Neural networks for small scale ORC optimization

This study concerns a thermodynamic and technical optimization of a small scale Organic Rankine Cycle system for waste heat recovery applications. An Artificial Neural Network (ANN) has been used to develop a thermodynamic model to be used for the maximization of the production of power while keeping the size of the heat exchangers and hence the cost of the plant at its minimum. R1234yf has been selected as the working fluid. The results show that the use of ANN is promising in solving complex nonlinear optimization problems that arise in the field of thermodynamics

Wear Behavior of AlSi10Mg Alloy Produced by Laser-Based Powder Bed Fusion and Gravity Casting

Herein, the sliding wear behavior of AlSi10Mg samples realized using laser‐based powder bed fusion (LPBF) is investigated via pin‐on‐disc (PoD) tests, before and after T6 heat treatment. The changes in the microstructure, density, and hardness induced by heat treatment are correlated with the tribological behavior of the alloy. Furthermore, short wear tests are conducted and the resulting wear tracks are investigated through scanning electron microscopy (SEM), equipped with an energy‐dispersive spectroscopy (EDS) microprobe to elucidate how the wear mechanisms evolve with sliding distance. For comparison, gravity cast (GC) AlSi10Mg samples are also characterized and tested. The as‐built additive manufacturing (AM) sample exhibits the lowest wear rate and coefficient of friction because of its high hardness and relative density, whereas the heat‐treated sample shows the worst behavior in comparison with the GC samples. The results suggest a significant influence of porosity on the wear behavior of AM alloys

Evaluation of cavitation erosion resistance of Al-Si casting alloys: effect of eutectic and intermetallic phases

In the present paper, the influence of eutectic and intermetallic phases on cavitation resistance of Al-Si alloys was studied. In fact, Al-Si alloys are commonly used for the production of components, such as cylinders, pistons, pumps, valves and combustion chambers, which in service may incur in cavitation phenomenon. Samples of AlSi3, AlSi9 and AlSi9CuFe were characterized from the microstructural point of view. Hardness measurements were also performed. Subsequently, cavitation tests were carried out according to ASTM G32 standard and the erosion mechanism was examined by scanning electron microscope. It was found the both eutectic and intermetallic phases enhance cavitation resistance, expressed in terms of mass loss. Particularly, intermetallic particles with complex morphologies provide a positive contribution, exceeding that of other microstructural features, as grain size. The effect of T6 heat treatment was also evaluated. It was confirmed that the precipitation of fine strengthening particles in the Al matrix successfully hinders the movement of dislocations, resulting in a longer incubation stage and a lower mass loss for heat-treated samples in comparison with as-cast ones. Finally, the relationship between cavitation resistance and material hardness was investigated

Cavitation erosion resistance of 1.2709 alloy produced via Laser-Powder Bed Fusion

Maraging steels, like 1.2709 (18Ni-300), are attractive materials for the aerospace, automotive, tooling, and bearing gear industries because of their high yield, tensile strength, and good toughness. The low-carbon martensite matrix and nanoscale intermetallic precipitates combine to provide distinctive mechanical properties. In particular, due to their low carbon content, these steels are easily weldable and are therefore appropriate for additive manufacturing (AM) processes like laser-based powder bed fusion (LPBF). The tooling and molding industry has just lately started using this fabrication technique to create inserts with conformal cooling channels that can extend the lifetime of the insert and core while boosting the cast quality. These parts are frequently exposed to high levels of stress, wear, and even aggressive conditions. In this context, this research focuses on a peculiar, and thus understudied, erosion phenomenon known as cavitation erosion. According to the ASTM G32 standard, the cavitation erosion resistance of 1.2709 maraging steel samples produced by additive manufacturing as well as by forging was investigated. Microstructural analyses were carried out to evaluate the effect of the different microstructures resulting from the different manufacturing techniques on erosion behavior. When compared to the forged maraging steel, the AM one shows less resistance to the initiation of the erosion phenomenon. Nevertheless, the wear rates of the two materials are comparable

Optical-flow-based motion compensation algorithm in thermoelastic stress analysis using single-infrared video

Thermoelastic stress analysis (TSA) is a non-contact measurement technique for stress distribution evaluation. A common issue related to this technique is the rigid-displacement of the specimen during the test phase, that can compromise the reliability of the measurement. For this purpose, several motion compensation techniques have been implemented over the years, but none of them is provided through a single measurement and a single sample surface conditioning. Due to this, a motion compensation technique based on Optical-Flow has been implemented, which greatly increases the strength and the effectiveness of the methodology through a single measurement and single specimen preparation. The proposed approach is based on measuring the displacement field of the specimen directly from the thermal video, through optical flow. This displacement field is then used to compensate for the specimen's displacement on the infrared video, which will then be used for thermoelastic stress analysis. Firstly, the algorithm was validated by a comparison with synthetic videos, created ad hoc, and the quality of the motion compensation approach was evaluated on video acquired in the visible range. The research moved into infrared acquisitions, where the application of TSA gave reliable and accurate results. Finally, the quality of the stress map obtained was verified by comparison with a numerical model.</p

