Breviary Technical Ceramics


      Joining and Bonding Techniques




8.1 Principles

The materials to be bonded and the demands to be placed on the bond are crucial for the choice of bonding technique.
Design appropriate for ceramics means, for example, that when bonded with metals, the ceramic should be placed under compressive stress whenever possible, and that tensile or bending loads be transferred to the metal

Figure 185: Factors affecting joints

The behaviour of the functional unit takes the primary focus in every case. The reliability of the bond must be guaranteed against overloading and loosening during manufacture and use. The main task of the designer is to match the plastic, elastic, thermal and geometric expansion differences between this ceramic component and its surroundings. The suitability of the joining technique or combination of techniques is decided on a case-by-case basis. Joining is more than just a matter of adapting the expansion coefficient and elastic modulus. The interaction of material data, part design and contact surfaces demands close, multi-disciplinary cooperation between technologists, manufacturing technicians and constructors, particularly in order to overcome the internal stresses of the combined materials.

The designer should proceed in a manner suitable for the materials, and should pay attention to the following basic rules:

  • avoid stress concentrations and point-loads by
    o using large areas to apply forces,
    o parallel contact surfaces,
    o using elastic intermediate layers where appropriate and
    o force transfer without acute changes of direction.
  • avoiding tensile stress in the ceramic part and preferring compressive stress by:
    o press-fit joints (ceramic part on the inside),
    o compressive pre-stressing
    o properly arranged load application points.
  • avoiding impact or shock stress by:
    o applying loads over larger areas,
    o reducing applied load
    o supplying additional resilient, elastic and / or damping elements.
  • avoiding additional stress resulting from constrained thermal expansion by using
    o materials with similar thermal expansion coefficients,
    o resilient or elastic elements and
    o air gaps.
  • compensation of differences in deformation resulting from differing elastic moduli (if they increase the stress on the ceramic part) by:
    o resilient or elastic intermediate elements and
    o matching the stiffnesses.
  • Interlock/frictional jointing
    o geometrical interlocks avoid the need for further fasteners.
    o Frictional bonding compensates problems due to differences in thermal expansion coefficient and stiffness
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