Contact area

About: Contact area is a research topic. Over the lifetime, 12358 publications have been published within this topic receiving 256401 citations. The topic is also known as: contact patch & contact region.

Direct contact scanner and related method

Abstract: A direct contact scanner uses a fiber acoustic waveguide to convey ultrasound from an ultrasound transducer to a direct contact area. The waveguide extends from a main body of the scanner into an oblong nose, and terminates in a deflector. To minimize thickness of the nose, the waveguide and deflector are rotated about an ultrasound transmission axis of the waveguide, enabling the scanner to be used in a variety of situations where quarters are cramped. A coupling fluid conveys ultrasound between the deflector and a radome, which directly contacts the object to be scanned. Using the waveguide, an ultrasound transducer and supporting electronics may be distanced from the direct contact area and separated from the fluid, thereby insulating the fluid from possible electronic leakage currents and heat.

Forced Response Prediction of Constrained and Unconstrained Structures Coupled Through Frictional Contacts

Abstract: In this paper, a forced response prediction method for the analysis of constrained and unconstrained structures coupled through frictional contacts is presented. This type of frictional contact problem arises in vibration damping of turbine blades, in which dampers and blades constitute the unconstrained and constrained structures, respectively. The model of the unconstrained/free structure includes six rigid body modes and several elastic modes, the number of which depends on the excitation frequency. In other words, the motion of the free structure is not artificially constrained. When modeling the contact surfaces between the constrained and free structure, discrete contact points along with contact stiffnesses are distributed on the friction interfaces. At each contact point, contact stiffness is determined and employed in order to take into account the effects of higher frequency modes that are omitted in the dynamic analysis. Depending on the normal force acting on the contact interfaces, quasistatic contact analysis is initially employed to determine the contact area as well as the initial preload or gap at each contact point due to the normal load. A friction model is employed to determine the three-dimensional nonlinear contact forces, and the relationship between the contact forces and the relative motion is utilized by the harmonic balance method. As the relative motion is expressed as a modal superposition, the unknown variables, and thus the resulting nonlinear algebraic equations in the harmonic balance method, are in proportion to the number of modes employed. Therefore the number of contact points used is irrelevant. The developed method is applied to a bladed-disk system with wedge dampers where the dampers constitute the unconstrained structure, and the effects of normal load on the rigid body motion of the damper are investigated. It is shown that the effect of rotational motion is significant, particularly for the in-phase vibration modes. Moreover, the effect of partial slip in the forced response analysis and the effect of the number of harmonics employed by the harmonic balance method are examined. Finally, the prediction for a test case is compared with the test data to verify the developed method. DOI: 10.1115/1.2940356

Elastic and viscoelastic indentation of flat surfaces by pyramid indentors

Abstract: The present work presents the results of frictionless and adhesionless contact of flat surfaces by pyramid indentors. The materials of the contacting solids were modelled as homogeneous and isotropic, linear elastic, as well as linear viscoelastic. The theoretical analysis is complemented by experiments and numerical calculations. The results include explicit relations between the normal applied load and the depth of penetration, details of the contact area shapes, the surface stresses and the contact pressure distributions. The standard shapes of the Vickers, Berkovich and Knoop pyramids were examined in particular. Certain aspects of geometrical imperfections, transverse isotropy and adhesion were considered. When elasticity or viscoelasticity provide adequate models of material behavior, micro- or nano-indentation by sharp pyramid indentors can be very useful and perhaps the only possible test in probing mechanical properties of small volumes of materials. The results can be particularly useful in using instrumented indentation for assessing mechanical properties of materials at cryogenic temperatures, of bio-materials and of micro-electro-mechanical components.

Electrochemical cell system with side-by-side arrangement of cells

Abstract: An electrochemical cell system including an anode compartment and a cathode compartment separated by a membrane and electrode structure. This structure has an anode surface with a plurality of anodes in a side-by-side arrangement exposed to the anode compartment and a cathode surface with a plurality of cathodes in a side-by-side arrangement exposed to the cathode compartment. The anodes and cathodes are separated by a layer of ion exchange polymer and register with each other so that opposing pairs of anodes and cathodes form cells. The membrane and electrode structure further includes a plurality of current collector screens. The current collector screens have an anode contact area in contact with the anode, a cathode contact area in contact with the cathode and a feed through area extending between cells and crossing from the anode contact area to the cathode contact area to connect the anode and cathode of adjacent cells. The invention provides a polymer electrolyte membrane electrochemical cell system which can be less complicated, lighter in weight and/or is easier to manufacture that existing stack designs.