Blade as window breakers?

M

Minibear464

Joined
Jul 14, 2011
Messages
687
Just wondering if a knife blade could possible break a window. Also, would substituting blade steel for a carbide tip in a window breaker work? Such as the umnumzaan's window breaker.
 
a folder? not likely. some up-coming spydeys will have carbide glass breakers incorporated, i think. the rescue will have a glass breaker that emerges only when the knife is gripped in the closed position.
 
Seeing as a small window breaking hammer can shatter a car window no problem. I don't see why a knife couldn't as well. That being said. The blade would probably suffer some damage.
 
I wouldn't see a knife such as say a BK2 having any trouble at all breaking a window. I mean, its pretty much a one pound chunk of steel.
 
hank_rearden said:
a folder? not likely. some up-coming spydeys will have carbide glass breakers incorporated, i think. the rescue will have a glass breaker that emerges only when the knife is gripped in the closed position.
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It's been in existence for a while now. Many Microtech knives both manual and auto have a glass breaker, as mentioned the Umnumzaan, and a few others have it.
 
If I was going to break a window with a folder I would leave the knife closed and hit a hard shot with the butt-end of the knife. Just my two cents.
 
Aye... I'd use the handle instead. Especially if it's a fixed blade, where you most likely have the tang extending to/beyond the handle.
 
exactly. the blade is such an unlikely bearing point. the butt looks perfect by comparison (with or without a carbide tip.)
 
Tempered glass is kind of hard to break with a knife. It can be done, but it is not ideal. Household glass is no problem.

I was surprised the first time I tried to stab a window to break it (scrap car at friends, bored, young)... the knife bounced. Same with the next several blows. I did get it to break but it wasn't as easy as the movies make it. (btw this was from the outside going in, from the drivers side window. a smaller window or the windshield would be even harder. I suspect from the curvature of the window going from the inside out would be easier).

The harder the material hitting the window the easier it is...thats why carbides are used. Some thieves discovered the ceramic portion of a spark plug works well...they call them "ninja rocks" and use them to break through car windows.
 
I`d use the blade of my CQC-7. The tanto tip should go through a window without any problems. I want to try it out tho.
 
yeah most blades are softer than glass therefore you would need to deform or bend the glass till it shatters instead of using a harder implement to crack the glass and propagate the crack

Been toying the idea with drilling a divot in the butt of a fixed blade knife handle and super glueing some ceramic from a spark plug. You can see whole buncha ppl throwing spark plugs at windows ceramic end first and it pops the glass easy.
 
ecos said:
The harder the material hitting the window the easier it is...thats why carbides are used...
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Above a certain HRC, hardness of the glass breaker is less important than geometry and impact force. Carbides are used because they are inexpensive and require very little material support to resist deformation and fracture. Steel glass breakers are also very common as the steel is made up of carbides. However, steel tempering must be considered to place carbides in a sufficiently tough matrix at the intended point of impact. If the steel lacks carbides and is too soft, it will deform; but if the carbide-matrix is insufficiently elastic, it may fracture. Ceramic engineers have better success than metallurgists on this front, that's all.

An efficient glass-breaker reduces the amount of force (energy, momentum) required to fracture glass. This requires a geometry that focuses the energy of a blow to as small of a point as possible while also providing sufficient material support to prevent the glass-breaker from deforming substantially, i.e. losing impact energy and also distributing the force over a greater area of the glass being struck. Hardened steel (e.g. 60 HRC) with the same geometry as a SiC breaker may suffer only minor deformation on an impact with an unnoticeable difference in the amount of energy required to accomplish the task. A rounded stone off the street may require more energy to fracture the window but may suffer minimal fracture/deformation due to increased material support. An aluminum can can fracture a front windshield, as can a 30oz cup of soda with sufficient ice depending upon the amount of energy transferred on impact.

The Victorinox Rescue Tool uses a thin, replaceable glass breaker.

