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This study investigates dynamic instability in a high-speed drilling process. A pretwisted beam is used to simulate the drill. The time-dependent nature of the thrust force and the drilling depth is considered in the equation of motion of the drill. A moving Winkler-type elastic foundation assumption is applied to the drill tip to approximate the time-varying boundary conditions in the drilling process. Galerkin's method is used to formulate the characteristic equation in a discrete form. The variation of the instability regions of the drill system is solved and analyzed by employing the multiple-scales perturbation method. The numerical results indicate that the unstable regions suddenly enlarge and shift toward a lower frequency when the drill first contacts the work piece. The effects of the rotational speed, pretwisted angle, and thrust force of the drill on the variation of the dynamic instability in high-speed drilling are also studied and are found to be highly influential. [DOI: 10.1115/1.2722768] Keywords: drilling process, pre-twisted beam, instability

We investigate the effect of fiber elongation on power loss as rays propagate along deformed polymer optical fibers (POFs). Variations in core diameter, incident angle, stress and strain distributions, and necking of the POFs during fiber elongation are studied. The power losses in the deformed POFs are analyzed both experimentally and numerically. Theoretical analysis based on an elastic--plastic finite-element and a planar waveguide assumption is proposed. It is found that fiber elongation significantly affects the power loss in POFs, particularly at higher values of elongation. Good agreement between the measured results and the results simulated from the proposed model is obtained. The maximum difference is less than 5%. Results indicate that the proposed theoretical analysis based on an elastic--plastic finite-element model and a planar waveguide assumption is feasible to predict the power loss variation introduced by elongated deformations. A curve-fitted equation is also proposed to estimate the power loss of POFs under different fiber elongation conditions. OCIS codes: 060.0060, 060.2270, 060.2300, 060.2310.

This paper investigates the variations in dynamic stability of a cracked rotating periodic bladed disk assembly. A bladed disk composed of periodically shrouded blades is used to simulate the coupled periodic structure. To study mode localization, a number of apparently identical blades are distributed periodically around a rigid hub. For simplicity, the rigid hub is considered to be attached to a rigid shaft. The modal localization equations of the rotating cracked assembly are formulated using Hamilton's principle and Galerkin's method. The regions of instability in this cracked assembly are identified by means of the multiple scales perturbation method. The numerical results indicate that the modal localization effect introduced by local blade cracks destabilizes the shrouded blade group. One additional instability band at the localization frequency is introduced from the local crack. Furthermore, it is shown that the stability regions of a cracked rotating bladed disk assembly are significantly dependent on the rotational speed, shroud stiffness, and crack depth.

This study employs an elastic-plastic finite element model to investigate the effect of oblique rail surface crack on the wheel-rail contact stress distribution under partial slip rolling conditions. Numerical simulations are performed to explore the effects of the contact distance and tractive force on the contact pressure and tangential stress distributions, tip plastic energy, and critical wheel applied load. Contact elements are used to simulate the interaction between the surfaces of the wheel rail and the crack. The numerical results indicate that the contact stress distributions are influenced significantly by the presence of oblique cracks in the rail. The results also indicate that a higher friction force is induced on the crack surfaces when a greater tractive force is applied to the wheel. This increased crack surface friction force reduces the sliding between the crack surfaces and hence causes a reduction in the tip plastic energy. [DOI: 10.1115/1.2033006]

Dynamic equations of the interminent-motion of a globoidal cam driven system were derived in this study. The effects of roller mesh flexibility and cam profile curve on the residual vibration of a globoidal cam system were studied experimentally and numerically. Time varying roller mesh stiffness and damping coefficients were used to account for the periodic variation of the mesh stiffness in the dwell and the active periods respectively. Dynamic responses of a globoidal cam system in the active and the dwell periods were simulated and measured. The effects of cam profile and input shaft speed on the residual vibration were also studied in this work. Results indicated that the proposed model was feasible for the dynamic simulation of a globoidal cam system. [DOI: 10.1115/1.1767182]

This paper investigates the tip characteristics of an oblique crack in the wheel-rail contact problem. The wheel-rail normal contact pressure and interfacial shear stress distributions, and the stress intensity factors (SIF), are studied for oblique cracks of different inclinations, and the variations in both contact stress distributions near the crack edge are simulated under normal and traction loads, respectively. Contact elements are employed to model the interactions between the wheel-rail contact surfaces and the crack surfaces, respectively. The effects of crack orientation, crack length, and contact distance on the contact stress distributions and stress intensity factors, [K.sub.I] and [K.sub.II], are investigated. The results indicate that a wheel-rail traction force reduces [K.sub.II] significantly as the contact point travels over the crack edge. Furthermore, fluctuations in [K.sub.I] and [K.sub.II] are very significant with regard to early squat propagation of cracks. The results also demonstrate that applying Carter's contact model or the full slip contact model to the same wheel-rail contact crack problem yields significantly different stress intensity factor values.

Dual-in-line package (DIP) and butterfly package with fiber pigtails are widely used package styles in laser-based transmitters in lightwave communication systems. There is only limited information on optoelectronic joining applications where joint strength is important for package reliability, in spite of many studies on the laser welding technique. The dependence of laser beam penetration on the Au coating thickness in dual-in-line constructions has been studied and the experimental measurements are presented, using the finite-element method.