Experimental measurement and model validation of COD in pipe under bending with off-centered circumferential crack

The leak area of circumferential through-thickness crack in pipe under bending depends on the position of the crack with respect to the bending plane. In leak-before-break (LBB) analysis, the assumption that the crack is symmetrically placed with respect to the bending plane is not necessarily conservative. In this work, the crack opening of circumferential cracks, off-centered with respect to the bending plane, was investigated experimentally. Here, three pipe geometries and two crack lengths were investigated. For each crack, the centred and two off-centered configuration were examined. The crack opening displacement (COD) distribution along the crack length was measured for two selected bending load levels using digital image correlation (DIC) technique. These measurements have been used for verifying the solution provided by the hodograph cone method (HCM) as proposed by Bonora [1]

Use of Circumferentially Cracked Bar sample for CTOD fracture toughness determination in the upper shelf regime

In this work, the use of circumferentially cracked bar (CCB) sample to determine material fracture toughness in the upper shelf regime for carbon steels has been investigated. Since high fracture toughness materials are known to exhibit extensive crack tip blunting before ductile crack initiation, accurate specimen design is required to provide realistic fracture toughness measurement. Here, a CCB was designed to have similar loss of constraint as for SENT sample. Continuum damage mechanics was used to predict the occurrence of ductile crack initiation and propagation. Finite element analysis was performed to predict specimen response and to compare computed J-integral crack driving force with measured CTOD. Finally, experimental tests were performed on X65 carbon steel and the measured critical CTOD was compared with available fracture data obtained with SENT

Inhibitory effects of agmatine on monoamine oxidase (MAO) activity: Reconciling the discrepancies

Abstract Agmatine has been functionally characterized as an important hormone and co-neurotransmitter in mammals. Given its ability in binding Imidazoline sites, a regolatory site of monoaminoxydase, it has been suggested to be involved in many neurological aspects. However, its inhibitory effect on this enzyme still remains an unanswered question. This present study is aimed to asses whether different experimental conditions could affect the agmatine action on monoaminoxydase activity. We demonstrate that the monoaminoxydase inhibition by agmatine is obtained under alkaline conditions and a long time of incubation. No inhibitiory action was found for shorter times of reaction at elevated pH, or at neutral condition and long time of incubation. No inhibition was also detected by substituting the monoamineoxydase substrate tyramine with kynuramine, however, while in these conditions a remarkable inhibition was shown by two aminoxydase inhibitors tranylcypromine and idazoxan. Herein, we discuss a mechanism model and the functional consequences of agmatine action on monoaminoxydase

ultrafine particle generation by high velocity impact of metal projectiles

Ultrafine particle generation through mechanical processes was not carefully deepened so far, even if it could be related to the human health-based researches. In particular, the evaluation of ultrafine particles produced in battlefield scenarios can be useful to quantify the exposure of soldiers to particles carrying toxic heavy metals. In the present work ultrafine particle generation during high-velocity impact of metal projectiles was deepened performing symmetrical high velocity Taylor impacts of copper cylinder tests (Rod-on-Rod tests) by means of a gas-gun facility. Particle number distributions and total concentrations were measured through one-second-time resolution instruments in a chamber where impact events at different velocities were performed. Particle number generation per impact was also evaluated. Particle concentrations in the 106 part. cm-3 range were measured corresponding to particle generations higher than 1012 particles per impact, then comparable to those typical of combustion sources. Particle number distribution showed a unimodal distribution with a 10 nm mode. Summarizing, the performed experimental campaign revealed an extremely high generation of ultrafine particles from mechanical processes

mechanoluminescence of nylon under high velocity impact

The light emissions produced during deformation of solids induced by any mechanical action is called mechanoluminescence (ML). This phenomenon was reported mostly in hypervelocity impacts. Using high speed video-recording, the authors found evidence of ML for nylon at much lower impact velocity (of the order of 100 m/s). In order to understand the mechanism responsible for ML, Taylor impact experiments were planned and performed. Several impact configurations were investigated: Taylor anvil impact, Taylor impact on nylon anvil and rod-on-rod impact experiment. During the tests, the emitted light was measured using a wide-spectrum visible-to-infrared photodiode with response below 1 microsecond, and the signals were analyzed. The existence of a limiting impact velocity below which ML is no longer observed seems to be indicative of the fact that ML is controlled by the high pressure that is generated under uniaxial strain loading conditions. This result is consistent with the fact that, as soon as the compressive stress wave travels longitudinally in the Taylor sample and the pressure drops as a result of the arrival of the release waves, the ML no longer occurs. When tests were repeated in vacuum, no light emission in the visible range was observed. This finding seems to indicate that light emission occurs as a result of the oxidation of free radicals generated by the rupture of the polymer chains caused by the dynamic pressure wave

Strain Rate Effects on Fracture Behavior of Austempered Ductile Irons

In this work, the mechanical behavior of the austempered ductile iron (ADI) JS/1050-6 was investigated, with particular attention to the strain rate effects on the material ductility. Tensile tests at different strain rates (up to 103 s(-1)) and temperatures (ranging from 213 to 343 K) were performed. Samples with different geometries, smooth and round notched bars, were used to evaluate the effect of the stress triaxiality level on the strain at fracture. For each configuration, the evolution paths of stress and strain were extracted in the point where failure is expected performing numerical analyses at the continuum scale. Stress histories were used as input in a micromechanics analysis aimed to analyze the heterogeneous state of stress, determined by the presence of the graphite nuclei, under the different loading conditions obtained in the experiments. The main result is that, under dynamic conditions, the stress field redistribution, due to the adiabatic condition, postpones the failure occurrence, regardless temperature and strain rate effects on the matrix ductility