Micro-Hardness &Toughness of Brittle Materials

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  • Topic: Vickers hardness test, Rockwell scale, Hardness
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Formal Laboratory Report

Experiment EA3: Micro-hardness &Toughness of Brittle Materials

Objective

* To measure the hardness of microscope glass slide by using Micro Hardness Tester. * To measure the hardness of Sintered Alumina Disk by using Vickers Hardness Tester. * To determinate the facture toughness by using the crack lengths that obtains from both of the hardness tests. * To understand the different and relationship of glass and other ceramic materials.

Theory
The cost involved in measuring ceramic-based materials is quite high. Hence, indentation techniques have been widely used to evaluating the fracture toughness of brittle materials. In order to calculate the fracture toughness, hardness should be known by using Micro Hardness Tester or Vickers hardness tester.

Hardness measurement

The term Micro Hardness Test means the load is not exceeding 1 kgf when indentation is made. Commonly, the indenter that be used is Vickers diamond pyramid and a flat and polished sample surface is needed for this testing.

While the Vickers hardness test method is apply a load of 1 to 100 kgf to the polished surface of the test material. As the diagram shows below, since the force applied in the normal direction, an included angle of 136 degrees created between two faces that made during testing. The load usually removed after force applying for 10 to 15 seconds, and then a square shape is formed on the flat surface of ceramics. The length of two diagonals of this square can be measured by using the tester, which will be used in hardness calculation.

The Vickers hardness can be calculated by using load divide area of the square that obtained during the hardness testing.

Fracture toughness measurement

Fracture toughness is an inherent property of the materials. It describes crack resistance of a material.

During the fracture toughness measurement of ceramics, A Vickers indentation is pressed on a polished ceramic surface and cracks appeared around the indentation. The cracks are considered as the artificial defects and the length of it can be used to calculate the fracture toughness. The lengths of the cracks are in inverse proportion to the toughness and in direct proportion to load applied.

The formula for calculating the fracture toughness can be written as:

Procedure

Microscope glass slide experiment
1. Take a fresh microscope glass slide, and avoid the fingerprint. 2. Place the glass slide simple in right position of the Micro Hardness Tester by using a pair tweezers. 3. Apply a 1000g load on the sample for 10 seconds to press an indentation and crack on the surface of sample. 4. Measure the two diagonal lengths and two pairs of crack lengths. 5. Repeat the steps 3 and 4 for one more time, and calculate the average of diagonal length and crack length. 6. Repeat step3 to step5 to obtain diagonal length and crack length at load 500g, 300g, 200g, 100g.

Sintered alumina disks experiment
1. Take a sintered alumina sample, and avoid the fingerprint. 2. Place the sintered alumina simple in right position of the Vickers Hardness Tester by using a pair tweezers. 3. Apply a 10kg load on the sample for 10 seconds to press an indentation and crack on the surface of sample. 4. Measure the two diagonal lengths and two pairs of crack lengths. 5. Repeat the steps 3 and 4 for one more time, and calculate the average of diagonal length and crack length. 6. Repeat step3 to step5 to obtain diagonal length and crack length at load 5kg, 3kg, 2kg, 1kg.

Observation & Result

EXPERIMENT A

Equipment: Micro hardness TesterTest Sample: Microscope Glass Slide

Note:100g = 1 Newton for Load P

LoadP[ gf ]| Diagonal Length [ um ]| Crack Length [ um ]| | Test No. 1| Test No. 2| Average| Test No. 1| Test No. 2| Average| | d1| d2| d1| d2| d| c1| c2| c1| c2| c|
100| 18.42| 18.53| 18.05| 18.66| 18.42| 13.09...
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