Portable hardness testing originated from the need of employing practical tools fully integrated into the production process and in-life servicing. Initially, they were based on the traditional indentation methods such as Rockwell, Vickers and Brinell, with modifications to make them (semi-) portable. However, during the past four decades, especially usage of the Leeb rebound and the Ultrasonic Contact Impedance (UCI) techniques exploded. In this paper, an advancement of the UCI technology is described. By usage of an integrated load sensor, hardness monitoring at selected loads and even during continuous load increase is facilitated. We are exploring this principle both for real-time user guidance to reduce user dependence and increase accuracy, and also to observe the indentation vs. load behavior of the material during the UCI indenter penetration. Results of this study are presented, and the benefits to users are illustrated.

1. Advancements of ultrasonic contact
impedance (UCI) hardness testing based on
continuous load monitoring during the
indentation process, and practical benefits
15th Asia-Pacific Conference for Non-Destructive Testing (APCNDT2017)
Singapore, November 16, 2017
C. Frehner, R. Mennicke, F. Gattiker, D. Chai*
Proceq SA and Proceq Asia Pte Ltd.
© Proceq 2017-2018 1

2. © Proceq 2017-2018 Advancements of UCI hardness testing based on continuous load monitoring during the indentation process 2
UCI is one of the most commonly used portable
testing methods
• Portability: small probe,
even smaller nozzle
• Simplicity: straightforward
use, incl. uneven surfaces
• Speed: short
measurement cycle time

3. Dynamic principle → probe and material-
dependent conversion curves
© Proceq 2017-2018 Advancements of UCI hardness testing based on continuous load monitoring during the indentation process 3
Ultrasound excitation is used to determine the
hardness of the test piece
Longitudinal oscillation of
resonating rod
Vickers indenter forced
into test piece
Measured frequency shift
~ material properties

4. © Proceq 2017-2018 Advancements of UCI hardness testing based on continuous load monitoring during the indentation process 4
• UCI frequency shift is an indirect
measure of indentation size
• Indentation size measured directly
in stationary Vickers method
• Stationary Vickers method uses
diamond indenter
• Diamond indenter in UCI: same
tip shape as in stationary Vickers
International standards ASTM A1038 and DIN
50159 specify UCI in detail
Hardness scale: HV,
indicated as “HV(UCI)”

5. © Proceq 2017-2018 Advancements of UCI hardness testing based on continuous load monitoring during the indentation process 5
Compared to stationary methods, UCI is fast,
orientation-independent, precisely positioned
• Probe can be used in any
orientation
• Orthogonal to surface
• Precise positioning, high
accessibility
 Diamond indenter
 Thin and long nozzle
• Only 1-2 seconds of load
application

6. © Proceq 2017-2018 Advancements of UCI hardness testing based on continuous load monitoring during the indentation process 6
Heat-affected zones of welds
UCI is often used to test hard-to-access and
small pieces
Gear teeth Bearings
Image source: Wikipedia Image source: Wikipedia Image source: Wikipedia

7. © Proceq 2017-2018 Advancements of UCI hardness testing based on continuous load monitoring during the indentation process 7
• Thinner / lighter pieces:
 Oscillations
 Ultrasonic wave
reflections
 Adhesive coupling to
thicker / heavier pieces
• Average roughness depth
≤ 5 μm
For UCI, test pieces must fulfill requirements on
thickness, mass, surface roughness

8. © Proceq 2017-2018 Advancements of UCI hardness testing based on continuous load monitoring during the indentation process 8
The UCI nozzle must be used orthogonally to the
test piece surface
• Deviation from 90° angle:
biased hardness readings
• Small indentations in hard
materials: may allow probe
movement during testing
• ± 5° vs. the surface normal
is allowed by the standards
• Limitation more relevant as
test loads increase

9. © Proceq 2017-2018 Advancements of UCI hardness testing based on continuous load monitoring during the indentation process 9
New Proceq probe with adjustable test load
reduces the need for multiple probes
• Since 2016: latest
generation of UCI probes
• Integrated load sensor
• Test load set before first
reading of the series
A single probe can flexibly cover multiple applications in the same environment.
Test load Typical application
HV10 Cast material, forgings, weld inspection
HV5
General UCI applications, machine parts,
shafts, weld inspections, etc.
HV1
Thin-walled parts, coatings, bearings, tooth
flanks, etc.

10. © Proceq 2017-2018 Advancements of UCI hardness testing based on continuous load monitoring during the indentation process 10
• Complete indentation process
monitored and logged:
 Speed of applying the load
 Load curve
• User guided through all the
steps of the process
→ reduced user dependence
• Constant and continuous load
application
→ stable, reliable and
repeatable results
The integrated load sensor monitors the test load
application and the frequency shift

11. © Proceq 2017-2018 Advancements of UCI hardness testing based on continuous load monitoring during the indentation process 11
Monitoring of test load vs. frequency shift allows
better material characterization
0
20
40
60
80
100
120
90'500 91'000 91'500 92'000 92'500 93'000
Testload[N]
Resonating frequency [Hz]
272 HV5
547 HV5
859 HV5
• Left flank: indentation
process
• Right flank: release of the
probe
• Characterization of the
plastic deformation
Instrumented indentation
hardness test with a portable
UCI probe

12. © Proceq 2017-2018 Advancements of UCI hardness testing based on continuous load monitoring during the indentation process 12
Tests reveal the benefits of user guidance during
measurements with the new UCI probe
• 6 users, little to no UCI
prior experience
• User guidance: on vs. off
• Setup:
 Calibrated test block
 HV5 test load
 12 readings per person
• Measure of repeatability:
standard deviation after
removal of 2 outliers
0
5
10
15
20
25
Tester 1 Tester 2 Tester 3 Tester 4 Tester 5 Tester 6
Standard deviation on test block 864 HV5
w/o w user guidance

13. © Proceq 2017-2018 Advancements of UCI hardness testing based on continuous load monitoring during the indentation process 13
New UCI probes with continuous load monitoring
provide a swath of benefits
• One probe covers multiple applications
• Test load can be adapted to the application
• Measurement process can be precisely analyzed
• User guidance with hints and warnings
• Quality of measurement quantified, stored
• Significantly improved repeatability