Breaking a Ceramic Knife Blade
By Chuck Hawks and Rocky Hays
Our recent series of reviews of the excellent Schrade SCH 401, SCH 401L and SCH 402L folding knives with ceramic blades and carbon fiber scales (see the full reviews on the Cutlery page) piqued our curiosity about the strength of ceramic blades. Like most outdoorsmen, we have heard that one should never pry, twist, lever or strike a ceramic blade. These blades are intended for cutting flesh, skin, meat, vegetables and other soft tissue and are known to snap if used improperly. Nor should one cut on a hard surface for fear of chipping the edge.
At one of our weekly "Shooter's Coffee" meetings, we got to wondering just how fragile a ceramic blade really is. We resolved to find out by testing a ceramic blade to destruction.
Naturally, we were not about to intentionally destroy a fine Schrade folder, so we decided to purchase a low cost ceramic kitchen knife to serve as a test subject. Guns and Shooting Online Gunsmithing Editor Rocky Hays volunteered to do the actual testing.
For less than $10 at our local Bi-Mart department store we purchased a sacrificial ceramic paring knife. This, of course, did not come with a hollow ground, mirror polished blade like a Schrade folder, but for an economy substitute, we figured it would serve our purpose.
The kitchen knife's blade measured 0.060 inch thick, while the Schrade SCH 401L blade is 0.075 inch thick. In addition, we do not know if there are different grades of ceramic blades. All we know about these ceramic blades, for what it is worth, is that both knives were manufactured in the Peoples Republic of China.
This first photo shows Rocky's simple, but effective, test set-up. The knife blade was clamped between wooden blocks, a digital scale was positioned on the knife handle six inches from the ultimate location of the break and a bucket to which weight could be added until the blade snapped was attached to the scale. (Note the sand in the bucket on the floor.)
The second photo shows the cheap blade bending under a 4.06 pound (4 pound, 1 ounce) dead weight load, before ultimately failing after the addition of an additional 0.38 pounds of weight. Given its extreme hardness, edge retention and reputation for brittleness, we were surprised to find that a ceramic blade would visibly bend before breaking. It certainly did not bend close to 90-degrees, as will a top quality, steel blade from a Master Bladesmith, but we were impressed that the ceramic blade had any visible flex at all. Apparently they are not quite as brittle as we had thought.
The blade snapped at 4.44 pounds of weight. Since the weight was six inches, rather than 12 inches (one foot) from the break, the force that caused this particular ceramic blade to fail equates to 2.22 ft. lbs. This is not an impressive number compared to a steel knife blade, but all things considered, this cheap ceramic blade proved more durable than we had expected. Our testing, while certainly not definitive, increased our understanding of how ceramic blades fail.
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