tensile behavior and impact toughness of an alsi3mgcr alloy

Abstract: Recently, an innovative AlSi3Mg alloy with Cr and Mn additions was developed for the production of truck wheels by means of a non-conventional hybrid technique, which combines features of both low pressure die casting and forging processes. The presence of both Cr and Mn leads to the formation of an intermetallic phase rich in Cr, Mn and Fe with a globular or dendritic morphology. Furthermore, proper solution treatments cause the formation of dispersoids in the aluminium matrix. These dispersoids are responsible of enhancing the alloy performance due to dispersion hardening mechanism. In the present work, the tensile properties and the impact toughness of the alloy in as-cast and different heat-treated conditions were studied. Moreover, tensile and impact strength tests were performed on A356 samples in T6 condition machined from traditional LPDC wheels, whose results were compared with the performance of the innovative alloy. Fracture surfaces of tensile and Charpy specimens were observed by Scanning Electron Microscopy (SEM) in order to identify the role of the Cr-Mn containing intermetallic particles in the failure mechanism and the influence of the heat treatment parameters. Considering the static properties, the innovative alloy showed remarkable values of tensile strength, while ductility was improved only after heat treatment optimization. Poor impact toughness values were measured and the microstructural analysis confirmed the presence of coarse intermetallic secondary phases, acting as crack initiation and propagation particles, on the fracture surfaces

Investigation of mechanical properties of AlSi3Cr alloy

In the present paper, microstructural and mechanical properties of an innovative AlSi3Mg alloy were studied. Particularly, the effect of the addition of Cr and Mn on tensile strength and impact toughness was evaluated. In fact, the presence of these elements leads to the formation of an intermetallic phase with a globular or polyhedral morphology. It was therefore investigated the role played by Cr-Mn containing particles in the failure mechanism and the influence of the heat treatment parameters. Moreover, tensile and impact tests were performed on A356 samples in T6 condition, whose results were compared with the performance of the innovative alloy. Considering the static properties, the innovative alloy showed remarkable values of tensile strength, while ductility was improved only after heat treatment optimization. Poor impact toughness values were measured and the microstructural analysis confirmed the presence of coarse intermetallics, acting as crack initiation and propagation particles, on the fracture surfaces

Evaluation of cavitation erosion resistance of Al-Si casting alloys: effect of eutectic and intermetallic phases

In the present paper, the influence of eutectic and intermetallic phases on cavitation resistance of Al-Si alloys was studied. In fact, Al-Si alloys are commonly used for the production of components, such as cylinders, pistons, pumps, valves and combustion chambers, which in service may incur in cavitation phenomenon. Samples of AlSi3, AlSi9 and AlSi9CuFe were characterized from the microstructural point of view. Hardness measurements were also performed. Subsequently, cavitation tests were carried out according to ASTM G32 standard and the erosion mechanism was examined by scanning electron microscope. It was found the both eutectic and intermetallic phases enhance cavitation resistance, expressed in terms of mass loss. Particularly, intermetallic particles with complex morphologies provide a positive contribution, exceeding that of other microstructural features, as grain size. The effect of T6 heat treatment was also evaluated. It was confirmed that the precipitation of fine strengthening particles in the Al matrix successfully hinders the movement of dislocations, resulting in a longer incubation stage and a lower mass loss for heat-treated samples in comparison with as-cast ones. Finally, the relationship between cavitation resistance and material hardness was investigated

Investigation of mechanical properties of AlSi3Cr alloy

In the present paper, microstructural and mechanical properties of an innovative AlSi3Mg alloy were studied. Particularly, the effect of the addition of Cr and Mn on tensile strength and impact toughness was evaluated. In fact, the presence of these elements leads to the formation of an intermetallic phase with a globular or polyhedral morphology. It was therefore investigated the role played by Cr-Mn containing particles in the failure mechanism and the influence of the heat treatment parameters. Moreover, tensile and impact tests were performed on A356 samples in T6 condition, whose results were compared with the performance of the innovative alloy. Considering the static properties, the innovative alloy showed remarkable values of tensile strength, while ductility was improved only after heat treatment optimization. Poor impact toughness values were measured and the microstructural analysis confirmed the presence of coarse intermetallics, acting as crack initiation and propagation particles, on the fracture surfaces

Thermoelasticity and ArUco marker-based model validation of polymer structure: application to the San Giorgio's bridge inspection robot

Experimental procedures are often involved in the numerical models validation. To define the behaviour of a structure, its underlying dynamics and stress distributions are generally investigated. In this research, a multi-instrumental and multi-spectral method is proposed in order to validate the numerical model of the Inspection Robot mounted on the new San Giorgio's Bridge on the Polcevera river. An infrared thermoelasticity-based approach is used to measure stress-concentration factors and, additionally, an innovative methodology is implemented to define the natural frequencies of the Robot Inspection structure, based on the detection of ArUco fiducial markers. Established impact hammer procedure is also performed for the validation of the results.</p