Front view of the automated high throughput tribometer. Various critical components include: (1) friction/wear head, (2) normal load cell, (3) adhesion head, (4) robotic arm, (5) probe hopper, (6) linear actuator, (7) x-y positioning stage, (8) lateral load cell, and (9) vacuumed sample stage.
Adhesion head. (a) Adhesion gripper rigidly holds the spherical probes and normal load cell monitors the sample-probe interaction force. (b) Plot of normal force versus time during an adhesion measurement. The adhesion head moves toward the sample surface until a contact is established with the spherical probe (point A). Downward motion continues and the initial rate of application of normal load (given by the slope of the curve: mN/ms) is high. However, the application rate decreases as the applied force approaches the target force and eventually becomes zero at point B where the applied force is equal to the target force. After a preprogrammed dwell time (point C), the head moves upward at a constant speed and the adhesion force is determined at the instant of surface separation.
Friction/wear head. Important components include: hydraulic grippers, position adjustable counter weights, and frictionless air bearing pivot point.
Adhesion plot. The negative force peak is a measure of adhesion force and the area under the force curve in the adhesion regime is a measure of interfacial adhesion energy.
Kinetic friction. (a) Lateral force versus distance. Trace and retrace lateral force signals are plotted for multiple normal loads (490, 980, and 1470 mN) and half the width of the trace-retrace loop is a measure of kinetic friction force. (b) The magnitude of kinetic friction is plotted against normal load to estimate the kinetic COF (given by the slope).
(a) Lateral force (tangential resistance force) versus time is plotted for sample A for 25 trace-retrace cycles, a normal load of 3 N, a probe velocity of 1 mm/s, and a sliding distance of 4 mm. (b) Lateral force versus time is plotted for sample B for 29 trace-retrace cycles, a normal load of 3 N, a probe velocity of 1 mm/s, and a sliding distance of 4 mm. (c) Kinetic friction versus cycle number for sample A. (d) Kinetic friction versus cycle number for sample B.
Static friction plots. (a) Lateral force versus time and (b) sample velocity versus time. The velocity plot indicates sample motion at t = 20 s and the corresponding static friction is approximately 200 mN. The experiment was performed at a lateral force application rate of 10 mN/s and an applied normal force of 1 N.
Adhesion plots of (a) epoxy, (b) PSA, (c) sandpaper, (d) Teflon, and (e) steel.
Kinetic friction versus cycle number plots of (a) epoxy, (b) PSA, (c) sandpaper, (d) Teflon, and (e) steel.
SEM images of (a) and (b) sandpaper and (c) and (d) steel. Hitachi TM3000 Tabletop SEM was used for surface analysis and the samples were coated with ∼15 nm osmium as part of SEM sample preparation. The red highlighted regions represent the contact area where the probe slid over the sample surface.
Kinetic COF, static COF, adhesion force, and adhesion energy of epoxy, PSA, sandpaper, Teflon, and steel samples.
Article metrics loading...
Full text loading...