Research by T. W. Shield

Single Crystal Notch-Tip Plasticity: Pure Copper

This work appeared in Acta Metallurgica, 44(4), 1996, pp. 1547-1561.

This image shows the surface of the single crystal of copper near the notch tip after loading and extensive plastic deformation. This pattern of slip bands in the second and third sectors (counted from ahead of the notch tip) is quite striking. Compare this pattern with the surface texture that develops during plastic deformation near a notch tip in a polycrystalline copper specimen.

The slip bands on the specimen surface are very thin and the large amount of shear present in them is visible as offset in the grating dots the slip lines pass through.

Below are images and movies of the notch tip strains in this as grown (very soft) copper single crystal at various stages in the loading process. The orientation of this specimen is identical to the orientation of the Iron-Silicon crystal discussed in [1]. The X-direction is horizontal and the Y-direction is vertical in these images and movies.

The loading history of the specimen studied here is shown on the load-displacement plot here. The time at which data was taken (the load levels referenced below) are also marked on this figure

Movies of the strain components evolution in false color. The movies were made by fading between the data in the images below. A solid blue background was added to avoid the apperance of shifting locations.

Improved Mpeg movies!!

I have come up with a better method of making the mpeg movies of the strain fields. Instead of fading between images, I now have software that lets me interpolate between the actual data files before the postscript is produced that is rendered to produce the images that go into the mpeg file.

Old method Mpeg movies

Strain images at the times data was taken, with scales:

The relavant strain space for this problem is E12 vs (E22 - E11)/2. The directions in the space can tell us where on the yield surface plasticity occured. Here are plots in this strain space at 400, 600 and 800 microns radius. The symbols denote the angle from the crack direction in degrees as shown. The arrows show the motion of the strain at these locations during loading from Level 3 to 7 to 8 to 9. These plots show that the loading is strongly non-proportional.

An optical micrograph of the specimen surface taken after unloading (load level J) is here. The slip systems in sectors 2 and 3 are clearly visible. This figure also shows the crystallographic specimen directions.

Figures from the paper:

"An Experimental Study of the Plastic Strain Field near a Notch Tip in a Copper Single Crystal During Loading," to appear in Acta Metallurgica et Materialia.

Note that these are low resolution rasterizations of postscript, many of the figures above are higher resolution.