Ecoflex polymer of different Shore hardnesses: Experimental investigations and constitutive modelling

Ecoflex, a commercially available silicone polymer, has attracted considerable attention due to its wide range of applications. The polymer has various Shore hardnesses that represent its wide range of stiffnesses. In this contribution, we have conducted a plethora of experiments under the uniaxial mode of tensile deformation. These experiments consist of loading-unloading cyclic tests, stretchability tests, single-step relaxation tests, Mullins effect tests, stress recovery tests, and temperature-dependence tests at different strain levels. All tests are revisited with Ecoflex of five Shore hardnesses ranging from Shore 00–10 to Shore 00–50. Extensive experimental findings illustrate that the material consists of an equilibrium stress part and an overstress part. Constitutive frameworks with an amplified strain invariant are proposed to predict the mechanical responses of Ecoflex over a wide range of Shore hardnesses. Afterwards, the frameworks are extended to capture the stress softening behaviour significantly observed in the material. Relevant examples illustrate that proposed constitutive models accurately predict stress-strain responses and the stress softening behaviour of Ecoflex. The current experimental study will work as a guide in selecting Ecoflex with an appropriate Shore hardness for applications in stretch sensors, soft robotics, and energy harvesters. Moreover, the novel concept of Shore-dependent modelling proposed herein can be applied to predict the stress-strain behaviour of other soft polymers appearing with various Shore hardnesses where there exist difficulties in obtaining experimental data of a particular Shore hardness.