T-stress determination using thermoelastic stress analysis

T-stress and mixed-mode stress intensity factors have been determined experimentally using thermoelastic stress analysis and using a finite element method. Pure mode I, strong mixed-mode I and II, and interacting cracks have been used as the case studies. A new technique has been proposed to identify the crack tip from thermoelastic images. It has also been shown that using three terms of Williams's stress field formulation to determine the T-stress, yields a more accurate solution than using only the first two terms of the expansion

Some experimental observations of crack-tip mechanics with displacement data

Estudio de la mecánica en el vértice de la grieta mediante datos de desplazamiento.In the past two decades, crack-tip mechanics has been increasingly studied with full-field techniques. Within these techniques, Digital Image Correlation (DIC) has been most widely used due to its many advantages, to extract important crack-tip information, including Stress Intensity Factor (SIF), Crack Opening Displacement, J-integral, T-stress, closure level, plastic zone size, etc. However, little information is given in the literature about the experimental setup that provides best estimations for the different parameters. The current work aims at understanding how the experimental conditions used in DIC influence the crack-tip information extracted experimentally. The influence of parameters such as magnification factor, size of the images, position of the images with respect the crack-tip and size of the subset used in the correlation is studied. The influence is studied in terms of SIF and T-stress by using Williams’ model. The concept of determination of the K-dominance zone from experimental data has also explored. In this regard, cyclic loading on a fatigue crack in a compact tension (CT) specimen, made of aluminium 2024-T351 alloy, has been applied and the surface deformation ahead of the crack tip has been examined. The comparison between theoretical and experimental values of KI showed that the effect of subset size on the measured KI is negligible compared to the effect of size of the image.Universidad de Málaga. Campus de Excelencia Internacional Andalucía Tech

Stress field around arbitrarily shaped cracks in two-dimensional elastic materials

The calculation of the stress field around an arbitrarily shaped crack in an infinite two-dimensional elastic medium is a mathematically daunting problem. With the exception of few exactly soluble crack shapes the available results are based on either perturbative approaches or on combinations of analytic and numerical techniques. We present here a general solution of this problem for any arbitrary crack. Along the way we develop a method to compute the conformal map from the exterior of a circle to the exterior of a line of arbitrary shape, offering it as a superior alternative to the classical Schwartz-Cristoffel transformation. Our calculation results in an accurate estimate of the full stress field and in particular of the stress intensity factors K_I and K_{II} and the T-stress which are essential in the theory of fracture.Comment: 7 pages, 4 figures, submitted for PR

Experimental and numerical analysis of in- and out- of plane constraint effects on fracture parameters: Aluminium alloy 2024

The influence of in- and out- of plane constraints on the behaviour of a crack under mode I loading conditions is studied. The independence of the stress intensity tensor, with respect to the specimen thickness B shows that under loss of constraint conditions higher order members of the Williams’ tensor expansion must be considered if the experimental results for increasing apparent fracture toughness resulting from decreasing specimen thickness are to be explained. This is achieved using the constraint curves that define the intensity field tensor along the crack propagation direction and can be alternative to the T-stress approach. This approach is then applied to crack instability assessment for program compact tension (CT — positive values of T-stress) and three point bending (3PB— from negative to positive values of T-stress) specimens with different thicknesses. The theoretical results are compared with experimental ones obtained from the research program on aluminium alloy 2024

Humor trotz(t) Stress? : Bedeutungen, Möglichkeiten und Grenzen bemerkenswerter Phänomene

Einleitung: Laut Lobsiger, Kägi und Burla (2016) ist jede vierte Pflegefachperson aus dem Beruf ausgetreten und jede sechste nicht mehr erwerbstätig. Belastende Situationen im Berufsalltag führen bei vielen Pflegefachpersonen zu Stress. Hält dieser über längere Zeit an, leidet die Arbeitszufriedenheit und die Gesundheit der Pflegefachpersonen. Im Extremfall droht gar ein Burnout. Eine Methode von Stressbewältigung ist der Humor. Richtig eingesetzt könnte dieser, Kündigungen und damit verbundene Fluktuationen innerhalb eines Pflegeteams reduzieren. Handlungsmethoden sind notwendig um präventives und gesundheitsförderndes Verhalten zu erzielen. Ziel: In dieser Arbeit sollen Empfehlungen für den Einsatz von Humor gegeben werden, die im Berufsalltag von Pflegefachpersonen eingesetzt werden können. Methode: Durch systematisierte Literaturrecherchen wurden sechs für das Thema relevante Studien identifiziert, zwei qualitative und vier quantitative. Diese Studien wurden kritisch beurteilt und Evidenzlevels zugeordnet. Ergebnisse: Die aus der Literatur gefilterten Ergebnisse wurden Kategorien zugeteilt: Humorverstehen, Work-Life-Balance, Kommunikation und Zeit. Schlussfolgerung: Zur Messung des Stresslevels von Pflegefachpersonen empfiehlt sich die Implementierung eines Assessmentinstruments. Humorvolle Bewältigungsstrategien werden für jede und jeden Einzelnen sowie für Pflegeteams abgegeben. Zur professionellen Anwendung von Humor sind Offenheit und der Wille notwendig. Richtig eingesetzter Humor ist eine Form der Bewältigung

A brief note on elastic T-stress for centred crack in anisotropic plate

The stress intensity factors (SIFs) and the T-stress for a planar crack with anisotropic materials are evaluated by the fractal finite element method (FFEM). The FFEM combines an exterior finite element model and a localized inner model near the crack tip. The mesh geometry of the latter is self-similar in radial layers around the tip. A higher order displacement series derived from Laurent series and Goursat functions is used to condense the large numbers of nodal displacements at the inner model near the crack tip into a small set of unknown coefficients. In this study, the variations of the SIFs and the T-stress with material properties and orientations of a crack are presented. The separation of the analytical displacement series into four fundamental cases has shown to be necessary in order to cover all the material variations and the orientations of a crack in the plate with general rectilinear anisotropic materials. © Springer 2005.postprin