Carbon Black/PDMS Based Flexible Capacitive Tactile Sensor for Multi-Directional Force Sensing

Flexible sensing tends to be widely exploited in the process of human–computer interactions of intelligent robots for its contact compliance and environmental adaptability. A novel flexible capacitive tactile sensor was proposed for multi-directional force sensing, which is based on carbon black/polydimethylsiloxane (PDMS) composite dielectric layer and upper and lower electrodes of carbon nanotubes/polydimethylsiloxane (CNTs/PDMS) composite layer. By changing the ratio of carbon black, the dielectric constant of carbon black/PDMS composite layer increases at 4 wt%, and then decreases, which was explained according to the percolation theory of the conductive particles in the polymer matrix. Mathematical model of force and capacitance variance was established, which can be used to predict the value of the applied force. Then, the prototype with carbon black/PDMS composite dielectric layer was fabricated and characterized. SEM observation was conducted and a ratio was introduced in the composites material design. It was concluded that the dielectric constant of carbon sensor can reach 0.1 N within 50 N in normal direction and 0.2 N in 0–10 N in tangential direction with good stability. Finally, the multi-directional force results were obtained. Compared with the individual directional force results, the output capacitance value of multi-directional force was lower, which indicated the amplitude decrease in capacity change in the normal and tangential direction. This might be caused by the deformation distribution in the normal and tangential direction under multi-directional force.

Bolted joint compliance analysis with account for the roughness of contact surfaces

Bolted joints are widespread in various industries. They are used both in detachable and in non-detachable connections. The main requirement for bolted joints is to ensure the strength of the connection and guaranteed contact pressure on the connected surfaces, i.e. joints, during the operation of the structure. As a rule, their design and calculation do not take into account the contact compliance of surfaces, which is determined by their macro- and microroughnesses. This problem leads to an overestimation of the joint strength and an underestimation of the predicted joint compliance. The study proposes a simple model which makes it possible by calculation to take into account the effect of the roughness of the contacting surfaces on the compliance of the joint without modifying the ANSYS application package. On the example of a flange connection, an experimental verification of the adequacy of the proposed model was carried out.

Thermal mechanical characterization of copolyester for additive manufacturing using FDM

The main purpose of this study is to highlight the thermal and mechanical characterization of printed copolyester-based polymer. The variety of benefits of this material, such as its food contact compliance and important mechanical properties, have proved to be effective in huge field of applications, including medical sector and packaging uses. However, it has not received much attention for 3D printing processes. As the printing temperature is a key parameter of fused deposition modeling (FDM) process, the present study is started by analyzing its effect on the mechanical properties of printed copolyester under tensile loading. Indeed, the determination of temperature optimal values to print this material with FDM process is done based on tensile properties, including tensile strength, Young's modulus, ultimate tensile and yield strength, ductility and fracture toughness. The fracture properties of printed copolyester are also discussed using “scanning electron microscopy” (SEM). The results indicate a strong effect of the extrusion temperature on tensile properties. In addition, the analysis of copolyester sample microstructure reveals several damage mechanisms within the printed parts that reflect different types of wires fracture form subjected to the same tensile loading.

Contact interaction between bodies with wavy relief taking into account interstitial compressible liquid

The non-frictional contact between two semi-infinite elastic bodies, one of which has a wavy surface, is considered for the case of interface gaps filled with a compressible barotropic liquid. The contact problem formulated is reduced to a singular integral equation (SIE) with the Hilbert kernel, which is transformed into a SIE with the Cauchy kernel for a derivative of a height of the gaps. A system of transcendental equations for a width of the gaps and a pressure of the liquid is obtained from the condition of boundedness of the SIE solution at the integration interval ends and the equation of state of a compressible barotropic liquid, and then it is solved numerically. The dependences of the width and shape of the gaps, the pressure of the liquid, the average normal displacement and contact compliance of the bodies on the applied load and bulk modulus of the liquid are analyzed.

Effect of compressible liquid on the contact between an elastic body and a rigid base with a periodic array of quasielliptic grooves

The frictionless contact between an elastic body and a rigid base in the presence of a periodically arranged quasielliptic grooves with in interface gaps in the presence of a compressible liquid is modeled. The contact problem formulated for the elastic half-space is reduced to a singular integral equation (SIE) with Hilbert kernel for a derivative of a height of the interface gaps, which is transformed to a SIE with Cauchy kernel that is solved analytically, and a transcendental equation for liquid’s pressure, which has been obtained from the equation of compressible barotropic liquid state. The dependences of the pressure of the liquid, shape of the gaps, average normal displacement and contact compliance of the bodies on the applied load and bulk modulus of the liquid are analysed.

On the Contact of Curved Rough Surfaces: Contact Behavior and Predictive Formulas

The statistical microcontact models of Greenwood–Williamson (GW), Kogut–Etsion (KE), and Jackson–Green (JG) are employed along with the elastic bulk deformation of the contacting solids to predict the characteristics of rough elliptical point contact such as the pressure profile, real area of contact, and contact dimensions. In addition, the contribution of the bulk deformation and the asperity deformation to the total displacement is evaluated for different surface properties and loads. The approach involves solving the microcontact and separation equations simultaneously. Also presented are formulas that can be readily used for the prediction of the maximum contact pressure, contact dimensions, contact compliance, real area of contact, and pressure distribution.