Yield point phenomenon why

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. Pronounced yield drops may also be observed on initiation of plastic deformation in metal whiskers,8 while it is also possible to obtain a yield point from purely geometrical considerations.

Yield points have also been noted in ordered alloys where in the disordered state the effect was less pronounced or not present at all. A more common way in which yield points arise is associated with the interaction of dislocations and solute atoms. Generally, it is necessary to cool sufficiently slowly from the annealing temperature to allow segregation of solute to take place. This review will be confined to yield points occurring solely in this.

Yield-point effects, due to the interaction of solute atoms with dislocations, can also be observed during work-hardening. Both the initial yield point and jerky flow will be discussed in detail but static strain-ageing will be mentioned only briefly. Follow us on.

Who We Are 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. Membership Join Benefits Board Awards. New gauge length and the new area of cross-section are noted and the tensile test restarted. 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.