Sim Working Group of Force

SIM WORKING GROUP OF FORCE

Technical Protocol: Supplementary Comparison of Instrumented Charpy Impact Machines

Introduction

The Charpy test is more than 100 years old and is widely used in laboratories and industries all over the world to obtain information on the impact toughness of materials. This test method became an International Organization for Standardization (ISO) standard in 1983 and an American Society for Testing and Materials (ASTM) standard in 1933. Instrumented Charpy impact testing started as a laboratory curiosity in the early 1920's, but references on force-displacement (and force-time) data for impact loading appeared as early as 1879 [1]. The volume of work on instrumented impact testing increased drastically in the late 1960's. In the early 1970's, ASTM began to consider the standardization of test procedures for instrumented Charpy testing and published the first one in 2009 [2]. ISO issued a test standard for instrumented impact testing in 2000 [3]. Although several international standards have evaluated and standardized both the instrumented Charpy impact test and the non-instrumented test, there remains a need to obtain the impact force more accurately. To accomplish this, an international scale based on SI units needs to be established to reduce bias between National Metrology Institutes (NMIs).

During the ISO TC 164 SC4 meetings in Paris (2011) a comparison of instrumented Charpy tests was discussed as a means to reduce bias between NMIs. As a result of these discussions INMETRO and NIST have developed a plan to compare their results on instrumented Charpy machines.

The National Institute of Standard and Technology (NIST/USA) agrees to act as the Pilot Laboratory of a Supplementary Comparison among the SIM.MWG7 (Inter-American Metrology Institutes. Technical Committee of Mass and Related Quantity-Working Group of Force 7), in cooperation with the National Institute of Metrology Quality and Technology (INMETRO/Brazil) to develop the test protocol and planning for the comparison. The participants and test dates are listed in Table 1.

Table 1: The list of NMIs that have agreed to participate.

NMI, Country / Test Date
NIST, USA / August 2012
INMETRO, Brazil / October 2012
INMETRO, Brazil / December 2012
NIST, USA / February 2013

Procedure

The following technical protocol of this supplementary comparison has been presented to the participants for harmonization.

Test equipment

For this comparison, two sets of 10 reference specimens (supplied by the Pilot Laboratory) shall be tested by the participating Institutes. Each Institute shall carry out the Charpy impact testing and provide the values obtained for the required measurements in the results section. Each participant shall test reference specimens at low and high energy levels using the same instrumented striker and data acquisition system.

The tests shall be conducted according to the ISO 148 Standard Parts 1, 2 and 3 [4-6] and ISO 14556 [3] on instrumented impact testing. Figure 1 gives the dimensions of the standard size Charpy V-notch reference specimen, followed by Table 2 which gives the nominal dimensions and tolerances. Figure 2 shows a cross section of the 8 mm instrumented striker. Table 3 gives a list of the components that shall be received by/shipped to the participants in this supplementary comparison.

Figure 1: Dimensions of the Charpy V-notch reference specimen.

Table 2: Nominal dimensions and tolerances of the Charpy V-notch reference specimen.

Length (L): / 55,00 (+ 0,00; -0,30) mm
Width and height (W and H): / 10,00 ± 0,07 mm
Depth of V-notch (d): / 2,000 ± 0,025 mm
Angle of V-notch (?): / 45,0 ± 1,0 °
Radius of V-notch (R): / 0,250 ± 0,025 mm

Figure 2: The cross section through the striker provides approximate dimensions for the instrumented striker used in this comparison. The strain gauges are positioned on both sides of the 4 mm thick beam that supports the striking edge. The center of the gauge is approximately 7 mm behind the leading edge of the striker and 12 mm down from the top of the striker. The center of strike is about 10 mm from the top of the striker.

Table 3: List of components to be used in the supplementary comparison.

