Structural Analysis Sandwich

Prévia do material em texto

8º step: verification of shear stress at the core like in last step, they used it the formulations of shear to verification it.
9º step: verification of displacements in this moment to do a comparation with admissible displacements.
Usually, they use like maximum value Wz= l/300, but sometimes the 
Limit is Wz= l/600, where is characteristic length usually the distance between supports
Application of spreadsheet
After this study and analyses of this theories of sandwich structures, it was created a software for to auxiliary to the designers, in the Microsoft excel, to calculate the best use it.
After this analysis, the designers choice the best characteristics for your project, they did several calculations, like as faces thicknesses, core, etc.
They repeat this analysis so the result to be satisfactory, if needed it.
Example:
Case 1
We have a gap axb=3,0mx1,0m, we wait for win with a sandwich board
 just supported, submitted to a load uniformly distributed q0 = 0,001N/mm².
The material base of face will be aluminum 5052 and for we can to compare we modified the materials of the core.
(a)Core in expanded polystyrene; 
(b)Core in polyurethane;
c) PVC core;
(d) balsa core; 
(e) phenolic nucleus
Solutions
The prope00 00rties of the cores are obtained through Tables 1 and 3, for the calculates we have the data that was introduced in the spreadsheet, the security verifications alred did. (step 6 to 9)
We can watch, the material of the core and yours thicknesses don’t suffer any alteration, and looking at the graphics, in the figure 6, the total mass it has a little variation that don’t be related to total thicknesses of structure. 
 In this case, the board with a lower density was the polyurethane core and the higher density a with expanded polystyrene core, to resist the same distributed load.
Case 2.
We have a gap of axb=3,0mx1,0m, we can win with a sandwich board, just supported, submitted to a load uniformly distributed q0 = 0,001N/mm².
The material of the core will be expanded polystyrene.
(a) aluminum face 5052;
(b) carbon steel face;
(c) face in woven glass / epoxy 1581-F155;
(d) face in plywood / pine; and
(e) 304 stainless steel face
Figure 6 - Comparative Chart aluminum face 5052
Figure 7 - Comparative Chart core of expanded polystyrene
Solutions 
The properties of the cores are obtained through Tables 1 and 3, for the calculates we have the data that was introduced in the spreadsheet, the security verifications alred did. (step 6 to 9).
We can to watch in the figure 7.
To this sandwich board fixed the material of the core, generating
 A big variation in the total thickness of the parts (figure 7), because so the core so the faces suffered for it wins the gat determinated with the load employee in the structure.
In the graphic we can to watch the totals mass, being the part with the lower presents the bigger thickness.
f the design criterion is to reduce the density, the board must be used with plywood / polystyrene core, with a total thickness of 25 mm and a mass of 3.24 kg / m².
Final considerations
When designing using sandwich structures, it should be borne in mind that properties of two different materials are being associated to improve the mechanical characteristics of the structure. At this point, the designer must define whether the calculation will be done considering the theory of beams or boards, and also at that moment are defined the materials to be used in the making of the sandwich panel.
Through this mechanical, structural analysis, a calculation routine was formulated, systematizing the data and equations referring to the structures, to facilitate the execution of the projects. The assembly of a spreadsheet to assist in the calculations contributed positively, since the checks became more agile and easy to be done, which made possible the accomplishment of several checks with the data provided for the properties of the materials, being enough for the designer to specify the thicknesses of the faces and core. The comparison made it possible to check the best options for making the sandwich panels.
References 
ALLEN, HG Analysis and Design of Structural Sandwich Panels. Hungary: Pergamon Press, 1969. 
AMERICAN SOCIETY FOR TESTING AND MATERIALS. Standard ASTM C364 / C364M07: standard test method for edgewise compressive strength of sandwich constructions. West Conshohocken, PA, 2007.
 AMERICAN SOCIETY FOR TESTING AND MATERIALS. Standard ASTM C393-00: standard test method for flexural properties of sandwich constructions. West Conshohocken, PA, 2000. 
AMERICAN SOCIETY FOR TESTING AND MATERIALS. ASTM Standard D695-02a: standard test method for compressive properties of rigid plastics. West Conshohocken, PA, 2002. 
AMERICAN SOCIETY FOR TESTING AND MATERIALS. ASTM D1781-98 Standard: standard test method for climbing drum peel for adhesives. West Conshohocken, PA, 2004. 
AMERICAN SOCIETY FOR TESTING AND MATERIALS. ASTM D3499-94 Standard: standard test method for toughness of wood based structural panels West Conshohocken, PA, 2005. 
AMERICAN SOCIETY FOR TESTING AND MATERIALS. ASTM D3500-90 Standard: standard test methods for structural panels in tension. West Conshohocken, PA, 2003. 
AMERICAN SOCIETY FOR TESTING AND MATERIALS. ASTM Standard D3501-05a: Standard Test Methods for structural wood based panels in compression. West Conshohocken, PA, 2005. 
AMERICAN SOCIETY FOR TESTING AND MATERIALS. ASTM D3502-76 Standard: Moisture absorption of compressed wood products. USA: ASTM 1976. 
AMERICAN SOCIETY FOR TESTING AND MATERIALS. ASTM D3503-76 Standard: swelling and recovery of compressed wood products due to moisture absorption. West Conshohocken, PA, 1976. 
CALLISTER JR, WD Materials Science and Engineering: an introduction. 5. ed. Rio de Janeiro: LTC 2002. 
GAGLIARDO, DP Structural Analysis Sandwich: design parameters. 2008.174 f. Dissertation (Master of Engineering) - Faculty of Civil Engineering, Architecture and Urbanism, University of Campinas, Campinas, 2008. 
JONES, RM Mechanics of Composite Materials. Tokyo: McGraw-Hill Kogakusha, 1975. 
Mendonca, PTR Composite Materials & Structures-sandwich: design and analysis. Barueri, SP: Manole, 2005. 
TIMOSHENKO S. Strength of materials. Rio de Janeiro: LTC 1985. 
TITA, V. Design and structures Manufacture of composite material Polymeric. Class notes. University of São Paulo, School of Mechanical Engineering, 2007. 68 p.