Fracture Behavior of Bio-Inspired Functionally Graded Soft–Hard Composites Made by Multi-Material 3D Printing

Fracture Behavior of Bio-Inspired Functionally Graded Soft–Hard Composites Made by Multi-Material 3D Printing: The Case of Colinear Cracks

Mirzaali, Mohammad J. (TU Delft Biomaterials & Tissue Biomechanics)
Herranz de la Nava, Alba (Student TU Delft)
Gunashekar, Deepthishre (Student TU Delft)
Nouri Goushki, M. (TU Delft Biomaterials & Tissue Biomechanics)
Doubrovski, E.L. (TU Delft Mechatronic Design)
Zadpoor, A.A. (TU Delft Biomaterials & Tissue Biomechanics)

2019

The functional gradient is a concept often occurring in nature. This concept can be implemented in the design and fabrication of advanced materials with specific functionalities and properties. Functionally graded materials (FGMs) can effectively eliminate the interface problems in extremely hard–soft connections, and, thus, have numerous and diverse applications in high-tech industries, such as those in biomedical and aerospace fields. Here, using voxel-based multi-material additive manufacturing (AM, = 3D printing) techniques, which works on the basis of material jetting, we studied the fracture behavior of functionally graded soft–hard composites with a pre-existing crack colinear with the gradient direction. We designed, additively manufactured, and mechanically tested the two main types of functionally graded composites, namely, composites with step-wise and continuous gradients. In addition, we changed the length of the transition zone between the hard and soft materials such that it covered 5%, 25%, 50%, or 100% of the width (W) of the specimens. The results showed that except for the fracture strain, the fracture properties of the graded specimens decreased as the length of the transition zone increased. Additionally, it was found that specimens with abrupt hard–soft transitions have significantly better fracture properties than those with continuous gradients. Among the composites with gradients, those with step-wise gradients showed a slightly better fracture resistance compared to those with continuous gradients. In contrast, FGMs with continuous gradients showed higher values of elastic stiffness and fracture energy, which makes each gradient function suitable for different loading scenarios. Moreover, regardless of the gradient function used in the design of the specimens, decreasing the length of the transition zone from 100%W to 5%W increased the fracture resistance of FGMs. We discuss the important underlying fracture mechanisms using data collected from digital image correlation (DIC), digital image microscopy, and scanning electron microscopy (SEM), which were used to analyze the fracture surface.

multi-material 3D printing
fracture toughness
hard–soft interfaces
functionally graded materials

http://resolver.tudelft.nl/uuid:25e07ce6-6a92-4dde-81db-86c2bea3389c

https://doi.org/10.3390/ma12172735

1996-1944

Materials, 12 (17)

Institutional Repository

journal article

© 2019 Mohammad J. Mirzaali, Alba Herranz de la Nava, Deepthishre Gunashekar, M. Nouri Goushki, E.L. Doubrovski, A.A. Zadpoor