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"Blade damage, cross-sections and heat-treatment" - Introduction on designing historical weapons

An article based on the representation of Adam Bodorics - owner and lead designer of Landsknecht Emporium - at R(h)einhau 2025.

The goal of the original representation and this article is to provide simplified answers and explanations of questions often asked about the durability of particular designs. Why are certain designs more prone to damage or failure? How could these perceived issues be handled? What are the main guidelines behind the designs of Landsknecht Emporium products?

Violent interaction between physical objects is an extremely complicated subject, and is often further complicated by expectations, biases, and insufficient or incorrect knowledge. This article uses the same gross simplifications of concepts based on physics, material science, and experimentation as the original representation. First, a clarification of certain terms:

“Originals” mainly refer to sidearms with a knifelike hilt construction from the 15th to 16th centuries.
“Period”, “in period”, and similar descriptions refer to the aforementioned 15th-16th centuries unless specified otherwise.
The following will concern cases where no verifiable material or manufacturing fault can be found, yet the blade nicks, chips, takes a set, or breaks. This presentation is not an attempt to shirk responsibility for verifiable material or manufacturing faults.

Main attributes and their interactions

The quality, durability, and specifications of any bladed product have a couple of common factors as major contributors to their attributes. These factors also have to be taken into account during the design and/or redesign of the product. Some of these factors are either less well-known or often misunderstood by users due to a lack of easily available information on the matter. In the first half of the article, we'll take a close but not too technical look at these factors.

Heat-treatment

This factor is one of the most well-known, but also often misunderstood - in a greatly simplified way, hardness is the material’s resistance to plastic (non-reversible) deformation, in other words, the capability of withstanding any and all foreign objects trying to clip through the object by pushing it aside. It is most commonly measured on the Rockwell scale in units of HRC. The industrial standard for the measurement of hardness is to use a value with a spread of 2 (f.e, 40-42, 50-52, etc). This accuracy can be achieved relatively simply within industrial settings and is sufficient for the vast majority of the use cases of steel. While there are technical solutions for achieving an exact HRC value, their cost-to-benefit ratio is very unfavorable for most applications.

When two solid objects interact with each other with enough force to cause plastic deformation, both objects will deform. If there is a difference in the hardness of the objects, the harder object will deform the softer object to a greater degree, but the harder object will also suffer deformation with the same exact force (see Newton’s third law). The greater the difference in hardness, the less plastic deformation the harder object will suffer, but the amount of deformation will always be greater than zero. A simple example from our everyday life is that we practically never use kitchen knives for cutting steel or materials that have comparable hardness. Yet, kitchen knives require regular honing and (at least) occasional re-sharpening. Just try to tell a professional chef or butcher not to sharpen or hone their knives for a week and watch their face.

So, to make a blade extremely resilient to plastic deformation, all you have to do is max out hardness, at least in theory - the keywords being "in theory". This solution would work perfectly with completely rigid but unbreakable theoretical objects. Unfortunately, reality and physics prove this theory wrong in practice, as with many other things. Hardness indirectly defines what happens if you stress the material beyond its critical point. Again, greatly simplified – very soft things like putty deform while very hard things like glass shatter. A very similar thing is happening to steel – you can repousse annealed plate, and you can see the glasslike cracks on WW2 German armor in photos. At less extreme differences, a blade heat-treated to 46-48 HRC will take sets and the edges will roll or get burrs, while one heat-treated to 56-58 HRC will be more prone to breaking and the edges chipping from the same impacts.

Thoughness

As said, hardness indirectly defines what happens past the critical point. This can be loosely defined as Toughness. We can describe toughness as the resiliency of the material against fatigue, or repeated stress. Toughness defines how much total energy the material can absorb before rupturing or tearing, in simple terms, failing. Energy applied to the material is not just a momentary effect, though - the absorbed energy can be displaced in some way (f.e, with movement), but at least part of it is always absorbed, effectively degrading the all-time toughness of the material. Bending and other deformations will continuously lower the toughness of the material if repeated over and over. This will inevitably lead to the failure of the material - usually with a fracture - even if the applied force never even approaches the breaking point (known as the critical stress level, critical force level, failure point, etc.) in itself.

Generally speaking, the higher the HRC value of a certain piece of steel is, the lower its toughness will be. In other words, the harder the steel is tempered, the more rigid/brittle it will be, and the more and/or more often you bend it, the sooner it will break. There are exceptions to this, like 80crv2 steel, which is prone to temper embrittlement; thus, a lower hardness corresponds to a lower toughness, although these types of steel are rather the outliers than the norm.

