NBSIR 79-1597

Examination of Components

from a Mahler-Weber PJ-260

Aircraft

T. Robert Shives

Fracture and Deformation Division

Center for Materials Science

National Measurement Laboratory

National Bureau of Standards

Washington, D.C. 20234

Failure Analysis Report

September 1978

Issued January 1979

Prepared for Bureau of Aviation Safety

National Transportation Safety Board

Washington, D.C. 20594

NBSIR 79-1597

EXAMINATION OF COMPONENTS

FROM A MAHLER-WEBER PJ-260

AIRCRAFT

T. Robert Shives

Fracture and Deformation Division

Center for Materials Science

National Measurement Laboratory

National Bureau of Standards

Washington, D.C. 20234

Failure Analysis Report

September 1978

Issued January 1 979

Prepared for Bureau of Aviation Safety

National Transportation Safety Board

Washington, D.C. 20594

U.S. DEPARTMENT OF COMMERCE, Juanita M. Kreps, Secretary

Jordan J. Baruch, Assistant Secretary for Science and Technology

NATIONAL BUREAU OF STANDARDS, Emest Ambler, Director

FIGURES (continued)

11. Representative SEM fractograph from an area away from that indicated

by the arrow in figure 8.

12. Fracture surface of part no. 10 as received at NBS

13. Representative SEM fractograph from part no. 10.

14. Fracture surface of part no. 12 as received at NBS.

15. Representative SEM fractograph from part no. 12.

16. Fracture surface of part no. 17 as received at NBS.

17. Representative SEM fractograph from part no. 17.

18. Longitudinal section intersecting the fracture attached to part no. 2.

19. Section through part no. 5 showing the fracture profile.

20. Longitudinal section through part no. 7 showing the fracture

profile at the top.

21. Longitudinal section through part no. 7 showing the fracture profile

at the top.

22. Longitudinal section through part no. 9 where apparent fatigue

striations were detected.

23. Longitudinal section through part no. 9 where the fracture mode was primarily dimpled rupture.

24. Longitudinal section through part no. 10 showing the fracture profile

at the top.

25. Fracture profiles of the two layers of part no. 12.

26. Longitudinal section through part no. 12 in a region away from the

fracture showing significant secondary cracking.

27. Longitudinal section through part no. 17 showing the fracture profile

at the top.
.
SUMMARY

The National Transportation Safety Board requested that the National

Bureau of Standards characterize the fractures and determine the hardness

of a number of components from a Mahler-Weber PJ-260 aircraft that had

crashed and burned. Of the fractures examined, one exhibited evidence of

a fatigue fracture mechanism. All of the other fractures appeared to

have occurred via ductile overload. One of the components exhibited

significant secondary cracking that had likely occurred before the time

of the aircraft failure. That same component exhibited many large

longitudinal stringer type inclusions.

Examination of Components From a Mahler-Weber PJ-260 Aircraft

1 . INTRODUCTION

1.1 Reference

National Transportation Safety Board, Washington, D.C. 20594. This

examination was conducted at the request of Mr. James F. Wildey II in a letter dated November 15, 1977.

1. 2 Parts Submitted

A number of steel components from the aft fuselage/tail section of a Mahler-Weber PJ-260 aircraft, N4030B, were submitted to the National

Bureau of Standards for examination. The parts, which were labeled 1 through 17, were submitted with the following descriptions:

Part No. Part Description

1 Aft vertical fin spar/fuselage rudder post. This part

mates with part no. 2.

2 Rear tail landing gear spring support and flying wire

attachment.

3 Forward tail landing gear spring attachment tube. Parts

nos. 3, 4, and 5 should mate.

4 Left fuselage diagonal tube.

5 Left lower fuselage longeron.

6 Left forward horizontal stabilizer. Parts nos. 6 and

7 mate

7 Left forward inboard horizontal stabilizer spar.

8 Left rear inboard horizontal stabilizer spar. Parts

nos. 8 and 9 should mate.

9 Left rear inboard horizontal stabilizer spar.

10, 11 Left horizontal stabilizer flying wire attachment bolt.

12 Right fuselage lower (inboard) horizontal strut attach

fitting and bolt.

13 Lower end of right horizontal strut.
.
Part Ho. Part Description

14, 15 Rear fuselage tubes. These tube sections may have been

between part nos. 2 and 3.

16 Left inboard horizontal stabilizer rib.

17 Right horizontal upper (outboard) horizontal strut

attach bolt.

The parts are shown as received at NBS in figure 1.

