Mattia Merlin

A comparative study on the effects of three commercial Ti–B-based grain refiners on the impact properties of A356 cast aluminium alloy

The effect of three commercial Ti–B-based grain refiners on the impact properties of the A356 cast aluminium alloy was assessed. The impact tests were performed by means of an instrumented Charpy pendulum. During impact testing, the maximum load and the total impact energy, as well as its complementary contributions, the energy at maximum load and the crack propagation energy, were measured. Impact properties were studied as a function of size and shape of the main microstructural features, which were analysed by means of optical microscopy and scanning electron microscopy. The results show that the influence of grain refinement on microstructure involves beneficial and detrimental concurrent effects which strongly affect impact properties. The total impact energy decreases with the addition of all the grain refiners due to a shift from a mixed transgranular–intergranular fracture mode to a more severe transgranular mode. Crack initiation and propagation occur mainly through the fracture of Fe-intermetallics and brittle Si particles, and the mechanism of void coalescence. No direct correlation between grain size and impact properties is found. Moreover, the aspect ratio of eutectic Si particles does not change with grain refinement, implying that there are no mutual poisoning effects between Sr and B. Total impact energy is found to depend on both SDAS and β-platelets size. The concurrent effects of SDAS and β-platelets average maximum length on total impact energy can be taken into account by the multiple regression analysis technique.

Comparative Assessment of Two Constitutive Models for Superelastic Shape-Memory Wires Against Experimental Measurements

Two constitutive models representative of two well-known modeling techniques for superelastic shape-memory wires are reviewed. The first model has been proposed by Kim and Aberayatne in the framework of finite thermo-elasticity with non-convex energy [1]. In the present article this model has been modified in order to take into account the difference between elastic moduli of austenite and martensite and to introduce the isothermal approximation proposed in [1]. The second model has been developed by Auricchio et al. within the theory of irreversible thermodynamics with internal variables [2]. Both models are temperature and strain rate dependent and they take into account thermal effects. The focus in this article is on investigating how the two models compare with experimental data obtained from testing superelastic NiTi wires used in the design of a prototypal anti-seismic device [3, 4]. After model calibration and numerical implementation, numerical simulations based on the two models are compared with data obtained from uniaxial tensile tests performed at two different temperatures and various strain rates.

A Shape Memory Alloy-Based Morphing Axial Fan Blade—Part I: Blade Structure Design and Functional Characterization

The possibility to realize adaptive structures is of great interest in turbomachinery design, owing to the benefits related to enhanced performance and efficiency. To accomplish this, a challenging approach is the employment of Shape Memory Alloys (SMAs), which can recover seemingly permanent strains by solid phase transformations whereby the so-called Shape Memory Effect (SME) takes place.This paper presents the development of a heavy-duty automotive cooling axial fan with morphing blades activated by SMA strips that works as actuator elements in the polymeric blade structure. Concerning the fan performance, this new concept differs from a conventional viscous fan clutch solution especially during the non-stationary operating condition. The blade design was performed in order to achieve the thermal activation of the strips by means of air stream flow. Two polymeric matrices were chosen to be tested in conjunction with a commercially available NiTi binary alloy, whose phase transformation temperatures were experimentally evaluated by imposing the actual operating thermal gradient.The SMA strips were then thermo-mechanically treated to memorize a bent shape and embedded in the polymeric blade. In a specifically designed wind tunnel, the different polymeric matrices equipped with the SMA strips were tested to assess the fluid temperature and surface pattern behavior of the blade. Upon heating they tend to recover the memorized shape and the blade is forced to bend, leading to a camber variation and a trailing edge displacement. The recovery behavior of each composite structure (polymeric matrix with SMA strips) was evaluated through digital image analysis techniques. The differences between the blade shape at the initial condition and at the maximum bending deformation were considered.According to these results, the best coupling of SMA strips and polymeric structure is assessed and its time-wise behavior is compared to the traditional time-wise behavior of a viscous fan clutch.Copyright

A Shape Memory Alloy-Based Morphing Axial Fan Blade—Part II: Blade Shape and Computational Fluid Dynamics Analyses