Component / Description
Instrumented striker / Commercially available, MP Testing
Strain amplifier / Commercially available, Micro Measurements
Data acquisition box / Commercially available, National Instruments
Cables
Calibration software / NIST/INMETRO
Data acquisition software / NIST/INMETRO
Data analysis software / NIST/INMETRO
Jig for striker calibration / NIST/INMETRO
Charpy Supplementary comparison data sheet.xls

Prior to conducting measurements, the participants shall calibrate the instrumented striker using a uniaxial machine equipped with a calibrated load cell. The striker is removed from the Charpy machine to perform this calibration. In addition, the laboratories shall document measurements from their last direct verification of the Charpy machine used in the supplementary comparison, and shall also conduct an indirect verification using specimens provided by the Pilot Laboratory. If the indirect verification indicates a significant problem, the problem shall be corrected prior to conducting the instrumented comparison testing.

Assembly of the instrumented striker

The following procedure shall be followed by each participant laboratory to mount the striker on their Charpy impact machines:

- lift and support the pendulum and remove the non-instrumented striker;

- position the instrumented striker on the pendulum and engage the positioning pins;

- torque the bolts to the value 74,6 N·m, as specified by the manufacturer;

- attach the cable to the pendulum arm and ensure there is no interference in the swing path;

- connect the striker cables to the strain amplifier;

- connect the strain amplifier and the encoder to the data acquisition system;

- conduct several impact tests with dummy specimens to seat the striker and check the output signals and re-check the striker bolts torque.

Testing

- Test temperature: (22,0 ± 2,0) ºC;

- test 10 low energy (20 J nominal) reference specimens;

- test 10 high energy (100 J nominal) reference specimens.

Results

The values obtained for impact force, time, calculated displacement (from time/force data), velocity and absorbed energy (from both the encoder and instrumented striker data) shall be reported in the "Charpy Supplementary comparison_data sheet.xls", provided by the Pilot Laboratory with this protocol. The data sheet shall be submitted to the Pilot Laboratory following testing. In addition, the raw data output from the data acquisition system (calibration and test data) shall be submitted to the Pilot Laboratory.

Status Report of Progress

The instrumented Charpy impact tests are to be performed by each participating laboratory according to the schedule given in Table 1. If circumstances occur that will cause a delay or a change to this schedule, the Pilot Laboratory shall be immediately notified. The Pilot Laboratory will determine how to accommodate the problem.

Transportation

The components listed in Table 3 shall be sent to the participating laboratories in a timely fashion in order to meet the testing schedule given in Table 1. The components are configured to be shipped in a single transport case supplied by the Pilot Laboratory. Each participating Institute shall bear customs and transport costs to receive the components and related administrative fees associated with sending the components back to the Pilot Laboratory.

Upon receipt of the components at a participating laboratory, they shall be inspected for damage and the Pilot Laboratory shall be notified of the receipt as soon as possible by email or fax using the form given in Annex A. If any of the items listed in Table 2 appears to be damaged, the damage shall be described in detail and testing shall be postponed until the Pilot Laboratory gets in contact.

The broken reference specimens shall be packaged and returned to the Pilot Laboratory prior to shipping the instrumented testing components. The broken reference specimens shall be taped together as pairs and their fracture surfaces shall be protected. The specimens shall be assigned their own identification numbers that correspond to the data report.

The instrumented striker and data acquisition system shall be re-packaged in the transport case for shipping. A shipping number will be provided by the Pilot Laboratory. The shipping addresses for the participants are given in Annex B. Immediately after shipping the components, notify the Pilot Laboratory by email or fax using the form given in Annex A.

General report

The following information shall be provided in the report, as a minimum.

a) A short description of the Charpy impact machine used for the tests and the name of the manufacturer.

b) The results of the instrumented striker calibration.

c) The results of the direct verification of the Charpy impact machine.

d) Deviations from this technical protocol and/or from the reference documents.

e) Raw and characteristic values of impact force and displacement.

f) Characteristic values of impact velocity and absorbed energy.

g) Description of the analysis software.