1. 3 Background Information

The information in this section was furnished by the Federal Aviation

Administration through the National Transportation Safety Board.

The aircraft lost the right horizontal stabilizer strut during

aerobatic flight due to the failure of the right fuselage lower (inboard)

horizontal strut attach fitting and bolt and the right horizontal upper

(outboard) strut attach bolt. The aircraft landed without further incident.

The left horizontal stabilizer strut was removed prior to the next flight.

The aircraft was then flown to approximately 1500 feet (AGL) without the

left and right struts and performed aerobatic maneuvers. After what appeared

to be a normal descent, and during a normal turn at approximately 400 feet

(AGL) , the aircraft appeared to encounter empennage flutter. The left

horizontal tail (horizontal stabilizer and elevator) separated from the

aircraft in flight and the aircraft crashed and burned. One of the rear

fuselage tubes (part no. 14) and the left horizontal tail were found along

the flight path. The other unburned parts were thrown clear of the crash

fire.

The Federal Aviation Administration, through the National Transportation

Safety Board, requested that the following tasks be performed:

1. Characterize the fracture between parts nos. 1 and 2.

2. Characterize the fracture separating parts nos. 3, 4 and 5 and

determine the hardness of the material in these parts.

3. Characterize the fracture between parts nos. 6 and 7 and

determine the hardness of the material.

4. Characterize the fracture between parts nos. 8 and 9 and

determine the hardness of the material.

5. Characterize the fracture between parts nos. 10 and 11.

2. PURPOSE

2

6. Characterize the fracture in part no. 12.

7. Characterize the fracture in part no. 17 and determine whether

part no. 12 or part no. 17 failed first.

3 . RESULTS OF EXAMINATIONS AND TESTS

3 . 1 Fractographic Examination

The fractures were examined macroscopically and with the scanning

electron microscope (SEM) . In those cases where both mating fracture

surfaces were available, only the one appearing to be in the best condition

was examined with the SEM.

For the fracture between parts nos. 1 and 2, the fracture had passed

through part no. 1 adjacent to the point where the two parts had been

welded together. Both fracture surfaces had suffered considerable

mechanical damage as can be seen in figure 2 where both fracture surfaces

are shown. In addition to the mechanical damage, there was a black

deposit on the fracture surfaces and on the surrounding areas. The fracture

surface remaining with part no. 2 was selected for examination with the SEM.

It was cleaned ultrasonically with paint remover to remove the black

deposit, and then with petroleum ether. There appeared to be some corrosion

product on the fracture surface, so some further cleaning was undertaken

with ammonium citrate to remove the rust. An SEM fractograph from this part

is shown in figure 3. The fracture mode is unclear.

Among parts nos. 3, 4 and 5, the fracture surface of part no. 5 appeared

to be in the best condition, even though the material was rather severely

deformed adjacent to the fracture, and the fracture itself had suffered

considerable mechanical damage. The fracture surface of part no. 5 was the

only one of this group that was examined with the SEM. It is shown in

figure 4 as it was received at NBS. In the region of the fracture that had

not been damaged, dimpled rupture was the fracture mode. A representative

fractograph is shown in figure 5.

For the fracture between parts nos. 6 and 7, the fracture passed through

part no. 7 close to the point where part nos. 6 and 7 were welded together.

The fracture surface of the major portion of part no. 7 was examined with

the SEM. As can be seen in figure 6, this fracture exhibited much less

mechanical damage than the previous two fractures that were discussed.

Dimpled rupture was the fracture mode exhibited. A representative fractograph is shown in figure 7.

For the fracture between parts nos. 8 and 9, the fracture surface of

the major portion of part no. 9 was examined with the SEM. This fracture

is shown in figure 8 as it was received at NBS. As can be seen in the

figure, the fracture exhibited rather severe mechanical damage. In a region where there was very little mechanical damage, there was evidence

3

of apparent fatigue striations. This region is indicated by the arrow in

figure 8. Two fractographs showing examples of the striations appear in

figures 9 and 10. The remaining part of the fracture that was examined

with the SEM exhibited dimpled rupture as the fracture mode. A representative

fractograph is shown in figure 11.

For the fracture between parts nos. 10 and 11, part 10 was selected for

examination with the SEM. The fracture surface of part no. 10 is shown as received at NBS in figure 12. There was considereable deformation adjacent

to the fracture of this part, and there was some necking. The fracture mode

exhibited by the fracture was dimpled rupture. A representative fractograph

is shown in figure 13.

