Note: Download Basics of Mechanical Engineering at the end of the article.
Tabular Column for Basics of Mechanical Engineering:Principal Stresses, Principal planes, Maximum Shear stress, Maximum Shear Stress Planes with Formulas: When you are going for an interview or writing any competitive exam then a compulsory question will be asked on either of the above terms in terms of a Definition or a Numerical. If it is a numerical question, it generally carries 2 marks and if it is a theory question, it may be 1 mark or 2 marks. So, I am focussing on the definitions as well as formulas related to those terms. The Definitions and their Representation were presented below either in the form of text or in the form of Images. If you want formulas, then try to copy from the images. 1.Principal Stresses:
- The maximum or minimum normal stress is the principal stress.
- These principal stresses are used in the design.
- The plane on which principal stresses will be acting is called the principal plane.
- On the principal plane, shear stress must be zero.
- Any plane in the material without shear stress is by default principal plane.
- In a 2-D system, there are two principal planes separated by 90 degrees. On these planes, shear stress is zero.
3.Maximum Shear stress(in 2D Plane stress system): The Maximum Shear Stress in the 2D Plane stress system is presented below. 4.Maximum Shear Stress Planes: The plane on which maximum shear stress is acting called as maximum shear stress plane and the formula of Maximum Shear Stress Planes will be collected from the above image placed in the maximum shear stress section.
- In a 2D system, there are two (Tow max) planes separated by 90 degrees.
- The angle between any one principal plane and the nearest (Tow max) plane is 45°.
- On (Tow max) plane, there will be normal stress and which is in the middle of (Sigma 1) and (Sigma 2) by magnitude.
- The magnitude of shear stress on mutually perpendicular planes must be the same.
- The sum of normal stresses on mutually perpendicular planes must be constant.
7.Resilience: The ability of the material that can absorb energy without undergoing any shape change is called Resilience. Determination of Resilience:
- The resilience of the material will be determined by calculating the area under stress v/s strain curve up to an elastic point.
- Resilience says about the strength and ductility properties of the material.
- If a material possesses higher the resilience means it will absorb more energy against shape change.
8.Punch Die Clearance in Design:
Explanation about the Punch Die Clearance in Design:
- When the hole has to be held to size i.e.the hole in the sheet metal is to be accurate, the punch is made to the size of the hole and dies opening size is obtained by adding clearance to punch size.
- In blanking operation, where the size of the blank is to be maintained accurately, die opening size is exactly equal to blank size and clearance is to be subtracted from die opening size to get punch size.
9.Quasistatic Process: A system is made to undergo a series of change of states such that it is in thermodynamic equilibrium at each and every state. Then the locus of all these states is called a quasistatic process.
- It is an ideal and very slow process.
Assumptions of Ideal gas:
- Molecular separation is very high.
- Molecules do not occupy any volume.
- The molecular collisions are elastic in nature.
- There are no inter-molecular forces of attraction are present.
10.SI Unit of Pressure: SI Unit of Pressure: The unit of pressure in the SI system is the pascal (Pa), defined as a force of one Newton per square meter. SI Unit of Pressure-Units of Pressure:
- 1 atm =101.325KPa
- 1bar =10^5 Pascals
- 1torr =1mm of Hg
- For High Pressures, go for ‘Hg’ manometers
- For Low Pressures, go for ‘water’ manometers.
Basics of Mechanical Engineering: 11. What is Strength? The definition of strength is as follows… The ability of the body to resist external loads without failure is called Strength.
- Strength is a material property.
- It is constant for the material.
- Any design is a strength-based design only.
12.Mechanical Properties of Metals: When you want to apply any type of load on a particular member, you need to know its material properties, density, etc. For that, in this article, I am exploring the necessary properties of metals in a detailed manner. 11 Properties of Metals: The Properties of Metals which are essential for a mechanical engineer are as follows.
- Bond: It possesses a metallic bond.
- Strength: The strength of the metal is very high when compared to plastics and ceramics.
- Binding Energy: The distance between the atoms is less and thereby the Binding energy is high.
- Ductility: It possesses good ductility also.
- Conductivity: The metals possess good electrical conductivity because of the presence of free electrons.
- Thermal Conductivity: The metals possess good thermal conductivity.
- Density: The metals possess high density which means that the weight of the metal is more and this is one of the disadvantages of metals.
- Corrosiveness: The metals are highly corrosive to the environment.
- Servicing Temperature: The servicing temperature of the metal is 800̊ C-1000̊ C.
- Hazardous: It is not hazardous and is environmentally friendly.
- Recyclability: The metals are partially recyclable in nature.
13.Properties of Ceramics: The mixture of metal oxide powders like the Powder of Aluminum oxide, Powder of Silicon Oxide and the Powder of Zirconium oxide are collectively called as ceramics. The various Properties of Ceramics are shown below in a detailed manner.
Top 11 Properties of Ceramics:The Properties of Ceramics which plays a crucial role in the field of mechanical engineering are as follows:
- Bond: The ceramics possess both Ionic and Covalent bonds.
- Strength: The strength of the metal is greater than the strength of Ceramics and that is greater than the strength of Polymer.
- Distance between atoms: The distance between the atoms of metal is less than the Ceramics and is less than the Polymers.
- Brittleness: The ceramics are brittle in nature.
- Conductivity: The ceramics possess bad electrical conductivity because of the absence of free electrons.
- Thermal Conductivity: The Ceramics possess bad thermal conductivity but they can sustain at high temperatures easily.
