Failure Knowledge Database / 100 Selected Cases

Brittle fracture of Liberty Ships
March 1943, Oregon State, USA
KOBAYASHI, Hideo ( Tokyo Institute of Technology )ONOUE, Hisahiro ( Tomoe Giken Co., Ltd. )(Summary)
As part of the government project during W orld War II, U nited S tates planed c ontinuous b lockconstruction of all-welded cargo vessels (DWT 11000, "Liberty Ship"). The construction was started withoutbreak of the Pacific war from 1942.
2708 L iberty Ships w ere c onstructed fro m 1939 to 1 945. 1031 damages or ac cidents due t o brit tle
fracture w ere reported by April 1, 1946. More t han 200 L iberty Shi ps w ere si nk or d amaged beyond a ll
hope of repair. "Schenectady" is one of those, which broke in two with a large sound when it was moored at
wharf (see Fig. 1).
The accident was caused by occurrence and development of brittle crack, which were due to the lack of
fracture toughness of welded joint. The accident should be the most expensive and huge scale experimentsof t he ce ntury. Th e accident show ed im portance of fr acture toughness, w hich m arked t he b irth of t hefracture mechanics.
1. Component
Cargo vessel “Schenectady” (DWT 11000 Liberty Ship) (T-2 tanker)
2. Event
By executive order of President Roosevelt, the United States started the production of all-welded cargovessel (DWT 11000 Liberty Ships) in 1942 in order to meet the demands of the Pacific War.
These cargo vessels were used as troopships of large amount of military logistics to ensure eventual US
victory in the Pacific. These ships were, therefore named “Liberty Ships.”
Nineteen pre- existing s hipyards a nd eighteen newly built sh ipyards were set aside for the e xclusive
construction of the Li berty Ships. A total of thir ty-seven factories worked night and day on an assemblyline i n or der to produce t he Li berty Shi ps. W elded st ructure of the shi p e nable the continuous bl ock
manufacturing.

This m anufacturing m ethod of c argo ship w as s imilar t o t hat us ed in Jap an d uring t hesame period.
Since the outbreak of World War II in 1939, the US had been constructing warships. However, the scale
involved in the Liberty Ship construction for th e Pacific War was amazing. Between 1939 and 1945, thethirty-seven shipyards produced 5,777 ships (2,708 were Liberty Ships) which were equivalent to DWT 56
million.
Many damages and accidents of cargo vessel were occurred, and especially for Liberty Ships. The vast
majority of these accidents were related to brittle fracture. By 1st of April 1946, 1441 cases of damage had1

Failure Knowledge Database / 100 Selected Cases

been reported for 970 cargo vessels, 1031 of which were to Liberty Ships. Total numbers of 4720 damages
were reported.
These numbers vary by source. Parker's work states that the number of construction of cargo vessel was
4694 and t hat th e n umber of dam aged L iberty Sh ips was 12 89 w ith 2 33 b eing s unk or incurring s erious
damage. It is im portant to keep in mind the discrepancies due to the difference of assortment and counting
period.
Occurrence and progress of brittle cracks may result i n catastrophic failure if the condition is satisfied.
In January 1943 at the Oregon shipyard, the Liberty Ship "Schenectady" suddenly broke in two with a large
sound when it was mooring at outfitting basin. In March 1943 at the outside New York port, “Manhattan”,
which was on sailing, was also broke in two. A total of seven ships were broken like this.
3. Course
A comm ittee for in vestigating t hese ac cidents of c argo vessels w as est ablished i n 1943.

