Machine Design - 1 - Mechanical Engineering MCQ

A lap joint is that in which one plate overlaps the other and the two plates are then riveted together.

A butt joint is that in which the main plates are kept in alignment butting (i.e. touching) each other and a cover plate(i.e. strap) is placed either on one side or on both sides of the main plates.

A n-riveted joint is that in which there is n number of rows of rivets in a lap joint and there is a n number of rows of rivets on each side in a butt joint.

The given figure shows Double riveted lap joint.

When the rivets in the various rows are opposite to each other, as shown in figure then the joint is said to be chain riveted. On the other hand, if the rivets in the adjacent rows are staggered in such a way that every rivet is in the middle of the two rivets of the opposite row, then the joint is said to be zig-zag riveted.

The primary functions of cutting fluids in machining are:

• Lubricating the cutting process primarily at low cutting speeds
• Cooling the workpiece primarily at high cutting speeds
• Flushing chips away from the cutting zone
• To protect the machine tool and workpiece against corrosion

Lead screw is large screw with a few threads per inch used for cutting threads. It has ACME threads with included angle of 29^o for easy engagement and disengagement of half nut.

The maximum efficiency of screw jack is:

A bearing is said to be hydrostatic bearing if it has a static fluid (liquid or air) along the surface of the shaft/journal where the fluid will be supplied externally and the pressure is generally maintained by an external pump; thus enabling non-contacting operation and the ability to support a load. Hydrostatic bearings can support large loads without journal rotation and provide large (accurate and controllable) direct stiffness as well as damping (energy dissipation) coefficients.

In case of hydrodynamic bearing the pressure is developed by the high speed journal at higher rpm, this helps the movement of thin film of lubricant. For Journal bearings mostly converging fluids are employed.

Welded joint is permanent joint and riveted joint has semi-permanent joint. Strength of welded joint is more than rivet joint.                    

The rivets are used to make permanent fastening between the plates such as in structural work,ship building, bridges, tanks and boiler shells.

A screwed joint is mainly composed of two elements i.e. a bolt and nut. The screwed joints are widely used where the machine parts are required to be readily connected or disconnected without damage to the machine or the fastening.

A key is a piece of mild steel inserted between the shaft and hub or boss of the pulley to connect these together in order to prevent relative motion between them. It is always inserted parallel to the axis of the shaft. Keys are used as temporary fastenings and are subjected to considerable crushing and shearing stresses. 

A knuckle joint is used to connect two rods under tensile load. This joint permits angular misalignment of the rods and may take compressive load if it is guided. The automotive engine piston is connected to the small end of connecting rod by means of piston pin. This is one major application of knuckle joint. The valve rod in a steam engine is connected to an eccentric rod by Knuckle joint.

Flexible couplings are usually used to transmit torque from one shaft to another when the two shafts are slightly misaligned. They can accommodate varying degrees of misalignment up to 3° and some parallel misalignment.

Universal coupling is a rigid coupling that connects two shafts, whose axes intersect if extended.

Oldham’s coupling is used to connect two parallel shafts whose axes are at a small distance apart.

Tearing Efficiency 

Endurance limit (S_e), also known as fatigue limit is the stress level below which a specimen can withstand cyclic stress indefinitely without exhibiting fatigue failure.

Misalignment and improper belt tensioning can cause sheaves to wear prematurely, and when that happens, a formerly flat groove sidewall can take on a concave shape and the surface that interacts with the belt can be damaged. Eroded sheave sidewalls can reduce V-belt drive efficiency up to 12 percent. So to avoid it, when a single belt is damaged, it is preferable to change the complete set to ensure proper alignment.

The principal features of the British Standard Whitworth (BSW) thread form are that the angle between the thread flanks is 55 degrees and the thread have radii at both the roots and the crests of the thread.

The woodruff key is an easily adjustable key. It is a piece from a cylindrical disc having segmental cross-section. This key is largely used in machine tool and automobile construction.

A key attached to one member of a pair and which permits relative axial movement is known as feather key. It is a special type of parallel key which transmits a turning moment and also permits axial movement.

A flat saddle key is a taper key which fits in a keyway in the hub and is flat on the shaft. A hollow saddle key is a taper key which fits in a keyway in the hub and the bottom of the key is shaped to fit the curved surface of the shaft.

Gib-head key is a rectangular sunk key with a head at one end known as gib head. It is usually provided to facilitate the removal of key.

The positive clutches are used when a positive drive is required. The simplest type of a positive clutch is a jaw or claw clutch.

Friction Clutches: The force of friction is used to start the driven shaft from rest and gradually brings it up to the proper speed without excessive slipping of the friction surfaces. Example: Disc or plate clutches, Cone clutches, Centrifugal clutches.

In normal situations, where bolts are subjected to shock or impact loads,the stress in the threaded part of the bolt will be higher than that in the shank. Hence a great portion of the energy will be absorbed at the region of the threaded part which may fracture the threaded portion because of its small length.

If the shank of the bolt is turned down to a diameter equal or even slightly less than the core diameter of the thread then shank of the bolt will undergo a higher stress. This means that a shank will absorb a large portion of the energy, thus relieving the material at the sections near the thread. The bolt, in this way, becomes stronger and lighter and it increases the shock absorbing capacity of the bolt because of an increased modulus of resilience. This gives us bolts of uniform strength.

Bolt of Uniform Strength with Reduced Shank Diameter

A second alternative method of obtaining the bolts of uniform strength is to drill an axial hole through the head as far as the thread portion such that the area of the shank becomes equal to the root area of the thread.

Bolt of Uniform Strength with Drilled Hole

Fluid bearings are bearings in which the load is supported by a thin layer of rapidly moving pressurized liquid or gas between the bearing surfaces.

They can be broadly classified into two types:

Fluid dynamic bearings/ hydrodynamic bearings: are externally pressurized fluid bearings, where the fluid is usually oil, water or air, and the pressurization is done by a pump.

Hydrodynamic bearings: are rely on the high speed of the journal (the part of the shaft resting on the fluid) to pressurize the fluid in a wedge between the faces.

Let p be the normal intensity of pressure at a distance r from the axis of the clutch.

Since the intensity of pressure varies inversely with the distance in the uniform wear theory,

∴ p.r = C (a constant)

A spherical plain bearing is a bearing that permits angular rotation about a central point in two orthogonal directions. The outer surface of the inner ring and the inner surface of the outer ring are spherical and are collectively considered the raceway and they slide against each other. The centre point of the sphere in the outer ring raceway is at the bearing axis. Therefore, the bearings are self-aligning and insensitive to misalignment of the shaft relative to the housing, which can be caused, for example, by shaft deflection. Spherical roller bearings are designed to accommodate heavy radial loads, as well as heavy axial loads in both directions.