Mohammad Ahmadi

Monitoring the initiation and growth of delamination in composite materials using acoustic emission under quasi-static three-point bending test

Control and optimization of machining processes are important issues affecting the development of productivity. Monitoring systems have become indispensable in the evaluation of materials during machining. In this paper, the path toward the delamination-free drilling of glass/epoxy composite material is established using some novel methods based on acoustic emission features. Acoustic emission monitoring with three techniques, sentry function, acoustic emission energy distribution, and acoustic emission count distribution, are developed to detect and realize the critical force at the onset of delamination process on glass/epoxy composite materials. The three-point bending test simulates thrust force, the most effective factor in delamination, throughout the process of drilling without backup plate. Sentry function is regarded as a new method based on the combination of AE information and mechanical behavior of composite materials. The sentry function was used to study the initiation and growth of delamination process. Two types of specimen with different layups, woven [0, 90]s and unidirectional [0]s, leading to different levels of damage evolution, were studied. Results show that AE parameters and sentry function method are useful tools for the examination of initiation and the growth of delamination during drilling process and can help to avoid delamination damage while drilling.

Investigation of phase object trace duplication in moire deflectometry

In a deflectometry experiment for finding the temperature distribution around a hot wire as a phase object, the trace of the wire in a moiré pattern is duplicated, and it is observed that the separation of the wire traces varies when the distance between two gratings of a moiré deflectometry setup is changed. By investigation of moiré deflectometry, it is found that the object trace duplication cannot be interpreted by ray deflection theory, which is based on geometric optics. By using diffraction theory, the effect of a phase object on a moiré pattern is studied, and some generalized formulations are presented. It is demonstrated that the deformation of moiré fringes does not originate from the wavefront derivative, but superposition of two separated wavefronts causes fringe deformation. By this approach, the accuracy of ray deflection analysis is improved. Finally, the results of this model are simulated, and the simulation has good agreement with the experimental model.

Determination of refractive index by Moiré deflectometry

Determination of refractive index is an important characteristic of material which is crucial parameter for physicists and engineers. Moiré deflectometry technique is convenient, easy-aligning, nondestructive, non-contact and fairly accurate method for refractive index measurement of gas, liquid, solid. In this paper we investigate the theory of the technique and simulate some relations then finally measure refractive index of a glassy lamella, n=1.536.

Applying an optimized proxy-based workflow for fast history matching

History matching is still one of the main challenging parts of reservoir study especially in giant brown oil fields with lots of wells. In these cases, history matching with conventional manual technique needs many runs and takes months to get a match. In this work, an innovative approach was suggested for fast history matching in a real brown field. The workflow was employed based on an optimized proxy model for history matching of a field consisting of 14 active wells with multiple responses (which are production rate and pressure data) in the south part of Iran. The main important features of the proposed algorithm were defining a proxy model which is response surface method in which 21 model parameters were incorporated based on cubic centered face method. The proxy model was then optimized by one of the most famous algorithms which is genetic algorithm. Proxy model was successfully performed using 256 samples leading into p- value of 0.531 and R2 of 0.91 dataset. As a result, the proposed workflow and algorithm showed good and acceptable results for history matching of studied real model.

Measurement of refractive index profiles in optical waveguides by moiré deflectometry technique

Measurement of refractive index profiles in optical waveguides is an important issue for controlling manufacturing procedures and determination of some important characteristics of waveguides. In this paper, an optical waveguide is considered as a phase object. When collimated laser beams are illuminated on waveguides, the refractive index gradient distorts the plane waves, then the distortion is determined by use of the moiré deflectometry method. Dimensions of the waveguides under study are on the order of 10xa0μm, so the moiré deflectometry setup was changed and optimized for measuring in the micrometer dimensions. This modified and generalized moiré deflectometry technique helps to intensify plane wave distortion thousands of times and expands it to be measurable. Finally, by analysis of moiré fringes, we succeeded in determining the refractive index profile of an optical waveguide by approximation of semi-cylindrical symmetry.