Magnitude Of Tangential Force Research Articles

Scratching of Al 2O 3 under pre-stressing

Pre-stressing scratching tests have been preformed on polished surfaces of Al 2O 3 ceramic under a Rockwell diamond indenter which moved with uniform speed and constant normal load to investigate how the pre-stress contributes to the material removal mechanism. With the measurement of acoustic emission signals as well as indenter tangential forces, surface damages and cross-section of grooves of Al 2O 3 ceramic were evaluated under the action of different values of pre-stress. It was found that the scratched groove width was increased with the increasing of pre-stress when same normal loads were applied. The existence of pre-stress tends to restrain the crack propagation along the direction of pre-stress, and obvious plastic deformation at the bottom of scratched groove has been observed. Moreover, the fluctuation of tangential force was obviously enhanced, and the magnitude of tangential force in the test of pre-stress was higher than that of without pre-stress. The acoustic emission signals showed that fewer damages were produced in the process of scratching with an appropriate pre-stress. However, the continuing increase of pre-stress would aggravate the machining process.

Durability of Cu–Al coating on Ti–6Al–4V substrate under fretting fatigue

The durability and degradation mechanisms of Cu–Al coating on Ti–6Al–4V substrate under fretting fatigue condition were examined. Fretting fatigue tests were conducted at several applied stress amplitudes with a constant normal contact load. Surface profile measurements on the contact zone showed a gradual coating wear with increasing fretting fatigue cycles at the low applied stress amplitudes, and the coating survived up to one million cycles. At the high applied stress amplitudes either the coating was separated from the substrate due to insufficient interfacial strength or the specimen fractured at locations away from the contact area. The static coefficient of friction (COF) was lower on the coated substrate than that on the un-coated substrate before the application of fretting fatigue loads. After the exposure to fretting fatigue cycles, the static COFs of the coated and the un-coated substrates were almost equal. The surface of the coated substrate thus became relatively rougher with cycling than that of the un-coated substrate from fretting action. Similar behavior was observed from the evolution of tangential force with cycling. The fretting loops between the tangential force and relative slip amplitude of the coated and un-coated substrates were similar, i.e. shapes were almost identical except for the difference in the magnitude of tangential force.

Fracturing at Contact Surfaces Subjected to Normal and Tangential Loads

A variety of rock engineering problems including drilling, cutting, abrasion, and milling involve rock tool contact and indentation. The pattern of indentation fractures and the role of slip conditions, surface roughness, tool radius and initial flaw size for an arbitrarily loaded contact are not fully known. The present paper aims to identify the elastic stress field for a contact subjected to both normal and tangential loads, and evaluate the condition for the fracture initiation and propagation. Stress fields within two spheres at contact are available when either only normal load is applied or when tangential load causes full-slip conditions. It is shown here that through appropriate superposition of the above two solutions, the stress field under partial-slip conditions, as well as during the unloading of tangential force may be determined. Maximum tensile stress increases significantly under partial-slip conditions as compared to the full-slip case even though the same magnitude of tangential force is applied. The location of maximum tensile stress moves inward from the trailing edge as the tangential force is unloaded. The stress-intensity factors for a penny-shaped crack which initiates at the contact periphery, and follows the minimum principal stress trajectory are obtained and utilized to study indentation fracturing. The dependency of critical loads on initial flaw size, indenter radius and slip conditions is quantified. The predictions of fracture density and spacing under a sliding indenter are achieved through a simple estimate of shielding interaction between adjacent fractures. Relation of these evenly spaced fractures with the formation of wear grooves on sliding surfaces is discussed.

Fracturing at contact surfaces subjected to normal and tangential loads

Abstract A variety of rock engineering problems including drilling, cutting, abrasion, and milling involve rock tool contact and indentation. The pattern of indentation fractures and the role of slip conditions, surface roughness, tool radius and initial flaw size for an arbitrarily loaded contact are not fully known. The present paper aims to identify the elastic stress field for a contact subjected to both normal and tangential loads, and evaluate the condition for the fracture initiation and propagation. Stress fields within two spheres at contact are available when either only normal load is applied or when tangential load causes full-slip conditions. It is shown here that through appropriate superposition of the above two solutions, the stress field under partial-slip conditions, as well as during the unloading of tangential force may be determined. Maximum tensile stress increases significantly under partial-slip conditions as compared to the full-slip case even though the same magnitude of tangential force is applied. The location of maximum tensile stress moves inward from the trailing edge as the tangential force is unloaded. The stress-intensity factors for a penny-shaped crack which initiates at the contact periphery, and follows the minimum principal stress trajectory are obtained and utilized to study indentation fracturing. The dependency of critical loads on initial flaw size, indenter radius and slip conditions is quantified. The predictions of fracture density and spacing under a sliding indenter are achieved through a simple estimate of shielding interaction between adjacent fractures. Relation of these evenly spaced fractures with the formation of wear grooves on sliding surfaces is discussed.

Model for Frictional Behavior of Wheat on Structural Materials

ABSTRACT DIRECT shear tests were performed to study fric-tional behavior of wheat on aluminum, galvanized steel, plywood and concrete. The results showed that the conventional coefficient of friction concept defines the upper bound of tangential force along the contacting surfaces. The magnitude of tangential force is dependent on both the normal force and relative displacement between grain and structural material surfaces. An exponential function was proposed to model the wheat-structural material frictional behavior. Tests were performed to determine the frictional behavior of 10.2% moisture content (w.b.) wheat on four structural materials. Model simulations compare favorably with test data. The average relative differences between model simulations and experimental data are 15.96%, 9.76%, 11.78% and 9.54% for wheat-aluminum, wheat-galvanized steel, wheat-plywood and wheat-concrete interfaces.