Why do stress concentrations occur around cutouts in sheet materials for laser cutting?

July 1, 2026

Why do stress concentrations occur around cutouts in sheet materials for laser cutting?

Cutouts, holes, and notches interrupt the natural line of force in a sheet. As long as a sheet is whole, stress is distributed fairly evenly. Once you remove material, tensile forces, bending, and residual stress have to route around that opening. That is exactly where a weaker area develops.

With sheet materials for laser cutting, this manifests as:

small cracks starting from an inside corner
breakage at narrow connecting pieces
deformation after cutting
an increased risk of damage during assembly or use
dimensional changes in sensitive parts of the design

This effect is not unique to one material. It can occur with acrylic, MDF, plywood, hardboard, cardboard, and other sheet materials, although each material reacts differently.

What do we mean by stress concentrations?

By stress concentration, we mean a place where mechanical stress accumulates more strongly than in the rest of the sheet. This often happens at transitions in the shape, for example at:

sharp inside corners
slots with a narrow end
small holes
V-shaped notches
cutouts close to the outer edge

A simple way to look at it: the more abruptly the shape changes, the greater the chance that stress will not flow smoothly but will “get stuck” at one small point.

During laser cutting, there is the added factor of the material being heated locally. This can make existing internal stress more visible or amplify it, depending on the material type, thickness, sheet quality, and settings. Read more about this in How does internal stress affect the dimensional stability of sheets.

Why are cutouts extra sensitive?

A cutout not only removes material but also makes the remaining shape dependent on narrower sections. As a result, the sheet becomes locally less rigid and weaker.

Sharp inside corners are notorious

At a sharp inside corner, stress converges in a very small area. This makes such a corner a logical starting point for a crack or break. A rounded inside corner usually distributes this load more favorably.

Narrow bridges break more easily

If two larger surfaces are only connected by a narrow piece of material, that piece becomes a weak link. You often see this with decorative patterns, letters, slots, and snap-fit joints.

Holes close to edges weaken the sheet

An opening that is too close to the outer edge leaves little residual material. This increases the chance of the edge breaking out, splitting, or warping.

Which material types are particularly sensitive to this?

Not every material behaves the same. That is why it is wise to always evaluate the material, thickness, and design as a combination. In the collection All sheet materials and thicknesses, you can see which sheet types and thicknesses are relevant for your application.

Acrylic

Acrylic is dimensionally stable and popular for clean cut edges, but it can react more sensitively to stress buildup around sharp details, especially with narrow parts and small inside corners. The material variant also plays a role: cast and extruded acrylic can behave differently in practice during cutting, engraving, and subsequent mechanical loading.

MDF and plywood

With Wood and MDF, fiber direction, composition, and internal differences in the sheet play a role in addition to shape. Plywood can react differently locally due to layers and glued joints. MDF is more homogeneous, but narrow parts remain vulnerable if too little material is left.

Cardboard, paper products, and hardboard

Thinner sheet materials can absorb less absolute load. As a result, you are more likely to see tearing, curling, or deformation if cutouts are too close together or the remaining shape becomes too fragile.

Which factors amplify the problem?

Stress concentrations are not only caused by shape. Several factors can increase the effect.

Material thickness

Thinner sheets lose rigidity relatively quickly around openings. Thicker sheets can provide more material around a cutout, but that does not automatically mean every design is suddenly safe. The ratio between opening, residual material, and overall shape remains decisive.

Internal stress in the sheet

Some sheets already have internal stress from production, storage, or previous temperature fluctuations. During laser cutting, this stress can be released, causing parts to warp, skew, or prove prone to cracking after cutting. Extruded acrylic, for example, has a lot of internal stress in the sheet.

Heat input during laser cutting

Too much heat in small details can further stress a sensitive area. With wood, overheating can also lead to discoloration; see also Why do burn marks appear on wood during laser cutting.

Design proportions

The less residual material there is between two openings, the greater the risk. This also applies to long, narrow slots and narrow arms in a pattern.

