Prediction of ductile fracture in anisotropic steels for pipeline applications

Large diameter steel pipelines for gas transportation may experience extreme overloads due to external actions such as soil sliding, faults movements, third part interactions. In these scenarios the material undergoes severe plastic strains which locally may reach the fracture limits. Due to the manufacturing process, the steels used in such applications have an anisotropic behavior both for plasticity and fracture. In this paper two steel grades have been characterized in view of anisotropic plastic fracture. Fracture tests have been planned to characterize the fracture behavior under different stress states and in different directions to define the anisotropic sensitivity. Finite element modelling, incorporating an anisotropic plasticity formulation, has been used to calculate the local fracture parameters in the specimens and to define the complete ductile fracture locus. An uncoupled damage evolution law has been finally used to evaluate the fracture limits on real pipelines failed in full scale laboratory tests. The strain to fracture prediction has been verified by local strain measurements on the fractured pipes. The model robustness has been also verified on global parameter predictions, such us the burst pressur

Analysis of anisotropic hardening in high strength steel (HSS) in line pipes for strain-based applications

In this paper are reported the results of an extensive and innovative mechanical characterization carried out on three large diameter line pipes for gas transportation useful to calibrate a new plasticity finite element numerical simulation (FEM) model developed at Rina Consulting – Centro Sviluppo Materiali. In particular, the anisotropic hardening for the materials has been characterized by tensile tests carried out in the base material of the pipe with tensile specimen extracted along different orientations, considering also the pipe through thickness direction

Analysis of the micro-voids fraction in structural steels and its evolution during plastic deformation until failure

In this work the results of an experimental analysis performed on different steels of commercial use having different microstructure and yield value are reported. The materials were characterized by performing tensile and torsion tests, bringing the material up to rupture. The specimens were extracted according to different orientations to verify the influence of anisotropy on the size and distribution of micro-voids present in the broken material. After the mechanical tests, an analysis was made of the amount of micro-voids present in the original, not deformed material and in the deformed material until failure. The results obtained show that for all the analyzed steels the initial fraction of micro-voids is negligible, and no growth or formation of further voids is observed as the applied plastic deformation increases, even for strain values close to rupture

The role of loneliness in the association between chronic physical illness and depressive symptoms among older adults: A prospective cohort study

BACKGROUND: Chronic physical illness increases the risk of subsequent depressive symptoms, but we know little about the mechanisms underlying this association that interventions can target. We investigated whether loneliness might explain associations between chronic illness and subsequent depressive symptoms. METHODS: We used English Longitudinal Study of Ageing data, a prospective cohort of adults over 50. Our exposure was chronic illnesses (wave two) including arthritis, cancer, diabetes, cardiovascular disease, stroke, and chronic obstructive pulmonary disease. Loneliness scores were a mediator on the short University of California, Los Angeles Loneliness Scale at wave three. Depressive symptom scores (outcome) were measured using the Centre for Epidemiologic Studies Depression Scale (wave four). We examined associations of chronic physical illness with loneliness and depressive symptoms in univariable and multivariable regression models. RESULTS: Fully-adjusted models included 2436 participants with the depression outcome and 2052 participants with the loneliness outcome. Chronic physical illness was associated with 21 % (incident rate ratio = 1.21, 95%CI = 1.03–1.42) higher depression scores at follow-up. We found no evidence of an association between chronic physical illness and loneliness and therefore did not proceed to analyses of mediation. LIMITATIONS: More prevalent chronic illnesses could have driven our results, such as cardiovascular disease. CONCLUSIONS: Chronic physical illnesses increase the risk of depressive symptoms in older adults. However, we did not find any that chronic physical illnesses were associated with an increased risk of subsequent loneliness. Therefore, interventions targeting loneliness to reduce depression in older adults with chronic physical illness may be insufficient

High efficiency, low power IC step-down controller for ultra-low power applications

Nowadays the evolution of Smart Technology has led to an increasing need for efficient power management systems, especially for low power and wearable applications. In such architectures, in order to minimize power consumption and achieve higher efficiency, switching regulators for power management are almost mandatory. When dealing with ultra-low power applications (average load current of hundreds of μA), the main source of losses is the control system itself, so the main challenge is to minimize the steady-current consumption for the entire control system and adapt it with load conditions.In this paper a novel control architecture principle that maximizes efficiency is proposed, and the whole system and its sub-parts are described in detail. Its main feature is an extremely low bias current (tens of nA), with an operating power consumption that is frequency-dependent; whilst high-side switch on-time is kept almost constant, system frequency is adapted with load requirements, obtaining thus a controller consumption that is proportional with load demands