Experimental testing and numerical simulations for life prediction of gate valve O-rings exposed to mixed neutron and gamma fields

EPDM O-rings of gate valves employed for the construction of a second-generation accelerator for the production of neutron-rich Radioactive Ion Beams were studied in order to assess their sealing performance both during the facility service time and the post-service storage phase. Several O-ring specimens were at first exposed to different dose levels of mixed neutron and gamma radiations. Correspondent modifications of physical and mechanical properties of the material were investigated by means of uniaxial tensile tests, dynamic mechanical analyses, aging, compression set and vacuum leak tests. A hyperelastic strain energy function was adopted to fit the mechanical response of the material as a function of the absorbed dose. The minimum squeeze degree that guarantees O-ring sealing efficiency at different irradiation levels was determined by varying the interference between O-rings and grooves. A finite element model of the vacuum leak test was then set up to assess the contact pressure level required to ensure sealing. Numerical simulations of the gate valve main O-ring were subsequently carried out. By comparison of the predicted contact pressure and strain levels with experimental results, a life prediction map, as function of the service time, the storage time and the O-ring squeeze degree, was proposed

Effects of fiber layout on strength and failure of 3D printed notched composites

This study investigates the effect of printing strategies on the strength of additively manufactured notched fiber reinforced composite specimens. Specimens with varying notch geometries (two radii and two opening angles) and fiber layouts (unreinforced, unidirectional, quasi-isotropic and concentric) were 3D printed and tested under tension. Digital image correlation provided surface strain field data. Results showed that fiber deposition patterns significantly impact notch sensitivity, failure loads and mechanisms, with notch geometry being of secondary importance. The unidirectional layout achieved the highest strength but with progressive failure, while quasiisotropic specimens failed abruptly from the notch. The concentric layout shielded the notch region but induced premature failure away from the notch due to transverse stress. Stress concentration factor approaches, which work well for conventional laminates, have limitations for 3D printed composites due to local differences and complex interactions. Optimizing fiber deposition, instead of geometry, emerges as a promising design route. Combining unidirectional and contouring algorithms may improve performance. However, further studies utilizing multiscale modelling and local failure analyses are needed to fully understand failure mechanisms and guide optimal notch designs for 3D printed composites. With improved understanding and design methods, 3D printing promises to unlock new possibilities for structurally efficient notched composite parts

Influence of micro-notches on the fatigue strength and crack propagation of unfilled and short carbon fiber reinforced PEEK

Short carbon fiber reinforced (SCFR) PEEK is a highly attractive material for lightweight structures; improving knowledge about the influence of local imperfections on its fatigue behavior is essential for the design of real components. To this aim, fatigue strength and crack propagation of two grades of SCFR PEEK and neat matrix were investigated by testing at different stress levels specimens with a micro-notch consisting of a small blind hole (range diameter 0.1–1 mm). Overall, the presence of a micro-notch resulted in a decrease of fatigue strength compared to un-notched condition, but with different sensitivity and crack propagation patterns; while a higher fiber volume fraction enhanced fatigue strength and resistance to crack propagation, the combination of a lower fiber content and inclusion of additive particles had a negative effect. Crack propagation in the notched region was also evaluated. The average values of Paris' law exponential coefficients were similar and within the range of literature values, without apparent correlation with reinforcement type. Preliminary investigations in the presence of the smallest micro-notches seem to indicate the presence of a threshold size below which the influence of a small notch is comparable with that of material inherent defects, but further testing is necessary

Design of AGV systems in working environments shared with humans: A multi case study

To meet the challenges and needs of an ever-changing market and as part of the fourth industrial revolution, factories are transforming into increasingly automated environments. A widely used and well-established solution today is Automated Guided Vehicles (AGVs), which often work closely with humans in crowded environments. Thus, in addition to flexibility, another important criterion associated with automatic handling systems is safety. The purpose of this work is to show how the involvement of three different but equally important roles in the design of an AGV system can benefit the whole project. The advantage of considering three different perspectives is the possibility of obtaining a more complete vision from the earliest stages of implementation, avoiding, as far as possible, the need to make changes in the next stages, which would generate higher costs than necessary. The article is based on two case studies, each one set in a major European manufacturing company: the first one is an Italian automotive manufacturer and the second one is a Swedish manufacturer of mechanical components. Both case companies apply AGVs in their material handling processes and, accordingly, have experience of both implementing and operating AGV systems. The article applies semi-structured interviews to study the three key roles, highlighting the key points for each role and showing the common issues that emerged from the interviews

Evaluation of Maine Coon cat behavior during three different management situations

