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

(1)采用有限面积断裂理论计算含端缺口的木梁的抗弯强度。理论结果与实验结果吻合得很好。有限小面积的最佳尺寸为晶粒方向1.5mm，径向或切向0.2mm。对螺栓连接进行了理论和实验研究，结果表明螺栓连接与螺栓连接具有良好的相关性。用图像相关法观察了剪切过程中的应力-应变关系，明确了剪切本构方程是非线性的或近似弹塑性的。引入线性断裂力学，特别是应力强度因子K，是估算螺栓连接破坏或极限载荷的简单实用方法，但要准确估算还需进一步研究（N.SOBUE）。(2)用蒙特卡罗方法估计杉木层压后变异的减少。考虑到粘结性和压缩弹塑性行为的增强作用，可以更好地估计强度变化（H.MIHASHI）。(3)利用扩展离散元法（EDEM）对木材裂纹萌生后的裂纹扩展进行了理论研究。木材断裂过程分析（m.h ota）有待进一步改进。通过扭转木材，观察了木材在剪切作用下的塑性行为。表明在混合模态应力作用下，Hill型方程比Jenkin型方程更适合屈服行为（H.YOSHUHARA）。实验研究了I和II混合模式下的断裂。所有断裂标准均不符合实验结果（k.s atto）。实验观察到，采用紧致拉伸、三点弯曲和单侧裂纹拉伸三种不同方法测量的k值差异不大（N.SUZUKI）。

(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) .