Search Results for fracture mechanics analysis

This article describes concepts and tools that can be used by the failure analyst to understand and address deformation, cracking, or fracture after a stress-related failure has occurred. Issues related to the determination and use of stress are detailed. Stress is defined, and a procedure to deal with stress by determining maximum values through stress transformation is described. The article provides the stress analysis equations of typical component geometries and discusses some of the implications of the stress analysis relative to failure in components. It focuses on linear elastic fracture mechanics analysis, with some mention of elastic-plastic fracture mechanics analysis. The article describes the probabilistic aspects of fatigue and fracture. Information on crack-growth simulation of the material is also provided.

This article illustrates the role that fracture mechanics can play in failure analysis. It describes the important failure criteria as relations between design and materials factors, which are used to correlate fracture mechanics analysis to the observations of a failure analysis. Descriptions include an indication of how the factors are typically evaluated. The article also provides information on subcritical fracture mechanics. Finally, a group of failure analysis examples explain how fracture mechanics parameters can be determined and how they may be fitted into an overall failure investigation.

This article describes the underlying fundamentals, applications, the relevance and necessity of performing proper stress analysis in conducting a failure analysis. It presents an introduction to the stress analysis of bodies containing crack-like imperfections and the topic of fracture mechanics. The fracture mechanics approach is an important part of stress analysis at the tips of sharp cracks or discontinuities. The article reviews fracture mechanics concepts, including linear elastic fracture mechanics, elastic-plastic fracture mechanics, and subcritical fracture mechanics. It also provides information on the applications of fracture mechanics in failure analysis.

This article briefly introduces the concepts of failure analysis and root cause analysis (RCA), and the role of failure analysis as a general engineering tool for enhancing product quality and failure prevention. It reviews four fundamental categories of physical root causes, namely, design deficiencies, material defects, manufacturing/installation defects, and service life anomalies, with examples. The article describes several common charting methods that may be useful in performing an RCA. It also discusses other failure analysis tools, including review of all sources of input and information, people interviews, laboratory investigations, stress analysis, and fracture mechanics analysis. The article concludes with information on the categories of failure and failure prevention.

This article provides ASTM standard definitions for fatigue and describes the approaches that are used to design finite or infinite life, used in a complementary sense in fatigue design. It explains four distinct phases of fatigue: nucleation, structurally dependent crack propagation, crack propagation, and final instability. The article discusses the significant role that fatigue plays in industrial design applications.

Fracture control is a systematic process to prevent fracture during operation that depends on the criticality of the component, the economic consequences of the structures being out of service, and the damage that would be caused by a fracture failure. This article describes the key principles of fracture control and reviews the concepts of damage tolerance analysis. It further presents practical guidelines to obtain useful and reasonable answers from damage tolerance analysis. The article concludes with information on fracture mechanics and fatigue design.

Thermomechanical fatigue (TMF) refers to the process of fatigue damage under simultaneous changes in temperature and mechanical strain. This article reviews the process of TMF with a practical example of life assessment. It describes TMF damages caused due to two possible types of loading: in-phase and out-of-phase cycling. The article illustrates the ways in which damage can interact at high and low temperatures and the development of microstructurally based models in parametric form. It presents a case study of the prediction of residual life in a turbine casing of a ship through stress analysis and fracture mechanics analyses of the casing.

Failure analysis is a process of acquiring specified information regarding the appropriateness of the design of a part, the competence with which the various steps of its manufacture have been performed, any abuse suffered by it in packing and transportation, or the severity of service under which failure has occurred. Beginning with a discussion of the various stages of failure analysis of glass and ceramic materials, this article focuses on descriptive and quantitative fracture surface analysis techniques that are used in the examination of glass and surfaces created by fracture and the interpretation of the fracture markings seen on these surfaces. Details are provided for the procedures for locating fracture origins, determining direction of crack propagation, learning the sequence of crack propagation, deducing the stress state at the time of fracture, and observing interactions between crack fronts and inclusions, etc. A separate fractography terminology is provided in this article.

Optimized modeling of fracture-critical structural components and connections requires the application of elastic-plastic fracture mechanics. Such applications, however, can require sophisticated analytical techniques such as crack tip opening displacement (CTOD), failure assessment diagram (FAD), and deformation plasticity failure assessment diagram (DPFAD). This article presents the origin and description of FAD and addresses R6 FAD using J-integral. It details the fracture criteria of BS 7910. The factors to be considered during the use of FAD and the applications of FAD are also reviewed.

Thermomechanical fatigue (TMF) is the general term given to the material damage accumulation process that occurs with simultaneous changes in temperature and mechanical loading. TMF may couple cyclic inelastic deformation accumulation, temperature-assisted diffusion within the material, temperature-assisted grain-boundary evolution, and temperature-driven surface oxidation, among other things. This article discusses some of the major aspects and challenges of dealing with TMF life prediction. It describes the damage mechanisms of TMF and covers various experimental techniques to promote TMF damage mechanisms and elucidate mechanism coupling interactions. In addition, life modeling in TMF conditions and a practical application of TMF life prediction are presented.

This article addresses macroscale fracture appearances, microscale fracture-surface appearances or morphologies, fracture mechanisms, and those factors that influence fractures and fracture appearances. Some of the macroscopic and microscopic features identified by the failure analyst to evaluate the fracture surfaces of metals and plastics are described and compared.

This article briefly introduces the concepts of failure analysis, including root-cause analysis (RCA), and the role of failure analysis as a general engineering tool for enhancing product quality and failure prevention. It initially provides definitions of failure on several different levels, followed by a discussion on the role of failure analysis and the appreciation of quality assurance and user expectations. Systematic analysis of equipment failures reveals physical root causes that fall into one of four fundamental categories: design, manufacturing/installation, service, and material, which are discussed in the following sections along with examples. The tools available for failure analysis are then covered. Further, the article describes the categories of mode of failure: distortion or undesired deformation, fracture, corrosion, and wear. It provides information on the processes involved in RCA and the charting methods that may be useful in RCA and ends with a description of various factors associated with failure prevention.

The inclusion of damage tolerance design and a systematic review of design procedures allow the U.S. Air Force to design, manufacture, and maintain systems that are structurally safe and economically prudent. After a brief introduction of fracture mechanics, this article describes the particular aspects that relate to damage tolerance in aircraft design. It discusses the use of fracture mechanics as a method of predicting failure, understanding failure mechanisms, and suggesting inspection methods to protect against failure in pressure vessels. Various programs of U.S. Air Force to design aircraft structure, namely, airframe structural integrity programs, engine structural integrity program, and mechanical subsystems structural integrity program are also discussed.

The approaches to spectrum life prediction in components can be classified into two types, namely, history-based methods, using the life-fraction rule or other damage rules, and postservice evaluation methods. This article discusses the variables affecting the material crack growth rate behavior and those essential elements in making spectrum crack growth life prediction. It provides information on life assessment for bulk creep damage.

This article discusses the various options for controlling fatigue and fractures in welded steel structures, with illustrations. It describes the factors that influence them the most. The article details some of the leading codes and standards for designing against failure mechanisms. Codes are presented for fitness-for-service and standards for fatigue and fracture control.