Loading...
Please wait, while we are loading the content...
Similar Documents
Biaxial Testing of 2195 Aluminum Alloy Using Cruciform Specimens Lithium
| Content Provider | Semantic Scholar |
|---|---|
| Author | Johnston, William M. Pollock, W. D. Dawicke, David S. |
| Copyright Year | 2002 |
| Abstract | ABSTRACT A cruciJorm biaxial test specimen was used to test the effect ofbiaxialloading on the yield behavior of aluminum-lithium alloy 2195. FifteencruciJorm specimens were tested Ji_om two thicknesses of 2195-T8 plate,0.45 in. and 1.75 in. These results" were compared to the results" Jbomuniaxial tensile tests" of the same alloy, and cruciJorm biaxial tests" ofaluminum alloy 2219-'187. KEYWORDS Biaxial, Finite Element Analysis, 2195-T8, 2219-T87, von Mises, Yield Surface, Yield Locus,Aluminum Alloy, Aluminum-Lithium Alloy. INTRODUCTION Aircraft and spacecraft structures are often subjected to multi-axial stresses. These structures aredesigned and sized using various yield criteria. These yield criteria relate the multi-axial stress state toyielding based on assumptions about the material behavior. The Space Shuttle External Tank wasinitially designed using the maximum shear stress yield criterion. This criterion has been shown to beaccurate for ductile, isotropic materials and requires only a uniaxial tensile test to characterize thematerial yielding behavior. For non-isotropic materials, the maximum shear stress yield criterion canresult in either over-designed or under-designed structures, depending on the material behavior and thestresses in the structure. Testing that simulates the multi-axial stress state is often preferred to validate theload carrying capability of the material.The Space Shuttle External Tank is fabricated from aluminum alloy 2219, a ductile, isotropic materialwhose behavior agrees well with the von Mises yield theory [1]. Figure 1 shows the maximum shearstress and von Mises yield theories. At stress ratios of 1:0, 1:1 and 0:1, both theories are equal.Elsewhere however, the maximum shear stress theory predicts lower yield strength. During the SuperLightweight Tank Program, the Space Shuttle External Tank was redesigned using aluminum-lithium (A1-Li) alloy 2195-T8. This alloy is not isotropic, and has significantly weaker tensile strength fororientations other than the rolling direction. Due to this non-isotropic strength behavior, uncertaintyexisted regarding safe use of biaxial yield criterions which use a single yield strength value. Therefore,testing was performed to confirm both that the design criteria used would not allow yielding, and that thedesign was not overly conservative.Additionally, the proof testing of the External Tank is performed at room temperature, but the tank'soperating temperature is cryogenic. For A1 2219, this is conservative because the fracture toughness andyield strength increase with decreasing temperature. However, the combined effects of biaxial loadingand decreased test temperature on 2195 were unknown.The objectives of this research were:(1) to determine the yield behavior of A1-Li 2195-T8 for two |
| File Format | PDF HTM / HTML |
| Alternate Webpage(s) | https://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/20020085397.pdf |
| Language | English |
| Access Restriction | Open |
| Content Type | Text |
| Resource Type | Article |
