Considerations for Selecting Testing Machines for Metal Material Performance Testing

Selection of Metal Material Performance TestingTesting MachinePrecautions

1. Metal material testing machines are mainly selected for large loads.Steel Strand Testing Machine(50kN—2000kN), and some materials such as metal sheets, metal wires, and metal foils require small load testing machines.
2. The conventional tests for metal materials include tensile, compression, bending, shear, high-temperature tensile, and high-temperature endurance tests.
3. For customers requiring multiple testing methods, the convenience of machine operation should be considered.
4. For tests primarily focused on metal tensile, the tensile space should be considered for convenience.
5. For tests primarily focused on metal compression, the lower space for compression should be considered for convenience.
6. For materials with a single variety, hydraulic fixtures can be considered (fixtures are not disassembled).
7. For tests involving multiple materials that require changing different fixtures, it is recommended not to configure hydraulic fixtures (disassembly is inconvenient) and to use manual tensile fixtures instead.
8. When conducting tensile tests on metal materials, the national standard GB228-2002 specifies the requirements for tensile tests on metal materials: "In the elastic range and up to the upper yield strength, the separation rate of the steel strand testing machine's grips should be kept as constant as possible and within the specified stress rate range (material elastic modulus E/(N/mm2)<150000, stress rate control range is 2—20 (N/mm2)s-1; material elastic modulus E/(N/mm2)≥150000, stress rate control range is 6—60 (N/mm2)?s-1). If only the lower yield strength is measured, the strain rate during the yield period of the sample's parallel length should be between 0.00025/s and 0.0025/s. The strain rate within the parallel length should be kept as constant as possible. In the plastic range and up to the specified strength (specified non-proportional elongation strength, specified total elongation strength, and specified residual elongation strength), the strain rate should not exceed 0.0025/s." To meet the above testing conditions, the testing machine's control should be able to achieve three closed-loop control functions, which can control stress, strain, displacement, etc.
9. For tensile tests on metal materials that require obtaining the elastic modulus and Rp0.2, electronic extensometers should be configured. (It is recommended that the deformation of the extensometer be 5—10mm.)
10. When testing high-hardness metal materials, there are special requirements for the hardness of the jaws and pressure plates, which customers should specify when ordering the testing machine.
11. Requirements for metal material tensile samples: Conventional materials are generally made into dumbbell-shaped samples, such as plates and rods. For high-hardness, alloy materials (with very low elongation or brittle materials), it is recommended that customers use shoulder samples for testing, as this is reliable and does not waste jaws, and is also convenient to operate. For straight bar samples (small diameter rods), corresponding jaws should be configured based on the different hardness and surface finish of the samples, and users can provide samples and specifications for customization. Often, one set of jaws cannot meet the needs for multiple specifications. For small metal samples (especially high-strength), special fixtures need to be customized. It is recommended that users make the gripping part of the sample's jaws as long as possible during sample preparation to ensure reliable gripping and facilitate the clamping of the electronic extensometer.
12. Different hardness and surface finish of steel wires require different fixtures and jaws; it is best for customers to provide samples for better selection of corresponding fixtures (our company's steel wire fixtures are no less than eight types).
13. High-temperature testing of metals: The high-temperature furnace body is required to be rotatable, so that the testing machine can perform room temperature tests. The temperature during high-temperature tensile tests on metals is generally in the range of 300℃—900℃. High-temperature samples include rods (Φ5, Φ10) and plates (δ=1—, δ=3—6, special δ=8—12). High-temperature tensile tests require the configuration of high-temperature extensometer rods, high-temperature fixtures, and extensometers when Rp0.2 is required.
14. When conducting tensile tests on steel strand materials, the requirements for the fixtures are relatively high, and the selection of fixtures directly affects the test data results.
15. Metal sheets used in the automotive industry have requirements for the n value and r value of the sheets.
16. Regarding the calibration of testing machines: Many users only use compression for calibration during measurement verification, thinking that tension has also been calibrated, which is a misunderstanding. In single-space models, the sensors are bidirectional, and the calibration coefficients for tension and compression are different; both compression and tension need to be calibrated. The calibration of tension in single-space models is more complicated and requires a reverser to convert tension into compression for calibration. This phenomenon does not exist in dual-space models, where a single sensor is configured as a unidirectional sensor; once compression is calibrated, tension is also calibrated, making calibration particularly convenient and cost-effective.
17,Testing MachineDivided into level 0.5 and level 1, users should choose a level 0.5 or level 1 testing machine according to their needs.
18. The calibration content of the testing machine: The items that need to be calibrated include: load, displacement, speed, deformation, etc.

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