Figure 3-12. Cryogenic experimental setup of the four-point bending test.

 The beam specimens are submerged initially in LN2 for about 5 minutes to reduce

thermal gradients in the specimens as shown in Figure 3-12. The specimen is placed in

the cryogenic container with the liquid nitrogen. When temperature of specimen reaches

the LN2 boiling temperature, LN2 boiling disappears. During this process, some

specimens experience delamination on the edge of mid-ply as shown in Figure 3-13.







 __._-"_ _,_ _-__ --/ -;
 --- ..- Crack Propagation Crack Tip


Figure 3-13. Crack propagation in the 900 layer of a graphite/epoxy laminate at cryogenic
 temperature.

 Finite element analysis is performed to investigate the formation of edge

delamination in the laminated specimen. The quarter region of an actual specimen is

modeled using 8-node 3-D solid elements. A contour plot of stresses in 2-direction is

shown in Figure 3-14 when the FE model is subjected to cryogenic temperature (T= 77

K).