## Composite structure analysis by hand

## Composite structure analysis by hand

(OP)

There are lots of resources for structural analysis using FEA but I don't want to even dabble with FEA until I can confidently get ballpark answers the old fashioned ways (Microsoft excel, pen and paper, calculator, etc).

Any resources for that?

Here's what I'm looking for

1) Resources for learning structural analysis of composite material structures the old fashioned way (pen and paper and some spreadsheets)

2) Mechanics of materials textbooks that use the generalized hooke's law

3) Structural analysis of fuselages that don't have a simple circular cross section

I've got a couple of great books that provide an introduction to composite materials for micromechanics, macromechanics, ply mechanics, and such. but they lack information on the methods for structural analysis of composite structures.

Any resources for that?

Here's what I'm looking for

1) Resources for learning structural analysis of composite material structures the old fashioned way (pen and paper and some spreadsheets)

2) Mechanics of materials textbooks that use the generalized hooke's law

3) Structural analysis of fuselages that don't have a simple circular cross section

I've got a couple of great books that provide an introduction to composite materials for micromechanics, macromechanics, ply mechanics, and such. but they lack information on the methods for structural analysis of composite structures.

## RE: Composite structure analysis by hand

## RE: Composite structure analysis by hand

We've used the solutions in the book to, for example, work out how different elements are handling through thickness shear and what proportion of discrepancies between models we get are down to element formulation, mesh size, etc... However, composites are complicated so analytical solutions often involve some variation the theme of multiplying laminated plate equations by some function, integrating by parts to get the equation in its weak integral form and implementing the boundary conditions... If you're doing this then you're not far off using the FE method anyway.

If you intend to develop yourself towards being able to do useful analysis on composite structures then you will have to get comfortable with numerical methods.If your concerned that FE is a bit of a black box then why not start with using finite differences to solve some simple problems? Once you're happy with FD then you could look at getting your head around finite volume and then/ or finite element methods? The Reddy book will be useful again here to as it goes through various means of handling through thickness deformation that you can then relate to how shell and continuum finite elements might behave when through thickness stresses are meaningful.

PS If you really want to get into composites then I'd suggest that learning about both experimental testing and manufacturing methods for composites (the performance of composite materials is inextricably intertwined with how they are made) are worth setting time aside for too.

## RE: Composite structure analysis by hand

For now, my plan is to start out by developing a small (4" diameter at most), simple cylindrical fuselage structure using quasi-isotropic laminates. From there, I then optimize the laminate. Won't get me the lightest structure but it'll have to do until I figure out the more complex techniques.

Can you recommend any resources about finite differences as applied to mechanics of materials?

## RE: Composite structure analysis by hand

Brian

www.espcomposites.com

## RE: Composite structure analysis by hand

Once you're happy with solving ODEs you can then move onto solving PDEs; a set of videos to get your feet wet on this, and from the same guy; is here: Link

If you're already comfortable with CLPT then you could try and apply some of the techniques in this video series to some simple problems. I'd choose to use worked examples from Reddy so that you can compare you're numerical results with analytical solutions

I, personally, think the treatment of FD, FV and FE methods is a bit lightweight but the videos are a good starting point. There are loads of other vides series out there; have a look for stuff that suits you. I've put a number of my students, new hires and interns onto Prof Gilbert's MITx/EdX 18.085 in the past (

~~Link)to learn more about numerical methods but am now evaluating this course as training material: Link It's quite fluids focused but the bonus is that it's got some interesting practical examples and you get useful Python practice thrown in with it (Disclosure; I'm a big fan of Python/SciPy/MatPlotLib/etc stacks and find it very annoying that most engineering grads come out of College with a need for thousands of dollars worth of MatLab licenses in order to be able to get stuck into even basic scientific computing).~~## RE: Composite structure analysis by hand

To give you an idea of how important I think an understanding of how composites are made and tested is: with the sole exception of my business partner (who is a strategy consultant by background, so I feel this is excusable), everyone in my company can make panels of various composite or bulk resin materials, manually and/or CNC cut a wide range of composite and near resin test specimens from such panels, end-tab them, apply strain gauges/DIC patterns/extensometers, test them, reduce the data, etc... Even then, my business partner can still VARTM a panel and understand some simple scripts even if he doesn't know how to run a test machine or LabView program.

## RE: Composite structure analysis by hand

Brian

www.espcomposites.com

## RE: Composite structure analysis by hand

Brian, in your upcoming book, think you can include a little section about composite GA structure in which there are little to no stiffeners but rather a sandwich skin to resist compression and buckling? Us homebuilt aviation enthusiasts would greatly appreciate that.

I ask because you've said elsewhere that your book would be geared towards commercial aircraft but I'd like to know how GA aircraft structures must do things differently. Unfortunately, the literature pertaining to small composite aircraft is substantially more limited that large commercial ones.

## RE: Composite structure analysis by hand

Can't say I have much knowledge of the homebuilt aircraft market and I wasn't aware that sandwich constructions might feature much here; I had (very briefly) once entertained the idea of putting together a Glassair kit many years ago but don't remember it using much in the way of sandwich constructions. Anyway.... Have you looked at literature relating to windturbines? Wind turbine blades make extensive use of sandwich constructions using structural foam cores. Through thickness shear cracking of the core and failure propagating along the profile, but a bit below, the skin-core bond and within the foam are modes of failure that wind turbine blade manufacturers have spend a fair bit of resources looking at and may be relevant to your interests.

## RE: Composite structure analysis by hand

You obviously did not look at the fuselage of the Glassair very much. The fuselage is a foam cored sandwich made in three sections , a left/right and bottom. The attached picture is of one I repaired in 1985 after the aircraft dropped a wheel of the edge of the runway and ground-looped at 40mph.

You can clearly see the construction in the picture.

You are judged not by what you know, but by what you can do.