Effects of material properties on anelastic behavior

Metallerin anelastik davranışı, metroloji biliminin özellikle kütle, basınç ve boyutsal alanlarında, yerçekimiyle ilgili deneylerde, yüksek hassasiyet gerektiren cihaz ve sensör elemanlarının tasarımıyla ilgili bir malzeme özelliğidir. Sensöre uygulanan yükün genliği ve onun uygulanma sıklığı cihazın ölçüm belirsizliğini etkiler. Metallerin anelastiklik özelliği, malzemenin iç sürtünmesinin kaynağı olarak değerlendirilmiş ve sönümlemenin, uygulanan yükün hızıyla orantılı olarak değiştiği modellenmiştir. Bazı mekanik modeller, metallerde uygulanan yükün izi olarak sönümlemeyi tanımlamak amacıyla kullanılmıştır. Gecikmiş cevabın ve sönümlemenin tanımlanmasında elastiklik modülü, frekans alanında karmaşık bir sayı olarak ele alınabilmektedir. Bu sayının gerçel ve sanal kısımları kuvvet ile ortaya çıkan şekil değişimleri arasındaki fazı ve faz kaymasını göstermektedir. Bu değerlerin oranı malzemenin modül kaybını vermektedir. Bu çalışmada anelastiklik ölçümü için, esnek elemanı bakır berilyum (Cu-Be) malzemeden imal edilmiş yeni bir ters sarkaç tasarlanmış ve performansının temel sınırları belirlenmiştir. Yeni sarkacın esnek elemanı dikey pozisyonda basma değil çekme gerilmesine maruz kalmaktadır. Bir çok esnek eleman çekme gerilmesi altında çalışmakta olup, basma gerilmesi uygulamalarında performansları kötüdür. Esnek elemanın çekme gerilmesine maruz kalabilmesi için, bağlandığı sarkaç koluyla yeni bir şekilde monte edilmiştir. Sarkacın kalite faktörü, üstel bir fonksiyon olarak azalan salınımların CCD (Charge-Coupled Device: Işığa duyarlı hassas bir cihaz) kamera ile, 2 s ile 30 s arasındaki periyotlarda tespit edilmesiyle elde edilen veriler kullanılarak hesaplanmıştır. Farklı içyapı özellikleri için modül kayıpları tespit edilip gerilmeye göre bu kayıpların miktarı araştırılmıştır.Anahtar Kelimeler: Anelastiklik, iç sürtünme, ters sarkaç, esnek eleman, bakır berilyum alaşımı.A new inverted pendulum with a copper-beryllium (Cu-Be) flexure element is designed and its performance is determined by detecting the respective angular changes of the pendulum using a ccd camera within an oscillation period range of 2 s and 30 s. A new arrangement was made by clamping of the flexure element and pendulum rod to avoid subjecting them to compression stress due to the weight of the overall pendulum mass on the flexure. This new form of inverted pendulum employs a flexure specially clamped to the pendulum rod to provide tension deformation under the weight of mass and could be used for dynamic testing of highly sensitive flexure elements. The quality factors of the pendulum were determined with respect to flexure elements by measuring free oscillations decaying exponentially. The results showed that the new inverted pendulum with a different connection between the flexure element and pendulum rod can be used to measure the anelasticity of materials and to test elements under bending deformation in a dynamic way. Many experimental apparatuses have been designed and used to investigate the anelastic behavior of materials. These are divided into three main types, in terms of the frequency of use: subresonance, resonance and supraresonance methods. The resonance method is particularly useful for the dynamic testing of the flexure in a pendulum. There are many types of pendulum apparatus and various clamping orientations are used for the measurement of anelasticity. The most frequently used type of pendulum to determine anelastic phenomena in materials is the torsion pendulum consisting basically of a mass as an inertia member suspended from a wire specimen that is subjected to a twisting deformation. The standard pendulum is used with various modifications. The simple pendulum is known as the basic arrangement of the standard pendulum, the specimen is under tension stress and subjected to bending stress but low frequencies cannot be easily generated because frequencies depend on the length of pendulum rod. The frequency changes in inverse proportion to the square root of the rod length so that periods of more than a few seconds require a very long pendulum rod, which is not useful for experimental purposes. An inverted pendulum is another version of the standard pendulum known as the "swinging type". It consists of a rod on the top of which a suspension mass placed. The rod is supported by a spring attached to its bottom in order to hold the pendulum rod vertically. The spring comes under compression stress and is subjected to a twisting deformation due to the suspended mass. The oscillation of the pendulum rod depends mainly on torque acting on the spring element and can easily vary over a wide band. Some researchers have used various types of combined and torsional pendulum apparatuses to determine the anelasticity of copper-beryllium flexures, for the purpose of designing a highly sensitive mass comparator. Different types of flexures were used as pivot elements. Some measurements were carried out by using an inverted pendulum with an instant steel flexure element which was under compression and subjected to bending deformation, and it has been shown that the inverted pendulum was a valuable tool for the study of internal friction, that it could be used to probe anelasticity within a wide band of frequencies, and that it allowed direct tests of the features of anelastic behavior that were hard to perform in other ways. An inverted pendulum is a valuable instrument for precision measurement, gravitational physics, and also for measuring the anelasticity of , which is one of the mechanical properties connected to designing highly accurate measurement devices and sensors used in the mass, force, pressure and dimensional fields of metrology. The frequency of an inverted pendulum can easily be changed over a wide band by either adding mass on top of the pendulum or by changing the centre of gravity of the suspended mass. This enables dynamic testing of metals, especially anelasticity in the flexure elements of the pendulum. This study covers the attempts of searching the relationships between microstructural material properties of flexure elements and their respective anelastic behavior by using an inverted pendulum.Keywords: Anelasticity, internal friction, inverted pendulum, flexure element, copper beryllium alloy

