Progressive damage in multidirectional laminates made of composite materials: its effect on guided wave propagation

Μελέτη διάδοσης τασικών κυμάτων σε πολύστρωτες διατάξεις ινωδών συνθέτων υλικών: αποτίμηση δομικής ακεραιότητας κατασκευαστικών στοιχείων

Progressive damage in multidirectional laminates made of composite materials: its effect on guided wave propagation

Αντωνίου, Αλέξανδρος

Antoniou, Alexandros

PhD Thesis

2009

The motivation for the present research was the integrity estimation of shell – like structures made of damage tolerant composite materials, using acoustic non destructive testing techniques. An experimental and theoretical study was held aiming to investigate the influence of the damage, accumulated in a loaded laminate, in measurable wave propagation characteristics. The thesis is separated in two major parts. One described with detail the damage simulation model and the other the damage effects on the wave propagation and the wave mechanics. The study was focused on damage modes developed in composite laminates under in – plane complex stress fields due to several loading conditions and various mechanical models were developed for simulation purposes. Emphasis was given in the description of the material performance under monotonic static loading. Thus, a phenomenological progressive damage model for gl/ep multiaxial laminates was developed. This was structured based on four pillars. Primarily, as the laminate basic building block, the unidirectional layer was mechanically characterized. Such an extended experimental procedure can hardly be found. Secondly, the test results defined the ply constitutive equation laws. The highly anisotropic material non – linearity was approximated with piece – wise linear incremental layer by layer stress analysis using tangential elasticity. The third pillar regarded the damage initiation conditions. Thus, well defined criteria widely accepted in composite design were implemented i.e. Puck, Shokrieh and Lessard, etc. Finally post failure strategies were deployed, simulating material mechanical properties degradation emerging during damage accumulation. The progressive damage model was incorporated in a shell element of a commercial finite element code. An extended validation procedure took place comparing numerical results with several uniaxial and innovative biaxial test data. During this procedure the G12 shear modulus dependence on the developed plane stress field was thoroughly studied, resulting in recommendations for the designer and the selection of the appropriate modulus value. Additionally, the material model was further enhanced, taking into account incompatible failures with its constitutive equations e.g. delamination. Having developed several tools that described damage existence or accumulation, this dissertation was finished with the structural integrity study, using the acousto – ultrasonics non destructive testing technique. The experimental and theoretical background for stress wave propagation in waveguides was presented. Numerically damaged material models were additionally inspected with numerical non – destructive tests, resulting in specific conclusions for damage effect on measurable wave propagation characteristics, e.g. phase velocity reduction with damage growth.

Επιστήμες Μηχανικού και Τεχνολογία

Μηχανική Υλικών

Structural integrity

Μονοαξονικές δοκιμές

Πρότυπο προοδευτικής αστοχίας

Guided waves

Τασική διάδοση σε κυματοδηγούς

Επιστήμες Μηχανικού και Τεχνολογία

Σχεδιασμός με ανοχή στη βλάβη

Κριτήρια αστοχίας

Anisotropic non - linearity

Biaxial tests

Damage tolerant design

Διαξονικές δοκιμές

Finite elements analysis

Materials Engineering

Acousto - ultrasonics

Πεπερασμένα στοιχεία

Non destructive testing

Engineering and Technology

Ακουστό - υπέρηχοι

Ανισότροπη μη γραμμικότητα

Failure criteria

Uniaxial tests

Μη καταστροφικός έλεγχος

Μηχανική Υλικών

Δομική ακεραιότητα

Progressive damage models

Ελληνική γλώσσα

Πανεπιστήμιο Πατρών

University of Patras

Πανεπιστήμιο Πατρών. Σχολή Πολυτεχνική. Τμήμα Μηχανολόγων και Αεροναυπηγών Μηχανικών. Τομέας Εφαρμοσμένης Μηχανικής

Εθνικό Κέντρο Τεκμηρίωσης και Ηλεκτρονικού Περιεχομένου (ΕΚΤ)

Εθνικό Αρχείο Διδακτορικών Διατριβών

Συλλογή ΕΑΔΔ