75 research outputs found
Value of the computertomographic findings in predicting the histological malignancy of cerebral gliomas.
No full textShape Memory Alloys Applied to Automotive Adaptive Aerodynamics
No full textShape memory alloys (SMAs) are gaining popularity in the fields of automotive and aerospace engineering due to their unique thermomechanical properties. This paper proposes a numerical implementation of a comprehensive constitutive model for simulating the thermomechanical behavior of shape memory alloys, with temperature and strain as control variables to adjust the shape memory effect and super elasticity effect of the material. By implementing this model as a user subroutine in the FE code Abaqus/Standard, it becomes possible to account for variations in material properties in complex components made of shape memory alloys. To demonstrate the potential of the proposed model, a skid plate system design is presented. The system uses bistable actuators with shape memory alloy springs to trigger plate movement. The kinematics and dynamics of the system are simulated, and effective loads are generated by the shape memory alloy state change due to the real temperature distribution in the material, which depends on the springs’ geometrical parameters. Finally, the performance of the actuator in switching between different configurations and maintaining stability in a specific configuration is assessed. The study highlights the promising potential of shape memory alloys in engineering applications and demonstrates the ability to use them in complex systems with accurate simulations
Advanced Material Thermomechanical Modelling of Shape Memory Alloys Applied to Automotive Design
No full textThis study introduces an innovative approach to enhancing aerodynamic efficiency in automotive applications by exploiting shape memory alloy technology. To this end, a thorough investigation of the thermomechanical behaviour of these alloys was conducted in the paper. Using a UMAT subroutine, the pseudoelastic effect and the shape memory effect of these smart materials were analysed numerically simultaneously, allowing accurate predictions of their behaviour under different loads, and facilitating the design and optimization of devices and systems based on SMAs. Therefore, the article proposes an innovative solution to optimize aerodynamic efficiency by using a Grille Shutter with variable openings. The Active Grille Shutter uses a bistable SMA actuator, allowing two optimal opening positions for specific load conditions. These actuators hold two stable states without energy consumption, ensuring efficient and reliable operation and allowing rapid transitions between the two states, making them ideal for applications that require timely responses. By using this specially designed and numerically analysed system, it has been confirmed that suitably dimensioned shape memory springs can guarantee a movement of the blades of the 90°, allowing an improvement in vehicle efficiency of about 4% at a speed of 140 km/h
Precast Segments with Sulphoaluminate Cement and GFRP Reinforcement
No full textDuring tunnel excavation by means of a tunnel boring machine (TBM), the lining consists of precast structural elements, placed by the TBM during the excavation process and used as support elements during the advancing phase. The use of concrete based on sulphoaluminate binders allows the production of the elements to be speeded up, a reduction in the number of segments stacked waiting for the required strengths to be achieved and provides a more eco-sustainable process avoiding the use of steam curing. In order to verify the feasibility of the proposed solution, two full-scale tests (bending test and TBM jacks thrust test) on metro tunnel precast segments were carried out. The internal reinforcement consisted of a next-gen Glass Fibre Reinforced Polymer (GFRP) cage. The use of GFRP reinforcement, to replace traditional steel, in tunnel segments provides several advantages mainly related to durability aspects or when the use of a provisional lining is foreseen
Endovascular treatment of vertebro-vertebral arteriovenous fistula. A report of three cases and literature review
No full textThis report describes endovascular approaches for occlusion of vertebro-vertebral arteriovenous fistula (VV-AVF) in a series of three cases and a review of the literature. Complete neuroimaging assessment, including CT, MR and DSA was performed in three patients (two female, one male) with VV-AVF. Based on DSA findings, the VV-AVF were occluded by endovascular positioning of detachable balloons (case 1), coils (case 2), or a combination of both (case 3) with parent artery patency in two out of three cases. In this small series, endovascular techniques for occlusion of VV-AVF were safe and effective methods of treatment. To date, there are no guidelines on the best treatment for VV-AVF. Detachable balloons, endovascular coiling, combined embolization procedures could all be considered well-tolerated treatments
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