• Novel tensile specimens enable characterization of bi-material interface strength. • Strain-fields verify tensile specimens simulate desired failure mechanisms. • Interfaced single-material specimens experience large plastic deformations. • Bi-material specimens adhesively fail at interfaces. • Normal-interfaced bi-material tensile samples approximate T-peel response. Recent advances in additive manufacturing have facilitated the development of versatile multi-material structures constructed by combining flexible and rigid constituents. The mechanical behavior of these structures is heavily dependent on the chemical and mechanical properties of their constituent materials and their bonding during layer-wise fabrication. There exists a lack of a generalizable approach to quantify the mechanical properties of these multi-material structures and the strength of their interfaces. This work investigates the use of standard test methods to characterize the stress–strain characteristics and interface strength of 3D printed single- and bi-material structures constructed from polylactic acid (PLA) and thermoplastic polyurethane (TPU). Geometrically modified standard tensile samples with interfacial designs intended to reflect normal, shear, and combined loading conditions are fabricated and tested. The test sample geometries are selected to simulate the interface stress conditions observed in T-Peel and lap-shear tests. Digital image correlation (DIC) is used to quantify the strain fields developed in the samples. The full-field strain response is then utilized to understand the underlying failure mechanisms at the material interfaces, further highlighting the divergence between the strain at the interface and the average strain fields across the samples. Postmortem analysis of the samples reveals significant plastic deformation at the materials interfaces in the single-materials samples, which are not observed in the bi-material samples. As a consequence of the minimal deformation of the adherends in the bi-materials samples, it is possible to directly compare their mechanical responses across sample classes through energy methods. The modified tensile samples successfully captured the interface failure of single material samples. Additionally, the novel testing protocols successfully captured the macroscale behavior of multi-material T-Peel and lap-shear samples.
Paupst et al. (Sun,) studied this question.