Use after cutting

A part can come out of the laser perfectly and still fail later. Think of assembly, screw pressure, clamping stress, bending, transport, or temperature fluctuations. Especially then, weak zones around cutouts become visible.

How do you recognize high-risk cutouts in your design?

You don't need to make extensive calculations to prevent many problems. Pay particular attention to visible risk points.

Warning signs in a design

sharp inside corners without rounding
narrow strips between two holes or slots
openings close to the outer edge
many small cutouts in a small area
long narrow parts with many interruptions

Fine decorative patterns in relatively brittle material. Mounting holes in an already narrow part.

Ask yourself these practical questions

Is there enough material left around the cutout? Will force be applied to this part later? Is the chosen thickness suitable for this shape? Does this level of detail suit the material type? Is a rounded corner possible without loss of function?

If you have doubts on several points, it is often smarter to reconsider your material choice and thickness first via the Knowledge base on sheet materials.

The best way to find out if a cutout will break is still simply to test it.

How do you practically reduce stress concentrations?

Often, you can greatly reduce the problem with a few adjustments to the design.

Round off inside corners

A rounded inside corner usually distributes stress better than a sharp corner. That is one of the simplest improvements for holes, slots, and internal cutouts.

Leave more material

Where possible, increase the distance:

Between a cutout and the outer edge. Between two holes. Between two slots. Between an opening and a narrow end.

More residual material usually means more reserve against breakage.

Make narrow bridges wider

If a shape relies on a narrow connecting piece, try to make it slightly wider. Especially with functional parts, this often immediately yields a more robust result.

Choose a more suitable sheet thickness

Sometimes the design itself is good, but the chosen thickness is too light for the shape. A different thickness or a different material might then be more logical than endlessly fine-tuning settings.

Match material and application

A decorative panel has different requirements than a snap-fit part, nameplate, template, or structural component. Therefore, choose not only based on color or price, but also on brittleness, rigidity, engraving properties, and load during use.

What can you do before laser cutting?

Good preparation prevents a lot of disappointment.

Check your design for vulnerable details

Zoom in on all inside corners, holes, and narrow strips. What looks good on screen may prove too fragile in sheet material.

Make a test piece

First, cut a small test part containing the critical zones. This often provides clarity faster than processing an entire sheet.

Look critically at protective film and surface

For some applications, you want to protect the surface from scratches or signs of wear during handling for as long as possible. For this, Protective film for laser use can be useful, depending on the material and working method. Protection does not solve stress concentration, but it does help with the clean processing of sensitive sheet parts.

Check storage and flatness

Sheets that have not been stored flat or that have experienced temperature fluctuations may already contain extra stress. This increases the risk of deformation around cutouts.

Common mistakes

Only looking at the outer shape

Many designs look sturdy as long as you only look at the outline. The real weak spots are often in the internal cutouts.

Combining overly fine details with overly thin material

An elegant pattern in thin material can be beautiful but quickly becomes vulnerable if too much material has been removed.

Thinking that a clean cut edge says enough

The fact that a part comes out of the machine cleanly does not mean it is strong enough for assembly or daily use.

Treating material types as interchangeable

You cannot design for acrylic, MDF, and plywood in exactly the same way. Each material reacts differently to heat, stress, and loading.

Not doing a test with new combinations

New sheet thickness, new design, or a different machine setting? Then a test cut is usually the safest route.

Practical conclusion

Stress concentrations around cutouts occur because forces no longer flow evenly through the sheet. Sharp corners, small openings, narrow bridges, and too little residual material make a design more sensitive to cracking, breaking, and deformation. This risk varies per material variant, thickness, machine, and application.

The best approach is practical: choose an appropriate material, use a logical thickness, round off critical shapes, and test vulnerable details on a small scale first. If you are working with wood-based sheets, check out the range in Wood and MDF. For transparent or colored plastics, Acrylic is a logical starting point. If you are ordering in larger quantities for a school, workshop, or company, you can find more information at Ordering via purchase order.

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