There are two aspects in this study: cylinder penetrations and XBP (Expendable Bottom Penetrometer) interpretations. The cylinder studies firstly investigate the relationship between the soil resisting force and penetration depth by a series of rateindependent finite element analyses of pre-embedded penetration depths, and validate the results by upper and lower bound solutions from classical plasticity theory. Furthermore, strain rate effects are modeled by finite element simulations within a framework of rate-dependent plasticity. With all forces acting on the cylinder estimated, penetration depths are predicted from simple equations of motion for a single particle. Comparisons to experimental results show reasonable agreement between model predictions and measurements. The XBP studies follow the same methodology in investigating the soil shearing resistance as a function of penetration depth and velocity by finite element analyses. With the measurements of time decelerations during penetration of the XBP, sediment shear strength profile is inferred from a single particle kinetic model. The predictions compare favorably with experimental measurements by vane shear tests.

Advanced composite materials have enabled the conventional aircraft structures to reduce weight, improve fuel efficiency and offer superior mechanical properties. In the past, materials such as aluminum, steel or titanium have been used to manufacture aircraft structures for support of heavy loads. Within the last decade or so, demand for advanced composite materials have been emerging that offer significant advantages over the traditional metallic materials. Of particular interest in the recent years, there has been an upsurge in scientific significance in the usage of adhesively bonded composite joints (ABCJ’s). ABCJ’s negate the introduction of stress risers that are associated with riveting or other classical techniques. In today’s aircraft transportation market, there is a push to increase structural efficiency by promoting adhesive bonding to primary joining of aircraft structures. This research is focused on the issues associated with the durability and related failures in bonded composite joints that continue to be a critical hindrance to the universal acceptance of ABCJ’s. Of particular interest are the short term strength, contamination and long term durability of ABCJ’s. One of the factors that influence bond performance is contamination and in this study the influence of contamination on composite-adhesive bond quality was investigated through the development of a repeatable and scalable surface contamination procedure. Results showed an increase in the contaminant coverage area decreases the overall bond strength significantly. A direct correlation between the contaminant coverage area and the fracture toughness of the bonded joint was established. Another factor that influences bond performance during an aircraft’s service life is its long term strength upon exposure to harsh environmental conditions or when subjected to severe mechanical loading. A test procedure was successfully developed in order to evaluate durability of ABCJ’s comprising severe environmental conditioning, fatiguing in ambient air and a combination of both. The bonds produced were durable enough to sustain the tests cases mentioned above when conditioned for 8 weeks and did not experience any loss in strength. Specimens that were aged for 80 weeks showed a degradation of 10% in their fracture toughness when compared to their baseline datasets. The effect of various exposure times needs to be further evaluated to establish the relationship of durability that is associated with the fracture toughness of ABCJ’s.