NATL INST OF STAND & TECH AlllOb 147610

REFERENCE

NIST Special Publication 260-164

Evaluation Specimens for Izod Impact

Machines (SRM 2115): Report of

Analysis

Tom Siewert

Jolene Splett

Ray Santoyo
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NIST Special Publication 260-164

Evaluation Specimens for Izod Impact

Machines (SRM 2115): Report of

Analysis

Tom Siewert Ray Santoyo

Materials ReliabilityDivision Materials Science and Engineering Laboratory

Jolene Splett

Statistical Engineering Division Information Technology Laboratory National Institute ofStandards and Technology

Boulder, Colorado 80305

October 2006

U.S. Department of Commerce

Carlos M. Gutierrez, Secretary Technology Administration

Robert Cresanti, Under Secretary of Commercefor Technolog}' National Institute of Standards and Technology

William A. Jeffrey, Director
Certain commercial entities, equipment, or materials may be identified in this document in order to describe an experimental procedure or concept adequately. Such

identification is not intended to imply recommendation or endorsement by the National Institute of Standards and Technology, nor is it intended to imply that the

entities, materials, or equipment are necessarily the best available for the purpose.

National Institute of Standards and Technology Special Publication 260-164

Natl. Inst. Stand. Technol. Spec. Publ. 260-164, 10 pages (October 2006)

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Mail: Stop SSOP, Washington, DC 20402-0001
Contents

1. Introduction 1

2. Experimental Design and Analysis 3

3. Material Homogeneity 5

4. Reference Value and Uncertainty 5

5. Discussion 6

6. References 7

iii

Evaluation Specimens for Izod Impact Machines

(SRM2115): Report of Analysis

Tom Siewert,* Jolene Splett, 1 and Ray Santoyo*

National Institute of Standards and Technology

325 Broadway

Boulder, CO 80305

In the past few years, we have received a number of requests to verify the performance of Izod impact machines, similar to what we offer for Charpy impact

machines. Although there are similarities between Izod and Charpy impact

testing, there are some notable differences that needed to be examined, including

test temperature (the Izod configuration precludes cooling), specimen orientation, and specimen length. This report describes the development of a final Izod specimen design and test procedure, that produced a suitable mean energy and a coefficient of variation similar to what is found in the Charpy program. Keywords: impact test; Izod impact; standard reference materials

1. Introduction

ASTM Standard E23, "Standard Test Methods for Notched Bar Impact Testing of Metallic Materials" (Ref. [1]) describes procedures for pendulum impact testing in both Charpy and Izod

configurations. It is most commonly used with the Charpy specimen configurations, and most

users are familiar with verification procedures. However, Standard E23 offers no guidelines for verification of Izod machine performance by test specimens. In fact, there are no known sources

for Izod verification specimens from any national measurement institute around the world. This

report describes the development of such specimens in two steps: (1) investigation of the effects of the differences between the Izod and Charpy configurations, and (2) characterization of the Izod specimens to a degree where they could be used to verify the performance of Izod impact

machines.

^Materials Reliability Division

Materials Science and Engineering Laboratory

Statistical Engineering Division Information Technology Laboratory

1
Figure 1 shows a Charpy impact specimen (on the left) and an Izod specimen (on the right). Both specimens have an identical cross section (10 mm by 10 mm) and an identical V notch

(located 27.5 mm from one end for Charpy specimens and 28 mm from one end for Izod

specimens). Figure 1 also shows a substantial difference in their overall length (55 mm for Charpy and 75 mm for Izod) due to the end clamp design of the Izod configuration.

