Blade
From Wikipedia, the free encyclopedia
- For other uses of the word blade, see Blade (disambiguation)
A blade is the flat part of a tool or weapon that normally has a cutting edge and/or pointed end typically made of a metal, most recently, steel intentionally used to cut, stab, slice, throw, thrust, or strike an animate or inainimate object.
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[edit] Materials For Production
Material for weapon blades has to be carefully selected to achieve a balance between hardness and toughness and their ratio to each is dependent upon the intended use of a blade. In antiquity, the main metal used was copper, then of iron. Perhaps the most well known is pattern welding, a technique used for katanas (samurai swords) and damascus steel blades. This was a very labor-intensive technique - and thus such swords were very expensive.
Various techniques may also be employed to make the blade stronger or harder. Copper and bronze can be "work-hardened" by simply hitting the blade with a hammer while it is cold. Blades made of steel with a high enough carbon content (greater than 0.2%) can be heat-treated by heating the steel up to a critical point (most alloys become non-magnetic at that point), then quenching it in water. Quenching puts an enormous amount of stress on the metal, and often a sword would break into pieces during that step. If the sword survived heat-treating, it would be tempered by heating it to a relatively low temperature for an extended period of time. The tempering process would make it slightly softer, but also tougher and "springier", and thus less likely to break or chip during the rigors of combat.
Case hardening is a process of increasing the carbon content at the surface of very low carbon steel. It is done by placing the object to be hardened in a sealed container along with carbon-containing material; in antiquity, this material was usually horn or hide. The container would then be heated until it was glowing red, and held at that temperature for awhile, based on the size of the part being hardened, allowing carbon to penetrate the steel by a few thousandths of a centimeter. At that point, the object would be dumped out of the container into a water bath to quench it, resulting in a very hard surface, but completely unhardened core. There is very little evidence of this having ever been done to swords except, perhaps, the very earliest of iron blades. Due to the inherent weakness of a sword's cutting edge, coupled with the high-impact stresses of combat, such a thin hardened surface over a soft core would provide very little advantage in terms of edge-holding, other than mild wear resistance.
Another important aspect of many blades are so-called "fullers". Despite popular belief, fullers were not "blood grooves" that facilitated quicker bleeding of the victim and easier removal after insertion, nor did they reduce the weight of a blade. Rather fullers helped to make a blade stronger and more durable at the core without reducing the strength or flexibility of the edges. They were made by positioning a heated blade over a bottom fuller, setting a like sized top fuller on the top side of the sword, and hitting the top fuller with a hammer.
[edit] Physics of Blades
The basic idea of a blade is very similar to a sharp point. The shape concentrates all the force onto a very small area, resulting in a high amount of pressure which allows it to penetrate matter.
A serrated blade (a blade which has many small "teeth") takes this further as each individual tooth concentrates the force on a smaller area which helps cut through harder materials. A serrated knife can cut through objects solely with a sliding motion with little pushing force, this is useful for tools which require these attributes such as bread knives.
Some bladed weapons (and tools) have curved blades. A curve can serve two purposes, the first is that it allows for slicing by continuing to "push" on the surface as it is drawn across it. The other effect is to allow the force to be concentrated in an even smaller area.
As a rule the blade must be made of a substance which is harder than (or as hard as) the material it is intended to cut. If this isn't the case the blade will either be unable to cut (as it absorbs all the energy as it is damaged) or will wear away very quickly (if it is hard enough to transfer enough of the energy to damage the material). In practical terms the material must also be tough enough to last (e.g. glass is very hard but it shatters easily and thus isn't very effective as a material for a blade).
The problem is further compounded by the fact that heat treatments, which increase hardness for better edge-holding, inevitably reduce the material's toughness. Essentially speaking, a balance must be found between how well the edge must hold, and how well it can last. Methods that can circumvent this somewhat do exist however; for instance differential hardening allows for an edge that can hold well, and a body that can withstand mechanical stress.
[edit] Geometry
An ideal blade would come to a perfect edge—not at all rounded—but that says nothing of the angle of that edge. The ideal angle is a function of the material being cut. For example, a tool bit for cutting metal may have nearly a 90° edge; it would probably not even be considered a blade. With very rigid materials such as metal, cutting deep into a piece with a blade would be impossible so deep cutting is done with a saw or grinder which provides kerf through which the cutting device can pass. With less-rigid materials such as a butternut squash, an acute blade prevents the blade from being pinched by the material. When cutting biomaterials such as tomatoes (which tend to have a low elastic modulus but high yield strain), the angle of the blade is less important since the material will bend, but the sharpness of the edge is important because if too much force is required, the material will be squashed rather than cut.
[edit] Dulling
Blades dull with use and abuse. This is particularly true of acute blades and those made of soft materials. Dulling usually occurs due to contact between the blade and a harder substance such as a ceramic or stone. To a first approximation, a harder material cannot be deformed by a softer material at their interface because the stress on both materials is the same at the interface and so the softer material will yield first. One exception to this is when the highest stress isn't at the contact point; this is why one can easily bend a steel paperclip even though an end of the same paperclip could scratch one's skin.
[edit] Variation in blades
[edit] Decoration
Decoration was often applied to the blade - usually engraving and sometimes inlaying with gold. In the 19th century, it became common to etch designs on the blade using acid and a wax template.
[edit] Shape
Swords may have either a straight blade or a curved one. A straight sword was primarily intended for hacking and stabbing, whilst a curved sword was better at slashing. The difference between a hacking cut and a slashing one is essentially the same as the difference between using a butcher's knife and a chef's knife; one forces an edge straight into a material while the other is pulled along the material to get more of a slicing action.
For a horseman, stabbing was not practical because it is hard to make a horse move swiftly backward should the thrust fail to strike the victim. The cavalryman would then be at the mercy of his erstwhile victim. This was not so important in massed cavalry charges, in any case in such attacks the cavalry would often be in closely packed formations in which slashing would not be possible. Consequently, European heavy cavalry generally had straight swords.
Some variation included
- the flame blade (undulated blade, for both psychological effect and some tactical advantage of using a non-standard blade: vibrations and easier parry)
- the colichemarde, essentially found in smallsword
[edit] Backsword
Cavalry that engaged in single combat or in looser formations normally had curved swords. In order to slice, a sword had to be drawn across the victim's skin, and a curved sword was more suitable for this. The blade was only sharpened on the outer edge and the radius of curvature was equal to the distance from the centre about which the blade was rotated - i.e. the distance from the blade to the shoulder.
In curved European swords, this was usually a full arm's length, but in the Middle East and Indian swords it is generally a much shorter distance - typically 50 cm or so (see scimitar). This gave Eastern cavalry a great advantage over their European counterparts because they were able to fight at a closer distance than the Europeans were used to and therefore get inside their sword arc.
Single-edged swords have a back (hence their generic name of backsword). This is the unsharpened edge. Early 19th century swords had a "pipe-backed" appearance, whereby they had a thickened ridge along the back to make the blade stronger.
