Table 5-17. Maximum E2 (milliStrain) induced by the change of material properties El,
E2, G12, Cl12, Tzero, a1, and a2 for 0.12 inch-thick [f250]s laminate
NominalMaximum E2 frOm deterministic analyses for 21 temperature
maximum
es=9.859 E1 Ez Gol pa~ 7,ero au at
9.320 9.399
0. 9*Nominal 9.901 1 0.469 9. 763 9. 909 9. 85 7
(5.47%~) (4. 67%~)
9.313
1.1* Nominal 9. 824 9.960 9. 981 10. 584 9.861 1 0. 333
(5.54%~)
Table 5-18. Probability of failure for 0. 12 inch-thick [ f 250]s laminate with improved
average material properties (Monte Carlo simulation with a sample size of
10,000,000)
All three
Nominal 1.1*E(Ez) 0.9*E( Tero) 0.9*E(a )
measures
Probability
0.0000605 0.0000117 0.0000116 0.0000110 0.0000003
of~failure
Summary
The design of hydrogen tanks for cryogenic environments poses a challenge
because of large thermal strains that can cause matrix-cracking, which may lead to
hydrogen leakage. The laminate design must use ply angles that are not too far apart to
reduce the thermal residual strains, compromising the ability of the laminate to carry
loads in two directions. These small ply angles can cause the laminate thickness to more
than double compared to what is needed to carry only the mechanical loads in the
application study here. Satisfying reliability constraints increased the thickness further.
Improving the probability of failure required increase of thickness. The most
influential uncertainty was variability in the tensile strain allowable in the direction
transverse to the fiberS, 82u. Limiting this variability can reduce the required thickness. Of
the different options studied in the chapter, quality control on the transverse tensile
allowable, 82u, prOVed to be the most effective option. Quality control at the -1.60 level
of 82u, COrresponding to rej section of about 5.5% of the specimens, can reduce the required