No abstract

The friction and wear properties of pure poly-tetra-fluoro-ethylene (PTFE), 35% carbon filled poly-tetra-fluoro-ethylene (PTFEþ35%C), and 17% glass fiber-reinforced polytetra-fluoro-ethylene (PTFEþ17%GFR) sliding against stainless steel under dry sliding conditions were studied by using a pin-on-disc tribometer. The effect of applied pressure and sliding speed on tribological properties of the polymer-stainless steel combination under dry sliding conditions was investigated. Tests were carried out at sliding speeds of 0.32, 0.64, 0.96, 1.0, 1.5, and 2.0 m/s and under applied pressures of 0.17, 0.34, 0.68, 1.02, 1.76, 3.53, 5.30, and 7.07 MPa. Optical microscopy was utilized to examine the worn surfaces of pure PTFE and it's composite. The results indicated that, for pure PTFE, carbon-filled PTFE and glass fiber-reinforced PTFE composites are used in this investigation; the friction coefficient decreases with the increase in applied load values. The maximum reduction in wear rate was obtained by glass fiber-reinforced PTFE composite. The specific wear rate for pure PTFE, carbon filled PTFE composite, and glass fiber-reinforced PTFE composite were in the order of 10 À13 , 10 À14 , and 10 À15 m 2 /N, respectively. The wear mechanism include adhesive and abrasive processes.

Yapılarda ölü yükü azaltmak amacı ile hafif betondan yapılmış elemanlar kullanılmaktadır. Bu amaçla da hafif beton üretiminde doğal ve yapay olarak elde edilen diatomit, yüksek fırın cürufu, hızar talaşı, rende talaşı, pomza gibi çeşitli hafif agregalar kullanılmaktadır. Böylece betonun birim ağırlığını azaltmak, betona ses ve ısı yalıtım özelliği kazandırmak veya atık maddeleri değerlendirmek mümkün olmaktadır. Bu çalışma kapsamında, bölgesel olarak üretilen fındık hasadı sonrası arta kalan ve genellikle yakıt olarak kullanılan fındık kabuğu granüle edilmiş, belli karışım oranları baz alınarak üretilen betonun mekanik ve fiziksel özellikleri uygulama açısından tartışılmıştır. Çalışma kapsamında; kütlece agrega miktarının %0-5-10-15-20-25-30-35-40 ve 50 oranında fındık kabuğu katkılı beton numuneleri üretilmiştir. Üretilen betonların slump, birim ağırlık, 28., 90. ve 180. günlerdeki basınç dayanımı değerleri ölçülmüştür. Fındık kabuğu miktarı arttıkça birim ağırlık ve basınç dayanımında azalmalar oluşmuştur. Fındık kabuğunun %50 oranında kullanılmasıyla birim ağırlık şahit betona göre % 25 azalmıştır. Bu da bina yükünün %25 azalması demektir. Sonuç olarak; yapılan deneysel sonuçları incelendiğinde granüle edilmiş fındık kabuğu kullanılmasıyla da hafif beton üretilebileceği görülmüştür. Böylece bina yükünün hafifletilebileceği ve ülkemizde çok miktarda olan fındık kabuğunun değerlendirilmesiyle ülke ekonomisine katkı sağlayacağı belirlenmiştir.

Presence of alkali silica in aggregates that are used in concrete production causes formation of cracks and decrease of performance over time in concrete.The first damage caused by ASR in Turkey had been observed in certain highway bridges in Izmir locality in 1995. It was found that some aggregates in other regions of Turkey also have a character to cause ASR.The purpose of the study was to minimize potential alkali silica reaction expansion in concrete and mortars produced with the aggregates that are used in constructions in our region.Accelerated mortar bar test method was employed in the study. It was observed in experimental study that that the use of 20-25% fly ash, 25-35% blast furnace slag and 10% silica fume and metakaolin as mineral additive reduced ASR.According to optimization studies, it is appropriate to use 5-10% silica fume, 5% metakaolin, 10-15% blast furnace slag and 10-20% fly ash as mineral additive in optimum mixtures giving ideal expansion value.It was found that the use of 65% of cement together with 35% silica fume, metakaolin, blast furnace slag and fly ash in mineral additive combinations prevents ASR.

In engineering applications when materials start sliding against each other the problem of friction and wear appears. In the case of polymers the friction between them can be attributed to two main mechanisms: deformation and adhesion. One of the important application fields for polymers is the medical engineering. In this field, the UHMWPE polymer is one of the important candidant polymer material. In this investigation, the friction and wear performance of GUR 1020 medical grade UHMWPE polymer under dry sliding conditions is evaluated. The sliding experiments were carried out on a pin-on-AISI stainless steel disc arrangement. Wear tests were carried out under room temperature, 50, 100and 150N load values and at 0.50, 1.0 and 2.0m/s sliding speed conditions. The results show that the coefficient of friction for GUR 1020 medical grade UHMWPE polymer is significantly influenced by applied load, sliding speed values. Furthermore, the coefficient of friction and specific wear rate increases with the increase in applied load and sliding speed values. The specific wear rate values for GUR 1020 medical grade UHMWPE polymer under dry condition is at the order of 8x10-14 m 2 /N. The friction coefficients vary between 0.12 and 0.20. Finally, the wear mechanism includes abrasive and adhesive processes.