VAMAS TWA #3
Project #11: Recording (Instrumented) Hardness Round Robin
Hardness III
Organized by the Federal Institute for Materials Research and Testing (Dr. Ullner) and the
National Institute of Standards and Technology (Mr. Quinn)
Objectives
- Evaluate the recording (instrumented) hardness method for ceramic materials. Load and displacements are continuously monitored.
- Evaluate several candidate hardness parameters that have been proposed for recording
hardness.
Approach
- Two materials: BK-7 optical glass and hot-isopressed silicon nitride.
The silicon nitride blocks were NIST's Standard Reference Material 2830, Knoop Microhardness of Ceramics.
- Monitor load and displacement during indentation with either Berkovich or Vickers
indenter. Maximum load of 1 N or 10 N.
- All labs furnished raw load-displacement data to BAM where it was analyzed with several
curve fitting and modelling procedures.
Status
All testing completed. 11 of 16 Laboratories returned data.
Final report completed and distributed.
Principal Findings
- Both the glass, grade BK-7, and the hot-isopressed silicon nitride are suitable as recording
hardness reference materials.
- Consistencies within a laboratory (repeatability) were generally good.
- Consistency between laboratories (reproducibility) were very poor. Up to a 4X variation
in hardness was observed. The between-lab variability was traced to poor displacement
measuring techniques. Stiffer frames and better displacement monitoring are needed for
many of the home-made systems.
- If "Universal hardness, HU" is measured, then a very detailed procedure for
extrapolating to the contact point is essential.
Standards Impact
- Current laboratory practices are unsatisfactory. Equipment improvements are essential.
Analysis procedures must be standardized. The data scatter in this exercise underscores
the need for standardization.
- VAMAS TWA #22, which is also coordinating an instrumented hardness round robin
may benefit from our experiences.
Publications
- C. Ullner and G. Quinn, "Round Robin on Recording Hardness," VAMAS Report #33, BAM,
Berlin, February, 1998.
- C. Ullner and G. Quinn, "Interlaboratory Study on Depth Sensing Hardness on Ceramics," to be
presented at IMEKO, 1999.
For more information or copies of the reports, contact:
Dr. Christian Ullner, BAM Unter den Eichen 87, D 12202 Berlin , GERMANY, Tel: (+49) 30 8104 3154,
email: christian.ullner@bam.de
or
Mr. George Quinn, NIST Ceramics Division, Gaithersburg, MD 20899, USA, Tel: (+001) 301 975 5765,
email: geoq@nist.gov
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