Design is the process of choosing the geometric shape, materials, manufacturing method, and other details needed to completely describe a machine, vehicle, structure, or other engineered item. This process involves a wide range of activities and objectives. It is first necessary to assure that the item is capable of performing its intended function. For example, […]
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Bending and Torsion Tests Various bending and torsion tests are widely used for evaluating the elastic modulus, strength, shear modulus, shear strength, and other properties of materials. These tests differ in a critical way from tension and compression tests, in that the stresses and strains are not uniform over the cross section of the test
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Notch Impact Test Notch-impact tests provide information on the resistance of a material to sudden fracture where a sharp stress raiser or flaw is present. In addition to providing information not available from any other simple mechanical test, these tests are quick and inexpensive, so they are frequently employed. Notch Impact Test In various standard
Hardness Testing Methods In engineering, hardness is most commonly defined as the resistance of a material to indentation. Indentation is the pressing of a hard round ball or point against the material sample with a known force so that a depression is made. The depression, or indentation, results from plastic deformation beneath the indenter, as
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Some materials have dramatically different behavior in compression than in tension, and in some cases these materials are used primarily to resist compressive stresses. Examples include concrete and building stone. Data from compression tests are therefore often needed for engineering applications. Compression tests have many similarities to tension tests in the manner of conducting the
In analyzing the results of tension tests, and in certain other situations, it is useful to work with true stresses and strains. Note that engineering stress and strain are most appropriate for small strains where the changes in specimen dimensions are small. True stresses and strains differ in that finite changes in area and length
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A wide variety of tensile behaviors occur for different materials. Even for a given chemical composition of a material, the prior processing of the material may have substantial effects on the tensile properties, as may the temperature and strain rate of the test. Trends for Different Materials Engineering metals vary widely as to their strength
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Elastic Constants Initial portions of stress–strain curves from tension tests exhibit a variety of different behaviors for different materials as shown in Fig. 1. There may be a well-defined initial straight line, as for many engineering metals, where the deformation is predominantly elastic. The elastic modulus, E, also called Young’s modulus, may then be obtained
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An engineering component, such as a beam, shaft, tension member, column, or machine part, must not deform excessively or fail by fracture or collapse. At the same time, the cost and often the weight must not be excessive. The most basic consideration in avoiding excessive deformation is to limit the deflection due to elastic strain.
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Mechanical Testing of Materials Samples of engineering materials are subjected to a wide variety of mechanical tests to measure their strength or other properties of interest. Such samples, called specimens, are often broken or grossly deformed in testing. Some of the common forms of test specimen and loading situation are shown in Fig. 1. The
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