Papers by Keyword: Intrusion

Abstract: Two fatigued materials with f.c.c. lattice, i.e. pure polycrystalline copper and austenitic Sanicro 25 stainless steel, were subjected to the study of the persistent slip markings (PSMs) developed on the surface of the suitably oriented grains. They were observed using scanning electron microscopy (SEM) and thin surface FIB lamellae were prepared and studied by transmission electron microscopy (TEM). The aim was to correlate the specimen surface profile with the underlying internal dislocation structure. The localization of the intensive cyclic slip into persistent slip bands (PSBs) of the material was observed and associated with the PSMs on the specimen surface. Extrusions, intrusions and the dislocation structure appertaining to them were analysed, documented and discussed in relation to the models of fatigue crack initiation.

Abstract: Atomic force microscopy (AFM) and focused ion beam technique (FIB) were adopted to study the early stages of surface relief evolution in 316L steel and polycrystalline copper fatigued with constant plastic strain amplitudes at different temperatures (316L steel at 93, 173 and 573 K; copper at 83, 173 and 295 K). Qualitative and quantitative data on the morphology and shape of persistent slip markings (PSMs), occurrence of extrusions and intrusions and the kinetics of extrusion growth are reported. They are discussed in relation with recent physically based theories of surface relief formation leading to fatigue crack initiation.

Abstract: Cyclic plastic straining in crystalline materials is localized to persistent slip bands (PSBs) and results in formation of persistent slip markings (PSMs) consisting of extrusions and intrusions. Intensive plastic strain in PSBs results in dislocation interactions and formation of point defects. The extended model based on point defect formation, migration and annihilation is presented describing surface relief formation in the form of extrusion-intrusion pairs. Point defect migration and resulting mass transfer is the principle source of cyclic slip irreversibility leading to crack-like defects - intrusions. Fatigue cracks start in the tip of sharp intrusions.

Abstract: This paper examines pipeline safety and develops a mathematical model for predicting illegal intrusion. The model idealizes a typical pipeline structure as a pipe-in-pipe double beam, consisting of the process pipe encased in a larger diameter outer carrier pipe resting on an elastic soil foundation. Intrusion is considered to consist of hammering and cutting activities on the casing pipe which transmits shock motion to the process pipe. From the solution feedback control algorithms have been proposed for designing surveillance instruments which assist in mitigating the problem of illegal intrusion for harvesting of crude oil. A point sensor was used to simulate the response to intrusive hammering action induced on the casing pipe in a 2 m segment of the process pipe in an example. Sensor was conFigureured to measure displacement response at intervals of 2 seconds at (0.00, 0.06, 0.12,..., 2.00) m sampling points. The displacements indicated within the model assumption of zero damping, were 4.62 x 10^-4 m and 4.24 x 10^-4 m at the left and right hand anchors. A deflection of around-2.67 x 10^-4 m was obtained at 0.94 m.

Abstract: Recent observations relevant to the early stages of the fatigue damage of crystalline materials are reviewed. Experimental evidence on the localization of the cyclic plastic strain and on the surface relief formation in cyclic loading of 316L austenitic stainless steel is presented. The focused ion beam is used for exposing three-dimensional evidence of persistent slip markings (PSMs). PSMs consist of extrusions and parallel or alternating intrusions which develop during cyclic loading. Monte Carlo simulations of vacancy generation within persistent slip band (PSB) and their migration to the matrix where they annihilate on the edge dislocations are used to simulate the growth of extrusions and intrusions. The results of the simulations are compared with experimental data and discussed in terms vacancy models of fatigue crack initiation.

Abstract: The possibilities of atomic force microscopy in studying surface features and early fatigue damage in materials are reviewed. Examples of a true relief arising on the surface of cyclically strained materials as recorded by atomic force microscopy are given. Characteristic features of the surface relief are well-defined persistent slip markings consisting of extrusions and intrusions. The shape of extrusions and intrusions can be obtained by observation of metal surface and replicas and in combination with high resolution scanning electron microscopy. The growth of extrusions during fatigue life is reported for austenitic and ferritic stainless steels. The experimental data are compared with models of the localized cyclic plastic straining and predictions of the fatigue crack nucleation models.