DONE

I'm all done with my thesis now. Wow. Ok, that's all. No more stress from THAT. whew... Quite a journey.

Abstract 4

This study aims to get close to the tension-tension portion of the Forming Limit Curve (FLC) of 38 um thick CP Gr2 Titanium with the use of the bulge test. With the miniaturization trend of technology, the forming abilities of Ti have to be evaluated because it is well known that the formability changes when moving from macro to micro scale. The hydraulic bulge test creates pure biaxial tension by clamping a flat foil sample to obtain a fixed boundary condition and then applying pressure on one side to promote material deformation. In order to ensure that pure biaxial tension has taken place, the strain history will be recorded by taking measurements of the strain at specific pressure intervals from the start up to the burst pressure. If the strain history has equal major and minor strains, pure biaxial tension is confirmed. Strain is measured by studying the deformation of a grid of 50 um in diameter circles that are on top of the thin foil. This thesis tests four different bulge diameters of 20 mm, 15 mm, 10 mm, and 2 mm. When bulge diameter decreases, size affects are expected to increase. Theoretical calculations will be compared to LS-Dyna simulations and experimental results to check whether the theory continues to apply when moving to the smaller diameter thin foil. The wide range of diameters tested from 20 mm to 2 mm will allow for clarification of any trends when undergoing miniaturization in forming.

Abstract 3

Title:

Hydraulic Bulge Testing of CP Gr2 Ti to Quantify Size Effects on the Forming Limit Curve when Undergoing Miniaturization

Abstract Draft 3:

This study aims to get close to the tension-tension portion of the Forming Limit Curve (FLC) of 38 um thick CP Gr2 Titanium with the use of the bulge test. The FLC helps to predict the forming behavior of sheet metal by showing safe and failure strain zones with minor and major strains as the axes. Various tests, including the tensile test, limited dome height test, cruciform test, and bulge test are used for obtaining data for different portions of the FLC. With the miniaturization trend of technology, the forming abilities of Ti have to be evaluated because it is well known that the formability changes when moving from macro to micro scale.

The hydraulic bulge test involves clamping a flat foil sample to obtain a fixed boundary condition and then applying pressure on one side to promote material deformation. If the boundary is circular and secure, pure biaxial tension takes place at the top of the bulge as the material deforms. Micro limited dome height tests already produce excellent FLCs, but the equibiaxial portion is difficult to obtain due to frictional effects. The bulge test is essentially friction free due to the use of hydraulic pressure, and its data can be used to complete the FLC for CP Gr2 Ti. In order to ensure that pure biaxial tension has taken place, the strain history will be recorded by taking measurements of the strain at specific pressure intervals from the start up to the burst pressure. If the strain history has equal major and minor strains, pure biaxial tension is confirmed.

Strain is measured by studying the deformation of a grid of 50 um in diameter circles that are on top of the thin foil. Since the Ti is 38 um thick, the strain at the top of the specimen is assumed to be approximately the same throughout the thickness. A scanning electron microscope takes pictures of the strain zone of interest. After pictures are taken, ImageJ software is used to fit ellipses to the deformed circles. The major and minor axes of the fitted ellipses are used to calculate the major and minor strains. 

This thesis tests four different bulge diameters of 20 mm, 15 mm, 10 mm, and 2 mm. When bulge diameter decreases, size affects are expected to increase. Theoretical equations for the bulge test exist, which include parameters such as pressure, thickness, dome height, diameter, radius of curvature, and material constants. Theoretical calculations will be compared to LS-Dyna simulations and experimental results to check whether the theory continues to apply when moving to the smaller diameter thin foil. The wide range of diameters tested from 20 mm to 2 mm will allow for clarification of any trends when undergoing miniaturization in forming. This study will compare theoretical, numerical, and experimental results in order to bridge the gap between the macro and micro scale.

Abstract 2

This was my first rough draft of the abstract. Bad.

Commercially Pure Grade 2 Titanium is commonly used in chemical, medical, and aerospace industries because of its high specific strength and excellent corrosion resistance. In order to limit the cost and weight in design, an accurate forming limit diagram (FLD) is desired to know the limits of the 38 micron thin foil's formability. In order to determine the equibiaxial tension portion of the FLD, experimental testing will take place with the hydraulic bulge test. In order to see any affects of bulge diameter, three different tool dies of 10 mm, 15 mm, and 20 mm will be utilized. The major and minor strains will be determined by first capturing images of the post-test grid with SEM and then using Fiji/ImagJ software. LS-DYNA software will also allow for a comparison between computational and experimental results. A linear 45 degree strain path is expected for each die diameter bulge test. A decrease in diameter is known to increase the burst pressure. The resulting forming limit diagram will help with efficient designs using Titanium thin foil. In the future, the affects of a combination of strain paths could be analyzed to determine potential new manufacturing methods.
I guess my idea of an abstract is different from what is needed for a thesis proposal abstract, which is ok. Now I will make another attempt. Some new aspects:
-Explain bulge test
-Add reasoning: testing to see if macro-scale equations still apply when going to smaller scale
-Clean up grammar, avoid using the same phrases multiple times


