Characterization of Early-Age Elastic–Plastic Properties of 3D Printed Materials Using Indentation Testing (2025-12)¶

Understanding the evolving mechanical properties of fresh, 3D printed construction materials is critical for ensuring buildability, structural stability, and failure resistance during the printing process. However, existing characterization methods are often time-consuming, invasive, or unable to simultaneously capture key parameters such as cohesion, internal friction, and stiffness. This paper introduces an indentation-based methodology for efficiently characterizing the early-age, time-dependent elastic–plastic behavior of 3D printed cohesive–frictional materials. An analytical model is developed by idealizing the indentation process as hemispherical cavity expansion under internal pressure, with material behavior governed by the Mohr–Coulomb failure criterion. The model accommodates cylindrical flat punch, spherical, and conical indenter geometries, and uniquely enables the extraction of the cohesion and internal friction angle from a single test, using the elastic modulus derived from the initial loading branch of the indentation curve. Validation against finite element simulations demonstrates excellent agreement across a range of input parameters. In addition, the model correctly captures the theoretical transition to the purely cohesive limit as the internal friction angle approaches zero. The methodology is experimentally demonstrated using an early-age cement mortar developed for 3D concrete printing. Practical limitations associated with the conical indenter, including excessive localized densification and calibration challenges, are addressed by adopting a non-self-similar flat punch. Test results show that both the elastic modulus and cohesion evolve with curing time according to power-law relationships indicative of accelerated hydration, while the friction angle remains relatively constant. Complementary unconfined compression tests corroborate these trends, and curing rate discrepancies due to specimen size are resolved using a maturity-based correction based on an Arrhenius framework. Overall, this approach offers a fast and scalable means for extracting key material parameters from a single indentation test. By enabling accurate, time-resolved material characterization, it supports improved quality control and structural modeling in additive manufacturing applications involving cohesive–frictional or purely cohesive materials.