Evaluation of the wood quality by soft X-ray of crack formation in wood as a result of nailing.

钉接节点的力学性能对木结构的合理设计具有重要意义。综上所述，钉入引起的裂缝尺寸是影响钉入节点强度的重要因素。本研究有两个对象；一是研究钉钉引起的裂纹扩展，二是用一种新的方法评价各种木材的质量。对钉入引起的裂纹扩展进行了研究，但大多数研究只讨论了表面裂纹特征。一些论文研究了木材裂缝的轮廓。但是，用钉后切割木材来测量裂缝长度是一种耗时的方法。对裂纹腔进行染色看起来是一种很有前途的方法，但染色不能完全渗透到小裂纹中。在本研究中，提出了新的方法。采用钡渗透法研究了木材钉伤致裂纹的形成。得到以下结论：1)钡渗透法是测量裂纹形成的有效方法。2)裂缝有三种类型；试管形状，椭圆形形状和玉米形状。3)钉法的效果、钉柄的形状、钉点的形状对裂缝长度有很大影响。4)在同一树种内，裂纹尺寸与木材密度、裂纹尺寸与钉径之间存在高度相关。可以表示为L=krhod^2，其中L为裂纹长度，rho为木材密度，k为常数。5)杉木钉钉时裂纹小，抗拔强度高。6)幼木比成熟木开裂少。裂缝的形成与木材的种类和质量有关。钡渗透法是评价国产软木材质量的有效手段。

The mechanical properties of nailed joints are very important for the rational design of timber structures. Above all, crack size induced by nailing is important factor for the strength of nailed joints. There are two objects in this study ; one is to investigate the crack propagation caused by nailing and the other is to evaluate the various kinds of wood quality by a new method.Crack propagation caused by driving a nail has been studied but most of the studies discussed only surface crack characteristics. Some papers have examined the profile of cracks in wood. However, cutting wood after nailing to measure the crack length is a time-consuming method. Staining the crack cavities looks like a promising method, but the stain does not penetrate into a small crack thoroughly. In this study, new methods are proposed. Crack formation in wood induced by nailing was investigated by barium permeation method.The following conclusions were obtained.1) The barium permeation method is effective to measure the crack formation.2) There were three types of cracks ; test tube shapes, oval shapes and corn shapes.3) The effect of nailing methods, the shape of the nail shank, and the shape of nail points have a great influence on the crack length.4) Within a species, there is a high degree of correlation between crack size and wood density, and between crack size and the diameter of nails. It can be expressed as L=krhod^2 where L is a crack length, rho is the wood density, and k is a constant.5)Hinoki generates less crack when nailing and has high withdrawal strength.6)Juvenile wood was cracked less than mature wood.7)Crack formation is related to wood species and quality. The Barium permeation method is an effective measure to evaluate the quality of the domestic soft wood.