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PhD "ZOOM" SEMINAR
Wednesday, June 17, 2020 at 14:00
Mixed Mode Fracture Behavior of a Multi-Directional Plain Weave Composite - an Interface Delamination Between a 0◦/90◦ and a +45◦/-45◦ Weave
Orly Dolev
Ph.D. candidate under the supervision of Professor Leslie Banks-Sills

Currently, the advantages of composite materials, such as high strength and toughness to weight ratios, corrosion and fatigue resistance, make these materials very desirable to work with, especially in the aerostructure industry. However, composite structures are sensitive to the presence of damage such as delamination, which is one of the most typical failure modes in laminate composites. The main problem is that most of composite structural damage is difficult to detect or follow. The lack of accurate and reliable fracture toughness, fatigue and damage tolerance properties, which enable the evaluation of damage growth within a structure, results in an over-designed structure due to the high safety margin regulations. In order to better understand the mixed mode I/II fracture (initiation and propagation) behavior of a carbon/epoxy multi-directional (MD) woven composite containing a delamination between two plain woven plies, with tows in the 0◦/90◦ and +45◦/-45◦ directions, a comprehensive investigation has been performed, involving analytical, numerical and experimental work.
Mixed-mode fracture toughness tests were carried out on an MD laminate making use of the Brazilian disk (BD) specimen, containing a delamination, at various loading angles in order to obtain a wide range of mode mixities. Employing the experimentally and numerically obtained results at fracture, a two and three-dimensional failure criterion were generated. A statistical analysis with a 10% probability of unexpected failure and a 95% confidence was performed, in order to account for scatter in the results. These failure criteria may be used for safer design purposes for the investigated interface.
Fracture toughness tests for delamination initiation and propagation under quasi-static loading were carried out making use of three beam-type specimens: double cantilever beam (DCB), calibrated end-loaded split (C-ELS) and mixed mode end-loaded split (MMELS), with the following modes of deformation: nearly mode I, nearly mode II and one in-plane mixed mode ratio, respectively. Based upon the experimentally and numerically obtained results, a fracture toughness resistance G_iR-curve was generated, for each kind of beam-type specimen. In addition, the critical values of the interface energy release rate for initiation G_ic and steady-state propagation G_iss were determined.
Quantification of the critical energy release rate G_ic values obtained for delamination initiation in all tested specimens, as a function of the in-plane mode mixity, was presented and discussed.

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https://zoom.us/j/4962025174
The meeting will be recorded and made available on the School’s site.

השתתפות בסמינר תיתן קרדיט שמיעה = עפ"י רישום שם מלא + מספר ת.ז.  בצ'אט

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https://us04web.zoom.us/j/79530182251
Meeting ID: 795 3018 2251

Speaker: Tal Mund

M.Sc. student under the supervision of Prof. Alex Bronstein

Wednesday, May 6^th, 2020 at 15:00

        ZOOM  Seminar

EEG Source Localization Using Compressed Measurements and the Fabrication of an Anisotropic Phantom Head Model

Abstract

One of the greatest challenges of modern-day science community is understanding how our brain functions. In a human head, a neural activity is usually modeled as a current dipole activation with a specific position and orientation. Brain imaging techniques such as EEG, MEG, fMRI etc. are used to evaluate the neural activities location, orientation and magnitude. One can study the spatiotemporal behavior of the head’s neural circuits using these techniques. However, for us to better understand how our brain works, we need to collect a vast amount of data. One of the main advantages of EEG is its portability, since competing imaging techniques such as fMRI and MEG are stationary. A mobile EEG device can continually collect data from research subjects as they perform their everyday tasks. By compressing the EEG measurements, the hardware requirement of a portable EEG device is reduced, which in turn makes it cheaper and lighter. Hence getting closer to a portable EEG device. In this work, the possibility of using a compressed set of EEG measurements was simulated and analyzed. In addition, a phantom mimicking the electromagnetic properties of the human head is presented. A phantom head is considered an essential validation step between computer simulations and the data processing of EEG recordings on humans. The fabrication is based on 3d-printing technology combined with an electrically conductive gel. The novel key features of the phantom are the controllable anisotropic electrical conductivity of the skull and the densely packed monopolar current sources permitting interpolation of the measured gain function to any dipolar current source position and orientation within the head.

סמינר זה יחשב כסמינר שמיעה לתלמידי תואר שני, למי שמתחבר לסמינר דרך הזום.

You are invited to attend a lecture On Thursday, 30 April 2020, 15:00

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https://us04web.zoom.us/j/73978006567

HIGH POWER DYNAMIC STRUCTURED LIGHT 3D RECONSTRUCTION SYSTEM BASED ON RESONANCE DOMAIN DIFFRACTIVE OPTICS

By:

Omer Stein

M.Sc student under  the supervision of Prof. Michael Golub,

Prof. Menachem Nathan, Prof. Shlomo Ruschin

Abstract

Structured light is one of the most common 3D data acquisition technique used in industry. Traditionally, structured light methods are used to obtain 3D information of an object, using predetermined illumination patterns to encode spatial data for later triangulation and reconstruction. A multitude of pattern types exist, which achieve varying degrees of depth resolution, depending on the needs of the user and the demand on the system. Means of projecting these patterns vary as well, including off the shelf DLP projectors, scanning mirror laser projectors and diffractive optics based laser projectors. Diffractive optics based projectors are one of the most cost effective and power efficient options, but are limited in projection angles. Traditional DLP or scanning mirror projectors can have high angles of projection, but can be very large and power consuming, lack illumination power, or present an eye safety hazard. In this work, we show the feasibility of a gray coded structured light 3D reconstruction system, based on resonance domain diffractive optical elements previously developed by our group, which allow for wide fanout angles with very high diffraction efficiency and close to diffraction-limited fidelity of the projected intensity patterns, leading to a compact, low cost, high preforming 3D reconstruction system. We present the design, characteristics, simulation and experimental results of our proposed setup, using real world objects, and compare our results with comparable commercially available projectors.