Papers by Amir Refahi Oskouei
In recent years, due to achieving desired properties, increasing application of Composite in vari... more In recent years, due to achieving desired properties, increasing application of Composite in various industries is observable. Exact determination and evaluation of failure mechanisms lead to modified designs and helps assessment of loading in composite structures, specially sandwich panels. In this paper, failure mechanisms during bending of Foam / Glass-Polyester Sandwich panels, which degraded by pre-impact of various energy, have been investigated by acoustic data analysis. 4 different Lay-up techniques for laminates with 4 types of with and without pre-impacts and totally 16 samples were studied. Matrix crack, fiber de-bonding, fiber breakage and foam crack were the mechanisms were investigated through sample failure photos, acoustic frequency count analysis, extracted energy in each frequency range and force-time diagrams. Results showed that brittle failure mechanisms containing matrix crack and foam crack release more condensed and in lower frequency range with higher energy acoustic counts in comparison with ductile failure mechanisms like as fiber de-bonding and fiber breakage. Ductile failure mechanisms release more scattered in higher frequency range but with lower energy acoustic counts. Acoustic Results which applied to assess failure mechanisms validated by visual pictures and force diagrams also lead to a new frequency range determination for foam crack (190 to 220 kHz).
یلک د گژاو نا : کیتسوکآ نشیما یچیودناس لناپ ماکحتسا یا هبرض مزیناکم یاه تسکش چ هدیک زا لناپ رد یچ... more یلک د گژاو نا : کیتسوکآ نشیما یچیودناس لناپ ماکحتسا یا هبرض مزیناکم یاه تسکش چ هدیک زا لناپ رد یچیودناس یاه هزاس یاه فلتخم ،اضفاوه ،یتشک و هب هریغ لیلد تبسن ماکحتسا هب نزو ،لااب قیاع یتوص و یترارح و یصاوخ ریظن اهنآ هدافتسا یم ددرگ . هعلاطم رب یور مزیناکم تسکش رد تیزوپماک اه و هب صوصخ لناپ یچیودناس یاه زا دراوم هب زور دروم قیقحت یم دشاب . رد نیا هلاقم یارب هعلاطم تمواقم هب هبرض و عاونا بویع داجیا هدش رد لناپ یچیودناس یاه یتیزوپماک هشیش / یلپ رتسا اب موف یلپ ناتروا اب 3 عون هیلا ینیچ ،فلتخم زا هداد یاه شور نومزآ ریغ برخم کیتسوکآ نشیما هدافتسا هدش تسا . اب لیلحت نامزمه هداد یاه کیتسوکآ و هعلاطم یاهرادومن ورین ییاجباج و ریواصت یمشچ هنومن اه سپ زا هبرض یاه توافتم 20 ، 38 و 60 ،لوژ یسررب یاهمزیناکم تسکش داجیا هدش تروص هتفرگ تسا . نیدب روظنم رادومن ییاجباجورین و یژرنا کیتسوکآ رد ره هزوح یسناکرف رد نیح هبرض ریسفت هدش و طابترا اهنآ اب عاونا تسکش خر هداد رد هنومن ،اه مزیناکم تسکش خر هداد لیبقزا تسکش زاف هنیمز یلپ ،رتسا ،فایلا شیادج فایلا زا زاف هنیمز رد نیا عون یچیودناس لناپ جارختسا هدش تسا ....
The present study introduces two quantitative parameters to compare the accuracy of ultrasonic C-... more The present study introduces two quantitative parameters to compare the accuracy of ultrasonic C-scan testing and X-ray radiography methods in the damaged area detection under low-velocity impact in polymer-based composites. For this purpose, the hand lay-up technique of composite processing was employed to prepare the composite specimen. A composite specimen consisting of the glass fiber reinforced with the unsaturated polyester resin was considered for this investigation. The impact tests at different energy levels were carried out to create three damaged areas in this composite specimen. Because the glass/polyester specimen had a transparent surface, a digital scanner was used to obtain an ideal image of specimen representing the region and edge of the impacted areas. Two image quality factors were introduced as quantitative parameters to compare the ultrasonic C-scan and X-ray radiography results with those of an ideal image. The results of this study showed that the ultrasonic ...
