Predicting planar motion behavior under contact uncertainty

Performing complex assembly tasks with robots requires fine-motion planners able to cope with uncertainty and contact motions, and this is a recognized difficult issue. This paper proposes a method to predict the behavior of motions under contact uncertainty in order to check the feasibility of paths generated by gross-motion planning algorithms from a nominal model of the environment. This pragmatical approach enables the extension of gross-motion planning techniques to constrained-motion planning problems, ensuring the feasibility of the task despite the uncertainties. The approach has been implemented for assembly tasks in the plane with three degrees of freedom.     

Structural integrity and petrochemical industry

Abstract

The importance of engineering structural integrity in the petrochemical industry, which has broader implications for energy applications, is discussed in the context of the history of many serious accidents that have taken place in refineries, storage facilities and processing plants in recent years. A number of critical incidents from around the world are reviewed, and several cases investigated in North America are cited. These demonstrate the important role of well conducted regular inspections, based on sound advanced planning, in maintaining in service assessment of fitness for purpose of plant. The significant contribution of risk based inspection procedures, together with the need for a sound knowledge of potential degradation mechanisms, is emphasised. Finally, it is noted that there is a need for a safety conscious organisational culture underpinned by robust, relevant and continued training and development, for the entire workforce including management and supervisory staff.     

Thermal analysis applied to estimation of solidification kinetics of Al–Si aluminium alloys

Abstract

Evaluation of solidification kinetics by thermal analysis is a useful tool for quality control of Al–Si melts before pouring provided it is rapid and highly reproducible. Series of thermal analysis records made with standard cups are presented that show good reproducibility. They are evaluated using a Newton's like approach to get the instantaneous heat evolution and from it solidification kinetics. An alternative way of calculating the zero line is proposed which is validated by the fact that the latent heat of solidification thus evaluated is within 5% of the value calculated from thermodynamic data. Solidification kinetics was found highly reproducible provided appropriate experimental conditions were achieved: high enough casting temperature for the cup to heat up to the metal temperature well before solidification starts; and equal and homogeneous temperatures of the metal and of the cup at any time in the temperature range used for integration.     

In situ observation of phase selection in undercooled Ni–Al melts

Abstract

Raney-Ni type Ni–68·5 at-% Al alloys are used for catalytic applications in the chemical industry. In this work, melt undercooling experiments were performed by means of the electromagnetic levitation technique. High-energy X-ray diffraction was used to determine the solidification pathway and the origin of microstructure peculiarities in gas atomised powders. The direct observation of the phase selection in Ni–68·5 at-% Al has unambiguously revealed the primary phase formation of β-AlNi to be independent of the level of undercooling up to a maximum of 320 K. On cooling the β-AlNi phase undergoes a fast peritectic transformation L + AlNi → Al₃Ni₂ and is therefore not found in the as-solidified microstructure.     

Strength Improvement of Adhesively-Bonded Joints Using a Reverse-Bent Geometry

Adhesive bonding of components has become more efficient in recent years due to the developments in adhesive technology, which has resulted in higher peel and shear strengths, and also in allowable ductility up to failure. As a result, fastening and riveting methods are being progressively replaced by adhesive bonding, allowing a big step towards stronger and lighter unions. However, single-lap bonded joints still generate substantial peel and shear stress concentrations at the overlap edges that can be harmful to the structure, especially when using brittle adhesives that do not allow plasticization in these regions. In this work, a numerical and experimental study is performed to evaluate the feasibility of bending the adherends at the ends of the overlap for the strength improvement of single-lap aluminium joints bonded with a brittle and a ductile adhesive. Different combinations of joint eccentricity were tested, including absence of eccentricity, allowing the optimization of the joint. A Finite Element stress and failure analysis in ABAQUS^® was also carried out to provide a better understanding of the bent configuration. Results showed a major advantage of using the proposed modification for the brittle adhesive, but the joints with the ductile adhesive were not much affected by the bending technique.     

Stability analysis and robust control for fixed-scale teleoperation

In this article we present a new theorem that reduces the stability problem of teleoperators from a structured singular value problem to a maximum singular value problem. A control scheme realizing an ideal response for fixed-scale teleoperation is proposed and its stability is proven analytically. Next, the ideal control scheme is extended to control schemes with a higher stability robustness. Also, for these more complicated schemes, stability analyses are performed making use of the new theorem and stability conditions are derived. Experiments on a 1-d.o.f. setup are conducted to confirm the validity of the proposed control schemes.     

Investigation into deoxidation during vacuum induction melting refining of nickel base superalloy using CaO crucible

Abstract

The influence of carbon and aluminium on deoxidation during vacuum induction melting (VIM) of a Ni-6Cr-2Mo-6W-5Co alloy using a CaO crucible has been studied. It has been found that carbon plays a dominant role in deoxidation during the melting stage, and about 50-70% of the initial oxygen can be removed. Thermodynamics calculations show that the C-O reaction is far from the equilibrium state, and experimental results for carbon and oxygen contents in the liquid alloy correspond with those when the CO partial pressure p _CO is 10³-10² Pa. Aluminium addition can further reduce the oxygen content to below 6 ppm. Thermodynamics calculations for the C-Al, Al-CaO and C-Al₂O₃ reactions demonstrate that they can all take place during the melting process. These reactions bring about reductions in the amounts of carbon and aluminium, respectively, of about 1.3-3.5 times and 20-50 times those required for deoxidation only.     

Stress analysis and strength estimation of butt adhesive joints of dissimilar hollow cylinders under impact tensile loadings

The stress variations in butt adhesive joints of dissimilar hollow cylinders subjected to impact tensile loadings are analyzed in elastic and elasto-plastic deformation ranges using a finite element method (FEM). The FEM code name employed is DYNA3D. The effects of Young's modulus ratio between dissimilar adherends and the adhesive thickness on the stress variations at the interfaces are examined. In addition, the process of rupture at the interfaces of the joint is simulated. The stress distributions in the joints under static loadings are also analyzed by FEM. The characteristics of the stress variations in the joints under impact loadings are compared with those in the joints under static loadings. Also, the joint strengths under impact loadings are estimated by elasto-plastic FEM. It is found that the maximum value of the maximum principal stress σ ₁ occurs at the outside edge of the lower interface. It is also found that the maximum principal stress σ ₁ at the lower interface decreases as the adhesive thickness increases. The characteristics of the joints under impact loadings are found to be opposite to those under static loadings. Furthermore, differences in the characteristics of the stress variations are shown between the dissimilar joints and the similar joints. In addition, the experiments were carried out to measure the strain response and strains in the butt adhesive joints under both impact and static loadings using strain gauges. Furthermore, joint strengths under both impact and static loadings were measured. Fairly good agreements are observed between the numerical and the measured results.     

Noise deconvolution for area fraction measurements

Abstract

A novel approach to area fraction measurement is developed to deal with the limitations of the segmentation method. The new approach takes advantage of the statistical nature of the noise within an image to deconvolute the image histogram and calculate, by means of fitting, the area fractions. Both segmentation and noise deconvolution approaches are critically discussed, and their limitations and advantages tested using two extreme backscattered electron images of a metal matrix composite. The deconvolution approach is shown to produce accurate results in a situation in which the segmentation approach fails.