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Harmonic motion:Oscillaratory motion may repeat itself regularly, as in the balance wheel of a watch, or display considerable irregularity, as in earthquakes . When the motion is repeated in equal intervals of time (T), it is called periodic motion. The repetition time T is called the period of oscillation, and its reciprocal, f=1/T, it is called the frequency. If the motion is designed by the time function x(t), then any periodic motion must satisfy the relationship x(t) = x(t +T). The simplest form of periodic motion is harmonic motion. It can be demonstrated by a mass suspended from a light spring. If the mass is displaced from its rest position and released, it will oscillate up and down. By placing a light source on the oscillating mass, its motion can be recorded on a light-sensitive filmstrip, which is mado to move past it at a constant speed.The motion recorded on the film strip can be expressed by the equation x = A.sin2(pi).t/T where A is the amplitude of oscillation, measured from the equilibrium position of the mass, and T is the perion. The motion is repeated when t=THarmonic motion is often represented as the projection on a straight line of a point that is moving on a circle at constant speed as shown in Fig 1.1-2. ( Theory of vibration with applications- Willia Thomson- page 6)

WIPER BENDING: Bending is the operation of deforming a flat

sheet around a straight axis where the neutral plane lies. it is a very common forming process for changing sheet and plate in to channel, drums, tanks, etc. Wiper bending is used for 90 degree bends only. Here the work is held firmly to the die, and the punch bends the extended portion of the blank. ( Manufacturing Processes - R.K. Rajput - page 178 )

Corrosion ( as a mechanical failure mode) : corrosion may be defined as the undesired deterioration of material through chemical or electrochemical interaction with the environment, or destruction of materials by means other than purely mechanical action.

Failure by corrosion occurs when the corrosive action renders the corroded device incapable of performing its design function.Corrosion often interacts synergistically with another failure mode, such as wear or fatique, to produce the even more serious combined failure modes, such as corrosion-wear or corrosion- fatique. ( Mechanical design of machine elements and machines - Jack A. Collins, Henry R Busby, Geoerge H. Stabb- page 64 )

Electro-magnetic Clutches: The rear axle differential, center differential, and transfer case ( Figure 10-42) on some vehichles are equipped with electromagnetic clutches for lockup of the differential. The clutch may be controlled by a switch ar by a traction control computer. When one wheel or axle loses traction and speeds up, the computer energizes the clutch, which locks up the differential and provides equal power to both wheels or axles. The electromagnetic clutch consist of an actuator coil, an armature, an a stack of steel clutch plates. When the clutch is energized, a magnetic field is produced to compress the clutches, thereby locking the differential. ( Manual transmission and transaxles - Jack Erjavec - page 470)