Advancing the Techniques of Thermoleastic Fracture Mechanics of Composite Materials

CMS 9713356 PI：犹他州大学John A.Nairn：通过使用热弹性断裂力学公式处理复合材料中常见的残余应力，解决复合材料中的断裂问题的新技术使用四个方面的方法开发：针对复合材料的新的精确的热弹性断裂分析的推导；包括变分断裂力学在内的近似技术的发展，观察到的有限断裂事件的分析，以及实验验证。精确技术为复合材料断裂分析提供了新的工具，并被用来取代应力强度因子技术，后者对于各向同性和均匀的材料是强大的，但对复合材料的用处要小得多。近似技术的目的是找到通用工具来准确确定精确分析中出现的量。这些技术将基于新的变分定理，这将使我们有可能导出有用的能量释放率的上下限。“有限断裂事件”是指观察到复合材料通常是由于一系列离散的断裂事件(例如，纤维断裂、铺层开裂或脱粘)而不是连续的裂纹扩展而失效的。目前的工作开发断裂力学工具来处理这种离散的断裂事件。通过对复合材料实际失效过程的应用，验证了所有分析方法的有效性。

CMS 9713356 PI: John A. Nairn University of Utah New techniques for solving fracture problems in composites that treat the residual stresses commonly arising in composite materials by using thermoelastic fracture mechanics formulations are developed using a four-pronged approach: the derivation of new exact thermoelastic fracture analyses specific for composites; the development of approximate techniques including variational fracture mechanics, the analysis of observed finite fracture events, and experimental verification. The exact techniques provide new tools for analysis of composite fracture and are used in place of stress intensity factor techniques, which are powerful for isotropic and homogeneous materials, but are much less useful for composites. The approximate techniques are aimed at finding general tools for accurately determining the quantities appearing in the exact analyses. These techniques will be based on new variational theorems that will make it possible to derive useful upper and lower bounds for energy release rate. The term "finite fracture events" refers to the observation that composites often fail by a series of discrete fracture events (e.g., fiber fracture, ply cracking, or debonding) rather than by continuous crack growth. The present work develops fracture mechanics tools for dealing with such discrete fracture events. All analysis methods are verified by application to real and relevant failure processes in composite materials.