Κίνητρο της παρούσας διατριβής αποτέλεσε η αποτίμηση της δομικής ακεραιότητας κελυφοειδών κατασκευών από σύνθετα υλικά που παρουσιάζουν ανοχή στη βλάβη, με τη χρήση ακουστικών τεχνικών μη καταστροφικού ελέγχου. Στόχος ήταν η πειραματική και θεωρητική μελέτη επίδρασης της αστοχίας, που αναπτύσσεται σε μια πολύστρωτη μετά από φόρτιση, σε μετρήσιμα χαρακτηριστικά της κυματικής διάδοσης. Χωρίζεται σε δύο τμήματα, στη μοντελοποίηση της βλάβης και στη μελέτη επίδρασης αυτής στην κυματική διάδοση. Η έρευνα εστιάστηκε σε μορφές αστοχίας που συναντώνται σε πολύστρωτες υπό επίπεδη εντατική κατάσταση και συσσωρεύεται κατά το πάχος τους στη διάρκεια φόρτισης. Για την προσομοίωση της δημιουργήθηκαν διαφορετικά μηχανικά μοντέλα. Έμφαση δόθηκε στην προσέγγιση της συμπεριφοράς του υλικού υπό μονότονη στατική φόρτιση. Γι’ αυτό αναπτύχθηκε ένα φαινομενολογικό πρότυπο προοδευτικής αστοχίας για gl/ep πολύστρωτες. Η δομή του στηρίχθηκε σε τέσσερις πυλώνες. Πρώτον στην πειραματική διαδικασία χαρακτηρισμού μηχανικών ιδιοτήτων της μονοαξονικής στρώσης, ως το βασικό δομικό υλικό μιας πολύστρωτης. Ο ενδελεχής χαρακτηρισμός του υλικού σπάνια συναντάται σε τέτοια έκταση. Δεύτερον από τις δοκιμές προέκυψαν οι καταστατικές εξισώσεις της στρώσης. Η προσέγγιση της ανισότροπης μη – γραμμικότητας του υλικού έγινε με βηματική, γραμμική ανά βήμα, τασική ανάλυση στο επίπεδο της στρώσης χρησιμοποιώντας εφαπτομενική ελαστικότητα. Ο τρίτος πυλώνας αφορά στον προσδιορισμό έναρξης αστοχίας. Υιοθετήθηκαν κριτήρια ευρείας αποδοχής στο σχεδιασμό με σύνθετα υλικά, όπως π.χ. του Puck, των Shokrieh και Lessard κ.α., προτείνοντας και έναν νέο συνδυασμό τους. Τέλος, στρατηγικές υποβάθμισης των μηχανικών ιδιοτήτων της στρώσης προσομοίωσαν το αποτέλεσμα της συσσώρευσης αστοχίας μετά την έναρξή της. Το πρότυπο προοδευτικής αστοχίας ενσωματώθηκε σε στοιχείο κελύφους εμπορικού κώδικα πεπερασμένων στοιχείων. Ακολούθησε αξιολόγηση του, συγκρίνοντας τα αριθμητικά αποτελέσματα με πλειάδα μονοαξονικών και πρωτότυπων διαξονικών πειραμάτων. Η διαδικασία αυτή οδήγησε αφενός στην σημαντική για τον σχεδιασμό παρατήρηση εξάρτησης του μέτρου διάτμησης από το υπάρχον επίπεδο εντατικό πεδίο και αφετέρου στην εξέλιξη του προτύπου ώστε παρά τον περιορισμό των καταστατικών εξισώσεων που το διέπουν να μπορεί να προσομοιώσει τη διαστρωματική αποκόλληση. Έχοντας αναπτύξει τα εργαλεία περιγραφής της βλάβης, η διατριβή ολοκληρώνεται με τη μελέτη δομικής ακεραιότητας, χρησιμοποιώντας τη μη – καταστροφική τεχνική των ακουστό - υπέρηχων. Παρουσιάζεται το πειραματικό και θεωρητικό υπόβαθρο της διάδοσης τασικών κυμάτων σε κελύφη. Πρότυπα πολύστρωτων που υπέστησαν αριθμητική βλάβη υποβλήθηκαν σε αριθμητικές μη – καταστροφικές δοκιμές, καταλήγοντας σε συμπεράσματα όπως π.χ. τη μείωση της φασικής ταχύτητας με τη συσσώρευση βλάβης. / 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.