The fracture surface of part no. 12 is shown in figure 14 as it was received at NBS. This fracture had been rather severely damaged mechanically

and many of the fracture features had been obliterated. Nevertheless,

dimpled rupture could be seen as the fracture mode. A representative fractograph is shown in figure 15.

The fracture surface of part no. 17 is shown in figure 16 as it was received at NBS. This part did not exhibit the degree of macroscopic

deformation and necking that can be seen in part no. 10. The fracture

mode exhibited by part no. 17 was dimpled rupture. A representative

fractograph is shown in figure 17.

3 . 2 Metallographic Examination

Longitudinal sections intersecting the fractures were taken through the

parts whose fractures were examined with the SEM in order to examine the

fracture profiles and to facilitate taking hardness measurements.

A longitudinal section through the fracture surface of part no. 1 that

was attached to part no. 2 showing the fracture profile appears in figure 18.

At this location, the fracture passed through the heat affected zone in part

no. 1 adjacent to the weld connecting part nos. 1 and 2. A considerable

amount of deformation is exhibited adjacent to the fracture near the outside

surface of part no. 1 (left side of the fracture profile in figure 18) , but

very little deformation is evident adjacent to the rest of the fracture

profile. The fracture profile is relatively smooth. A higher magnification

examination revealed no significant secondary cracking.

Part of the fracture profile of part no. 5 is shown in figure 19. There

was a significant amount of deformation at the fracture adjacent to both the

inside and the outside surfaces of the tubing. The fracture profile is

relatively smooth and there is no significant secondary cracking.

The fracture profiles in two longitudinal sections through part no. 7 are shown in figures 20 and 21. The outside of the tubing wall is at the

right in figure 20 and at the left in figure 21. In both locations, the

4
WBU&

•-

' ml' 'mm

3
fracture profile is about 45° to the longitudinal axis of the tubing. In

figure 21, the fracture appears to pass through the heat affected zone of

the weld connecting part nos. 6 and 7 together, whereas in figure 20, the

fracture passes through material that appears to have no visual effects

from the welding operation — hence, the difference in the microstructure

between the two figures. Some macroscopic deformation was evident near

the fracture in both sections. There was no significant secondary cracking.

Two longitudinal sections through part no. 9 showing the fracture

profile appear in figures 22 and 23. The section shown in figure 22 was taken through the region of the fracture where apparent fatigue striations

were detected. There was some deformation evident in the section shown

in figure 23, but very little in the section shown in figure 22. The

fracture profile in figure 22 is much smoother than that of figure 23. The

reason for the difference in microstructure between the two sections is

analogous to that given above for part no. 7 — namely, in figure 23, the

fracture passed through the heat affected zone of the weld connecting

part nos. 8 and 9, whereas in figure 22, the fracture passed through

material apparently unaffected by the welding operation. There was no significant secondary cracking.

A longitudinal section through part no. 10 showing a portion of the

fracture profile appears in figure 24. There was a considerable amount

of deformation and necking in the vicinity of the fracture. There was no significant secondary cracking.

As can be seen in figure 14, part no. 12 consisted of two layers of

steel at the fracture. At the location where the part was sectioned, there

was some deformation adjacent to the fracture, but very little necking. The

fracture profiles of the two layers are shown in figures 25a and 25b. There

was no significant secondary cracking in the section shown in figure 25a.

There was a small amount of secondary cracking adjacent to the fracture in

the layer shown in figure 25b, but away from the fracture, there was significant secondary cracking. Some of this cracking can be seen in

figure 26 at a magnification of 100X. At higher magnifications, e.g.,

500X, it appeared that the grains in the microstructure terminate at the

cracks, which would imply that the cracks were present before the material

was heat treated. In addition to the cracking, there are a number of

longitudinal stringer type inclusions that parallel the one indicated by

the arrow in figure 26. In some places, the secondary cracking follows the

inclusions.

A longitudinal section through part no. 17 intersecting the fracture is

shown in figure 27. There was some deformation adjacent to the fracture.

There was no significant secondary cracking.

3.3 Hardness Measurements

Rockwell A (HRA) hardness measurements were made on several of the

components. Four measurements were made in each case. The average HRA

value and the HRA range for each component are given in the following table.

5
.

