Browsing by Author "Dr. J. W. Eischen, Committee Member"

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    Calculation of the Generalized Stress Intensity Factors for a V-notched Anisotropic Body
    (2002-04-30) Shipman, Benjamin Howard; Dr. J. W. Eischen, Committee Member; Dr. E. C. Klang, Committee Member; Dr. F. G. Yuan, Committee Chair
    A robust method for calculating a generalized stress intensity factor for a V-notched anisotropic body under symmetric and/or anti-symmetric deformation is derived for plane stress or plane strain. The compact formulation for the generalized stress intensity factors is derived based on Stroh formalism. A path-independent line integral together with an auxiliary field solution, called the interaction M-integral, is utilized to solve for these generalized stress intensity factors. Through numeric evaluation of the interaction M-integral using a finite element solution, the generalized stress intensity factors can be found. These generalized stress intensity factors can be used to predict the failure conditions without the need for a detailed notch-tip field solution. Since the interaction M-integral is path-independent, the calculation can be carried out in the region away from the notch tip where a conventional finite element solution is sufficient to perform this analysis. Numeric results for the generalized stress intensity factors are given for a thin rectangular plate with double edge notches. The specimen geometry used follows that in the ASTM standard D 5379/D 5379M-93 for shear property testing of fiber-reinforced composite materials. The method is first verified for three example problems. Then, the generalized stress intensity factors are given for a wide range of notch depths and angles for isotropic and anisotropic material property cases. Two in-plane fiber orientations of a unidirectional fiber-reinforced graphite/epoxy composite are considered. Two loading cases are given to produce symmetric and anti-symmetric deformation. The generalized stress intensity factor results given here for anti-symmetric deformation are unprecedented.
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    Feasibility Investigation of Laser Welding Aluminum Alloy 7075-T6 through the use of a 300 W, Single-Mode, Ytterbium Fiber Optic Laser.
    (2005-08-07) Paleocrassas, Alexander Grant; Dr. F. Wu, Committee Member; Dr. J. W. Eischen, Committee Member; Dr. J. F. Tu, Committee Chair
    Aluminum alloys are important structural materials because of their high strength to weight ratio. Unfortunately, due to their high reflectivity and complexity in heat treatment, aluminum alloys are some of the hardest metals to be laser welded successfully and very high laser power is usually required. In this study, the feasibility of using a 300 W, Single-Mode, Ytterbium Fiber Optic Laser for aluminum welding is investigated. The objective is to explore an application area with low power and low welding speed. As the fiber laser offers much better beam quality (M2 less than 1.05), the results show that, with proper control of welding parameters, the success of aluminum welding can be achieved at considerably low laser power with minimal formation of typical welding defects (porosity, cracking etc.). However, the focusing becomes highly critical as exceeding a certain power density can lead to defects such as blowholes and porosity. The deepest penetration achieved was just over 1 mm at 300W and 2 mm/sec. Other welding processes achieve about three to four times as much penetration at the expense of seven times more power. Further development of this process can lead to a more efficient use of power.