The effects of strain rate, size (height × width), and pre-existing crack length on the mechanical response of polycaprolactone electrospun membranes were investigated by tension tests conducted at room temperature. In particular, tensile tests were performed with three different strain rates for strain rate effect tests, seven different geometries for elucidating the size effect, and three different initial notch lengths for crack growth experiments. The electrospun membranes were produced by the electrospinning technique using a polycaprolactone solution prepared in 1, 1, 1, 3, 3, 3-hexafluoro-2-propanol as the solvent. Scanning electron microscopy was utilized to show the continuous fiber structure without bead formation. The average fiber diameter was calculated as 1.113 ± 0.270 μm by using scanning electron microscopy images of the membranes. The chemical structure of polycaprolactone was analyzed by Fourier transform infrared spectroscopy, and the toxicity and cell viability of the electrospun membranes were shown by CellTiter 96® Aqueous One Solution Cell Proliferation Assay (MTS test). It was observed that the ultimate tensile strength and Young’s modulus decreased, and the elongation at failure value increased as the strain rate decreased from 10−1 to 10−3 s−1. Besides, positive strain rate sensitivity was observed on the mechanical response of electrospun polycaprolactone membranes. Moreover, the dependency of mechanical response on the size geometry has been well studied, and the optimum height and width combinations were specified. Also, crack growth was studied in terms of both macroscopic and microstructural deformation mechanisms and it is observed that individual fiber deformations and interactions are highly effective on the mechanical behavior and also propagation of the crack. Consequently, in this study, the size and strain rate effects and crack growth on the mechanical response of electrospun polycaprolactone membranes have been investigated extensively, and the results presented herein constitute an essential guideline for the usage of polycaprolactone electrospun membranes at different loading scenarios.
This study presents the dynamic and buckling analysis of the laminated composite thin arch plate frame
structures employing Classical Plate Theory with Finite Element Analysis. For this purpose, the effects of the radius of curvature, aspect ratio, and stacking order of such structures on the first ten natural frequencies, mode shapes, critical buckling load, and the first unstable regions are investigated. Besides, the two-bay curved plate frame structure is investigated. In order to perform dynamic and buckling analyses, a computer code is developed and executed via MATLAB. The results are compared and validated with those of ANSYS. It is concluded that the aspect ratio or the stacking order affects the dynamic characteristics of the curved plate frame structure considerably while the radius of curvature relatively has less impact on such dynamic properties of the structure.
In this study, hydrogen diffusion profiles of different metallic materials were investigated. To model hydrogen diffusion, 1D and 2D mass diffusion models were prepared in MATLAB. Iron, nickel and titanium were selected as a material of choice to represent body-centered cubic, face-centered cubic, and hexagonal closed paced crystal structures, respectively. In addition, hydrogen back diffusion profiles were also modeled after certain baking times. Current results reveal that hydrogen diffusion depth depends on the microstructure, energy barrier model, temperature, and charging time. In addition, baking can help for back diffusion of hydrogen and can be utilized as hydrogen embrittlement prevention method. Since hydrogen diffusion is very crucial step to understand and evaluate hydrogen embrittlement, current set of results constitutes an important guideline for hydrogen diffusion calculations and ideal baking time for hydrogen back diffusion for different materials. Furthermore, these results can be used to evaluate hydrogen content inside the material over expensive and hard to find experimental facilities such as, thermal desorption spectroscopy.
In this study chromium electroplating process, corresponding hydrogen embrittlement and the effects of baking on hydrogen diffusion are investigated. Three types of materials in the form of Raw 4340 steel, Chromium electroplated 4340 steel, and Chromium electroplated & baked 4340 steel are used in order to shed light into the aforementioned processes. Mechanical and microstructural analyses are carried out to observe the effects of hydrogen diffusion. Mechanical analyses show that tensile strength and hardness of the specimens deteriorate after chrome-electroplating process due to the presence of atomic hydrogen. XRD analyses are carried out for material characterization. Microstructural analyses reveal that hydrogen enters into the material with chromium electroplating process, and baking after chromium electroplating process is an effective way to prevent hydrogen embrittlement. Additionally, effects of hydrogen on the tensile response of ?-Fe based microstructure with similar chemical composition of alloying elements are simulated through Molecular Dynamics (MD) method.
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