Does the Bone Cement Affect Miniscrew Stability?

Objective:The purpose of this study was to determine whether bone cement increased the resistance of miniscrews against pull-out and shear forces.Materials and Method:Sixty commercially available miniscrews were placed into bovine bone samples (one each) at a 90° angle, using a custom-made orientation jig and controlling torque (30 N-cm) and rotation (20 rpm) with a rechargeable screwdriver. The miniscrews were inserted using three different methods: self-drilling, predrilling, and predrilling with bone cement application. Pull-out strengths and shear tests were performed using a universal testing machine.Results:Nonparametric Kruskal-Wallis tests were used for comparisons between groups, and Bonferroni-adjusted Mann-Whitney U tests were used to detect different group(s) (α/3=0.016). There was a statistically significant difference between the pull-out strengths of the groups (p<0.01). The self-drilling group had a significantly lower pull-out strength at failure than the other groups (p<0.016). The pullout strengths of the miniscrews placed with bone cement had a significantly higher pull-out strength than the predrilling group. In shear tests, there was no statistically significant difference among the groups.Conclusion:This study is the first report demonstrating the effects of bone cement on stability and resistance to failure at the bone-miniscrew interface. These results show that the use of miniscrews with bone cement is a promising method that may extend the limits of force application

Ostenitik paslanmaz çelik ortopedik implantların iyon nitrürlemeyle yorulma dayanımlarının artırılması

