采用标准三点弯曲梁砼试件，利用试验中测得的最大荷载Pmax及对应的裂缝口张开位移CMODc计算了砼裂缝亚临界扩展量Dac。提出了由虚拟裂缝闭合力s（x）产生的应力强度因子cKI的实用解析方法，进而计算了砼双K断裂参数ini KIC及un KIC。采用这一方法，只需在试验中测得最大荷载Pmax及对应的裂缝口张开位移CMODc、砼弹性模量及抗拉强度即可确定双K断裂参数并且无需对cKI进行数值积分。大量的计算分析表明，这一实用解析方法不但可使计算过程进一步简化，而且具有很高的精度。

The edoubIe-e notched no: ched specimen made of normal s: rengrh tin, crete has been stlbsected to compressive loads, kis shown that a shear crack develops at the notch tip. Visual observation and evaluation of displacement measurements have proven that this specimen allows pure mode I testing, It was possible to determine fracture toughness KIIc, Recommendations for the testing are made.

In this paper a mode It fracture testing method has been developed for wood from analytical, experimental and numedcaI investigations. Analytical resufls obtained by other researchers showed that the specimen geometry and loading type used for the proposed mode Ⅱ testing method results in only mode Ⅱ stress intensity and no mode Ⅰ stress intensity at the crack tip Experiments have been carded out to determine mode II fracture toughness A'iic and fracture energy GIIF from the test data collected from both spruce (picea afiies) and popIar (popuIus nigra) specimens. It was found that there existed a very good relation between fracture toughness Kiic and fracture energy GIlF when the influence of orthotropic stiffness EI in mode Ⅱ was taken into account. It verified that for this mode Ⅱ testing method the formula of LEFM can be employed for calculating mode Ⅱ fracture toughness even for highly orthotropic materiaIs like wood In the numerical studies for the tested spruce specimen, the crack propagation process, stress and strain fields in front of crack tips and the stress distributions along the ligament have been investigated in detail. It can be seen that the simulated crack propagating process along the ligament is a typical s hear cracking pattem and the development of cracks along the ligament is due to shear stress concentrations at the crack tips of the specimen. It has been shown that this mode Ⅱ fracture testing method is suitable for measuring mode Ⅱ fracture toughness/(ElC for highly orthotropic materials like wood.

混凝土断裂能的尺寸效应一直是研究的热点问题之一。借助于断裂功的概念，目前采用不同的试件形式来测试混凝土断裂能GF。其中，楔入劈拉试件因其在实际操作过程中的诸多优点而有希望成为测试混凝土断裂能GF的标准。本文采用楔入劈拉法研究了试件韧带高度对GF的尺寸效应影响。在测试过程中为得到稳定的荷载位移下降段而采用了柔度测试法。根据RILEM推荐的公式计算混凝土断裂能GF时，对荷载一位移曲线的尾部进行了合理的拟合处理，并考虑了试验夹具自重的影响。结果发现混凝土断裂能GF数值随试件韧带高度的增加有上升的趋势，具有明显的尺寸效应。进一步证实了尺寸效应是传统意义上的混凝土断裂能的属性特征。

本文基于作者及其合作者近年新提出的两端切口Ⅱ型断裂试件几何和相应的应力强度因子公式的基础上，建议一种无切口Ⅱ型断裂试件。然后对不同切口长度的Ⅱ型断裂试件和不同高度和宽度的无切口Ⅱ型断裂试件的断裂破坏过程采用以微面模型（Micro-Plane Model）为基础的三维非线性有限元分析商用程序进行数值模拟，发现无切口试件在韧带上由剪切应力集中引起剪切裂缝后，在韧带区形成纯Ⅱ型断裂和剪切裂缝扩展过程。然后较为系统地研究了试件宽度和试件高度对断裂破坏过程和断裂破坏形态的影响。