Bert
December 18th, 2003, 03:43 PM
Several people have made claims in various threads here as to vod of substances they've made. When pressed, at least one admitted he'd just guessed, using as a basis the amount of damage caused to a target compared to that caused by another substance with a published vod available- (See Maniak's posts in the Plastickexplosives (http://www.roguesci.org/theforum/showthread.php?s=&threadid=127&perpage=50&highlight=plastick&pagenumber=2) thread)
I've seen two methods of determining vod- one by using a loop of det cord of a known vod with the ends placed against a length of the material to be measured for vod a known distance apart, the vod is calculated by the offset from the center of the loop of det cord that the shockwaves from the explosion fronts meet, which can be found by placing the loop of det cord on a lead sheet and observing the placement of the deeper dent caused the meeting of the two converging shock waves.
The second method is basically the same, but uses a length of shock tube instead of det cord and no lead witness plate is required- The shock tube will burst at the point where the two shock waves meet, the measurement of offset may be taken directly from the remains of the fired length of shock tube.
These methods require a column of explosive large enough to sustain a detonation, and the first measurement must be far enough from the point of initiation for the shock wave to have "settled down" to an even speed. They're somewhat dependant on the containment of the charge and diameter of the column too, which is why you may see that data included in tables of measurements in CPOE & etc.
Can anyone suggest other methods? Most particularly, ones that would not require commercial det cord or shock tube, nor other equipment that isn't both fairly cheap, easy to haul out to the woods and widely available (portable oscilloscopes and high speed triggering mechanisms would not do).
As an aside, what is state of the art in current commercial and military practice?
(edit)
My first idea is to adapt a cheap, portable commercial sky screen type chronograph. Haven't completely figured out the triggering though, and I'm just guessing that one of these would be capable of measuring speeds in the range necessary. In my preliminary scheme, the charge would be set midway between the screens and a projectile attached to the sample in two places a known distance apart. Ideally, they would then be blown through the sensor areas of the two screens at a time interval equal to the time necessary for the shock wave to progress between the two points, assuming equal distance to the sensors and equal velocities imparted to the projectiles. The placement between sensors would be easy, equal velocities being imparted is a BIG assumption with no way to check... And in the higher vod's, some engineering might be needed to keep the projectiles from merely being shattered.
Anyone else got any ideas?
I've seen two methods of determining vod- one by using a loop of det cord of a known vod with the ends placed against a length of the material to be measured for vod a known distance apart, the vod is calculated by the offset from the center of the loop of det cord that the shockwaves from the explosion fronts meet, which can be found by placing the loop of det cord on a lead sheet and observing the placement of the deeper dent caused the meeting of the two converging shock waves.
The second method is basically the same, but uses a length of shock tube instead of det cord and no lead witness plate is required- The shock tube will burst at the point where the two shock waves meet, the measurement of offset may be taken directly from the remains of the fired length of shock tube.
These methods require a column of explosive large enough to sustain a detonation, and the first measurement must be far enough from the point of initiation for the shock wave to have "settled down" to an even speed. They're somewhat dependant on the containment of the charge and diameter of the column too, which is why you may see that data included in tables of measurements in CPOE & etc.
Can anyone suggest other methods? Most particularly, ones that would not require commercial det cord or shock tube, nor other equipment that isn't both fairly cheap, easy to haul out to the woods and widely available (portable oscilloscopes and high speed triggering mechanisms would not do).
As an aside, what is state of the art in current commercial and military practice?
(edit)
My first idea is to adapt a cheap, portable commercial sky screen type chronograph. Haven't completely figured out the triggering though, and I'm just guessing that one of these would be capable of measuring speeds in the range necessary. In my preliminary scheme, the charge would be set midway between the screens and a projectile attached to the sample in two places a known distance apart. Ideally, they would then be blown through the sensor areas of the two screens at a time interval equal to the time necessary for the shock wave to progress between the two points, assuming equal distance to the sensors and equal velocities imparted to the projectiles. The placement between sensors would be easy, equal velocities being imparted is a BIG assumption with no way to check... And in the higher vod's, some engineering might be needed to keep the projectiles from merely being shattered.
Anyone else got any ideas?