Fracture toughness and allowable loads are affected by in-plane and out-of-plane constraints, and the influences are studied in stiffened plates. Under small scale yielding condition, a new correction model of fracture toughness is developed by using the constraint parameter r_p0^1/2 which is based on the size of crack tip plastic zone. Then the fracture behaviors are investigated under three kinds of situations: (i) Stress intensity factor (SIF) is focused on solely; (ii) SIF and in-plane constraint (i.e. T₁₁) are considered; (iii) In the framework of correction model based on r_p0^1/2, SIF and the combined effects of in-plane and out-of-plane constraints are taken into account. The results show that both in-plane and out-of-plane constraints have significant effects on fracture toughness, allowable loads and crack arrest effects, and their influences cannot be neglected in stiffened plates generally. The evaluations based on r_p0^1/2 are more reasonable, because the proposed model considers in-plane and out-of-plane constraint effects comprehensively and the equation of fracture toughness is derived from the actual testing data.

断裂韧性和许用载荷受平面内和平面外约束的影响，并且在加筋板中研究了这些影响。在小尺度屈服条件下，利用基于裂纹尖端塑性区尺寸的约束参数r _{p 0} ^1/2建立了一种新的断裂韧性修正模型。然后研究了三种情况下的断裂行为：（i）应力强度因子（SIF）单独关注；(ii) 考虑 SIF 和面内约束（即T ₁₁）；(iii) 在基于r _{p 0} ^1/2的修正模型框架内, SIF 以及平面内和平面外约束的综合影响都被考虑在内。结果表明，面内和面外约束对断裂韧性、许用载荷和止裂效果都有显着影响，在加筋板中，它们的影响一般不可忽视。基于r _{p 0} ^1/2的评价更为合理，因为所提出的模型综合考虑了面内和面外约束效应，断裂韧度方程是从实际试验数据中推导出来的。