Properties Of material considered for selection of Mechanical Material

Properties to be considered in selection of materials 



Strength :-

 It is measured by the tensile sensible strength. To guard against permanent deformation, the elastic limit is considered For ductile materials, yield point is used instead of elastic limit.

Rigidity :-

It is important where deflections are limited by service requirements.

Resistance to fatigue :-

   It is measured by endurance limit and is important for members subjected to cyclic loading. Harmful surface effects have to be carefully controlled during heat treatment. 

Damping capacity :-

It is the energy dissipated as by a unit volume of the material during a completely.
reversed cycle of stress. It is related to internal friction in the material and is represented by a mechanical-hysteresis diagram. High damping capacity is desirable to decrease vibration, chatter and noise.

Resilience :-

It is important in cases where material is subjected to shock loading. Hardness. It limits wear and is of importance in bearing surfaces which have relative motion and in which fluid lubrication does not exist. Ductility is desirable to relieve stress concentration in parts subjected to static loading.

Corrosion resistance :-

 It is important in members subjected to corrosive environment. Its effect is especially serious in the presence of stress concentration in cyclic loading. other such considerations depending on application are weight, electrical properties, thermal properties, resistance to wear, casting and forging characteristics, machinability, low friction etc.

Cast Iron :-

  It is the cheapest of the cast metals and can be easily cast into any size and form. Gray iron is easily machinable but is not as abrasive wear resistant as chilled iron. White iron is hard and difficult to machine. Chilled cast iron is produced by rapid cooling to provide hard wear-resistant surface Cast iron has high damping capacity, making it suitable for beds, bases and frame of machinery subjected to vibrations.

Malleable iron :-

    It is made by transforming white- iron castings by heat treatment that converts it into a matrix of ferrite containing nodules of temper carbon, and thus it becomes tough and ductile, resistant to impact, and easily machinable.

 wrought iron :-

   It is a mechanical mixture of highly refined metallic iron and a small quantity of slag It is resistant to corrosion in ordinary atmospheres and welds readily

Cast steel :-

 It is used for castings of improved properties. It is stronger and tougher, weighs less for the same strength or stiffness, and has a higher endurance limit than cast iron. Corrosion resistance can be improved by alloying

wrought steel :-

 A large variety of wrought steels are available. Mechanical properties can be markedly controlled by the composition and heat treatment. It may be forged, swaged, drawn, welded and machined. It finds innumerable applications in engineering.

Brass and bronze :-

 are used in machinery parts in both cast and wrought form. Brass is used where moderate strength and ductility, resistance to corrosion or good wearing qualities are desired. Bronze is superior to brass in these properties but is more expensive. Phosphor bronze has relatively high tensile strength, yield point, endurance limit and shock-resistance properties.
loading...

 Aluminium :-

 Aluminium and its alloys have variety of uses. Pure aluminium resists oxidation, is highly ductile and has good forming properties, but it has poor casting characteristics and machining properties.
Aluminium-copper alloys have high ultimate strength and endurance limit and improved casting characteristics and machinability, but poor corrosion resistance. Aluminium silicon alloys have better corrosion resistance and mechanical properties but poorer machinability. Duralumin (aluminium copper- magnesium and manganese alloy) is suitable for parts requiring severe working and has good corrosion resistance and strength.

Magnesium :-

 alloys are corrosion-resistant in salt free atmosphere, and galvanic corrosion can be prevented by coatings. These can be cast, wrought or extruded and their weight is around one-fifth that of steel.

Titanium alloys :-

Titanium alloys  are developed for useful strength and corrosion resistance at temperature range between -230°C and 540°C.

Rubber :-

 It is an excellent material for seals and diaphragms for water lubricated bearings, for parts subjected to vibratory forces. It should be protected from high temperature, oil and sunlight.

Non-metallic materials :-

Plastics have low cost light weight, good resistance to shock and vibration, self lubrication, ease of fabrication. However, these have low strength, high thermal expansion, low heat resistance, high creep and deformation under load and embrittlement at low temperature.

Fibreglass :-

 (combination of glass, filler and resin) has N high tensile strength and corrosion resistance. It has replaced steel metal in both flat plate form and in matched-met processes where the parts are moulded in the preformed shape

Post a Comment

Previous Post Next Post

Contact Form