It is well known that the formability of metals change when moving from macro to micro scale. This study aims to get close to the tension-tension portion of the Forming Limit Curve (FLC) of 38 um thick CP Gr2 Titanium. The hydraulic bulge test involves clamping a sample to obtain a fixed boundary condition and then applying pressure on one side to promote material deformation. If the boundary is circular and secure, pure biaxial tension takes place at the top of the bulge as the material deforms. Micro limited dome height tests already produce excellent FLCs, but the equibiaxial portion is difficult to obtain due to frictional effects. The bulge test is essentially friction free due to the use of hydraulic pressure, and its data can be used to complete the FLC for CP Gr2 Ti. In order to ensure that pure biaxial tension has taken place, the strain history will be recorded by taking measurements of the strain at specific pressure intervals from the start up to the burst pressure. A grid of 50 um in diameter circles are placed on the foil and are measured post-deformation with the use of SEM and ImagJ. This thesis tests three different bulge diameters of 20 mm, 15 mm, and 10 mm. When bulge diameter decreases, size affects are expected to increase. Theoretical calculations of dome height will be compared to LS-Dyna simulations and experimental results to check whether the equations continue to apply when moving to the smaller diameter thin foil. This study will compare theoretical, numerical, and computational results in order to bridge the gap between the macro and micro scale.


I'll stop it there for today.

Title and Abstract

I have my committee together, and the next step is to propose my thesis. I need to have my ideas solidly together and be prepared for any questions.

So first: what will my title be?

Hydraulic Bulge Test of Commercially Pure Grade 2 Titanium for the Forming Limit Diagram on the Mesoscale

Hydraulic Bulge Test of CP Gr2 Titanium for Right Hand Side of the Forming Limit Diagram

Forming Limit Diagram of CP Gr2 Titanium with Hydraulic Bulge Test

Something like that? I should emphasize that I am focusing on the right hand side and particularly equibiaxial tension. Ok, I can work with that.


Abstract
-Intro: Why is this research important? (1-2 sentences)
Commercially Pure Grade 2 Titanium is commonly used in chemical, medical, and aerospace industries because of its high specific strength and excellent corrosion resistance. In order to limit the cost and weight in design, an accurate forming limit diagram (FLD) is desired to know the limits of the 38 micron thin foil's formability.

-Methodology (1-3 sentences): specific approach (theoretical, experimental, computational), measured variables and control parameters, (not step by step)
In order to determine the equibiaxial tension portion of the FLD, experimental testing will take place with the hydraulic bulge test. In order to see any affects of bulge diameter, three different tool dies of 10 mm, 15 mm, and 20 mm will be utilized. The major and minor strains will be determined by first capturing images of the post-test grid with SEM and then using Fiji/ImagJ software. LS-DYNA software will also allow for a comparison between computational and experimental results.

-Results (3-8 sentences): In my case, expected results. Specifics
A linear 45 degree strain path is expected for each die diameter bulge test. A decrease in diameter increases the burst pressure.

-Conclusion (1-2 sentences): significance of results, future steps
The resulting forming limit diagram will help with efficient designs using Titanium thin foil. In the future the affects of a combination of strain paths could be analyzed to determine potential new manufacturing methods.

And now, all together:
Commercially Pure Grade 2 Titanium is commonly used in chemical, medical, and aerospace industries because of its high specific strength and excellent corrosion resistance. In order to limit the cost and weight in design, an accurate forming limit diagram (FLD) is desired to know the limits of the 38 micron thin foil's formability. In order to determine the equibiaxial tension portion of the FLD, experimental testing will take place with the hydraulic bulge test. In order to see any affects of bulge diameter, three different tool dies of 10 mm, 15 mm, and 20 mm will be utilized. The major and minor strains will be determined by first capturing images of the post-test grid with SEM and then using Fiji/ImagJ software. LS-DYNA software will also allow for a comparison between computational and experimental results. A linear 45 degree strain path is expected for each die diameter bulge test. A decrease in diameter is known to increase the burst pressure. The resulting forming limit diagram will help with efficient designs using Titanium thin foil. In the future, the affects of a combination of strain paths could be analyzed to determine potential new manufacturing methods.


After meeting with my advisor, the above abstract is too "short." I need to make it sound more technical. Ehh, why? I like making my writing easy to understand. But oh well.

So I'm working on organizing myself. I have various projects and duties to attend to. I want to produce a good, actually beneficial thesis, and I can do it - through the use of organization. Perhaps updating this blog more can help. I have taken my final for my class already, and all I have left in front of me is a design project for an interview, a lot of grading, and this thesis.

Update 4/18

It's crunch time, and I'm not talking about lunch. The bulge test has to give me what I need in terms of a thesis. I will need to propose a thesis real soon.

What do I know already?

CP Ti grade 2 is the material I am working with. That is, commercially pure titanium grade 2. This material is used a lot in industry. It has superior corrosion resistance and has a high strength to weight ratio. This means it can supply good performance with a lesser amount of material. Because of its corrosion resistance, it is applicable in chemical, medical, and aerospace industries. It is quite expensive though, so that limits its reach into other industries that can easily use other cheaper material.

