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Experimental evaluations of impact damage resistance and residual compression strengths after impact are presented for nine laminated fiber reinforced composite material systems. The experiments employ a small scale specimen for assessing the impact damage resistance and impact damage tolerance of these materials. The damage area detected by C-scan is observed to develop linearly with the impact velocity for impact velocities higher than a threshold value. Brittle material systems have lower threshold velocities and higher damage area growth rates than toughened systems. The impact damage resistance of each material system can be characterized with threshold velocity V_c and damage area growth rate C. The residual compressive Strength after impact was observed to decrease linearly with the damage area equivalent diameter. The rate of compressive strength reduction, K_d, has been observed to be independent of the material properties. The impact damage can be simulated from quasi-static indentation test in which the damage due to these two loading conditions are quite similar. The residual compressive strength can also be simulated from specimens with similar damage size resulting from quasi-static indentation load. / Ph. D.

An iterative penalty finite element model is developed for the analysis of three-dimensional coupled incompressible fluid flow and heat transfer problems. The pressure is calculated by solving the momentum equation using known values of velocities, velocity gradients, and flow stresses from previous iteration. An iterative solution algorithm which employs the element-by-element data structure of the finite element equations is used to solve large systems of algebraic equations resulting from finite element models of real world problems. Three different iterative methods (ORTHOMIN, ORTHORES and GMRES) are implemented and tested to determine the efficiency of each algorithm terms of CPU time and storage requirements. Jacobi/Diagonal preconditioning is used to scale the system of equations and improve the convergence of the iterative solvers. The developed iterative penalty finite element model is extended to analyse three-dimensional manufacturing processes such as casting, extrusion and forming of metals. For numerical simulation of extrusion and forming, flow formulation is used since these operations involve large deformations. The viscosity of the metal at elevated temperatures is calculated from the flow stress. The formulation uses the enthalpy method to account for the transfer of latent heat during phase change. The fluid inside the mushy region (between liquid and solid regions) is assumed to obey D’Arcy’s law for flow through porous materials. The permeability of the material is determined as a function of liquid fraction. This forces the velocities in the solid region to zero. In the finite element model, the effects of convection during phase change of the material are included. A method for calculation of the movement of liquid metal-air interface during mold filling process is presented. The developed model predicts the location of the interface (defined by a pseudo-concentration value) by solving for its movement due to forced convection. Also during filling analysis, only the filled and interface elements are used for flow field calculations. / Ph. D.

A numerical model was developed to analyze the effectiveness of active and passive secondary support systems on the stability of a retreating longwall tailgate opening. The range of loading conditions that any tailgate can be subjected to was identified to form the basis of numerical modeling. The tailgate entry was considered as a part of roof-pillar-floor system, whose behavior is controlled largely by the structural integrity of each member. Numerical modeling was then conducted on tailgate openings to determine roof, floor, and rib responses, including failure modes to a variety of loading conditions for wood cribs and roof trusses employed as active and passive means of secondary support. Trends were developed from numerical modeling to determine optimum load capacity and paints of application for reducing the potential for entry failure. / Master of Science

see document conclusions / Master of Science

The objective of this project is to develop a methodology to measure and predict the strength and the stiffness of red alder (Alnus rubra) nailed pallet connections subjected to repetitive loading. Joint tests were conducted to define the mechanical properties of bottom block pallet connections. The primary tests were conducted to define the strength and stiffness of joint specimens tested in cyclic lateral loading, using three different side member thicknesses and four types of nails. Also, the influence of other specific variables on joint performance was evaluated including friction, pattern, moisture content, number of nails per joint, specific gravity, and rate of loading. In total, 23 sets of nailed joint specimens, with 15 replications each, were constructed and tested. The use of a reversing cyclic lateral loading procedure permits documentation of the effect of dynamic loading on the load-slip response of the connection. Analysis of the data included the creation of two envelope curves, the initial and the final (stabilized) curve. The data obtained from the two curves was used to find the “best” model for predicting the strength and stiffness of the connections. Four models were identified but only one of these was found useful for prediction purposes. Finally, experimental capacity loads were found to be at least three times greater than the national design specification allowable design loads. / Master of Science

Poisson's ratio for aluminum is estimated from velocity profile measurements of a free-free beam under dynamic loading conditions A weighted least-squares method is used to select a beam model which is subsequently used to determine the transverse and anticlastic radii of curvature. The model of the beam velocity profile is selected using forward regression with the possible regressor set formed by products of Legendre polynomials in x and y, the two-dimensional coordinates of the beam. The resulting model is manipulated to extract the transverse and anticlastic radii of curvature of the beam which are then used to find local and global estimates of Poisson's ratio. Estimates for Poisson's ratio are found for three different forcing frequencies and three force amplitudes at each frequency. The frequencies selected correspond to the frequencies of the operating shapes dominated by the first, second, and third bending modes. A statistical analysis is performed to assess the quality of the estimates of Poisson's ratio. Results show that the estimates of Poisson fs ratio are dependent on the forcing frequency and forcing amplitude. All estimates are below the accepted value of .33 for aluminum. Contributions of plate modes adversely affect the estimates. Estimates based on the first and third operating shapes exhibit a lower variance than the estimate based on the second operating shapes. / Master of Science