Summarizing the above, we "simply" need an ideal mix of hardness and toughness. What is this ideal mix? This depends on what we expect from the end result, but generally, sharp blades require good edge retention, and blunts are required to be long-lasting. So let's make the sharps as hard as possible without making them brittle, and the blunts as tough as possible without getting down to the point where you can tie a knot on the blade.

Flexibility

Speaking from a technical standpoint, flexibility is not the attribute of the material, but a property measured in mechanical structures. Contrary to popular belief, heat-treatment doesn’t really affect flexibility, at least not in the way users generally think. You need the same amount of force to bend the same piece of metal to the same degree, regardless of whether it’s annealed (soft) or heat-treated to 56-58 HRC. Heat-treatment only defines what happens after or during that bending - whether or not the steel takes a set, returns true, cracks (gets damaged), or breaks (fails).

In a greatly simplified way, we can say that the maximum flexibility of any blade will be determined by its largest area in its cross-section, regardless of its shape. While in practice this is more complicated, the thickest cross-sectional area of the blade will always be the most prevalent factor for determining flexibility, no matter how thin the thinnest part is. The thicker the thickest section is, the more rigid the blade will be; making it thinner will make it more flexible.

In case of swords, flexibility is almost exclusively determined by the cross-section and the length over which the force is applied - in other words, the mechanical structure of the blade. If we apply the same force to the tip of a short and a long blade, the measured flexibility will differ significantly. (This is also one of the reasons why measuring the flexibility of blades in kg on a scale might be very misleading.) A more in-depth explanation/verification of this claim can be seen by learning more about the Young’s modulus (commonly referred to as tensile strength), and checking if it changes from cold hardening or heat-treatment. (Spoiler: it does not.)

We experimented with hardnesses between 46-48 HRC and 52-54 HRC on our blunt blades over the years. The latter was a very short-lived experiment early on, and it performed as expected – that is, badly. The former technically worked fine, but after an increasing number of complaints of edges getting damaged, we reluctantly went up to the 48-50 HRC range, then finally to the 50-52 HRC range, which is the current standard hardness of our blunt blades.

Adams note: "While I personally dislike the decreased toughness and much prefer to avoid damaged edges by at least not cutting into each other's edges intentionally, but making contact with either the flat of the blade or the side of the "bevels", the feedback available to us shows that it’s the closest to the ideal mix for the majority of our customers."

Cross-sections and design philosophy I.

All the above attributes have to be taken into consideration while designing any kind or type of blade. The application of these attributes is, however, not a straightforward process where we pick certain attributes, sizes, and shapes and get an ideal end result. A blade should always be considered as a complex mechanical system, and the effects of the attributes on this system always apply to the whole system itself, meaning that choosing any one specific value may (and usually will) affect what we can reasonably expect to work for the specific values of other attributes.

The effects and importance of cross sections

An often-neglected or misunderstood parts of any sword design are the cross sections. While both the Oakeshott and Elmslie typologies include these for their classification, they are much more important than that. Any blade might (and usually does) have multiple types of cross sections along its length, not just in terms of size but shapes as well. Cross sections affect virtually all attributes of a sword - weight, weight distribution, flexibility, cutting ability, general handling, and behaviour of the blade. By making the right changes in the cross-sections within a blade, not just the amount, but the location and direction of the flexibility can also be tailored to specific needs.

Cross sections play a major role in determining the durability and cutting capability of a blade as well. A fun and very representative example of the importance of the cross-section is reviews or tests, in which either the maker or the reviewer shows the quality of the steel and/or heat-treatment, by cutting through mild steel, then slicing some paper. This is usually meant to prove either a superior, very special type of steel alloy or a perfectly made heat-treatment. In reality, a blade made of the humble 51crv4 steel, heat-treated by eye, barely exceeding a measured 50HRC hardness - in some spots, but mostly even below that - can be capable of the above-described feat if the cross-section is made robust enough with a sufficiently smooth surface finish, especially on the edge. This quick reality check is demonstrated by Adam in the video below (please disregard the sorry state in which the workshop was at the time of filming :) )

If the cross-section is sufficiently thick, it can support the edge and protect it from rolling or chipping. It does this, however, at the cost of increasing resistance while passing through the medium, decreasing the cutting potential of the blade. That’s why splitting axes are thick and razors are thin – or, to again offer a less extreme example, bone cleavers are thick, fillet knives are thin.
Most of the originals interpreted by modern users as being good cutters with good handling tend to have blades on the thinner, flatter end of the spectrum, especially in the last third of the blade. Consequently, sharp reproductions aiming to represent those originals will also need to be flat and thin. While this itself isn't too hard to achieve, if we wish to keep the characteristics of the blade (mostly) unchanged for a blunt training weapon and its sharp counterpart, things get much more complicated very quickly.

