1.Introduction
1.1 performance and use
HVD-50AP Vickers hardness tester is a new type of hardness tester which use accurate mechanical and combine optical, electric with computer software programs. This kind of hardness tester changed the traditional hardness test method which use the weight of the weight to be the method of loading test force. It simplified the structure of hardness tester and improved overall accuracy of hardness tester. It is used to measure Vickers hardness or Knoop hardness. By inputting the length of diagonal into integration calculator, then user can calculate and get the hardness value. This kind of hardness tester measure the hardness according to GB and ISO standard.
The difference between Vickers indenter and Knoop indenter: The Vickers is square underside of the pyramid -shaped indenter and the Knoop is diamond-shaped underside of the pyramid -shaped indenter. In additional, test the Vickers hardness only need to measure the length of the two diagonal, however, the Knoop hardness just need measure the length of one diagonal.
The features & using scope of Vickers hardness tester:
l Compared with Brinell, Rockwell hardness tester, the Vickers hardness tester used more widely. It can test the hardness from the most soft material to the most hard material.
l Adopted the square underside of the pyramid -shaped indenter, test the same specimen with different test force can get similar hardness. So, the option of test force more flexible.
l Since the indentation is clear, more easy to measure the length of the diagonal. Test data more accuracy.
1.2 Model difference
HVD-50MP Vickers hardness tester Observation - Test - Measurement operated by manual (Manual Turret).
HVD-50AP Vickers hardness tester Observation - Test - Measurement automatically by stepping motor (Auto Turret).
1.3 Test description
Vickers hardness measurement is a judgment for the permanent indentation size of the material. Figure 1-1
At the beginning of the measurement, the hardness tester makes the indenter down until the indenter touches the surface of the specimen. Test force begins loading to reach the point which has been set. Then the hardness tester will hold the test force for some time which has been set.
At the end of the duration time, the test force will return to initial point. Then turn the turret to the position of 20× objective lens, measuring the diagonal of the indentation. The two thin lines of the micrometer eyepiece can be adjust to stick the opposite angles of the indentation. User just click the endoder on eyepiece, the D1, D2 data will calculate automatically, and the hardness data will display on screen directly.
1.4 Equipment appearance
The appearance of Vickers hardness tester(Figure 1-2)
Figure 1-2 the appearance of the hardness tester
1. Optical path (CCD camera use) 2. Digital Micrometer eyepiece 10X
3. 10× objective 4. Indenter 5. Working table
6. Elevated lead screw 7. Hand wheel 8. LCD screen
9. Membrane keyboard 10. Horizontal adjustment screw
11. Conversion optical path knob 12. 20X objective
13. Standard hardness block 14. Power switch
15.RS232 interface 16. power socket
17. Reset switch 18. Printer 19. Turret
1.5 Principles of Vickers hardness
Using the test force to press the square diamond indenter into the surface of the specimen. Holding some time, then unload the test force and measuring the diagonal length of the indenter in the surface of specimen. Figure 1-3
Figure 1-3 Vickers hardness test principle
Vickers hardness value =test force ÷the superficial area of the indentation. The indentation is considered to have a square base surface and the same indenter angle with the ideal shape.
Vickers hardness value can be calculated by the following formula:
HV=0.102F/S=0.102×2Fsin(α/2)/D2=0.1891F/D2
In the formula：HV---Vickers hardness value
F---test force，N
S--- superficial area，mm2
D---the average length of the two indentation diagonal，mm
α---indenter face angle=136°0′
if the unit of the test force is kgf，then the Vickers hardness value can be calculated by the following formula:
HV=F/S=2Fsin(α/2)/D2=1.854F/D2