دییامن هدافتسا لیذ ترابع زا هلاقم نیا هب عاجرا يارب : Please cite this article using: A. Refahi O... more دییامن هدافتسا لیذ ترابع زا هلاقم نیا هب عاجرا يارب : Please cite this article using: A. Refahi Oskouei, Design, Using acoustic emission to assess mass fractions of composite materials based on wavelet packet analysis, Modares Mechanical Engineering, Vol. 15, No. 7, pp. 307-312, 2015 (In Persian) هتفر راکب داوم یمرج رسک ییاسانش تهج نشیما کیتسوکآ شور يریگراکب رد تیزوپماک هتسب کجوم لیلحت ساسا رب يرمیلپ ياه يا
The Journal of the Acoustical Society of America, 2008
Stress corrosion cracking could occur wherever a specific corrodent and sufficient tensile stress... more Stress corrosion cracking could occur wherever a specific corrodent and sufficient tensile stresses coexist. In the objective to monitor online the SCC on real structures, it seems reasonable to characterize and recognize acoustic emission during static U-bend tests. The present study is concerned with static tests on 304 stainless steels in two different media (5% HCl and 5% H2SO4) in order to find a criterion to distinguish, the two different mechanism of SCC (anodic dissolution and hydrogen embrittlement) by characteristic parameters and waveform analysis of AE signals. In the next stage, effect of residual stress on stress corrosion cracking in chloride solution has been studied. Three samples have been prepared: one of them was stress relieved; the second one was made sensitive to SCC by heat treatment and the last one was cold worked by rolling. Cumulative count, amplitude distribution and waveform analysis were selected as AE-parameters. AE with amplitudes ranging from 39 to 65 dB with different counts and energy occurred during SCC of SS-304 at room temperature. According to the results, acoustic emission is able to be used as robust technique for mechanism detection of SCC. In addition it can be used to measure the effect of residual stress in manufacturing process on SCC.
Materials & Design, 2011
This paper addresses a new method based on the combination of mechanical behavior and acoustic em... more This paper addresses a new method based on the combination of mechanical behavior and acoustic emission (AE) information of composite materials during mode I delamination. The method is based on a special purpose function, called sentry function, which is defined as the logarithm of the ratio between mechanical energy and acoustic energy (f = Ln(E s /E a)). The sentry function is used to study the delamination process and to evaluate the delamination fracture toughness in mode I. The relationship between cumulative fracture toughness energy release rate (G I) and the integral of the sentry function during crack propagation showed a transition point with two sensitive regions below and above it. This behavior can be followed to obtain the critical strain energy release rate value (G Ic). Results obtained by means of the sentry function are compared with results obtained by a methodology proposed by other authors.
S. A. Arhamnamazi, N. Banimostafa Arab, A. Refahi Oskouei, F. Aymerich, Impact Area Assessment in... more S. A. Arhamnamazi, N. Banimostafa Arab, A. Refahi Oskouei, F. Aymerich, Impact Area Assessment in the Carbon Fiber Reinforced Polymer Composite using Radiography and Ultrasonic C-scan testing methods, Modares Mechanical Engineering, Vol. 18, No. 03, pp. 332-338, 2018 (in Persian) اب نبرک فایلا اب هدش تیوقت ِیرمیلپ هیاپ تیزوپماک رد هبرض زا یشان بیع هیحان یبایزرا شبور یتوصارف نومزآ و یفارگویدار شور ود C
Materials Today: Proceedings
Journal of Materials Science, 2016
In using acoustic emissions (AEs) for mechanical diagnostics, one major problem is the discrimina... more In using acoustic emissions (AEs) for mechanical diagnostics, one major problem is the discrimination of events due to different types of damage occurring during loading of composite materials. Unsupervised pattern recognition analyses (fuzzy c-means clustering) associated with a principal component analysis (PCA) are the tools that are used for the classification of the monitored AE events. Composites at different layups are used with the acoustic emission technique. A cluster analysis of AE data is achieved and the resulting clusters are correlated to the damage mechanisms of the material under investigation. Time domain methods are used to determine new relevant descriptors to be introduced in the classification process to improve the characterization and the discrimination of the damage mechanisms. The results show that there is a good fit between clustering groups and damage mechanisms. Additionally, AE with a clustering procedure are effective tools that provide a better discrimination of damage mechanisms in glass/polyester composite materials.
Proceedings of the Interntional Congress on Ultrasonics, 2007
Materials & Design, 2012
In using acoustic emissions (AEs) for mechanical diagnostics, one major problem is the discrimina... more In using acoustic emissions (AEs) for mechanical diagnostics, one major problem is the discrimination of events due to different types of damage occurring during loading of composite materials. Unsupervised pattern recognition analyses (fuzzy c-means clustering) associated with a principal component analysis (PCA) are the tools that are used for the classification of the monitored AE events. Composites at different layups are used with the acoustic emission technique. A cluster analysis of AE data is achieved and the resulting clusters are correlated to the damage mechanisms of the material under investigation. Time domain methods are used to determine new relevant descriptors to be introduced in the classification process to improve the characterization and the discrimination of the damage mechanisms. The results show that there is a good fit between clustering groups and damage mechanisms. Additionally, AE with a clustering procedure are effective tools that provide a better discrimination of damage mechanisms in glass/polyester composite materials.
The Journal of the Acoustical Society of America, 2008
In this paper a new method for locating the AE source with one sensor is presented. When acoustic... more In this paper a new method for locating the AE source with one sensor is presented. When acoustic emission signals propagate in wave‐guided, they have multi‐mode and dispersion characteristics. The separation of the modes at the sensors could make it possible to extract the exact information about the source that produced the waves. Based on the modal nature of AE, it can be understood that a good location would have two methods to determine the arrival times. One is determined on the same part of the waves (not only the same mode, ...