While designing a blunt blade based on a sharp version, several, often-contradictory requirements need to be balanced. The presence of certain requirements will mainly depend on the goals of the designer and, in conjunction with the intended use-cases for the item. For our company, our priorities concerning performance are in order

aesthetics
handling and safety
durability

It's best to discuss these points separately.

Aesthetics

It's important to note that when talking about aesthetics, we don’t necessarily mean “prettiness” or “shininess”, but rather the distinct overall look of Messers, swords, and other weapons, both when we speak about originals and our own products. This can be a balancing act on its own, because we have to take into account that our products are expected to have a much higher quality compared to originals. Combined with the fact that we prefer to use period-accurate techniques in our production, many of which do not translate well into modern technology and quality expectations and technologies, the final design has to accommodate the assembly methodology and tools used, accounting for tool marks, assembly tolerances, etc. The majority of originals, including high-status pieces, are made with generous tolerances, which most of us would see as “sloppy”. (Insert closeup of pimp shit)

In the case of messers, the peened shafts of Nagels often show deep hammer marks; they aren't flush with the cross, the bore going through the cross and blade is rarely countersunk, etc. To represent the average low-to-mid status Messer, we should do the same. To meet the modern ideals and expectations for cleanliness and neatness, we should countersink the holes and sand the peens completely flush with the cross. We already experienced that there isn’t a perfect solution here. If the peen isn't sanded perfectly smooth and into one plane with the crossguard, we get complaints and remarks about it being sloppy and badly assembled. When the peens are sanded perfectly into one plane with the crossguard with no visible joints, we meet some salty comments saying the Nagel is possibly glued in. We see similar patterns with many details of the products over the years.

Another often made comment on this topic is "it could/should be done better for the price" or, in another interpretation, "I can do it better". The first and foremost thing to consider is that we mainly use historical techniques in production, meaning that more than 90% of the production is done by hand, making labor the largest part of our costs. While many things could certainly be "done better", with handmade products, you quickly reach the point of diminishing returns - in other words, refining some of the details to be considered "good enough" for those making these complaints could roughly double the production time, making the price significantly higher, with us making not so much more. When receiving these questions, we often think about saying: "Great, could you do it consistently on ten pieces a day? That's about half of the amount we need, but still impressive! If you can do 20, you're hired!"

Handling

A somewhat self-evident point – in our opinion, a blunt representing a specific sharp model or a specific original should handle and have specifications and behaviour as close to it as possible, which means that it should at least have approximately the same weight and weight distribution. Remember this later on, as it is one of the main factors for making designing the same product with a sharp and a blunt blade quite difficult.

Safety

Safety is another complicated matter. Since our production manager has been involved in designing and producing protective equipment for military and law-enforcement personnel for about 10 years, and he has also been the lead designer of ISO standardized safety equipment, we have very mixed feelings about this topic. We'd like to get back on this in more detail in another article, but to keep things somewhat short, safety equipment advertised for HEMA is generally lacking, not just in administrative terms, but mostly in basic understanding of the requirements of protective gear designed and used for high-force impacts. Things are only made worse by the lack of any globally accepted, central governing bodies, making general rules and equipment requirements hugely dependent on any individual or group preference. Some groups may safely spar with even extremely stiff blades having small impact surfaces at the tips with minimal protective gear, while other groups may encounter injuries even with very flexible blades and tips with large surface areas combined with "heavy" protection, while both claim to fence with full contact and in a safe manner. This can make designing products that are considered safe by all users quite challenging in practice. To add another layer of complexity, while it’s not necessarily evident, flexibility or the lack of it is relevant not just for thrusts but for cuts as well. A portion of the impact’s energy always dissipates into vibration. More flexible blades vibrate more, thus absorbing a higher amount of energy from the impact. For our designs in the context of safety, limiting the penetrating capability of thrusts is the most important goal, achieved firstly by leaving the tips relatively wide and thick, and secondly by making the blades as flexible as possible without hurting the handling and aesthetics too much.

