Comparison of in-plane compression of additively manufactured Ti6Al4V 2D auxetic structures: Lattice design, manufacturing speed, and failure mode

Eren Z., Gokcekaya O., Balkan D., et al. Comparison of in-plane compression of additively manufactured Ti6Al4V 2D auxetic structures: Lattice design, manufacturing speed, and failure mode. Materials and Design 241, 112885 (2024); https://doi.org/10.1016/j.matdes.2024.112885.The metal-based 2D auxetic lattice structures hold the potential for multifunctional tasks in aerospace applications. However, the compression response of those manufactured by powder bed fusion process is underexplored. This study proposes a comprehensive comparison of in-plane quasi-static compression performance of 2D auxetic lattice structures, utilizing three designs (anti-tetrachiral (ATC), double arrow-headed (DAH), and tree-like re-entrant (TLR)), manufactured with stiff Ti6Al4V by the electron beam powder bed fusion process (PBF-EB) with various manufacturing speeds. The results revealed unique failure patterns and superior energy absorptions among 2D lattice structures in the literature. TLR design enhanced energy absorption by overcoming failures between DAH columns and exhibited the lowest standard deviations in specific energy absorption (SEA) values (9.75 %–12.62 %). Besides, Kernel average misorientation (KAM) values followed the order of DAH, TLR, and ATC, and inversely correlated with SEA values. ATC structures with the lowest KAM outperformed DAH and TLR by 47.5 % and 6.44 %, respectively. Scan speed variations affected SEA and porosity values differently for each lattice design while exhibiting similar microstructure characteristics. The findings in this study propose a significant contribution to the development of aerospace sandwich structures where harsh environments exist and employment of 2D topologies are required

A NUMERICAL MODEL FOR BALLISTIC IMPACT RESPONSE OF COMPOSITE ARMORS

In this study, we present a numerical model to simulate the ballistic impact of a rigid right circular cylinder (RCC) projectile into a woven fabric target. The numerical solution of transverse ballistic impact on a laminar biaxial fabric is obtained using a forward finite-difference method. The ballistic impact analysis for different materials of targets made of aramid and polyethylene fibers are simulated to investigate the effect of fabric material on the ballistic resistance. Numerical simulations are performed to reveal the influences of crimp factor and fabric material on the ballistic performance of woven fabrics. Various cases have been presented showing the variations of yarn strains, yarn velocities, and yarn displacements over time

Accuracy of Strain Solution of a Laminated Composite Plate via Galerkin's Method

Abstract This paper deals with the detailed analysis and discussion of nonlinear static analysis of a laminated composite plate subjected to uniform pressure load. Governing equations of the plate are derived by the use of the virtual work principle. The geometric nonlinearity effects are taken into account with the von Kármán large deflection theory of thin plates. Approximate solutions for a simply supported plate are assumed for the plate domain. The single term approximation functions are selected by considering the nonlinear static deformations of plate. The solution is obtained using the Newmark method in MATLAB software. The plate is also modeled and analyzed using ANSYS software using SHELL91 elements. The variation of membrane, linear and nonlinear bending terms are obtained along a characteristic line on the plate and the numerical and finite element results are compared. The results are discussed in detail considering the nonlinear static behavior of the laminated composite plate and the main reasons of discrepancies are discussed. Dynamic behavior of the plate is explained considering the nonlinear static behavior.</jats:p

Anlık basınç yüküne ve balistik çarpmaya dayanıklı, takviye elemanlarla güçlendirilmiş ince cidarlı kompozit sandviç plakların çok-hedefli genetik algoritmalar ile optimal tasarımı ve deneysel doğrulaması

