Browsing by Author "Case, Scott Wayne"

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    Mechanics of Fiber-Controlled Behavior in Polymeric Composite Materials
    Case, Scott Wayne (Virginia Tech, 1996-05-28)
    Modern durability and damage tolerance predictions for composite material systems rely on accurate estimates of the local stress and material states for each of the constituents, as well as the manner in which the constituents interact. In this work, an number of approaches to estimating the stress states and interactions are developed. First, an elasticity solution is presented for the problem of a penny-shaped crack in an N-phase composite material system opened by a prescribed normal pressure. The stress state around such a crack is then used to estimate the stress concentrations due to adjacent fiber fractures in a composite materials. The resulting stress concentrations are then used to estimate the tensile strength of the composite. The predicted results are compared with experimental values. In addition, a cumulative damage model for fatigue is presented. Modifications to the model are made to include the effects of variable amplitude loading. These modifications are based upon the use of remaining strength as a damage metric and the definition of an equivalent generalized time. The model is initially validated using results from the literature. Also, experimental data from APC-2 laminates and IM7/K3B laminates are used in the model. The use of such data for notched laminates requires the use of an effective hole size, which is calculated based upon strain distribution measurements. Measured remaining strengths after fatigue loading are compared with the predicted values for specimens fatigued at room temperature and 350°F (177°C).
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    Micromechanics of strength-related phenomena in composite materials
    Case, Scott Wayne (Virginia Tech, 1993-05-05)
    Micromechanical models are presented which can be used to evaluate: stress concentrations in the vicinity of single and multiple fiber fractures in unidirectional composites under axial loading; the tensile strength of unidirectional composites; fiber coatings that can be used to maximize the transverse strain-to-failure and longitudinal shear strain-to-failure of composites; and the compression strength of composite materials containing embedded cylindrically shaped sensors or actuators. In each case, with the exception of the longitudinal shear model, the micromechanical predictions are compared with the experimental results. In the cases of the fiber fracture model and the transverse strain-to-failure model, these experimental results are obtained by employing a macro-model composite. It is demonstrated that the constituents of the macromodel composite can be systematically altered in order to study physical parameters such as fiber volume fraction and fiber coatings.