The factor of safety is a measure of reserve strength provided to take care of any unexpected or unpredicted conditions that may arise due to uncertainties in the properties of the material, magnitude & direction of the load and operating conditions. gears, bearings, bushes, piston-cylinders etc.) are examples of other failure criteria.ģ.3 Factor of Safety & Allowable Stresses bearings, clutches, brakes etc.) and wear (for components having sliding or rolling motion e.g. Bearing Pressure (for components rubbing against each other with appreciable relative velocity e.g. Therefore Ultimate Tensile Strength is considered as failure criterion for brittle materials. In brittle material, very small plastic deformation occurs and fracture takes place once the stress developed reaches Ultimate Tensile Strength. When stress developed in a ductile material reaches the yield strength, it starts yielding and excessive plastic deformation occurs, therefore Yield strength is taken as failure criterion for ductile materials. Same way, excessive stresses may result in yielding or fracture of a machine element making it unable to perform its desired function. Excessive deformation of a particular element may lead to unwanted interference between the machine elements or jamming of the machine and therefore deformation is considered as a failure criterion. It may happen if its stress or deflection crosses the acceptable limit.
#Static loading free
After the determination or estimation of applied load, load acting on different members of the machine are determined with the help of free body diagrams and basic equilibrium equations of forces and moments.Ī machine element is said to have failed when it ceases to perform its intended function.
Also sometimes the service loads are estimated with the help of record of service failures and strength analysis. Sometimes experimental methods are used to obtain a statistical definition of the load. Loads acting on a machine member may be directly known or may have to be calculated using basic concepts of engineering mechanics etc. the load on vehicle chassis which depends on road condition and driving practices. But often the loads are difficult to determine e.g. load on a shaft running at known speed and transmitting a known value of torque. Sometimes the operating loads are easily determinable e.g. All the stress and deflection analysis is useless and the component cannot function satisfactorily if the operating loads are not calculated or predicted correctly. Impact load (load applied with certain velocity) and shock load (suddenly applied load) are also types of dynamic load.ĭetermination of appropriate loads acting on a machine member is a critical and challenging task. load acting on the connecting rod of an internal combustion engine. Dynamic load is the load which changes in magnitude or direction or both with respect to time e.g.
Static load is the load which does not change in magnitude or direction and gradually increases to a steady value e.g. Load may be classified as static or dynamic. All the machine members are subjected to different types of loads that may be acting because of energy, torque or power transmission, their self weight, frictional resistance, inertia or centrifugal forces or due to temperature gradient.
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