Örgülü Kompozit Plaklarda Darbe Deneylerinin İrdelenmesi

Konferans Bildirisi -- Teorik ve Uygulamalı Mekanik Türk Milli Komitesi, 2008Conference Paper -- Theoretical and Applied Mechanical Turkish National Committee, 2008Bu çalışmada örgülü cam-elyaf/epoksi kompozit plakların darbe davranışları incelenmiştir. Enerji profili diyagramı, hasarlı numune görüntüleri ve ilgili kuvvet-çökme eğrilerini karşılaştırmak suretiyle, hasarlı numunelerin hasar gelişiminin tespit edilebileceği gösterilmiştir. Örme açısının tabakalı plakların darbe direnci ve hasar mekanizmaları üzerindeki etkisi de araştırılmıştır. Ayrıca, maksimum kuvvet, maksimum çökme ve maksimum temas süresi gibi darbe karakteristiklerinin darbe enerjisi ile değişimleri de sunularak bu karakteristiklerin hasar gelişimi ile arasındaki ilişki kurulmuştur.In this study, impact behavior of woven glass fabric -epoxy composite plates is examined. It is shown that the damage process of individual specimens can be reconstructed from comparing the energy profile diagram, images of damaged specimens and corresponding load-deflection curves. The effect of weave angle on impact resistance and damage mechanisms of laminated plates is also investigated. In addition, variation of the impact characteristics such as maximum force, maximum deflection and maximum contact time versus impact energy is presented. The correlation between those characteristics and damage process is also constructed

Tabakali Kompozitlerde Fiber Yönlenme Açisinin Darbe Davranişina Etkisi

Konferans Bildirisi -- Teorik ve Uygulamalı Mekanik Türk Milli Komitesi, 2008Conference Paper -- Theoretical and Applied Mechanical Turkish National Committee, 2008Bu çalışmada, cam lifi-epoksi kompozitlerinde tabaka sıralanışının darbe davranışına etkileri incelenmiştir. [90/0]₆, [30/0]₆ ve [15/0]₆ şeklinde olmak üzere üç farklı tabakalı kompozit aynı fiber oranları ve tabaka sayısı olacak şekilde üretilmişlerdir. Daha sonra, darbe testi için bu kompozitlerden 100 mmx100 mm boyutlarında numuneler kesilmiştir. Numuneler üzerine düşük hızlı darbe testleri DYNATUP GRC 8200 darbe cihazı kullanarak yapılmıştır. Darbe enerjileri delme oluşuncaya kadar kademeli olarak arttırılmıştır. Darbe cihazı zamana bağlı olarak yük, hız, çökme ve absorbe edilen enerji değerlerini vermektedir. Darbe enerjisi ile absorbe edilen enerji arasındaki ilişkiyi göstermek amacı ile enerji profili yöntemi kullanılmıştır. Sonuçlar, [15/0]₆ kompozitinin yük-çökme eğrisinde maksimum yük değeri civarında geniş olması ve çökmenin fazla olmasından dolayı fazla enerji absorbe etme kapasitesine sahip olduğunu göstermiştir. Bununla birlikte [90/0]₆ kompozitinin maksimum yük değeri en yüksek olmasına karşın çökme değerinin en küçük olmasının sonucu olarak en düşük enerji absorbe etme kapasitesine sahip olduğu görülmüştür.In this study, the stacking sequence effects on impact behavior of glass-epoxy composite laminates have been investigated. Three different laminated composites designated as [90/0]₆, [30/0]₆ and [15/0]₆ were manufactured with the same fiber volume fraction and layer numbers. They were then cut into 100mm x 100mm specimens for impact testing. The low velocity impact tests were performed on the specimens by using a DYNATUP GRC 8200 drop weight testing machine. The impact energy was gradually increased for consecutive tests until perforation took place. The instrumented impact test machine gives the time versus load, velocity, deflection and absorbed energy histories. Energy profiling method was used showing the relationship between impact energy and absorbed energy. Results show that the [15/0]₆ composite load-deflection curve has a large plateau around the peak force and highest deflection value, resulting in the highest perforation threshold. However, the [90/0]₆ composite has the highest peak force but lowest deflection value, resulting in the lowest energy absorption capacity for perforation

Tabakali Kompozit Plaklarda Eliptik Süreksizlik Bölgesinin Kritik Burkulma Yükü Üzerine Etkisi