- Density: The Density of Metal is greater than Density of Ceramics and that is greater than the Density of Polymers.
- Corrosiveness: The Ceramics are Anti-Corrosive to the environment because they are already in corrosive form.
- Servicing Temperature: The servicing temperature of the metal is 3000̊ C.
- Hazardous: It is not hazardous to the environment.
- Recyclability: The ceramics are non-recyclable in nature.
14.Compare Mass and Weight: Mass of the body:
- Mass of the body does not vary from place to place and it is not affected by the gravitational force.
- It is represented by “m”.
- Unit of mass “m”=Grams
- Weight of a body varies from place to place and depends on the acceleration due to gravity existing at that place.
- It is represented by “W”.
- The formula for weight of the body is
- If “g” is positive then the sign of “W” cannot changes whereas
- If “g” is negative then the sign of “W” changes.
15.The ratio of Specific heat at Constant Volume and Constant Pressure: The ratio of Specific heat: It is defined as the ratio of specific heat at Constant Pressure to Specific heat at Constant Volume. It is represented by Gamma(γ) (γ or Gamma) = Cp/Cv. A ratio of Specific heat at Constant Volume and Constant Pressure Specific heat at Constant Volume and Constant Pressure: The ‘γ‘ value is different for different gases and is as follows.
- γ = 1.63 for monoatomic gases.
- γ = 1.4 for Diatomic Gases.
- γ = 1.33 for Triatomic gases.
16.Post Heating in Welding:
- Post-heating is done in order to relieve further residual stresses present in the weld pool after heat treatment process also.
- If post-heating is not done, then residual stresses develop as cracks and propagate throughout, resulting in the failure of the material.
- Therefore Preheating and Post heating must be done during welding.
17.Pre heating in Welding Process:
Need of Preheating in Welding process: Preheating in Welding involves heating the base metal, either in its entirety or just the region surrounding the joint, to a specific desired temperature called as preheating temperature, prior to welding. In this article, I am going to publish about, what is the need of Pre-heating in welding process in a detailed manner.
Heating may be continued during the welding process, but frequently the heat from welding is sufficient to maintain the desired temperature without a continuation of the external heat source.
18.Stepper Motor: Explanation of Stepper Motor along with its Importance: Stepper Motor is widely used in the field of Robotics where high precision is needed. In this article, I will be explaining about the stepper motor and its importance in a detailed way.
Explanation of Stepper Motor:The stepper motor is taking electrical energy input in the form of pulses and converting into mechanical energy in the form of revolutions. But, by changing no. of pulses of electrical energy to a motor (or) by changing the rate of pulses of electrical energy input to the motor, the speed of the stepper motor can be changed. Because of the presence of inertia effect of moving parts, even though the power supply is stopped to the motor, it is not possible to stop the motor axis immediately. Hence, the tool is traveling some more distance and therefore accuracy of the components produced is poor. i.e. The positional accuracy of the machine tool will become poor. This is the complete explanation of the stepper motor in detailed. There is an advanced of a stepper motor i.e. servo motor which will work much effectively than it and can be used in various installations. 19.Difference between Specific gravity and Specific Volume: Specific Volume: It is the reciprocal of Density which is defined as the ratio of Volume of the body to its unit mass. It is denoted by (ν)
- Specific Volume(ν)= Volume of the body/unit mass.
- Units = m3/Kg
20. What is Thermocouple? These are used to measure the temperature at a particular point. They are manufactured by using two dissimilar materials belonging to thermoelectric series.
- One is higher order element and another is a lower order element and 2 junctions are made.
- One junction is kept at Ice Point and Another junction is kept at the place whose temperature is to be measured.
- Due to the difference in temperature, an EMF is generated and this EMF is related to temperature.
21. What is the Seebeck Effect? Development of EMF due to the difference in temperature is called a Seebeck effect.
22. What are Pyrometers? They can function on the principle of radiation. They are used to measure the temperature’s from a distance.
23.What is Pressure?
It is defined as the ratio of Force acting per unit Area of the cross-section.
Measurement of pressure is done by the manometer.
Unit of Pressure in S.I. system is “Pascal”.
The eloborative units were presented above at Point No.10
The Sum of Atmospheric pressure and Gauge pressure is called Absolute Pressure. or
The Difference between Atmospheric pressure and Vaccum pressure is also called as Absolute Pressure
|Absolute Pressure=Atmospheric pressure+Gauge pressure|
25.What is Vaccum Pressure? It is defined as the difference between Atmospheric Pressure and the Absolute Pressure
|Vaccum Pressure = Atmospheric Pressure-Absolute Pressure.|
26.Numerical based on vaccum and atmosphere: Vaccum and Atmosphere are the two most popular terms used in the thermodynamics. So, let’s do a numerical on it. Therefore, In this article, I am going to explain about the simple Numerical based on vaccum and atmosphere in a detailed manner. Numerical based on Vaccum 1. A mass of 1Kg falls to a distance of 10m in Vaccum. What is Work done? Sol: Work done = Zero Numerical based on Atmosphere: 1. A mass of 100N falls through a distance of 10m overcoming drag resistance of 5N. What is the work done? Sol: W =F*S =FSCos(theta) = FCos(theta)*S =resisting force*distance =5*10 =50Nm
27.Difference between Engineering Mechanics and Strength of Materials: This type of questions will be asked in the interview point of view and the answer for this question is well explained in the next paragraph.