In this paper, acoustic emission (AE) monitoring with a wavelet-based signal processing technique... more In this paper, acoustic emission (AE) monitoring with a wavelet-based signal processing technique is developed to detect the damage types during mode I delamination on glass/polyester composite materials. Two types of specimen at different midplane layups, woven/woven (T3) and unidirectional/unidirectional (T5), leading to different levels of damage evolution, were studied. Double cantilever beam (DCB) is applied to simulate delamination process for all specimens. Firstly, the obtained AE signals are decomposed into various wavelet levels. Each level includes detail and approximation that are called components and related to a specific frequency range. Secondly, the energy distribution criterion is applied to find the more significant components each one of which is in relation to a distinct type of damage. The results show that the energy of AE signals has been concentrated in three significant components for both of the specimens. There is a difference in energy distribution of similar components of two specimens. It indicates that there is a dissimilar dominant damage mechanism for two different interfaces during the delamination process. Additionally, the microscopic observation (SEM) is used to determine how the different fracture mechanisms are related to the dominant corresponding wavelet components.
Materials and Design, Mar 2011
This paper addresses a new method based on the combination of mechanical behavior and acoustic em... more This paper addresses a new method based on the combination of mechanical behavior and acoustic emission (AE) information of composite materials during mode I delamination. The method is based on a special purpose function, called sentry function, which is defined as the logarithm of the ratio between mechanical energy and acoustic energy (f = Ln(Es/Ea)). The sentry function is used to study the delamination process and to evaluate the delamination fracture toughness in mode I. The relationship between cumulative fracture toughness energy release rate (GI) and the integral of the sentry function during crack propagation showed a transition point with two sensitive regions below and above it. This behavior can be followed to obtain the critical strain energy release rate value (GIc). Results obtained by means of the sentry function are compared with results obtained by a methodology proposed by other authors.
Micromachines, 2016
With a mortality rate over 580,000 per year, cancer is still one of the leading causes of death w... more With a mortality rate over 580,000 per year, cancer is still one of the leading causes of death worldwide. However, the emerging field of microfluidics can potentially shed light on this puzzling disease. Unique characteristics of microfluidic chips (also known as micro-total analysis system) make them excellent candidates for biological applications. The ex vivo approach of tumor-on-a-chip is becoming an indispensable part of personalized medicine and can replace in vivo animal testing as well as conventional in vitro methods. In tumor-on-a-chip, the complex three-dimensional (3D) nature of malignant tumor is co-cultured on a microfluidic chip and high throughput screening tools to evaluate the efficacy of anticancer drugs are integrated on the same chip. In this article, we critically review the cutting edge advances in this field and mainly categorize each tumor-on-a-chip work based on its primary organ. Specifically, design, fabrication and characterization of tumor microenvironment; cell culture technique; transferring mechanism of cultured cells into the microchip; concentration gradient generators for drug delivery; in vitro screening assays of drug efficacy; and pros and cons of each microfluidic platform used in the recent literature will be discussed separately for the tumor of following organs: (1) Lung; (2) Bone marrow; (3) Brain; (4) Breast; (5) Urinary system (kidney, bladder and prostate); (6) Intestine; and (7) Liver. By comparing these microchips, we intend to demonstrate the unique design considerations of each tumor-on-a-chip based on primary organ, e.g., how microfluidic platform of lung-tumor-on-a-chip may differ from liver-tumor-on-a-chip. In addition, the importance of heart–liver–intestine co-culture with microvasculature in tumor-on-a-chip devices for in vitro chemosensitivity assay will be discussed. Such system would be able to completely evaluate the absorption, distribution, metabolism, excretion and toxicity (ADMET) of anticancer drugs and more realistically recapitulate tumor in vivo-like microenvironment.
Stress corrosion cracking could occur wherever a specific corrodent and sufficient tensile stress... more Stress corrosion cracking could occur wherever a specific corrodent and sufficient tensile stresses coexist. In the objective to monitor online the SCC on real structures, it seems reasonable to characterize and recognize acoustic emission during static U-bend tests.
Journal of …, Jan 1, 2011
Abstract In sandwich structures, delamination along the interface between the face sheet and the ... more Abstract In sandwich structures, delamination along the interface between the face sheet and the core is one of the most common failure modes, and it is often referred to as the adherent or adhesive interface in adhesively bonded joints. The three modes of fracture achieved for ...
Key Engineering …, Jan 1, 2011
1Non-destructive Testing Lab., Department of Mechanical Engineering , Amirkabir University of Tec... more 1Non-destructive Testing Lab., Department of Mechanical Engineering , Amirkabir University of Technology, 424 Hafez Ave.,15914, Tehran, Iran. 2Department of Mechanical Engineering, KN Toosi University of Technology, Tehran, Iran. ... Keywords: Sandwich ...
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Papers by Amir Refahi Oskouei