Breviary Technical Ceramics






7 Ceramics-appropriate design

In contrast to most other materials, forming in ceramic technology takes place before the thermal processing that leads to the formation of the desired material and during which the formed component is liable to shrink.

The true ceramic material is only present after the firing process has been completed. This strongly influences the design of ceramic parts.

Figure 129:
The creation of materials


The use of typical metallic and polymeric materials (steel, cast-iron, aluminium alloys, nickel-based alloys, etc.) for machine and tool construction, automotive construction and process engineering is deeply ingrained in most design engineers. Many generations of engineers have accumulated experience with these materials, and have passed this on in the education of new engineers.
The situation his very different when it comes to the application of newly developed materials, or to new uses for materials that may have been familiar for a long time but which to date have only been used for a restricted range of applications. This is the case for technical ceramic materials.

When a technical problem has to be solved, the designer must create a number of technical elements; if ceramic materials are to be used, he must pay particular attention to the need for the design to be appropriate for the material.

Ductile materials react to small area/local overloads, compensating for them through elastic extension in accordance with Hooke's law, with some plastic deformation in reserve.
This does not apply to materials that are hard and therefore brittle - and also not flaw-tolerant. There are therefore considerable differences between the local loading capacity of parts made of ductile (metallic) materials and of brittle/hard (ceramic) materials. This therefore also calls for different design rules.

The designer will find some analogies in the basic rules for designing parts of cast materials and in the manufacturing possibilities relevant to powder metallurgy.
The combination of ceramic with metallic components presents a Mass Prod.s of problems in addition to the design of the parts themselves.
In most applications, a single component in the product (for example, replaceable wearing parts) is manufactured using ceramic materials, and is combined with the neighbouring metallic parts and assemblies.

It is the job of the design engineer to make use of the outstanding properties of technical ceramics and to apply them effectively and economically, while reducing the effect of their limiting properties. This is what is understood under the concept of design for ceramics.


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