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ON THE MECHANISM OF PROPOGRATION OF A BRITTLE FRACTURE IN STEEL EUR 286 e

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Work performed by the

Metaalinstituut T.N.O., Delft, Netherlands under the Euratom contract No.068­61­11 RDN

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TRANSACTIONS OF THE METALLURGICAL SOCIETY OF AIME

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Neither the Euratom Co:

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use of a n y information, apparatus, method, or process disclosed in this document m a y not infringe privately owned rights; or $ § M

of any information, a p p a r a t u s , method or process disclosed in this document.

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This reprint is intended for restricted distribution only. It reproduces, by kind permission of the publisher, an article from „TRANSAC-TIONS OF THE METALLURGICAL SOCIETY OF AIME". For further copies please apply to Dr. G. Derge, Editor of the Metal-lurgical Society of AIME, Metals Research Laboratory, Carnegie Institute of Technology Pittsburg 13, Pa (USA)

Dieser Sonderdruck ist für eine beschränkte Verteilung bestimmt. Die Wiedergabe des vorliegenden in „TRANSACTIONS OF THE METALLURGICAL SOCIETY OF AIME" erschienenen Auf-satzes erfolgt mit freundlicher Genehmigung des Herausgebers. Bestel-lungen weiterer Exemplare sind an Dr. G. Derge, Editor of the

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E U R 2 8 6 . e

R E P R I N T

ON T H E MECHANISM OF PROPAGATION OF A B R I T T L E FRACTURE IN STEEL by H.C. van ELST, W.L. K O R B E E and C A . VERBRAAK. European Atomic Energy Community - EURATOM

Work performed by the Metaalinstituut Τ.N.O., Delft, Netherlands, under the Euratom contract No. 068-61-11 RDN.

Reprinted from „Transactions of the Metallurgical Society of AIME". Summary not available.

E U R 2 8 6 . e

R E P R I N T

ON T H E MECHANISM OF PROPAGATION OF A B R I T T L E F R A C T U R E IN STEEL by H.C. van ELST, W.L. K O R B E E and C.A. VERBRAAK. European Atomic Energy' Community - EURATOM

Work performed by the Metaalinstituut Τ.N.O., Delft, Netherlands, under the Euratom contract No. 068-61-11 RDN.

Reprinted from „Transactions of the Metallurgical Society of AIME". Summary not available.

E U R 2 8 6 . e

R E P R I N T

ON T H E MECHANISM OF PROPAGATION OF A B R I T T L E FRACTURE IN STEEL by H.C. van ELST, W.L. K O R B E E and C.A. VERBRAAK. European Atomic Energy Community - EURATOM

Work performed by the Metaalinstituut Τ.N.O., Delft, Netherlands, under the Euratom contract No. 068-61-11 RDN.

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On the Mechanism of Propagation

of a Brittle Fracture in Steel

H. C.

van Eist, W. L

Korbee,

and

C. A. Verbraak

I N a recent paper,1 one of us has presented some

experimental evidence on the relationship between twinning and brittle fracture in steel.

From metallographic examinations of brittle fracture it could be derived that mechanical twins and microcracks are formed already in front of a running brittle fracture. A tentative explanation based on the evaluation of the statistical distribution of mechanical twins vs various angles to the frac­ ture was given in the above mentioned paper. It was suggested that these twins are caused by stress waves emitted by a running brittle fracture.

With the aid of high-speed photography and the use of photo-stress sheet we are now able to study in more detail the propagation of a brittle fracture and the emittance of s t r e s s waves connected with fracture.

A typical example is given in Fig. 1. In this figure a running brittle fracture in an ordinary Thomas steel is shown. The experiment was performed on a Robertson apparatus and the stress waves caused by the fracture were made visible with photo-stress

H.C. V A N ELST, W . L . KORBEE, and C.A. VERBRAAK are Senior Scientist, Electrical Engineer, and Head of the

Department for Basic Research, respectively, Metaalinstituut Τ . N . O . , Delft, The Netherlands. This work is sponsored by EURATOM U.S. Joint R. and D. Board under Contract no. 068-61-11-RDN.

Manuscript submitted June 28, 1962. IMD

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a r e a a new stressfield will be built up, which on r e l e a s e s t a r t s a new s t r e s s wave and the s a m e sequence is repeated. An extensive p r o g r a m m e on the observation of running brittle fracture in various steels is now being performed in our Institute. More detailed description of the phenom­ ena observed and also quantitative calculations will be published in due course.

' C . A. Verbraak: Brittle fracture and twinning in s t e e l , Materialprü­

fung, 1961, vol. 3, no. 10, p. 383.

Fig. 1—Running brittle fracture in Thomassteel. Photo­ graph obtained with a 1 μββο flash of 5 wattsec timed 150 μεβο after the initiation of the fracture. Stress waves recorded with the aid of photo­stress sheet (1/8 in.) glued to the steelplate.

sheet glued to the steel plate. A 1 μβεο flash of 5 wattsec timed 150 μββο after the initiation of the fracture was used in this experiment. F r o m this photograph it can be concluded that s t r e s s waves apparently a r e not emitted continuously but r a t h e r intermittently by the running brittle fracture.

Three different s t r e s s waves emitted by the running fracture at successive times can be seen on the photograph. These were obtained as i s o ­ clinics, where the directions of the principal tensions were parallel and perpendicular to the fracture path {i.e., the direction of polarizer and analyzer respectively). At A a. stressfield is being built up at the tip of the running fracture, at S a s t r e s s wave can be seen that was emitted at an e a r l i e r time, whereas the s t r e s s wave at C was emitted at a still e a r l i e r time and is reflected already by the weld of the testplate.

It is too early yet to draw any definite conclu­ sions. Taking into account, however, our former work we would suggest the following preliminary and tentative mechanisms of the propagation of a brittle fracture. The r e l e a s e of a stressfield at the tip of a running fracture s t a r t s a s t r e s s wave running with a velocity of nearly five times the velocity of the fracture itself. This s t r e s s wave may cause twinning and the formation of m i c r o c r a c k s in front of the fracture until the energy of the s t r e s s wave is dissipated too much to form twins. In the a r e a where twins and microcracks a r e formed the running fracture can now follow an easy path. As soon as the fracture approaches the end of this

TRANSACTIONS OF

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