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

(1)采用有限区域断裂理论计算了含端部切口木梁的抗弯强度。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：晶粒方向1.5mm，径向或切向0.2mm。螺栓连接也进行了研究，理论和实验，并观察到良好的相关性。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（增田）。线性断裂力学的引入，特别是应力强度因子K的引入，被认为是估算螺栓连接失效或极限载荷的简单实用的方法，但要得到准确的估算还需要更多的研究（N.SOBUE）。(2)用蒙特卡罗方法估计了杉（日本雪松）纹层的变化减少。考虑到压缩过程中的粘附和弹塑性行为的增强效应，观察到更好的强度变化估计（H.MIHASHI）。（3）利用EDEM（Extended Distinct Element Method）从理论上研究了木材裂纹萌生后的裂纹扩展。对木材断裂过程的分析还需进一步改进（M.OHTA）。通过扭转木材，观察了剪切时的塑性行为。这表明Hill型方程比Jenkin型方程更适合于混合型应力下的屈服行为（H.YOSHUHARA）。实验研究了Ⅰ型和Ⅱ型混合模式下的断裂。没有一个断裂准则符合实验结果（K.SATO）。实验观察到，用紧凑拉伸、三点弯曲和单侧裂纹拉伸（铃木）三种方法测得的Ks值相差不大。

(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) .