Konferans Bildirisi -- Teorik ve Uygulamalı Mekanik Türk Milli Komitesi, 2008Conference Paper -- Theoretical and Applied Mechanical Turkish National Committee, 2008Bu çalışmada, tabakalar arasında meydana gelen eliptik süreksizlik bölgesinin (delaminasyon) tabakalı kompozit plakların burkulma davranışları üzerine etkisi deneysel ve nümerik olarak incelenmiştir. Deneysel çalışmalarda kullanılmak üzere, 100x140x2.5 mm boyutlarında ve [(0/90)3]s takviye açısına sahip cam lifi-epoksi kompozit malzemeler üretilmiştir. Delaminasyonun kompozit malzemenin tam ortasında olduğu kabul edilmiştir. Yükleme yönünde ve yükleme yönüne dik olmak üzere iki şekilde delaminasyon tasarlanmış ve dikey delaminasyon için a=30 mm b=75 mm, yatay delaminasyon için ise a=75 mm b=30 mm boyutları seçilmiştir. Burada a yükleme eksenine göre delaminasyonun genişliğini b ise uzunluğunu ifade etmektedir. Üretimi yapılan eliptik delaminasyonlu tabakalı kompozit plaklar, iki kenarı ankastre diğer iki kenarı serbest sınır şartı kullanılarak burkulma deneyine tabi tutulmuşlardır. Nümerik çalışmalarda ise, eliptik delaminasyona sahip üç boyutlu sonlu elemanlar modeli ANSYS 10.0 paket programı vasıtası ile oluşturulmuştur. Nümerik çalışmalarda öncelikle, deneyleri yapılan numunelerin kritik burkulma yükü değerleri sonlu elemanlar yöntemi ile elde edilen kritik burkulma yükü değerleri ile karşılaştırılmış ve sonuçlar arasında iyi bir uyum olduğu tespit edilmiştir. Daha sonra, delaminasyonun kritik burkulma yükü üzerindeki boyutsal etkisini incelemek için sadece sonlu elemanlar yöntemi kullanılmış ve farklı eliptik delaminasyon boyutlarına sahip üç boyutlu sonlu elemanlar modelleri oluşturulmuştur. Bütün bu deneysel ve nümerik çalışmaların sonucunda, kritik burkulma yükünün delaminasyonun artması ile azaldığı, dikey eliptik delaminasyonlarda bu azalmanın daha fazla olduğu tespit edilmiştir.In this study, effect of elliptic delamination occurred among the layers on buckling behavior of laminated composite plates has been investigated experimentally and numerically. For the experimental studies, glass-epoxy composite materials having 100x140x2.5 mm dimensions and [(0/90)3]s fiber orientation have been produced. It has been assumed that the delamination is at just the middle of the composite material. Two delamination types, such as in the parallel and perpendicular to load line, have been planned and then the dimensions have been selected 108 a=30 mm b=75 mm and a=75 mm b=30 mm, for the vertical delamination and the horizontal delamination, respectively. Here, a expresses to width of the delamination and b expresses to height of the delamination according to the load axis. The produced laminated composite plates having elliptic delamination have been subjected to buckling test using two edges clamped and other two edges free boundary conditions. In the numerical studies, three dimensional finite element models having elliptic delamination have been designed with the assistance of ANSYS 10.0 finite element program. Firstly, experimental critical buckling load values of the specimens have been compared with its values obtained with finite element methods and it has been determined that there is a good harmony between experimental and finite element results. Then, the finite element method has been used to investigate the dimensional effect of the delamination on the critical buckling load and three dimensional finite element models having different elliptic delamination dimensions have been constituted. In the end of all of these experimental and numerical studies, it has been established that the critical buckling load decreases when the delamination dimension increases and this decrease is too much for vertical elliptic delaminations

A case of heart failure mimicking COVID-19 pneumonia: The role of clinical and chest computed tomography findings in the differential diagnosis

Acute heart failure (HF) is one of the most common cardiac emergencies. Pulmonary edema caused by HF may mimic an exudative disease on chest computed tomography scans. Coronavirus disease 2019 (COVID-19) emerged in China in December 2019 and quickly spread around the world. During this pandemic period, the need to exclude the possibility of COVID-19 pneumonia in patients with acute dyspnea may cause a delay in the diagnosis and treatment of patients with acutely decompensated HF who have similar symptoms. This case report describes a diabetic patient admitted with dyspnea one week after she suffered an acute myocardial infarction. The objective of this report is to draw attention to the differential diagnosis of HF and COVID-19 pneumonia

The Effects of Steroid Therapy on Bone and Eyes in Children with Nephrotic Syndrome

