The determination of fracture-mechanical properties is often very challenging, because the available standards like ASTM E1820 need specific size-requirements for the specimen dimensions to obtain valid fracture toughness. Especially in the ductile regime, where the presence of plasticity around the crack tip is affected by the multiaxial stress state and its triaxiality, the size-requirements are frequently not met. The fulfilment of the size-requirements needs the testing of big specimens, which is often not possible. If we now think of specimens, which are irradiated in test modules for future fusion reactors, their size cannot be as big as required, because the available volume for irradiation is restricted. This fact highlights the need of Small Specimens Test Techniques (SSTT) for the determination of fracture-mechanical properties in the ductile regime.

The presented work focuses on an approach for the determination of fracture-mechanical properties in the ductile regime including stable crack growth and crack-resistance behavior. The authors have developed the initial approach some years ago and within this work the approach was simplified as much as possible. The basic idea of the approach is, that the crack growth can be simulated using Finite Element Method combined with a cohesive zone model. The cohesive zone model is a two parametric model, namely the cohesive stress ${\sigma }_c$ and the cohesive energy ${\mathrm{\Gamma }}_c$, which are identified on small specimens only. The new simplified approach was now validated on ferritic-martensitic steel Eurofer97 at room temperature.

In the past, the approach used complicated features like a CCD camera system and has now been simplified in a way that no CCD camera system is required. The main part of the approach is the identification of cohesive zone parameters (cohesive stress ${\sigma }_c$ and energy ${\mathrm{\Gamma }}_c$) on small specimens. The cohesive stress ${\sigma }_c$ can be determined on notched round tensile specimens with different notch root radius to account for different stress states or stress triaxialities in the specimen. With dedicated Finite Element modelling a local fracture stress dependent on stress triaxiality can be identified. The cohesive energy ${\mathrm{\Gamma }}_c$ can be carried out by simulating the small fracture-mechanical specimen using the Finite Element Method combined with the cohesive zone model and parameter fitting to experimental results. The cohesive energy ${\mathrm{\Gamma }}_c$ is treated to be identified, if the simulated crack-resistance curve describes the experimental behavior.

After identification of these parameters, a big fracture-mechanical specimen can be simulated using the cohesive zone parameters already determined on small specimens. Finally, the crack-resistance curve of a big specimen can be predicted and a valid fracture toughness can be identified if the size-requirements of the big specimens are met. In case the requirements are not fulfilled, a bigger specimen geometry can be simulated until all size criteria are met. With this method, the testing of big specimens can be avoided. For the future there is a Round Robin exercise planned including defined test matrices to demonstrate the general applicability of the approach.

断裂力学性能的确定通常非常具有挑战性，因为诸如ASTM E1820之类的可用标准需要特定尺寸的试样尺寸才能获得有效的断裂韧性。特别是在延性状态下，裂纹尖端周围的塑性受到多轴应力状态及其三轴性的影响，因此常常无法满足尺寸要求。满足尺寸要求需要对大样本进行测试，而这通常是不可能的。如果我们现在考虑在将来的聚变反应堆的测试模块中辐照过的标本，它们的尺寸就无法达到要求的大小，因为辐照的可用体积受到限制。

提出的工作集中于确定延性状态下断裂力学性能的方法，包括稳定的裂纹扩展和抗裂性能。作者几年前已经开发了初始方法，并且在这项工作中，该方法已尽可能简化。该方法的基本思想是，可以使用有限元方法结合内聚区模型来模拟裂纹扩展。内聚力区模型是两个参数模型，即内聚应力${\sigma }_C$ 和凝聚力 ${\mathrm{\Gamma }}_C$，只能在小样本上识别。新的简化方法现已在室温下在铁素体-马氏体钢Eurofer97上得到验证。

过去，该方法使用了诸如CCD摄像机系统之类的复杂功能，现在已经简化为不需要CCD摄像机系统。该方法的主要部分是识别内聚区参数（内聚应力）。${\sigma }_C$ 和能量 ${\mathrm{\Gamma }}_C$）放在小样本上。内聚应力${\sigma }_C$可以在具有不同缺口根半径的缺口圆形拉伸试样上确定，以说明试样中不同的应力状态或应力三轴性。通过专用的有限元建模，可以确定取决于应力三轴性的局部断裂应力。内聚能${\mathrm{\Gamma }}_C$可以通过使用有限元方法结合内聚力区域模型和参数拟合实验结果来模拟小型断裂机械样本来进行。内聚能${\mathrm{\Gamma }}_C$ 如果模拟的抗裂曲线描述了实验行为，则将其识别。

在确定了这些参数之后，可以使用已经在小样本上确定的内聚区参数来模拟大的断裂力学样本。最后，如果满足大样本的尺寸要求，则可以预测大样本的抗裂曲线，并可以确定有效的断裂韧性。如果不满足要求，可以模拟更大的试样几何形状，直到满足所有尺寸标准为止。使用这种方法，可以避免大样本的测试。未来计划进行一次循环演习，其中包括定义的测试矩阵，以证明该方法的一般适用性。