1,721,041 research outputs found
Modelling of Magnetorheological Fluids for Blank Holder Control in Stamping
No full textGiven the increasing demand for precision and geometrical accuracy in sheet metal forming processes, the control of process parameters guarantees product soundness and the meeting of dimensional and geometrical specifications, avoiding defects such as wrinkles and tears. In recent years, the development of control and actuation systems for stamping processes have been concerned mainly with the blank holder (BH), the device that regulates the flow of material by holding the sheet flange during forming. The choice of BH actuation type depends on process characteristics (e.g. available space, required load, available working stroke, etc.), and its implementation often results from a trade-off between process requirements and actuator characteristics. Indeed, conventional BH actuators suffer from intrinsic limited re-configurability in the case of small batch production or drift in process parameters.
In this context, Magneto-Rheological (MR) fluids represent one of the most versatile and promising solutions for the development of rapidly configurable and controllable closed loop systems. Technologies based on MR fluids have been applied mainly in automotive and civil anti-seismic systems, although recent research has shown promising applications in vibrations damping systems for metal cutting and blanking.
The main objective of this work is to apply innovative MR fluid-based devices to BH control in sheet metal forming processes, with the aim of exploiting the advantages of these materials and overcoming the limitations of conventional actuators.
A new semi-active actuator for BH control is designed and considered as a reference case for the investigation of MR fluid behaviour. A new approach is introduced, based on numerical modelling in a multi-physics environment, with the definition of a viscosity model able to describe MR fluid behaviour.
Open-loop and closed-loop algorithms are designed to control MR fluid behaviour, with the aim of fine-tuning the actuator load in respect of process measurements. The numerical model and algorithms are then experimentally tested and validated.
Building on these bases, the application of MR fluids and evaluation of relative performance is extended to an experimental test, which reproduces the deep drawing process. In this scenario, the whole system, composed of the MR fluid actuator and the control algorithms, is implemented to control the BH, demonstrating good capabilities in controlling metal flow and improving the geometrical accuracy of the stamped parts.Given the increasing demand for precision and geometrical accuracy in sheet metal forming processes, the control of process parameters guarantees product soundness and the meeting of dimensional and geometrical specifications, avoiding defects such as wrinkles and tears. In recent years, the development of control and actuation systems for stamping processes have been concerned mainly with the blank holder (BH), the device that regulates the flow of material by holding the sheet flange during forming. The choice of BH actuation type depends on process characteristics (e.g. available space, required load, available working stroke, etc.), and its implementation often results from a trade-off between process requirements and actuator characteristics. Indeed, conventional BH actuators suffer from intrinsic limited re-configurability in the case of small batch production or drift in process parameters.
In this context, Magneto-Rheological (MR) fluids represent one of the most versatile and promising solutions for the development of rapidly configurable and controllable closed loop systems. Technologies based on MR fluids have been applied mainly in automotive and civil anti-seismic systems, although recent research has shown promising applications in vibrations damping systems for metal cutting and blanking.
The main objective of this work is to apply innovative MR fluid-based devices to BH control in sheet metal forming processes, with the aim of exploiting the advantages of these materials and overcoming the limitations of conventional actuators.
A new semi-active actuator for BH control is designed and considered as a reference case for the investigation of MR fluid behaviour. A new approach is introduced, based on numerical modelling in a multi-physics environment, with the definition of a viscosity model able to describe MR fluid behaviour.
Open-loop and closed-loop algorithms are designed to control MR fluid behaviour, with the aim of fine-tuning the actuator load in respect of process measurements. The numerical model and algorithms are then experimentally tested and validated.
