Definition
An indentation hardness tester is an instrument that evaluates a material's ability to resist local plastic deformation by measuring the size or depth of the indentation produced by a material under a specific load. Its measurement results are usually expressed in terms of hardness value, which is one of the important indicators of material mechanical properties and is widely used in materials science, quality control and engineering research.
Principle
The basic principle of indentation hardness measurement is based on the static load press-in method. The instrument presses the indenter of a specific shape and material into the surface of the specimen under the action of the specified test force, and the test force is removed after a certain period of time. By measuring geometric parameters such as diagonal length, diameter or depth left by the indentation on the surface of the specimen, it is converted into a hardness value according to the corresponding hardness calculation formula. Different hardness scales correspond to different indenter shapes, test forces and calculation formulas, so as to adapt to the characteristics of different materials.
Taking Vickers hardness as an example, its calculation formula is: HV = 0.102 * (2F * sin(136°/2)) / d², where F is the test force (in Newton) and d is the arithmetic mean (in mm) of the two diagonal lengths of the indentation. This formula reflects the relationship between the test force and the projected area of the indentation.
Measurement method
Common indentation hardness measurement methods mainly include Brinell hardness method, Vickers hardness method, and Knoop hardness method. The Brinell hardness method uses a ball indenter for softer or medium-hardness coarse-grained materials, and the hardness is calculated by measuring the diameter of the indentation. The Vickers hardness method uses a regular tetragonal diamond indenter with a wide range of test forces and is suitable for a wide range of materials from soft metals to hard ceramics, measuring the diagonal length of the indentation. The Knoop hardness method uses a diamond-shaped tetrapyramid diamond indenter that produces shallow and long indentations that are suitable for measuring thin layers, brittle materials, or tiny areas. The operation process usually includes specimen preparation, selection of ruler and test force, application of load, load holding, unloading, and indentation measurement and calculation.
Influencing factors
Indentation hardness measurement results are influenced by a variety of factors. In terms of specimens, surface roughness, flatness, cleanliness, uniformity and anisotropy of the material itself will introduce measurement deviations. In the test conditions, the size of the test force, the application rate, and the stability of the holding time are the key parameters. Environmental factors such as temperature fluctuations may affect the mechanical structure of the instrument and the state of the specimen. In addition, the operator's measurement reading errors, especially the optical system's interpretation of the indentation diagonal, can also affect the accuracy of the final result. Therefore, standardized testing processes and regular instrument calibration are the basis for data reliability.
Application:
Indentation hardness testers are widely used in industrial and scientific research. In the metalworking industry, it is used to test the hardness of raw materials, heat-treated workpieces, and monitor the process flow. In automotive and aerospace manufacturing, it is used to evaluate the hardness of the hardness of the case hardness or coating of components such as gears and bearings. In the field of material research and development, with microscopic devices, micro-hardness measurement can be carried out to study the mechanical properties of phase composition or gradient materials. In the electronics industry, it can be used to assess the hardness of solder joints or tiny joints. In addition, it is also commonly used for inbound inspection and factory inspection of product quality.
Selection considerations
When choosing an indentation hardness meter, it is necessary to comprehensively consider multiple technical parameters and application requirements. First, it is necessary to clarify the hardness range, specimen size and shape of the material to be tested to determine the appropriate hardness scale (such as Brineles, Vickers, Knoop) and its corresponding test force range. For tests that require thin layers, small parts, or the location of specific microstructures, models equipped with optical microscopes or automated platforms should be selected. When measurement efficiency is required, products with a high degree of automation and automatic turret and indentation measurement functions can be considered. The long-term stability of the instrument, ease of calibration, and compliance with relevant international standards (e.g. ISO 6506, ISO 6507, ASTM E92, etc.) are also important considerations. Finally, evaluate the space conditions and budget of the laboratory to choose equipment that strikes a balance between functionality, accuracy, and cost.