Tez (Doktora) -- İstanbul Teknik Üniversitesi, Fen Bilimleri Enstitüsü, 1998Thesis (Ph.D.) -- İstanbul Technical University, Institute of Science and Technology, 1998Soğuk şekil değiştirmiş, AISI 316L ostenitik paslanmaz çelikler yıllardır, çeşitli dizaynlarla internal tesbit araçlarının yapımında başarıyla kullanılmaktadır. Metalik cerrahi implant malzemeleri insan vücudunun ılık ve tuzlu ortamında korozyona maruz kalırlar. Kırık kemiklerin tesbitinde kullanılan ortopedik kemik tesbit plakları, invivo koşullarda değişken ve bileşik eksenel, eğme ve burulma şeklindeki yüklere maruz kalırlar ve buna bağlı olarak istenmeyen implant hasarları oluşabilmektedir. Yorulma, implant hasarları içinde en sık karşılaşılan hasar türüdür. Korozyon gibi yorulma hasan da malzeme yüzeyinden ya da yüzeyle ilgili olaylardan kaynaklandığından, ortopedik implantlann yüzeylerinin ileri yüzey işlemleri kullanılarak modifiye edilmesi ile implant hasarlarının azaltılabileceği açıktır. Son yıllarda, paslanmaz çeliklerin iyon nitrürleme ile yüzeylerinin sertleştiril-mesi giderek artan bir önem kazanmakta ve bu işlemden sonra malzemenin yorulma, aşınma ve korozyona karşı direncinin birlikte artırılması umulmaktadır. Bazı çalışmalarda belli işlem koşullan altında yapılan iyon nitrürleme ile bunun mümkün olabileceği gösterilmiştir. Bu çalışmada iyon nitrürleme ostenitik paslanmaz çelikten cerrahi implant malzemelerine uygulanarak, yorulma dayanımlannda önemli artış yapılabileceğinin gösterilmesi amaçlanmıştır. Sonlu elemanlar yöntemiyle plakta oluşan gerilme ve şekil değişimleri belirlenmiştir. İyon nitrürlemeden sonra yapılan yorulma deneylerinde, pratikte tesbit plaklannın çoğunlukla hasara uğradığı, uzun ömürlü yorulma koşullan altında, yorulma ömrünün en az 10 kat artınlabildiği, iyon nitrürlem? ile ostenitik paslanmaz çelikten imal edilen kemik tesbit plaklannın yorulma dayanımlannın %60 oranında artınlabileceği görülmüştür. A "biomaterial" has been defined as any substance or combination of substances, syntetic or natural in origin, that can be used for any period of time, as a whole or as a part of a system that treats augments or replaces any tissue, organ or function of the body. Biomaterials may be utilized in variety of ways with in the skeletomuscular system. In particular, biomaterials have been used in artificial joints bone bonding, fracture fixation, percutaneus leads, catheters, absorbable sutures, dental materials and so. The mechanical requirement of artroplasty most often call for the use of stainless steel and a variety of alloys, including nickel, cobalt and titanium. Ceramic and same plastic materials have also been used in certain bone and joint replacement. Orthopaedic implants are artificial mechanical devices that are mounted to the skeletal system of the human body for various purposes, such as supporting bones, replacing bones or joints and reattaching tendons or ligaments. The implant devices are unique in that they exposed to living cells, tissues and biological fluids, which are not only dynamic but also a hostile environment. These surgical implants are usualy made of one of the three major types of metallic materials: austenitic stainless steel, cobalt-chromium alloys or titanium and its alloys. The design of the implant is dictated by the anotomy and physilogy of the skeletal structures of the human body. Every fracture of a bone in human skeletal systems leads to a complex tissue injury involving bone and surrounding soft tissues. Immediately after the fracture and during the repair phase, local circulatory disturbances and manifestations of local inflamation, as well as pain and reflex immobilization have been observed. These factors, lead to so called fracture disease. For healing of fracture disease, which usualy depends on the types of the failures of bones, immediately precise anotomical reduction (the complete matching of fracture surfaces) of bone parts is required. And this can be performed by appliying the internal or external fixation techniques or joint replacement. Osteosynthesis of suitable closed fractures of superficially located bones might be performed by transcutaneous stapling or direct bone stapling after small skin incisions by applications of high-strength steel staples. Depending on their function the implants are considered under two main categories, such as prostheses and fracture fixation implants. Internal fixation implants are preferred to provide temporary stabilization for closed fractures, whereas the prosthetic devices serve as joint replacement for a life time.DoktoraPh.D

In vitro effect of cavity disinfectants on the bond strength of dentin bonding systems