Objective: The aim of this study was to evaluate complications of long-term steroid usage on the eyes and bone metabolism, which can be detected at early stage, and to encourage the necessary precautions. Methods: This retrospective study was performed with data of patients who took steroid therapy for nephrotic syndrome and were followed up between June 2006-May 2011 at Necmettin Erbakan University. Results: Fifty-six patients were included in this study. The mean age of the patients was 4.22.3 years. The patients were examined in 3 groups according to steroid therapy. Group 1 was defined as patients who had not received steroids in the past year and who were in the remission stage, Group 2 comprised patients who had received steroids in the last year and who were in the remission stage, and Group 3 was made up of patients who were in the active nephrotic period and had received steroids. In terms of biochemical parameters (serum urea, creatinine, calcium, phosphorus, magnesium, alkaline phosphatase, parathyroid hormone, osteocalcin, vitamin D, triglycerides), there was no statistically significant difference between the 3 groups. Group 3 had a higher ratio of calcium/creatinine and protein/creatinine in spot urine than Groups 1 and 2. Of 56 patients, 40 patients had eye examinations. There was no statistically significant difference determined in terms of side effects of steroid treatment. Conclusion: Pediatricians should be very careful while following up the children who use steroids at a young age due to the possibility of cataract development and side effects on bone metabolism

Effects of balloon pulmonary angioplasty procedure on electrocardiographic parameters in patients with chronic thromboembolic pulmonary hypertension

Aim: The aim of the present study was to evaluate the value of electrocardiography (ECG) in predicting post-operative hemodynamic improvement in patients with chronic thromboembolic pulmonary hypertension (CTEPH) undergoing balloon pulmonary angioplasty (BPA).Material and methods: A total of 32 patients were included in the study. During ECG analysis, parameters that have been suggested to be related to right ventricular hypertrophy and/or dilatation were evaluated. The sig-nificance of the change in each parameter obtained at the pre-BPA visit and at the scheduled control visit 6 months after BPA was tested. In addition to ECG analysis, data related to right heart catheterization (RHC) and echocardiography, B-type natriuretic peptide (BNP) levels and World Health Organization (WHO) functional classifications of all patients were also recorded. The relationship between the amount of possible change in ECG parameters and the amount of possible change in hemodynamic parameters was investigated.Results: The Daniel score, which has been suggested to have prognostic value in acute pulmonary embolism, decreased from 8.22 +/- 5.68 to 6.56 +/- 5.55 after the BPA procedure (p: 0.035). Among all parameters studied, only T wave height (V2 t) in V2 derivation changed significantly from-0.77 +/- 2.39 to 1.27 +/- 2.58 mm (p: 0.036). The amount of change in V2 T was found to significantly correlate with the amount of change in systolic right ventricular pressure, mean pulmonary artery pressure, pulmonary vascular resistance, and systemic vascular resistance.Conclusion: Postprocedural T wave changes in lead V2 might serve as a marker of hemodynamic improvement in patients with CTEPH who undergo BPA

Prevalence of Coronary Artery to Pulmonary Artery Collaterals in Patients with Chronic Thromboembolic Pulmonary Hypertension: Retrospective Analysis from a Single Center

Background Our aim was to determine the prevalence of coronary artery-pulmonary artery collaterals in patients with chronic thromboembolic pulmonary hypertension (CTEPH) by retrospectively evaluating coronary angiograms of eligible consecutive patients who had undergone pulmonary endarterectomy (PEA). We also aimed to evaluate predictors and potential clinical associates of these collaterals. Methods Coronary angiograms of 83 consecutive CTEPH patients who had undergone coronary angiography before PEA operation between January 1, 2012 and June 1, 2015 were retrospectively evaluated for presence of coronary artery-pulmonary artery collaterals. Medical records of all patients were also retrospectively reviewed for demographic information, cardiovascular risk factors, preoperative right heart catheterization reports, operation reports, and follow-up data. Data of CTEPH patients with coronary artery-pulmonary artery collaterals were compared with data of CTEPH patients without such collaterals. Results There were 15 patients (18.1%) with definite and 4 patients (4.8%) with probable coronary artery-pulmonary artery collaterals among the study population. CTEPH patients with collaterals had higher preoperative pulmonary artery pressures, higher pulmonary vascular resistance (PVR) and lower cardiac index values compared with CTEPH patients without collaterals. However, CTEPH patients with collaterals displayed higher amount of reduction in PVR after PEA compared with patients without collaterals. There were no significant differences between groups regarding incidence of reperfusion injury or mortality. Conclusion Prevalence of coronary artery-pulmonary artery collaterals seems to be increased in our CTEPH patients compared with the general population. The presence of coronary artery-pulmonary artery collaterals is often combined with proximal disease with the possibility of increased reduction of PVR after PEA operation

The effects of iron replacement on functional capacity in patients with group 1 and group 4 pulmonary hypertension

Objective: Abnormal iron handling complicates pulmonary hypertension and causes functional limitation and poor outcomes. Although preliminary results in group 1 pulmonary hypertension patients support the use of iron replacement, whether this applies to other PH subgroups is not known