Stress strain diagram with explanation

Very useful information concerning the behaviour of material for engineering applications can be obtained by making a tension test and plotting a curve showing the variation of stress with respect to strain. Therefore, the results of tension test are expressed by means of this curve. A stress-strain diagram for ductile material like mild steel is shown in the figure below.

Proportional Limit :

It is observed from the diagram that the stress strain relationship is linear from the point O to A. After A curve begins to deviate from the straight line. 

Hooke's law states that stress is directly proportional to strain. 

The term proportional limit is defined as the stress at which the stress-strain curve begins to deviate from the stress line so point A indicates the proportional limit.

Modulus of Elasticity :

Modulus of elasticity is the ratio of stress to strain up to point P. 
It is given by the slope of the line OP 

E = tanƟ = AP/OP = Stress / Strain

Where, 

Stress = Vertical line perpendicular to point A on the X-axis point named P = AP

Strain = Horizontal distance from O to P = OP

Elastic Limit :

When the specimen is stressed beyond point A and up-to point B. It will regain its initial size and shape when the load is removed. This indicates that the material is an elastic stage up to the point E. So the E is called the elastic limit.

The Elastic Limit of the material is defined as the maximum stress without any permanent deformation.

Proportional limit and Elastic limit are very close to each other.

Yield Strength :

When the specimen is stress beyond point B, plastic deformation occurs and the material starts yielding. It is seen from the diagram that beyond point B, the strain increases at a faster rate up to a certain point then a small reduction in load and the curve drops down point C. So B is called upper yield stress point and C is called lower yield stress point.

The Yield Strength is defined as the maximum stress at which a marked increase in elongation occurs without an increase in the load.

Ultimate Tensile Strength :

After the point C plastic deformation of the specimen increases. The material becomes stronger due to strain hardening, and higher and higher load required to deform the material. Finally, the load increase so stress reach a maximum value, as given by the point D. The stress corresponding to the point D is called ultimate stress point. 

The Ultimate Tensile Strength is the maximum stress that can be reached in the tension test.

Breaking or Rupture point :

For ductile material, the diameter of the specimen begins to decrease rapidly beyond the ultimate stress point D. There is a start reduction in cross-sectional area is called necking.

As the tensile stress progress and load increases the fracture takes place. This is shown by point E. So E is called breaking or rupture point.

Therefore, ultimate tensile strength is considered as failure criterion in brittle materials.

Difference between open and closed coil spring

The springs are classified as :

1. Closely coiled spring
2. Open coiled spring

Difference between them are as following below :

• A helical spring is said to be closely coiled when the spring wire is coiled so close in open coiled spring wire is coiled in such a way, that there is large gap between adjacent coil.
• In closely coiled spring helix angle is very small usually less than 10 degree while in open coiled spring helix angle is large about to more than 10 degree.
• Closely coiled spring is also known as tension or extension spring while open coiled spring is known as compression spring.
• In open coiled spring both torsional and bending stresses are significant because of large helix angle while in closely coiled spring only torsional stresses are predominant.

Applications of closely coiled spring :

• Garage door assemblies
• Vise-grip pilers
• Carburetors 

Applications of open coiled spring :

• Ball point pens
• Pogo sticks
• Valve assemblies in engines 

Advantages and disadvantages of clamp coupling

A device for uniting the ends of a shaft by means of conical binding-sleeves, which by longitudinal motion wedge themselves between the shaft ends and an outer cylinder, thus binding the whole together. Let us have a deep insight into the pros and cons of clamp coupling in this article. 

Advantages of clamp coupling :

• It is easy to assemble and dismantle.
• It can be easily removed without shifting the shaft in an axial direction.
• As compared with flange coupling, clamp coupling has small diametral dimensions.

Disadvantages of clamp coupling :

• Clamp coupling is unsuitable for shock loads.
• It is necessary to provide a guard for the coupling to comply with the factory regulation act.
• There is difficulty in the dynamic balancing of the coupling. Therefore, it is not possible to use the clamp coupling for high-speed applications.

Clamp coupling

What is clamp coupling?

Answer :

• A device for uniting the ends of a shaft by means of conical binding-sleeves, which by longitudinal motion wedge themselves between the shaft ends and an outer cylinder, thus binding the whole together.

Clamp coupling is a coupling method that can be used when joining two piping units or hoses.

The clamp coupling is also called compression coupling or split muff coupling.

Clamp coupling is a rigid type of coupling. In this coupling, the sleeve is made of two halves, which are split along a plane passing through the axes of shafts. The two halves of the sleeve are clamped together by means of bolts and a small clearance is provided in the parting plane between two halves. Therefore, when the bolts are tightened, a force is exerted between the sleeve halves and the shaft.