The ability of a morphing blade to change its geometry according to the different operating conditions represents a challenging approach for the optimization of turbomachinery performance. In this paper, experimental and computational fluid dynamics (CFD) numerical analyses on a morphing blade for a heavy-duty automotive cooling axial fan are proposed. Starting from the experimental results proposed in the first part of this work, a morphing blade, made of shape memory alloy (SMA) strips embedded in a polymeric structure, was thoroughly tested. In order to assess the ability of the strips to reach a progressive and smooth shape changing evolution, several experiments were performed in a purpose-built wind tunnel. The morphing blade changed its shape as the strips were thermally activated by means of air stream flow. The bending deformation evolution with the increasing number of thermal cycles was evaluated by digital image analysis techniques. After the analyses in the wind tunnel, CFD numerical simulations of a partially shrouded fan composed of five morphing blades were performed in order to highlight the evolution of the fan performance according to air temperature conditions. In particular, the capability of the blade activation was evaluated by the comparison between the fan performance with nonactivated blades and with activated blades. The results show a progressive stabilization of the shape memory behavior after the first cycle. The blade deformation led to a significant improvement in the fan performance at a constant rotational velocity. The CFD numerical simulation points out the differences in the overall performance and of three-dimensional fluid dynamic behavior of the fan. This innovative concept is aimed at realizing a sensorless smart fan control, permitting (i) an energy saving that leads to fuel saving in the automotive application fields and (ii) an increase in engine life, thanks to a strong relationship between the engine thermal request and the cooling fan performance.

A Shape Memory Alloy-Based Morphing Axial Fan Blade: Part II — Blade Shape and CFD Analyses

The ability of a morphing blade to change its geometry according to the different operating conditions represents a challenging approach for the optimization of turbomachinery performance. In this paper experimental and CFD numerical analyses on a morphing blade for a heavy-duty automotive cooling axial fan are proposed.Starting from the experimental results proposed in the first part of this work, a morphing blade, made of Shape Memory Alloy (SMA) strips embedded in a polymeric structure, was thoroughly tested. In order to assess the ability of the strips to reach a progressive and smooth shape changing evolution, several experiments were performed in a purpose-built wind tunnel. The morphing blade changed its shape as the strips were thermally activated by means of air stream flow. The bending deformation evolution with the increasing number of thermal cycles was evaluated by digital image analysis techniques.After the analyses in the wind tunnel CFD numerical simulations of a partially shrouded fan composed of five morphing blades were performed in order to highlight the evolution of the fan performance according to air temperature conditions. In particular, the capability of the blade activation was evaluated by the comparison between the fan performance with non-activated blades and with activated blades.The results show a progressive stabilization of the shape memory behavior after the first cycle. The blade deformation led to a significant improvement in fan performance at a constant rotational velocity. The CFD numerical simulation points out the differences in the overall performance and of three-dimensional fluid dynamic behavior of the fan.This innovative concept is aimed at realizing a sensorless smart fan control, permitting (i) an energy saving that leads to fuel saving in the automotive application fields and (ii) an increase in engine life thanks to a strong relationship between the engine thermal request and the cooling fan performance.© 2015 ASME

A shape memory alloy-based morphing axial fan blade, part I: Blade structure design and functional characterization

