A model for the behavior of low-density, open-cell foam under compressive strain is proposed. Using this model, a tractable relationship between the normalized permeability and the applied strain is developed. An experimental study of the effect of strain on the permeability of open-cell polyurethane foams is presented. The experiments are performed using a Newtonian fluid in the fully laminar regime, where viscous forces are assumed to dominate. The model is found to describe the experimental data well and be independent of the foam cell size, the direction of flow with respect to the foam rise direction, and the properties of the saturating fluid. In a companion paper, the model for the permeability of open-cell foam is combined with Darcy's law to give the contribution of viscous fluid flow to the stress-strain response of a reticulated foam under dynamic loading. Published by Elsevier Ltd.

The response of a reticulated, elastomeric foam filled with colloidal silica under dynamic compression is studied. Under compression beyond local strain rates on the order of 1 s−1, the non-Newtonian, colloidal silica-based fluid undergoes dramatic shear thickening and then proceeds to shear thinning. In this regime, the viscosity of the fluid is large enough that the contribution of the foam and the fluid-structure interaction to the stress response of the fluid-filled foam can be neglected. An analytically tractable lubrication model for the stress-strain response of a non-Newtonian fluid-filled, reticulated, elastomeric foam under dynamic compression between two parallel plates at varying instantaneous strain rates is developed. The resulting lubrication model is applicable when the dimension of the foam in the direction of fluid flow (radial) is much greater than that in the direction of loading (axial). The model is found to describe experimental data well for a range of radius to height ratios (∼1–4) and instantaneous strain rates of the foam (1 s−1 to 4×102 s−1). The applicability of this model is discussed and the range of instantaneous strain rates of the foam over which it is valid is presented. Furthermore, the utility of this model is discussed with respect to the design and development of energy absorption and blast wave protection equipment.

Thin-walled, cylindrical structures are found extensively in both engineering components and in nature. The weight to load bearing ratio is a critical element of design of such structures in a variety of engineering applications, including space shuttle fuel tanks, aircraft fuselages, and offshore oil platforms. In nature, thin-walled cylindrical structures are often supported by a honeycomb-or foam-like cellular core, as for example, in plant stems, porcupine quills, or hedgehog spines. Previous studies have suggested that a compliant core increases the buckling resistance of a cylindrical shell over that of a hollow cylinder of the same weight. In this paper, we extend the linear-elastic buckling theory by coupling it with basic plasticity theory to provide a more comprehensive analysis of isotropic, cylindrical shells with compliant cores. We examine the optimal design of a thin-walled cylinder with a compliant core, of given radius and specified materials, for a prescribed load bearing capacity in axial compression. The analysis gives the values of the shell thickness, the core thickness, and the core density that maximize the load bearing capacity of the shell with a compliant core over an equivalent weight hollow shell. The analysis also identifies the optimum ratio of the core modulus to the shell modulus and is supported by a Lagrangian optimization technique. The analysis further discusses the selection of materials in the design of a cylinder with a compliant core, identifying the most suitable material combinations. The performance of a cylinder with a compliant core is compared with competing designs (optimized hat-stiffened shell and optimized sandwich-wall shell). Finally, the challenges associated with achieving the optimal design in practice are discussed, and the potential for practical implementation is explored.

a b s t r a c tThis paper proposes a new methodology for the finite element (FE) modelling of failure in adhesively bonded joints. Cohesive and adhesive failure are treated separately which allows accurate failure predictions for adhesive joints of different thicknesses using a single set of material parameters. In a companion paper (part I), a new smeared-crack model for adhesive joint cohesive failure was proposed and validated. The present contribution gives an in depth investigation into the interaction among plasticity, cohesive failure and adhesive failure, with application to structural joints. Quasi-static FE analyses of double lap-joint specimens with different thicknesses and under different levels of hydrostatic pressure were performed and compared to experimental results. In all the cases studied, the numerical analysis correctly predicts the driving mechanisms and the specimens' final failure. Accurate fatigue life predictions are made with the addition of a Paris based damage law to the interface elements used to model the adhesive failure.

Summary The Bakken is one of the most prolific plays in North America, but even with the deployment of horizontal wells and hydraulic fracturing, anticipated recovery factors under primary depletion are usually in the range of 10% to 20%. Waterflooding has been a nearly ubiquitously deployed technology in conventional reservoirs to enhance recovery beyond primary depletion. However, the Bakken's ultra-tight, largely oil-wet nature limits the potential of waterflooding. Moreover, the challenges associated with sweep after the formation has been hydraulically stimulated must also be overcome. To address these challenges an optimally-spaced well to well surfactant flooding technology is proposed. Optimal well spacing, from a flooding perspective, can mitigate rapid breakthrough while minimizing the distance through the matrix that the injection fluid must travel. An optimally designed chemical system can enhance imbibition rates and favorably alter wettability to enable economic recovery. Moreover, environmental and community benefits can be realized by utilizing abundant produced water to operate a surfactant flooding process in the Bakken. This paper discusses a comprehensive experimental program exploring the potential of surfactant flooding in the Bakken along with a field communication study and corresponding scaled-up, well-to-well flooding models for an optimized surfactant flooding process. Results from the experimental program are provided which showcase the potential of advanced chemical systems. A brief overview of a core-scale natural fracture study and field-scale well-to-well communication study is provided. Lastly, up-scaled models, showing the potential societal and economic benefits that can be attained from an optimally designed surfactant flood, are presented.