5. MECHANICAL PROPERTIES AND （5。）.pdfVIP

5. MECHANICAL PROPERTIES AND PERFORMANCE OF MATERIALS Samples of engineering materials are subjected to a wide variety of mechanical tests to measure their strength, elastic constants, and other material properties as well as their performance under a variety of actual use conditions and environments. The results of such tests are used for two primary purposes: 1) engineering design (for example, failure theories based on strength, or deflections based on elastic constants and component geometry) and 2) quality control either by the materials producer to verify the process or by the end user to confirm the material specifications. Because of the need to compare measured properties and performance on a common basis, users and producers of materials use standardized test methods such as those developed by the American Society for Testing and Materials (ASTM) and the International Organization for Standardization (ISO). ASTM and ISO are but two of many standards-writing professional organization in the world. These standards prescribe the method by which the test specimen will be prepared and tested, as well as how the test results will be analyzed and reported. Standards also exist which define terminology and nomenclature as well as classification and specification schemes. The following sections contain information about mechanical tests in general as well as tension, hardness, torsion, and impact tests in particular. Mechanical Testing Mechanical tests (as opposed to physical, electrical, or other types of tests) often involves the deformation or breakage of samples of material (called test specimens or test pieces). Some common forms of test specimens and