The rep ort

completed three years thereafter on July 15th, 1946, and the committee was dissolved.
The investigation into the cause of the accidents was wide-ranging and systematic research on structure
and welding. The interim report suggested the importance of modification of structural design that reduces
stress concentrations, improvement of w eld quality that eliminates initial defect, and reduction of residual
stresses by weld ing. Howe ver, th e lack of st eel t oughness was n ot suf ficiently reco gnized; i nsufficientattention w as paid for t he material. It w as on ly co nsidered that “ rimmed steel” is preferred t han “ killedsteel”. So-c alled “ welding s teel” whi ch possesses supe rior fract ure t oughness a nd weld crack resista nce
was not used in the wartime. The production of the welding steel was started after the war. It was regulated
to use for vessel's body later.
The final report concluded that the number of accidents due to welding structure was statistically small
and it w ill h ave n o pr oblem by the cou ntermeasures. It is also s tated that t he c onstruction of the large
number of cargo vessels enable the transportation of military logistics which helped the victory. Overall theproject, t herefore, w as t hought suc cess. Th e res ults of th is re port sh ow U S nationality of p ositive
philosophy whic h kept affirming the we lding j oints in spite of the m any accidents. The L iberty shi p
program had technical pr oblems, but w hen c ombined w ith v ictory in World War II, it w as hailed as asuccess. This program w hich depends on t he stre ngth of U S's material su periority w as jus t li ke U S.
Technology progresses with failures.
The accidents should be the most expensive and huge scale experiments of the century. The accidents
showed importance of fracture toughness, which marked the birth of the fracture mechanics.
4. Cause
At the present day, it is t hought that the low weldability of steel was the m ain cause of the acc idents.
Furthermore, secondary causes included both the stress concentration due to poor design and initial defectof welding.
Steel experiences ductile fracture at high temperatures and brittle fracture at low temperatures; therefore,
steel s hows t he c haracteristic of d uctile-to-brittle transition. Bri ttle fractur e us ually occ urs under t he2

Failure Knowledge Database / 100 Selected Casesconditions of low-temperature, high-loading rate, and multi-axial stress constraint, which can be evaluatedby Charpy Impact Test. Absorption energy measured by the tes t is c alled the notch toughness. Low notch
toughness at low temperature is oft en the cause of brittle fracture. In other words, notch toughness at l ow
temperature should be high to prevent brittle fracture. The low weldability of steel induces both a reductionof notches toughness at low temperature and weld crack.
The brittle fr actures t hat occurred i n the Li berty Sh ips w ere c aused by low n otch toughness at low
temperature of steel a t wel ded j oint, w hich start ed at w eld crac ks or stress c oncentration points of thestructure. External forces o r residual stress due to w elding progress the frac ture. Almost all ac cidents bybrittle fract ures occ urred i n w inter (low tem perature). In so me cases, residual stress ismain cause of

fracture, which was typified by the accident of Schenectady ship.
5. Immediate Action
The L iberty Ship ac cidents generated i nternational interest i n d eveloping hi gh weld ability st eels. The
conclusion is to i ncrease notch t oughness at l ow te mperature. M etallurgical i mprovement such as low
carbonization or addition of deoxidization element Mn and Si is effective to prevent weld crack.
On the other hand, t heory of fracture m echanics th at was origi nated in physics was app lied t o th e
problem of britt le fracture. And then, fracture mechanics were syste matized in the engineering mechanics
field. This takes the form of expressing the intensity of a stress field around a crack tip through the use of
the stress intensity factor K. If this value exceeds the fracture property Kc of the material then fracture mayoccur. Fracture property of material Kc is called fracture toughness. Fracture toughness was taken over thenotch toughness. The introduction of fra cture mechanics has m ade the quantitative assessment of f racture
toughness possible.

As a consequence, brittle fracture accidents rarely occur now.

6. Countermeasure- Use of high weldability steels in order to ensure notch toughness at low temperature.
- Quantitative assessment of brittle fracture by fracture mechanics.
7. Knowledge
Through the Liberty Ship accidents, several problems of welding structure - such as fracture toughness
at l ow tem perature, wel d defect, re sidual st ress du e to wel ding, an d wel ded st ructures whi ch co uld notprevent cr ack growth as c ompared t o t he rivete d st ructures - bec ame clear .

The rea lization of thes e

problems marks the start of the discipline of fracture mechanics.
The important precept was, however, the size effect which affect the fracture pattern. The main materialof ship is low carbon steel. Small size sp ecimen test of the st eel shows elongation before fract ure (plasticcollapse) whi le large str ucture m ade by sam e material s hows a lmost no plast ic def ormation (fracturetoughness). Even ductile materials, therefore, shows same fracture pattern as brittle materials.
8. Background
Iron m anufacturing t echnology has completed i n 19th ce ntury. Th e 20 th c entury w as t he ce ntury of3

Failure Knowledge Database / 100 Selected Cases

mass production and consumption of iron and steel. At the beginning of the 20th century, the center of ironand s teel m anufacturing m oved from Europ e t o t he US. The firm , " US S teel," had a st eel output t hat
matched the entire German steel production.

