On the stress recovery behaviour of Ecoflex silicone rubbers

Abstract

Silicone rubbers are promising materials that have extensively been used in many areas, including wearable electronic devices, actuator materials in soft robotics, and energy harvesters. Ecoflex, a commercially available polymer, is a group of silicone rubbers appearing with various Shore hardnesses that has become popular in recent years. While silicone rubbers in their real applications are subjected to repeated loadingunloading conditions, their mechanical behaviour under cyclic loading in different deformation modes and the corresponding stress recovery behaviour are yet to be well investigated. In this contribution, we conduct loading-unloading cyclic experiments in different time gaps between the first cycle and the second cycle to demonstrate the stress recovery behaviour after stress softening happens during the first cycle. For that, three different modes of deformations, i.e., uniaxial tension, planar tension, and equibiaxial tension tests are selected. Besides, Shore hardness dependence with different strain levels is also taken into consideration. The results show that the stress softening could recover significantly with time. These findings will help to understand the mechanical behaviour of Ecoflex silicone rubbers before selecting them in practical applications that are exposed to repeated loading-unloading cycles.

Intercalation of silsesquioxane surfactant in layered double hydroxide for silicone rubber composites: Enhancing interfacial interactions toward improvement of mechanical, thermal, and gas barrier properties

“…It was worth noting that the strong interfacial interactions between the SR matrix and modified Ca‐Mg‐Al LDH particles and the uniform dispersibility of modified Ca‐Mg‐Al LDH in the SR matrix were responsible for the gradual increase in mechanical strength 45,46 . In the four repeated loading‐unloading tests below, the SR composites showed a decrease in stress during loading compared to the previous loading at the same strain level due to the so‐called Mullins effect or stress softening 47 . Furthermore, the 1st derivative of the first loaded SR composites (Figure 6E) could be sequentially divided into three stages: strain‐hardening (the slope of stress–strain curves increases with strain), strain‐weakening behavior (the slope of stress–strain curves decreases with strain), and elastic region.…”

Monitored indentation for the detection of inclusions in elastomer material

“…Ecoflex™ silicone materials exhibit an isotropic incompressible hyper-viscoelastic behavior. 9,10 The constitutive behavior of such material is usually derived from the strain energy density W , which can be written in terms of the strain gradient F through the right Cauchy-Green deformation tensor C, defined as C ¼ F T F. The strain energy is decomposed into three parts, related to: (i) the hydrostatic loads applied to the material, W vol , (ii) the hyperelasticity of the material, W H , and (iii) its viscosity, W μ . In the case of incompressible materials, W vol vanishes, yielding…”

Strain rate, temperature and deformation state effect on Ecoflex 00-50 silicone mechanical behaviour

“…In [19], tests similar to the previously described ones were performed on Ecoflex Shore 00-10, 00-20 and 00-50: it was found that all the considered Ecoflex grades have similar behaviour concerning time and temperature dependence, and that material stiffness, hysteretic behaviour, the range of time over which stress-relaxation phenomena occur, and strain-induced or relaxation induced softening, increase with the increase of Shore hardness. These results, although insightful of the material mechanical behaviour, are limited to the uniaxial tension deformation state; in order to completely describe the material response, other deformation states more resembling real application conditions should be tested; some preliminary results for pure shear and equibiaxial deformation states are reported in [20], where larger apparent stress softening is observed for pure shear and equibiaxial deformation modes with respect to uniaxial tension; furthermore, residual deformation after unloading, which was not observed in uniaxial tensile tests in [3], is noted in the other deformation states.…”