Peter Jan Slikkerveer

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.

Model for patterned erosion

Sandblasting is a well-known process for patterning window glass and mirrors. The technique is now being developed for the production of technical structures with high precision. This paper presents a model for the evolution of powder-blasted structures in masked glass substrates. The model assumes that the shapes originate primarily as a result of the dependence of erosion on impact angle. At second strike the rebounding particles give an extra contribution to the erosion process. An analytical solution is presented for the model without the second strike. Although the solution was sought for erosion of grooves, it can also be used to construct the shapes of other mask patterns. The model containing the second strike has been solved numerically. The results have been compared with experimentally obtained shapes. The model gives a good qualitative description of the observed phenomena. In quantitative terms, it compares reasonably well with experimental results, considering the simplifications in the model. Effects of particle size, mask hindering and mask wear were not included and the rebound characteristics of particles were included in a simplified form only. For improvement of the model more experimental data is needed in these fields.

Erosion of elastomeric protective coatings

Elastomeric coatings are widely used as protective coatings against solid particle erosion. In powder blasting, the materials are used to obtain patterned erosion of the substrate. This paper investigates the erosion behaviour of three photosensitive materials suitable for powder-blasting masks. The erosion resistance of the materials is characterised as a function of impact velocity and angle of incidence. The results are used to construct an analytical model to describe the evolution of patterned coatings through erosive wear. The results of this model have been verified qualitatively in powder-blasting experiments. The model and the experiments show that erosion at oblique angles is the dominant erosion mechanism, even when the abrasive jet is directed perpendicular to the substrate surface. This means that the erosion resistance of elastomeric material should preferably be tested at glancing impact angles.

Simulation model for the erosion of brittle materials

The erosion rate and surface roughness in erosion processes scale with the impact energy of the particles. The particle size and velocity distributions are therefore important parameters for a simulation model. A Monte Carlo simulation model has been developed to predict the erosion rate and surface roughness as a function of material properties of the target and of the abrasive particles. The description of the interaction between particle and substrate is based on indentation fracture mechanics. The results have been checked for the applicability to real-life abrasive jet machining. The erosion rate compares favourably with the erosion rate observed during erosion experiments on glass. The surface roughness, however, is larger then the experimental surface roughness. Probably, this can be attributed to the influence of the stylus radius on the surface roughness. The simulation model is a useful tool to study parameter variations in erosion processes of brittle materials. Various extensions to the model are possible to refine the model. With a few modifications, the model is expected to be suitable for simulation of three-body abrasion as well.

Towards prediction of flux effects in powder blasting nozzles

Abstract The efficiency of solid-particle erosion generally decreases with increasing particle flux. The particles rebounding from the surface collide with incoming particles, which results in a decrease in their velocity and the inflicted damage. This effect, called ‘the fluxe effect’, was modelled by Anand et al. [K. Anand, S.K. Hovis, H. Conrad, R.O. Scattergood, Flux effects in solid particle erosion. Wear. Vol. 118, 1987, pp. 243–257.] with a single-parameter fit model. Although this fit parameter was assumed to be constant, experiments have yielded a wide range of values for it, making the model unsuitable for flux-effect predictions. This paper shows for one erosion process—glass by alumina particles—that the variation in the fit parameter correlates with the particle velocity. The obtained relation describes the flux-effect data of three types of nozzles with sizes from 1.5 to 12 mm. Within this erosion process it is suitable for interpolation between process conditions and nozzle sizes. This result may be seen as a first step to a universal model for prediction of flux effects for all types of erosion processes.

5.2: A Fully Flexible, Cholesteric LC Matrix Display

Flexible cholesteric texture liquid crystal displays are demonstrated. The 4.2″ diagonal display can be bent over a 20-mm radius of curvature, even during operation. The driving parameters and the cell-gap homogeneity are comparable to those of glass based cells. Images with 16 gray levels are shown on the display.

Angularity determination of abrasive powders

Abstract The influence of particle shape on abrasive processes is not well understood, but the angularity of the abrasive powders is assumed to be an important parameter. For that purpose an automatic angularity determination program was developed, based on the curvature of a two-dimensional projection of a particle. This paper describes the algorithm used and the preliminary measurements and results. Aspects still open for improvement are: filtering of the pixel noise, reproducibility and the discriminative power of the algorithm. The most important question to answer was: “What is a corner?”. In fairness it should be concluded that this question can only be answered successfully in combination with a particular application.

Validation of the erosion map for spherical particle impacts on glass

Hard spherical particles may exhibit a variation in impact damage on a softer target depending on the particle diameter and particle velocity. In this paper quantitative equations will be derived for these transitions in material behaviour. These equations have been presented in an erosion map of particle size against impact velocity. The equations used for the erosion map presented here resembles the mathematical relationships presented by others. The difference with earlier reports is that in this paper not only proportionalities are given but also the prefactors are determined. The theoretically derived erosion map has been validated for spherical particle impacts on borosilicate glass. The results show that the theoretical derived erosion map is generally correct. Most remarkable is the existence of cone cracks in the plastic regime.

16.2: A Fully Flexible Colour Display

A flexible version is shown of a state of the art passive matrix LCD; a full colour STN display. By using polymer substrates, “ultra-thin” optical layers (like retarders, colour filters and polarisers) and a flexible backlight a fully flexible CSTN demonstrator is obtained, that can be bend to a radius of 40 mm during operation.