Processing and damping behaviour of porous copper

Abstract

The well distributed open cellular porous copper was fabricated by present powder metallurgy technique based on space holder method, Depending on the volume fraction and size of the space holding particle, the porosity can be varied in the wide range of 30–85% and pore size from micron to millimetre in magnitude of order respectively. The damping behaviour and related relative dynamic modulus of the porous copper were investigated by a multifunction internal friction apparatus as a function of temperature from room temperature to 600°C. The results of investigation disclose that the porous copper can obtain a higher damping capacity than that of bulk one. In addition to this, an internal friction peak was found in the spectra of internal friction against temperature for the porous copper, it was proposed that the viscous sliding of the grain boundaries should be responsible for the appearance of the peak, and the dependence of the peak on porosity can be understood in terms of the anelastic relaxation mode of grain boundary.     

Synthesis and properties of polyester-based TPUs prepared by solution polymerisation

Abstract

The polyester based thermoplastic polyurethane elastomers (TPUs) were prepared by one-step solution polymerisation to obtain a product with completely linear molecular structure and with excellent solubility. The synthesis technique was determined by investigation of the influence of solvent and catalyst on the viscosity of the reaction system and the mechanical properties of the resulting product. The effects of the molecular structure on the mechanical, damping and crystallisation properties of TPUs were studied in terms of the type of diisocyanate, mass fraction of hard segment, type and molecular weight of soft segment, and type of chain extender. The structure and morphology of TPUs were characterised by FTIR, GPC and AFM analysis. There was microphase separation in the molecules of TPU, in which the hard-segment phase was dispersed in the soft-segment phase.     

Damping characteristics of machine structures assembled by bonding: a beam in which two steel strips are partially joined by an adhesive

Machine structures assembled by adhesive bonding are expected to possess a high damping capacity because of the high damping capacity of the adhesive. In this study, the damping characteristics of a beam in which two steel strips were partially joined by an adhesive have been investigated. The primary aim of this study was to clarify the damping characteristics of adhesively bonded structures and to establish an estimation method for the damping capacity. In the analysis, strain energy distributions in the adhesively bonded beam in motion are analyzed by the finite element method. Then the damping capacity of the beam is derived using the strain energies and damping ratios of the two materials, i.e. the steel strips and the adhesive, which were obtained beforehand in independent experiments. The validity of the proposed estimation method for the damping capacity and the effects of the thickness of the adhesive and vibration modes on the damping capacity were confirmed by experiments. Satisfactory agreement was shown by comparing the estimated values of the damping capacity of the beam with the experimental results. Furthermore, the temperature dependence of the damping capacity was examined.     

A globally stable state feedback controller for flexible joint robots

The paper addresses the problem of controlling the joints of a flexible joint robot with a state feedback controller and proposes a gradual way of extending such a controller towards the complete decoupling of the robot dynamics. The global asymptotic stability for the state feedback controller with gravity compensation is proven, followed by some theoretical remarks on its passivity properties. By proper parameterization, the proposed controller structure can implement a position, a stiffness or a torque controller. Experimental results on the DLR lightweight robots validate the method.     

Mechanism of post-weld heat treatment cracking in Rene 80 nickel based superalloy

Abstract

Microstructural studies carried out on Rene 80 (approximate composition 60Ni–14Cr–9.5Co–4Mo–5Ti–3Al–0.17C–Zr–B, wt-%) weldments before and after post-weld heat treatment (PWHT) revealed abundant evidence of constitutionally liquated and resolidified grain boundaries extending from the mushy zone into the heat affected zone (HAZ). While total dissolution of γ' occurred along such grain boundaries, a much lesser degree of γ' dissolution was noted in the adjacent material. During the PWHT, a high density of γ' precipitated out both within the mushy zone and in the constitutionally liquated and resolidified grain boundary regions in the HAZ. As the dissolution and reprecipitation of γ' occurred fairly uniformly throughout the mushy zone, the ensuing aging contraction stress/ strain was fairly uniformly distributed in the region. In contrast, in the adjacent part of the HAZ, an extreme volume of γ' precipitation occurred locally along the grain boundary regions, a result of the highest concentration of γ' forming solutes and the complete dissolution of γ' during welding in these regions. This, combined with the much stronger adjacent grain matrix, caused the aging contraction stress and strain to become highly concentrated along the grain boundary regions in the HAZ. This promoted the formation of PWHT cracks along such grain boundaries, which then propagated along the grain boundary into the mushy zone and beyond.     

Novel technology for improving damping capacity of aluminium foam by interface layer

Abstract

A novel technology of designing interface layer using macromolecule resin element, polystyrene, to enhance the damping capacity of aluminium foam is successfully attempted. The interface layer was fabricated by coating a polystyrene film on the pore surface of the aluminium foam using a similar sol–gel technology. Results of the measurements show that the introduction of interface layer not only improves the mechanical strength, but also significantly enhances the damping capacity that can be an order increase relative to the corresponding aluminium foam matrix in the temperature range of room temperature to 80°C. The involved damping mechanisms include the intrinsic damping and interface damping of the constituents. The latter should be dominant as a result of relatively easy energy dissipation through interfacial friction.