Analytical Solutions for Stress and Displacement Fields in Disks under Arbitrarily Distributed Loads

The general series solution (GSS) approach is presented, in order to determine the stress and displacement fields in disks under arbitrarily distributed normal and tangential loads. An Airy stress function in series form is selected. Stresses are expressed by infinite coefficients. Thus displacements are expressed by the infinite stress coefficients. And self-equilibrated loads acting on the side edge are extended to Fourier series. Stress coefficients are related to loading coefficients by stress boundary conditions. Then five examples show the validity of this approach. The GSS approach might lead to industrial applications in rock mechanics, petroleum and mining engineering, etc.

Spherical Elastic–Plastic Contact Model for Power-Law Hardening Materials Under Combined Normal and Tangential Loads

The contact between a power-law hardening elastic–plastic sphere and a rigid flat under combined normal and tangential loads in full stick is studied in this work. The displacement-driven loading is used since the frictional contact problems under the displacement-driven loading are widespread in the fields of metal forming and orthogonal cutting. The loading process is as follows: First, a normal displacement-driven loading is imposed on the rigid flat and kept constant; then, an additional tangential displacement-driven loading is applied to the rigid flat. The elastic–plastic contact behavior in presliding is investigated with a proposed finite element (FE) model, including the tangential force, the von Mises stress, the normal force, the contact pressure, and the contact area. The effect of the strain-hardening exponent on contact behavior is considered. It is seen that the tangential force increases nonlinearly with the increase of the tangential displacement, exhibiting gradual stiffness reduction which implies that the junction becomes more plastic. The von Mises stresses moves along the direction of the tangential load, while the maximum stress moves to the contact surface from the below. The normal force diminishes as the tangential load increases, and more obviously for the lower hardening exponent cases. The contact pressure also decreases more significantly for the lower hardening exponent cases. In addition, smaller exponents result in a greater increase of the contact area. The empirical expressions of the tangential force and the contact area in the tangential loading process are also proposed by fitting to the FE results.

Wear Induced by Stochastic Sliding Impacts

Vibrations of the steam generator tubes in nuclear power plants induce stochastic impacts between the tubes and their supports. As a consequence, wear is generated. A test rig is designed and used to perform impacts between two metal crossed cylinders with various incidence angles and impact velocities. The normal and tangential components of the contact load are measured during the tests. Rate and duration of impacts, instantaneous ratio between normal and tangential loads for each impact are deduced. Influence of incidence angle and impact velocity on impact duration, ratio between tangential and normal loads during impact and wear volume is highlighted.

Three-dimensional dynamic surface grasping with dry adhesion

Most robotic grasping research focuses on objects that are either not large in comparison to the gripper or have small graspable features; however, there are important applications that involve large flat or gently curved surfaces. Examples include robots that grasp the solar panels of space craft, handle large panels in manufacturing, or climb or perch on surfaces. We present a solution for grasping such surfaces consisting of groups of tiles coated with a controllable gecko-inspired adhesive. The tiles are loaded with two sets of tendons: one for distributing the forces evenly while grasping and the other for release. The gripper is passive and can attach and detach with little effort so that it does not disturb either the robot or the object to be grasped. The maximum gripping force in the normal direction can be over 1000 times greater than the required detaching force. The gripper is also fast, allowing a flying quadrotor to attach to a surface milliseconds after the tiles make contact. We present a model of the gripping mechanism and use the model to design the layout of the tiles to best support anticipated normal and tangential loads.

Mechanics Modeling of Blade/Disk Contacts

A predictive procedure capable of calculating dovetail surface contact loads in gas turbine engines is developed. The procedure determines contact normal and tangential loads, for a complete mission involving radial blade and thermal loads. Once Finite Element calculations to determine empirical constants for a specific blade/disk geometry are completed, the predictive procedure handles complicated load histories in near real-time for both single and double tang dovetails. The resulting load histories can be combined with Singular Integral Equations to calculate edge-of-contact stresses. The resulting contact stresses have been used to successfully predict fretting fatigue lives under controlled laboratory conditions.