Engineering & Analysis Methods > Material Strength Composites: Laminate Approach

About polynomial approach for laminate allowables and margins of safety

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cmcho:
I think AML approach does not provide an adequate description of the laminate behavior. Instead, the polynomial approach is better if the data is available. I assume some coefficients of the polynomial and tried to find how it works. But I failed to figure it out. Questions are

1) In the laminate trial of Material Manager, I could not find the laminated based failure results in Failure Analysis tab of the Laminate Analysis Form. Is it not able to do analysis with laminate failure criteria in the Laminate Analysis Form?

2) When I tried it in Worksapces with an example included in the software in which I modified the laminate material choice with my assumed material with polynomial laminate allowabes, it showed MOS with laminate allowables. However I could not interpret how it was obtained and what it means exactly [Does MOS in tension mean only 0-ply direction or minimum value among tensions in 0, 90 and 45 ply direction?]. There is no description or example about polynomial laminate allowables in the package. Could you help me about this by showing examples or providing descriptions?

Thanks.

Phil:
I agree that the AML approach does not fully describe the full definition of a laminate, however, it is very widely used in industry and that is why it is included in HyperSizer.  As you pointed out, if the data is available, the polynomial approach is superior because it more fully describes the laminate.

1. The Laminate Analysis form does not perform laminate based failure analyses.  This form only performs ply based failure analyses.

2. The polynomial based allowables work exactly the same as the AML based allowables in laminate based failure analysis.  The only difference is in how the strain allowable is derived.  In both the polynomial approach and in the AML approach, HyperSizer  looks in each of the four principal directions, -45, 0, 45, 90, and in each direction:

a) calculates the %0, %45, and %90 in this direction
b) plugs these percentages into the user defined polynomial to find the strain allowable
c) then calculates a margin of safety using the strain in this direction along with the strain allowable

After calculating the allowables and the margin of safety in each direction, HyperSizer then returns the minimum of these four margins to the failure tab.

Also see:

http://hypersizer.com/faq/index.php?topic=76.0

cmcho:
Thanks, Phil.

Is there easy way to find or check in laminate based failure
1) ply direction (0,90,+45,-45) that gives minimal margin of safety in the presence of inplane force only
2) the ply that gives minimal margin of safety in the presence of bending moments
3) margin of safety in tension, compression and shear for each ply - This is because some margin of safety should be combined  in tension and shear or in compression and shear

cmcho:
I found the location of the detailed analysis results and also found the followings.

1) ply direction (0,90,+45,-45) that gives minimal margin of safety in the presence of inplane force only - found
2) the ply that gives minimal margin of safety in the presence of bending moments - inner & outer surface of some representative plies but not all the plies. I did not verify the strain level of the hypersizer in the presence of bending
3) margin of safety in tension, compression and shear for each ply - This is because some margin of safety should be combined  in tension and shear or in compression and shear - I think need to recalculate the combined margin of safety for each laminate. I hope this can be implemented sometime.

When I use material properties for three different temperature environment (-75 dry, 72, 180 wet), I think the hypersizer does not use all three conditions because no change is found in number of candidates. Is this correct? If so, which temperature condition is be used?

Phil:
Hi,

For your questions 1 through 3, I assume you are still looking at laminate based strain analyses and not ply based analyses.

1.  The best way to get this type of information for now is the go to the sizing form | Options menu and turn on the flag "Generate More Detailed Reports...".  Then analyze your component and when the analysis is complete, go to Options | Material and Analysis Detail.  You should be able to find the margins of safety in each of the four directions.   The intent is to fold this detail into the stress reports, however as of now, that detail is not included.

2. When doing the laminate based analysis, HyperSizer does not look at every ply.  It looks at the outer surface of the outer ply of the laminate and the inner surface of the inner ply.   There is no distinction between bending strains and in-plane strains.  The strains used in the laminate based analyses are the total combined bending plus in-plane strain.

3. I believe what you are asking about is an interaction criterion.  For example, Tsai-Hill or something like that.  The laminate based analysis does not include an interaction criteria.  To use interaction criteria, you must use ply based analyses.

For question 4, this is applicable to either laminate based or ply based analysis.

When you put in different temperatures on the material form, you are not telling HyperSizer to analyze at those different temperatures, you are defining how the material properties vary with temperature.  By default, HyperSizer analyzes assuming RTD properties at 72 F.

If you want to analyze at different temperatures, you must create a thermal load set.  If you are using a FEM, see the Pro User manual, finite element reference to create a thermal load set.  If using a workspace,  on the FBD tab, for each mechanical condition, click the "Thermal Load Set" radio button and then you can enter a temperature for the analysis.