Accession Number : ADA302071

Title :   Nonlinear Vibrations of Cracked Beams.

Descriptive Note : Final rept.,

Corporate Author : ILLINOIS UNIV AT URBANA

Personal Author(s) : Weaver, Richard L. ; Sundermeyer, Jeffry N.

PDF Url : ADA302071

Report Date : 10 MAR 1995

Pagination or Media Count : 9

Abstract : It was proposed to seek experimental confirmation of theoretical predictions that the opening and closing of cracks in structures during vibration can provide dramatic qualitative and quantitative signatures at crack presence, even if the crack is very small. Cracked and uncracked laboratory-sized beams were driven by superpositions of two harmonic loads. Responses at the difference or sum of the two driving frequencies - theoretically indicative of nonlinearity, and large it that frequency is a natural trequency of the beam were compared to the predictions ot previously developed theory. The proposed technique, in which the beam is driven by the super-position of two harmonic signals whose difference or sum is equal to the natural frequency at the beam and the response is monitored at the natural frequency, was found, as expected, to be a good way of measuring nonlinearity. After laboratory background nonlinearities were reduced, it was found that the remaining nonlinearity of a cracked beam was substantially greater than that of the uncracked beams and that the proposed technique may be capable of detecting it and identifying its opening load. The work has implications for remote nondestructive evaluation of cracks in vibrating structures and in general for the structural dynamics of systems with contact nonlinearities. Further work is recommended in automating the tests and further exploring and minimizing the causes of baseline nonlinearity, and attempting to quantitatively characterize the nonlinear crack signatures. (MM)

Descriptors :   *VIBRATION, *BEAMS(STRUCTURAL), *CRACK PROPAGATION, PLASTIC DEFORMATION, ALUMINUM ALLOYS, STRUCTURAL PROPERTIES, CRACKING(FRACTURING), CRACKS, HARMONICS, BENDING, STEEL, RESONANT FREQUENCY, NONLINEAR SYSTEMS, SIGNATURES, FATIGUE(MECHANICS), NONLINEAR ANALYSIS.

Subject Categories : Mechanics
      Structural Engineering and Building Technology

Distribution Statement : APPROVED FOR PUBLIC RELEASE