Durtability

We have good reason to leave this aspect for last. Our current assembly methods are severely overengineered compared to most originals, and the material quality is way above what was available in the contextual historical period. Even our thin-edged blunts have much more material in the edge than a sharp version would have of the same model. If there isn’t a verifiable material or manufacturing defect, yet the item in question gets destroyed, then, while sounding harsh and blunt, the user probably had a measurable, if not significant, role in the occurrence of the failure. It's true that there are ways to design and make near-indestructible training tools at the cost of aesthetics and handling. There are already great options for training tools that allow practically any kind of use with impunity; they are made of synthetics. Still, as we always emphasize, our whole company, design, and production philosophy is built around the creation of products that are as close to historical originals as possible, while factoring in modern-day expectations and reasonable safety measures as much as possible without deviating from our first goal.

Practical applications and thoughts on them

As mentioned and implied above, a lot of design choices come down to personal preferences, be it the personal preference of the designer or the perceived preference of their target audience. We prefer having edges as thin as possible while maintaining sufficient thickness for safe sparring. This helps simulate the behaviour of originals as closely as possible, which can very much include damage. We know perfectly well that direct, perpendicular blocking did happen and is part of a few historical techniques with the edges colliding, but we also know that the resulting damage was known, understood, accepted, and even accounted for in each case. Regardless of this, it will always have a severe impact on the long-term survival of the blade. While we don’t agree with all of the conclusions and ideas of John Clements - and even in what we agree with come with their own caveats as well - it is undeniable that he compiled several good sources on edge damage spanning several centuries in THIS essay.

We also have to accept that at least a part of historical sword users viewed their swords as consumable tools. This stance might not have been universal, and it’s entirely possible to fence by relegating perpendicular edge blocks to a last-ditch maneuver. At the same time, we also know from period diaries that the rank and file often used their swords as tools, and this resulted in a lot of broken weapons. So many, in fact, that Barnabe Rich recommends issuing them hatchets rather than swords. About a century later, George Monck goes as far as to recommend issuing them a “good stiff Tuck not very long” instead of swords, otherwise “half the Swords you have in your Army amongst your common men, will upon the first March you make be broken with cutting of Boughs”. It feels reasonable to say, being more mindful and aware of what your items can and can’t do will benefit you, just as it would have benefited the rank and file of the 16th-17th centuries.

Our opinion is that everyone is completely free to use and take care of their property as they wish, but if one treats their objects as consumables, then one should be prepared for them needing to be replaced sooner or later - the rougher the use, the more frequent the need for a replacement should be expected. We also think that if we are to think about HEMA as a sport, we have to accept that the equipment used is a consumable, just like in every other sport.

With all that said, we do intend to listen and cater to customer needs. The thick-edged versions of our blades are a result of us improving edge durability without having too much of an impact on handling, aesthetics, and safety. The way to achieve this was to increase the thickness of the edges, compensating for the extra weight by removing material from just behind the edge, and if needed for the specific design, by making the main fuller a bit wider and deeper.

A deep dive in practical application of design theory

After clearing up some definitions, discussing important guidelines for creating sword designs, and giving you a generalized description of our design and production philosophy, it's time to take a deeper look into how and why the previously discussed matters affect the design work in practice.

Let's check how the above-discussed theoretical points and requirements apply in practice to our Rutger R5B product by going through some of the basic steps of designing a blunt blade based on a sharp one.

Application of theory and options for redesigning the blade - the example is our Rutger R5B rugger

Designing this particular product started with Adam taking detailed measurements of an original item, currently in possession of the Matthias Rex Museum at Visegrád. Below you can see the finished design of the sharp model, made from the tracing (projected outline) of the original piece, corrected with the measurements taken.

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Original distal taper and profile drawing of the Rutger R5B based on the original artifact

This rugger has a decent profile taper on the blade, although the general shape is remarkably simple. The distal taper seems to be uninteresting at first glance. However, by taking a closer look at the tang, some quite interesting features of this item can be revealed - part of which we can find on many originals, in fact. In general, it's uncommon for original knifelike items to feature a rectangular cross-section that we see on modern reproductions and blunt fencing tools. A large number of the originals have a distal taper in the grip, lowering overall weight and giving another point of correction for the handling and behaviour of the blade. The lack of these features becomes more general as we go forward in time, and simple rectangular tangs become the norm sometime in the late 17th-early 18th century. However, the original artifact is dated to the 16th century and, as seen on the above drawing, has a somewhat rare feature on top of the previously described ones, namely that the thickest section of the distal taper is placed below the base of the blade, providing significant extra weight for the grip.

