Session: 13-02-02: Advances in the Mechanics of Architected Materials II

Paper Number: 173812

Auxetic-Reinforced Mortar: X-Ray Micro-Ct Observations of Damage Evolution and Failure Mechanisms 

Auxetic materials have garnered significant attention for their unique deformation response under uniaxial loading, however, their use in structural load-bearing applications is limited by their inherently low bulk modulus compared to materials with positive Poisson’s Ratio. This study investigates the potential of harnessing auxetic behavior in an interpenetrating phase composite (IPC) to improve the strength of a brittle matrix. Such matrices are common in structural systems but are prone to failure through cracking. In this work, a mortar matrix is reinforced with continuous steel truss lattices occupying a small volume fraction of the IPC. A variety of lattice geometries, including re-entrant and convex forms, are examined to evaluate how lattices with different effective Poisson’s ratio influences the composite’s mechanical behavior. While prior computational studies have demonstrated that auxetic reinforcement increases confining pressure within the matrix—contributing to improved performance—substantial questions remain regarding the progressive evolution of damage and failure in these systems that are likely responsible for the high energy absorption and sustained residual strength throughout large deformations that have been experimentally observed. Specifically, the relative contributions to damage progression from local interactions between the reinforcement and matrix (e.g. crack bridging) versus the average confining effect have not been observed. Additionally, the role of evolving mechanical properties due to large deformations in the reinforcement have not been experimentally validated. Gaining insight into these aspects is critical for establishing the structure–property relationships needed to design high‑performance auxetic‑reinforced composites.

To build this understanding, this study employs interrupted mechanical tests to investigate how auxetic steel truss lattices influence damage evolution and failure mechanisms in a brittle mortar matrix. Damage and defect progression are analyzed both quantitatively and qualitatively to deepen understanding of the underlying mechanics. Eight mortar specimens were tested in compression; five incorporated truss lattice reinforcement, including both auxetic and non-auxetic designs, allowing for direct comparison of the effect of auxetic on performance. Each specimen underwent a controlled interrupted loading protocol involving incremental loading, unloading, and imaging with X-ray computed tomography. This approach produced a series of 3D images capturing internal damage progression at various stages of deformation. A Fast Random Forest algorithm was trained and applied to the images to conduct voxel classification for characterization of the initial defects and formation of damage. Quantitative analysis of these images and the spatial damage patterns were correlated with mechanical test data to assess how auxetic reinforcement affect the failure mechanisms and structural performance. The findings demonstrate that embedding auxetic truss lattice reinforcement led to higher ultimate strength and greater residual stress compared to specimens reinforced with non-auxetic lattices. Furthermore, auxetic-reinforced specimens demonstrated enhanced effective ductility in their bulk response, as quantified by the   index. These improvements in bulk performance are further explained through both quantitative and qualitative analyses of damage and defect evolution, which reveal reduced cracking and lower overall damage in the auxetic-reinforced specimens. The distinct and more progressive damage pattern observed in these specimens reflects a different failure mechanism introduced by the auxetic architecture.

Presenting Author: Andrew Gross University of South Carolina

Presenting Author Biography: Andrew Gross is an Assistant Professor in the Department of Mechanical Engineering at the University of South Carolina. He earned his Ph.D from the University of Texas at Austin and completed postdoctoral training at Harvard University. His areas of expertise include the development of novel mechanical test specimens spanning the micro and centimeter scales, in situ mechanical testing, ductile fracture, and the thermomechanical behavior of architected materials. He is a recipient of the DARPA Young Faculty Award for his work to simplify the determination of complex constitutive properties of elastoplastic materials using heterogeneous stress states and digital image correlation.

Authors:

Rimah Al Aridi University of South Carolina
Vincent Dinova Savannah River National Laboratory
Natalie Wieber Savannah River National Laboratory
Dale Hitchcock Savannah River National Laboratory
Timothy Krentz Savannah River National Laboratory
Simos Gerasimidis University of Massachusetts Amherst
Thomas Vitalis University of Massachusetts Amherst
Andrew Gross University of South Carolina