Abstract The specimen geometry has a significant influence on the Charpy impact strength. This is often a problem when it comes to the analysis of materials that can only be prepared with a curved shape, or which, like some biological structures, are naturally given in curved form like nutshells. The question repeatedly arises to what extent the curvature influences the impact strength. Hence, the present study deals with the dependence of the specimen geometry like specimen thickness, curvature and notches on the impact properties of concrete, gypsum, polyurethane (PUR) and epoxy-based (EP) samples. Increasing sample thickness from 2 to 10 mm resulted in increased toughness for brittle materials, whereas more ductile materials did not show any significant change in toughness. Increasing span length showed an increase of the unnotched impact strength for brittle gypsum, while toughness increased for a more ductile PUR sample. For the curved specimens both, the unnotched and the notched Charpy impact strength could be shown to increase with a reduction of the specimen radius (higher curvature) while the notch-sensitivity was not significantly affected. Material-specific linear relationships between the impact strength and the curvature of the samples were found. These relationships were used to create a model to calculate the influence of the curvature on the impact strength. For all materials, the characteristic values of a normalised flat standard sample could be well predicted from measured values of curved specimens. This calculation approach was used to predict the impact strength of an isotropic biological sample (sweet potato) concerning a flat sample and different curved specimens. The results show a good trend with the measured values.

中文翻译：

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样品厚度、曲率和缺口对夏比冲击强度的影响——一种标准化弯曲试样和生物结构冲击强度的方法

摘要 试样几何形状对夏比冲击强度有显着影响。在分析只能制备成弯曲形状的材料时，这通常是一个问题，或者像某些生物结构一样，像坚果壳一样自然地以弯曲形式给出。曲率在多大程度上影响冲击强度的问题反复出现。因此，本研究涉及试样几何形状（如试样厚度、曲率和缺口）对混凝土、石膏、聚氨酯 (PUR) 和环氧基 (EP) 样品冲击性能的依赖性。将样品厚度从 2 毫米增加到 10 毫米导致脆性材料的韧性增加，而更具延展性的材料的韧性没有任何显着变化。增加跨度长度表明脆性石膏的无缺口冲击强度增加，而韧性更好的 PUR 样品的韧性增加。对于弯曲试样，无缺口和缺口夏比冲击强度都可以显示出随着试样半径的减小（更高的曲率）而增加，而缺口敏感性没有受到显着影响。发现了冲击强度和样品曲率之间的材料特定线性关系。这些关系用于创建模型来计算曲率对冲击强度的影响。对于所有材料，归一化平面标准样品的特征值可以从弯曲试样的测量值很好地预测。该计算方法用于预测各向同性生物样品（红薯）对扁平样品和不同弯曲样品的冲击强度。结果显示出与测量值的良好趋势。