Probing the micromechanics of a multi-contact interface at the onset of frictional sliding

Abstract

Abstract. Digital Image Correlation is used to study the micromechanics of a multi-contact interface formed between a rough elastomer and a smooth glass surface. The in-plane elastomer deformation is monitored during the incipient sliding regime, i.e. the transition between static and sliding contact. As the shear load is increased, an annular slip region, in coexistence with a central stick region, is found to progressively invade the contact. From the interfacial displacement field, the tangential stress field can be further computed using a numerical inversion procedure. These local mechanical measurements are found to be correctly captured by Cattaneo and Mindlin (CM)'s model. However, close comparison reveals significant discrepancies in both the displacements and stress fields that reflect the oversimplifying hypothesis underlying CM's scenario. In particular, our optical measurements allow us to exhibit an elastoplastic like friction constitutive equation that differs from the rigid-plastic behavior assumed in CM's model. This local constitutive law, which involves a roughness-related length scale, is consistent with the model of Bureau et al. [Proc. R. Soc. London A 459, 2787(2003] derived for homogeneously loaded macroscopic multi-contact interfaces, thus extending its validity to mesoscopic scales.

Normal contact and friction of rubber with model randomly rough surfaces

“…To ensure comparable semi-infinite contact conditions, SA samples remained in adhesive contact against a ∼ 15 mm thick PDMS slab. The experiments were performed with a home made setup described in [20,21]. Using a combination of cantilevers and capacitive displacement sensors, both the normal (P ) and interfacial lateral (Q) forces are monitored in the range [0-2.5] N with a resolution of 10 −3 N. This setup also provides simultaneous imaging of the microcontacts with the combination of a high resolution CCD camera (Redlake ES2020M, 1600×1200 pixels 2 , 8 bits) and a longworking distance Navitar objective.…”

“…The total true area of contact A is then obtained by summing all microcontact areas. In addition, assuming the validity of Hertzian contact theory at the scale of the asperity and knowing E, radii of curvature R of each asperity and ν = 0.5 the Poisson's ratio [20,21], the disks radii a i are a direct measure of the local normal forces p i since…”

Optical measurements of real contact area and tangential contact stiffness in rough contact interface between an adhesive soft elastomer and a glass plate

“…Using the DIC method, we performed in situ measurements of the surface displacement field in the apparent contact interface (Chareauminois and Fretigny, 2008;Prevost, et al, 2013). The typical results from the surface displacement measurement in the X-and Y-directions, u X and u Y , are shown in Fig.…”

“…8 and 9. From the theoretical and experimental approaches performed by Bureau et al (2003) and Prevost et al (2013), the small displacement due to the lateral deformation of the contacting asperities was derived in accordance to the following equation:…”

“…For example, Schallamach (1971) first discovered a surface instability, such as the propagation of the detachment waves across the contact zone during sliding motion. In recent years, as presented in the references by Chareauminois and Fretigny (2008) and Prevost et al (2013), the digital image correlation (DIC) method has been focused on visualizing the surface displacement and stress fields within the contact interface. These research studies will be helpful for the understanding…”