27 KB565 KB25 KB200020242006Ahmed-Benyahia, AliBoukharouba, TaoufikLaksimi, AbdelouahedOuali, Nourdineletnik:40številka:57 stranistr. 199-205ISSN:1580-2949COBISSID:577450URN:URN:NBN:SI:doc-OH04PT9DenInštitut za kovinske materiale in tehnologijeMateriali in tehnologijekompozitilaminatiBehaviour and optimisation of multi-directional laminate specimens under delamination by bending|This work forms part of a study of the behaviour and characterisation of a ( q) multi-directional glass/epoxy composite loaded in modes I and II by bending. For the mode I loading the tests were performed on double cantilever beam (DCB) specimens. These tests resulted in two types of delamination: delamination in the median plan for the low angles (q L 33.5°) and a delamination in staircases for the high angles (33.5° L q L 67.5°). The delamination in staircases creates an unsymmetrical specimen that generates a shear effort in the crack tip and the loading can no longer be considered as pure mode I, but rather a mixed mode (I + II) and sometimes mode (I + II + III). The starting-energy release rate and the propagation energy are often difficult to characterise for these materials, because the start of the delamination is preceded by a transverse cracking of the most tensed plies if the specimen test thickness is relatively weak, and in the propagation phase, the delamination is accompanied by a large rate of transversal cracks. For the low angles, exposed fibres and imprints of fibres is the aspect that dominates the fracture surfaces. Occasional broken fibres and cusps at the intersections of the plan of the rupture with the wefts were also observed. For the large angles, the number of broken fibres is more important than in the case of low angles. A thickness optimisation of the DCB specimen was made in order to avoid the appearance of transverse cracking before the start of the delaminationV tem delu je predstavljen del raziskave vedenja in karakterizacije (plus minusq) večsmernih kompozitov steklo-epoksi, obremenjenih na upogib na način I ali II. Pri načinu I so bili preizkusi obremenietve izvršeni na dvojnih konzolnih nosilcih (DCB). Pri teh preizkusih sta se pojavili dve vrsti delaminacije: delaminacija v osrednji ravnini pri majhnih kotih (qL 35°) in stopničaste delaminacije pri velikih kotih (33,5° L q L 67,5°). Pri tej delaminaciji je nastal asimetrični preizkušanec, ki je ustvaril strig v konici razpoke, zato obremenitev ni bila več čiste vrste I, ampak mešane vrste (I + II), včasih celo (I + II + III). Za te materiale je pogosto težko opredeliti hitrost sprostitve začetne energije in energijo propagacije, ker pred delaminacijo nastanejo prečne razpoke na najbolj obremenjenih plasteh, in če je preizkušanec relativno tanek, pri prapagaciji delaminacijo spremlja velika hitrost nastajanja prečnih razpok. Za majhne kote so značilnost preloma gola vlakna in odtisi teh vlaken. Občasno smo opazili tudi prelomljena vlakna in konice na presečišču ravnine preloma in prečenih vlaken. Pri velikem kotu je število zlomljenih vlaken večje kot pri majhnih kotih. Optimizacije debeline DCB-preizkušanca je bila pripravljena z namenom, da bi preprečili prečno pokanje pred delaminacijoTEXTznanstveno časopisjejournalsSlovenian National E-content AggregatorNational and University Library of SloveniaInštitut za kovinske materiale in tehnologije