The forming limit diagram is helpful in determining how much stretching can take place before the material fractures. It plots the major true strain vs minor true strain against each other. What does this mean? Well, here's a picture:

From this picture, you can see some cool things. The darker red line is what people want to achieve with testing. Uniaxial tension is achieved with a tensile test. It's where the material is stretched in one direction and shrinks in the other direction. Poisson's ratio is involved in there too. The left side of the FLD for CP Ti gr2 has been tested for already at NIU. Micro limited dome height was used to get that data. However, the right side is more difficult to get with that method. There is friction involved with the limited dome height test. So here is where my thesis comes in. 

The bulge test uses nothing but air to deform the material. That means that there is essentially no friction involved, which is good for data. For a perfect circular bulge, there is equibiaxial tension. Both the major and minor axes are strained by the same amount. Perfect! This can find the tip of the right hand side FLD. My thesis is essentially just trying to find that right hand side.

Is this enough of a thesis? I don't think so. For this reason, I will try to use different diameters of bulge to find out if there is an effect on the strain path. Perhaps the smaller diameter bulge tests behave slightly differently. Who knows? Furthermore, I can take pictures at different points of the bulging process. This can give me a strain history at various pressures. Maybe this is important in some way?

This has been studied on the macro scale before, but we are working with 38 micron thick material here. This means that the macro scale experiments may no longer be an accurate model for our purposes. It's time to do some more literature review and ask some questions.

Some questions:

1. What macro scale experiments have been conducted already on this material?

2. What experiments of similar material have been conducted already?

3. If other material has been tested, what can be expected to be the same or different?

4. What constitutes a macro vs micro size? 

5. Have other materials shown variations in macro vs micro characteristics?

Update 4/6

Oh boy, do I have a bunch to talk about! I kind of forgot about this blog, honestly. I've been able to gain a lot of traction with the bulge test, and I think that's the way that I'll end up going with my thesis. Yes, the biaxial tensile test machine is still in the works, but I have actually performed bulge test experiments already.

So where shall I go with this? I ended up getting a new MultiMoto shield for the arduino. It worked flawlessly, so I am now able to control the speeds of the four linear actuators independently. All I would need to take care of with that is to make speed vs PWM input curves for each actuator. That way the speeds could be perfectly controlled as desired. The other MultiMoto shield that only half worked (before spring break) was returned to the seller. They tested it and determined that it was indeed a dud! Yay, it wasn't my fault that the older shield didn't work! Hallelujah.

For the biaxial machine, though, we still need some grippers to hold the 38 micron titanium specimen. Yes, that may be difficult. The grippers themselves aren't too difficult to make, but aligning them is a challenge in and of itself. The current clamping method is quite rickety at the moment.

But Hallelujah, the bulge test is where the fun has been happening! Imagine bolting some metal together with some o-rings and just pumping in nitrogen to 400 psi. Yeah, it's quite nerve-racking. But after a few times you find out that it's actually not that bad of a pop when a failure occurs.

Anywayyyyy, I got the machined parts back from the machine shop and was super pumped when my o-ring grooves fit the o-rings perfectly. I love how quickly the machine shop gets stuff done, too. It's definitely a change of pace from some of my past experiences.

Above you can see the beautifully shiny 303 stainless steel parts. Aren't they pretty? <3 Those o-ring grooves are meant to hold the nitrogen in the system, and they sure have been doing a good job. Hurray for the random internet source I used! 

Since we were really scared and didn't know quite what to expect, I clamped the bulge test parts underneath a table and put a blast shield in the way. This reminds me a lot about my senior design project where we just spun a bunch of magnets at a couple thousand RPM. I should consider safety a bit more in the future maybe. In the picture above, though, you can clearly see some bulging occurring in the titanium sheet.

And above here you can see some bent metal. Except instead of titanium it was aluminum. This aluminum burst at pressures of maybe 100 psi or less. Very weak! Because the pressure was still so low, the metal didn't fly off anywhere. That's what I need to happen with the titanium samples. However, that will be quite unlikely. Therefore, a different plan of attack is necessary.

Here you can see a picture of a bulge test of the titanium at 430 psi. The 440 psi test burst, so there aren't any good pictures of that. Notice the crease around the edge of the 20 mm diameter bulge? Yeah, that's the sign of a stress concentration (more on that later).

Here is a picture of all of the samples we tested. Titanium bursts at around 440 psi while Aluminum burst at quite low pressures. The 2 mm bulge test on the bottom left of the picture did not show much promise at all for us. We simply cannot achieve enough pressure to bulge that small diameter.

We tried using strips of Ti over whole blank sizes of other material. 100 micron thick Al did not work well. Two 50 micron blanks of brass was too strong. A single 50 micron brass blank underneath a strip of Ti seemed to work well. By using different strip geometries, different strain paths can be achieved throughout the testing. Also notice that the Ti on the bottommost sample still failed at the edge of the bulge. This indicates a stress concentration. I have had the inside radius of the tooling cut down to a 1.5 mm radius. This has worked well thus far.

More later.