Effect of Micro-Groove Textures on the “Stick-Slip”Behaviors of Tribology of Soft Materials

The soft polymers, an important component of modern materials have a wide range of applications in the field of mechanical engineering, biomedicine and aerospace. Compared with hard materials, such as metals, ceramics, ect., the soft polymers usually feature a periodic behavior of “stick-slip” in their surficial tribological performances due to the low elastic modulus and viscoelasticity, which has attracted much scientific attention. The “stick-slip” is a surficial instability stemming from the adhesive interaction in contact region, behaving as two contact counterparts first strongly stick, and then suddenly rupture for a relative motion in the time domain. The normal load and interfacial sliding velocity have a great influence. From the viewpoint of engineering, the unstable tribology behavior of “stick-slip” on polymer surface is very easy to cause disturbances for the mechanical systems (such as car tires, wipers, and lip seals), resulting in the vibrations and noises. As a result, how to effectively restrain and control the “stick-slip” tribological behavior on the soft polymer surfaces seems an interesting question, which also has important significance for the mechanical engineering. In the present paper, the textures of micro-grooves on PDMS (Polydimethylsiloxane) surfaces had been fabricated using laser processing. We studied the effects of micro-grooves on the tribology behavior of “stick-slip” on soft surfaces during a dry sliding, and also analyzed the influences of the parameters of groove orientation angle, groove width, normal load and sliding velocity. In the experimental section, PDMS (Sylgard 170, Dow Coming Corp, USA) was selected as the base material, and the sample was fabricated into the shape of symmetrical wedge structure; the two parts of A and B from the Sylgard 170 product were mixed with the mass ratio of 1:1, and then was cured at 70℃ for 1 h. After the demolding, the PDMS sample was a black solid with the Young′s modulus of about 0.68 MPa and the Shore hardness of about 40 HA. Tribological tests of samples were carried out using a homemade setup. A smooth glass as the lower specimen was connected to an electric displacement table, and the PDMS sample was fixed an adaptive fixture connected to the sensor which was assembled on the upper balance cantilever beam. The homemade testing device also integrated an inverted digital microscope to observe and recorded the contact area in situ during tribological testing. Results showed that groove textures could effectively restrain the “stick-slip” behavior of soft material surface and reduce the resistance force of friction, but to what extent depended on the design of inclination angles of grooves. In general, the performance of 90° micro-groove textures in the friction reduction was better than that of other two cases (0° and 45°) because of the discontinuous design along the direction of sliding. For the case of 0° inclination angle, the increase of groove width intensified the inhibition effect on the “stick-slip” behavior of friction; however, grooves with the inclination angle of 90° performed inversely that the “stick-slip” behavior of friction decayed with the decrease of the groove width. In addition, the interfacial sliding velocity and the width of groove textures were also two important parameters which had strong influences on the tribological behaviors of soft material surfaces. The increase of sliding velocity would reduce the oscillation period and vibration amplitude of the interfacial “stick-slip” behavior though an increase appearing in the surface friction of PDMS sample.