Applications of clamp coupling :

The main application of clamp coupling is for line shaft in power transmission.

Clamp coupling is designed on the basis of standard proportions for sleeve halves and clamping bolts.

For sleeve halves :

D = 2.5 d 
L = 3.5 d

Where,
D = Outer diameter of sleeve halves ( mm )
L = Length of sleeve ( mm )
d = Diameter of shaft ( mm )

For clamping bolts :

d₁ = 0.2d + 10 mm

When d < 55 mm

and d₁ = 0.15d + 10 mm

When d > 55 mm 

Where, 

d₁ = Diameter of clamping bolt ( mm )

Difference between clamp coupling and muff coupling

What is clamp coupling?

Clamp coupling is also known as split-muff or compression coupling, clamp coupling. Sleeve or muff is made in two halves in this coupling, which is divided along the plane passing through the shaft axes. Using bolts, which are placed in recesses made in the sleeve halves, these two halves are clamped together.

What is muff coupling?

Muff coupling is also known as sleeve coupling is made into two halves parts of the cast iron and they are joined together by means of mild steel or bolts.

Let us have a deep insight into the difference between clamp and muff coupling.

Difference between clamp and muff coupling :

In muff coupling, torque is transmitted by shear resistance of keys, on the other hand, torque is transmitted partly by means of friction between the sleeve halves and the shaft and partly by sheer resistance of key is a case of clamp coupling.

Ductility property

Ductility of metal by which that permits it to be permanently drawn, bent or twisted into various shapes without breaking.

The ductility of the material enables it to draw out into thin wire on the application of the load.

The ductility decreases with the increase of temperature.

It is determined by percentage elongation and percentage reduction in the area of metal.

The types of metal commonly used, because of their high level of ductility, include the following: gold, silver, copper, and steel.

Ductile metals are greatly preferred for aircraft use because of their ease of forming and resistance to failure under shock loads.

The power of changing shape without breaking when the material is subjected to percussion is called malleability, a property closely related to ductility and illustrated by the same class of metals. 
When we can see the same case properties it is necessary to know the difference between them.

Ductility and malleability are examples of

Ductility and malleability are examples of what?

Answer :

• Physical properties

Properties for which no change of identity takes place and the properties can be easily observed by touch, viewing, senses. 

Examples of physical properties are melting point, density, mass, volume, etc. 

You can also check it out :

• Malleability and ductility of metals can be accounted for due to
• Malleability and ductility are characteristic of substances with
• Difference between malleability and ductility
• Ductility property 

How to test malleability

• Malleability is measured possibly in relationship to hardness

Malleability is mostly tested as hardness. The most common hardness tests are Rockwell and Brinell tests. They determine the resistance of a material to indentation. Ductility is also similar to malleability. Ductility is usually measured by elongation and reduction of area as determined in the tensile test.

Malleability is a mechanical property of matter but is most commonly used in reference to metals.

This is important in metalworking, as materials that crack or break under pressure cannot be hammered or rolled. One thing is that brittle metal and plastic are made moulded where malleable metals can be formed by using stamping or pressing.

• Ductility is usually measured by a bend test.

Ductility is the most important parameter to consider in metal forming operations such as rolling, extrusion, and drawing.

Increasing levels of carbon decrease ductility. 

There may be some differences looked like the same properties so whenever we talk about malleability at that time ductility also comes in to picture. 

Difference between kinematic viscosity and dynamic viscosity

What is Dynamics viscosity?

It is a quantity measuring the force needed to overcome internal friction in a fluid.

What is Kinematic viscosity?

It is a quantity that represents the dynamic viscosity of a fluid per unit density. 

Let us have a deep insight into the difference between kinematic and dynamic viscosity. 

Difference :

• Measure a fluid's resistance to flow when an external force is applied is called dynamic viscosity while measure it under the weight of gravity is kinematic viscosity.
• Kinematic results are dependent on the density of the fluid and density is not a factor with dynamic viscosity.

The unit of measure for the dynamic viscosity is Centipoise (cP). 

The unit of measure for the kinematic viscosity is Centistokes (cSt).

• For measuring dynamic viscosity rotational viscometers are used while for kinematic viscosity capillary tube is used.
• In dynamic viscosity, the viscosity related to an external force applied to non-newtonian fluids while kinematic viscosity inherent viscosity of Newtonian fluids, that does not change with a change in applied force.
• Dynamic viscosity is the quantitative expression of fluid’s resistance to flow whereas kinematic viscosity is the dynamic viscosity of a fluid divided by its density.
• Dynamic viscosity is symbolized by either µ or ‘n’ while kinematic viscosity is mathematically symbolized by v.
• Dynamic viscosity is sometimes referred to as absolute viscosity, or just viscosity, whereas kinematic viscosity is sometimes referred to as momentum diffusivity.

