Question

on metal, beams doing four-point bending test

1. Why is there interest in measuring strains at different depths of the beam specimen?

2. If the strains were measured at a point between the load point and the support, instead of at the middle of the span, would you expect the readings to be larger or smaller than at midspan? Why?

Answer 1

solution -

1. with the application of load, the beams comes under the influence of forces and stresses are generated and beam attains a curvature. The stresses generated are not uniform throughout the depth of the cross-section. they vary with depth.

As the stresses are different at different depth, the strains developed are also different and so we need to measure the strains at different depths.

2. The strains measure between the load and the support will be smaller in magnitude than the strains measured at the mid point of the beam.

In 4 point bending test, the load is symmetrically placed wrt center/ mid point thus at the center the is under the influence of both the loads as compared to support which are majorly under one load consideration. so, more strains are developed at the mid-point than between load and supports.