Jean-Louis Chermant

Image analysis and mathematical morphology for civil engineering materials

Abstract The scope of this paper is to present the main tools of image analysis to investigate materials and, specially, civil engineering ones. First the acquisition methods are described. The different operators for filtering, segmentation and binary image processing are presented and illustrated on different images. The influence of the observation field on these operators and the bias correction is also introduced. Then the problem of the parametrical characterization is presented: stereological parameters and functions related to size distributions, dispersion and anisotropy. Finally, the model methods based on image analysis are recalled. Some annexes illustrate this paper to precise main basic notions to understand the morphological tools.

Some fields of applications of automatic image analysis in civil engineering

Abstract This paper illustrates the use of automatic image analysis technique to investigate the morphology of cement, concrete and fibre-reinforced concrete. First the methods to be used for powders and secondly for mortar and concrete are introduced. The dispersed phases are characterized by classical morphological parameters: these also enable to accede to the hydration process. The covariances give quantitative information on the homogeneity and dispersion of the different components: gravel, air-voids and cement paste. Air-voids are characterized by granulometric distributions and their mean free paths. Rose of directions gives information on feature orientation: fibres, microcracks for fibre-reinforced concrete, etc. Finally probabilistic models can be used to simulate the microstructure of such materials.

The creep mechanism of ceramic matrix composites at low temperature and stress, by a material science approach

Abstract This paper deals with the creep mechanism for ceramic matrix composites reinforced by long ceramic fibers in a ceramic or glass-ceramic matrix, tested at low stresses (

Why automatic image analysis? An introduction to this issue

Abstract This short paper introduces this special issue on the use of automatic image analysis applied to cement and concrete materials. One paper gives a very short overview of the methods to be used, and the others illustrate by many examples why the techniques of image analysis have to be used for cement and concrete materials. It evidences the importance of knowledge of the morphology of objects. These different papers are presented according to a certain morphological classification.

Cryomilling of Al/AlN powders

Abstract Elemental powders of 80 vol% 5000 Al-alloy (3 wt.% Mg) and 20 vol% AlN were milled in different mechanical conditions and at three different temperatures (in liquid nitrogen (cryomilling), low temperature (about −50°C) and room temperature). The effects of these parameters on the milling efficiency of Al and AlN and on the mechanical alloying were investigated. The cryomilling of both Al and AlN resulted in a rapid decrease in size of the coherently diffracting domains (

AlN dispersed reinforced aluminum composite

Abstract In this paper the first results are presented on nitriding of aluminium powder and the fabrication of Al-AlN composites after milling and hot-pressing. Nitriding appears to follow a complex process. High energetic milling of these powders is an important factor in obtaining homogeneous materials with AlN nanometric grains. TEM and EDX nanoanalyses have shown that Al grains are surrounded by AlN nanocrystals, with some A12O3 needles and AlON crystals. Physical properties — thermal expansion, thermal conductivity, electrical conductivity, hardness, Youngs modulus, fracture strength — of these composites change with the AlN content, and the values for 0 vol.% AlN (process powders) always correspond to higher or lower values than for pure Al (unprocessed powders), reflecting the fact that processing introduces impurities. A comparison of composites fabricated from composite powders and from a mixture of Al-AlN commercially available powders is interesting. Generally these new composites exhibit better properties than those for Al-SiC or Al-Al2O3 composites with an apparently similar reinforcement content.

Automatic image analysis and morphology of fibre reinforced concrete

Abstract Automatic image analysis is an efficient tool to quantify the morphology of materials. Moreover, it can aid to understand their mechanical behaviour. Several applications of automatic methods are presented to investigate concrete reinforced by ribbon shaped amorphous cast iron fibres. Introducing ribbons into the plain matrix entrapped air voids. This affected the workability and, later on, the compressive strength of the fibre reinforced concrete (FRC). Both were improved by additions of superplasticizer in order to keep the water to cement ratio constant. The influence of the superplasticizer and fibre contents on the compactness of the FRC was characterized by the dimensional and the spatial distributions of the air voids. The orientations of fibres and microcracks were quantified by Fourier image transforms. Due to the casting procedure of the FRC, the fibres were located in “horizontal layers”, perpendicular to the casting axis. Whatever the direction of compression with respect to the layers of fibres, the microcrack network was getting more and more oriented in the direction of compression as stresses increased. The analysis of fibre and microcrack orientations suggests that, under uniaxial compression, the inelastic strain domain should be characterized by an anisotropic biaxial damage model, whose principal axes are the orthogonal and parallel directions to the layers of fibres.

DAMAGE MECHANICS APPLIED TO CONCRETE REINFORCED WITH AMORPHOUS CAST IRON FIBERS, CONCRETE SUBJECTED TO COMPRESSION

The evolution of damage in compression, due to microcracking, is investigated in concrete reinforced by amorphous cast iron fibers and compared to damage in non reinforced concrete whose workability and strength were similar. As microcracking is anisotropic, two damage variables are defined, d1 in the orientation of compression and d2 in a perpendicular orientation. Damage values are calculated as a function of the loss of stiffness measured during loading-unloading cycles. Since the fiber arrangement is 2D (isotropic transverse), it is shown that damage is delayed in a reinforced concrete stressed in an orientation perpendicular to the fibers. On the other hand, due to fiber/concrete debonding, damage is greater when the compression is applied in an orientation parallel to the fibers. The damage behavior of the non reinforced concrete is intermediate. (A)

On a first creep model for a 2D SiCf–SiC composite

For ceramic matrix composites, damage is generally of a highly complex nature, with several damage mechanisms and strong unilateral features depending on whether microcracks are open or closed. During high temperature, inelasticity or viscoplasticity can occur. This paper deals with the application of a damage mechanics approach, based on continuum mechanics, to solve these problems of inelasticity and damage. The models are constitutive relationships able to describe and predict the damage state of a structure at any time, and at any point, up to the final fracture. These equations include all physical information coming from the micro-, meso- and macro-scales. Using microscopic observation of the tested specimens, the possible mechanisms involved in the measured inelasticity are discussed, in order to establish the evolution of the chosen viscoplastic potential.

Morphological characterization of ceramic-ceramic composites by image analysis

Abstract In this paper the potential of automatic image analysis for quantification of the morphology of composite materials is presented, and parameters related to the different types of porosity and to the fibres are given. It is shown that this technique could also be used to model the microstructure of ceramic matrix composites.