ASTM A1038-05

NOTICE: This standard has either been superseded and replaced by a new version or withdrawn.
Contact ASTM International (www.astm.org) for the latest information
Designation:A1038–05
Standard Practice for
Portable Hardness Testing by the Ultrasonic Contact
Impedance Method
This standard is issued under the fixed designation A 1038; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. A
superscript epsilon (e) indicates an editorial change since the last revision or reapproval.
1. Scope defined indenter, for example, a Vickers diamond, with a fixed
force against the surface of the part to be tested.
1.1 This practice covers the determination of comparative
3.1.3 calibration—determination of the specific values of
hardness values by applying the Ultrasonic Contact Impedance
the significant operating parameters of the UCI instrument by
Method (UCI Method).
comparisonwithvaluesindicatedbyastandardizedworkbench
1.2 This standard does not purport to address all of the
hardness tester or by a set of certified reference test pieces.
safety concerns, if any, associated with its use. It is the
3.1.4 verification—checking or testing the UCI instrument
responsibility of the user of this standard to establish appro-
to ensure conformance with this practice.
priate safety and health practices and determine the applica-
3.1.5 surface finish—all references to surface finish in this
bility of regulatory limitations prior to use.
practice are defined as surface roughness (that is, Ra = average
2. Referenced Documents
roughness value).
2.1 ASTM Standards:
4. Significance and Use
A 370 Test Methods and Definitions for MechanicalTesting
4.1 The hardness of a material is a defined quantity having
of Steel Products
many scales and being dependent on the way the test is
E10 Test Method for Brinell Hardness of Metallic Materi-
performed. In order to avoid the creation of a new practice
als
involving a new hardness scale, the UCI method converts into
E18 Test Methods for Rockwell Hardness and Rockwell
common hardness values, for example, HV, HRC, etc.
Superficial Hardness of Metallic Materials
4.2 The UCI hardness test is a superficial determination,
E92 Test Method for Vickers Hardness of Metallic Mate-
only measuring the hardness condition of the surface con-
rials
tacted. The results generated at a specific location do not
E 140 Test Method for Hardness Conversion Tables for
represent the part at any other surface location and yield no
Metals
information about the material at subsurface locations.
E 384 Test Method for Microindentation Hardness of Ma-
4.3 The UCI hardness test may be used on large or small
terials
components at various locations. It can be used to make
3. Terminology hardness measurements on positions difficult to access, such as
tooth flanks or roots of gears.
3.1 Definitions:
3.1.1 UCI method—Ultrasonic Contact Impedance, a hard-
A. GENERAL DESCRIPTION OF INSTRUMENTS
ness testing method developed by Dr. Claus Kleesattel in 1961
AND TEST PROCEDURE FOR UCI HARDNESS
based on the measurement of the frequency shift of a resonat-
TESTING
ingrodcausedbytheessentiallyelasticnatureofthefinitearea
of contact between the indenter and the test piece during the
5. Apparatus
penetration.
5.1 Instruments used for UCI hardness testing generally
3.1.2 UCI hardness test—a hardness testing practice using a
consist of (1) a probe containing a rod with a defined indenter,
calibrated instrument by pressing a resonating rod with a
for example, aVickers diamond, attached to the contacting end
per Test Method E92 and Test Method E 384, (2) vibration
This practice is under the jurisdiction of ASTM Committee A01 on Steel,
generating means, (3) vibration detecting means, (4) electronic
Stainless Steel and Related Alloys and is the direct responsibility of Subcommittee
means for the numerical evaluation, and (5) a digital display,
A01.06 on Steel Forgings and Billets.
indicating the measured hardness number.
Current edition approved Jan. 1, 2005. Published February 2005.
For referenced ASTM standards, visit the ASTM website, www.astm.org, or 5.2 UCI Probes—There are different probes available for
contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM
UCI hardness testing.They typically cover static loads ranging
Standards volume information, refer to the standard’s Document Summary page on
from 1 N to 98 N. See also Appendix X1. They come also in
the ASTM website.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.
A1038–05
different sizes with longer and shorter sensor rods for specials
applications. And they are developed in two versions, that is,
manually operated or equipped with a servo-motor for auto-
matic testing.
