Disk Mechanical Test Development

Abstract

The target disks are held in a circular slot in a stainless steel holder. The holder is sized and toleranced so that the disks fit without constraint in the holder at the temperature of the parts under the irradiation condition. The target is a stack of 29 mm diameter disks 0.5 mm thick separated by 0.25 mm coolant gaps. The hottest disks reach a temperature of 1263 K at the center. Figure 1 shows the temperature contour plot of the hottest disk, Disk 14. Temperature increase causes thermal expansion through the thickness and radially. The radial thermal expansion in particular causes thermal stresses, aggravated by the fact that the center heats significantly more than the edge. Thus the center of the disk expands radially but the relatively cool outer edge constrains that motion. The resulting thermal stress is shown in Figure 2, showing a peak thermal stress of 281 MPa at the center. Stress/strain curves for molybdenum are shown in the plot in Figure 3. From the curve at 982°C, it is evident that plastic deformation will result, with a maximum deformation of 0.002 in (0.05 mm). Actual deformation is shown in Figures 4 and 5 in one radial plane and in the "Z" direction through the thickness.