Influence of roughness on mechanical strength of direct bonded silica and Zerodur® glasses Direct bonding is of particular interest for optical system manufacturing for spatial application. This process requires very precise physical and chemical preparations of surface, especially roughness controls. Thus, this paper proposes to understand and discuss the roughness influence on mechanical strength and bonding energy of an elementary mechanical structure after a room temperature bonding and an annealing at optimal temperature. First, surfaces are characterised and roughness is measured. At the same time, the performances of fused silica and Zerodur® glasses are compared. Then interface properties are measured using double shear and wedge tests. At the end of the paper, a discussion, based on literature models, is proposed to explain the existence of an optimum of roughness put in evidence in experimental results.

Direct bonding is of particular interest for optical system manufacturing for spatial application. This technology is already used in terrestrial optical system manufacturing because of the very high precision of the process and complex geometries are able to bond. However, even if a first prototype already passed with success space environment test, quantification and improvement of the mechanical strength of assemblies are essential to validate the assembly's life expectancy and to validate the European Space Agency standards. So, this work proposes to study the influence of process parameters, such as roughness, relative air humidity during room temperature bonding, annealing time and temperature, on mechanical strength of an elementary mechanical structure using a double shear test procedure and cleavage tests. At the same time, the performances of fused silica and Zerodur ® glasses are compared. For the process considered in this study, a parallel is made between chemical phenomena, surface roughness and mechanical strength. In the end, cleavage tests confirm the choice of the optimal process parameters and highlight a damaging phenomenon of bonded interfaces with successive re-adhesion.

Direct bonding is a process that does not require the use of any adhesive material. This process is based on short-range interatomic attraction forces such as hydrogen bonds. In this paper, chemical analyses and mechanical tests were performed in order to characterize silicon surfaces and the mechanical resistance of the bonded interfaces formed by these surfaces. Various methods of modelling adhesive contacts in order to predict the mechanical resistance of these assemblies are then compared.

The interferometer of the third generation meteorological satellite is composed by two corner cubes. The specifications, in terms of optical performances-wave front error (WFE)-and mechanical and thermal environments are very stringent compared to the actual knowledge. To answer to the mass, optical and mechanical specifications, a lightweighted hollow corner cube have been designed. An integration process based on enhanced molecular adhesion have been developed and tested in collaboration with CNES and LMA. This process required a fine polishing of the three mirrors of the corner cube before adhesion in order to obtain a very low flatness, roughness and angle precision. The mechanical resistance of the enhanced molecular adhesion process have been validated on three mockups submitted to shock and vibrations. The optical performances have been demonstrate on flight model corner cubes.

Fused silica direct bonding is of particular interest for optical system manufacturing for spatial applications. However, in order to validate the European Space Agency standards, a better understanding of the assemblies mechanical behavior is required. Therefore, it is important to develop some predictive tools to determine numerically mechanical strength of complex assemblies. In this paper, a cohesive zone model is proposed to model the direct bonding interface behavior. In order to determine the mechanical strength of the interface, a propagation test, and an initiation test on a free edge the cleavage test have been performed on direct bonded fused silica samples. The FIT test (Flexible Initiation Test) is also used to identify the properties of the direct bonding joint. At the end, a comparative analyses is proposed between experimental results and finite elements models of the propagation and initiation tests.