The possibility to realize adaptive structures is of great interest in turbomachinery design, owing to the benefits related to enhanced performance and efficiency. To accomplish this, a challenging approach is the employment of Shape Memory Alloys (SMAs), which can recover seemingly permanent strains by solid phase transformations whereby the so-called Shape Memory Effect (SME) takes place.This paper presents the development of a heavy-duty automotive cooling axial fan with morphing blades activated by SMA strips that works as actuator elements in the polymeric blade structure. Concerning the fan performance, this new concept differs from a conventional viscous fan clutch solution especially during the non-stationary operating condition. The blade design was performed in order to achieve the thermal activation of the strips by means of air stream flow. Two polymeric matrices were chosen to be tested in conjunction with a commercially available NiTi binary alloy, whose phase transformation temperatures were experimentally evaluated by imposing the actual operating thermal gradient.The SMA strips were then thermo-mechanically treated to memorize a bent shape and embedded in the polymeric blade. In a specifically designed wind tunnel, the different polymeric matrices equipped with the SMA strips were tested to assess the fluid temperature and surface pattern behavior of the blade. Upon heating they tend to recover the memorized shape and the blade is forced to bend, leading to a camber variation and a trailing edge displacement. The recovery behavior of each composite structure (polymeric matrix with SMA strips) was evaluated through digital image analysis techniques. The differences between the blade shape at the initial condition and at the maximum bending deformation were considered.According to these results, the best coupling of SMA strips and polymeric structure is assessed and its time-wise behavior is compared to the traditional time-wise behavior of a viscous fan clutch.Copyright

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.

Effect of the Addition of Nickel Powder and Post Weld Heat Treatment on the Metallurgical and Mechanical Properties of the Welded UNS S32304 Duplex Stainless Steel

No presente estudo, foi investigado o efeito da adicao de po de niquel e a aplicacao de um tratamento termico pos-soldagem (PWHT) nas propriedades de soldagem do aco inoxidavel lean duplex UNS S32304, a fim de melhorar a microestrutura e as propriedades mecânicas. Po de niquel foi diretamente vertido na abertura da junta e misturado com o metal de adicao durante o processo de soldagem a arco com eletrodo de tungstenio e protecao gasosa (GTAW). Alem disso, o tratamento termico foi estabelecido em 1100 °C por 10 min. As juntas foram caracterizadas por microscopia optica (MO) e a evolucao das percentagens de fase nas diferentes zonas foi estudada por meio da tecnica de analise de imagem. Os ensaios de tracao e de microdureza foram realizados, a fim de avaliar a melhoria das propriedades mecânicas das juntas. Os resultados mostraram que tanto a adicao de po de niquel durante o processo de soldagem e o tratamento termico pos-soldagem permitiram melhorar as propriedades mecânicas da junta soldada. PWHT mostrou o melhor efeito em restaurar a percentagem igual de ferrita e austenita comparado com a adicao de po de niquel.

Correlation between Aging Effects and High Temperature Mechanical Properties of the Unmodified A356 Foundry Aluminium Alloy

In this study, the effect of aging on the mechanical properties of unmodified A356 aluminium casting alloy with trace additions of Ni or V was investigated. Trace elements were added in concentrations of 600 and 1000 ppm of Ni and V, respectively. Samples from sand and permanent mould castings in as cast and T6 heat-treated conditions were tested. Tensile tests were performed at both room and high temperature (235 °C). Taking into account the results from both testing conditions, Vickers hardness was measured in order to endorse the hypothesis of artificial aging occurring during high temperature tensile tests. In order to study this effect, a series of specimens was aged at 235 °C for different aging times, and aging curves were plotted. The occurrence of static and dynamic aging was evaluated by comparing hardness values of tensile specimens and aged samples, particularly in the range of 5-20 min, as this range corresponds to the time necessary for pre-heating and testing of the tensile samples. A basic correlation between tensile strength and hardness is also given.

Using shape memory alloys for improving automotive fan blade performance: experimental and computational fluid dynamics analysis

In recent years, a considerable effort has been devoted towards the application of advanced techniques for turbomachinery efficient fluid dynamic control during operations. A novel strategy to dynamically modify and optimize the performance during operations takes advantage of shape memory alloys properties. Experimental and numerical analyses on a morphing polymeric blade for an automotive axial fan are presented. The blade shape change was achieved by shape memory alloys strips, thermomechanically treated, embedded in the blade and thermally activated by hot air stream flow. Measurement of fluid temperature, blade surface temperature pattern and three-dimensional shape change of the blade during activation was performed by means of an innovative image analysis technique in a purpose-built wind tunnel. Computational fluid dynamics numerical simulations were performed to study performance variations and three-dimensional fluid dynamic behavior of the fan originated from the shape memory effect.