Nowadays the research in the space field aims at developing a completely re-usable vehicle, as it would greatly reduce the cost of access to space. For this reason, innovative materials are studied, which can be used in the extreme environment of the re-entry in the atmosphere, in particular the extreme temperatures. Ceramic matrix composites are a class of material with suitable requirements, as they can withstand the structural role even in extreme thermal environment. This thesis is aimed to characterize the tensile behavior of UHTCMC, a unidirectional C⁄(ZrB_2 SiC) composite supplied by CNR ISTEC, focusing on nonlinear aspects and damage tolerance aspects, which are fundamental for the development of a design approach for future re-usable vehicles. Tensile tests are performed for different lamination sequences, obtaining the elastic response, inelastic phenomena, strength and damage modes of the material. Then a numerical model is developed, capable of describing the tensile behavior of the material. A bi-phasic approach is treated, which splits the material properties between two idealized phases, matrix and fibers. A custom VUMAT subroutine is developed and implemented in the SIMULIA Abaqus environment, containing a plasticity model and orthotropic damage. Three different damage laws, function of plastic strains, are calibrated for the matrix phase material to capture the tensile behavior of the specimens with 0°, 90° and 45° oriented plies. The results obtained from the numerical analyses are confronted with the experimental ones, in order to validate the model developed. A good correlation between experimental and numerical results is achieved: the elastic response, as well as the different inelastic behaviors showed by the lamination sequences are correctly captured by the model.
La ricerca spaziale punta allo sviluppo di velivoli completamente riutilizzabili, in modo da poter ridurre notevolmente il costo di accesso allo spazio. Per questo motivo, materiali innovativi vengono continuamente studiati, che posseggano caratteristiche che gli permettano di resistere alle condizioni di estrema temperatura della fase di rientro in atmosfera. I materiali compositi a matrice ceramica sono una classe di materiali che possiede questi requisiti, possono svolgere un ruolo strutturale anche in condizioni di elevate temperature. Questa tesi ha come scopo la caratterizzazione a trazione di UHTCMC, un materiale composito unidirezionale C⁄(ZrB_2 SiC) prodotto da CNR ISTEC, con particolare attenzione alla tolleranza al danno, tipica dell’ambiente aeronautico. Prove di trazione sono eseguite per diverse sequenze di laminazione, ottenendo la risposta elastica, comportamenti inelastici, resistenza e le modalità di rottura del materiale. Un modello numerico viene sviluppato, in grado di descrivere il comportamento a trazione del materiale. Un approccio bifasico, che divide le proprietà del materiale nelle due fasi idealizzate di fibra e matrice, viene utilizzato. Una VUMAT subroutine viene sviluppata e implementata nell’ambiente SIMULIA di Abaqus, contenente un modello di plasticità e danno ortotropo. Tre differenti leggi di danno, funzione delle deformazioni plastiche, vengono calibrate per la fase matrice, per catturare il comportamento a trazione dei provini con strati orientati a 0°, 90° e 45°. I risultati numerici ottenuti vengono confrontati con quelli sperimentali, per validare il modello. Una buona correlazione tra risultati sperimentali e numerici viene ottenuta: la risposta elastica e i diversi comportamenti inelastici delle diverse sequenze di laminazione vengono correttamente catturati dal modello.
Analysis and modelling of mechanical response in ceramic matrix composites for ultra-high temperature applications
ZANARDI, BARTOLOMEO
2021/2022
Abstract
Nowadays the research in the space field aims at developing a completely re-usable vehicle, as it would greatly reduce the cost of access to space. For this reason, innovative materials are studied, which can be used in the extreme environment of the re-entry in the atmosphere, in particular the extreme temperatures. Ceramic matrix composites are a class of material with suitable requirements, as they can withstand the structural role even in extreme thermal environment. This thesis is aimed to characterize the tensile behavior of UHTCMC, a unidirectional C⁄(ZrB_2 SiC) composite supplied by CNR ISTEC, focusing on nonlinear aspects and damage tolerance aspects, which are fundamental for the development of a design approach for future re-usable vehicles. Tensile tests are performed for different lamination sequences, obtaining the elastic response, inelastic phenomena, strength and damage modes of the material. Then a numerical model is developed, capable of describing the tensile behavior of the material. A bi-phasic approach is treated, which splits the material properties between two idealized phases, matrix and fibers. A custom VUMAT subroutine is developed and implemented in the SIMULIA Abaqus environment, containing a plasticity model and orthotropic damage. Three different damage laws, function of plastic strains, are calibrated for the matrix phase material to capture the tensile behavior of the specimens with 0°, 90° and 45° oriented plies. The results obtained from the numerical analyses are confronted with the experimental ones, in order to validate the model developed. A good correlation between experimental and numerical results is achieved: the elastic response, as well as the different inelastic behaviors showed by the lamination sequences are correctly captured by the model.| File | Dimensione | Formato | |
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2022_07_Zanardi.pdf
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https://hdl.handle.net/10589/191727