Petrus Cornelis Paulus Bouten

Erosion and damage by sharp particles

Abstract Sandblasting is an old technique for decoration of glass surfaces. In recent years, this technology has developed into an industrial process for technical structuring of brittle materials. This paper derives relations for the parameters from the basic indentation models that are important for an industrial process: erosion rate, surface roughness and strength. Quantitative estimates for these parameters and for transitions that occur in the erosion process are determined. The theory reveals the kinetic energy of the particles as a global scaling rule for the erosion process. Experimental validation shows that the quantitative relations for transitions are reasonable. The relation for the erosion rate gives the correct dependence on kinetic energy, overestimating the erosion by only a factor of four. The prediction of surface roughness is of the correct order of magnitude, whereas the strength relation is reasonable. The scaling rule is found to be very valuable.

Doubly coated optical fibres with a low sensitivity to temperature and microbending

In order to prevent microbending losses in optical fibers over a wide temperature range, a new buffer coating and a new top coating have been developed. The buffer coating has a low Youngs modulus over a wide temperature range, whereas the top coating has a modulus which is high compared with the modulus of the coatings that are generally used. The application of these coatings results in fibers with a very low microbending sensitivity. However, at low temperatures added optical loss is observed which correlates with a change in the radial stress state of the buffer coating from compression to tension. It is demonstrated by model calculations as well as by experiments that these optical losses can be avoided if the thickness of the buffer layer does not exceed a critical value. The new coatings are shown to provide a good protection of the fiber from mechanical damage. >

The strength of glass sheets perforated by erosion

Abstract A new type of large flat display requires large thin glass sheets having various types of fine-pitch structures. Powder blasting is used as an accurate “mechanical etching” process for the production of these sheets. A patterned erosion-resistant mask protects part of the surface during the powder blasting. The abrasive processing introduces mechanical damage and sets limits on the handling possibilities of the large structured glass sheets. The failure stresses of uniformly eroded glass and structured glass are determined. The failure stress of glass uniformly eroded by sharp particles perpendicular to the surface depends on the kinetic energy of the particles. The same dependence on the kinetic energy is observed for oblique impact when only the normal velocity component is taken into account. The measured failure stresses of glass surfaces eroded by almost round particles and sharp particles compare well. The erosion theory predicts a different strength behaviour. Asperities on a limited number of the impacting round particles seem to control the failure stress of the eroded glass. The failure stress of the structured glass sheet depends on the loading geometry. For various types of loading geometry, stress concentration factors are calculated for the investigated eroded structure. The local failure stresses, calculated from the strength tests on structured glass and the appropriate stress concentration factors, agree well with the failure stress estimated from the uniformly eroded glass surfaces.

Drawing influence on the lifetime of optical fibres

Strength and lifetime measurements carried out on optical fibers with different residual tensile stress at the surface are discussed. This stress was optically measured and included in the theory of fiber strength and lifetime. The strength results were compared with measurements done on pure silica fibers without residual stress. In lifetime predictions, this residual tensile stress in the outside region of the fiber has to be taken into account. However, the decrease in intrinsic strength was much larger than the increase in residual stress in the outside region of the fiber. This phenomenon, which is not well understood, depends on drawing conditions. >