http://hdl.handle.net/10256/4388 Sun, 10 Aug 2025 18:43:45 GMT 2025-08-10T18:43:45Z http://hdl.handle.net/10256/26996 A strategy for efficient modelling of composite delamination in large structures Daniel, Pierre M. ENG- Delamination, the separation of composite laminate layers, is a major issue in industries using fibre-reinforced polymers, such as airliners, automobiles and wind turbines. While existing numerical models can accurately simulate delamination, their high computational cost limits large-scale applications. Traditional modelling uses a layerwise approach with fine refinements, increasing computational demand. This research presents a more efficient strategy using an adaptive framework. The model starts with a single element for the laminate’s thickness, adding refinements only where delamination occurs. This approach reduces unnecessary computational effort. A key challenge is detecting the onset of delamination in unrefined models. To address this, a new method reconstructs out-of-plane stresses across the laminate thickness, which is initially modelled with a single element. Once a crack is introduced adaptively, its growth must be modelled using large elements (e.g. 5 mm). An energy-based criterion (Virtual Crack Closure Technique) is coupled to a novel cohesive law modelling the crack advancement while dissipating the fracture energy. A new algorithm extends the energy-based growth criterion to distorted meshes and enables the modelling of complex delamination fronts. Used separately in industry, the stress reconstruction method helps identify high-stress regions in large structures for more detailed analysis, while the energy-based cohesive model enables fast damage tolerance assessments. When combined, these innovations form a novel modelling strategy tailored for large structures. A proof-of-concept test demonstrates that the computational cost is drastically reduced while maintaining accuracy. This research benefits industries relying on composite structures. In aerospace, faster delamination modelling reduces development costs. In automotive applications, it supports the adoption of lightweight composites, improving the energy efficiency of the vehicles. For these reasons, this thesis contributes to the energy transition towards lower greenhouse gas emissions; CAT- La deslaminació, la separació de les capes d'un laminat compost, és un problema important en indústries que utilitzen polímers reforçats amb fibra, com l'aeronàutica, l'automoció i les turbines eòliques. Tot i que els models numèrics existents poden simular amb precisió la deslaminació, el seu alt cost computacional en limita l'aplicació a gran escala. Els mètodes de simulació tradicionals utilitzen un enfocament per capes amb refinaments fins, fet que augmenta la demanda computacional. Aquesta investigació presenta una estratègia més eficient mitjançant un marc adaptatiu. El model comença amb un sol element per al gruix del laminat i afegeix refinaments només allà on es produeix la deslaminació. Aquest enfocament redueix l'esforç computacional innecessari. Un dels principals reptes és detectar l'inici de la deslaminació en models no refinats. Per abordar aquesta qüestió, es proposa un nou mètode que reconstrueix les tensions fora del pla al llarg del gruix del laminat, inicialment simulat amb un sol element. Un cop s'introdueix una esquerda de manera adaptativa, el seu creixement s'ha de simular amb elements grans (per exemple, 5 mm). Un criteri basat en l'energia (tècnica del tancament virtual de l’esquerda del anglès Virtual Crack Closure Technique) es combina amb una nova llei cohesiva per simular la propagació de l'esquerda mentre es dissipa l’energia de fractura. Un nou algorisme amplia el criteri de creixement basat en l'energia a malles distorsionades i permet simular fronts de deslaminació complexos. Utilitzats per separat en la indústria, el mètode de reconstrucció de tensions ajuda a identificar les regions d'alta tensió en estructures grans per a una anàlisi més detallada, mentre que el model cohesiu basat en energia permet avaluacions ràpides de la tolerància als danys. Quan es combinen, aquestes innovacions formen una estratègia de simulació nova adaptada a estructures de gran escala. Una prova de concepte demostra que el cost computacional es redueix dràsticament mentre es manté la precisió. Aquesta investigació beneficia les indústries que dissenyen estructures de materials compostos. En el sector aeroespacial, la simulació més ràpida de la deslaminació redueix els costos de desenvolupament. En aplicacions d'automoció, facilita l'adopció de materials compostos lleugers, millorant l'eficiència energètica dels vehicles. Per aquestes raons, aquesta tesis