JOURNAL OF SOUND AND VIBRATION Journal of Sound and Vibration 299 (2007) 1049–1073 Dynamic lateral torsional post-buckling of a beam-mass system: Experiments O. Yogev, I. Bucher, M.B. Rubin à Faculty of Mechanical Engineering, Technion—Israel Institute of Technology, 32000 Haifa, Israel Received 9 January 2006; received in revised form 3 August 2006; accepted 9 August 2006 Available online 4 October 2006 Abstract The phenomenon of static lateral torsional buckling of a beam with a narrow rectangular cross-section is well known. Specifically, a beam is clamped at one of its ends and is subjected to a shear force at its other end which causes deformation in the principal plane with stiffest resistance to bending. Above a critical value of load, a bifurcation occurs and the beam twists and experiences out-of-plane deformation which tends to transfer bending to the plane of weakest resistance. Here, attention is focused on an experimental study of dynamic lateral torsional buckling. In the experiment, a beam is attached to the shaft of a motor at one of its ends and a relatively large mass is attached to its other end. Rotation of the motor causes deflection of the beam in its principal plane of stiffest bending resistance. By increasing the excitation frequency and/or amplitude of oscillation of the motor’s shaft, the shear force applied by the mass on the beam’s end exceeds a critical value which causes dynamic lateral torsional buckling of the beam. Special techniques have been developed to produce and measure this phenomenon and the data has been presented in a form that can be used for future validation of analytical or numerical models. r 2006 Elsevier Ltd. All rights reserved. 1. Introduction Lateral torsional buckling of a cantilever beam subjected to a shear force is a well-known phenomena in static stability theory [1, Section 6.3]. Specifically, when the beam has a rectangular cross-section with its height h much greater than its width w, the stiffness to bending is much greater when the shear load is directed in the height direction than when it is directed in the width direction. Furthermore, when the shear load directed in the height direction reaches a critical value, the resistance to torsion is substantially reduced and lateral torsional buckling occurs as the beam twists and deforms out-of-plane with a tendency to transfer bending to the plane of weakest resistance. Dugundji and Mukhopadhyay [2] studied bending-torsional vibrations of a ribbon. In their experiment the ribbon was free at one of its ends and the other end was clamped to a translational shaker that excited motion oriented in the stiffest cross-sectional bending direction. Their experiment and analysis focused on nearly ARTICLE IN PRESS www.elsevier.com/locate/jsvi 0022-460X/$ - see front matter r 2006 Elsevier Ltd. All rights reserved. doi:10.1016/j.jsv.2006.08.006 à Corresponding author. Tel.: +972 4 829 3188; fax: +972 4 829 5711. E-mail address: mbrubin@tx.technion.ac.il (M.B. Rubin).