DEX is a small materials testing machine that should be capable of running tensile and compressive tests at up to 600N of force. The machine can be manufactured by anyone with access to a laser cutter with at least a 24x12" bed, and nearly any FDM 3D Printer. A bill of materials of purchased parts required to complete the machine is below.
DEX is a small materials testing machine that should be capable of running tensile and compressive tests at up to 600N of force.
DEX runs a [squidworks](https://gitlab.cba.mit.edu/squidworks/squidworks) controller. To run, use the 'dex' branches of [cuttlefish](https://gitlab.cba.mit.edu/squidworks/cuttlefish) and [ponyo](https://gitlab.cba.mit.edu/squidworks/ponyo)
A [stress - strain plot](https://en.wikipedia.org/wiki/Stress%E2%80%93strain_curve) is a very useful piece of information when characterizing materials.
## Comparison to Instron 4411
To see how we do against a real instron, I tested identical samples on the DEX as well as on an Instron '4411' with a 5kN load cell. In the plot below (I'm using cuttlefish to plot the .csv that I saved from Bluehill, the Instron software), the leftmost plot is taken on the 4411, and the lazier slope belongs to the DEX.
While the samples fail around the same load, the difference in elongation is ~ 1.5mm wide: this is almost surely the machine's own deflection, stretch in the belts, etc.
This obviously warrants correction. One way to do this is to build a stiffer machine, however, we will be chasing up the cost and complexity if we do this. Rather, we should throw some more control at it. To start, we can circle back to our attempts at [subpixel tracking](https://gitlab.cba.mit.edu/calischs/subpixel_tracking), or attach a small linear stage directly to our fixturing elements. For this, I am imagining something like the [AMS5311](https://ams.com/as5311), which should do some 12 bits inside of a 2mm throw (for 0.4um resolution). Either can be added to existing systems, given network controllers / modular browser code. Since I want to integrate it elsewhere, it's likely that the camera option comes first.
## TODO
To generate these curves, the DEX slowly pulls samples (normally some 'dogbone' shape [below](#testing-notes)) apart, while measuring the amount that it stretches (~ the strain), and the amount of force it exerts as it is stretched (~ the stress). These types of machine are common in industry, commonly referred to by their leading brand name 'Instron', or as 'Universal Testing Machines'.
```
- encapsulate branches for ponyo, cuttlefish.
- bs ?
- put rpi setup back on desk with dex, branch, close
- revisit with cameras, rate control
```
#### Controller TODOs:
```
- extension rate is important, include this
- assign meaning to charts and graphs (date / location / etc)
- this should be generic json-object making, yeah?
- save tests as .json objects (optionally) develop program for reading
- overlay multiples, save images
- read-in csv as well
- save images of tests (genpurp canvas save tool?)
```
#### Circuit TODO:
## Hardware
```
- draw / fab temp and humidity sensor (looks like Bosch BME280 828-1063-1-ND)
- better implementation of load cell amplifier ? filippos' part number ? nice unit to have.
```
## Building a Displacement Exercise
The DEX is an open-source piece of materials testing equipment. The machine can be manufactured by anyone with access to a laser cutter with at least a 24x12" bed, and nearly any FDM 3D Printer. A bill of materials of purchased parts required to complete the machine is below, totaling some ~ $500 USD.
The machine is made largely from [laser cut](https://hackaday.com/2015/09/03/how-to-build-anything-using-delrin-and-a-laser-cutter/)[delrin](https://hackaday.com/2015/09/22/drawbacks-of-lased-delrin-and-how-to-slip-around-them/) and 3D printed (commodity FDM) parts.
The machine is made largely from [laser cut](https://hackaday.com/2015/09/03/how-to-build-anything-using-delrin-and-a-laser-cutter/)[delrin](https://hackaday.com/2015/09/22/drawbacks-of-lased-delrin-and-how-to-slip-around-them/) and 3D printed (commodity FDM) parts.
