Damage Investigation in Aluminium Alloys by X Ray Tomography

International audienceno abstrac

Adaptive 3D algorithm to detect bridging ligaments during intergranular stress corrosion cracking of stainless steel

This paper presents an adaptive algorithm to identify holes in 3D objects which cannot be labelled with standard techniques, such as 6 or 26-connectivity based methods. The algorithm consists of two stages. The first one lies in the application of a voxel coding technique to make a transformation of an object into a set of clusters, where a cluster is a set of connected voxels. The set of clusters gives important information about the object topology. In the second step, the algorithm extracts and analyses clusters to detect holes. The algorithm was satisfactorily tested on several 3D crack images from a stress corrosion cracking experiment on a stainless steel sample. In this case, the “holes” in the crack are bridging ligaments of solid material which connect the opposing faces of the crack. Discussion of results obtained and proposals for future work are presented

Adaptive 3D algorithm to detect bridging ligaments during intergranular stress corrosion cracking of stainless steel

This paper presents an adaptive algorithm to identify holes in 3D objects which cannot be labelled with standard techniques, such as 6 or 26-connectivity based methods. The algorithm consists of two stages. The first one lies in the application of a voxel coding technique to make a transformation of an object into a set of clusters, where a cluster is a set of connected voxels. The set of clusters gives important information about the object topology. In the second step, the algorithm extracts and analyses clusters to detect holes. The algorithm was satisfactorily tested on several 3D crack images from a stress corrosion cracking experiment on a stainless steel sample. In this case, the “holes” in the crack are bridging ligaments of solid material which connect the opposing faces of the crack. Discussion of results obtained and proposals for future work are presented

Klasteryzacja k-średnich obrazów teksturowych lamelarnych mikrostruktur stopów tytanu

This paper presents an implementation of the k-means clustering method, to segment cross sections of X-ray micro tomographic images of lamellar Titanium alloys. It proposes an approach for estimating the optimal number of clusters by analyzing the histogram of the local orientation map of the image and the choice of the cluster centroids used to initialize k-means. This is compared with the classical method considering random coordinates of the clusters.W artykule przedstawiono implementację metody klasteryzacji k-średnich, do segmentacji dwuwymiarowych rentgenowskich obrazów mikro tomograficznych lamelarnych stopów tytanu. Zaproponowano metody szacowania optymalnej liczbę klastrów oraz wyboru centro idów poprzez analizę histogramu mapy lokalnych kierunków obrazu. Dokonano porównania zaproponowanych metod z losowym doborem początkowego położenia klastrów

Damage assessment in metallic structural materials using high resolution synchrotron X-ray tomography

International audienceno abstrac

Grain Boundary Engineering for Crack Bridging: A New Model for Intergranular Stress Corrosion Crack (IGSCC) Propagation

This chapter introduces a new intergranular stress corrosion crack (IGSCC) propagation model based on grain bridging by crack resistant, low energy grain boundary, (GB), and their related triple junction density (TJD). A stochastic model considers the frequency of immune GBs with respect to the microstructural probability of arresting a crack at a TJ. This is reflected in the maximum critical crack length, and influencing factors such as grain size and total probability of crack arrest. The observation of grain bridging has suggested a new approach of predicting intergranular stress corrosion crack length distributions. The key premise of this model is that bridges arise from the local arrest at "cul-de-sac" (2-CSL TJ) or unfavorably orientated triple junctions (1-CSL TJ). Crack arrest by a single junction is not expected to significantly affect the behavior of a crack with a size greater than several grains. The cumulative effect of grain bridging gives rise to a shielding stress, which reduces the stress intensity factor at the crack tip. Several microstructure dependent factors lead to the shielding stress. First, the number of bridges per unit area is assumed to vary in proportion to the resistance factor. Second, the bridge size, and thus its contribution to the shielding stress, depends on the grain size, which is related to the spacing of effective TJs. Finally, the degree of shielding is assumed to build up and then saturate at steady state with increasing crack length. © 2008 Elsevier Ltd All rights reserved