MrAcheson said:
A great example of this is the aforementioned "hydrostatic shock". But what do you expect from articles often written by MDs (like Fackler) who probably haven't had physics since the freshmen year of their undergraduacy? If my work in biomedical engineering taught me anything, it was that medical doctors don't do equations or math unless it involves calculating a pharmaceutical dosage.
You noticed that too.
MrAcheson said:
However, I don't think you are attacking their argument. Instead you are attacking some sort of caricature of their argument based on their flawed terminology. For instance several of your criticisms of Fackler hinge on his use of the term "sonic". Is he actually restricting his analyses to pressure waves of sonic frequency or is he simply applying an poor technical description (from my perspective) to his own work?
Actually, I don't think Fackler has actually published any of his own research showing anything at all about the ballistic pressure wave ("sonic" or otherwise). He references a paper by Harvey et. al., makes some vague comments about not seeing any effects in his experiments (that aren't designed to see pressure wave effects), and references a private communication about Vietnam era trauma surgeons not seeing broken bones or blood vessels resulting from a pressure wave.
So while you might be right that I shouldn't make a point about Fackler's imprecise language, in his zeal to denounce the valid research of Sunseon et al, Fackler strains the bounds of credulity in areas where a medical doctor really should know better.
Fackler writes:
A review of 1400 rifle wounds from Vietnam (wound Data and Munitions Effectiveness Team) should lay to rest the myth of “distant” injuries. In that study, there were no cases of bones being broken, or major vessels torn, that were not hit by the penetrating bullet.
How can a medical doctor refute modern observations (using new methods) of microscopic damage to nerve cells by referring to the absence of observations of broken bones or torn blood vessels in a Vietnam-era observations from trauma surgeons? The Vietnam-era study was not looking for distant nerve damage, and they did not employ the methods used by Suneson et al.
MrAcheson said:
Also most of my experience with damage through pressure wave effects (like hydrodynamic ram) show that the vast majority of damage from a pressure wave is derived from the initial overpressure and impulse which is of very short duration. Once the projectile fully enters the medium (in this case a fluid tank), the actual overpressure drops precipitously and you enter a new phase characterized by cavity formation. Now I'm talking about a phenomenon occuring in a newtonian fluid, not human body tissues which are very non-newtonian, but some of the theory is certainly applicable.
Look up some of the journal articles I've referenced, as well as some of the articles on the fluid percussion model of traumatic brain injury.
There is also a study in rabbits showing that TBI can result from underpressure.
MrAcheson said:
In my experience, Fackler's assessment of pressure wave then temporary cavity is not unusual or even considered particularly controversial.
That doesn't mean it is correct. The leading edge of the pressure wave propagates at the speed of sound in the medium. But concluding that's all there is to the ballistic pressure wave would be like concluding that an earthquake is over after the P wave has passed.
Think about Doc Edgerton's photographs of a bullet passing through an apple. First, the bullet passes through the apple, and the photograph shows the apple with two bullet holes and the bullet a few inches past the apple. Since the bullet has exited the apple, it is clear that the leading edge of the pressure wave (sonic velocity) has reached the surface of the apple, but the apple remains whole until a later component of the pressure wave causes the apple to explode. (Do a web search on "How to Make Applesauce at MIT."
Putting a high-speed pressure gauge into ballistic gelatin demonstrates that there is a lot more to the ballistic pressure wave than the compression waves that travel the speed of sound. Putting the ballistic gelatin into something to simulate a rib cage and skin demonstrates even more longer-duration activity of the ballistic pressure wave.
Some of the references cited in the initial post actually insert a high-speed pressure gauge into the living test subject. Now, these guys think like biologists, so they get thrown a bit by the fact that the leading edge of the pressure wave arrives in a time consistent with the speed of sound in water. They may have failed to realize that the duration of the wave indicates either that there are more slowly traveling components to the wave and/or that the wave reverberates around for some time.
Suneson et al. report that the leading edge of the wave travels a distance of roughly 0.5m in about 0.34 milliseconds. Yet the duration of the wave is 1.5 milliseconds. Clearly, there is more to the wave than the leading-edge sonic component.
Our own work indicates that the ballistic pressure wave can have a duration as long as 10 milliseconds for bullets impacting the thoracic cavity. The wave components that arrive first (sonic velocities) have more high-frequency components, and the later arriving wave components are a mixture of high-frequency components (possibly reflections of the leading edge) and lower frequencies.
At this point, it remains an open question whether the leading edge (high-frequency) or later (lower frequency) components play a greater role in incapacitation. This question is worth addressing in later research because one might design bullets to concentrate more energy in the more effective frequency range.
For now, we have shown that incapacitation is well-correlated with the peak pressure magnitude.
Michael Courtney