In-situ measurements of fatigue damage evolution by electrical resistance method

Fatigue damage is one of the main failure mechanisms of structures. In the present work Electrical Resistance Changes (ERC) were measured during fatigue tests on notched carbon steel specimens. ERC measurements were performed by monitoring the change in electrical resistance in real-time without interrupting the test at various pre-selected time intervals. The temperature of the specimens was also on-line monitored during the test in order to deduce its effect on the electrical resistance. The comparison of the resistance data measured at initial and different phases of fatigue tests showed the existence of temporal variations associated to fatigue damage: in particular the resistance first decreases, in the initial stages of loading, and subsequently, starting approximately from half-life presents an increase with the number of load cycles due to the internal micro-damage’s accumulation. In the final stages of the fatigue test, prior the final fracture, it increases rapidly, in the propagation phase of the crack. In conclusion, the applied experimental method proved to be valid for studying the evolution of damage and to predict and evaluate fatigue life effectively

RPAS-Based Framework for Simplified Seismic Risk Assessment of Italian RC-Bridges

Existing reinforced concrete (RC) bridges that were designed in the decades between 1950 and 1990 exhibit inadequate structural safety with reference to both traffic loads and hazard conditions. Competent authorities are planning extensive inspections to collect data about these structures and to address retrofit interventions. In this context, Remotely Piloted Aircraft Systems (RPASs) represent a prospect to facilitate in-situ inspections, reducing time, cost and risk for the operators. A practice-oriented methodology to perform RPAS-based surveys is described. After that, a workflow to perform an in-situ RPAS inspection oriented to a photogrammetric data extraction is discussed. With the aim to connect the advantages of the RPAS technologies to the seismic risk assessment of bridges, a simplified mechanic-based procedure is described, oriented to map the structural risk in road networks and support prioritization strategies. A six-span RC bridge of the Basilicata road network, representing a typical Italian bridge typology is selected to practically describe the operating steps of the RPAS inspection and of the simplified seismic risk assessment approach

Bio-induced reduction of Cr(VI) in aquifers by organic substrates injection

Hexavalent chromium is a primary toxic element used in galvanic processes, in metallurgical industry and for the production of dyes and pigments. Conventional methods for Cr(VI) remediation, pump&treat and excavation, are expensive and require a large amount of energy and time. Innovative technologies include bio-induced reduction, that is Cr(VI) reduction to Cr(III) by injection of organic substrates that are readily biodegraded by autochthonous microorganisms in the aquifer, resulting in reducing conditions. Lab scale batch tests were carried out, with two different soil (A and B) and solid/liquid ratios (25% and 50% on weight basis). Initial Cr(VI) concentrations were 5000 or 10000 µg/L. Ultrafiltration permeates of cheese whey and beer distillation residues were used as the organic substrates. In all microcosms, dissolved oxygen decreased from about 6 mg/L to values <1 mg/L after 1-2 d incubation, and the redox potential from approximately +250 mV to -400 mV by 11 d. After about 40 days, the highest Cr(VI) abatements were obtained in soil A microcosms fed with beer distillation residues, as soil A had an initial total heterotrophic bacteria concentration three orders of magnitude higher than soil B. Fe(II) availability was also a key factor in Cr(III) co-precipitation

Numerical and experimental validation of SMArt thermography for the inspection of wind blade composite laminate

none3noAn innovative active thermography technique is proposed for the inspection of typical wind blade material. The proposed technique is based on the use of a multifunctional material obtained adding a grid of Shape Memory Alloy wires, which would serve also as a protection against lightning, to a traditional glass fibre composite panel. This technique, called SMArt thermography, which exploits the SMA wires as internal heat sources, has been compared to a traditional pulsed thermography in the case of a representative panel of unidirectional glass fibre and epoxy matrix with embedded SMA wires and artificial defects. The experimental results of the two techniques are reported and compared to the result of a numerical FEM transient model, in order to establish the reliability and the detectability limit of the proposed technique. The FEM model has been proven to be a useful tool for the definition of the multifunctional material at a design stage.openMarta De Giorgi; Riccardo Nobile; Andrea SaponaroDE GIORGI, Marta; Nobile, Riccardo; Saponaro, Andre

experimental evaluation of artificial defects using smart thermography

Abstract SMArt termography is an innovative and promising technique that could be useful for the detection of damages of large components subjected to in-service loads, like wind blade. This technique requires building traditional carbon or glass fiber reinforced composite laminates adding a regular net of Shape Memory Alloy (SMA) wires in the matrix. These wires confer to the composite material additional features. In particular, the electro-thermal properties of SMA could be used as an internal heat source to be used for the control of the component using the traditional numerical technique used to elaborate the raw thermal data. Despite of other thermography techniques, SMArt thermography is characterized by a quite reduced amount of heating power, which produces a limited increasing of the temperature of the component subjected to control. On the other hand, the numerical elaboration of thermal data acquired from IR camera is more sensitive and require a deeper comprehension of the phenomena. In this work, a GFRP composite panel containing several artificial defects has been studied both from a numerical and experimental point of view, in order to determine the sensitivity of the technique, the limit of applicability and practical indications about the reliability of the technique

