4.5. Implementation
Taxonomically patelloids and chitons are widely apart. Yet, their mineralized teeth share a number of highly functional characteristics: upright position during grazing; leading surface that is curved over an angle of about 90°; heterogeneous distribution of hardness and stiffness, which is higher in the leading part than in the trailing part; internal structure consisting of structural elements in the leading part that are parallel to the leading surface and of structural elements in the trailing part that are oriented at a sharp angle to the leading surface. We have argued that this combination of traits is fundamental for an optimal design of a tooth, since it provides for a small rake angle, sharp wedge angle, a positive clearance angle and minimizing failure and wear of the tooth. Considering the effectiveness of radular teeth as cutting tools, they can be used as a model in designing man-made cutting devices. An optimal design for a tooth in an industrial cutting device should contain the following characteristics: leading surface positioned perpendicular to the work piece; leading surface curved over 90°; the hardness and stiffness of the materials in the leading part are larger than in the trailing part; an internal structure is present, in the leading part consisting of elongated laminae or fibres oriented parallel to the leading surface, and in the trailing part consisting of laminae or fibres that make an angle of about 60° to the leading surface. Technologically, there should be no obstacles to actually construct such a tooth. Modern material science offers a wealth of materials and techniques to perform such a task. For instance, the use of composite materials could provide for an internal structure, in which an oriented fibrous material (e.g., SiC) is embedded in an amorphous matrix material (e.g., Al), analogous to the goethite crystals embedded in amorphous SiO2 in the patelloids. An internal structure of an array of laminae can also be manufactured in steel by warm rolling of the material. Also, an internal structure consisting of oriented rods can be manufactured either by solidification of a steel melt in which a temperature gradient is installed, or by introduction of oriented elongated germ crystals in a cooling melt. For the construction of an inhomogeneous distribution of hardness a number of techniques are available. For example, the leading side of a steel tooth could be hardened by simply scanning a laser beam over its surface. Hardnesses of up to 1500 VDH could thus be obtained. Also, a powdered substance of TiC or SiC could be fused with the material of the leading part of a steel tooth by means of laser technology. Here also hardnesses of up to 1500 VDH could be obtained.