Aluminum is used as a structural member in marine applications because of its low weight. One challenge is to design against failure of aluminum structures in fire. A parametric study was performed to quantify the effects of parameters on the compression failure of aluminum plates during a fire. A thermo-structural apparatus was designed to perform compression tests on aluminum samples consisting of a compression load frame, a hydraulic system, and electric heaters. The effect of dimensional variation on failure behavior was examined. Aluminum 5083 and 6082 alloys were tested with three thicknesses, two lengths and two widths. Three heat fluxes and various buckling stresses were used. Micro Vicker's hardness values were measured before and after testing to quantify the effect of heating on the strength of the aluminum. In general, lower applied stress resulted in higher failure temperature and longer time to failure. Dimensional variations had a negligible effect on failure behavior. The 5083 alloy has a minimum stress level of 50% of the buckling stress at 10kW/m2 and 10% of the buckling stress at 20kW/m2, while the 6082 alloy has a minimum stress level of 75% of the buckling stress at 10kW/m2 and 25% of the buckling stress at 20kW/m2. The 6082 failed at higher temperatures and longer failure times than the 5083. The presence of insulation on the exposed surface decreased the temperature rise, resulting in longer failure times. Vicker's hardness decreased with heating in general. The results describe the effects of parameters of the failure of aluminum. / Master of Science

The interest in the use of aluminum as a structural material in marine applications has increased greatly in recent years. This increase is primarily due to the low weight of aluminum compared to other structural materials as well as its ability to resist corrosion. However, a critical issue in the use of any structural material for naval applications is its response to fire. Past experience has shown that finite element programs can produce accurate predictions of failure of structural components. Parameter studies conducted within finite element programs are often easier to implement than corresponding studies conducted experimentally. In this work, the compression-controlled failures of aluminum plates subjected to an applied mechanical load and an applied heat flux (to simulate fire) were predicted through the use of finite element analysis. Numerous studies were completed on these finite element models. Thicknesses of the plates were varied as well as the applied heat flux and the applied compressive stresses. The effect of surface emissivity along with the effect of insulation on the exposed surface of the plate was also studied. The influence of the initial imperfection of the plates was also studied. Not only were the physical conditions of the model varied but the element type of both the solid and shell models as well as the mesh density were also varied. Two different creep laws were used to curve fit raw creep data to understand the effects of creep in the buckling failure of the aluminum plates. These predictions were compared with experiments (from a previous study) conducted on aluminum plates of approximately 800mm in length, 200mm in width, 6-9mm in thickness and clamped at both ends to create fixed boundary conditions. A hydraulic system and a heater were used to apply the compressive load and the heat flux respectively. Comparisons between predicted and experimental results reveal that finite element analysis can accurately predict the compression-controlled failure of aluminum plates subjected to simulated fire. However, under certain combinations of the applied heat flux and compressive stress, the mesh density as well as the choice of element may have a significant impact on the results. Also, it is undetermined which creep curve-fitting model produces the most accurate results due to the influence of other parameters such as the initial imperfection. / Master of Science

