A master thesis from Aalborg University
Development of test tool for evaluation of cohesive zone parameters in DCB composite specimens
[Udvikling af test værktøj til evaluering af kohæsiv zone parametre i DCB kompositemner]
Author(s)
Term
4. term
Education
Publication year
2014
Submitted on
2014-12-19
Pages
204 pages
Abstract
Dette kandidat projekt på uddannelsen Design af Mekaniske Systemer (DMS) ved Aalborg Universitet, omhandler udviklingen og tilblivelsen af et testfikstur til bestemmelse af brudmekaniske parametre i glasfiberforstærkede, såkaldte double cantilever beam (DCB) emner. Test fiksturet, der er konstrueret på Aalborg Universitet, er i stand til at teste for brudmekaniske revne parametre under modus I såvel som modus II og blandingsmodus mellem I og II. For at verificere testfiksturet er et værktøj fabrikeret, hvorpå strain gauges er monteret. Sammen med digital image correlation (DIC) og en i et specielt fikstur indbygget last celle, har det derved været muligt at verificere at der under tests ikke bliver introduceret urigtige snitkræfter. Test fiksturet har været anvendt til at teste DCB emner fremstillet af glasfiber og epoxy. Som revnestarter er der indlagt en 20 μm tynd slipfilm mellem de midterste lag i laminatet. Der er testet for modus II uden success da ingen revnevækst blev observeret. For blandingsmodus, med modusforholdet 0.5, er der yderligere udført forsøg. Her blev revnevækst observeret i ét forsøg. Forsøgene måtte dog afbrydes pga. store rotationer af prøveemnet. Derimod er der ved modus I, på bagrund af tests, fundet en kritisk energifrigørelsesgrad, som er anvendt i et programmeret script til brug ved FEM analyse. Her er de ved tests fundne data anvendt til at simulere revnevækst for lignende emner.
This master thesis main goal has been to develop a test tool, to test for fracture mechanics parameters under mode I, mode II and mode mixity loading using pure moments. The tests specimens are double cantilever beam (DCB) specimens, made from fiber reinforced composites. The test tool, that has been developed and manufactured at Aalborg University. For the verification, that the test tool produces the correct moments and no spurious shear forces are introduced during a test, a test device with strain gauges bonded, has been used together with Digital image correlation (DIC). The test tool has been used to test specimens fabricated from fiberglass and epoxy. Here a 20 μm slip film has been inserted between the middle layers to act as a crack starter. Successful mode I tests were conducted and the fracture parameters were used in a programmed finite element script capable of simulating the fracture process of a specimen with the same properties as the one tested.
Keywords
DCB ; Cohesive zone ; Fracture mechanics ; Composite ; glass fiber ; Test ; digital image correlation ; mode I ; Mode II
Documents
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