NBSIR 73-117

M

Fractographic Examination of Sabreliner

Landing Gear Fracture

T. Robert Shives

Metallurgy Division

Institute for Materials Research

National Bureau of Standards

Washington, D. C. 20234

March 1, 1973

Failure Analysis Report

Prepared for Bureau of Aviation Safety

National Transportation Safety Board

Department of Transportation

Washington, D. Co 20591

NBSIR 73-117

FRACTOGRAPHIC EXAMINATION OF SABRELINER LANDING

GEAR FRACTURE

T. Robert Shives

Metallurgy Division

Institute for Materials Research

National Bureau of Standards

Washington, D. C. 20234

March 1, 1973

Failure Analysis Report

"This document has been prepared for the use of Bureau

of Aviation Safety, National Transportation Safety Board,

Department of Transportation, Washington, D. C. Responsibility for its further use rests with that agency.

NBS request that if release to the general public is contemplated, such action be taken only after consultation

with the Office of Public Affairs at the National Bureau

of Standards."

U. S. DEPARTMENT OF COMMERCE, Frederick B. Dent, Secretary

MATIONAL BUREAU OF STANDARDS, Richard W. Roberts. Director

TABLE OF CONTENTS

Page

1. GENERAL INFORMATION 1

1.1 Reference 1

1.2 Accident Identification 1'

1.3 Part Identification 1

2. PURPOSE 1

3 . EXAMINATION 1

4. DISCUSSION AND CONCLUSIONS 2

5 . ACKNOWLEDGEMENT 3

FIGURES

1. Fracture surface of the submitted part as received . . 4

2. View of the fracture 4

3. SEM showing fracture surface in slower crack

propagating region , 5

4. SEM showing fracture surface in slower crack

propagating region 5

5. SEM from fracture surface at location 1, figure 1 ... 6

6. SEM from fracture surface at location 2, figure 1 ... 6

7. SEM from fracture surface at location 3, figure 1 ... 7

I 8. SEM from fracture surface at location 4, figure 1 ... 7

i

I 9. SEM from fracture surface m faster crack

propagating region 8

I 10. Part of field shown in figure 9 » ....... = .. . 8

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Fractographic Examination of Sabreliner

Landing Gear Fracture

1. GENERA.L INFORMATION

1 . 1 Reference

Bureau of Aviation Safety, National Transportation Safety

Board, Department of Transportation, Washington, D. C.

Request by Mr. W. L. Holshouser, September 3, 1972.

1 . 2 Accident Identification

Sabreliner, NA265-40, N360N, White Plains, New York,

August 28, 1972. NTSB accident No. NYC 73-I-N037.

1. 3 Part Identification

A small part from a failed landing gear from the above

mentioned aircraft containing part of a fracture face was

submitted for examination. This part had been cut from a larger part of the failed landing gear. A photomacrograph

of the fracture surface of the submitted part is shown in

figure 1.

2. PURPOSE

The submitting agency requested a fractographic

examination of the part

.

3. EXM^INATION

The crescent shaped area of the fracture was very dark

in color compared to the rest of the fracture surface. The

dark area was the region of apparent slower crack propagation.

The principal crack origin appears to be at the location

indicated by the arrow in figure 1. At least one crack arrest

line could easily be detected in the slower crack propagation

region. There was a fairly sharp change in the fracture

plane at the point where the slowly propagating crack front

stopped and the rapidly propagating crack began (figure 2)

.

After visual and macroscopic examinations, the fracture

surface was cleaned in an ultrasonic cleaner with water and

detergent, and then examined with a scanning electron

microscope. The crescent shaped portion of the fracture

- 1

-

surface v/as covered with a film which was probably composed

of corrosion product. Examples of the film covered surface

are shown in figures 3 and 4. The film was sufficiently

thick in most areas to mask the features of the fracture

surface

.

In order to remove this film, the fracture surface was

cleaned by replication (as for transmission electron microscopy) . Replication was repeated until a clean replica

could be removed from the fracture surface, indicating that

no more material could be removed from the fracture surface

by this technique.

The fracture surface was again examined with a scanning

electron microscope. The fracture was still difficult to

characterize because the effects of corrosion obscured some

of the fracture features.

Near the fracture origin (locations 1 and 2, figure 1)

,

intergranular cracking appeared to be the dominant fracture

mode. Examples of this are shown in figures 5 and 5. In

figure 6, the fracture features are less distinct than in

figure 5. If intergranular cracking is indeed the fracture

mode observed, then the probable mechanism of fracture

exhibited in figures 5 and 6 is stress corrosion cracking.

