In this study, three-dimensional dynamically loaded stationary crack problems are evaluated by taking into consideration elastoplastic material properties. These types of problems, in which elastoplastic cracked structures are loaded dynamically, has been a great challenge for many scientists, due to the fact that the solutions are much more complicated and computationally time consuming than corresponding static problems. Analysis of dynamically loaded problems where elastoplastic materials exist within the structure has become a very important research subject recently, because of the inadequacy of the static solutions in many critical applications. The basic difference between a static and a dynamic problem is the fact that stresses or stress intensity factors in a dynamic analysis can be much higher than the corresponding static values. In the case of a sudden dynamic loading, failure due to fracture can happen unexpectedly, e.g. fracture during impact loading. This analysis may be very important in various applications in the semiconductor industry, automotive vehicles, high speed machinery and military applications.;There are some basic differences between static and dynamic fracture problems in which elastoplastic materials are present. These differences can be summarized with the inclusion of some effects which are not present in a typical static problem; inertia effects which leads to the propagation of stress waves, strain rate and temperature dependency of the material properties that affect the yield stress of the material, and the necessity for a time integration to calculate the fracture parameters w.r.t time, such as the stress intensity factors, dynamic J-integral and the crack tip opening displacement (CTOD). In this dissertation, the main task of interest can be subdivided into three different parts, in order to demonstrate the analysis methodology developed in the course of this study.;The first part will show the basic principles of linear elastic dynamic fracture modeling, including the finite element formulation of the dynamic analysis and the calculation of stress intensity factors for dynamic linear elastic fracture problems. These problems may be in the form of a homogenous cracked structure, or an interface crack which lies between two dissimilar materials. The analysis of the fracture problem is demonstrated with the aid of the Enriched Finite Element Method, which embeds special elements around the crack tip, called enriched elements. The dynamic analysis involves explicit and implicit time integration methods, and these methods will also be explained in this part. The engineering meaning of dynamic linear elastic fracture mechanics (LEFM) is demonstrated and compared with known results from the literature.;Analyzing cracked structures with elastoplastic material properties needs a step-by-step procedure and this will be described in the second part of this study. A dynamic time integration algorithm for nonlinear elastoplastic analysis is explained and comparisons are made with known results from the literature. Possible effects of strain rate and temperature on the yield stress of a plastically deforming material are also investigated. For a problem in which the crack tip zone is assumed to be elastic (small scale yielding conditions under LEFM rules), the stress intensity factors may still be considered as an appropriate parameter for fracture characterization. However, if the crack tip zone is not small and LEFM rules can not be justified, then different parameters should be utilized to characterize the fracture problem. At this point, it is expected that J-integral and CTOD calculations can be very useful to be able to quantify the crack problem. For the calculation of the J-integral in a cracked body, a special technique is definitely required, and the domain integral algorithm will be developed and applied for this purpose.;The analysis that is presented in this dissertation mostly involves dynamically loaded problems. In a dynamic problem, there are numerous time steps that may lead to a very computationally time consuming process, especially if the number of DOFs is high. In addition, if the problem requires an elastoplastic analysis, then these time considerations for the solution of a specific dynamic problem can become an overriding issue. Finite Element (FE) problems sometimes can become far too large, in terms of the total DOFs, for efficient in core memory storage. In order to deal with both of these computational matters, the development of parallelized versions of the current research FE code was considered to be necessary. Results regarding improvements associated with parallel computing developments are presented in the last chapter.;Most of the numerical examples presented in this study were evaluated using a specialized FE software that was developed at Lehigh University ME&M department. In a few instances, ANSYS commercial software, was used to compare results, with software developed by the author.
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机译：在这项研究中，通过考虑弹塑性材料的性能来评估三维动态加载的静态裂纹问题。这些类型的问题，其中动态加载弹塑性破裂结构，对许多科学家来说是一个巨大的挑战，这是因为与相应的静态问题相比，解决方案要复杂得多且计算耗时。由于许多关键应用中静态解决方案的不足，因此分析结构中存在弹塑性材料的动态加载问题已经成为非常重要的研究课题。静态和动态问题之间的基本区别在于，动态分析中的应力或应力强度因子可能远高于相应的静态值。在突然的动态载荷情况下，由于断裂而导致的故障可能会意外发生，例如冲击载荷时断裂。该分析在半导体工业，汽车，高速机械和军事应用中的各种应用中可能非常重要。；存在弹塑性材料的静态和动态断裂问题之间存在一些基本区别。这些差异可以用一些典型静态问题中不存在的影响来概括。导致应力波传播的惯性效应，影响材料屈服应力的材料特性的应变率和温度依赖性，以及需要进行时间积分以计算断裂时间wrt的参数，例如应力强度因子，动态J积分和裂纹尖端开口位移（CTOD）。本文将感兴趣的主要任务分为三个不同的部分，以说明本研究过程中开发的分析方法。第一部分将介绍线性弹性动力断裂建模的基本原理，包括动态线性弹性断裂问题的动力学分析有限元公式和应力强度因子的计算。这些问题可能是均质的裂纹结构，或者是两种不同材料之间的界面裂纹。借助富集有限元方法演示了对断裂问题的分析，该方法在裂纹尖端周围嵌入了称为富集元素的特殊元素。动态分析涉及显式和隐式时间积分方法，本部分还将对这些方法进行说明。演示了动态线性弹性断裂力学（LEFM）的工程意义，并将其与文献中的已知结果进行了比较。；分析具有弹塑性材料特性的裂纹结构需要分步进行，这将在本部分的第二部分中进行描述。研究。解释了一种用于非线性弹塑性分析的动态时间积分算法，并与文献中的已知结果进行了比较。还研究了应变速率和温度对塑性变形材料的屈服应力的可能影响。对于假定裂纹尖端区域具有弹性的问题（在LEFM规则下为小规模屈服条件），仍可以将应力强度因子视为断裂特征的合适参数。但是，如果裂纹尖端区域不小且无法证明LEFM规则，则应使用不同的参数来表征断裂问题。在这一点上，期望J积分和CTOD计算对于量化裂纹问题非常有用。为了计算裂纹体中的J积分，必定需要一种特殊的技术，为此将开发并应用领域积分算法。本文的分析主要涉及动态载荷问题。在一个动态问题中，有许多时间步长可能导致非常耗时的计算过程，尤其是在自由度数量很高的情况下。另外，如果问题需要进行弹塑性分析，那么解决特定动态问题的这些时间考虑因素可能成为首要问题。就总自由度而言，有限元素（FE）问题有时可能变得太大，以至于无法有效地存储核心内存。为了处理这两个计算问题，认为有必要开发当前研究FE代码的并行版本。上一章介绍了与并行计算开发相关的改进结果。本研究中提出的大多数数值示例都是使用由Lehigh University ME＆M部门开发的专用有限元软件进行评估的。在少数情况下，ANSYS商业软件用来比较结果和作者开发的软件。
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