Proof Testing Aluminum and Titanium Thin-Walled Tubes for Aerospace Applications

Proof testing aerospace components aids in verifying the structural integrity of flight hardware. This process is often an important step in the certification process for critical parts. Though proof testing is a common practice at NASA and in industry, there is often a need to understand better the effectiveness of proof testing pressure systems discovering cracklike flaws or defects. Often proof tests are used in requirements and in practice as technical rationale for screening critical defects in a part in lieu of performing a non-destructive inspection. The intent of this work is to define proof test failure envelopes for thin-walled tubes composed of two materials: aluminum and titanium. Both materials are common in aerospace thin-walled tubing applications which is why these were the materials chosen for this study. The fracture mechanics software NASGRO was used to perform a parametric study on the effect of defects in thin-walled tubes subjected to proof testing. For both materials, the parameters varied in the NASGRO analyses were aspect ratio, proof test pressure, thickness, diameter, and flaw multiplier. With each case defined as a through crack or failure, the results were then pulled into MATLAB in order to parse through the data and produce failure envelope plots. Failure envelopes were created by meshing a surface in between the minimum proof pressure failing data points. As expected, based on material properties, the plots indicated the aluminum material would fail at much lower proof tests than the titanium. The parametric data and failure envelopes may be used as general qualitative insight on the effectiveness of proof testing thin-walled tubes of similar alloys.