TÜBİTAK MAG Proje15.07.2017Analitik ve sayısal hesaplamaların yapılabilmesi için İTÜ Uçak ve Uzay Bilimleri FakültesiKompozit yapı laboratuvarında bulunan MTS (Universal test makinası) cihazı kullanılarak,proje kapsamında temin edilen kompozit malzemelerin mekanik özellikleri belirlenecektir.Daha sonra, anlık basınç yükü deneyleri gerçekleştirilecek ve literatürde var olan basınçfonksiyonlarına kıyasla daha genel analitik bir yaklaşım ortaya konulacaktır. Plağın çarpmadayanımının incelenmesinde LS-DYNA ticari sonlu elemanlar yazılımı kullanılacaktır. Anlıkbasınç yükü altındaki plak davranışı ise ANSYS sonlu elemanlar yazılımı ve yazılacak olan birMATHEMATICA kodu ile incelenecektir. Yapılan hesaplamalar ve analizler sonucundakatmanlı sandviç kompozit plağın bir ön yapısal tasarımı gerçekleştirilecektir. Projedekiaraştırmacıların önceki çalışmaları ve literatürdeki diğer çalışmalar anlık basınç yükünün plaküzerindeki değişiminin ve zamanla olan değişiminin seçilen basınç fonksiyonu tarafından çokiyi temsil etmesi gerektiğini ortaya koymaktadır. Dolayısıyla optimizasyon çalışmalarınageçmeden önce anlık basınç yükü deneyleri gerçekleştirilecek ve literatürde var olan basınçfonksiyonlarına kıyasla daha genel analitik bir basınç fonksiyonu yaklaşımı ortayakonulacaktır. Ayrıca balistik plağın anlık basınç yükü altındaki davranışı testlerle doğrulanmışolacaktır.Anlık basınç yükü, MTS ve çarpma deneylerinden elde edilecek veriler kullanılarak,MATHEMATICA ortamında geliştirilecek geometrik doğrusal olmayan kodun, yinegeliştirilecek olan çok hedefli genetik algoritma koduna entegre edilmesi sonucunda optimalsandviç plak tasarımları elde edilecektir. Son olarak, optimal tasarımlı plaklar üzerinde anlıkbasınç yükü ve balistik çarpma testleri gerçekleştirilecek; plakların bu şiddetli etkileredayanımları incelenecektir. Ayrıca, sayısal çözücünün doğruluğu ve hassasiyeti, ANSYS ticarisonlu elemanlar yazılımı sonuçları ile kıyaslanacaktıThin-walled composite sandwich plates have been widely used in civil and militaryaerospace industry, ships, high technology space vehicles and defense industry as loadcarrying structural components for a long period of time. In addition, these structures findwidespread application in rockets, helicopter body and cargo doors, rotor blades, satellitesolar panels and structural components, reflector antennas and body parts, ship bodyexterior parts and ceilings, cabin compartments and air shields. Trains, trams, sailing speed-boats, racing cars are also among vehicles that sandwich composites are used in. Becausethe conventional metallic armors are relatively heavy, composite sandwich materials findincreasing application in armor components of military vehicles due to their low density, highmodulus of elasticity, minimum thermal expansion properties.Sandwich structures, are preferred to the conventional materials such as metallic alloys dueto their high stiffness/weight ratio, high load carrying capacity, fatigue resistance, corrosionresistance, fracture toughness, thermal and acoustic isolation and resistance to multi-axialcompression loading properties. In addition, it is possible to obtain optimal designs by thevariation of parameters such as stacking sequence, fiber orientation of composite layers andlayer thicknesses of sandwich structures.In order to reach the desired optimal design, how the parameters such as the choice ofmaterials of plate layers, the fiber orientations of composite materials, choice of epoxy, layerthicknesses and number of layers should be was investigated. For this purpose, a stochasticevolutionary optimization algorithm, the genetic algorithms, was utilized. The optimalgeometry and stacking sequence obtained by numerical analyses was verified byexperimentation on a realistic model. As a result of these studies, the outcomes such asutility models were obtained.Sandwich composite structures, especially the ones used in military applications, canexperience intense effects such as blast loads and ballistic impact loads. The blast loadsthat effect the aerospace structures emerge from events such as atmospheric gusts andsonic booms. Sonic boom occurs in supersonic flight of aircrafts and missiles duringexceeding the speed of sound. Other events that result in blast loadings to the structureemerge from close distance thermo-chemical or thermo-nuclear explosions. On the otherhand, the impact loads arise from the ballistic effects of high speed structural particles thatresult from different caliber ammos, fragmentation munitions or bombs and close distanceexplosions or hitting shrapnel.In the project, optimal desingn and testing of thin-walled stiffened composite sandwichplates, which are resistant to blast loads and ballistic impact loads, by using multi-objectivegenetic algorithms was performed. The laminated composite sandwich plates which have some particle impact resistant layers were designed. In addition, the excessive displacementand strains that arise from blast loads were avoided by the use of stiffeners.In the design stage of the project, the MTS (universal test machine) in the CompositeStructures Lab. In İTÜ Faculty of Aeronautics and Astronautics were utilized to obtain themechanical properties of composite materials in order to carry out the analytical andnumerical analyses. For the impact resistance analysis of the plate, LS-DYNA commercialfinite element software were used. On the other hand, the response of plate under blast loadwas analyzed by ANSYS finite element software and a code was developed by usingMATHEMATICA. A preliminary optimal design of laminated composite sandwich plate wasobtained as a result of the computations and the analyses. In addition, the response ofballistic plate under blast load was verified against experimentation. The strength andbehavior of the plate under ballistic impact were confirmed by the experiments (NIJStandard-0101.06) that will be carried out in the ballistic impact test laboratory of Uyar Grupthat has been established by the support of TUBITAK.The data obtained from blast load, MTS and impact tests, and the code developed inMATHEMATICA environment was integrated into the developed multi-objective geneticalgorithm optimization code and optimal sandwich plate designs were obtained. Finally, blastand ballistic impact tests were carried out on the plates and the resistance of these platesto these strong effects were investigated. In addition, the accuracy and precision of thenumerical solution were compared to the ANSYS commercial finite element software.Optimal designs for the plates, which were obtained from the theoretical analyses weremanufactured basically from Kevlar, glass and carbon fiber fabrics of differently woven typesand different thicknesses by using polymer based epoxy resin.In order to determine the blast load, the “blast load test assembly” designed by Prof. Dr.Zahit Mecitoğlu and his team through the TUBITAK project with ID: 106M450 that exists inthe inventory of ITU Faculty of Aeronautics and Astronautics was used. The pressuredistribution over the plate, resulting from the explosion, was obtained by miniature pressuresensors that are placed on spesific points. Straingages were used to obtain the time variationof strain on spesific points over the sandwich plate.As a result, a multi-objective multi-parameter genetic algorithm optimization code based onGalerkin solver was developed to determine the stacking sequences, orientation angles,layer thicknesses, stiffener dimensions and locations to obtain light composite sandwichstructures resistant to impact and blast loads. This program that was developed, was alsoprogrammed in a parametric fashion for quick integration to material variability and differentblast and impact scenarios

