Static Failure Analysis of Composite Tube with Ply Drops Subjected to Combined Bending and Compression Loads
Author
Pastor, Ines Ruiz
Term
4. term
Education
Publication year
2018
Abstract
Denne afhandling undersøger en alternativ eksperimentel metode til at studere trykbrud i kompositrør med indlejrede lagafslutninger (ply drops). Ved at påføre en excentrisk trykkraft på et unidirektionelt E-glas/polyester-rør skabes en kombineret belastningstilstand af tryk og bøjning, som lokalt forstærker spændingerne ved ply drop. Tre VARTM-fremstillede rør med intern ply drop blev testet quasi-statisk med centreret og excentrisk last (a = 2R/3), suppleret af last–forskydningsmålinger, strain gauges og videoregistrering. Under centreret tryk opnåede røret en brudlast på 188 kN med abrupt fiberbrud langs hele omkredsen ved den øvre ply drop. Ved excentrisk last reduceredes brudlasten til 135–138 kN, og videodata viste delaminationsinitiering omkring 110 kN før endeligt brud. Strainmålinger bekræftede høje tøjninger i den tynde sektion og en svagt belastet zone på den modsatte side, i overensstemmelse med kombineret tryk–bøjning. Brududviklingen initierede ved ply drop som delamination og fortsatte med kink-banding til fiberbrud. En finittelementmodel blev anvendt til at analysere mulige spændingskomponenter, der udløser brud, og til at sammenligne fjernfeltets spændingstilstand med konventionelle fladprøver; fjernfeltet i røret er lidt mere komplekst, men opsætningen kan fungere som et benchmark for trykmodeller af kompositter med indlejrede ply drops.
This thesis investigates an alternative experimental approach to study compressive failure in composite tubes with embedded ply drops. By applying an eccentric compressive load to a unidirectional E-glass/polyester tube, a combined compression–bending state is created that concentrates stresses near the ply drop. Three VARTM-fabricated tubes with an internal ply drop were tested quasi-statically under centered and eccentric loading (a = 2R/3), with load–displacement measurements, strain gauges, and video recording. Under centered compression the tube failed at 188 kN by sudden fiber fracture around the circumference at the upper ply drop. With eccentric loading, failure loads decreased to 135–138 kN, and video captured delamination initiation at about 110 kN prior to final failure. Strain measurements confirmed elevated strains in the thin section and a lightly loaded opposite side, consistent with combined compression–bending. Failure initiated at the ply drop as delamination, progressed via kink-banding, and led to fiber failure. A finite element model was used to analyze stress components that may trigger initiation and to compare the far-field stress state with flat specimens; although the far-field stresses in the tube are slightly more complex, the setup could serve as a benchmark case for compression models of composites with embedded ply drops.
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