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Dynamic tribological response of fractured and shear -damaged surfaces

Hongfa Huang, University of Nebraska - Lincoln

Abstract

When deformed under confining stresses, materials may undergo shear cracking/damage with the fractured/damaged surfaces being closed. This occurs, for example, in the failure of ceramic armor under ballistic impact. The friction of the closed surfaces plays an important role in the dynamic response. Although microcracking models that include friction have been proposed, tribological studies on the fractured/damaged surface pairs is lacking. In this research, a novel experimental method for characterizing the dynamic tribological response of fractured or shear-damaged surfaces has been developed. The method consists of a dynamic tribometric experiment based on the torsional Kolsky bar technique, and of an integrated optical profilometric examination that enables comparison of the initial and tested surfaces. ^ Using this method, the dynamic tribological responses of aluminum alloy (Al) and silicon carbide (SiC) matched fracture surface and shear-damaged SiC surface pairs have been studied in detail, including the dependencies on roughness, wear evolution and wear debris. The experimental work covers sliding velocities 0.04 to 6.50 m/s and the contact stresses 0.15 to 1.9 GPa. In addition, modeling work has been conducted to evaluate the key factors affecting the tribological behavior of Al fracture surfaces. Realistic surface modeling and finite element simulations have been performed to elucidate the possible micromechanisms governing the tribological response of brittle fracture surfaces. ^ Nonlinear shear responses of Al surfaces show shear stresses soften exponentially with increasing wear. In contrast, the transient tribological response of initially flat SiC surfaces displays substantial “hardening” while the surfaces undergo microscopic shear damage. Similar behavior was also found in the case of SiC shear-damaged surfaces without debris. Despite variations in the initial conditions and transient behaviors, the steady state response of these surfaces shows approximately the same kinetic frictional coefficient of 0.61. Surprisingly, the shear response of SiC engaged fracture surfaces gives a significantly lower friction coefficient of 0.36. Further numerical study suggests that shear dilatancy occurs during the friction tests, resulting in a significant reduction of contact area, and thus a lower nominal value of frictional coefficient. ^

Subject Area

Applied Mechanics|Engineering, Mechanical

Recommended Citation

Huang, Hongfa, "Dynamic tribological response of fractured and shear -damaged surfaces" (2003). ETD collection for University of Nebraska - Lincoln. AAI3092556.
http://digitalcommons.unl.edu/dissertations/AAI3092556

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