NIST offers Charpy impact specimens in a variety of energies (from near 15 J to 200 J) that are designed to span the capacity range of most impact machines. For the initial evaluation of Izod machines, we decided to start with a single energy range, and selected the material used in the low-energy range for Charpy machines (SRM 2092). The material is heat treated to the highest

strength, so it has a high resistance to fracture but for only a short period of time (Ref. [2]), which produces a fairly low absorbed energy value, near 15 J on a Charpy machine. As the force must be counterbalanced by the machine, this sharp blow also translates to a quick shock load to the machine anvil and striker, an effective, yet simple evaluation of the quality of the machine

and its mounts. However, the Izod test procedure requires aligning and clamping the specimen in an Izod vise (a relatively slow process), and so this necessitates testing at room temperature,

instead of the -40 °C temperature used for the SRM 2092 Charpy procedure. This upward shift in temperature was expected to raise the absorbed energy slightly, and is one example of the procedural changes that needed to be evaluated.

Figure 1. Photograph comparing a Charpy specimen (left) and Izod specimen (right).

2
2. Experimental Design and Analysis

A group of Izod specimens was machined and heat treated along with one of our standard batches of low-energy Charpy reference specimens (LL104), using the same shop and steel. The

specimens were all tested at the same time, in the NIST Charpy reference laboratory by the same

technician. Standard Charpy specimens will fit in an Izod machine, but not vice versa. Thus, we

decided to test all feasible combinations of specimens and machines to validate the Izod results. Data were collected at room temperature for the two kinds of specimens, Izod and Charpy, as follows.

1 . A NIST Charpy reference machine was used to test five Charpy specimens.

(Charpy/Charpy)

2. A NIST Izod machine was used to test five Charpy specimens. (Izod 1 /Charpy)

3. A NIST Izod machine was used to test 25 Izod specimens. (Izod 1 /Izod)

4. An external Izod machine was used to test 10 Izod specimens. (Izod2/Izod) The raw data are shown in Figure 2 for each of the four machine/specimen combinations, or treatment groups.

Visual inspection of the raw data indicates that there is greater variation in measurements

obtained with the NIST Izod machine than measurements obtained with the NIST Charpy

machine, regardless of specimen type. In addition, the data points do not overlap at all for

Energy, J

18

141 , * , ,

1 Charpy/Charpy IzocH/Charpy lzod1/lzod Izod^/lzcd Machine Type / Specimen Type

Figure 2. Measurement results for four treatment groups. Some test results are nominally the same, so not all data points are visible on the graph.

3
Charpy/Charpy and Izodl/Charpy treatment groups. The apparent discrepancy between the two NIST machines (Charpy and Izodl) can be attributed to the difference in toss energy, as only one end of the specimen is free to move as the specimen is struck in the Izod configuration. The

possible shift in data means between Charpy specimens tested in the NIST Izod machine to Izod specimens tested in the NIST Izod machine might be at least partially explained by a change in stiffness between the two specimens in the Izod mount. The external Izod machine appears to agree with the NIST Izod machine fairly well. The values for Charpy specimens tested on the Charpy machine at room temperature were several joules higher than the certified value of LL104 (tested at -40 °C), a quite reasonable and expected difference. Figure 3 displays group means along with error bars (±2sJ^n~j ). A one-way analysis of variance to compare group means indicates that at least one mean is different from the others (p value <0.0001). Next, we compared each group to Izodl /Izod

separately to determine whether other treatment groups can validate the Izodl /Izod results. Table

1 displays the results of the comparisons of the individual treatment groups.

Mean, J

18

17

16

14 Charpy/Charpy Izodl/Charpy Izodl/lzod lzod2/lzod Machine Type / Specimen Type Mean energy H— 2*standard error

Figure 3. Treatment group means with error bars. The error bars are twice the standard error of the mean.

Table 1 . Pairwise comparisons of treatment group means.