As already discussed in this article, we prefer to make blunt-bladed practice tools that have preferably identical handling as their sharp counterpart, but at least bring them as close to each other as reasonably possible. Let's see how we could achieve that, first starting from the same 8mm material we use for the production of the sharp Rütger. Leaving the tang unchanged might help us, so let's keep its original size and dimensions for the first iteration. As we know, a safe sparring weapon needs to have a thick edge both for durability and for safety. If we aim to have the best possible durability, we have to use a basic rectangle - this shape provides the largest amount of support possible behind the edges, thus minimizing edge rolling and burrs (for a theoretical perfect material and heat-treatment at least). To keep the handling of the sharp and the blunt versions identical, but at least similar, we have to remove material from the blade - we wish to keep the tang unchanged, thus the weight difference can only be reduced by making the blade narrower. By a lot.

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Blunt-bladed Rütger R5B with rectangular cross-sections. The blade width is halved to keep the original weight

As seen in the above picture, the shape and aesthetics of the rectangular rugger are remarkably different compared to the original sharp item. We established that we'd like to have the same aesthetics for the blunt-bladed version, as we have for the sharp one. We also know that while a thick edgeline is preferable for safety, so is the flexibility of the blade. The simple rectangular cross-sections will result in a very stiff blade, especially in thrusts, no matter how thick or large the tip is made.

While using the simple rectangular cross-sections might seem like a good idea at first glance, and they can provide outstanding durability, they are potentially the worst in terms of safety and aesthetics. We need another solution - let's start by adding extra material to the sharp blade to ensure we have a thick enough edge-line for safe sparring, let's say 2mm thickness for this example.

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Blunt-bladed Rutger R5B with trapezoid cross-sections

This is most easily done by modifying the general triangle-like cross sections of the sharp blade into trapezoids, with the same height as the original triangles. This results in a durable edgeline supported on its full width along the full length of the blade. We also achieve an edgeline thick enough to be considered safe for sparring. We also added a lot of material to the blade, making handling terrible and flexibility practically nonexistent.

Looking at two specific points on the length of the blade - at the base we added about 28% extra weight, and at the last third of the length we increased the weight of the cross-section by 57%. While the actual math is a bit more complicated, we can simply use the average of these percentages to get a grasp about the extra weight introduced on the blade - adding 42,5% weight on average to the 880 grams of the sharp blade results in 374 grams worth of "gains", making the weight of the blunt blade 1254 grams.

On one hand, now we have a similarly shaped blunt and sharp blade; also, the edgeline of the blunt is sufficiently thick for sparring and will be very durable. On the other hand, we made huge sacrifices by adding a large amount of weight and discarding any potential for making the blade at least a tiny bit more flexible than the sharp one.

To counteract these effects, we have to remove material. This can not be done on the edgeline, as we determined 2mm thickness to be the thinnest edgeline we can consider safe in this example. We also want to avoid removing material directly from behind the edge, because we want to keep the edge as durable as possible, for which a full-width backing on the cross-section is our best choice. At the same time, we'd like to get at least a bit more flexibility, which requires lowering the area values of the cross-section along the blade. What we can do: removing material from the flat of the blade, by leaving a relatively wide part of the cross-section untouched, we yield a lower overall weight and enhance handling without majorly affecting the durability of the edge-line. So let's add a fuller on both sides on 2/3 of the blade's width, with a grinding wheel that has a 125mm radius.

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Adding a wide fuller while leaving the spine and the edgeline untouched removes most of the extra material - not all of it, though

We managed to reduce the average extra weight from 42,5% to 11%. A very noticeable change, bringing the total weight down from the previous 1254 grams to 976,8 grams. We also kept the edge thick and durable, and still have enough material in the thinnest section of the blade so it can withstand a reasonable amount of flexibility for a reasonably large number of bending cycles. We still have a noticeably heavier blunt blade than the sharp, but they are much closer to each other. By reducing the weight in the blade, we also improved the dynamics and handling of the blade, mainly by moving the PoB closer to the grip. At the same time, we also made the largest cross-sectional area significantly smaller, resulting in a measurably more flexible blade that is still representative of how the sharp blade would behave in a thrust. We still can play around with how the fuller is executed, though. We can, for example, use a smaller diameter grinding wheel for the fuller. If we make the fullers with the same width (2/3 of the total width of the blade), we will get deeper fullers, meaning we removed more material, resulting in lower weight, shorter PoB, and a more flexible blade.

