Rheology is defined as the study of the flow and deformation of matter. This article begins with an examination of flow behavior. It describes the geometries and methods employed for rheological testing of polymers in their molten state. It also discusses materials that are predominantly in the solid state and the methods employed for solids testing. Examples of unidirectional and dynamic oscillatory testing are provided for different mechanical behaviors.

This article reviews the applied aspects of creep and stress-rupture failures. It discusses the microstructural changes and bulk mechanical behavior of classical and nonclassical creep behavior. The article provides a description of microstructural changes and damage from creep deformation, including stress-rupture fractures. It also describes metallurgical instabilities, such as aging and carbide reactions, and evaluates the complex effects of creep-fatigue interaction. The article concludes with a discussion on thermal fatigue and creep fatigue failures.

The principal types of elevated-temperature mechanical failure are creep and stress rupture, stress relaxation, low- and high-cycle fatigue, thermal fatigue, tension overload, and combinations of these, as modified by environment. This article briefly reviews the applied aspects of creep-related failures, where the mechanical strength of a material becomes limited by creep rather than by its elastic limit. The majority of information provided is applicable to metallic materials, and only general information regarding creep-related failures of polymeric materials is given. The article also reviews various factors related to creep behavior and associated failures of materials used in high-temperature applications. The complex effects of creep-fatigue interaction, microstructural changes during classical creep, and nondestructive creep damage assessment of metallic materials are also discussed. The article describes the fracture characteristics of stress rupture. Information on various metallurgical instabilities is also provided. The article presents a description of thermal-fatigue cracks, as distinguished from creep-rupture cracks.

A heavily worked 304 stainless steel wire basket recrystallized and distorted while in service at 650 deg C (1200 deg F). This case study demonstrates that heavily cold worked austenitic stainless steel components can experience large losses in creep strength, and potentially structural collapse, under elevated temperature service, even at temperatures more than 300 deg C (540 deg F) below the normal solution annealing temperature. The creep strength of the recrystallized 304/304L steel was more than 1000 times less than that achievable with solution annealed 304H. These observations are consistent with limitations (2000 Addendum to ASME Boiler and Pressure Vessel Code) on the use of cold worked austenitic stainless steels for elevated temperature service.

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.

Microstructural examinations on transverse cross sections of a steam reformer tube, showed the presence of large macrovoids elongated in the radial direction and emanating from the internal surface of the tube. The macrovoids were located at the interdendritic regions, and were partially filled by a Mn-Fe bearing chromium oxide film. The areas adjacent to the oxide film were chemically depleted in C, Cr and Mn and rich in Fe and Ni. Associated with this depletion were a large concentration of microvoids. It was suggested that the dissolution of carbides in areas surrounding the macrovoids and the concentration of stresses at their tips, caused extensive localized plastic deformation which led to the formation of microvoids and subsequently to the spalling of the oxide film. The non-protective character of the film induced a progressive deterioration of the grain boundaries properties. Grain boundary sliding and dislocation motion were enhanced, causing a local increase in the steady state strain rate and the premature failure of the tube.

This article describes the general aspects of creep, stress relaxation, and yielding for homogeneous polymers. It then presents creep failure mechanisms in polymers. The article discusses extrapolative methods for the prediction of long-term creep failure in polymer materials. Then, the widely used models to simulate the service life of polymers are highlighted. These include the Burgers power-law model, the Findley power-law model, the time-temperature superposition (or equivalence) principle (TTSP), and the time-stress superposition principle (TSSP). The Larson-Miller parametric method, one of the most common to describe the material deformation and rupture time, is also discussed.

This article provides some new developments in elevated-temperature and life assessments. It is aimed at providing an overview of the damage mechanisms of concern, with a focus on creep, and the methodologies for design and in-service assessment of components operating at elevated temperatures. The article describes the stages of the creep curve, discusses processes involved in the extrapolation of creep data, and summarizes notable creep constitutive models and continuum damage mechanics models. It demonstrates the effects of stress relaxation and redistribution on the remaining life and discusses the Monkman-Grant relationship and multiaxiality. The article further provides information on high-temperature metallurgical changes and high-temperature hydrogen attack and the steps involved in the remaining-life prediction of high-temperature components. It presents case studies on heater tube creep testing and remaining-life assessment, and pressure vessel time-dependent stress analysis showing the effect of stress relaxation at hot spots.

The failure of a reformer tube furnace manifold has been examined using metallography. It has been shown that the cause of failure was thermal fatigue; the damage was characterized by the presence of voids produced by creep mechanisms operating during the high temperature cycle under high local stress. The study indicates that standard metallographic procedures can be used to identify failure modes in high temperature petrochemical plants.