There was some evidence of corrosion fatigue as shown

in figures 7 and 8 (locations 3 and 4, respectively, figure 1)

.

What appear to be striations can be seen in both figures.

The fracture surface in the faster crack propagating area

beyond the crescent shaped area exhibited dimpled rupture as

shown in figures 9 and 10. The mode of fracture here is

ductile overload.

4. DISCUSSION AND CONCLUSIONS

As mentioned above, it is difficult to arrive at definite

conclusions about the mode of fracture. The best interpretations of the scanning electron photomicrographs indicate that

a crack, which originated at the location shown by the arrow

in figure 1, probably started and propagated initially by

stress corrosion cracking. It then grew by a combination of

stress corrosion cracking and corrosion fatigue. When the

crack had propagated to the end of the dark crescent region,

the remaining cross section of the part failed from ductile

overload.

- 2 -
II

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1
There was a film, probably a corrosion product, on the

slower crack propagating region of the fracture surface.

Repetitive replication was, for the most part, successful

in removing enough of this film so that some of the

features of the fracture surface could be seen.

5. ACKNOWLEDGEMENT

Mr. D. B. Ballard of the Lattice Defects and Microstructures Section assisted in the interpretation of the

scanning electron photomicrographs. Mr. L. C. Smith of the

Mechanical Properties Section assisted in the specimen

preparation for the scanning electron microscope examination.

- 3 -
I
Figure 1. Fracture surface of the submitted part as

received. Arrow indicates fracture origin.

Numbers 1 through 4 indicate areas of the

fracture surface examined with the scanning

electron microscope. X 6

r Figure 2. View of the fracture surface showing the change

in the plane of the fracture at the junction

(arrow) between the slower propagating part of

the fracture and the faster propagating part of

the fracture. X 3

Figure 3. SEM showing fracture surface in slower

crack propagating region before cleaning

by replication. X 1375

Figure 4. SEM showing fracture surface in slower

crack propagating region before cleaning

by replication. X 2400

Figure 5. SEM from fracture surface at location 1,

figure 1, showing apparent intergranular

cracking as the dominant mode of fracture

in this region. Two grain boundaries are

indicated by arrows. X 117 5

Figure 6. SEM from fracture surface at location 2,

figure 1, showing apparent intergranular

cracking as the dominant mode of fracture

in this region. Two grain boundaries are

indicated by arrows. X 115 0

Figure 8. SEM from fracture surface at location 4,

figure 1, showing what may be fatigue

striations. X 2300

Figure 9. SEM from fracture surface in faster crack

propagating region showing dimpled

rupture. X 510

' Figure 10. Part of field shown in figure 9 at

higher magnification. X 2000

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3RM NBS-n4A (1-71) ' U.S. DEPT. OF COMM. 1. HUBLICATIoN OR REPORT NO. \^ Gov't Accession

B.BUOGRAPHIC DATA j NBSIR 73-117 |

3. Recipient's Accession No.

i. TITLE AND SUBTITLE

1 FRACTOGRAPHIC EXAMINATION OF SABRELINER

1 LANDING GEAR FRACTURE

5. Publication Date March, 1973

6. Performing Organization Code

i.AUTHOR(S)

T. Robert Shives

8. Performing Organization

NBSIR 73-117

[.PERFORMING ORGANIZATION NAME AND ADDRESS

1 NATIONAL BUREAU OF STANDARDS

DEPARTMENT OF COMMERCE

WASHINGTON, D.C. 20234

10. Ptoject/Task/'Work Unit No. 3120412

\, Sponsoring Organization Name and Address

1 BUREAU OF AVIATION SAFETY

i National Transportation Safety Board

Department of Transportation

13. Type of Report & Period

Covered Failure

Analysis Report

14. Sponsoring Agency Code

Washington. D. C. 20591

i;. SUPPLEMENTARY NOTES

!

'4. ABSTRACT (A 200-word or less factual summary of most significant information. If document includes a significant

bibliography or literature survey, mention it here.) , Part of a fracture surface from a failed aircraft landing

gear was examined with a scanning electron microscope. The

fracture appeared to have initiated in stress corrosion

cracking, and then propagated in a combination of stress

j corrosion cracking and corrosion fatigue. When the crack had

propagated to the end of the dark, crescent shaped region,

the remaining cross section of the part failed from ductile

j overload.

!

I'. KEY WORDS (Alphabetical order, separated by semicolons) ~~~~ Corrosion fatigue; fatigue; fractography ; stress corrosion cracking

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