contribueix a la transició cap a una reducció de les emissions de gasos amb efecte d'hivernacle Mon, 28 Apr 2025 00:00:00 GMT http://hdl.handle.net/10256/26996 2025-04-28T00:00:00Z http://hdl.handle.net/10256/26703 Characterization of the mixed-mode interlaminar fracture toughness of an additive manufacturing continuous carbon fiber reinforced-thermoplastic composite Santos, Jonnathan D.; Fotouhi, Sakineh; Guerrero Garcia, José Manuel; Blanco Villaverde, Norbert There is a lack of knowledge concerning the interlaminar fracture toughness under mixed-mode ratios of 3D-printed composites. In this work, several additive manufacturing (AM) continuous Fiber Reinforced Thermoplastic (cFRT) specimens have been tested to characterize the initiation and propagation of interlaminar fracture toughness under three different mixed-mode GII/(GI + GII) ratios: 25, 50, and 75%. The results obtained do not exhibit the common tendency seen in traditional laminated composite materials, in which the fracture toughness increases with the mixed-mode ratio. While the fracture toughness for the 50% mixed-mode ratio falls between the corresponding mode I and mode II values, the fracture toughness for the 25% and 75% ratios falls outside this range. To provide a reasonable explanation, fractography and microstructure analyses were conducted to quantify fiber, matrix, and void contents. It was concluded that this uncommon behavior is probably related to the intrinsic variability of the material and manufacturing process Thu, 17 Apr 2025 00:00:00 GMT http://hdl.handle.net/10256/26703 2025-04-17T00:00:00Z http://hdl.handle.net/10256/26596 Discrete ply modelling of aeronautical intermediate-scale notched carbon fibre reinforced thermoplastic specimens subjected to multiaxial loading Guerrero Garcia, José Manuel; Bouvet, Christophe; Dufour, John-Eric; Serra, Joël Several finite element models developed at the mesoscale level are available for predicting the strength and failure progression of composite materials. However, this kind of damage models are commonly validated by comparing with typical coupon-scale testing specimens under uniaxial loading, which are not fully representative of aeronautical structures subjected to complex multiaxial loads. In this work, the Discrete Ply Model (DPM) is employed to reproduce intermediate-scale experimental tests carried out on carbon fibre reinforced thermoplastic samples, with a sharp central notch of 100 mm, tested in the VERTEX rig under tension, shear, and combined tension and shear loading. The tests show early buckling (particularly for the shear and combined cases) and development of post-buckling for almost the entire loading. The numerical results obtained demonstrate that the strengths, the fluxes as a function of the applied strains, deformed shapes, buckling modes, crack propagations and failure patterns are predicted with reasonable accuracy Sun, 01 Jun 2025 00:00:00 GMT http://hdl.handle.net/10256/26596 2025-06-01T00:00:00Z http://hdl.handle.net/10256/26595 Micro-scale fiber/matrix stress concentrations in unidirectional glass/carbon hybrid composites under transverse loading Turan, Ecem; Guerrero Garcia, José Manuel; Lomov, Stepan V.; Sabuncuoglu, Baris Fiber/matrix interface stresses and micro-scale stress concentrations (SCs) under transverse loading were analyzed for hybrid composites, reinforced with glass and carbon fibers. A finite element model was implemented using parametric modeling technique to determine the stresses in the matrix and fiber/ matrix interface. Several micro-scale finite element models were generated for the analyses with various combinations of fiber material, fiber size, volume ratio and fiber spatial distribution models. Models with single fiber type (non-hybrid composites) were also analyzed to understand the hybridization effect on the stresses. The results reveal the effect of the presence of different fiber types and their arrangement on the micro-scale stress distributions and fiber/ matrix interface behavior. Under transverse loading, when the same type of fibers are aligned with the loading direction, the SCs on the stiffer fibers are larger than the case in the composite with the single stiffer fiber type. When these fibers are aligned with the direction perpendicular to the loading, the SCs on the stiffer fibers are lower. Fiber material type was more effective than the fiber size and fiber volume ratio enhances the effect of hybridization on the stress distributions. According to the authors' knowledge this is the first study investigating the transverse SCs in hybrid composites at the micro-scale level Thu, 06 Feb 2025 00:00:00 GMT http://hdl.handle.net/10256/26595 2025-02-06T00:00:00Z