Types of metal tests
Relevance
In order to control the quality of production, various types of metal tests (chemical, physical, mechanical, etc.) are used. The main task of such tests is a comparative analysis of the characteristics according to the specified parameters. For example, metal fatigue tests are conducted to determine the endurance limits of the material under certain operating conditions. As a rule, cyclic loads are carried out for this purpose.
One of the most important parameters of structural elements is strength, which is tested, among other things, by bending tests of metals using tensile and compressive stresses.
Tensile or rupture tests on metals are no less common. This test is aimed at determining the elastic limit of the material, yield strength, strength and its relative elongation as well as contraction. Another method of testing metals and alloys is the determination of hardness according to generally accepted scales:
-Brinell;
-Rockwell;
-Vickers.
The following non-destructive testing of metals is carried out chemical, mechanical, technological, and metallographic. The purpose of testing is to evaluate the quality of the material and determine its performance characteristics.
Mechanical methods
Mechanical testing methods are used to determine the resistance of alloys to various types of loading and provide information about the strength and ductility of the material. They are tested under conditions of either progressive increase in stress (static loading) or impact loading (dynamic loading).
Tensile testing. Standard specimen has the following parameters established by GOST: for round specimen the length is equal to l0d; for flat specimen the length is equal to 11, Z of specimen cross-sectional area, expressed in mm2. The test is carried out on a special machine. The specimen is stretched along the axis until it breaks, with automatic recording of the strain diagram.
Hardness test. If the alloy is hard (tempered steel) and for thin sheet steel, hardness is determined by Rockwell test by pressing a 1.59 mm diameter ball or diamond cone into the sample. Rockwell HR can be converted to
Bend Testing. The test determines the ability of a sheet metal to deform according to a given shape. The sample is cut from the sheet without any surface treatment and bent on a special press.
Impact test (brittle strength test). The test is carried out on special pendulum-type bars by placing standard notched specimens there. This test determines the ability of the alloy to resist the action of dynamic loads. The more ductile the metal, the greater the resistance to impact loads.
Fatigue Testing. This test determines the resistance to cyclic loading and vibration to which the material will not fail. A bend fatigue test machine is commonly used. A cylindrical specimen is subjected to compressive and tensile loads.
Creep test -This test determines a material's resistance to prolonged loading at elevated temperatures. The test duration is several thousand hours. Reliable results can only be obtained using specialized equipment with precise control of specimen temperature and accurate control of dimensional changes.
Fracture tests. The sample with the neck is broken by impact and the resulting fracture is examined under a microscope, revealing inclusions, pores and hairs. This test makes it possible to evaluate grain size, the thickness of the hardened layer, and the depth of cementation.
Optical and physical methods
Microscopic examination. A metallurgical or polarizing microscope is used to inspect the fracture structure. The fracture of the material is examined, revealing inclusions, pores, and hairs. This test makes it possible to estimate the size and shape of grains, phase relations, thickness of the hardened layer, and the depth of carburization.
Radiographic examination. This method is often used to control the quality of welds. Pores, segregation and cracks are detected on the radiograph obtained. By performing irradiation in two perpendicular projections it is possible to precisely determine the location of the defect.
Magnetic powder inspection is suitable for ferromagnetic materials such as nickel, iron, and cobalt alloys. Superficial and some types of internal defects of ferromagnetic materials can be detected by depositing magnetic powder on a magnetized sample.
Chemical methods
Chemical testing determines the accuracy of the chemical composition, the presence or absence of necessary impurities. When pickling, the surface of the metal is exposed to chemical solutions to detect porosity, segregation
The method of spectroscopic analysis allows for the rapid qualitative determination of small amounts of impurities which cannot be detected by other chemical methods. Using instruments such as polychrometers, quantometers, and quantovacs, the spectrum of the sample is analyzed, after which the indicator indicates the percentage composition of the metal under study.
