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 1

© Proceq 2017 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

Dynamic principle → probe and material-

dependent conversion curves

© Proceq 2017 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

© Proceq 2017 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)”

© Proceq 2017 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

© Proceq 2017 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

© Proceq 2017 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

© Proceq 2017 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

© Proceq 2017 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

HV5General UCI applications, machine parts,

shafts, weld inspections, etc.

HV1Thin-walled parts, coatings, bearings, tooth

flanks, etc.

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• 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

© Proceq 2017 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

Test

load [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

© Proceq 2017 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 outliers0

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

© Proceq 2017 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