5.3 Summary of Practice—In conventional workbench
hardness testing like Brinell or Vickers testing according to
Test Methods E10, E92 and E 384, the hardness value is
determined optically by the size of the indentation in the
material generated by a certain test load, after the indenter has
been removed. In the mobile hardness test under applied load
according to the UCI method, however, the size of the
produced indents are not determined optically. Instead the
contact area is derived from the electronically measured shift
ofanultrasonicresonancefrequency.TocarryouttheUCItest,
FIG. 2 Hardness Value versus Frequency Shift of the Oscillating
a probe containing the rod with the indenter is excited into a
Rod
longitudinal ultrasonic oscillation of about 70 kHz by piezo-
electric ceramics—the so-called zero frequency, which occurs
case of motor driven probes. The instrument carries out the
when the indenter is vibrating in air.
evaluation and calculations, and displays instantaneously the
A spring inside the probe applies the specified test load, the
hardness value, for example, HV(UCI).
vibrating tip penetrates into the material creating an elastic
UCI Vickers (1)
contact, which results in a positive frequency shift of the
F
resonatingrod.Thisshiftisrelatedtothesizeoftheindentarea
Df 5 f~E · A! and HV 5
eff
A
(contact area of the indenter with the material). The size, in
↑_________________↑
turn,isameasureforthehardnessofthetestmaterialatagiven
modulus of elasticity, for example, HV(UCI) according to Eq
The frequency shift is a function of the indentation size of a
1.
defined indenter, for example, a Vickers diamond, at a given
Therefore, the frequency shift is relatively small for hard
modulus of elasticity of the measurement system.
materials, because the indenter penetrates not very deep into
Eq 1 describes the basic relation in comparison to the
the test material leaving only a small indent. definition of the Vickers hardness value: Df = Frequency shift,
The frequency shift becomes larger if the indenter penetrates
A = indentation area, E = effective elastic modulus (contains
eff
deeper into the material, indicating medium hardness, in theelasticconstantsofboththeindenterandthetestpiece), HV
accordance with the larger test indentations. Analogously, the
= Vickers hardness value, F = Force applied in the hardness
frequency shift becomes largest when soft materials are tested test.
(see Fig. 2).
5.4 The Influence of the Elastic Constants—As can be seen
Theinstrumentconstantlymonitorstheresonancefrequency,
in Eq 1, the frequency shift not only depends on the size of the
calculates the frequency shift when the specified test load has
contact area but also on the elastic moduli of the materials in
been reached either after the internal switch has triggered the
contact. To allow for differences in Young’s modulus, the
corresponding measurement frequency in the case of handheld
instrument has to be calibrated for different groups of materi-
probes or after a specific dwell time has been elapsed in the
als. After calibration, the UCI method can be applied to all
materials, which have the corresponding Young’s modulus.
As manufactured, the UCI instrument usually has been
calibrated on non-alloyed and low-alloyed steel, that is, certi-
fied hardness reference blocks according to Test MethodE92.
Besides this, some instruments may be calibrated quickly, also
atthetestsite,formetalssuchashigh-alloyedsteels,aluminum
or titanium.
6. Calibration to Other Materials
6.1 A test piece of the particular material is needed. The
hardness value should than be determined with a standardized
workbench hardness tester like one for Vickers, Brinell or
Rockwell according to Test Methods and Definitions A 370.It
is recommended to take at least 5 readings and calculate the
average hardness value. Now carry out a set of at least 5 single
Legend:
UCI measurements on your test material according to instruc-
T = Piezo Transducer
R = Receiver
tions in 10.6, adjust the displayed average value to the before
O = Oscillating rod
measured hardness of the material and thus find the calibration
V = indenter, for example, Vickers diamond
value which is necessary for further measurements on this
m = test material
FIG. 1 Schematic Description of the UCI Probe particular material in the desired hardness scale and range.
A1038–05
Some instruments allow storing all calibration data and sympatheticoscillations(forexample,thinblocks,tubes,pipes,
adjustment parameters for hardness testing of different mate- etc.). Most disturbing are flexural vibrations excited by the
rials. They can be recalled to the instrument as needed. vibrating tip. These should be suppressed by suitable means.
