This study focused on modeling and experimentally validating the interface strength of Functionally Graded Materials (FGMs) manufactured using the Fused Filament Fabrication (FFF) process. Interface zones in multi-material printed parts often experience stress concentrations, cracking, or delamination, especially with abrupt material changes. This project aimed to address those issues by using gradient transitions and multi-scale numerical modeling to improve reliability.
🔍 Objectives
Investigate how varying gradient transition lengths influence interface strength.
Compare performance of direct vs. graded and interlocked transitions.
Use simulation to predict stress fields and validate with experimental data.
🧪 Experimental Design
Tensile specimens made from ABS and CF/ABS were printed with different interface geometries:
Direct transition
Interlock pattern
Gradient transitions with lengths of 5%, 10%, 30%, and 100%
All samples were printed using 0/90 layups and tested under standard ASTM D638 conditions.
📌 Result: Gradient transitions improved tensile strength by up to 84% over direct interfaces and improved stiffness by up to 15%. Interlock patterns offered moderate gains but also introduced additional stress points at geometry transitions.
🧠 Modeling Approach
A three-scale homogenization framework was developed:
Microscale: Captured fiber morphology and orientation using representative volume elements (RVEs).
Mesoscale: Modeled interbead voids and composite behavior across layers.
Macroscale: FE simulations of tensile specimens using graded material properties.
📈 Figure 1: Predicted stress distribution at various gradient lengths shows a clear reduction in interfacial stress concentrations in graded designs compared to sharp material transitions.
✅ Key Findings
Gradient transitions reduced interface failures and improved load transfer.
Model predictions closely matched experimental results, validating the FE implementation.
🧪 Application
This research supports the use of voxel-based digital design and FFF printing for optimized FGM parts in aerospace, automotive, and biomedical applications where reliable multi-material bonding is critical.
📚 References
Hasanov, S. (2021). Numerical Modeling and Experimental Characterization of Functionally Graded Materials Manufactured by the Fused Filament Fabrication Process [Doctoral dissertation, Tennessee Technological University]. ProQuest Dissertations Publishing. https://www.proquest.com/openview/15651078a3e62aa678f8cf3af0811840/1
