Search Results for stress-based four-point method

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.

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 reviews the various types of mechanical testing methods, including hardness testing; tension testing; compression testing; dynamic fracture testing; fracture toughness testing; fatigue life testing; fatigue crack growth testing; and creep, stress-rupture, and stress-relaxation testing. Shear testing, torsion testing, and formability testing are also discussed. The discussion of tension testing includes information about stress-strain curves and the properties described by them.

This article begins with a discussion on the classification of hydrogen embrittlement and likely sources of hydrogen and stress. The article describes several hydrogen embrittlement test methods, including cantilever beam tests, wedge-opening load tests, contoured double-cantilever beam tests, rising step-load tests, and slow strain rate tensile tests. It also describes the interpretation of test results and how to control hydrogen embrittlement during production.

Fatigue crack growth rate testing and data analysis are performed to characterize the crack propagation resistance of material environment combinations in order to predict crack growth life under anticipated stress histories. This article presents analyses performed on the numerical output of crack growth rate tests, including the analysis framework for modeling fatigue crack growth rate data. It describes the numerical methods for calculating da/dN as a function of stress intensity factor. The article discusses the principles in fatigue crack growth damage analysis.

The main objective for the study of combined-stress fatigue is to obtain fatigue data for axles and to find the criterion for fatigue limit under combined stress. This article begins with a description of the stress states of combined stress and stress fields near crack tips. It provides an account of the various biaxial and multiaxial fatigue testing methods, specimen geometries, and stress intensity factors important in the study multiaxial fatigue. Widely used test methods are the torsion-rotating bending fatigue test and biaxial and triaxial fatigue tests. Common specimen geometries include rectangular plate specimens, cruciform specimens, compact tension shear specimens, compact shear specimens, mode II crack growth specimen, circumferentially notched cylindrical specimens, tubular specimens containing a slit, and solid cylindrical specimens containing a small hole or initial crack.

Modeling will help reduce machining problems and thereby enable more rapid introduction of high-performance materials and components. This article discusses the technical needs of aircraft engine and airframe structural components and modeling of heat-treat-induced residual stress by finite-element residual-stress analysis. It describes the two-dimensional (2-D) and three-dimensional (3-D) procedures involved in finite-element residual-stress analysis. The article deals with the 2-D and 3-D machining distortion validation on engine-disk-type components. It describes methods for obtaining machining-induced residual stresses, including detailed finite-element analysis of the cutting process, the simple fast-acting mechanistic model, and the semi-empirical linear stress model. The article concludes with information on the modeling benefits and implementation of modeling in a production environment.

This article discusses the standard test methods that can be applied to many types of welds: tension, bending, impact, and toughness testing. It provides information on four qualification stages, namely, the weld material qualification, base material qualification, the weld procedure qualification, and the weld service assessment. The article describes two general types of measurements for residual stress in welds: locally destructive techniques and nondestructive techniques. Locally destructive techniques include hole drilling, chip machining, and block sectioning. Nondestructive techniques include X-ray diffraction, neutron diffraction, Barkhausen noise analysis, and ultrasonic propagation analysis. The article concludes with an overview of weldability testing.

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.

Testing of fiber-reinforced composite materials is performed to determine uniaxial tensile strength, Young's modulus, and Poisson's ratio relative to principal material directions, that helps in the prediction of the properties of laminates. Beginning with an overview of the fundamentals of tensile testing of fiber-reinforced composites, this article describes environmental exposures that often occur during specimen preparation and testing. These include exposures during specimen preparation, and planned exposure such as moisture, damage (impact), and thermal cycling techniques. The article also discusses the test procedures, recommended configurations, test specimen considerations, and safety requirements considered in the four major types of mechanical testing of polymer-matrix composites: tensile test, compression test, flexural test, and shear test.

Bend tests are conducted to determine the ductility or strength of a material. This article discusses the different bend tests with emphasis on test methods, apparatuses, procedures, specimen preparation, and interpretation and reporting of results. The types of bend tests discussed are bending ductility tests, bending strength tests (ASTM E 855), bend tests as per EN 12384 and JIS 3130, and computer-aided bending tests. The three standard bending strength tests are the cantilever beam bend test, the three-point bend test, and the four-point bend test. European Standard EN 12384 specifies a bend test to determine the modulus of elasticity in bending. Japanese Industrial Standard JIS 3130 specifies two tests to determine the elastic limit of spring plate or strip: the repeated deflection spring test and the moment type spring test.