Sometimes attaching the test piece to a heavy metal block by
7. Comparison with Other Hardness Testing Methods
means of a viscous paste, grease or oil film suffices to quench
7.1 As opposed to conventional low load hardness testers, the flexural waves. Nevertheless, a minimum wall thickness of
the UCI instruments do not evaluate the indentation size 2 to 3 mm is recommended.
microscopically but electronically according to the UCI 8.4 Influence of the Oscillation—The UCI method is based
method. The UCI method yields comparative hardness mea- on measuring a frequency shift. Parts less than about 300 g can
surements when considering the dependency on the elastic go into self-oscillating causing erroneous or erratic readings.
modulus of the test piece. Test pieces of weights less than the minimum or pieces of any
After removing the test force, an indentation generated by weight with sections less than the minimum thickness require
the UCI probe using a Vickers diamond as indenter and rigid support and coupling to a thick, heavier non-yielding
mounted in a test stand is practically identical to a Vickers surface to resist the oscillation of the UCI probe. Failure to
indentation produced by a workbench tester of the same load. provideadequatesupportandcouplingwillproducetestresults
The indentation can be measured optically according to the lower or higher than the true hardness value.
standard Vickers test if care is taken to apply the force 8.5 Surface Curvature—Test pieces with curved surfaces
accordingtoTestMethodE92andifaVickersindenterisused may be tested on either the convex or concave surfaces
in the UCI probe. In this case special arrangements or probe providing that the radius of curvature of the specimens is
attachments have to be used to provide verification of the matchedtotheappropriateprobeandprobeattachmentinorder
actual test force of the UCI probe. to ensure a perpendicular positioning of the probe.
8.6 Temperature—The temperature of the test piece may
8. Test Piece
affect the results of the UCI hardness test. However, if the
8.1 Surface Preparation—The applied test force (that is, the probe is exposed to elevated temperature for only the time of
selected UCI probe) must not only match the application but measurement, measurements are possible at temperatures
also the surface quality and roughness of the material. While higher than room temperature, without influencing the perfor-
smooth, homogeneous surfaces can be tested with low test mance of the UCI instrument.
loads, rougher and coarse-grained surfaces require test loads as
9. Verification of the Apparatus
high as possible. However, the surface must always be free of
9.1 Verification Method—Prior to each shift or work period
any impurities (oil, dust, etc.) and rust.
the instrument shall be verified as specified in Part B.Any UCI
The surface roughness should not exceed '30 % of the
hardness testing instrument not meeting the requirements of
penetration depth (Ra# 0.3 3 h) with:
Part B shall not be used for the acceptance testing of products.
Force [N]
h[mm] 5 0.062 3 (2)
Œ
Hardness [HV]
10. Procedure
Penetration depth of the Vickers diamond pyramid for a
10.1 Test Procedure—To perform a hardness test, the probe
certain hardness (in HV) and test load (in N) id is shown in Eq
is connected to the indicating unit and the instrument is turned
2.
on.The probe is held firmly (using a probe grip if needed) with
Table 1 provides the recommended minimal surface rough-
its axis in a perpendicular position relative to the test piece
ness for certain UCI probes that use a Vickers indenter. If
surface. Hold the probe with both hands to achieve the best
surface preparation is necessary, care must be taken not to alter
possible result. Carefully exert steady pressure against the test
the surface hardness by overheating or cold working. Any
piece during the loading phase. Make sure that the vertical
paint, scale or other surface coatings shall be completely
probe position is maintained as long as the load is effective.
removed. Failure to provide adequate surface finish will
Some instruments indicate the end of the measurement by an
produce unsteady readings. Coarse finishes will tend to lower
acoustic signal and display the hardness value instantaneously.
the measured value.
10.2 Alignment—To prevent errors from misalignment
8.2 Minimum Thickness—Thincoatingsorsurfacelayerson
move the UCI probe with slow and steady speed. The probe
bulk material must have a minimum thickness of at least ten
should be perpendicular with respect to the surface. The
times of the indentation depth of the indenter used (see Fig. 3
maximum angular deviation from the perpendicular position
for a Vickers indenter) corresponding to the Bueckle’s rule:
should be less than 5 degrees. Avoid twisting of the probe
S =10 3 h.
min housing. There should be no lateral forces on the indenter.
8.3 Minimum Wall Thickness—Distinct reading variations
Therefore, avoid slip.
may especially occur with a specimen thickness of less than
10.3 Test Direction—Hardness testing according to the UCI
about 15 mm if the test material is excited to resonance or
method generally can be carried out in any direction, without
the necessity of corrections depending on the loading. Ther
...