Another thing to keep in mind is that auto-glass (at least in windshields) tends to be "safety-glass", i.e. if the impact energy exceeds the threshold of the shield's endurance, it fractures readily into teeny tiny pieces, distributing the force of impact as much as possible (so that less energy is transferred into moving glass projectiles and also reducing the incidence of large shards).


Glass breakers are VERY common on folding knives... but often they are unnecessary as any part of a knife with sufficient material support behind the proper geometry can be used to break glass if given sufficient momentum. But in most folding knives (and small/mid-sized fixed blades), insufficient momentum can be imparted to the tip of the knife do get the job done. Use the pommel or some other relatively pointed edge that you can get some force behind.
 
brandonc said:
I wouldn't hesitate to use my ZT0300 or CS spartan.
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lol... Just toss the spartan at a window, open or closed, and it'll break the window :p


And I've heard that the ceramic vs glass is akin to hitting a diamond in just the right spot. The two materials for some odd reason are perfect for breaking and being broken by each other without much effort.
 
My glass breaker is an old Cold Steel carbon V Trail Master that I keep tucked in between the center console and the passenger seat of my car. I keep the sheath unbuttoned so it's ready for action. It also makes a quick defensive weapon if trapped in your seat belt and you can't get to your folder in your pocket.
 
Minibear464 said:
So the blade won't be able to break the glass? How much HRC would you need to break it easily though?
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Again, it's not so much about the HRC, it's about the distribution of energy on impact, i.e. how much pressure (force/area) are you exerting on the glass and how much of the energy is the glass able to deflect/disperse rather than absorb. A slow-moving large object of high HRC (e.g. brick) impacting the window with a flat surface thereby distributing its kinetic energy over a wider area may have less chance of breaking the glass than an aluminum can of relatively low HRC with the same kinetic energy impacting the glass at a tiny point.

In practice this means that the glass breaker need only be hard enough to not have all of it's energy dispersed through material deformation on impact.
If we are comparing ONLY hardness of objects, i.e. controlling for shape as well as mass and speed (kinetic energy) etc., then harder objects will deform less upon impact and so require less impact energy to break the pane of glass... but how much less energy? Steel at air-temperature is relatively hard even at only 30 HRC (well below ceramic levels). Putting an equal amount of energy into a steel vs. ceramic glass-breaker identically shaped like an arrow field-point (standard glass-breaker shape), I doubt you'd be able to detect by hand a difference in the amount of energy required to break a pane of glass. If one was hardwood or hard-rubber instead, THEN the difference would be detectable - the softer material would require more energy to induce the crack. I don't have any numbers though.
 
chiral.grolim said:
Again, it's not so much about the HRC, it's about the distribution of energy on impact, i.e. how much pressure (force/area) are you exerting on the glass and how much of the energy is the glass able to deflect/disperse rather than absorb. A slow-moving large object of high HRC (e.g. brick) impacting the window with a flat surface thereby distributing its kinetic energy over a wider area may have less chance of breaking the glass than an aluminum can of relatively low HRC with the same kinetic energy impacting the glass at a tiny point.

In practice this means that the glass breaker need only be hard enough to not have all of it's energy dispersed through material deformation on impact.
If we are comparing ONLY hardness of objects, i.e. controlling for shape as well as mass and speed (kinetic energy) etc., then harder objects will deform less upon impact and so require less impact energy to break the pane of glass... but how much less energy? Steel at air-temperature is relatively hard even at only 30 HRC (well below ceramic levels). Putting an equal amount of energy into a steel vs. ceramic glass-breaker identically shaped like an arrow field-point (standard glass-breaker shape), I doubt you'd be able to detect by hand a difference in the amount of energy required to break a pane of glass. If one was hardwood or hard-rubber instead, THEN the difference would be detectable - the softer material would require more energy to induce the crack. I don't have any numbers though.
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This is good info, one point I would like to make it that you need to hit the glass as close to the corner as you can. The glass will break much easier in the corner. I have broken tempered glass with the tip of an antenna, axes, pommel of a folder, various hand tools basicly anything that you can get a bit of momentum and has a small surface area for striking and aim for the corner of the glass.
 
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