Laboratory Instruments

Sample requirements:

• Flat and smooth: polished surface
• Stable: not moving under the load
• bulk materials with proper size can be hold on the stage or small specimen with resin embedded/polished.
• Bad specimens will generate false reading.

Preparation:

1. Check the power switch of hardness tester and printer
2. Check indenter type mounted.
3. Sample should be stable: not rocking or moving under the load. Bulk materials with proper size and polishing can be hold by the vise. Small specimens should be resin embedded and polished. Using crazy glue to mouting tile on 1-1/2" aluminium stub or epoxy.
4. Bad specimens will generate false reading.

Indentation:

1. Check the load you need and the setting of dwelling time.
2. Mount your specimens.
3. Focus on specimen surface at low mag and switch to high mag.
4. Find a clean area for indentation at high mag.
5. Switch turret to indenter poistion.
6. Press start to make an indentation.
7. Read the length of indent under optical lens. Indenter interacted with surface flaw should be elminated from measurement.

Change indenter tip:

1. Unscrew the protetion sheath of the indenter
2. Unscrew the fix screw half turn while holding the tip with finger or tweezers. Do not over turn.
3. Carefully remove the tip. Do not let it fell.
4. Mount the indenter. Secure the fix screw and protection sheath.

Finish:

1. Switch off the power for hardness tester and printer.
2. Cover the machine with plastic cover.
3. Take printed records and attach to your notebook.
4. Sign off logbook.

Indentation crack measument for fracture toughness

• Follow the standard procedure to make indentation via microhardness tester or Instron.
• Clean specimen with isopropanol and blow with clean compressed air.
• Follow standard SEM sample preparation step to image indents and measure the length of indentation induced cracks.


• where B is an empirical constant, 0.016, W is the load in Newtons, C is the crack length from the center of the indent to the crack tip in meters, E is the Young's modulus in GPa and H is the Vickers hardness in GPa.(Ref 1: Anstis et al., Journal American Ceramic Society. 1981; 64(9): 533-538. Ref 2:Y.W. Fan et al. Biomaterials 28 (2007) 3034–3042)

Tips:

• Use highest brighness of illumination when measuring indent.
• Machine doesn't recognize which indent is mounted.
• Distance between indents should be at least two times larger than the size of indent.