Malleability and ductility of metals can be accounted due to

Malleability and ductility of metals can be accounted for due to What?

Answer :

• Presence of elastic force

Both the properties are deformation due to the elastic forces while malleability is subjected to compressive force while ductility is subjected to a tensile force. 

Malleability and ductility have different properties have but both are account for the same characteristics.

Malleability and ductility are characteristic of substances with

Malleability and ductility both are the ability of a material to deform to a greater extent before the sign of crack but the difference between malleability and ductility is just in between forces. Malleability is for compressive force while ductility is for tensile force.

Malleability and ductility both are characteristics of substances with metals. 

While all metals are elements that are known to be malleable and ductile as their parts of properties.

In order to understand the two properties or characteristics of malleability and ductility which are good accounts in almost every branch of the mechanical field. It will be necessary to think of the malleable or ductile metals.

Viscosity to density

Density is deriving form viscosity. But one question in your mind How? Let us discuss that in this article.

We all know that viscosity and density are important properties of the fluid as well as in fluid mechanics. both are same but also some difference between viscosity and density are there. Viscosity is how well liquid stick to each other while density is a measurement of the molecular weight of the composition. 

There are two types of viscosity :

1. Kinematic viscosity 
2. Dynamic viscosity 

Kinematic viscosity measures the comparative rate at which a liquid or gas flows whereas dynamic viscosity measures a gas's or liquid's resistance to flow as force is applied to it.

For calculating density you must know both the kinematic and dynamic viscosity of a gas or liquid. 

Knowing just one of the values is not enough, because neither viscosity value has a direct enough mathematical relationship to density.

We can calculate the density of any liquid or gas if we know dynamic viscosity and kinematic viscosity by giving formula below.

Density = Dynamic viscosity / Kinematic viscosity

For example :

Consider a fluid with a dynamic viscosity of 10 Pascal seconds and a kinematic viscosity of 2 square meters per second, the equation would look like this :

Substituting value in above formula :

Density = 10 / 2

Perform the calculation and express the density in kilograms per cubic meter. you can get the answer that looks like this :

Density = 10 / 2 = 5 kilograms per cubic meter

Why use Castigliano's theorem

You can apply Castigliano's theorem if you should have some background with :

• Deflection of a beam/cylinder due to axial loading, bending, torsion.
• For calculating the normal moment of inertia.
• For calculating the polar moment of inertia.
• Deriving equations for linear changes in quantities.
• Using singularity functions but it is often used in conjunction with Castigliano’s Theorem.
• Determining the deflection of beams 
• Castigliano’s Theorem uses strain energies at the locations of forces to determine the deflections.
• For determining of deflections for objects with changing cross-sectional areas.

Muff coupling application

Applications of muff coupling are as follows :

• Piece couplings
• Grooved muff couplings for vertical applications
• Through bore muff couplings
• Stepped bore muff couplings
• Ribbed muff couplings
• 3 piece muff couplings

All of above can be made in different material like cast iron, carbon steel aluminium and stainless steel.

Difference between viscosity and friction

What is Friction?

The most common resistive force we experience every day is called friction is caused by the contact of two rough surfaces.

What is Viscosity?

Viscosity is just the friction between two fluid layers when the two layers move relative to each other.

Viscosity is kind of a special case of friction.

Friction and viscosity are two properties that matter a lot. Let us have a deep insight into the difference between viscosity and friction. 

Main difference :

Friction is used to refer to forces that resist relative motion, whereas viscosity refers specifically to resistive forces that occur between layers of fluid when fluids attempt to flow.

Difference between viscosity and friction : 

• Friction is due to the resistance of relative motion between two solid surfaces where viscosity is due to cohesion or adhesion between two surfaces.
• The viscous force depends on the velocity gradient and area of contact and frictional force independent of the area of contact and relative velocity.
• The force resisting the relative motion of solid surfaces, fluid layers, and material elements sliding between them is called friction while the viscosity of a fluid is a measure of its resistance to gradual deformation through shear stress or tensile stress.
• Friction between solid matter does not depend on speed difference while friction in fluids depends on speed between adjacent layers by means of their viscosity.
• The viscosity of liquid decrease with increase in temperature, Where friction independent of temperature.

Similarity :

• Both properties came in to play whenever there is relative motion.
• Both oppose the relative motion.
• Both depend upon the nature of the surface.
• Both can be erased by intermolecular force.

You can also want to know the difference between related terms like the difference between viscosity and density.