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Same fuller width with a smaller wheel radius = more weight reduction, even a bit too much

That's the step where either a lot of calculations or some trial and error with prototypes becomes unavoidable. The smaller wheel diameter with the same fuller width means deeper fullers on both sides, leaving us with thinner material at the bottom of the fuller lines. This means another significant reduction in weight (roughly -12%, a final weight of 774,4 grams), which we can add to the tip to make it rounded and thicker, enhancing safety. Unfortunately, though, we also created a potential weak point - if the fullers are too deep, the material on their bottom line will be simply too thin, making it prone to material failure regardless of material or heat-treatment quality. With enough experience, we can make some educated guesses on what widths and wheel diameters will work best, but that's still just part of the story.

same fuller width with R125 and R100 grinding wheels - resulting 0,35mm difference in thickness in one fuller. We have two of them. A huge difference, considering that our edge is 2mm thick

This isn't just an issue with the final product, though - keeping very tight tolerances in handmade parts while also fabricating a lot of them is not an easy task. When making the design, we have to take into account the tolerances we can reliably reproduce, even on 50+ products in a production batch if necessary. Keeping the R100 fuller at the exact depth leaves very little room for error, effectively leaving us no room for any potential corrections in the cross-section.

We also have to keep in mind that our stock removal process starts with very coarse, low-grit grinding belts - the thickness of the workpiece will be uneven, the surface will have deep grooves, making it unsightly and fragile - the sharp, deep grooves act as stress collecting points on which the blade becomes much more prone to breaking. Due to this, the surfaces require egalization with progressively finer sanding belts until all the grooves perpendicular to the length of the blade are removed. The egalization is also the first step for creating the final surface finish, although a couple more, even finer belts and different types and sizes of grinding wheels, also have to be used to achieve the satin finish that is the standard surface for most of our products. So when determining the depth of the initial fuller, we also have to think of the material that's removed by the egalization process, and the surface refinement as well, and account for the tolerances of each of these processes.

From our already existing designs and earlier experiences, it quickly became obvious that creating the blunt design from the same 8mm stock while preserving the handling characteristics of the sharp blade is not reliably repeatable with our current production processes and with the handmade nature of our products in general.

For the second attempt, let's start the process from 5mm stock. We can jump through the first few steps of the previous attempt (rectangular, simple trapezoid, etc) as we already know they will be inadequate or require further adjustments. So let's try a different approach. What happens if we create a fuller on the whole width of the blade, leaving the blade at the original 5mm thickness of the stock, and remove the extra material along the spine?

The cross-sectional area of the blade will be significantly smaller, meaning that the blade will be much more flexible. At the same time, we are able to more than double the thickness of the edge, enhancing its durability. We even have quite a strong backing for the edgeline. Unfortunately, there are multiple caveats here. First, just like in the previous example, the thinnest section of the blade will be very thin, making reliable production and durability an issue. In fact, the differences in the thicknesses of the cross-section became larger, which leads to another issue when the blade has to withstand any kind of bending.

Any material with measurable thickness has two main reactions to bending: elongation and compression, both of which describe length changes on the surface and inside the material. This will happen everywhere except for a very small area of the material, which is called a neutral zone. The length of the neutral zone remains unchanged, regardless of the degree of bending applied. Elongation will happen on the "outside" of the bend, in other words, the side that has its middle point moved the farthest from its original position. Compression will happen on the "inside" of the bend. These two effects are happening in the material structure at the same time, creating internal stress. This effect is further enhanced by the inherent properties of steel - practically any kind of steel is more resistant to elongation than it is to compression - and any even remotely sharp edges, for example, like those we create with the above-discussed wide fuller combined with 5mm edge thickness. The larger the difference between the elongation on one side and the compression on the other side, the larger the internal stress will be.

This internal stress will accumulate on any imperfection of the surface, as well as inside the material, on any spots where the structure of the steel is imperfect, or has even some slight contamination. Part of the structural imperfections can be rearranged inside the material with multiple cycles of specific steps in the heat-treatment process, but completely removing them would require equipment and technologies used for the fabrication of jet engine turbine blades. That's not something that most of us would be willing (or able to) afford for our swords. This also won't remove contamination from the steel, which is oftentimes not detectable due to its small and hidden nature, before the failure of the material. With all that said, stress caused by the difference of elongation and compression accumulating either on the surface of the blade or inside the material will result in a failure (brake) in the long term, so it's best to minimize the amount of accumulating stress by not creating overly huge differences in one part of the cross-section.

Our conclusions

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