O grande desafio da Implantodontia é alcançar resultados a longo prazo com maior preservação dos tecidos ósseos, resposta adequada dos tecidos conjuntivos e manutenção da estabilidade secundária adequada para a retenção de próteses. Estes fatores evitam a perda indesejável tanto do tratamento reabilitador quanto dos tecidos ósseos de suporte. A região extraoral apresenta menores espessuras ósseas em comparação às regiões de maxila e mandíbula, especialmente no osso temporal. Portanto, os seguintes aspectos foram investigados: (i) Análise pelo Método dos Elementos Finitos (FEA) de 16 modelos virtuais, com aplicação de forças estáticas de tensão e compressão nos pontos médios entre os implantes. Três implantes maxilofaciais extraorais foram posicionados no osso temporal, onde um deles foi posicionado sobre o processo mastóide. Este estudo foi totalmente realizado em ambiente computacional. Foram empregados dois tipos de conexões protéticas e intermediários retos de conicidades 20º e 45º, posicionados virtualmente no modelo de osso temporal, com paralelismo entre eles. Foi desenhada uma barra virtual para retenção protética do tipo barra-clipe da prótese auricular. Foram consideradas as melhores configurações aquelas apresentando distribuição uniforme e branda das tensões de von Mises sobre o tecido ósseo adjacente aos implantes. (ii) Confecção de corpos de prova com graus variáveis de pigmentação para (a) melhorar a reprodutibilidade da coloração (b) entender e reduzir o processo de descoloração para melhorar a longevidade das próteses. Um elastômero maxilofacial tipo A foi pigmentado intrinsecamente de acordo com os seis tons da Escala de Fitzpatrick. Uma técnica de pigmentação foi desenvolvida a partir dos resultados obtidos a partir de uma Escala de Fitzpatrick impressa em papel e dos pigmentos intrínsecos de cores primárias. Este dimetil-metilvinil-siloxano reforçado por platina A 223-30 (Factor II, Inc., Lakeside, AZ, USA) apresenta dureza \"Shore-A\" 30. As amostras foram expostas a fotoenvelhecimento acelerado, e sua degradação mapeada com Espectroscopia UV/Vis/NIR. Concluiu-se que: (i) Os implantes com conexão cone Morse plataforma 3.7 tem melhor comportamento biomecânico com intermediários de 45o e altura de 2mm. Sugere-se planejamento cirúrgico visando a instalação a 3 horas para o temporal esquerdo e 9 horas para o temporal direito, mais 6 horas (mastóide). Implantes com conexão cone Morse plataforma 4.0 apresentaram comportamento biomecânico desejável com intermediários de 20o e alturas de 2mm or 4mm. Para implantes com conexão cone Morse plataforma 4.0, sugere-se a instalação a 6-9-12 horas para o temporal direito, e 12-6-3 para o esquerdo, visando comportamento biomecânico adequado. Sugere-se que os implantes extraorais Brånemark hexágono externo com plataforma 4.1 regular ou expandida sejam preferencialmente empregados com intermediários de 20o. (ii) O SiO2 5% pode ser adicionado à preparação do silicone para retardar o desbotamento da prótese maxilofacial. O TiO2 traz mudanças visuais significativas e pode ser considerado como opacificador. / Major challenges in Implantology include: achieving longevity of implants, bone tissue preservation, connective tissue suitable answer and maintenance of secondary stability in order to retain prosthesis. These factors avoid the undesirable loss of both rehabilitation treatment and supporting bone tissues. The extraoral region has less bone depth compared to the maxilla and mandible regions, especially for the temporal bone. Therefore, the following aspects were investigated: (i) Finite Elements Analysis (FEA) of 16 virtual models, with static application of tension and compression forces in medium points between implants. Three extraoral maxillofacial implants were placed on the temporal bone, which one of them was placed on the mastoid process. This study was made entirely in a computational environment. Two prosthetic connection types and straight Intermediários were employed, with conicities of 20º and 45º, placed virtually on the temporal bone model, mutually parallel. A virtual bar for bar-clip prosthetic retention of auricular prosthesis was designed. The best configurations were considered to be the ones presenting uniform and mild von Mises tension distribution over the bone tissue around the implants. (ii) Generation of samples with varying degree of pigmentation to (a) improve the reproducibility of the colouration (b) understand and minimise the discolouration process to improve prosthetics longevity. A maxillofacial elastomer type A was intrinsically pigmented according to the six tones of the Fitzpatrick Scale. A pigmentation technique was developed from spectroscopy outcomes of paper printed Fitzpatrick Scale and the primary colors pigments. This platinum reinforced dimethyl methylvinyl siloxane A 223-30 (Factor II, Inc., Lakeside, AZ, USA) presents \"Shore-A\" hardness 30. The samples were exposed to accelerated photo aging, and their degradation mapped with UV/Vis/NIR Spectroscopy. The effects of exclusion of oxygen and inclusion of nanoparticle fillers during prosthetic formulation were investigated. It was concluded that: (i) Morse taper prosthetic connection 3.7 platform implants, should be employed with 45o abutments with 2mm height. The surgical planning shall be for placement 3 hours for the left temporal bone and 9 hours for the right, and in 6 hours (mastoid). Morse taper prosthetic connection 4.0 platform implants behaved biomechanically desirably with 20o abutments in 2mm or 4mm heights. For the Morse taper connection 4.0 platform implants, their placement shall be in 6-9-12 hours, for the right temporal, and 12-3-6, for the left temporal, in order to achieve proper biomechanical behaviour. The Brånemark extraoral external hexagon implant, with 4.1 platform (normal or expanded) should preferrably be used with 20o abutments. (ii) The SiO2 5% may be added to the silicone preparation in order to slow maxillofacial prosthesis colour fading. The TiO2 brings visually significant changes and may be considered as an opacifier.