.
The approximately equivalent HRB or HRC average values are given for

convenience

HRA

Component Average Range HRB Equiv. HRC Equiv,

3 61 60-61 99

4 66 65-66 31

5 62 62 23

6 64 63-65 27

7 58 56-59 95

8 64 63-65 27

9 62 61-63 23

4. DISCUSSION

Most of the components had been mechanically damaged before being

submitted for examination. In addition, some of the components were

covered with a black deposit, possibly as a result of the fire that

occurred when the aircraft crashed. Because of the mechanical damage,

some of the fracture features had been obliterated. Nevertheless, it

appeared that all of the fractures except for the one between part nos. 8

and 9 occurred due to ductile overload with dimpled rupture as the

predominant fracture mode. Dimpled rupture is the expected fracture

mode when the fracture mechanism is ductile overload. Several of the

fractures occurred near welds connecting two components.

There was evidence of fatigue striations on the fracture surface of

component no. 9 indicating that a crack had initiated and propagated

some distance via fatigue before the time of the accident. The fatigue

portion of the fracture passed through material that was close to the

weld that connected part nos. 8 and 9.

In part no. 12, the fact that the grains in the microstructure

terminate at the secondary cracks suggests that the cracking was probably

present before the material was heat treated. The very long longitudinal

inclusions in this part are considered detrimental, but they do not appear

to have contributed to the fracture.

The NTSB had requested that NBS determine whether part no. 12 or part no. 17 failed first. It was not ascertained from the results of

the NBS examination which of these parts failed first. However, part

no. 12 did have a defect that was apparently present before the time of

the failure of the aircraft.

6
S

,
In each of the components for which the hardness was determined, the

hardness was rather consistent. There was, however, a significant

variation in hardness among the various components.

5. CONCLUSIONS

1. The fracture surface of part no. 9 exhibited apparent fatigue

striations indicating that fracture probably initiated via a fatigue crack.

2. The fracture surfaces of all the other components that were examined

exhibited dimpled rupture indicating ductile overload as the fracture

mechanism.

3. Part no. 12 exhibited significant secondary cracking. This cracking

was likely present before the failure of the aircraft.

4. Part no. 12 exhibited a significant number of large, detrimental

longitudinal inclusions.

5. Several of the fractures occurred in the vicinity of welds connecting

two components.

6. ACKNOWLEDGEMENT

Metallographic specimen preparation and hardness measurements were

performed by Leonard C. Smith of the NBS Fracture and Deformation Division.

The photographic work was performed by Mr. Smith, and by Todd Eudy and

Marcia Cline, both formerly of the NBS Fracture and Deformation Division.

7
.

.
Figure

1.

Parts

of

the

Mahler-Weber

PJ-260

aircraft

as

received.

Figure

2.

Fracture

surfaces

of

part

no.

1

(top)

and

part

no.

2

(bottom)

as

received

at

NBS

Figure 3. Representative SEM fractograph from part no. 2. X 900

Figure 4. Fracture surface of part no. 5 as received at NBS. X 2

Figure 5. Representative SEM fractograph from part no. 5.

rupture is the primary fracture mode.

Dimpled

X 950

Figure 6.. Fracture surface of part no. 7 as received at NBS. X 2

Figure 7 Representative SEM fractograph from part no. 7. Dimpled

rupture is the primary fracture mode. X 550

Figure 8. Fracture surface of part no. 9 as received at NBS. Arrow

indicates region of apparent fatigue striations as shown

in figures 9 and 10. X 2
1

XJ

X 0 N 0 \ n o X

J
Figure 9. SEM fractograph from the region of the fracture of part no. 9

indicated by the arrow in figure 8. Apparent fatigue

striations are evident. X 610

Figure 10. SEM fractograph from another area of the region indicated

by the arrow in figure 8. Apparent fatigue striations

are evident. X 1210

Figure 11. Representative SEM fractograph from an area away from that

indicated by the arrow in figure 8. The primary fracture

mode is dimpled rupture. X 1300

Figure 12. Fracture surface of part no. 10 as received at NBS. X 5

Figure 13. Representative SEM fractograph from part no. 10.

primary fracture mode is dimpled rupture. X

The

1100

Figure 14. Fracture surface of part no. 12 as received at NBS. X 5

Figure 15. Representative SEM fractograph from part no. 12. The

primary fracture mode exhibited here is dimpled

rupture. X 925

Figure 16. Fracture surface of part no. 17 as received at NBS. X 5

Figure 17. Representative SEM fractograph from part no. 17. The primaryfracture mode exhibited is dimpled rupture. X 1000

Figure 18. Longitudinal section intersecting the fracture attached to

part no. 2. The fracture profile is at the top in the

figure. Deformation is present at the left at the fracture.

