Design of machine elements ppt

 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 

Unit 1 what is machine design. 1. Machine Design:Machine Design: Machine design is defined as the use ofMachine design is defined as the use. General Procedure in Machine Design. 9. Detailed drawing. Need or aim. Synthesis. Analysis of the FORCES. Material selection. Design of elements. Presentation on theme: “DESIGN OF MACHINE ELEMENTS”— Presentation transcript: The theoretical or form stress concentration factor is defined as the ratio of. Design of machine elements such as piston, crank shaft, gear,etc. Computer aided design: Use of computer systems to assist in the creation, modification. View Design of Machine Elements – Lecture replace.me from ME at University of Moratuwa. Machine Elements and Design Presentation Outline.❿
 
 

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Design of machine elements ppt.Machine Elements in Mechanical Design

 

Determine the mean and alternating nominal stresses. Moore Test. Moore test is adjusted for a particular application. Determine the endurance limit of the material. Comment on the robustness of the design.

It is subjected to a reversing bending moment of ft lbs and a steady torque of ft lbs. The shaft has a profile keyway. H W Shaft Dia. Recently uploaded Lecture – Project, Planning and Control.

Soil Nailing 1 [Autosaved] 1. Lecture 1 System Fundamental Concept. Electrochemical Waste Water Treatment. Introduction of design of machine element 1. What is design???? What is Machine??? A machine is made up of mechanisms that work together to satisfy the requirements of what the machine needs to accomplish. What is Machine Design??? The designer only makes minor alternation or modification in the existing designs of the product. The designer starts from the existing design, but final product may differ quite markedly from the original product.

Types of Machine Design 7. This type of design depends upon mathematical formulae of principal of mechanics. Types of Design based on method 9. Based on industrial considerations and norms viz. To decide the relative arrangement of the constituent elements. Factors to be considered in Machine Design The objective of, a standard is to reduce the variety and limit the number of items to a reasonable level.

Standardization The purpose of a code is to achieve a specified level of safety. The dimensions of the trapezoidal cross-section of the belt, viz. The tolerances or upper and lower limits for various sizes of holes and shafts are specified in IS on ‘Recommendations for limits and fits for engineering’. IS explains method for indicating surface texture on technical drawings.

For example, IS is a code of practice for design, manufacture, erection and testing of cranes and hoists. Standards are used in mechanical engineering design P is the applied effort required to overcome load, W. Examples are rocker arm, bell crank lever etc. Mechanical advantage of such levers is greater than one as effort arm is larger than the load arm. Lever used in safety valve is an example of lever of this class.

The effort arm is larger than the load arm; therefore the mechanical advantage is more than one. The effort arm, in this case, is smaller than the load arm; therefore the mechanical advantage is less than one. Due to this, the use of such type of levers is not recommended. However a pair of tongs, the treadle of a sewing machine etc. Reaction force acting on the fulcrum can be calculated.

Determination of Forces If the load and effort are parallel to each other, as shown in figure, reaction on the fulcrum is the algebraic sum of these two forces. But if the load and effort are inclined to each other at an angle q, as shown in figure, reaction R at the fulcrum can be determined as: Design of Lever Arms Arms are subjected to bending moment and their section is estimated from bending stress consideration. Figure shows lever with fulcrum located between the load and the effort point.

Bending moment is zero at the point of application of forces and is maximum at the fulcrum. Values of moment of inertia, I and distance of farthest fibre from neutral axis, y for these sections are given in table Common Sections used for Lever Arms Therefore using suitable values of I and y for selected section, its dimensions can be finalised so that the bending stress remains within the allowable limits.

Often the arms are made with cross-section reducing from central portion to the point of application of load. This is done to save material using uniform strength condition. Critical section of the lever section of maximum bending moment becomes weak due to hole made for pin. To compensate for the reduced strength, width of that section is increased or boss is provided as shown in figure Design of Fulcrum Fulcrum of lever is a pin joint as shown in figure. Pin is designed based on bearing and bending considerations as discussed below.

Bearing Failure The permissible bearing pressure [Pbearing] depends upon relative velocity, frequency of relative motion and the lubrication condition between the pin and the bush.

Lower values are used for high relative velocity, frequent motion and intermittent lubrication conditions. If dp and lp are diameter and length of the pin respectively, bearing pressure is given by, Shear Failure Pin is subjected to double shear and maximum shear stress is given by Bending Failure As discussed in the design of pin for knuckle joint, when the pin is loose in the eye, which is a desired condition here for relative motion, pin is subjected to bending moment.

It is assumed that: Load acting on the pin is uniformly distributed in the eye and uniformly varying in the two parts of the fork. It is difficult to forge curved levers with complicated cross-sections and have to be cast.

Suitable heat treatment processes are also often employed to improve wear and shock resistance of lever. Factor of safety of 2 to 3 on yield strength is generally used. You just clipped your first slide! Clipping is a handy way to collect important slides you want to go back to later. Now customize the name of a clipboard to store your clips. Visibility Others can see my Clipboard.

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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 is caused by means of a progressive crack formation which are usually fine and of microscopic size. The failure may occur even without any prior indication. The fatigue of material is effected by the size of the component, relative magnitude of static and fluctuating loads and the number of load reversals.

As the specimen rotates, the bending stress at the upper fibres varies from maximum compressive to maximum tensile while the bending stress at the lower fibres varies from maximum tensile to maximum compressive. In other words, the specimen is subjected to a completely reversed stress cycle.

This is represented by a time-stress diagram as shown in Fig. It may be noted that the term endurance limit is used for reversed bending only while for other types of loading, the term endurance strength may be used when referring the fatigue strength of the material.

It may be defined as the safe maximum stress which can be applied to the machine part working under actual conditions. We have seen that when a machine member is subjected to a completely reversed stress, the maximum stress in tension is equal to the maximum stress in compression as shown in Fig.

In actual practice, many machine members undergo different range of stress than the completely reversed stress. This may be due to two reasons. The larger member will have a larger distribution of weak points than the smaller one and on an average, fails at a lower stress. Larger members have larger surface Ares.

This is important because the imperfections that cause fatigue failure are usually at the surface. This factor leads to increase in the probability of crack initiation.

This factor must be kept in mind while designing large sized components.

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