Objective: To evaluate the effect of two cavity disinfectants, a 2% chlorhexidine and a 1% benzalkonium chloride solution, on the shear and tensile bond strengths of dentin bonding systems to dentin. Method and materials: Superficial dentin was exposed from 84 freshly extracted human third molars. The teeth were randomly assigned to two main groups according to the bonding agent used, either One Step or Optibond Solo. Each dentin bonding system had six test groups (three for shear, three for tensile testing), and each test group had a control and two cavity disinfectant groups. In the control groups, dentin bonding systems were applied after etching the dentin, whereas in the cavity disinfectant groups, dentin was conditioned and treated for 20 seconds with the disinfectants before applying the dentin bonding systems. A hybrid resin composite then was applied to all treated samples. After storage in distilled water at 37degreesC for 24 hours, shear and tensile tests were performed. Data were analyzed using Kruskall-Wallis and Mann-Whitney U tests. Results: The mean shear and tensile bond strengths of One Step and Optibond Solo were not significantly different from each other, and the cavity disinfectants also had no significant effects on shear and tensile bond strength values versus the controls. Conclusion: The results indicate that the use of 2% chlorhexidine and 1% benzalkonium chloride solutions as cavity disinfectants after etching the dentin did not affect the shear and tensile bond strengths of One Step and Optibond Solo

Investigation of Microstructural Properties of Thermal Barrier Coating (TBC) System Consisting of YSZ Topcoat and NiCrAlY Bond Coat

Termal bariyer kaplamalar (TBC), endüstriyel gaz türbinlerinde ve hava araçlarının türbin motorlarının sabit ve hareketli parçalarında, esas işlevi gören malzemeyi sıcak gazların olumsuz etkilerinden korumak ve termal verimi artırmak amaçlarıyla kullanılmaktadırlar. Bir TBC sistemi tipik olarak; istenen amaca hizmet eden altlık malzemeden, ısıl yalıtım sağlayan seramik bir üst kaplamadan, altlık malzemeyi oksitlenmeye karşı koruyan ve üst kaplama ile altlık malzeme arasındaki termal uyumsuzluğu önleyen metalik bir bağ kaplamadan ve kaplama prosesiyle başlayıp servis koşullarında büyümeye devam eden bir oksit tabakasından oluşmaktadır. Bu çalışmada, ağırlıkça %8 oranında yitriya ile kararlı hale getirilmiş zirkonya (8YSZ; ZrO2-8Y2O3) içerikli üst kaplamalar APS (Atmosferik Plazma Sprey) yöntemiyle ve NiCrAlY içerikli metalik bağ kaplamalar HVOF (Yüksek Hız Oksi Yakıt) yöntemi kullanılarak üretilmiştir. TBC sisteminin mikroyapısal özellikleri, porozite oranları ve mikrosertlik ölçümleri sırasıyla, taramalı elektron mikroskobu (SEM), mikroyapı analiz yazılımı ve mikrosertlik test cihazları kullanılarak gerçekleştirilmiştir

The Evaluation of Pullout Tests of An Expandable Newly Designed Screw

Biomechanical evaluation of pullout forces of newly designed cortical screws with openable tips was done in the tibia bone of the young bulls. Newly designed expandable titanium 14 cortical screws with openable tips were inserted in fresh tibia bone. Of these screws, 7 were used as controls. The bones were fixed with polymethylmethacrylate after the insertion of the screws. Screw heads were attached to a custom device and prepared for pullout tests. The elastic modulus values (Newton/mm(2)), yield forces (Newton) and maximum forces (Newton) of expandable and control groups were assessed. The median of yield forces (Newton) of expandable cortical screw group was found to be statistically higher than that of normal group (P=0.025). The median of maximum forces of expandable cortical screw group was found to be significantly higher than that of normal group (P=0.003). In the comparison of paired groups, it was found that the pullout forces of expandable cortical screws were significantly superior to that of normal control group. In the light of these results, it was concluded that such kind of newly designed screws are able to contribute to fracture fixation in the future, allowing more bone contact without enlarging the diameter of the screw