Yunwei Xu and Prof. Qingda Yang
Mechanical and Aerospace Engineering
Typical composites exhibit complex, multiple fatigue damage events that are strongly coupled and developed in a stochastic microstructure. The gradual progression of such damages is of primary concern for safety and tolerance design of composite structures. Those traditional methods based on linear elastic fracture mechanics are not effective and efficient for such complex damage processes. In order to accurately assess/predict the composite fatigue life, it is necessary to explicitly account for the progressive evolution of all major types of discrete damage events with high fidelity. We developed an orthotropic augmented finite element method (AFEM) to accurately and efficiently account complicated multiple fracture problems in composites. A composite laminate may develop multiple types of cracks at different locations depending on the in-situ stress environments. Typical composite exhibits complex asymmetric mechanical behaviors between tension- and compression-dominant stress state. Strong nonlinearity in shear stress-strain is also critically important for delamination crack growth. Therefore in our A-FEM formulation, we adopt the mechanism-based Sun’s criteria for crack initiation under general in-situ stress states. Upon satisfaction of a certain criteria, a cohesive crack will be initiated within an element. The element will be augmented into two subdomains connected by a specified mixed-mode cohesive law of the initiated crack type. The elemental equilibrium of this augmented problem will be solved using a newly developed consistency-check based algorithm, which has been proven to have mathematical exactness for piece-wise linear cohesive laws. A rigorous verification and validation process will be presented to demonstrate that the developed orthotropic A-FE can initiate and propagate various types of cracks under different stress environments, and can predict the entire stress-strain curves (linear and nonlinear). Further, we shall demonstrate that, this element can be used together with any cohesive interface elements to account for the important damage coupling between ply cracking and interlaminar delamination.
Mark A. Ciappesonid, Myeong-Lok Seolab, Rusnė Ivaškevičiūtėac, Furman V.Thompsone, Dong-Il Moonab, Sun Jin Kimab, Jin-Woo Hanab, M.Meyyappana, Sung Jin Kimdf
a Center for Nanotechnology, NASA Ames Research Center, Moffett Field, CA
bUniversities Space Research Association, NASA Ames Research Center, Moffett Field, CA 94035, USA
c Faculty of Physics, Vilnius University, LT-10222 Vilnius, Lithuania
d Department of Electrical and Computer Engineering, University of Miami,
e MSFC:ES43, NASA Marshall Space Flight Center, Huntsville, AL 35824, USA
f Biomedical Nanotechnology Institute (BioNIUM), University of Miami, Miami
Additive manufacturing has experienced massive technological leaps in the past years. Despite this progress an important class of devices energy harvesters haven’t seen much progress in 3D printing capability. This is due to incompatibility of materials and fabrication processes associated with conventional energy conversion devices. Here we present an all 3D printed energy harvesting device utilizing the triboelectric effect. Triboelectric nanogenarators (TENG) are grating disks fabricated by assembling a 3D printed: case package, electrode layer, and triboelectric layer. We investigated the effects of material and structural designs. The 3D printed TENG was able to provide an open circuit voltage of 231V, a short circuit current of 18.9μA, and a max power of 2.13 mW, sufficient for wireless electronics. This device with its fabrication technique presents a step forward for additive manufacturing, energy harvesting, and sustainability.
Cagri Oztan and Emrah Celik
Department of Mechanical & Aerospace Engineering
This research aims to fabricate thermoelectric modules with commercial Acrylonitrile Butadiene Styrene (ABS) polymer-based filament doped with Bismuth Telluride (Bi2Te3) using an FDM type 3D printer. Resultant modules pose a potential source for energy harvesting in environments suffering from waste heat due to their capability of converting the temperature difference to electricity. This research also allows production of thermoelectric materials in any desired shape, thanks to the versatile nature.
Cassie Bennett, Farrah Mohammed, Anabel Alvarez-Ciara, Michelle A Nguyen, and Abhishek Prasad
Department of Biomedical Engineering
Retracted by author.
R. Mylavarapu1 , N.W. Prins1 , S. Debnath1 , S. Geng2 , E.A. Pohlmeyer3 , J.C. Sanchez4 , and A. Prasad1
1 Department of Biomedical Engineering, University of Miami, Coral Gables, FL 33146 2 The Center for Computational Science, University of Miami, Coral Gables, FL 33146 3 John Hopkins University Applied Physics Laboratory, Laurel, MD 20723 4 DARPA, Arlington, VA 22203
Retracted by author.