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to have constant velocity, the gear pair must have same module and same no. of teeth

The mechanical properties of a material are those properties that involve a reaction to an applied load. The mechanical properties of metals determine the range of usefulness of a material and establish the service life that can be expected. Mechanical properties are also used to help classify and identify material. STRENGTH: The strength of a material is its ability to withstand an applied load without failure or plastic deformation.In machine design yield point or ultimate tensile / shear / compressive strength is used while designing. Stiffness: Stiffness is the rigidity of an object — the extent to which it resists deformation in response to an applied force. The complementary concept is flexibility or pliability: the more flexible an object is, the less stiff it is. Hardness: Hardness is a measure of how resistant solid matter is to various kinds of permanent shape change when a compressive force is applied. Some materials (e.g. metals) are harder than others (e.g. plastics). Elasticity: the ability of an object or material to resume its normal shape after being stretched or compressed. On a stress-strain diagram it is considered to be below proportional limit.But widely this point is taken as the yield point by drawing a line offset by 0.2% parallel to the straight line until it intersects the curve. Plasticity: It describes the deformation of a (solid) material undergoing non-reversible changes of shape in response to applied forces. Brittleness: A material is brittle if, when subjected to stress, it breaks without significant plastic deformation. Brittle materials absorb relatively little energy prior to fracture, even those of high strength.

Tolerances are allowed so it aid in interchangeability of the product during use, assembly and when subjected to different conditions. It is most derived from the purpose of which the product is to be used for. Environment i.e temperature , application depending on speeds, assembly so it can suit global use.

This is one important point missing in the two previous answers. The "cc rating" of an engine is a volume measure, as previously stated, but it is not the actual cylinder volume. Rather, it is the swept volume of the cylinder, also called the "displacement" of the cylinder. The actual cylinder volume is always somewhat greater than this value because the piston at TDC does not leave zero cylinder volume. The small volume remaining at TDC is called the "clearance volume," the volume available for the early stage of combustion. DrD

Few points Hemispherical ends are used to reduce the stress concentration Cylindrical shape along its lenght is used to store more amount of gas or fuel.since for the same radius cylinders have more volume than spheres. Easy to manufacture the cylindrical vessels Ease in transportation

Hi Joshua, I've just read your message and I couldn't agree with you more. The Diesel engine and the gas engine ARE both internal combustion engines. It's a very amateurish mistake that I've made and I apologise to anyone who may have been misled by this. I can't imagine what I was thinking of when I wrote it. Thanks for your correction. Roger

Petrol get ignited with at low temp. But for diesel high temp is required for combustion. ..This sole purpose is not achieved by spark plugs so we go with compression ignition. ...thus we don't have spark plugs in diesel engine. ..

Petrol get ignited with at low temp. But for diesel high temp is required for combustion. ..This sole purpose is not achieved by spark plugs so we go with compression ignition. ...thus we don't have spark plugs in diesel engine. ..

In normal helical gears there is no problem of impact stresses but there are axial thrusts on the bearings of shafts on which they are mounted.these gears are good for moderate power transmission because bearing can be designed.But in very high power transmission design of bearing for a small and compact system becomes very tough and unemployable.Thus herringbone gears were designed to eliminate these axial thrusts.This gear contains both right hand helical profile and left hand helical profile on same gear as you can see in diag. .The axial components of transmission force is cancelled by each other on same gear.Thus eliminating the problem of thrust force. these gears are used in racing cars where high power transmission is required and bearing size can not be increased after certain limit.

HAI Amit kumar, This is hari can u please explin me in breif About this line"To reduce the internal pressure"

because in cylinders there is no sharp corners or edges like rectangular or other shaped container that's why there is no stress concentration.

Dear sourabh, very good job. Please promote this website as a good source of knowledge in the field of mechanical engineering. Some times the questions make us to think about the topics which are not present in any book. Also I want to suggest you that please implement this website with spelling suggestions and correction during typing. we all type fast and this increase chance of mistakes during typing. So it should be better to have a right spelling suggestion while typing. Regards...

Normally spur gear are the replaced by other gears like helical, double helical gears,bevel gears etc. Spur gear is normally used in lower speed due its its ability of generating zero axial thrust. Now in order to maintain constant gear ratio or speed ratio, their centre of pitch circle must be from fixed and the pitch circle of two mating gears should meet at a point and the line of action should meet at pitctch point in order to satisfy the law of gearing.