New methods for implementing cohesive zones in computational mechanics were derived by re-interpreting cohesive-zone “traction laws” as “strength models” and using concepts from damage mechanics. When applied to pure mode I or mode II loading, this approach is identical to prior methods. But, when applied to mixed-mode loading, it defines a new approach called strength cohesive zone modeling (or “strength CZM”). Compared to previous methods, strength CZM provides improved modeling for problems with changing mode mixity, allows independent selection of normal and tangential strength models, and reveals limitations in any method based on effective displacements. New modeling shows that mode mixity, which changes during crack growth, depends on cohesive zone properties and on which end of the cohesive process zone is interpreted as the crack tip. These observations suggest many prior experimental results need reanalysis. By considering a range of independent strength models, strength CZM predicts that all $G_I$-$G_{II}$ failure envelopes are convex. Precracking steps recommended in delamination testing protocols are considered. Strength CZM can realistically model precracking while prior methods generate unrealistic predictions.

通过将内聚区“牵引定律”重新解释为“强度模型”，并使用损伤力学的概念，得出了在计算力学中实现内聚区的新方法。当应用于纯模式I或模式II加载时，此方法与以前的方法相同。但是，当应用于混合模式加载时，它定义了一种称为强度内聚区建模（或“强度CZM”）的新方法。与以前的方法相比，强度CZM可以改进模式混合性问题的建模，可以独立选择法向和切向强度模型，并且可以揭示基于有效位移的任何方法的局限性。新的模型表明，模式混合在裂纹扩展过程中会发生变化，它取决于内聚区的性质以及内聚过程区的哪一端被解释为裂纹尖端。这些观察结果表明许多先前的实验结果需要重新分析。通过考虑一系列独立的强度模型，强度CZM预测所有$G_{\mathrm{一世}}$--$G_{\mathrm{一世}\mathrm{一世}}$失效包络是凸的。考虑分层测试协议中建议的预裂步骤。强度CZM可以现实地模拟预裂化，而现有方法会生成不切实际的预测。