Search Results for catastrophic failure

Life assessment of structural components is used to avoid catastrophic failures and to maintain safe and reliable functioning of equipment. The failure investigator's input is essential for the meaningful life assessment of structural components. This article provides an overview of the structural design process, the failure analysis process, the failure investigator's role, and how failure analysis of structural components integrates into the determination of remaining life, fitness-for-service, and other life assessment concerns. The topics discussed include industry perspectives on failure and life assessment of components, structural design philosophies, the role of the failure analyst in life assessment, and the role of nondestructive inspection. They also cover fatigue life assessment, elevated-temperature life assessment, fitness-for-service life assessment, brittle fracture assessments, corrosion assessments, and blast, fire, and heat damage assessments.

The key to any successful part development is the proper choice of material, process, and design matched to the part performance requirements. Understanding the true effects of time, temperature, and rate of loading on material performance can make the difference between a successful application and catastrophic failure. This article provides examples of reliable material performance indicators and common practices to avoid failure. Simple tools and techniques for predicting part mechanical performance integrated with manufacturing concerns, such as flow length and cycle time, are demonstrated. The article describes the prediction of mechanical part performance for stiffness, strength/impact, creep/stress relaxation, and fatigue.

Stress-corrosion cracking (SCC) occurs under service conditions, which can result, often without any prior warning, in catastrophic failure. Hydrogen embrittlement is distinguished from stress-corrosion cracking generally by the interactions of the specimens with applied currents. To determine the susceptibility of alloys to SCC and hydrogen embrittlement, several types of testing are available. This article describes the constant extension testing, constant load testing, constant strain-rate testing for smooth specimens and precracked or notched specimens of SCC. It provides information on the cantilever beam test, wedge-opening load test, contoured double-cantilever beam test, three-point and four-point bend tests, rising step-load test, disk-pressure test, slow strain-rate tensile test, and potentiostatic slow strain-rate tensile test for hydrogen embrittlement.

Catastrophic failure best typifies the characteristic behavior of brittle solids in the presence of cracks or crack-like flaws under ambient conditions. This article provides a description of the concepts of fracture mechanics of brittle solids and focuses on the various testing methods developed to characterize the fracture behavior of brittle solids with examples. These include the fracture toughness test method and R-curve test method at ambient and elevated temperatures. The article also includes information on the evaluation of fracture-toughness test results and the behavior of R-curve.

Drawing is a process by which a workpiece is pulled against a die to produce a wire, bar, or tube with smaller cross sectional area compared with the initial stock. This article discusses the variables that affect the drawing process and the parameters that influence friction, lubrication, and wear. These parameters include process, lubricant, workpiece, and tooling. The article provides information on dry and wet lubrication in wire drawing. The dry lubrication refers to use of solid lubricants while wet lubrication refers to the practice of providing a liquid lubricant to the workpiece-die interface. The article describes the most common types and causes of die wear: abrasive wear, adhesive wear, surface fatigue wear, thermal fatigue wear, and catastrophic failure. It concludes with a discussion on the surface treatment and texturing that are used to reduce die wear in drawing operations.

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.

Detailed analyses and test correlations are typically required to support design development, structural sizing, and certification. This article addresses issues concerning building block levels ranging from design-allowables coupons up through subcomponents, as these levels exhibit a wide variety of test-analysis correlation objectives. At these levels, enhanced analysis capability can be used most effectively in minimizing test complexity and cost while also reducing design weight and risk. The article discusses the examples of tests for which good correlative capability has shown significant benefit. These include notched (open and/or filled hole) tension and compression, inter/intralaminar shear and tension, and pin bearing.