Based on the data from Table 4-1, we selected the allowable strain to be 1.54% for the

probabilistic design and 1.1% (1.4 safety factor) for the deterministic design.

Table 4-2. Transverse strains of an angle-ply laminate (+ 25)4S under the same loading
 condition as Table Al
 Room LN2 LHe LHe
 temperature temperature temperature temperature
 (77 OF or 25 OC) (-320 OF or (-452 OF or (-452 OF or
 196 OC) -269 OC) -269 OC)a
Mechanical load
 390 330 200 50"
(Mpa)
Total Ez -0.00261 0.00360 0.00527 0.00656a
Thermal Ez 0.00393 0.00669 0.00699 0.00699a
Mechanical Ez -0.00654 -0.00309 -0.00172 -0.00043a
a Older data obtained from Aoki et al (1999)

 Table 4-3 shows the strain allowables for the lamina, where other strain allowables

except 82u WeTO prOVided to us by NASA. The strain allowables may appear to be high,

but this is because they are applied to strain including residual strains that develop due to

cooling from stress-free temperature of 3000F. A quasi-isotropic laminate will use up its

entire transverse strain allowable of 0.011, when cooled to -4520F. Thus, this value is

conservative in view of the experiments by Aoki et al. (2000) that indicated that the

laminate can carry 0.325% mechanical strain at cryogenic temperature.

Table 4-3. Strain allowables for IM600/133 at -4230F
Strain sy" sy' sy, es' 77,7;
Allowablesa 0.0103 -0.0109 0.0110 or 0.0154b -0.0130 0.0138
a Strains include residual strains calculated from the stress-free temperature of 300 OF
b The value 0.0110 is obtained from the extreme value 0.0154 divided by a safety factor
 of 1.4

 Deterministic Design of Angle-Ply Laminates

 It is estimated that the minimum thickness needed to prevent hydrogen leakage is

0.04 inch, so it may be acceptable to permit matrix cracking if the undamaged part of the

laminate has a minimum thickness of 0.04 inch. For the cracked part of the laminate, the