RESUMEN
The issue of large deflections of textiles occurs primarily when analyzing the "drape" of curtains, tablecloths and other flat textile products. The correct drape is particularly important from an aesthetic point of view. Additionally, there is a problem with the stability of the folds created during the drape process. The analysis of this problem is difficult due to the occurrence of large deflections and non-linear properties of the material. In this article, a selected fragment of the above-mentioned issue was tested, relating only to the stability of the fold formed under given loading conditions. A typical example is a fabric resting on a flat surface and loaded with compressive forces. The presented considerations lead to obtaining the deflection curve for a given self-weight and compressive force. Additionally, the obtained shape was tested for stability. Two shape parameters used in the analysis can be applied for the simulation of different shapes of the deflection curve. The analysis has been made using the energy method relating to the total potential energy of the object. The obtained results may be used in algorithms and simulation programs for fabric folding, buckling and for another applications in the area of textile mechanics.
RESUMEN
Parallel kinematic machines have been applied in aerospace and automotive manufacturing due to their potentials in high speed and high accuracy. However, there exists coupling in parallel kinematic machines, which makes dynamic analysis, rigidity enhancement, and control very complicated. In this article, coupling characteristics of a 5-degree-of-freedom (5-dof) hybrid manipulator are analyzed based on a local index and a global index. First, velocity analysis as well as acceleration analysis of the robot is conducted to provide essential information for dynamic modeling. Then the dynamic model is built based on the principle of virtual work. Whereas the mass matrix is off-diagonal, a local coupling index as well as a global index is defined, based on which coupling characteristics of the robot are analyzed. Results show that distributions of coupling indices are symmetric due to its structural features. And dimensional parameters, structural parameters, as well as mass parameters have a large influence on the system's coupling characteristics. Research conducted in the article is of great help in optimal design and control. Meanwhile, the method proposed in the article can be applied to other types of parallel kinematic machines or hybrid manipulators.
RESUMEN
The study of the knee natural motion, namely the unresisted motion that the knee exhibits in the absence of external loads, provides insights into the physiology of this articulation. The natural motion represents the baseline condition upon which deformations of its passive structures (i.e., ligaments and cartilage) take place when loads are applied. Moreover, during natural motion, the strain energy density stored within ligaments and cartilage is minimized. This reduces the chance of microdamage occurrences and the corresponding metabolic cost for tissue repairing. The study of the knee natural motion is thus fundamental in understanding the joint physiology. This paper shows that the line of action of resultant forces of all the knee constraints provided by the passive structures must intersect the instantaneous helical axis (IHA) to make the knee natural motion possible. In other words, the lines of action of all these constraints must cross the same line at each flexion angle to guarantee the natural motion of the joint. This geometrical property is first proven theoretically and then verified in four in vitro and one in vivo experiments. The geometrical characterization of the knee natural motion presented in this study provides a fundamental property that must be satisfied to allow the correct joint mobility. The knowledge of this property may thus allow the definition of better models, treatments, and devices.
RESUMEN
In order to found continuum mechanics, two different postulations have been used. The first, introduced by Lagrange and Piola, starts by postulating how the work expended by internal interactions in a body depends on the virtual velocity field and its gradients. Then, by using the divergence theorem, a representation theorem is found for the volume and contact interactions which can be exerted at the boundary of the considered body. This method assumes an a priori notion of internal work, regards stress tensors as dual of virtual displacements and their gradients, deduces the concept of contact interactions and produces their representation in terms of stresses using integration by parts. The second method, conceived by Cauchy and based on the celebrated tetrahedron argument, starts by postulating the type of contact interactions which can be exerted on the boundary of every (suitably) regular part of a body. Then it proceeds by proving the existence of stress tensors from a balance-type postulate. In this paper, we review some relevant literature on the subject, discussing how the two postulations can be reconciled in the case of higher gradient theories. Finally, we underline the importance of the concept of contact surface, edge and wedge s-order forces.
RESUMEN
@#Objective To discussing the methods used in creating non linear developable biomechanical models of skeletal muscle.Methods One of the basic tools of the analytical approach in analytical mechanics, the principle of virtual work for deformable systems, was used to create the model. By means of method of Lagrange multipliers, the problems of constraints, such as the incompressibility of skeletal muscle, were effectively tackled. Results and Conclusion The biomechanical models of skeletal muscle has been developed. The program of this model can be used to obtain nodal displacement coordinates of given nodal coordinates and parameters.