Ozon, Kantaron, Kekik ve Gül Yağlarının Bazı Patojenik Mikroorganizmalara Karşı Antimikrobiyal Aktivitelerinin Belirlenmesi

AMAÇ: Antibiyotiklere dirençli bakterilerin sayısındaki artış, tedavi basamağında alternatif bitkisel ürünlerin kullanılmasına olan ilginin dramatik bir şekilde artışına da sebep olmuştur. Bu çalışmadaki amacımız, ticari olarak elde ettiğimiz ozon, gül, kantaron ve kekik yağlarının klinik olarak önemli bakteri ve mantarlara karşı olan antimikrobiyal etkilerinin gösterilmesidir.YÖNTEM: Ozon, gül, kantaron ve kekik yağlarının Escherichia coli, Proteusvulgaris, Proteusmirabilis, Stenotrophomonas maltophilia, Enterococcus spp., Acinetobacter baumannii, Streptococcus spp., Citrobacter freundii, Staphylococcus aureus ve Candida albicans isimli mikroorganizmalara karşı antimikrobiyal aktiviteleri test edilmiştir; Disk difüzyon metodu (Kirby-Bauer) kullanılmış ve oluşan zon çapları ölçülerek anti-mikrobiyal etki ortaya konulmuştur.BULGULAR: Sadece birkaç antibiyotiğe karşı duyarlı olan Stenotrophomonas maltophilia başta olmak üzere birçok bakteri, kekik yağına karşı duyarlı olarak tespit edilmiştir. Gram pozitif bakterilerin ve Kandida suşlarının kekik yağına, Gram negatif bakterilerden daha dirençli oldukları görülmüştür. Bunun yanı sıra Escherichia coli ve Staphylococcus aureus suşlarının ise gül yağına karşı duyarlı oldukları tespit edilmiştir. Bazı herbal yağların ve ozon yağının muhtemel antimikrobiyal etkileri bu çalışma ile ortaya koyulmaya çalışılmıştır.SONUÇ: Kekik yağının antimikrobiyal etkinliği ozon, gül ve kantaron yağından oldukça yüksek düzeyde tespit edilmiştir. Sonuç olarak başta kekik yağı olmak üzere bitkisel uçucu yağlar, antimikrobiyal aktivitelerinden dolayı tıbbi ilaç uygulamalarına iyi bir alternatif olabilme potansiyeli taşımaktadır.AIM: The increase in antibiotic-resistant bacteria has dramatically revived the interest in plant products as alternative antimicrobial agents to prevent the efficiency of pathogenic microorganisms. Our aim in this study is to show the antimicrobial activities of commercially obtained thyme, rose, centaury and ozone oils against the clinically important bacteria and yeasts.METHODS: The antimicrobial activity of the thyme, rose, ozone and centaury oils were tested against Escherichia coli, Proteus vulgaris, Proteus mirabilis, Stenotrophomonas maltophilia, Enterococcus spp., Acinetobacter baumannii, Streptococcus spp., Citrobacter freundii, Staphylococcus aureus and Candida albicans strains. Disc diffusion method (Kirby-Bauer) was used to show the antimicrobial activity by measuring the zone diameters.RESULTS: Most bacteria including Stenotrophomonas maltophilia (which is only sensitive to a few antibiotics) are found sensitive to the thyme oil. Gram positive bacteria and yeasts found more resistant than the Gram negative bacteria to the thyme oil. Escherichia coli and Staphylococcus aureus found sensitive to the rose oil. The anti-microbial activities of some herbal oils and ozone oil and rose oil were tried to be shown.CONCLUSION: The thyme oil has a stronger antimicrobial activity than the rose, ozone and centaury oils. Herbal essential oils, especially thyme oil, are candidates to be alternatives in medical applications due to their anti-microbial effects

