Impact tests are performed on two circular circumferential frame segments using a drop tower apparatus. These frames have a nominal radius of 120 inches, a forty-eight - degree included angle, a thin-walled cross section in the shape of the letter J, and are typical of the transverse fuselage frames found in a large transport aircraft. The material is a 2D triaxial braided composite of carbon fiber yarns. Impact speeds of the 91.6 lb drop mass are 23.7 ft/s or less. This speed range is the order of the vertical speed considered in a survivable crash on a runway. Transient response characteristics and failure sequence are compared to nominally identical frames tested quasi-statically in a previous study. The peak load at the first major failure event and the corresponding displacement are larger in impact tests than in the quasi-static tests. However, the fracture sequence in the vicinity of the impact location is similar to what was observed in the static tests. Preliminary transient simulations of the frame impact tests using the LSDyna software were also performed. Using the available composite material failure criteria in the software, reasonable correlation was achieved between the simulation and the tests on the load-displacement plot. The computed strains distributions did not compare as well to the measured strains at the first major failure event. / Master of Science

Significant proportion of composite industry is currently produced using prepregs, cured in autoclave which is very expensive and time consuming process. Dry textile preforms in conjunction with liquid molding techniques can lead to significant reductions in material costs, manufacturing costs and cycle times. These dry preforms are typically 2D woven or braided fabrics which also required lay-up and have low interlaminar properties. Through thickness reinforcement provides solution for this problem as it gives better interlaminar properties as well as near net shape performing. Various 3D performing methods are discussed and reviewed in this research where 3D weaving comes out as ideal process to develop near net shape preforms with more efficiency and better material performance. This research highlights the advantages and limitations of conventional 3D weaving processes. A number of approaches for improving the flexibility of 3D weaving process have been presented including changing fiber architecture in different sections of the preform, tapering in the width and thickness directions and finally to change the fiber orientation. It is concluded that multi step and taper fabrics can be produced on conventional weaving by some modifications. Furthermore, a novel 3D weaving machine is designed and developed after reviewing various patents and weaving methods to overcome limitations of conventional weaving machine. Key criterions from limitations of conventional weaving processes are considered and modified such as multiple weft insertion, limited warp stuffer movement, linear take-up to develop 3D weaving machine. In order to achieve isotropic material, two textile technologies are combined to get final requirements. 3D weaving can provide us fibres in 0° and 90° direction with through thickness reinforcement, whereas braiding can satisfy the requirement of bias direction fibres. Near net shape preforms such as taper and multistep are produced and laminated. Preliminary testing is performed on these laminates to evaluate fibre architectures. Further work is required in terms of machine modification which can provide weave design flexibility to explore various multilayer weave architectures. Thorough testing is required to evaluate and define structure performance and effect of fibre damage during weaving process.

Cette thèse s'inscrit dans le cadre d'un projet globalde collaboration avec le groupe Cobra Europe. La motivation principale estde comprendre et de modéliser les mécanismes physiques de dégradations etde rupture d'un tissu préalablement conçu pour répondre à un cahier des charges identifié.Ce travail poursuit alors les acquis de la thèse de Piezelen s'intéressant aux mécanismes de dégradation conduisantà la ruine d'un tissu et en introduisant des grandeurs susceptibles d'être une aide à leur conception. Un travail d'investigation expérimentale multi-échelle sur tissus vierge et endommagé est d'abord mis en œuvre afin d'analyser et de caractériser les phénomènes dedégradation qui peuvent y apparaître. Les essais mécaniques de traction résiduelle (avec ou sans cyclage préalable) sont réalisés sur bande (échelle macroscopique) pour déceler une chute de la contrainte à rupture. Les observations par tomographie très haute résolution permettent d'accéder au cœur même des constituants du tissu (échelle mésoscopique). Elles ont révélé la cause principale de la ruine d'un tissu :la rupture des fils de chaîne, avec des informations telles que sa localisation ainsi que l'orientation de la normale à la surface de rupture. Un travail de modélisation multiéchelle est ensuite mené sur le tissu afin de rendrecompte des mécanismes de dégradation observés au préalable. Sous des sollicitationsmacroscopiques représentatives des conditions de service avec lesquellesle tissu considéré est utilisé (traction/flexion), la cellule périodiquedu Volume Elémentaire Représentatif est investiguée. Notammentune analyse très complète de l'état de contraintes (hétérogénéité, gradient, triaxialité, orientation préférentielle) est faite dans les fils de renfort.De cela, des grandeurs jugées pertinentes pour analyser n'importe quel tissu sont identifiées.Ces grandeurs sont en accord avec les observations expérimentales. Elles ontpermis finalement de comprendre et d'expliquer le processus de ruine du tissu.Egalement, avec l'expérience acquise tout au long de ce travail, ces mêmesgrandeurs ont été utilisées en vue d'effectuer le classement de deux types d'architectures tissées. Ceci ouvre la voie pour la troisième thèse qui systématisera et affinera la démarche. / This PhD work is part of global collaboration project with Cobra Europe company.The main motivation is to better understand in order to model the physical degradation mechanisms of woven composite with a well specified design.The present work takes benefit of the results issued from Piezelthesis. It aims at investigating the mechanisms of degradation leading to the failure of woven fabrics but also at introducing relevant parameters dedicated to their design.A multiscale experimental investigation on virgin and degraded samples of fabric is first carried out in order to analyze and characterize the damage phenomena observed within these samples.Tensile tests (with or without pre-cycling) were performed on the composite material (at the macroscopic scale) to detect a decrease in the stress at failure. Tomographic inspections with high resolution allowed for observations inside the constituents of the fabrics (mesoscopic scale)Thus, the main origin of the failure of the fabric was revealed : the warp yarn break with its localisation and information about the orientation of the normal to the fracture surfaces. A multiscale modeling was then performed, motivated by the degradation mechanisms observed previously. Under macroscopic loading representative of in service solicitationapplied to the present woven fabric (tension/bending), the periodic cell of theRepresentative Volume Element was investigated. Namely, a complete analysis of the stress state (heterogeneity, gradient, triaxiality, orientation) is carried out within the reinforcing yarns. It turns out that relevant parameters able to analyze any woven fabric were identified. Their characteristics were in good agreement with the experimental evidences. Furthermore, they allowed for a better understanding of the failure process of the fabric. With the experience acquired during the present work, these parameters were utilized to classify two specific woven architectures.This opens the perspective of a third thesis dedicated to refine and render systematic the present approach.

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