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error in finding the “effective length” adds uncertainty to the elastic modulus estimation. The

boundary condition created by the fixture made of a c-clamp and the lab bench makes the set-up

slightly deviates from the simple cantilever model. The issue can be alleviated by simply adding

a piece of aluminum plate between the clamp and the beam. A special fixture tool with a

rectangle shape that rigidly clamps the beam can provide the ideal boundary condition. On the

other hand, a conventional method of determining elastic modulus can be used in conjunction to

the existing method for comparison: apply a series of known load to the tip of the beam while

measuring strain, so the stress-strain plot can be created for extracting the elastic modulus.

The current laboratory uses a quarter-bridge Wheatstone set-up. The laboratories can be

extended by introducing half-bridge and full bridge set-up for uniaxial bending strain

measurement. In addition to providing temperature compensation and higher sensitivity, the

different set-ups enable compensation for the effect of transverse strain, and/or for the effect of

lead wire resistance. (Acromag)

Multi-axial strain measurement with a cantilever opens up opportunities for enriching the

current vibration laboratory and developing new laboratories. Besides principle stress and strain

under bending, which can be directly derived from strained measured in different directions,

Poisson’s ratio and stress concentration factor are among the characteristics the set-up can

measure.

Poisson’s ratio of the material can be measured with two strain gauges mounted along

longitudinal and lateral axis at corresponding locations on opposite sides of the beam. In a

laboratory used at Arizona State University, a range of known stresses is applied to acquire the

corresponding longitudinal and lateral strain when the beam reaches stable state. The dataset is

examined for outliers and then used to calculate an average Poisson’s ratio.

(Poisson's Ratio,

2003)

Stress concentration factor of a specific geometric discontinuity, such as a hole on a

cantilever, can be measured with a group of very small strain gauges with fine grids. The

characterization can be performed when the beam is loaded with point bending and/or tension

with different methods. The laboratory taught at New Mexico Tech fitted the measured data into

a stress distribution function to find the constants, which contribute to the calculation of the

concentration factor. (Ruff) Other data analysis methods for laboratories range from deliberate

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Vishay 2310 Guía de usuario Pagina 14