Today, cats are one of the most widespread and beloved companion animals: they share their life with people and are perceived as social partners by their owner. The knowledge and understanding of cat-human communication and of the behavior exhibited in response to different emotions is essential to improve the management of housed cats. The aim of this study was to analyze and compare the behavior of cats in three different situations that can occur in house cats' lives. Ten Maine Coon cats, four males and six females, ranging in age from one to 13 years, belonging to a single private owner and managed under the same conditions, were exposed randomly to three different contexts for five minutes (waiting for food, isolation in unknown environment, and brushing). All the situations were video-recorded and subsequently analyzed. The behaviors oriented to environment, oriented to food bowl, locomotion, active interactions, yawning, lip licking and swallowing, and salivation mainly characterized waiting for food, while isolation appears principally characterized by behaviors such as hiding, scratching, worried positions, and exploration. Withdrawal, passive interactions, aggressive behaviors, facial discomfort, and purring characterized brushing. Vocalizations were significantly more frequent during isolation and brushing than during waiting for food, but it is possible that the characteristics of the vocalizations in these two situations are different. Our principal finding is that cats showed different behavioral patterns in the three situations and, in particular, their behavior during brushing was very different than in the two other situations. It can be hypothesized that these different behavioral responses are due to the different emotional states elicited by each of the three challenging and potentially stressful situations. Further investigation is being carried out to better understand cats' behaviors and emotions to improve cats' management in the household

Una procedura per la valutazione dei limiti di utilizzo di O-Ring sottoposti ad intensi fasci di neutroni

Si presenta una procedura per la previsione della durata di utilizzo di O-ring in materiale polimerico impiegati nei bersagli per la produzione di fasci di ioni radioattivi. Si sono dapprima condotte prove di tenuta a vuoto e analisi a elementi finiti di un O-ring di riferimento operante con diversi livelli di interferenza con la cava, identificando la precompressione limite per la tenuta e la corrispondente pressione di contatto con la cava. Si sono poi effettuate prove di trazione e di Compression Set su campioni di O-ring in EPDM, preventivamente sottoposti a diversi livelli di irraggiamento in campi misti di neutroni e gamma, analizzando l’effetto della dose assorbita sul comportamento meccanico del materiale e sulle corrispondenti proprietà resistenziali, e definendo opportune leggi costitutive. Si sono infine simulate le progressive modifiche di comportamento della guarnizione indotte dall’irraggiamento, prevedendone la durata in esercizio in termini di tenuta e di resistenza strutturale

Experimental and Numerical Dynamic Properties of Two Timber Footbridges Including Seasonal Efects

This paper deals with experimental and numerical dynamic analyses of two timber footbridges. Both bridges have a span of 35 m and consist of a timber deck supported by two timber arches. The main purpose is to investigate if the dynamic properties of the bridges are season dependent. To this end, experimental tests are performed during a cold day in winter and a warm day in spring in Sweden. The frst bending and transverse mode frequencies increase 22% and 44%, respectively, due to temperature efects in the case of Vega Bridge. In the case of Hägernäs bridge, the corresponding values are 5% and 26%. For both bridges, the measured damping coefcients are similar in winter and spring. However, the damping coeffcients for the frst bending and transverse modes are diferent for both footbridges: about 1% for the Hägernäs bridge and 3% for the Vega bridge. Finite-element models are also implemented. Both numerical and experimental results show good correspondence. From the analyses performed, it is concluded that the connections between the diferent components of the bridges have a signifcant infuence on the dynamic properties. In addition, the variation of the stifness for the asphalt layer can explain the diferences found in the natural frequencies between spring and winter. However, due to the uncertainties in the modelling of the asphalt layer, this conclusion must be taken with caution

Autophagy-related protein LC3 and Beclin-1 in the first trimester of pregnancy

Autophagy is a degradation process that acts in response to environmental stressors. Recently, autophagy has been detected in normal term, preeclamptic and intrauterine growth-restricted placentas. The object of this work was to investigate the presence of autophagy in first trimester voluntary interruption of pregnancy placental villi by the expression of autophagy-related proteins, light chain 3 (LC3), and Beclin-1. In first trimester placental villi laser scanning confocal microscopy (LSCM) analysis revealed LC3 and Beclin-1 immunoreactivity prevalently located in villous cytotrophoblasts. Using LSCM, LC3, and Beclin-1 were localized to the cytoplasm of the trophoblast layer in human full-term placentas. Beclin-1 expression and LC3 activation were confirmed by western blotting. These data emphasize that autophagy activation is different among cytotrophoblasts and syncytiotrophoblasts depending on the gestational age and thus we speculate that autophagy might play a prosurvival role throughout human pregnancy