The machine which starts to move in reverse direction after removal of effort, is called reversible machine. Simple rope and pulley drive is a reversible machine. The machine, which does not move in reverse direction after removal of effort, is called irreversible or self-locking machine. Screw jack, worm and worm wheel, and winch crab are examples of irreversible machine.
Category: Advance Concept Mechanical Eng
Expression for Maximum Mechanical Advantage
From law of machine For maximum mechanical advantage denominator should be minimum. Therefore, will be minimum when W will be very large in comparison to C, i.e., is negligible. Hence, maximum mechanical advantage, Maximum efficiency, The graphical representation of relationship between load and efficiency is shown in Figure 13.3. Figure 13.3 Relationship Between Load and Efficiency
Frictional Loss in Lifting Machine and Law of Machine
Frictional loss is the part of the inputs or work done by the effort used to overcome the friction of the machine. No machine can be 100% frictionless; therefore, some parts of the inputs are always used to overcome the friction of the machine. Thus, the efficiency of the real machine always lies below 100%.… Continue reading Frictional Loss in Lifting Machine and Law of Machine
TERMINOLOGY RELATED TO THE LIFTING MACHINES
Velocity Ratio (VR): It is ratio of distance moved per unit time by effort to the distance moved per unit time by load. , where y is distance moved by the effort (P), and x is distance moved by the load (W). Mechanical Advantage (MA): It is ratio of load lifted and effort applied on a lifting machine. Its significance is… Continue reading TERMINOLOGY RELATED TO THE LIFTING MACHINES
INTRODUCTION
A machine is a device, which is capable to do some work on application of some effort. Here, effort means input in the form of force or energy supplied to the machine to do work. The work may be explained in the form of load lifting. An illustrative example of a lifting machine is explained… Continue reading INTRODUCTION
RELATION BETWEEN MODULUS OF ELASTICITY AND MODULUS OF RIGIDITY
Modulus of rigidity (G) is the ratio of shear stress (τ) and shear strain (γ). Let us consider an elemental cube ABCD be subjected to a simple shear stress τxy as shown in Figure 12.24 (a). An equivalent system with principal stresses τxy and –τxy are acting along the diagonals as shown in Figure 12.24 (b). The distorted condition of the cube is shown in Figure 12.24… Continue reading RELATION BETWEEN MODULUS OF ELASTICITY AND MODULUS OF RIGIDITY
RELATION BETWEEN MODULUS OF ELASTICITY AND BULK MODULUS
Suppose a block is subjected by three-dimensional forces P as shown in Figure 12.23. Figure 12.23 Fluid Pressure and Volumetric Strain of a Cube Bulk modulus is a ratio of fluid pressure and volumetric strain. It is denoted by K. Here –ve sign is used for reduction in volume. Let us consider a cube of unit length is subjected to… Continue reading RELATION BETWEEN MODULUS OF ELASTICITY AND BULK MODULUS
RELATION BETWEEN STRESS AND VOLUMETRIC STRAIN
STRESS AND STRAIN FOR IMPACT LOAD
Impact load is a load which is applied to a body with some velocity as shown in Figure 12.21. Suppose a load W released from a height h on a collar of a rod of length l and change in length due to impact loading is δl. Now, work done by impact load W is Figure 12.21 Impact Loading on a Rod Suppose the equivalent load for… Continue reading STRESS AND STRAIN FOR IMPACT LOAD
STRESS AND STRAIN DUE TO SUDDENLY APPLIED LOAD
Suppose W is a load suddenly applied on the collar of a rod and extension due to the load application is δl as shown in Figure 12.20 (a). The original length of the rod is l. The work done by the load W is U = W × δl Now consider the equivalent weight for same work is P which is applied gradually. Work done by gradually applied load P [Figure 12.20… Continue reading STRESS AND STRAIN DUE TO SUDDENLY APPLIED LOAD