Worldwide, ESSILOR International provides customers with Progressive Addition Lenses (PAL), which replace bifocal lenses. Thermal replication is one process to produce glass moulds for PAL, using sagged glass on a ceramic slumping block. In this paper, thermal replication for producing PAL glass moulds is developed through 3D modelling and experimentation. Our numerical approach is validated by comparing it with experimentation on the global 3D topology of the sagged glass. It is also validated by using more severe optical comparison criteria, developed by ESSILOR International to analyze the conformity of their products. Through modelling, the thermal replication is analyzed by studying the evolving contact between the sagged glass and the ceramic slumping block during the thermal cycle and the glass flow on the upper side of the sagged glass.

A thin tube made in single crystal is submitted to tension-torsion loading. The axis of the tube coincides with the 〈001〉 material axis. Local strain measurements made by means of strain gages experimentally demonstrate that the deformation is mainly localized in the 〈110〉 type zones. This is confirmed by microstructural observations of replicas. An experimental loading surface in these soft zones is derived. An analysis of the experimental data is successfully made through the Schmid law, involving both cube and octahedral slip.