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Discussion Starter · #1 ·
The primary goal of most of my research cannon experiments was to record the mechanisms of composite armor damage and/or penetration as it happened. This information is valuable in designing composite armor. Samples were fitted with measurement guages, shot and the effects recorded. But these events are brief, normally lasting less than a thousandth of a second on small samples. Some of the most valuable information lasted less than 18/100,000 of a second. In order to maximize the learning that can be gained, the electrical measurement ciruit has to respond almost instantly.

I designed and built all of my own circuits using common parts from electronics stores. Usually, I was measuring the time span between two signals. In order to do this I designed my circuits to yield four possible voltages (V), for example: 0 V, 2 V, 4 V, or 6V. If neither switch worked, the circuit continued to indicate 0V. When the first switch was closed, the circuit went from 0V to 4V. When the second switch was closed, the circuit yielded an additional 2V. If both switches worked properly, the circuit would jump from 0V to 4V when the first switch was closed and then from 4V to 6V when the second switch was closed. In this manner, I knew if both switches had worked properly and the time between their closings.

The first switch was of my own design and construction. I fabricated it and mounted it on the front face of the armor. It was physically closed by the projectiles impact. The first switch also served to initiate the oscilloscope's data recording.

The second switch was not truly a switch, but a custom built, piezoresistive, z-axis carbon strain gauge. These were manufactured to my specifications by the company that invented them. When the damage wave reached it, the gauge changed resistance and a voltage was created in the circuit.

Batteries were used as the electrical power source, but they were not alone. Batteries depend upon the speed of their chemical reactions to begin supplying electrical current. Unfortunately, batteries are way too slow to work by themselves. The answer was to include capacitors in the circuit.

My circuit was able to provide electrical power at the correct level within 6.7/10,000,000 of a second after the projectile impacted the armor. During a period in which over 300 shots were fired from the research cannon, only one target failed to provide data and that was due to lab visitor playing with an alignment bolt.

The real secret to research success is to check your circuits and switches over and over. I checked my ciruit and switches at least six times before every shot. There is no magic, just tedious, painstaking effort. What I did with my circuit and switches is no different than the ammo reloading efforts put forth by a skilled, long range rifle competitor.
 

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Do you primarily measure the insensity of the damage waves, the harmonics (feq / amplitude), or do you also look at the patterns the waves travel in?

i.e.:

do the waves tend to be uniform and radiate out equally from the point of impact?

Do you look at the effects of internal strucures of the target has on the waves?

For example if the target were a composite of fibers layed down in alternating layers where the direction of the fibers was changed with each layer, vs a single material.

what about composites of varying materials?

how does internal bracing affect the results?


(Ok, I admit it, I'm a science geek when it comes to this stuff...)

the discussions have been great!

Thanks

:devil:
 

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One technique I've seen for determining stresses and the like, involves embedding the sensor into the target. Basically a lattice of material is glued to the target. The material is such that the peizo electric charge is generated between an X and a Y wire pair. The propagation of the coordinates can give you the speed and direction of the waves as they travel through the target. (of course the sensor is destroyed with each use, which makes it costly...)

The data is captured via computer, with a very large FiFO buffer to queue up the large number of events that happen in a very short amount of time.

(I know, more geekiness...but I'm really enjoying this thread.)

:devil:
 

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Discussion Starter · #4 ·
Aslan said:
Do you primarily measure the insensity of the damage waves, the harmonics (feq / amplitude), or do you also look at the patterns the waves travel in?

i.e.:

do the waves tend to be uniform and radiate out equally from the point of impact?
I was looking for the wave speed and how the waves propagate. Some interesting patterns do occur that are frequency related.

Do you look at the effects of internal strucures of the target has on the waves?
Somewhat, the big thrust in textile-based, composite armor has been the effects of different weave patterns.

what about composites of varying materials?
Since you know the Young's modulus, density, etc. of the desired material, many initial tests of weave effects can be run using cheaper materials. Later tests can be run using the desired material.

how does internal bracing affect the results?
Different uses of the term internal bracing come to mind, structural and material. Which one are you asking about?
 

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Discussion Starter · #5 ·
Aslan said:
One technique I've seen for determining stresses and the like, involves embedding the sensor into the target. Basically a lattice of material is glued to the target. The material is such that the peizo electric charge is generated between an X and a Y wire pair. The propagation of the coordinates can give you the speed and direction of the waves as they travel through the target. (of course the sensor is destroyed with each use, which makes it costly...)

The data is captured via computer, with a very large FiFO buffer to queue up the large number of events that happen in a very short amount of time.

(I know, more geekiness...but I'm really enjoying this thread.)

:devil:
I was using piezoresistive pressure gauges. They were not strain gauges in the usual sense. As these gauges are compressed, the energy of compression raises the energy level of the electrons. After sufficient compression, the resistance of the gauge is lowered. Used in the test circuit bridge, a voltage is produced and measured.

Future composite armor will incorporate its own damage assessment and repair capabilities. IMO, the best gauges for this role may be diffraction pattern, fiberoptic strain gauges, due to their ability to be woven in the armor during manufacture.
 
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