The characterization, testing, and nondestructive evaluation of ceramics and glasses are vital to manufacturing control, property improvement, failure prevention, and quality assurance. This article provides a broad overview of characterization methods and their relationship to property control, both in the production and use of ceramics and glasses. Important aspects covered include the means for characterizing ceramics and glasses, the corresponding rationale behind them, and relationship of chemistry, phases, and microconstituents to engineering properties. The article also describes the effects that the structure of raw ceramic materials and green products and processing parameters have on the ultimate structure and properties of the processed piece. The effects that trace chemistry and processing parameters have on glass properties are discussed. The article describes mechanical tests and failure analysis techniques used for ceramics.

The lifetime assessment of polymeric products is complicated, and if the methodology utilized leads to inaccurate predictions, the mistakes could lead to financial loss as well as potential loss of life, depending on the service application of the product. This article provides information on the common aging mechanisms of polymeric materials and the common accelerated testing methods used to obtain relevant data that are used with the prediction models that enable service life assessment. Beginning with a discussion of what constitutes a product failure, this article then reviews four of the eight major aging mechanisms, namely environmental stress cracking, chemical degradation, creep, and fatigue, as well as the methods used in product service lifetime assessment for them. Later, several methods of service lifetime prediction that have gained industry-wide acceptance, namely the hydrostatic design basis approach, Miner's rule, the Arrhenius model, and the Paris Law for fatigue crack propagation, are discussed.

Mechanical tests are performed to evaluate the durability of gears under load. Gear tooth failures occur in two distinct regions, namely, the tooth flank and the root fillet. This article describes the common failure modes such as scoring, wear, and pitting, on tooth flanks. Failures in root fillets are primarily due to bending fatigue but can be precipitated by sudden overloading (impact). The article presents contact stress computations for gear tooth flank and bending stress computations for root fillets. Specimen characterization is a critical part of any fatigue test program because it enables meaningful interpretation of the results. The article describes four areas of the characterizations: dimensional, surface finish/texture, metallurgical, and residual stress. The rolling contact fatigue test, single-tooth fatigue test, single-tooth single-overload test, and single-tooth impact test are some of the gear action simulating tests discussed in the article.

This article discusses the methods of analyzing the directional dependence of the mechanical properties of composites, especially those perpendicular to the major plane of the laminate. It provides a description of the common indirect load cases and direct out-of-plane load cases. The article concludes with a discussion on composite materials that are reinforced in the z-direction (also known as three-dimensional, or 3-D composites).

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.

Simulation programs are becoming more effective tools in reducing the need for physical testing and the avoidance of costly downstream problems by solving the problems upfront in the early development stage. This article provides a brief review of the history and applied analysis of simple forming operations. It focuses on metal stamping simulation based on the finite-element methods or model (FEM) with emphasis on software tools using the three-dimensional FEM technology. The article discusses two aspects of particular importance in finite-element analysis of sheet forming and springback analysis: the type of solution algorithm/governing equation and the type of element. The article provides information on various models for material yield criteria.

In x-ray diffraction residual stress measurement, the strain in the crystal lattice is measured, and the residual stress producing the strain is calculated, assuming a linear elastic distortion of the crystal lattice. This article provides a detailed account of the plane stress elastic model, and describes the most common methods of x-ray diffraction residual stress measurement, namely, single-angle and two angle techniques. It elaborates the major steps involved in x-ray diffraction residual stress measurement, explaining the possible sources of error in stress measurement. The article also outlines the applications of x-ray diffraction residual stress measurement with examples.

This article briefly introduces some commonly used methods for mechanical testing. It describes the test methods and provides comparative data for the mechanical property tests. In addition, creep testing and dynamic mechanical analyses of viscoelastic plastics are also briefly described. The article discusses the processes involved in the short-term and long-term tensile testing of plastics. Information on the strength/modulus and deflection tests, impact toughness, hardness testing, and fatigue testing of plastics is also provided. The article describes tension testing of elastomers and fibers. It covers two basic methods to test the mechanical properties of fibers, namely the single-filament tension test and the tensile test of a yarn or a group of fibers.

THE TENSION TEST is one of the most commonly used tests for evaluating materials. The material characteristics obtained from tension tests are used for quality control in production, for ranking performance of structural materials, for evaluation of alloys, and for dealing with the static-strength requirements of design. This article describes the stress-strain behavior during a tension test and provides the definition of terms such as stress, force, strain, and elongation. It explains the tensile properties obtained from the test results: the tensile strength and yield strength, which includes offset yield strength, extension-under-load yield strength, and upper yield strength. The article concludes with a description of the general procedures for conducting the tension test based on ASTM standards and the variability of tensile properties.