Enhanced tensile properties of 3D printed soft–hard composites due to Poisson's ratio mismatch: Experimental and numerical study

A novel design of soft–hard integrated composite is proposed by embedding hard lattices with controllable Poisson's ratio (PR) at large deformation into the soft matrix. Extensive numerical simulations of the hard lattices with controllable PR (HLCPR) and the designed hard lattice reinforced soft matrix (HLRSM) are conducted based on constitutive parameters of the soft and hard materials obtained from standard material tests. PolyJet 3D printing technique is employed to fabricate the studied HLCPR and HLRSM samples with lattice of PR from -0.8 to 0.8, and tensile tests were conducted with the help of DIC method to obtain their mechanical properties and capture the fracture behaviors. Numerical results agree well with the test results in terms of effective Young's modulus, strength and fracture behaviors. Results show that coupling between the soft matrix and the HLCPR due to deformation mismatch leads to significant enhancement of mechanical properties, and such coupling effect varies with the PR of the HLCPR. The HLCPR of PR -0.8 leads to the strongest coupling effect, while that of PR 0.4 exhibits the weakest. The soft matrix delays fracture initiation in the HLCPR and transforms the fracture mode from sudden rupture to a progressive failure. Results also demonstrate that HLRSM with HLCPR of -0.8 exhibits superior performance compared to that with an uncontrollable PR or breaking hard lattices. A theoretical model was also carried out to further interpret the deformation mismatch induced coupling effect. This study offers helpful guidance for developing high-performance composite materials and structures.