We evaluate Weibull’s approach and the coupled criterion (CC) ability to reproduce bending failure stress variations as a function of specimen size in two porous materials, namely gypsum or zinc oxide. Whereas both approaches well reproduce the size effect in gypsum specimens, only the CC succeeds in correctly predicting the failure stress variation for ZnO specimens. We thus question the basis assumption of increasing critical flaw size with increasing specimen size associated to Weibull’s approach. Employing the CC to predict prematurate specimen failure initiating from a critical pore, we determine a relation between the failure force decrease and the corresponding possible critical pore size range. For the three tested gypsum types, we estimate the critical pore size range to lie around 50–250 microns, not retrieving increasing critical pore size with increasing specimen size, as assumed in Weibull’s approach, but rather a constant critical pore size range for all specimens.

我们评估了 Weibull 的方法和耦合准则 (CC) 在两种多孔材料（即石膏或氧化锌）中再现弯曲破坏应力变化作为试样尺寸的函数的能力。虽然这两种方法都很好地再现了石膏试样的尺寸效应，但只有 CC 成功地正确预测了 ZnO 试样的失效应力变化。因此，我们质疑与 Weibull 方法相关的随着试样尺寸的增加而增加临界缺陷尺寸的基本假设。使用 CC 来预测从临界孔隙开始的过早试样失效，我们确定了失效力降低与相应可能的临界孔径范围之间的关系。对于三种测试的石膏类型，我们估计临界孔径范围约为 50-250 微米，