Springs are widely used in machinery, tools and equipment for many purposes such as energy storage and vibration damping. Prolonged vibration or oscillation and cycles induces crack propagation from the weak points on the spring. These crack initiations begin with the notch effect created by the external surface or the irregularities within the microstructure. As a result of the spring fatigue or unexpectedly ending its life, the machine can undergo irreversible damage to its dynamic structure [1].Various techniques are used to calculate fatigue life of the springs during design. Some of them have been tried to calculate the spring life using the FEM (finite element method) method [2]. Other methods are various mathematical and numerical models that have been put forward [3,4]. Although numerical models are used, there are various differences among these thecniques [5]. The main reason for the differences is due to outer and intrinsic factors such as microstructure characterization, surface hardness, surface roughness, application temperature and application frequencies [6,7]. For this reason, simulating the fatigue of the springs in a real environment will give the most realistic re-sult. Thus, irreversible damages can be prevented by determining the service life of the springs with the most accurate way [8].Helical compression springs are among the most used spring types in the industry. This type of springs can be used in high-stress ranges where operating conditions are critical such as engines, pumps and valves [9]. The fatigue life of helical compression springs depends on many factors including the condition of the outer surface, surface roughness, internal structure of the material, discontinuities in the material, working load, capacity, and frequency [10]. Therefore, compression springs should be tested under real conditions.There are many spring fatigue machine designs in the industry. However, no study has been encountered that determines the life of compression springs produced from high strength wires driven with a pneumatic system. Fatigue testing applied to multiple compression springs was not also coincided in the literature. In this study, a fatigue machine simulating the working conditions of compression springs was designed and produced. The operation and design of the mechanical, electrical, pneumatic systems of the machine were carried out. The working efficiency of the fatigue
Aluminium alloys have found usage in numerous industries due to some superior properties, such as high strength-to-weight ratios and high oxidation resistance. Aluminum alloys can be strengthened by some techniques. One of them, the most practical one, is precipitation hardening in aluminum alloys. By adding Cu, aluminum gains strength and hardness. In this work the machinability of unalloyed aluminum and aluminum alloyed with 4% and 8% of Cu have been investigated. Machinability assessment was executed in terms of surface roughness during turning operation. Specimens were manufactured by sand casting method, which is a commonly utilized casting operation. In machinability experiments, three different cutting tool materials were employed. Three different cutting speeds and three different feed rates have been used. Effect of these feeds, speeds and cutting tool materials on surface roughness has been studied. In addition, effect of Cu addition to aluminum alloys on surface roughness has been examined.
Steel pipe piles are used to reinforce the grounds. Due to high hardness of the rocky materials, in some cases, the tip surface should be developed with new designs in terms of geometry, material and heat treatment. In this study, a hardfacing welding, which reinforces the application point of the tip surface, was applied on the steel pipe pile shoe tip which was manufactured from S355J2 steel. Wear tests were applied and hardness measurements were made to explain wear behavior. According to the results, the hardened surface of the 3rd layer which was welded with FCH-360 flux cored wire showed higher hardness than other layers. Similarly, the highest wear resistance was obtained in this layer. Martensitic and bainitic structures with ferrite islets were observed from the first layer to the second layer. The bainite and ferrite isles were gradually transformed to martensite and maintained itself from first to third layer. The martensitic structure mainly controlled the hardness and wear resistance. The sizes of the martensite highly affected the hardness and wear resistance of the layer itself.
Bu çalışmada, cam küre takviye fazlı polimer matrisli kompozit malzemenin delinmesi sonucu ortaya çıkan delaminasyon faktörünün etkileri deneysel olarak incelenmiştir. Takviye fazı olarak ağırlıkça %5, %10 ve %20 takviye oranında cam küre kullanılmıştır. Matris malzemesi olarak Polipropilen tercih edilmiştir. Elde edilen sonuçlara göre, kesme hızı ve ilerleme arttıkça delaminasyon miktarında yükselmeler meydana gelmiştir. Elde edilen en düşük delaminasyon miktarı (1.18) 0.05 mm/devir ilerleme ve 15m/dk kesme hızında karbür takım türü ile elde edilmiştir. Ayrıca, kompozit içerisindeki takviye miktarı arttıkça delaminasyon faktörünün de yükseldiği saptanmıştır. En düşük delaminasyon miktarı %5 cam küre takviye içeren kompozit malzemede olmuştur.
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