investigation of Elasto-Plastic Interfacial Crack Tip Fields Using Infrared Interferometry

尽管塑性效应对金属-陶瓷、金属-金属和聚合物-金属夹层等一系列不同材料体系具有实际意义，但目前对塑性效应对界面断裂的影响的了解并不多。这一领域的工作在很大程度上仍然是分析/数值性质的，需要进行实验研究，以进一步联系局部和全局参数，并深入了解裂纹的萌生和扩展行为，就像弹性对应的情况一样。对裂纹尖端场的相似性、模混合度、J优势、裂纹扩展阻力等进行详细的实验研究，对于模拟界面裂纹的萌生和扩展具有重要意义。为此，利用新研制的红外干涉仪对弹性相似但塑性不同的双材料的界面断裂行为进行了实验研究。这项研究的目的是深入了解塑性特征不同但弹性相同的双材料试件界面裂纹尖端附近的塑性引入的不对称性。上述工作将利用PI最近开发的红外Twyman-Green干涉仪来研究全场、实时、非接触模式的裂纹尖端场，即使在存在广泛的塑性和表面粗糙的情况下也是如此。在这项技术中，通过有利的粗糙度与波长比，绕过了在使用可见光时出现塑性/损伤时遇到的表面粗糙度/纹理的限制。该方法还提供了一些优点，例如在按原样处理表面时有更大的自由度，并且它不需要参考曝光。

The current understanding the influence of plasticity effects on the interfacial fracture has been modest despite of the practical significance in a wide range of dissimilar material systems including metal-ceramic, metal-metal and polymer-metal sandwiches. The work in this area has largely remained analytical/numerical in nature and experimental investigations are needed to further relate the local and global parameters and gain insight into the crack initiation and growth behaviors as in case of elastic counterparts. A detailed experimental study of the similarities of crack tip fields, mode-mixity, J-dominance, crack growth resistance, to name a few, would be valuable for modeling interfacial crack initiation and crack growth. To this end, an experimental effort on interfacial fracture behavior of bi-materials that are elastically similar but plastically dissimilar is proposed using a newly developed infrared interferometer. The research is aimed at gaining insight into the asymmetries introduced by plasticity near the interfacial crack tip in bimaterial specimens that are dissimilar in their plastic characteristics but identical elastically. The above effort will utilize an infrared Twyman-Green interferometer recently developed by the PI for investigating crack tip fields in full-field, real-time, non-contacting mode even in the presence of extensive plasticity and surface roughening. In this technique, the limitation of the surface roughness/texture encountered with the onset of plasticity/damage when using visible light has been circumvented through a favorable roughness to wavelength ratio. The method also offers advantages such as greater latitude in working with surfaces in 'as-is' condition and it does not need reference exposures.