Building on these bases, the application of MR fluids and evaluation of relative performance is extended to an experimental test, which reproduces the deep drawing process. In this scenario, the whole system, composed of the MR fluid actuator and the control algorithms, is implemented to control the BH, demonstrating good capabilities in controlling metal flow and improving the geometrical accuracy of the stamped parts
Bloch–Floquet waves in flexural systems with continuous and discrete elements
No full textIn this paper we describe the dynamic behavior of elongated multi-structured media excited by flexural harmonic waves. We examine periodic structures consisting of continuous beams and discrete resonators disposed in various arrangements. The transfer matrix approach and Bloch–Floquet conditions are implemented for the determination of different propagation and non-propagation regimes. The effects of the disposition of the elements in the unit cell and of the contrast in the physical properties of the different phases have been analyzed in detail, using representations in different spaces and selecting a proper set of non-dimensional parameters that fully characterize the structure. Coupling in series and in parallel continuous beam elements and discrete resonators, we have proposed a class of micro-structured mechanical systems capable to control wave propagation within elastic structures
Computational Analytical Micromechanics: Linear Elastic FEA of random structure composites reinforced by heterogeneities of non canonical shape
No full textAuxetic two-dimensional lattices with Poisson’s ratio arbitrarily close to -1
No full textIn this paper, we propose a class of lattice structures with macroscopic Poisson's ratio arbitrarily close to the stability limit −1. We tested experimentally the effective Poisson's ratio of the microstructured medium; the uniaxial test was performed on a thermoplastic lattice produced with a three-dimensional printing technology. A theoretical analysis of the effective properties was performed, and the expression of the macroscopic constitutive properties is given in full analytical form as a function of the constitutive properties of the elements of the lattice and on the geometry of the microstructure. The analysis was performed on three microgeometries leading to an isotropic behaviour for the cases of three- and sixfold symmetries and to a cubic behaviour for the case of fourfold symmetry
A class of auxetic three-dimensional lattices
No full textWe propose a class of auxetic three-dimensional lattice structures. The elastic microstructure can be designed to have an omnidirectional Poisson's ratio arbitrarily close to the stability limit of -1. The cubic behaviour of the periodic system has been fully characterized; the minimum and maximum Poisson's ratio and the associated principal directions are given as a function of the microstructural parameters. The initial microstructure is then modified into a body-centred cubic system that can achieve Poisson's ratio lower than -1 and that can also behave as an isotropic three-dimensional auxetic structure
Thermoelastic effective properties and stress concentrator factors of composites reinforced by heterogeneities of noncanonical shape
No full textWe consider a linearly thermoelastic composite medium, which consists of a homogeneous matrix containing a statistically inhomogeneous random set of heterogeneities of arbitrary shape. The general integral equations connecting the stress and strain fields in the point being considered with the stress and strain fields in the surrounding points are obtained for the random fields of heterogeneities. The method is based on a recently developed centering procedure (Buryachenko 2010a) where the notion of perturbator is introduced and statistical averages are obtained without any auxiliary assumptions such as, e.g., effective field hypothesis implicitly exploited in the known centering methods. Effective properties (such as compliance and thermal expansion) as well as the first statistical moments of stresses in the phases are estimated for statistically homogeneous composites with the general case of both the shape and inhomogeneity of the thermoelastic heterogeneities properties. The explicit new representations of the effective thermoelastic properties and stress concentration factor are expressed through some building blocks described by numerical solutions for one heterogeneity inside the infinite medium subjected to the homogeneous remote loading. Numerical results are obtained for some model statistically homogeneous composites reinforced by aligned identical homogeneous heterogeneities of noncanonical shape. Some new effects are detected that are impossible in the framework of a classical background of micromechanics
Driving forces in moving-contact problems of dynamic elasticity: indentation, wedging and free sliding
No full textThe steady-state solution for an elastic half-plane under a moving frictionless smooth indenter of arbitrary shape is derived based on the corresponding transient problem and on a condition concerning energy fluxes. The resulting stresses and displacements are found explicitly starting from their expressions in terms of a single analytical function. This solution incorporates all speed ranges, including the super-Rayleigh subsonic and intersonic speed regimes, which received no final description to date. Next, under similar formulation the wedging of an elastic plane is considered for a finite wedge moving at a distance of the crack tip. Finally, we solve the problem for such a wedge moving along the interface of two elastic half-planes compressed together. Considering these problems we determine the driving forces caused by the main underlying factors: stress field singular points on the contact area (the super-Rayleigh subsonic speed regime), the wave radiation (intersonic and supersonic regimes) and the fracture resistance (the wedging problem). It was found that in addition to the sub-Rayleigh speed regime, where a the contact sliding itself gives no contribution to the driving forces, there exists a sharp decrease in the resistance in a vicinity of the longitudinal wave speed with zero limit at this speed
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