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Contact Edges (contact + edge)

Distribution by Scientific Domains
Polymers and Materials Science75%

Selected Abstracts

Fretting fatigue limit as a short crack problem at the edge of contact

FATIGUE & FRACTURE OF ENGINEERING MATERIALS AND STRUCTURES, Issue 5 2004
Y. KONDO
ABSTRACT This paper proposes a local stress concept to evaluate the fretting fatigue limit for contact edge cracks. A unique S,N curve based on the local stress could be obtained for a contact edge crack irrespective of mechanical factors such as contact pressure, relative slip, contact length, specimen size and loading type. The analytical background for the local stress concept was studied using FEM analysis. It was shown that the local stress uniquely determined the ,K change due to crack growth as well as the stress distribution near the contact edge. The condition that determined the fretting fatigue limit was predicted by combining the ,K change due to crack growth and the ,Kth for a short crack. The formation of a non-propagating crack at the fatigue limit was predicted by the model and it was experimentally confirmed by a long-life fretting fatigue test. [source]

Organic Field-Effect Transistors: Planarization of Polymeric Field-Effect Transistors: Improvement of Nanomorphology and Enhancement of Electrical Performance (Adv. Funct.

ADVANCED FUNCTIONAL MATERIALS, Issue 14 2010
Mater.
Contact geometry plays an important role in charge injection and transport in organic field-effect transistors. On page 2216, T. Kowalewski, L. M. Porter, et al. show a dramatic effect of electrode planarization on the polymer morphology at the contact edges and a resulting increase in fi eld-effect mobility in short channel length devices, and a corresponding decrease in contact resistance. The cover image shows atomic force micrograph of individual polymer nanofi brils spanning the length of a 10 µm channel transistor with planarized contacts. [source]

Planarization of Polymeric Field-Effect Transistors: Improvement of Nanomorphology and Enhancement of Electrical Performance

ADVANCED FUNCTIONAL MATERIALS, Issue 14 2010
Kumar A. Singh
Abstract The planarization of bottom-contact organic field-effect transistors (OFETs) resulting in dramatic improvement in the nanomorphology and an associated enhancement in charge injection and transport is reported. Planar OFETs based on regioregular poly(3-hexylthiophene) (rr-P3HT) are fabricated wherein the Au bottom-contacts are recessed completely in the gate-dielectric. Normal OFETs having a conventional bottom-contact configuration with 50-nm-high contacts are used for comparison purpose. A modified solvent-assisted drop-casting process is utilized to form extremely thin rr-P3HT films. This process is critical for direct visualization of the effect of planarization on the polymer morphology. Atomic force micrographs (AFM) show that in a normal OFET the step between the surface of the contacts and the gate dielectric disrupts the self-assembly of the rr-P3HT film, resulting in poor morphology at the contact edges. The planarization of contacts results in notable improvement of the nanomorphology of rr-P3HT, resulting in lower resistance to charge injection. However, an improvement in field-effect mobility is observed only at short channel lengths. AFM shows the presence of well-ordered nanofibrils extending over short channel lengths. At longer channel lengths the presence of grain boundaries significantly minimizes the effect of improvement in contact geometry as the charge transport becomes channel-limited. [source]

Friction evaluation of elastomers in lubricated contact

LUBRICATION SCIENCE, Issue 10 2009
Gregory F. Simmons
Abstract Friction testing of elastomers in lubricated contact is discussed with a focus on developing experimental arrangements that can produce worthwhile results. Practical issues unique to elastomers are covered as well as their solutions, including contact mechanics, material response to loading, contact edges, oil absorption, cleaning and specimen geometry. A critique of reciprocating laboratory testing machines, including high-frequency short stroke and low-frequency long stroke friction and wear machines, is conducted for their usefulness, as is critical analysis of a wide variety of specimen configurations with the aim of helping the laboratory experimenter to overcome many of the pitfalls associated with testing of elastomers in lubricated conditions. Results from experiments using various testing arrangements are analysed, and it is found that the synthetic ester and mineral oil used produced similar results. Copyright © 2009 John Wiley & Sons, Ltd. [source]