CRITERIA FOR SELECTION OF ENGINEERING MATERAIL BY : ASHISH SOMAN EN NO:

CRITERIA FOR SELECTION OF ENGINEERING MATERAIL The selection of material for specific application is invariably a lengthy and expensive investigation. Almost more than one material is suitable to the application and the final selection is compromise that weight the relative advantages and the disadvantages General Factor Consider For Selection Of The Material Are Below: General Factor Consider For Selection Of The Material Are Below: 1. mechanical strength 2. ductility 3.design 4. stability 5. availability 6. fabricating 7. corrosion resistance 8. cost

One of the most challenging task of an engg is the proper selection of material for particular job. An engineer mast be in position to choose the optimum combination of properties at the lowest possible cost without compromising the quality The properties and the behaviour of material depend upon several factors e.g composition, crystal structure, condition during service and the interaction among them The performance of material may be found satisfactory within certain limit and limitation or condition. However beyond these condition, the performance of material may not be found satisfactory Major Factor Affecting Selection Of Material: 1. Component shape 2. Dimensional Shape 3. Mechanical Properties 4. Fabrication requirement 5. Service requirement 6. Cost of material 7. Cost of processing 7. Availability of the material

Component Shape: All the major factor have complex effect on the selection of materials. The shape and size of a component has a great effect on the choice of the processing unit which ultimately effect the choice of the material. To make it more clear, we consider an example, let the best possible production is selected under given condition It is die casting, obliviously, now the choice of material with lower melting point becomes limited i.e one can only choose material with lower melting points, eg: aluminium, magnesium and thermoplastics Dimensional tolerance: There are some material which can b finished to close tolerance while others cannot. The require dimensional tolerance for finished component will, influence the choice of material.

Mechanical properties : To select a suitable material for specific condition, all mechanical properties, e.g hardness, strength etc guide us. Method of processing of material also effect the properties of a component e.g forged component can be stronger than the casted component. Fabrication requirement: Different type of work process may also give different type of fibre structure. However, investment casting can provide precise dimensions at low cost in comparison to machine operation. Service requirement: Service requirement are dimensionally stability, strength, toughness, heat resistance, corrosion resistance, fatigue and creep resistance, electrical and thermal conductivity etc Whereas fabrication requirement are castability.i.e ease in casting a material, weld ability- ease in welding the material, machinability- ease to machine a material

Cost of material: In most of the cases, the cost of raw material account about 50 per-cent of finished cost. Obviously, the cost of material is a major factor which influence the choice of the material and process. Cost of processing: We must note that the use of cheaper material will not always reduce the final cost of the component or product. Use of cheaper material may be associated with higher processing cost due to large number of operation to be performed and also more scrap. We can easily see that this sometimes make the overall cost more than that of expensive raw material in combination with low processing cost due to lesser number of operation

Availability of the material: We may find sometimes that availability of the material becomes a governing factor. When the desired material supply is limited, then a costly material which is available in ample quantity may be chosen. In the light above factors, sometimes it may be the case that two or more than two material are found suitable for particular component or job