Why yield point phenomenon

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You may not sell, rent, lease, distribute, broadcast, sublicense, or otherwise assign any rights to the Content or any portion of it to any third party, and you may not remove or modify any proprietary notices or labels on the Content. The ASM Heat Treating Society is the world's premier membership society dedicated to the advancement of heat treating as a theoretical and applied discipline. Become a member Log In Cart. Description Delivery Options. A material exhibits a yield point when a larger stress is required to initiate deformation by slip than to continue it.

In a normal tensile test this is usually observed as a drop in load at the start of gross yielding. Load drops may also be observed that are due to deformation twinning, but this will not be discussed here.

Annealed mild steel was once thought to be unique in showing an initial yield point but it is now known that the effect is quite general, and many examples occur in substitutional alloys. Several different thermal and mechanical treatments may result in the appearance of a yield point. A yield point can be produced on subsequent testing by quenching and by neutron irradiation in both single crystals and polycrystals. Reloading a deformed specimen immediately after unloading Haas en-Kelly effect , and decreasing the strain rate or increasing the temperature during testing work-softening , can also give rise to yield points.

This time the test is conducted till fracture. The load-displacement data is saved in an excel file. Transfer the file from the remote virtual laboratory location to the local computer for further analysis. Note the values of initial gauge length, L o , initial area of cross-section, A o , and final gauge length, L f. Show plots of i load-displacement curves, and ii engineering stress - engineering strain curves.

From the engineering stress-strain curves note the values of the lower and upper yield stress. From the engineering stress - engineering strain curves also obtain the following: i tensile strength, ii fracture strength, and iii percent total elongation. Second Specimen. Show plots of i load-displacement curves, and ii engineering stress - engineering strain curves up till stopping the test. Note the new values of gauge length, L 1 , initial area of cross-section, A 1 , and final gauge length, L f1.

This time show plots of i load-displacement curves, and ii engineering stress - engineering strain curves till fracture. Discussion and Conclusions. Comment on the stress-strain characteristics obtained for the first sample. Compare the stress-strain curve with that for the first sample for the second sample obtained after the interruption. List the important conclusions obtained in the experiment.

Mechanical Testing Laboratory.