4
Parameter Estimate, J Stand, error, J t Value Pr > |t| Charpy/Charpy - Izodl/Izod 0.893 0.249 3.59 0.0009 Izodl/Charpy - Izodl/Izod -0.950 0.249 -3.82 0.0004

Izod2/Izod - Izodl/Izod 0.176 0.190 0.93 0.4

Table 2. Summary statistics for Izod data. Izod machine #1 - NIST Izod machine #2 - External

ni 25 10 xi 15.836 J 16.012 J si 0.522 J 0.375 J u{xi ) = sj^ni 0.104 J 0.119 J 24 9

The analysis indicates that the means of the Izodl/Izod and Izod2/Izod treatment groups do not

differ significantly. However, the means for both Charpy/Charpy and Izodl/Charpy treatment groups differ significantly from Izodl/Izod. Thus, only the Izod2/Izod data can be used to confirm the Izodl/Izod data. The Charpy specimens measured on the NIST Izod machine do not (and were not expected to) validate the Izodl/Izod measurements, but do show the differences between (a) Izod specimens tested in an Izod machine, and (b) Charpy specimens in an Izod machine or Charpy specimens in a Charpy machine.

3. Material Homogeneity

The manufacturing process for Izod specimens was identical to that for Charpy specimens, the only difference being that the Izod specimens were machined to slightly different dimensional

specifications than those of Charpy specimens. Thus, the batch of Izod specimens is considered

to be fairly homogeneous, based on past experience with specimens manufactured for the Charpy

verification program.

4. Reference Value and Uncertainty

Table 2 displays the information necessary to compute the reference value and its associated

uncertainty for batch LL104 of Izod SRM specimens. The measurement equation used to determine the reference value is Y = X + B,

5
where X = xl = 15.836 J is the mean of the 25 measurements of Izod specimens taken on the NIST Izod machine, and B is an unknown bias that has a Type B rectangular distribution centered about zero. The reference value is 7 = ^ + 5 = 15.836 + 0 = 15.836 J. We used a method called BOB (Type B on Bias) to compute the uncertainty of the reference value using the NIST Izod within-machine variation and the variation between the two Izod machines. (See Ref. [3] for details regarding the BOB method.) The within-machine uncertainty, u(X) = u(x] ) = 0. 104 J, was computed using the 25 measurements on the NIST Izod machine and has vx = vx = 24 degrees of freedom. The between-machine uncertainty u(B) and associated degrees of freedom vB , ^) = ^J^36-16.012L QQ51

^

2V3 2V3

j(*2

u

2 (x, ) + u2 (x2 ) 0.62 => 1,

were computed based on the rectangular Type B distribution. The combined standard uncertainty of the reference value is

uc (Y) = ^u 2 (X) + ir (B) = yl(0A04)

2 +(0.051)2 =0.116 J. The Satterthwaite approximation (Ref. [4]) was used to compute the effective degrees of freedom

as follows:

oc = t "' {Y\ = 4= 15.5=>15. u\X)

| u\B) (0.104)

4

| (0.051)

4 vx vB 24 1

Thus, the expanded uncertainty associated with a 95 % confidence interval is u = Wis (wc ) = 2. 1 3 1(0. 116) = 0.247 J

.

6
5. Discussion

The results presented in this document indicate that an Izod machine verification program similar

to that for Charpy machines is feasible. We developed appropriate test methods and validated the NIST Izod measurement results with a secondary Izod machine. We computed a reference value and its associated uncertainty. The data for the two Izod machines agree well, but Izod data do

not agree with Charpy data, even when specimens are produced from the same batch of material. This disagreement may be due to inherent differences between the two types of machines, such

as, for example, differences in toss energy for the two machines.

6. References

[1] ASTM Standard E23, Standard test methods for notched bar impact testing of metallic

materials, ASTM International, West Conshohocken, Pennsylvania (2005).

[2] C. N. McCowan, T. A. Siewert, and D. P. Vigliotti, Charpy verification program:

Reports covering 1989-2002, NIST Technical Note 1500-9 (September 2003), p. 10.

[3] Levenson, M. S., Banks, D. L., Eberhardt, K. R., Gill, L. M, Guthrie, W. F., Liu, H. K., Vangel, M. G., Yen, J. H., and Zhang, N. F., An approach to combining results from multiple methods motivated by the ISO GUM, NIST Journal of Research 105(4): 571-579 (July-August

2000).

[4] B. N. Taylor and C. E. Kuyatt, Guidelines for evaluating and expressing uncertainty in NIST measurement results, NIST Technical Note 1297 (1994).

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