Hyperelastic constitutive modeling of hydrogels based on primary deformation modes and validation under 3D stress states

An improved direct shear characterisation technique for soft gelatinous and elastomeric materials

“… Note : For comparison, modulus of rigidity values from two other literature sources, Upadhyay et al [ 28 ] and Subhash et al, [ 7 ] are also presented.…”

“…Furthermore, Table 1 also compares the experimental shear modulus values determined in the present study to those found in previous studies. [ 5,7,28 ] While Subhash et al [ 7 ] measured the tensile and compressive moduli and Poisson's ratio ( υ ) for multiple concentrations of agarose hydrogel, the data can be extrapolated to calculate the shear modulus ( G ) of the material using where E is the average uniaxial modulus calculated from the tensile and compressive modulus values for each concentration. Averaging avoids any bias of using a single uniaxial modulus value.…”

“…Recently, Upadhyay et al [ 28 ] developed a single‐lap simple shear experiment for agarose gel and reported stress–strain response at multiple gel concentration levels, as shown in Figure 1. In this experiment, a rectangular prism‐shaped sample was glued via cyanoacrylate adhesive to the two aluminium lap plates, and the shear deformation on the surface of one side of the specimen was measured using 2‐D DIC.…”

“…For example, while the shear testing of human brain in Rashid et al [ 29 ] employed a linear variable displacement transducer for strain measurement that does not provide full‐field strain data, Zanon et al [ 30 ] utilised a specimen mounting technique that involved surface abrasion and chemical treatment, which can change material stiffness and might not be applicable on fragile hydrogel samples. In addition, like Upadhyay et al, [ 28 ] a single‐sided strain measurement was employed in Pasumarthy and Tippur [ 31 ] (also in Zanon et al [ 30 ] ), which fails to compensate for loading imperfections and may contribute to measurement uncertainty and errors. Thus, a major motivation of the present study is to overcome these limitations in the single‐lap shear testing of hydrogels, and to improve accuracy and repeatability of the obtained shear stress versus strain data.…”

“…Shear stress versus strain response of agarose gel (1.5, 2.5 and 4% wt. vol −1 ) reported by Upadhyay et al [ 28 ] three samples from each concentration were tested. The solid lines represent the average shear response of the sample, whereas the shaded regions represent the range of results for each concentration…”