Key Engineering Materials Vol. 409

Abstract: Within a model considered, each of bonds between contacting grains is treated as a two-state system and represented by a binary variable. Its two values refer to the two possible states of bond – intact or broken. A Monte Carlo simulation of fracture is carried out on a set of binary variables arranged to a cubic lattice. The transition from one configuration of broken bonds to another is governed by a Griffith-like energy associated with each of configurations. The results demonstrate i) the capability of the model to provide a useful information (e.g. the increase in roughness of fracture surface with increasing temperature, that is the transition from “brittle” to “plastic” failure), and ii) the advantage of simulation by using the graphics processing unit (saving of a computational time).

Abstract: The wear behaviour on prealloyed sintered steel parts TiCN PVD coating was analysed. Cylindrical specimens ( 40x30 mm3) were compacted to the green density of ~7.0 g.cm-3. The specimens were sintered in pusher furnace at the temperature of 1180°C for 40 minutes in an atmosphere of 25H2+75N2. Part of sintered specimens was then coated by Physical Vapour Deposition. Wear tests were carried out by means of a pin-on-disk tribometer. The results of profilograms (the values of surface roughness) and the wear curves (mass loss versus sliding distance) showed positive effect of coating on the wear resistance of the tested specimens.

Abstract: A quantitative description of overlaps on fractures in sialon ceramics, is presented in the paper. A conventional analysis, aiming at the determination of the percentage share of overlaps on the basis of quantitative fractography, was preceded by stereometric/fractal analyses. They enabled the selection of representative sections of samples and then, the production of transverse microsections in those places for an analysis of the fractures’ profiles using the light microscopy method and fractographic image analysis. Based on the compared results from both methods, a successful verification was made of the research methodology developed earlier for sintered carbides and proven for a chromium-molybdenum steel.

Abstract: This paper describes a new nondestructive approach for porosity measurement developed in response to a need for a more accurate porosity measuring method for solid samples. The conventional methods in X-ray CT imaging are based on image segmentation where a threshold is applied at a user-defined value. As a result, the uncertainty in the porosity measurement is introduced. Therefore, the new method, called the grey level method, which reflects the phenomenon of image processing and computation of ration between the volume of voids and the total volume of the entire sample, was considered and improved in term of image noise and artifacts. The volumes of 2D CT image as a surface are achieved by means of integrating the surface with operations relating to image histogram. The porosity value is given from the curve of a porosity distribution. Subsequently, the properties of individual pores were measured and comparison with conventional destructive method of porosity computation was carried out. Also limitations of industrial X-ray CT as well as their accuracy are discussed.

Abstract: A bimaterial structure composed of two elastic plates bonded together by an interface with a normal (transverse) crack in the first plate and subjected to monotonically temperature and tension loading is considered. The interface is assumed to exhibit brittle failure at critical shear stress value or progressive damage in a cohesive zone preceding delamination. Using modified Shear lag model, the analytical solution is provided specifying the length of debonding. The critical lengths of a partial debonding along the interface are calculated and the limit value of temperature at full debonding is obtained. The analytical predictions are compared with experimental data and numerical results of Lemaitre and Song. The comparison shows a good agreement and proves the validity of the model used.