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An experimental study of bending impact waves in beams

Investigation covers the propagation of flexural waves in an elastic beam of circular cross section subjected to an approximate step-function bending moment

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Abstract

An experimental study of the propagation of flexural waves in an elastic beam of circular cross section subjected to an approximate-step-function bending moment is given. The test beam was a low-carbon-steel bar 2 in. diam × 30-ft long and was suspended in a vertical position by a pin located near the upper end. The step moment was applied at the upper pinned end of the bar by an arrangement of two high-pressure, nitrogen-operated cylinders. The strains were measured with strain gages located at eight stations along the bar.

The experimental results are compared with results obtained from a solution of the “Timoshenko” beam by W. Flügge and E. E. Zajac for a semi-infinite pinned-end beam subjected to a suddenly applied bending moment at the pinned end. The experimental results are correlated with the predictions of the theoretical solution.

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Abbreviations

A :

cross-sectional area, in.2

A s :

effective shear area, in.2

C m =C b :

propagation velocity of a discontinuity in bending=\(\sqrt {E/\rho } \), fps

C v :

propagation velocity of a discontinuity in shear=\(\sqrt {GA_S /\rho A} \), fps

E :

Young's modulus, psi

G :

shear modulus, psi

I :

area moment of inertia of cross section, in.4

M 0 :

moment input, ft-lb

a :

radius of bar, in.

ω:

deflection normal to axis of bar, in.

x :

space coordinate

t :

time, sec

λ:

wave length, in.

ξ:

space coordinate, dimensionless

ρ:

mass density at beam, mass per unit volume

τ:

time, dimensionless

K :

physical constant=ρA/EI

Bibliography

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at time that paper was prepared; is now Mechanical Research and Development Engineer, Hallibuton Co., Duncan, Okla.

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Stephenson, J.G., Wilhoit, J.C. An experimental study of bending impact waves in beams. Experimental Mechanics 5, 16–21 (1965). https://doi.org/10.1007/BF02320899

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