The fracture passes through the heat affected zone of the

weld connecting part nos. 1 and 2.

Etchant: 4% picral X 80

Figure 19. Section through part no. 5 showing the fracture profile

(horizontal at the top)

Etchant: 4% picral X 200

Figure 20. Longitudinal section through part no. 7 showing the

fracture profile at the top. In this location, the

fracture passed through material that shows no visual

effects from welding.

Etchant: 4% picral X 100

Figure 21. Longitudinal section through part no. 7 showing the fracture

profile at the top. In this location, the fracture passed

through what appeared to be the heat affected zone of the

weld connecting part nos. 6 and 7.

Etchant: 4% picral X 100

Figure 22. Longitudinal section through part no. 9 where apparent

fatigue striations were detected. The fracture profile

is at the top. At this location, the fracture passed

through material that exhibited no visible effects from

the welding operation.

Etchant: 4% picral X 100

Figure 23. Longitudinal section through part no. 9 where the fracture

mode was primarily dimpled rupture. At this location, the

fracture passed through the heat affected zone of the weld

connecting part nos. 8 and 9.

Etchant: 4% picral X 100

Figure 24. Longitudinal section through part no. 10 showing the

fracture profile at the top.

Etchant: 4% picral X 100

a

b

Figure 25. Fracture profiles of the two layers of part no. 12. The

fracture profiles are at the top in figures a and b. The

layer shown in figure b exhibited secondary cracking away

from the fracture as shown in figure 26.

Etchant: 4% picral X 80

Figure 26.

Figure 27.

Longitudinal section through part no. 12 in a region away

from the fracture showing significant secondary cracking.

The field shown here is from the same section appearing in

figure 25b. In addition to the secondary cracking, there

are a number of long stringer type inclusions evident.

These inclusions are parallel to the longitudinal axis if

the part. The arrow indicates one of the inclusions.

Etchant: 4% picral X 100

1

f.

- gsSgaw 111

lip

* mH

Longitudinal section through part no. 17 showing the fracture

profile at the top.

Etchant: 4% picral X 100

BS-114A (REV. 9-78)

U.S. DEPT. OF COMM.

BIBLIOGRAPHIC DATA

SHEET

1. PUBLICATION OR REPORT NO. 2. Gov't. Access i mi No. 3. Reciptenf s Accession: No.

4. TITLE AND SUBTITLE

EXAMINATION OF COMPONENTS FROM A MAHLER-WEBER

PJ-260 AIRCRAFT

5. Publication Date

S. Performing Organization Code

7. AUTHOR(S)

T. Robert Shives

8. Performing Organ. Report No.

9. PERFORMING ORGANIZATION NAME AND ADDRESS

NATIONAL BUREAU OF STANDARDS

DEPARTMENT OF COMMERCE

WASHINGTON, DC 20234

-.I 11. Contract/Grant No.

12. SPONSORING ORGANIZATION NAME AND COMPLETE ADDRESS (Street, City, state, ZIP)

Bureau of Aviation SafetyNational Transportation Safety Board

Washington, D.C. 20594

13. Type of Report & Period Covered

Failure Analysis Report

15. SUPPLEMENTARY NOTES

| | Document describes a computer program; SF-185, FIPS Software Summary, is attached.

16. ABSTRACT (A 200-word or leas factual summary of moat significant information. If document includes a significant bibliography or

literature survey, mention it here.) The National Transportation Safety Board requested that the National Bureau of

Standards characterize the fractures and determine the hardness of a number of

components from a Mahler-Weber PJ-260 aircraft that had crashed and burned. Of

the fractures examined, one exhibited evidence of a fatigue fracture mechanism.

All of the other fractures appeared to have occurred via ductile overload. One

of the components exhibited significant secondary cracking that had likely

occurred before the time of the aircraft failure. That same component exhibited

many large longitudinal stringer type inclusions.

17. KEY WORDS (six to twelve entries; alphabetical order; capitalize only the first letter of the first key word unleas a proper name;

separated by semicolons)

Aircraft failure; dimpled rupture; ductile failure; fatigue; fatigue striations

18. AVAILABILITY OUnlimited

f~xl For Official Distribution. Do Not Release to NTIS

Order From Sup. of Doc., U.S. Government Printing Office, Washington, DC

20402, SD Stock No. SN003-003-

Order From National Technical Information Service (NTIS), Springfield, VA. 22161

19. SECURITY CLASS 21. NO. OF

(THIS REPORT) PRINTED PAGES

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