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Design of machine elements ppt.ME2303 DESIGN OF MACHINE ELEMENTS
This irregularity design of machine elements ppt the stress distribution caused by abrupt changes of form is called stress concentration. An object is strongest when force is evenly distributed over its area, so a reduction in area, e.
The real fracture strength elemeents a material is always lower than the theoretical value because most pppt contain small cracks or contaminants especially foreign particles that concentrate stress. Internal force lines are denser near the hole. Where, Kf and Pt are the fatigue stress concentration factor and theoretical stress concentration factor. Since the extensive data for estimating the notch sensitivity factor q is not available, therefore the curves, as shown in figure may be used for determining the values of q for two steels.
In Fig. In order to improve the situation, fillets may be provided, as shown in Fig. In such cases, design of machine elements ppt may be cut as shown in Fig. The variation in the size of the component should be as gradual as possible. The holes, notches and other stress raisers should be avoided. The proper stress de-concentrators such as fillets and notches should be provided wherever necessary. The parts should be protected from corrosive atmosphere.
A smooth finish of outer surface of the component increases the fatigue life. The material with high fatigue strength should be selected. The residual compressive stresses over the parts surface increases its fatigue strength.
Such type of failure of a material is known as fatigue. The failure may occur even without any prior indication. A standard mirror polished specimen, as shown in figure is rotated in a fatigue testing machine while the specimen is loaded if bending. This is represented by a time-stress diagram as shown in Fig. In actual practice, many machine members undergo different range of stress than the completely reversed stress.
This is important because the imperfections that cause fatigue failure are usually at the surface. Effect of size: Increasing the size especially section thickness results in larger surface area and creation of deaign.
This factor leads to increase in the probability of crack initiation. This design of machine elements ppt must be kept in mind while designing large sized components. Stress amplitude No. Higher the temperature, lower the fatigue strength. Moore rotating beam machine. The surface is polished in the axial direction. A constant bending load is applied. A record is kept of the number of cycles по этому сообщению to produce failure at a given stress, and the results are plotted in stress-cycle curve as shown in figure.
Most components do not have a polished surface. Scratches and imperfections on the surface act like a stress raisers and reduce the fatigue life of a part. Use either the graph or the equation with the table shown below. This is mainly due to the higher probability of flaws being present in larger components. For solid round cross section If the component is larger than 10 in.
The stress concentration factor seems to eelements sensitive to design of machine elements ppt notch radius and the источник статьи strength of the material. Iterate until you obtain the desired safety factor. Therefore, the greater emphasis must be /22273.txt to the combination of a variable eleemnts and a steady design of machine elements ppt mean tensile stress.
A Goodman line is used when the design is based on ultimate /20350.txt and may be used for ductile or brittle materials. If a suitable factor drsign safety F. The shaft is rotating at rpm and has a machine design of machine elements ppt surface. Determine the diameter, d, for 75 minutes life.
Use safety factor of 1. Create Presentation Download Presentation. Skip desing Video. Loading SlideShow in 5 Designn. Download Presentation. Share Presentations. Email Presentation to Friend. Deisgn Concentration. Uploaded on Jan 02, Related More ele,ents User.
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