Les nids d'abeille d’aluminium combinent légèreté et grande capacité d’absorption d'énergie. Ils sont alors de plus en plus utilisés dans les secteurs du transport (automobile, aéronautique …) pour contribuer conjointement à l’allègement structural et à la sécurité. Dans cette thèse, le comportement à l’écrasement des nids d'abeille est étudié en tenant compte de l'effet combiné de l'angle d'orientation dans le plan des cellules, de l’angle de chargement et de la vitesse de sollicitation, que la littérature ne relate pas. Un dispositif de chargement mixte compression/cisaillement est conçu pour mener l’étude expérimentale. L’analyse des résultats porte sur le pic initial d’effort, le plateau d’effort, ainsi que sur les modes de déformation. Les résultats montrent une augmentation de la résistance sous sollicitation dynamique dépendante de l’angle de chargement Ψ. Elle devient moins significative quand l’angle de chargement augmente jusqu’à atteindre un angle critique. Pour Ψ > Ψcritique, les réponses quasi-statiques sont même plus élevées que les réponses dynamiques. Une étude numérique est alors entreprise. Elle permet de comprendre ce phénomène qui est imputé aux mécanismes de déformation locaux des cellules. Les résultats numériques montrent également que l’effet de l’angle d’orientation □ dans le plan est plus prononcé sur la force tangentielle que sur la force normale, que cela influence également les modes d’effondrement et donc la réponse mécanique. Ces simulations numériques, couplées aux résultats expérimentaux, permettent alors de dissocier les composantes normale et tangentielle de la réponse des nids d’abeille et d’identifier les paramètres d'un critère macroscopique de résistance exprimé en fonction de la vitesse d'impact, de l'angle de chargement et de l'angle d'orientation dans le plan. Finalement, dans le but de réduire le coût des simulations numériques, un modèle élément fini (EF) réduit basé sur un critère de périodicité tenant compte de l'angle d'orientation dans le plan est proposé et son domaine de validité est évalué. / Aluminium honeycombs combine lightweight with an efficient energy absorption capability (specific energy). They are widely used as crash energy absorbing and protective structures in a wide range of transport applications (automotive, aircraft …) to reduce energy consumption and greenhouse gas emission. Reducing vehicle mass has however to be done while at least maintaining the same safety levels. In this thesis, the honeycomb behaviour is investigated under mixed shear-compression loadings taking into account the combined effect of the in-plane orientation angle and the impact velocity, which has not been deeply investigated in the literature. Experimental study based on an improvement of a mixed shear-compression loading device is realised. Experimental analysis focuses on the initial peak and average crushing forces as well as the deforming pattern modes. Comparing quasi-static and dynamic results, a dynamic enhancement depending of the loading angle Ψ is observed under mixed shear-compression loading until a critical loading angle (Ψcritical). Beyond, a negative enhancement is observed. Thus, a numerical study is carried out. The negative enhancement phenomenon is attributed to the collapse mechanisms which are affected by the loading angle Ψ. Numerical results also highlight that the in-plane orientation angle has an effect on the collapse mechanisms and consequently on the mechanical response. This effect is more pronounced on the tangential force than the normal force. The combined effect of the in-plane orientation angle and the loading angle is analysed on the three identified deforming pattern modes. Combining numerical and experimental results, the average crushing normal and shear forces are dissociated. Therefore, the parameters of a macroscopic yield criterion for the mixed shear-compression honeycomb behaviour depending of the impact velocity, the loading angle and the in-plane orientation angle are identified. Finally, in order to optimise the cost in CPU-time of the numerical simulation, a reduced FE model based on the periodicity procedure taking into account the in-plane orientation angle is proposed and its validity range is evaluated.

While composite structures exhibit exceptional strength and weight saving possibilities for engineering applications, sometimes their overall cost and/or material performance can limit their usage when compared to conventional structural materials. Meanwhile ‘biocomposites’, composite structures consisting of natural fibers (i.e. bamboo fibers), display higher cost efficiency and unique structural benefits such as ‘sustainability’. This analysis will determine if the integration of these two different types of composites are beneficial to the overall structure. Specifically, the structure will consist of a one internal bamboo veneer biocomposite ply; and two external carbon fiber weave composite plies surrounding the bamboo biocomposite. To acquire results of this study, the hypothesized composite structure will consist of varied trapezoidal corrugated specimens and tested in uniaxial compression loading. Thereafter, this test data will be used to ultimately design, manufacture, and test a structural biocomposite/composite box, intended to carry extremely high compressive loads; relative to its own weight. A finite element analysis of this test will be used to validate experimental data. After running the experiment, the carbon fiber with bamboo test sample results were compared to that of only carbon fiber test sample. The carbon fiber samples resulted in a maximum compressive load difference of only 23% higher loads when compared to the carbon fiber with bamboo, on average. These findings are discussed throughout.