Search Results for constant-stress testing

This article reviews the basic equipment and methods for creep and creep rupture testing. It begins with a discussion on the creep properties, including stress and temperature dependence, as well as of the extrapolation techniques that permit estimation of the long-term creep and rupture strengths of materials. The article describes the different types of equipment for determination of creep characteristics, including test stands, furnaces, and extensometers. It also discusses the different testing methods for creep rupture: constant-load testing and constant-stress testing. The article presents other testing considerations and concludes with information on stress relaxation testing.

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.

This article describes the incubation, nucleation, and propagation of stress-corrosion cracking and how to evaluate it using standard tests. It discusses constant-strain, constant-load, bending, and uniaxial tension testing and how they compare when evaluating smooth and precracked test specimens under elastic-strain, plastic-strain, and residual-stress conditions. The article provides guidance on specimen selection and preparation, strain rate, and test equipment. It also examines service and laboratory test environments and provides detailed information on how to test various steels and alloys and how to interpret test results.

Creep deformation is normally studied by applying either a constant load or a constant true stress to a material at a sufficiently high homologous temperature so that a measurable amount of creep strain occurs in a reasonable time. This article provides the phenomenological descriptions of creep and explains the testing and mechanism of creep in crystalline solids. It also presents information on the creep response of crystalline and amorphous solids.

This article reviews the basic mechanisms of elevated-temperature behavior and associated design considerations, with an emphasis on metals. It discusses the key concepts of elevated-temperature design. These include plastic instability at elevated temperatures; deformation mechanisms and strain components associated with creep processes; stress and temperature dependence; fracture at elevated temperatures; and environmental effects. The article describes the basic presentation and analysis methods for creep rupture. It provides information on the application of these methods to materials selection and the setting of basic design rules. The article examines the limitations of high-temperature components as well as the alternative design approaches and tests for most high-temperature components.

The four-point method to estimate fatigue life behavior from tensile properties allows the construction of fatigue life curves from more readily available handbook data. This article provides information on the strain-based four-point method and the stress-based four-point method. The effects of mean stress or strain on transition fatigue life are reviewed. The article describes the determination of four fatigue-life parameters either by curve fitting actual fatigue life test data or approximating the constants from tensile properties. It contains a table that lists the tensile properties of various alloys.

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.

This article describes a scientific approach to the planning and evaluation of fatigue tests based on the determination of probabilities for detected fracture positions within the observed range of fatigue scatter. It schematically illustrates a constant-amplitude stress cycling about a possible mean load that leads to the fracture of a single part or specimen. The article discusses the evaluation of the range of transition and of the finite-endurance range for fatigue curves. It concludes with a discussion on extrapolation from the range of finite endurance into the range of transition.

This article discusses stress relaxation testing on metallic materials, as covered by ASTM E 328. It reviews the two types of stress relaxation tests performed in tension, long-term and accelerated testing. The article illustrates load characteristics and data representation for stress relaxation testing used for the most convenient and common uniaxial tensile test. It concludes with information on compression testing, bend testing, torsion testing, and tests on springs.