Furthermore, the two world wars caused large increases insteel c onsumption. A s a conse quence o f the resul tant incre ase i n steel production, a ccidents related t ofracture of iron and steel started to increase. In order to cope with increased demand, the welded joint wasused to replace the riveted joint. The large number of accident related to brittle fracture that occurred atwelded joint led to the systematization of fracture mechanics.
9. On the Side
Griffith is generally considered to have founded fracture mechanics in 1921, but in truth it was probablyCharpy in 1912. As fracture has been a problem for human being from the use of tools, a few papers about
fracture w ere repor ted e ven b efore 20th c entury. Fr om the 19th to 20th ce ntury after th e i ndustrial
revolution (from the 18th to 19th ce nturies), heavy industry was bloo ming business. As a result, however ,many acci dents rel ated to brittle fract ure were experienced. T hese ac cidents w ere due t o the l ack ofunderstanding of the d uctile-to-brittle transition c haracteristics of st eels, whi ch were ne ver r ecognized
before. Engineers were confused because high strength and ductile steels showed low strength and brittle
property which were never expected. Charpy clarified the ductile-to-brittle transition property of steels anddeveloped the Charpy Impact Test to evaluate it.
In ge neral, s mall test pieces subjec ted t o te nsile l oading at room t emperature fr acture i n a ductile
manner aft er plastic defor mation where as l arge se ctions, especially at low tem peratures, fa il at less thantheir maximum tensile strength, a phenomenon that is known as brittle fracture.
Brittle fracture is usually caused under the conditions.
(1) Low temperature(2) High deformation rate(3) Increase of plasti c constraint (or triaxial stre ss) due t o lar ge size or existence of structural
discontinuities such as notches
It is required to have sufficient toughness or low ductile-to-brittle transition temperature under service
conditions.
The Charpy Impact Test can evaluate the du ctile-to-brittle transition. The test uses a sp ecimen with anotch w hich gives stro ng plastic constraint. A bsorption energy is measured w ith various spec imen
temperature (this is not ambient temperature) by applying a hummer impact to obtain high deformation rate
(see figure 2).
The objectives of the Charpy Impact Test is to determine:(1) Absorption energy(2) Ductile-to-brittle transition temperature (see figure 3)
Although absorption e nergy is a q ualitative v alue to e valuate m aterials, the amount can not be use ddirectly to the design in the same way as fracture toughness which is expressed by stress intensity factor.
It is very use ful t o know d uctile-to-brittle tra nsition t emperature of steels. A com ponent c an operat e4

Failure Knowledge Database / 100 Selected Cases

without the risk ofbrittle fracture ifthe serv ice temperature is above the ductil e-to-brittle transition

temperature. As the p lastic cons traint a nd th e d eformation rat e i n th e test is g enerally more severe t han
actual p lastic co nstraint a nd in-ser vice def ormation ra tes, t he d uctile-to-brittle tra nsition temperature
predicted by the test will results in a conservative estimate. Material and design standards often specify theabsorption ener gy rather t han a particular du ctile-to-brittle tra nsition t emperature. This re gulates theabsorption e nergy of upper shelf a t spec ified t emperature. S pecified temperature is above

theductile-to-brittle transition temperature. Specifying the absorption energy is, therefore, essentially the sameas defining a ductile-to-brittle transition temperature.
The Charpy Impact Test is simple and convenient, which is why it has been used for a century. Even in
the field of nuclear power plant, which is most advanced application field of fracture mechanics at present,
reduction of fracture toughness due to neutron radiation is predicted by Charpy Impact Test. In summary,fracture mechanics in the 20th century began and ended with the Charpy Impact Test.
10. Primary Scenario
01. Unknown Cause
02. Occurrence of Unknown Phenomenon
03. Insufficient Analysis or Research
04. Insufficient Prior Research
05. Lack of Reexamination/Review
06. Production
07. Hardware Production
08. Ship Building
09. All-welded Construction
10. Rejection of the Use of Weldability Steel
11. Lack of Notch Toughness at Low Temperature
12. Failure
13. Fracture/Damage
14. Brittle Fracture
15. Failure
16. Large-Scale Damage
17. Hull Breakage
18. Loss to Organization
19. Economic Loss
20. Delay of Termination of the War5Failure Knowledge Database / 100 Selected Cases

Fig. 1

Cargo vessel “Schenectady” which suffered catastrophic failure in calm harbor.

Fig. 2 Charpy Impact Test.

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Failure Knowledge Database / 100 Selected Cases

Absorption energy,Brittle fracture ratio

100%
Brittlefracture
ratio

Absorptionenergy0%Temperature
Fig. 3 Absorption energy, brittle fracture surface ratio vs. temperature.

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