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VAMAS TWA#3
Project #2: Hardness Round Robin
Hardness I
Organized by the National Physical Laboratory, United Kingdom, Dr. R. Morrell.

Objective

Evaluate Knoop, Vickers, and Rockwell Superficial 45N Hardness Methods on Ceramics.

Approach

Measure hardness of 2 sintered aluminas from UK.
Vickers microhardness at 200 grams and 1 kilogram. Knoop microhardness at 200 grams.

Outcome

Round robin successfully completed. 22 labs contributed.

Principal Findings

This was a very successful project which yielded important information and specific, constructive recommendations. The four key conclusions were:
  1. Specific technical recommendations for hardness testing can be made. After this project, NPL prepared a set of guidelines for immediate input to standards committees:
    VAMAS Technical Report #8, Sept. 1990, "Guidelines for Conducting Hardness Tests on Advanced Ceramic Materials, Morrell.
  2. Observer biases and random errors are the major sources of possible error (10-15%) in Vickers and Knoop hardnes measurments. Machine biases are ±0.7 - 0.9 in HR45N tests.
  3. Reference hardness blocks of high-hardness are needed.
  4. If hardness is to be used to compare materials or for a material specification, then measurement experimental errors must be recognized as an important limitation.
Standards Impacts

CEN TC 184-WG3 Prepared a standard based on the results:
ENV 843-4 Advanced Technical Ceramics - Monolithic Ceramics - Mechanical Properties at Room Temperature; Part 4: Vickers, Knoop and Rockwell Superficial Hardness Tests.
NIST prepared Standard Reference Materials (SRM) for Knoop (SRM 2830) and is preparing SRM 2831 for Vickers hardness.
ASTM standards C 1326 (Knoop) and C 1327 (Vickers) were influenced by this project.
ISO draft standard 14705 was influenced by this project.

Publications
  1. Butterfield, D. M. , Clinton, D. J., and Morrell, R., "The VAMAS Hardness Tests Round-Robin on Ceramic Materials," VAMAS Report #3, April 1989. (Available from National Physical Laboratory)
  2. Morrell, R., "Guidelines for Conducting Hardness Tests on Advanced Ceramic Materials," VAMAS Report #8, Sept. 1990. (Avail. National Physical Laboratory)
  3. R. Morrell, D. M. Butterworth, D. J. Clinton, "Results of the VAMAS Ceramics Hardness Round Robin," Euroceramics, Vol 3, Engineering Ceramics, eds. G. de With, R. A. Terpstra, R. Metselaar, Elsevier, London, 1989, pp 339-345.
For more information or copies of the reports, contact:
Dr. Roger Morrell, Bldg. 13,National Physical Laboratory, Teddington, Middlesex, TW11 OLW, UNITED KINGDOM, Tel: (+44) 181 943 6381, email: rm@npl.co.uk


The VAMAS TWA #3 Round Robins Between 1987 and 1999.

Click on the numbered projects in the image below for round robin details.



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