Looking for Feedback on Free Composite Design Tool

Hey all,

Autodesk Labs has just released project Cassidy, a free technology preview that allows users to simulate bending loads on 3D models of composite plates.

The standalone application for Windows imports your CAD file and walks you through the process of applying bending loads to the geometry.

We are looking for feeback to help us drive the direction of the technology. Please take a moment, download the project, and provide some feedback.

Learn more and download this free technology preview here: www.autodesk.com/cassidy

 

Looks like a good project. Lots of uses for this for sure.

 

Thanks rwatson! I'd be happy to hear more detailed thoughts if you could spare some time.

-Doug

 

Plate bending is the most elementary of plate analysis. Will it analyze plate with stiffeners or stiffeners only with different cross sections? Will it analyze cored laminate?

The software write up does not describe what kind of math is used in the analysis. Is it the classic lamination theory or the more complex form such as the Tsai-Hill,Tsai-Wu theory? Most software write ups discloses this early, including the load models available so that the user will be able to gauge quickly if the software is worth getting their feet wet. Check most software write up and it does describe the methodology used.

The pretty picture shows the degree of stress given a point load. So unless it is a homogenous layer, the user will not be able to know which ply/layer is failing.

 

These are great questions. I hope that we can eventually support stiffeners, various cross sections, and thick cores.

The analysis is based on FEA in the background, and we are modeling it at the homogenized (laminate level). Tsai-Wu is then used to predict FPF of the laminate.

Can you tell me which functionality would be most useful for you? This product is just a demonstration of what we can do, and your feedback will help us decide where to take it.

Regards.

-Doug

 

If it is FEA, well and good but if the inputs are wrong, results will be erroneous.

Composite design is in two parts, material property prediction and application.

Most Class Societies have formulae to predict the properties of the laminate. Unfortunately, these are minimum standards based on a particular type of matrix and fiber combination. Unless the designer is well experienced or has access to voluminous data of lab tested laminate, the inputs to material properties can be daunting. Most software defaults to a conservative value of a particular matrix/fiber combination. Inputting other values requires complex calculations to predict strength, modulus, thickness, weight, ect. of a laminate, otherwise, coupon test is the most reliable data.

For Marine Applications, typical load model is for the panel to be firmly fixed at all sides with a uniformly distributed load (water pressure). In this configuration, the maximum stress is at the base of the stiffener requiring the panel to be analyzed in conjunction with the stiffener. The design is partly dependent on the stiffener proportion and the reinforcing layers at the base fixity, hence the importance of the stiffener. There are about five load models commonly used in marine applications. The only application for a simply supported plate is for deck hatch.

The trend now is to use core material so it is a must that cored laminates can be analyzed for the software to be useful.

For advance design such as composite mast, the load model is compound as it has torsion and bending(compression/tension). For composite chain plates, creep and temperature degradation has to be factored in.

Marine composites in general use thick layers of varying material properties. While I am not a user of FEA, I was told that for the analysis to be accurate, I have to decouple each layer and to analyze layer by layer. I find it easier to use the classic lamination theory, plot it in Excel, and use some bells and whistle to identify which ply is critical or not needed.

For Aerospace Applications, the practice is to use numerous layers of thin laminates, sometimes as low as 6 mil thick. The layers are arranged to produce an almost isotropic laminate. This lends well to FEA analysis as the material is homogenous and is treated as a single laminate with degraded material property.

The criteria, however, is much more numerous. Safety factor is around 2 so material property input is has to be spot on. Factors like operating temperature, heat absorption, and heat migration has to be factored in. Composite aircraft has to be mated with metals (bushings, hard points, plates) so the thermal stress due to CTE is included in the analysis.

There are other areas that I did not cover. I hope you get an idea of what is needed for the software to be useful.

 

Really good information. I appreciate your feedback. In your post you mention various load criteria for marine applications.

Is the stiffener composite? If so, does it a different layup in the flange and web? What are the 5 load models used in Marine?

It seems as if marine applications are not using quasi-isotropic laminates. What layups are typically used?

From your discussion, it seems as if the most valuable information is at the ply level where you can identify critical plies and design the laminate for the specific application? What types of information would you like to visualize? Factor of Safety, stress, strain, failure index?

Thanks!

 

If you are serious about this, download LR Rules and regulation of Special Service Craft (here in BD Forum) and look up the hull construction in Composites Part 8. The load models are described in Chapter 3. Buckling and failure modes control are outlined in Chapter 7. Note that LR does not refer to Factor of Safety but uses Limiting Stress Fraction. Composite is a very difficult subject.

I am attaching also the ply analysis based on the classic lamination theory. This shows the layer by layer analysis of a laminate. Marine construction practice uses different materials in layers unlike in aerospace where a single type of material is oriented in varying degrees of orientation to obtain a quasi isothropic laminate. Note that in this ply by ply laminate analysis, only the individual ply is analyzed and not the interlaminar strength or "bondline". The bondline is the pure resin bonding the two laminate together. The resin is the weakest part of the laminate.

I also would like to see intralaminar (through thickness) analysis, the V shear. The sofware must be also able to do strain analysis as well as some Class Rules requires analysis by strain. It becomes very important when two ply of differing properties are laminated such as aramid and carbon.

To sum up, you need to be able to analyze;
1. Single skin laminate plate
2. Sandwich (cored) laminate plate
3. Single skin plate with stiffeners
4. Sandwich plate with stiffeners
5. Defined geometric shape with constant cross section (spar, composite mast, crossbeam)
6. Defined geometric shape with varying cross section. (spar, composite mast, crossbeam)

All of the above in varying load model as defined in LR.

 

I had pulled this comment earlier, but based on a suggestion,Ii will reinstate it, with a caveat.

"So this software doesn't seem terribly useful. I did calcs on quasi-iso layups as exercises in school by hand. It was painful, but if that is all this software can do, then the utility isn't amazing."

That said, I did hand calcs on flat plates of quasi iso layups. If this does it for larger parts of complex curvature, there might be some use. But given that small boats that are in-plane isotropic essentially have to be chopper gun boats, AND that it takes a lot of layers to make a real quasi-iso layup, then one might suspect that a larger boat made of uni layers is probably not going to be quasi-iso, but more optimized in construction/schedule?

But I don't design either for a living.

 

Thanks Fish Stretcher,

I agree that if all it did was calculations for quasi-isotropic layups, it would lose value.

The software can handle non-quasi isotropic layups, and is actually made to help optimize uni and woven laminates for complex geometries. Right now it is geared towards 3D curved plates in bending, but it could be expanded.

If you have time, you can download it for free here: www.autodesk.com/cassidy

Any other feedback is always welcome.

 

rxcomposite,

This is very valuable feedback yet again. I will take a look at the LR Rules for future reference.

Have you ever tried our Composite Design product for analyzing the layers of your composite? It does something very similar to your Excel spreadsheet. There is a free trial here if you're interested.

Interestingly enough, I have been hearing about support for inter laminar strength more and more. I'll take a deeper dive into it. How do you typically calculate the shear in your simulations? CLT is only in-plane, and I suppose typical plate or beam analyses could give you some sort of through thickness stress measure to compare against an allowable. Is this how you go about it?

I also understand the requests for closed cross-sections and plates with stiffeners... these designs are very typical.

Thanks,

-Doug