Beam (structure)

Abstract: A method is presented in which fracture mechanics is introduced into finite element analysis by means of a model where stresses are assumed to act across a crack as long as it is narrowly opened. This assumption may be regarded as a way of expressing the energy adsorption GC in the energy balance approach, but it is also in agreement with results of tension tests. As a demonstration the method has been applied to the bending of an unreinforced beam, which has led to an explanation of the difference between bending strength and tensile strength, and of the variation in bending strength with beam depth.

Abstract: A method is presented in which fracture mechanics is introduced into finite element analysis by means of a model where stresses are assumed to act across a crack as long as it is narrowly opened. This assumption may be regarded as a way of expressing the energy adsorption GC in the energy balance approach, but it is also in agreement with results of tension tests. As a demonstration the method has been applied to the bending of an unreinforced beam, which has led to an explanation of the difference between bending strength and tensile strength, and of the variation in bending strength with beam depth.

Abstract: This work presents the analytic and experimental development of piezoelectric actuators as elements of intelligent structures, i.e., structures with highly distributed actuators, sensors, and processing networks. Static and dynamic analytic models are derived for segmented piezoelectric actuators that are either bonded to an elastic substructure or embedded in a laminated composite. These models lead to the ability to predict, a priori, the response of the structural member to a command voltage applied to the piezoelectric and give guidance as to the optimal location for actuator placement. A scaling analysis is performed to demonstrate that the effectiveness of piezoelectric actuators is independent of the size of the structure and to evaluate various piezoelectric materials based on their effectiveness in transmitting strain to the substructure. Three test specimens of cantilevered beams were constructed: an aluminum beam with surface-bonded actuators, a glass/epoxy beam with embedded actuators, and a graphite/epoxy beam with embedded actuators. The actuators were used to excite steady-state resonant vibrations in the cantilevered beams. The response of the specimens compared well with those predicted by the analytic models. Static tensile tests performed on glass/epoxy laminates indicated that the embedded actuator reduced the ultimate strength of the laminate by 20%, while not significantly affecting the global elastic modulus of the specimen.

Abstract: It was recently predicted that nondiffracting beams, with beam spots as small as a few wavelengths, can exist and propagate in free space. We report the first experimental investigation of these beams.

Abstract: Tools We Need.- Of Fields and Forces.- Particle Dynamics in Electromagnetic Fields.- Electromagnetic Fields.- Beam Dynamics.- Single Particle Dynamics.- Particle Beams and Phase Space.- Longitudinal Beam Dynamics.- Periodic Focusing Systems.- Beam Parameters.- Particle Beam Parameters.- Vlasov and Fokker-Planck Equations.- Equilibrium Particle Distribution.- Beam Emittance and Lattice Design.- Perturbations.- Perturbations in Beam Dynamics.- Hamiltonian Resonance Theory.- Hamiltonian Nonlinear Beam Dynamics.- Acceleration.- Charged Particle Acceleration.- Beam-Cavity Interaction.- Coupled Motion.- Dynamics of Coupled Motion.- Intense Beams.- Statistical and Collective Effects.- Wake Fields and Instabilities.- Synchrotron Radiation.- Fundamental Processes.- Overview of Synchrotron Radiation.- Theory of Synchrotron Radiation.- Insertion Device Radiation.- Free Electron Lasers.