Figure 2-12. Maximum principal stress distribution in the LH2 Graphite/Epoxy
 composite tank. Tank pressure = 10 KPa and temperature = 50 K (AT= -405
 K).

 The liquid hydrogen composite tank is subjected to appropriate boundary

conditions in the ABAQUS FE model to simulate the situation at which it failed during

proof test [1]. The actual liquid hydrogen composite tank was modeled using 8-node solid

elements (see Figure 2-12). The quarter model of the composite tank has 137 elements

with 75 integration points in the thickness direction. The lay-up configuration of the

composite laminates is specified in the layered solid elements. The IM7/997-2 laminate

properties used for the macro-model are given in Table 2-5.

 The macro-level analysis was performed for two cases. In the first case, the tank

was exposed to cryogenic temperature without internal pressure. In the second case, an

internal pressure was applied in addition to cryogenic temperature. The displacement

contours shown in Figure 2-12 correspond to a pressure of 10 kPa and AT= -405 K. The

location denoted by the arrow in Figure 2-12 was selected for further investigation of

failure due to micro-stresses. The macro-level strains and curvatures in longitudinal and