Miliary tuberculosis Epidemiologicaland clinical analysis of large-case series from moderate to low tuberculosis endemic Country

WOS: 000394253800016PubMed ID: 28151863The aim of this study was to determine the clinical features, and outcome of the patients with miliary tuberculosis (TB). We retrospectively evaluated 263 patients (142 male, 121 female, mean age: 44 years, range: 16-89 years) with miliary TB. Criteria for the diagnosis of miliary TB were at least one of the followings in the presence of clinical presentation suggestive of miliary TB such as prolonged fever, night sweats, anorexia, weight loss: radiologic criterion and pathological criterion and/or microbiological criterion; pathological criterion and/or microbiological criterion. The miliary pattern was seen in 88% of the patients. Predisposing factors were found in 41% of the patients. Most frequent clinical features and laboratory findings were fever (100%), fatigue (91%), anorexia (85%), weight loss (66%), hepatomegaly (20%), splenomegaly (19%), choroid tubercules (8%), anemia (86%), pancytopenia (12%), and accelerated erythrocyte sedimentation rate (89%). Tuberculin skin test was positive in 29% of cases. Fifty percent of the patients met the criteria for fever of unknown origin. Acid-fast bacilli were demonstrated in 41% of patients (81/195), and cultures for Mycobacterium tuberculosis were positive in 51% (148/292) of tested specimens (predominantly sputum, CSF, and bronchial lavage). Blood cultures were positive in 20% (19/97). Granulomas in tissue samples of liver, lung, and bone marrow were present in 100% (21/21), 95% (18/19), and 82% (23/28), respectively. A total of 223 patients (85%) were given a quadruple anti-TB treatment. Forty-four (17%) patients died within 1 year after diagnosis established. Age, serum albumin, presence of military pattern, presence of mental changes, and hemoglobin concentration were found as independent predictors of mortality. Fever resolved within first 21 days in the majority (90%) of the cases. Miliary infiltrates on chest X-ray should raise the possibility of miliary TB especially in countries where TB is endemic. Although biopsy of the lungs and liver may have higher yield rate of organ involvement histopathologicaly, less invasive procedures including a bone marrow biopsy and blood cultures should be preferred owing to low complication rates

Impact of the HEAD-US Scoring System for Observing the Protective Effect of Prophylaxis in Hemophilia Patients: A Prospective, Multicenter, Observational Study

Objective: This study aimed to observe the preventive effect of prophylactic treatment on joint health in people with hemophilia (PwH) and to investigate the importance of integration of ultrasonographic examination into clinical and radiological evaluation of the joints