investigated theoretically by means of EDEM (Extended Distinct Element Method) . More improvement was necessary to analyze the fracture process of wood (M.OHTA) . Plastic behavior in shear was observed by torsioning wood. It makes clear that Hill type equation fits better than Jenkin type equation in yielding behavior under mixed modes stresses (H.YOSHUHARA) . Fracture under mixed modes of I and II were investigated experimentally. None of fracture criteria fit the experimental results (K.SATO) . It was obseved experimentally that there is a little difference between Ks measured by three different methods i.e.compact tension, three point bending and tension with one side crack (N.SUZUKI) .