More detailed documentation will follow.
### CAD
### CAD
CAD for the machine is available in this Repo, [under `cad/fusion`](https://gitlab.cba.mit.edu/jakeread/displacementexercise/tree/master/cad/fusion) - the `.f3z` file is a Fusion 360 parametric model of the machine. To source parts, consult the BOM below.
### BOM
### BOM
...
@@ -93,45 +65,54 @@ Part numbers are from [McMaster Carr](http://mcmaster.com) unless otherwise link
...
@@ -93,45 +65,54 @@ Part numbers are from [McMaster Carr](http://mcmaster.com) unless otherwise link
DEX runs a [squidworks](https://gitlab.cba.mit.edu/squidworks/squidworks) controller. The `dex` branches of [cuttlefish](https://gitlab.cba.mit.edu/squidworks/cuttlefish) and [ponyo](https://gitlab.cba.mit.edu/squidworks/ponyo) contain code that is known to work with the machine. Again, more documentation for these controllers is coming, for now - consult the repositories.
### Tools for Fabrication
- laser, 3dprinter
## Comparison to Instron 4411
- soldering iron for inserts
- arbor press is nice, but not necessary
### Dependencies
To see how we do against a real instron, I tested identical samples on the DEX as well as on an Instron '4411' with a 5kN load cell. In the plot below (I'm using cuttlefish to plot the .csv that I saved from Bluehill, the Instron software), the leftmost plot is taken on the 4411, and the lazier slope belongs to the DEX.
This repo is for the machine itself, it implements / uses / depends on the projects below:
While the samples fail around the same load, the difference in elongation is ~ 1.5mm wide: this is almost surely the machine's own deflection, stretch in the belts, etc.
I used the trotec w/ 80 watts power, doing two passes per cut at 0.25 speed and 100 power. The colors to setup with are:
This obviously warrants correction. One way to do this is to build a stiffer machine, however, we will be chasing up the cost and complexity if we do this. Rather, we should throw some more control at it. To start, we can circle back to our attempts at [subpixel tracking](https://gitlab.cba.mit.edu/calischs/subpixel_tracking), or attach a small linear stage directly to our fixturing elements. For this, I am imagining something like the [AMS5311](https://ams.com/as5311), which should do some 12 bits inside of a 2mm throw (for 0.4um resolution). Either can be added to existing systems, given network controllers / modular browser code. Since I want to integrate it elsewhere, it's likely that the camera option comes first.
Black, Red, Blue, Cyan, Green, Magenta
## Testing Notes
To export from Fusion, use Rhino for layout, export cut files as DXF, for the trotec the best move is to export as 'R12 Natural'. This will keep segments together.
The D683 ASTM Dogbones:
...
fixturing moves / top to bottom
# Roadmap
## Testing Notes
*2019-10-17*
Use the D683 ASTM Dogbone - normally Type 5.
One complete DEX exists in the MIT CBA shop, and has been validated against an Instron 4411. Current efforts are twofold:
(1) Working with the [materiom](https://materiom.org/) project (whose mission: to provide open data on how to develop bio-inspired materials for a circular economy), and the [fablab at cic](https://cic.com/fab), we are replicating the current design outside of the CBA shop, and building documentation while we do.
(2) To improve the machine's test accuracy, we are integrating CV processing into the control architecture, to use [subpixel tracking](https://gitlab.cba.mit.edu/calischs/subpixel_tracking). Further controller improvements from the squidworks project will also bring rate control on-board.
## Controller Desires
## Notes
```
- Where to build logs go? This repo -> gitlab, mtm.cba, etc.
- Future integration of Temperature and Humidity Sensors
- Higher quality integration of load-cell amplifier
- Developing control for Cyclic Loading, Fatigue, etc.
- Developing direct upload / websocket-to-database tools
- Dec. 5: controllers -> CIC and London
- Cuttlefish: manipulation, understanding, computing on test datasets in the browser.
