Browsing by Subject "Mechanical behavior"

Now showing 1 - 3 of 3

Open Access
Design and fabrication of auxetic PCL nanofiber membranes for biomedical applications
(Elsevier, 2017-12) Bhullar, S. K.; Rana, D.; Lekesiz, H.; Bedeloglu, A. C.; Ko, J.; Cho, Y.; Aytac Z.; Uyar, Tamer; Jun, M.; Ramalingam, M.
The main objective of this study was to fabricate poly (ε-caprolactone) (PCL)-based auxetic nanofiber membranes and characterize them for their mechanical and physicochemical properties. As a first step, the PCL nanofibers were fabricated by electrospinning with two different thicknesses of 40 μm (called PCL thin membrane) and 180 μm (called PCL thick membrane). In the second step, they were tailored into auxetic patterns using femtosecond laser cut technique. The physicochemical and mechanical properties of the auxetic nanofiber membranes were studied and compared with the conventional electrospun PCL nanofibers (non-auxetic nanofiber membranes) as a control. The results showed that there were no significant changes observed among them in terms of their chemical functionality and thermal property. However, there was a notable difference observed in the mechanical properties. For instance, the thin auxetic nanofiber membrane showed the magnitude of elongation almost ten times higher than the control, which clearly demonstrates the high flexibility of auxetic nanofiber membranes. This is because that the auxetic nanofiber membranes have lesser rigidity than the control nanofibers under the same load which could be due to the rotational motion of the auxetic structures. The major finding of this study is that the auxetic PCL nanofiber membranes are highly flexible (10-fold higher elongation capacity than the conventional PCL nanofibers) and have tunable mechanical properties. Therefore, the auxetic PCL nanofiber membranes may serve as a potent material in various biomedical applications, in particular, tissue engineering where scaffolds with mechanical cues play a major role.
Open Access
An equivalent circuit for collapse operation mode of CMUTs
(IEEE, 2010) Olcum, Selim; Yamaner F.Y.; Bozkurt, A.; Köymen, Hayrettin; Atalar, Abdullah
Collapse mode of operation of the capacitive mi-cromachined ultrasonic transducers (CMUTs) was shown to be a very effective way for achieving high output pressures. However, no accurate model exists for understanding the mechanics and limits of the collapse mode. In this work, we extend the analyses made for CMUTs working in uncollapsed mode to collapsed mode. We have developed an equivalent nonlinear electrical circuit that can accurately simulate the mechanical behavior of a CMUT under any large signal electrical excitation. The static and dynamic deflections of a membrane predicted by the model are compared with the finite element simulations. The equivalent circuit model can estimate the static deflection within 1% and the transient behavior of a CMUT membrane within 3% accuracy. The circuit model is also compared to experimental results of pulse excitation applied to fabricated collapse mode CMUTs. The model is suitable as a powerful design and optimization tool for the collapsed as well as the uncollapsed case of CMUTs. © 2010 IEEE.
Open Access
Microstructural association between mechanical behavior with bending fracture surfaces in Astaloy CrA sintered parts alloyed by Cu and C
(Elsevier Ltd, 2014) Khorsand H.; Ghaffari, M.; Ganjeh, E.
Application of powder metallurgy technique, a method presenting both economic and technical concepts for producing sintered parts, has been expanding in automobile and other engineering industries. Powder metallurgy parts usually possess residual porosity in their microstructures deteriorating mechanical performance. There have been many solutions to increasing of strength in these parts such as applying different heat treatment or adding alloying elements. It is well known that Fe-Cu-C is the one of main alloying system for both increasing the strength and decreasing cost of them. In this study, the microstructure, mechanical properties (transverse rapture strength and hardness), crack behavior and fracture modes of a low alloy Fe-Cr powder (Astaloy CrA) with different amount of copper (0, 1 and 2. wt.%) and carbon, in form of graphite (0.45, 0.6 and 0.8. wt.%) sintered at conventional condition have been investigated. Microstructural evolution showed adding copper and graphite as alloying elements could generate widespread of strength (857-1380. MPa) and hardness (170-295 HV5). Developing different phases in microstructure was the main reason for various mechanical properties. Crack coalescence phenomenon leads to fracturing with ductile (at sinter-necks) and brittle morphology. Micro-mechanism of fracture related to transparticle and interparticle crack propagation. © 2013 Elsevier Ltd.