Uncertainty evaluation

The measurement uncertainty should be estimated according to the ISO GUM [7] and NIST SP960-18 [8]. At least the following quantities affecting the uncertainty shall be documented.

 The measurement uncertainty of the instrumented striker calibration.

 The measurement uncertainty of the direct verification results that can be quantified, such as:

• Measurements of anvils and supports,
• Height of pendulum fall,
• Potential energy,
• Impact velocity,
• Test temperature
• Center of percussion,
• Friction/windage loss, and
• Scale accuracy.

 The measurement uncertainty of the indirect verification tests.

References

[1] B. W. Dunn, A Photographic Impact Testing Machine for Measuring the Varying Intensity of an Impulsive Force, Journal of the Franklin Institute of the State of Pennsylvania, Vol. CXLIV, No. 5, November, 1897.

[2] ASTM E2298 - 09 Standard Test Method for Instrumented Impact Testing of Metallic Materials, American Society for Testing and Materials, West Conshohocken, USA.

[3] ISO 14556 Steel - Charpy V-notch pendulum impact test - Instrumented test method, International Organization for Standardization, Geneva, Switzerland.

[4] ISO 148-1 Metallic materials - Charpy pendulum impact test - Part 1: Test method, International Organization for standardization, Geneva, Switzerland.

[5] ISO 148-2 Metallic materials - Charpy pendulum impact test - Part 2: Verification of test machines, International Organization for standardization, Geneva, Switzerland.

[6] ISO 148-3 Metallic materials - Charpy pendulum impact test - Part 3: Preparation and characterization of Charpy V reference test pieces for verification of test machines, International Organization for standardization, Geneva, Switzerland.

[7] ISO GUM - Guide to the Expression of Uncertainty in Measurement; 1ª edition 1993, corrected and reprinted 1995, International Organization for standardization, Geneva, Switzerland.

[8] NIST SP960-18 - Computing Uncertainty for Charpy Impact Machine Test Results, National Institute of Standards and Technology, Washington, DC, USA.

Annexes

Annex A - Notification of receipt and sending - Form to be sent by e-mail/fax.

Annex B - Addresses of the participating Institutes.

ANNEX A - Notification of receipt and sending - Form to be sent by e-mail/fax

To: / Chris McCowan
NIST, Division 853
325 Broadway
Boulder, CO, 80305-3328
Fax: / + 1 (303) 497-5939
Phone: / + 1 (303) 497-3699
e-mail: /
From:
Fax:
Phone:
E-mail:
Date:

Subject: Supplementary Comparison of Instrumented Charpy Impact Machines - Notification of receipt/sending.

Note: All components should be inspected upon receipt and prior to shipping to the next participant. If damage is observed, before or after commencing measurements, contact the Pilot Laboratory immediately.

Receipt of equipment:

I have received the reference specimens, the instrumented striker and the data acquisition system on ______(specify date). Describe any damage in detail in the Notes section below.

Shipment of equipment:

I have inspected and shipped the reference specimens, the instrumented striker and the data acquisition system on ______(specify date) to:

To:
Fax:
Phone:
E-mail:
Date:

Notes:

Signature:

ANNEX B - Addresses of the participating Institutes

Institute / Address / Tel/Fax/e-mail
NIST - National Institute of Standards and Technology
Material Measurement Laboratory
Materials Reliability Division
Mr. Chris McCowan / NIST, Division 853
325 Broadway
Boulder, CO, USA, 80305-3328 / Tel: + 1 (303) 497-3699
Fax: + 1 (303) 497-5939

INMETRO - Instituto Nacional de Metrologia, Qualidade e Tecnologia
Mechanical Metrology Division
Force Laboratory (Lafor)
Mr. Renato R. Machado / Inmetro/Xerem
Av. N. S. das Gracas, 50, Xerem, 25250-020,
Duque de Caxias, RJ, Brazil / Tel: + 55 21 2679 9050
Fax: + 55 21 2679 9795