Difference between viscosity and density

Viscosity and density are two very useful properties in describing the statics and dynamics of these substances while viscosity and density are both the same thing expressed in different forms truly different concepts.

What is Viscosity?

The viscosity is a measurement of the intermolecular forces and molecule shapes denote as μ.

What is Density?

The density is a measurement of the molecular weight of the composition denotes as ρ.

 Let us have a deep insight into the difference between viscosity an density. 

Difference : 

• Density says how much mass occupies a certain volume while viscosity is how well a liquid sticks together.
• Viscosity is the thickness or thinness of fluid while density refers to the space between its particles.
• Viscosity asked you the friction between two layers of the given fluid while density varies slightly with temperature. 
• Density and viscosity decrease with temperature, but viscosity has an exponential relationship and density has a linear relationship with temperature.
• Viscosity is applied for only fluids whereas density applied for all three types solid, liquid, gas.
• Viscosity is a physical property while density is a material property.
• Viscosity is how fast the particles move where density is how many particles are in it.
• A fluid with higher density will transition to turbulent flow quicker, and fluid with higher viscosity will have that transition later. so in a sense, they are inversely proportional.

Both of two properties are very different concepts, but together they can describe more than half of fluid's characteristics.

You can also want to know the difference between related terms like the difference between viscosity and friction.

Advantages of muff coupling

Muff coupling is also called sleeve coupling is the simplest type of rigid coupling that consists of a hollow cylinder whose inner diameter is the same as shaft. It is fitted over the ends of two shafts by means of a gif head key and power transmitted from one shaft to other by means of a key and a sleeve. Now, in this article, let us have a deep insight into the advantages of muff coupling.

Advantages of muff coupling : 

• Muff coupling is the simplest form of coupling with consisting of only two parts are sleeve and key.
• It is simple to design and manufacturer.
• It is cheaper than other types of coupling.
• It has compact construction with small radial dimensions.
• It has no projecting parts except the key head.
• The external surface of the sleeve is smooth this gives safety to the operator.

Muff coupling

What is muff coupling?

Answer :

• A coupling in which a hollow cylinder or muff is used to connect the abutting ends of two shafts.

In muff coupling, the muff is made into two halves and they are joined together by means of bolts. Where halves are made by cast iron and bolts are by mild steels. 

Muff coupling is also called sleeve coupling or box coupling.

Muff coupling is fall in the category of rigid coupling.

Features of muff coupling :

• Easy to manufacture.
• Components are easy to assemble and Dismantling.
• Their high torque capabilities make them suitable for higher RPM power transmission applications.
• Due to rigid connection lubrication is not required.
• Maintenance is minimal.
• Low operational cost due to no maintenance and no lubrication
• No moving part hence smooth and quiet operation.

Muff coupling is usually designed on shop floors by assuming standard proportions for the dimensions of the sleeve.

For the sleeve muff coupling the standard proportions used are as follows :

D = ( 2d + 13 ) mm 

L = 3.5 d

Where 

D = Outer diameter of the sleeve ( mm )

L = Axial length of the sleeve ( mm )

d = Diameter of the shaft ( mm )

What is coupling

This article is all about couplings and different types of coupling.

Coupling :

What is coupling?

Answer :

• A coupling can be defined as a mechanical device that permanently joins two rotating shafts to each other.

In other words, the coupling is a device for connecting parts of machinery.

The most common application of coupling is joining of shafts of two separately built or purchased units so that new machine can be formed.

Clutch and coupling doing work for the same purpose but the main difference between them is coupling is permanent connection while the clutch can connect or disconnect two shafts at the will of the operator.

The shafts to be connected by the coupling may have col-linear axes, intersecting axis or parallel axis with a small distance in between depending upon that different coupling are used.

Oldham coupling is used to connect two parallel shafts when they are at a small distance apart.

Hooke's coupling is used to connect two shafts having intersecting axes.

The axis is co-linear or in the same line, rigid or flexible coupling are used.

Advantage and disadvantage of woodruff key

Woodruff keys are semi-circular in shape, leaving a protruding tab when installed. A semi-circular pocket is a keyway in the shaft, the mating part is a longitudinal slot. They are used to improve the concentration of the shaft and the mating part, which is essential for operation at high speed. Let us have a deep insight into the pros and cons of woodruff key in this article. 

Advantages of woodruff key :

• It can be used on the tapered shaft because it can align by slight rotation in the seat.
• The extra depth of key in the shaft prevents its tendency to slip over the shaft.

Disadvantages of woodruff key :

• The extra depth of keyways in the shaft increases stress concentration and reduces its strength.
• The key does not permit axial movement between the shaft and the hub.