Solving the forward kinematics of parallel manipulators with a genetic algorithm

A floating point genetic algorithm is proposed to solve the forward kinematic problem for parallel manipulators. This method, adapted from studies in the biological sciences, allows the use of inverse kinematic solutions to solve forward kinematics as an optimization problem. The method is applied to two 3-degree-of-freedom planar parallel manipulators and to a 3-degree-of-freedom spherical manipulator. The method converges to a solution within a broader search domain compared to a Newton-Raphson scheme. © 1996 John Wiley & Sons, Inc.     

Load Transfer and Recovery Length in Parallel Wires of Suspension Bridge Cables

A new simplified contact model aimed at capturing the load transfer and recovery length in parallel steel wires, commonly used in main cables of suspension bridges, is presented. The approach is based on placing elastic–perfectly plastic spring elements at the contact region between the objects. These springs have varying stiffness (Model?I) or yielding (Model?II) depending on their proximity to the clamping loads. Their stiffness or yielding is highest when they are closer to this force, and it decays when they are farther away from the clamp. This decayed behavior is assigned according to Boussinesq’s well-known solution to a point load (applied on a half space). Both models converge quickly compared with a full contact model and recover Coulomb friction law on a two-dimensional (2D) benchmark problem. Moreover, when the same properties are chosen for all springs (disregarding Boussinesq solutions), the models reduce to the classical shear-lag model, which for high clamping (point) loads gives inaccurate results. The spring models are validated experimentally on a seven-wire tightened strand. In this case study, the outer wires are axially pulled, whereas the middle wire, slightly shorter than the outer wires, experiences no direct applied axial load. However, because the strand is radially fastened at several locations, the axial load is transferred to the inner wire by an interfriction mechanism between the wires. The strains at the center points of the outer and inner wires are measured via neutron diffraction for different clamping loads, showing that the inner wire is capable of recovering most of the load.     

Deformation inhomogeneity and representative volume in Pb/Sn solder alloys

To verify whether the deformation of the bulk test specimens represents that of small solder joints, we have used the concept of “representative volume.” The representative volume is defined as the smallest volume which represents the average inelastic and inhomogeneous deformation of the entire body. We have performed the first set of experiments to determine this representative volume by measuring the microscopic deformations of a large Pb/Sn eutectic alloy specimen as a function of applied strain. The results show that the representative volume of the specimen is very large compared to the size of the solder joints. Formerly with IBM T.J. Watson Research Center, Yorktown Heights, NY 10598     

Some approach to possible atmospheric impacts of a hydrogen energy system in the light of the geological past and present-day

Hydrogen has a considerable potential for becoming a major factor in speeding the transition of our carbon-based global energy economy ultimately to a clean, renewable and sustainable economy. The development of hydrogen production, transportation-storage and utilization technologies can play a central role in addressing growing concerns over carbon emissions and climate change, as well as the future availability and security of energy supply. However the widespread use of hydrogen may have unknown environmental effect due to increased anthropogenic emissions of molecular hydrogen and other gases to the atmosphere, through production, transportation-storage and utilization processes. It is recognized that hydrogen participates in stratospheric chemical cycles of H₂O and various greenhouse gases, and a substantial increase in its concentration might lead to changes in equilibrium concentration of constituent components of the stratosphere. More accurate modeling of the stratospheric processes as well as better understanding of several other factors such as hydrogen uptake in soil and its effect on microbial communities is required to assess potential adverse effects of hydrogen economy. It is critical for us to understand the potential adverse effect of widespread use of hydrogen and take necessary actions to understand and prevent its possible environmental impacts.     

Effect of gradients in multi-axial stress states on residual stress measurements with x-rays

The assumption, that stress components in the direction of the surface normal are negligible in traditional residual stress determination methods by X-rays, has been recently disproved. In this paper we investigate the effect of normal stresses on the accuracy of these traditional methods. It is shown that appreciable error can exist in surface stresses determined by such methods, if normal stresses are present. New procedures are proposed to minimize these errors.     

Equilibrium conditions for the average stresses measured by X-rays

True macro-stresses are measured with X-rays after material processing, only if there is auniform plastic deformation in the sampled volume that is different from that in the rest of the material. In this stress-field the components in the direction of the surface normal are usually negligible over the depth penetrated by X-rays (for example, peening). However, pseudo-macrostresses, or backstresses, arise when this condition is violated, for example, if there are second phase particles and there is a gradient of plastic deformation from particle to matrix. This pseudo-macrostress field is three-dimensional, and the stresses in the direction of the surface normal can be measured with X-rays. Equations are presented which allow estimates to be made of the magnitudes of the two kinds of stress fields.     

X-ray determination of encapsulation stresses on silicon wafers

Preliminary results of a systematic investigation of the behavior of encapsulating materials used in electronic packaging are reported. In this study, the radii of curvature of silicon wafers encapsulated with a filled epoxy are obtained by X-ray diffraction. The values recorded agree closely with Dektak scanning for thin coatings. However, deviations occur with thicker layers due to the fundamental difference in the parameter measured by both techniques. Analytical solutions are proposed for both one-and two-sided encapsulation. Results predicted for the one-sided coating describe a more severe state of stress within the package, and a correspondingly higher curvature than observed. X-ray radiographs and optical micrographs of molded packages reveal the presence of internal voids and surface cracks. Such defects relax the stresses within the composite system and may account for the discrepancy observed.