Bioremediation of Hexavalent Chromium—A Few Significant Site Histories in Italy

In Lombardy (Italy), about 25% of the sites ranked in the Regional Plan of Contaminated Sites are affected by Cr(VI) in groundwater and/or soil. Therefore innovative sustainable remediation techniques are under investigation, with pilot- or full-scale applications. In situ bioremediation has a significant role in the remediation techniques for its general sustainability in terms of environmental impact and costs. However, while organics can be mineralized, inorganics can only change their oxidation state, hopefully reducing their toxicity and mobility in the environment. Various patented products were used at five polluted sites in order to reduce Cr(VI) to Cr(III) via bio-induced reduction, bio-reduction and bioimmobilization. The experience pointed out that Cr(VI) concentration in groundwater can be significantly reduced (up to three order of magnitudes), but the unsaturated zone should be treated as well in order to solve the problem definitely. Soil heterogeneity is a critical issue and mixtures usually have to be injected at different depths. Iron, manganese and sulphate side-contamination can result in groundwater after injections

real time monitoring of damage evolution by nonlinear ultrasonic technique

Abstract In this work, the ultrasound technique was used to monitor the damage of material subjected to fatigue loads. Prediction of structural damage is critical for safe and reliable operation of engineered complex systems. In these measurements, conventional ultrasonic probes (transmitter and receiver) were stably fixed to the tested samples with steel brackets, in order to eliminate ever possible variability associated with the coupling of probes. The transmitted and received ultrasonic signals were recorded and analyzed using a digital oscilloscope. The data were converted into the frequency domain using an algorithm developed in Matlab based on Fast Fourier Transform (FFT) for received signal in dependence of the applied stress level and the accumulated fatigue damage was deeply studied in order to recognize quantitative effects, suitable for an experimental prediction of the integrity of the material. The acquired data were compared with the reference signal, at the beginning of the fatigue tests. Particular care has been paid to UT signal attenuation and to the study of the frequency spectrum as the number of load cycles varies. The applied experimental technique has proved efficient for detecting damage induced by mechanical stress

Too human inhuman: a paradigm shift in contemporary crime fiction

Actual sociology of deviance outlines moral pluralism or even fragmentation which characterize the social moral order. The paper assumes that social reality can be mirrored in media products, influencing their cultural trends, due to the fact that in the consumer society the product should maintain its appeal to the public. The actual moral ambiguity of social order has been thus resembled in crime fiction. The analysis clearly shows a transformation through a historical confrontation of serial killer mediatized representations, comparing Hitchcock’s Norman Bates in Psycho, and the character of Dexter from the homonymous tv show. The paper outlines a passage from the ‘monsterification’ of the former’s psychopathy to the humanization of the latter’s homicidal inhumanity

Study of damage of t-joint components by using different non-destructive techniques

The present research is focused on the use of different non-destructive techniques for detecting damage in CFRP composite structures obtained by an innovative technological process: Automated Fiber Placement. The component was a T-joint stringer adhesively bonded to a skin panel. The aim of the present work is to show the capability of these techniques to provide complementary information for detecting the damage in composites. Automated Fibre Placement consists in an automatic deposing of prepeg or dry plies on a specific mould. The innovation lies in the possibility to reduce the time of the manufacturing process of large and complex structures by using a robotic arm that contemporary deposes fibre tows and pre-polymerizes them. The resulting products present higher quality in terms of surface finish, internal flaws absent and higher mechanical properties. The T-joint component tested in the present research was addressed to both static and cyclic tests. After the damage was induced in the material it was performed a qualitative and quantitative study of the damage by using different nondestructive techniques: Thermoelastic stress analysis (TSA), Ultrasound tests (UT) and displacement/strain measurements provided by strain gages. Processing and post-processing procedures were developed to analyze the data from each tests and finally the comparison of the results allowed a complete characterization and an overview of damage in the component by observing specifically where and when it occurred and how many regions of the component were interested. Finally, dimension, shape and depth where assessed