Tailoring
of material architectures in three-dimensions enabled
by additive manufacturing (AM) offers the potential to realize bulk
materials with unprecedented properties optimized for location-specific
structural and/or functional requirements. Here we report tunable
energy absorption characteristics of architected honeycombs enabled
via material jetting AM. We realize spatially tailored 3D printed
honeycombs (guided by FE studies) by varying the cell wall thickness
gradient and evaluate experimentally and numerically the energy absorption
characteristics. The measured response of architected honeycombs characterized
by local buckling (wrinkling) and progressive failure reveals over
110% increase in specific energy absorption (SEA) with a concomitant
energy absorption efficiency of 65%. Design maps are presented that
demarcate the regime over which geometric tailoring mitigates deleterious
global buckling and collapse. Our analysis indicates that an energy
absorption efficiency as high as 90% can be achieved for architected
honeycombs, whereas the efficiency of competing microarchitected metamaterials
rarely exceeds 50%. The tailoring strategy introduced here is easily
realizable in a broad array of AM techniques, making it a viable candidate
for developing practical mechanical metamaterials.
Composites are finding lot of applications in aerospace, automobile and many other sectors due to their high strength to weight ratio and longer fatigue life. For assembly or electrical wiring purposes, often hole(s) are drilled into the laminate thereby reducing its strength. The strength prediction and damage mechanics study is of great importance in such structural applications. In this work, a three-dimensional finite element based progressive damage model (PDM) is presented for unidirectional carbon fiber reinforced polymer (CFRP) laminates having two holes in different configurations subjected to tensile loading. The developed model is suitable for predicting failure and post failure behavior of fiber reinforced composite materials. The material is assumed to behave as linear elastic until final failure. The three broad steps involved in this study are stress analysis, failure analysis and damage propagation which are implemented as a PDM involving finite element analysis. Hashin's failure criteria for unidirectional fiber composite is used for the damage prediction. It utilizes a set of appropriate degradation rules for modeling the damage involving material property degradation method. Digital image correlation (DIC) experiment is also carried out to perform whole field strain analysis of CFRP panel with different hole configurations. Whole field surface strain and displacement from finite element prediction are compared with DIC results for validation of the finite element model. Load-deflection behavior as well as path of damage progression is predicted by both PDM simulation and experiment. They are found to be in good agreement thereby confirming the accuracy of PDM implementation. Effect of spacing between the holes on stress concentration factor (SCF) is also further investigated.
Multilayered multi-material interfaces are encountered in an array of fields. Here, enhanced mechanical performance of such multi-material interfaces is demonstrated, focusing on strength and stiffness, by employing bondlayers with spatially-tuned elastic properties realized via 3D printing. Compliance of the bondlayer is varied along the bondlength with increased compliance at the ends to relieve stress concentrations. Experimental testing to failure of a tri-layered assembly in a single-lap joint configuration, including optical strain mapping, reveals that the stress and strain redistribution of the compliance-tailored bondlayer increases strength by 100% and toughness by 60%, compared to a constant modulus bondlayer, while maintaining the stiffness of the joint with the homogeneous stiff bondlayer. Analyses show that the stress concentrations for both peel and shear stress in the bondlayer have a global minimum when the compliant bond at the lap end comprises %10% of the bondlength, and further that increased multilayer performance also holds for long (relative to critical shear transfer length) bondlengths. Damage and failure resistance of multi-material interfaces can be improved substantially via the compliance-tailoring demonstrated here, with immediate relevance in additive manufacturing joining applications, and shows promise for generalized joining applications including adhesive bonding.
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