This article describes the visual, fractographic, and metallographic evidence typically encountered when analyzing stress rupture of turbine airfoils. Stress-rupture fractures are generally heavily oxidized, tend to be rough in texture, and are primarily intergranular and/or interdendritic in appearance compared to smoother, transgranular fatigue type fractures. Often, gross plastic yielding is visible on a macroscopic scale. Commonly observed microstructural characteristics include creep voiding along grain boundaries and/or interdendritic regions. Internal voids can also nucleate at carbides and other microconstituents, especially in single crystal castings that do not possess grain boundaries.

This article focuses on the life assessment methods for elevated-temperature failure mechanisms and metallurgical instabilities that reduce life or cause loss of function or operating time of high-temperature components, namely, gas turbine blade, and power plant piping and tubing. The article discusses metallurgical instabilities of steel-based alloys and nickel-base superalloys. It provides information on several life assessment methods, namely, the life fraction rule, parameter-based assessments, the thermal-mechanical fatigue, coating evaluations, hardness testing, microstructural evaluations, the creep cavitation damage assessment, the oxide-scale-based life prediction, and high-temperature crack growth methods.

This article describes the viscoelastic behavior of plastics in their solid state only, from the standpoint of the material deforming without fracturing. The consequences of viscoelasticity on the mechanical properties of plastics are described, especially in terms of time-dependencies, as well as the dependence of the viscoelastic character of a plastic on chemical, physical, and compositional variables. By examining the viscoelastic behavior of plastics, the information obtained are then applied in situations in which it may be important to anticipate the long-term properties of a material. This includes assessing the extent of stress decay in materials that are pre-stressed, the noise and vibration transmission characteristics of a material, the amount of heat build-up in a material subjected to cyclic deformation, and the extent a material can recover from any prior deformation. Several qualitative graphs are presented, which highlights the possible differences in the viscoelastic behavior that can exist among plastics.

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.

As the result of a leak detected in a plate-formed header at PENELEC'S Shawville Unit No. 3, an extensive failure investigation was initiated to determine the origin of cracking visible along the longitudinal weld seam. Fabricated from SA387-D material and designed for a superheater outlet temperature of 566 deg C, the 11.4 cm thick header had operated for approximately 187,000 h at the time of the failure. Discussion focuses on the results of a metallographic examination of boat samples removed from the longitudinal seam weldment in the vicinity of the failure and at other areas of the header where peak temperatures were believed to have been reached. The long-term mechanical properties of the service-exposed base metal and creep-damaged weld metal were determined by creep testing. Based on the utility's decision to replace the header within one to three years, an isostress overtemperature lead specimen approach was taken, whereby failure of a test specimen in the laboratory would precede failures in the plant. These tests revealed approximately a 2:1 difference in life for the base metal as compared to weld metal.

This paper describes the superplastic characteristics of shipbuilding steel deformed at 800 °C and a strain rate less than 0.001/s. After the superplastic deformation, the steel presents mixed fractures: by decohesion of the hard (pearlite and carbides) and ductile (ferrite) phases and by intergranular sliding of ferrite/ferrite and ferrite/pearlite, just as it occurs in stage III creep behavior. The behavior is confirmed through the Ashby-Verrall model, according to which the dislocation creep (power-law creep) and diffusion creep (linear-viscous creep) occur simultaneously.

This article provides an overview of the structural design process and discusses the life-limiting factors, including material defects, fabrication practices, and stress. It details the role of a failure investigator in performing nondestructive inspection. The article provides information on fatigue life assessment, elevated-temperature life assessment, and fitness-for-service life assessment.

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.

This article addresses some established protocols for characterizing thermoplastics and whether they are homogeneous resins, alloyed, or blended compositions or highly modified thermoplastic composites. It begins with a discussion on characterizing mechanical, rheological, and thermal properties of polymer. This is followed by a section describing molecular weight determination using viscosity measurements. Next, the article discusses the use of cone and plate and parallel plate geometries in melt rheology. It then reviews the processes involved in the analysis of thermoplastic resins by chromatography. Finally, the article covers three operations of thermoanalysis, namely differential scanning calorimetry, thermogravimetric analysis, and thermomechanical testing.

This article provides information on the development of finite element analysis (FEA) and describes the general-purpose applications of FEA software programs in structural and thermal, static and transient, and linear and nonlinear analyses. It discusses special-purpose finite element applications in piping and pressure vessel analysis, impact analysis, and microelectronics. The article describes the steps involved in the design process using the FEA. It concludes with two case histories that involve the use of FEA in failure analysis.

When complex designs, transient loadings, and nonlinear material behavior must be evaluated, computer-based techniques are used. This is where the finite-element analysis (FEA) is most applicable and provides considerable assistance in design analysis as well as failure analysis. This article provides a general view on the applicability of finite-element modeling in conducting analyses of failed components. It highlights the uses of finite-element modeling in the area of failure analysis and design, with emphasis on structural analysis. The discussion covers the general development and both general- and special-purpose applications of FEA. The special-purpose applications of FEA covered are piping and pressure vessel analysis, impact analysis, and microelectronic and microelectromechanical systems analysis. The article provides case histories that involved the use of FEA in failure analysis.