REG NASA-LLIS-0535-1996 Lessons Learned Design of Bonded Parts for Cryogenic Temperatures.pdf

1、Lessons Learned Entry: 0535Lesson Info:a71 Lesson Number: 0535a71 Lesson Date: 1996-11-01a71 Submitting Organization: LARCa71 Submitted by: Ruth M. AmundsenSubject: Design of Bonded Parts for Cryogenic Temperatures Description of Driving Event: On MIDAS, thin ceramic boards (1-inch x 1-inch x .030-i

2、nch thick) were bonded to a 1-inch hollow copper cube. The bond was cured at 75C, and then the assembly was cooled to 75K for operation. It was found that some boards would shatter for what seemed like no reason, even though an identical procedure was used for ones that survived many cycles undamage

3、d.It was eventually found that the stresses on the boards were intimately related to their exact mounting configuration. If the boards were mounted on the cube such that two edges were in contact, the shrinkage created by taking the assembly down to cryogenic temperatures caused the edges of the boa

4、rds to push on each other and stressed the boards to failure at the edges. Thus, testing the epoxy by bonding substrates to flat copper test pieces was not sufficient to ensure a successful bond.Lesson(s) Learned: When parts have different coefficients of thermal expansion (CTEs), the shrinkage crea

5、ted when they are taken down to cryogenic temperature will not only produce a shear stress in the epoxy bonding them together, but it can also produce bending stresses if the mounting design is not carefully planned for cryogenic temperatures.Recommendation(s): When a bond will be taken to cryogenic

6、 temperatures, carefully evaluate all possible stress conditions. This includes those that could be caused by a part being at its maximum tolerance for dimension or position, which could cause it to impinge on another part when cooled.Evidence of Recurrence Control Effectiveness: Provided by IHSNot

7、for ResaleNo reproduction or networking permitted without license from IHS-,-,-When the MIDAS cube was assembled with the boards not in contact, so that no stresses would be produced during shrinkage, the boards did not shatter during cooldown.Documents Related to Lesson: N/AMission Directorate(s):

8、N/AAdditional Key Phrase(s): a71 Hardwarea71 Parts Materials & ProcessesAdditional Info: Approval Info: a71 Approval Date: 1997-05-03a71 Approval Name: Elijah C. Kenta71 Approval Organization: 421a71 Approval Phone Number: 757-864-3345Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-