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The various aspects of weldability, seen as a material property, are introduced. These are illustrated by considering examples, in particular the recent advances in structural C–Mn and microalloyed steels. Important issues for the further development of the weldability of these materials are outlined. In concluding, the growing importance of mathematical modelling as a tool for the design of new weldable materials is emphasised.

The deformation kinetics of theα + βtitanium alloy Ti-6 A1-4V were investigated over the temperature range of 4.2 to 760 K. It was found that the Gibbs free energy of activation AG at 0 K and zero effective stress is ∼ 1.3 eV (∼ 1.25 × 105J/mole) (∼0.17 μob3), the maximum force for the dislocation-obstacle interaction is ∼ 80 × 10-6dyne (∼ 80 × 10-11N) (∼ 0.19 μob2) and the activation distance x0*at which the force first rises rapidly ∼ 1.5b. These quantities, and others, are the same as those for unalloyed titanium, where it was established that interstitial solutes are the obstacles controlling the dislocation motion. The results for the Ti-6A1-4V alloy are in slightly better accord with ρG being independent of temperature than proportional to the shear modulus, but the evidence is not conclusive.

The conditions on the required forces to initiate the sliding translation of a perfectly rigid cylindrical part inserted in a tube are defined in a model taking into account the effects of gravity. The theory presented can therefore be used to predict the behavior of heavy parts. The model is two-dimensional and restricted to static or quasistatic applications. It takes into account the inclination of the cylinder axis relative to that of the tube. Conditions on the applied forces for the stability of the cylinder with respect to its inclination are established. Jamming and wedging are thoroughly discussed. A short example is given at the end to illustrate how the theory presented can be used to analyze practical cases of application.

The conditions on the required forces to initiate the sliding translation of a perfectly rigid cylindrical part inserted in a tube are defined in a model taking into account the effects of gravity. The theory presented can therefore be used to predict the behavior of heavy parts. The model is two-dimensional and restricted to static or quasistatic applications. It takes into account the inclination of the cylinder axis relative to that of the tube. Conditions on the applied forces for the stability of the cylinder with respect to its inclination are established. Jamming and wedging are thoroughly discussed. A short example is given at the end to illustrate how the theory presented can be used to analyze practical cases of application.