REG NASA-LLIS-0522-1994 Lessons Learned Consider Stress Combinations During Design Analysis also do not Tap and Thread Acrylic Materials that will be Under Load.pdf

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1、Lessons Learned Entry: 0522Lesson Info:a71 Lesson Number: 0522a71 Lesson Date: 1994-08-12a71 Submitting Organization: LARCa71 Submitted by: Bernard LewisSubject: Consider Stress Combinations During Design Analysis, also, do not Tap and Thread Acrylic Materials that will be Under Load Description of

2、Driving Event: On 5-2-85, a mishap occurred at the water tunnel at Building 1234. While the tunnel was filled with water for leak checks, the test section door detached from the test section, resulting in 3500 gallons of water escaping the tunnel and the building. Significant damage resulted to the

3、test section door, model support mechanism, test section, flow channel, and the honeycomb flow straighteners.The cause of the accident was the prying action between the door and the adjacent wall. This prying action, which was not considered in the design analysis, created stresses in the lucite doo

4、r material beyond its flexural strength. There were other errors in the door design, to include: stresses were not combined (however, in the analysis performed - prying action not included - the material strength would have been sufficient for the loads considered). Acrylic materials should not be t

5、apped and threaded (manufacturers recommend use of oversize bolt holes, grommets, and washers to minimize stress from through bolting) as was done with the test section door; and, framing, which could have provided for the load, was not used. The tunnel critical design review stipulated that, due to

6、 the effects of vibration, the water tunnel and the jet exit facility should not be run simultaneously. Effects of the jet exit facility vibrations on the water tunnel were not considered in the analysis.Lesson(s) Learned: There are two lessons from this incident:1. During design analysis, stress co

7、mbinations must be considered2. Do not tap and thread acrylic materials that will be under load.Recommendation(s): Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-The following recommendations resulted from the investigation of this incident:1. Frame

8、 the test section door.2. Combine stresses in the loads analysis.3. Do not drill, or tap and thread, acrylic door material.4. In the loads analysis, consider the vibration effects on the water tunnel when opening the jet exit facility and the water tunnel at the same time.Evidence of Recurrence Cont

9、rol Effectiveness: Investigation Board recommendations to fix the problem were adopted.Documents Related to Lesson: N/AMission Directorate(s): N/AAdditional Key Phrase(s): a71 HardwareAdditional Info: Approval Info: a71 Approval Date: 1997-04-02a71 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-,-,-