HAL Id: jpa-00222421
https://hal.archives-ouvertes.fr/jpa-00222421
Submitted on 1 Jan 1982
HAL is a multi-disciplinary open access archive for the deposit and dissemination of sci- entific research documents, whether they are pub- lished or not. The documents may come from teaching and research institutions in France or abroad, or from public or private research centers.
L’archive ouverte pluridisciplinaire HAL, est destinée au dépôt et à la diffusion de documents scientifiques de niveau recherche, publiés ou non, émanant des établissements d’enseignement et de recherche français ou étrangers, des laboratoires publics ou privés.
STRENGTH OF OPTICAL FIBRES UNDER
COMBINED STRESSES AND AGING IN VARIOUS ENVIRONMENTS
A. Zaganiaris, J. Balay, A. Guillerme
To cite this version:
A. Zaganiaris, J. Balay, A. Guillerme. STRENGTH OF OPTICAL FIBRES UNDER COMBINED
STRESSES AND AGING IN VARIOUS ENVIRONMENTS. Journal de Physique Colloques, 1982,
43 (C9), pp.C9-587-C9-590. �10.1051/jphyscol:19829116�. �jpa-00222421�
STRENGTH OF OPTICAL FIBRES UNDER COMBINED STRESSES AND AGING IN VARIOUS ENVIRONMENTS
A. Zaganiaris, J.J. Balay and A. Guillerme
Centre National d'Etudes des Telecommunications, Route de Tregastel, 22301 Lannion, France
Résumé.~ Ce papier est un appercu des différents paramètres déterminant, du point de vue mécanique, des fibres optiques. A la lumière de la mécanique des cassures, des statistiques et analyses fractographiques de Weibull, quelques résultats sont pré- sentés et discutés.
Des évaluations des temps de vie faites dans différentes conditions sont présentées comme étant une fonction des propriétés mécaniques des fibres.
L'analyse de la configuration des contraintes corrélëes est liée à l'hypothèse réaliste que les fibres seront soumises dans les conditions expérimentales à un champ de contraintes complexe-
Les résultats obtenus, avec ceux de la stabilité à court et long terme des points de fusion sont particulièrement importants dans le domaine de la construction mé- canique.
Abstract. This paper is an overview of the various parameters determining the mechanical behaviour of the optical fibres . Some recent results are presented and discussed in the light of fracture mechanics, Weibull statistics and surface fractographic analysis.
Lifetime evaluations under various service environments are presented as a function of the mechanical properties of the fibre.
The combined stress configuration analysis is tied to the realistic assumption that the fibres will be subjected in operation conditions to a complex stress field.
The results together with those of short and long, term stability of fusion splices, are particularly important to engineering field installations.
As low-loss fibres are now routinely produced in many laboratories, the interest is being shifted towards the mechanical resistance and other properties whose knowledge seems necessary for use of the waveguides in a practical system.
The influence of the surface state on the fibre strength has to be particularly studied in order to avoid prematurate aging <Df the fibers and to choose the appro- priate outer protection of them.
Few data have been published on this field, most of them reporting statistical results of breaking tensile strength tests of fibers with different plastic protec- tions .
In this paper we present statistical results concerning the breaking strength, under combined torsional and tensile stresses, of various fibres are presented on Weibull plots. The relative resistance loss due to torsion is in good agreement with the theoretical calculations. On the other hand, static and dynamic fatigue experi- ments on a large number of fibre samples simultaneously are described and lifetime predictions are made from these results.
A variety of coatings was tested with respect to the permeability to water, by measuring the fracture stress of a large number of randommized samples previously placed in vacuum, hot moisture and laboratory atmosphere.
One of the starting points of fracture mechanics is the concept of the stress intensity factor Kl. Using Paris equation : K j
c=C
<_)f-^' a.ad the appropriate values for silica : Kj£ =0,798 MPa.m* and Y = 1,24 we can plot the stress to failure versus the initial flaw depth (FIG.O .
Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:19829116
C9-588 JOURNAL DE PHYSIQUE
The f i b r e l i f e t i m e i s e s s e n t i a l l y determined by t h e f i r s t p a r t of t h e (V,KI) p l o t , ( F I G . Z ) , t h e f l a w propagation time f o r t h e second and t h i r d p a r t s being too s h o r t t o be taken i n t o account. We have r e p o r t e d an experimental method f o r r e c o r d i n g t h e f l a w s i z e a s f u n c t i o n of t h e a p p l i e d s t r e s s i n o p t i c a l f i b r e s ( 1 ) . N e v e r t h e l e s s , i n d i r e c t t e c h n i q u e s l i k e s t a t i c and dynamic f a t i g u e a r e mostly used t o o b t a i n
mechanical s t r e n g t h and d u r a b i l i t y d a t a .
During c a b l i n g and e v e n t u a l l y i n s e r v i c e a s w e l l , f i b r e s w i l l undergo combined t o r s i o n a l and t e n s i l e s t r e s s e s . I n t h i s c a s e , t h e e q u i v a l e n t t e n s i l e s t r e s s d ' can be e m r e s s e d a s a f u n c t i o n of t h e number of t o u r s Der u n i t l e n g t h - N.
t h e f i b r e diameter D , breaking s t r e s s and t h e s h e a r
modulus G :
Hence, t h e l o s s of mechanical r e s i s t a n c e due t o t o r s i o n a l s t r e s s i s fi G.D,A/)
showing t h e i n f l u e n c e of t h e i n i t i a l t e n s i l e s t r e n g t h (FIG.3). The Weibull p l o t s
bf o r d i f f e r e n t l e v e l s of a d d i t i o n n a l t o r s i o n a l s t r e s s a r e r e p o r t e d i n FIG.4 i n comparison with t h e p l o t corresponding t o pure t e n s i l e s t r e s s .
The f r a c t u r e s u r f a c e of some f i b r e samples t e s t e d under combined s t r e s s e s were examined on the scanning e l e c t r o n microscope (FIG.5). The r e s u l t s p r e s e n t e d c l e a r l y s h a w some important d e p a r t u r e s from the pure t e n s i l e s t r e s s c a s e . The f a i l u r e o r i g i n i s determined whenever p o s s i b l e and t h e mechanical behavior of t h e f i b r e s under combined s t r e s s e s i s d i s c u s s e d . The experimental s e t up f o r s t a t i c and dynamic f a t i g u e o p e r a t e s with 34 samples simuPtaneously(FIG.6).~he s t a t i c f a t i g u e behavior of d i f f e r e n t CVD f i b r e s was s t u d i e d f o r t h r e e d i f f e r e n t e l o n g a t i o n s ( 2 ) . The f a i l u r e p r o b a b i l i t y i s p l o t t e d v e r s u s the time t o f a i l u r e using a l i n e a r r e g r e s s i o n . ( F I G . 7 ) . The s l o p e of t h i s curve i s and knowing t h e value of m from t h e Weibull p l o t , we can c a l c u l a t e the s t r e s s - c o r r o s i o n s u s c e p t i b i l i t y c o n s t a n t n , and make p o s s i b l e l i f e t i m e p r e d i c t i o n s f o r
Lifetime e v a l u a t i o n s of an average CVD f i b r e a r e shown i n m. The parameters n an B a r e given by s t a t i c o r dynamic f a t i g u e s t a t i s t i c a l t e s t s . L i f e t i m e depends on t h e s e r v i c e permanent s t r e s s G;; and t h e f i b r e i n i t i a l s t r e n g t h (i;.
( I ) - A. ZAGANIARIS, F. ALARD - Revue de Physique Appliquse -
Tome 2 , Mai 1977 - pp. 805-807
( 2 ) - J.P. J A G U I N - ThSse, Univ. de Rennes - Dgcembre 1980.
(3) - A. ZAGANIARIS : 7th E . C . O . C . Proceedingscopenhagen DK.
8-11 Sept. 1981 - p . 8-1.
INITIAL FLAW DEPTH($ fig'
TORSION T O U R /m fig 3
