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Three samples of quenched and tempered 4140 steel, with varying levels of oxygen and sulfur, were submitted to a series of bending fatigue tests.
The objective of this work is to introduce a method for the calculation of the tooth root load carrying capacity for gears, under consideration of the influence of the defect size on the endurance fatigue strength of the tooth root. The theoretical basis of this method is presented in this paper as well as the validation in running tests of helical and beveloid gears with different material batches, regarding the size distribution of inclusions. The torque level for a 50 percent failure probability of the gears is evaluated on the test rig and then compared to the results of the simulation. The simulative method allows for a performance of the staircase method that is usually performed physically in the back-to-back tests for endurance strength, as the statistical influence of the material properties is considered in the calculation model. The comparison between simulation and tests shows a high level of accordance.
As gear manufacturing techniques become more precise and demanding, there is a growing demand for cleaner, higher quality steel.
Gear designers face constant pressure to increase power density in their drivetrains. In the automotive industry, for example, typical engine torque has increased significantly over the last several decades. Meanwhile, the demands for greater fuel efficiency mean designers must accommodate these increased loads in a smaller, more lightweight package than ever before. In addition, electric and hybrid vehicles will feature fewer gears, with fewer transmission speeds, running at higher rpms, meaning the gears in those systems will have to endure life cycles far beyond what is typical with internal combustion engines.
Reduced component weight and ever-increasing power density require a gear design on the border area of material capacity. In order to exploit the potential offered by modern construction materials, calculation methods for component strength must rely on a deeper understanding of fracture and material mechanics in contrast to empirical-analytical approaches.
The aim of our research is to clearly show the influence of defects on the bending fatigue strength of gear teeth. Carburized gears have many types of defects, such as non-martensitic layers, inclusions, tool marks, etc. It is well known that high strength gear teeth break from defects in their materials, so itâ€™s important to know which defect limits the strength of a gear.