Stress- Strain Diagram Part-1

By -
Explain the stress- strain diagram neatly with relevant fig.
To select a material for using it in aircraft, we need to know what its life time is. How much it performs? and many more requirements. All these are for having a safe flight. The life time and every required factors will be known once if we know stress strain diagram.

In order to attain stress strain diagram, we need to have a specimen of desired standards. A standard specimen of the mild steel material is prepared as per BIS standards is given below.



Then we need to fix it properly in the universal testing machine. We can give tensile (widely used) or compressive load to the specimen. Load value has to be adjusted very smoothly. By determining the stress and strain at various magnitudes of the load, we can plot a diagram of stress versus strain.

Some common terminologies 

Load - The force applied to a material during testing.
Strain Gage or Extensometer - A device used for measuring change in length (strain).
Engineering stress - The applied load, or force, divided by the original cross-sectional area of the material at that instant.
Engineering strain- The amount that a material deforms per unit length in a tensile test.

Elastic deformation


When load acts on a material shown, it creates stress. when load is acting on a object, the object undergoes atomic bond changes, when removed it again retains its original bonding. This happens only within elastic limit. Some object is having linear elastic proportion when load applied, some follows non-linear.

Plastic deformation


From an atomic perspective, plastic deformation corresponds to the breaking of bonds with original atom neighbors and then reforming bonds with new neighbors. After removal of the load, the large number of atoms that have relocated, do not return to original position. Yield strength is a measure of resistance to plastic deformation.

Yield strength Determination:


Typical stress-strain behavior for a metal showing elastic and plastic deformations, the proportional limit P and the yield strength σy, as determined using the 0.002 strain offset method (where there is noticeable plastic deformation). P is the gradual elastic to plastic transition.


For more detail Refer part-2 








Comments

Post a Comment

Popular posts from this blog

Fire detection system in aircraft

By -
Image
What are the common fire detection methods followed in aircraft? Explain them with neat diagrams. Thermal Switch: Thermal switches are heat –sensitive units that complete electrical circuits at a certain temperature. They are connected in parallel with each other. If the temperature rises above a set value in any one section of the circuit, the thermal switch will close the electrical circuit and gives indication to the pilot through indication lights. Thermo-couple systems: A thermocouple gives the rate of temperature rise. A Thermocouple is the junction of two dissimilar metals which generates a small electric current that varies according to the temperature of the junction. For this reason it does not require an external power source. The dissimilar metals can be constantan and iron, Alumel and Chromel, or some other combination of metals or alloys which will produce the required results. The complete thermocouple circuit consists of the ‘cold’ junction, the ‘h...
Get more »

Vapour cycle cooling system in aircraft

By -
Image
Explain the vapor cycle cooling system used in aircraft with neat illustration. Also explain the physics behind the scene of working. Physical principle Liquids can be vaporized at any temperature by changing the pressure acting on it.  To clearly understand this concept, we will take an example of water contained in a vessel. When the vessel is at atmospheric pressure, the water will be boiling at 100°C when heating. If I am pressurizing the vessel to more than the atmospheric pressure, then water will not boil at 100°C. If I am creating a drop in pressure in the vessel by a vacuum pump, then water will boil at a temperature less than 100°C. Basic law of thermodynamics states that heat will always flow from hot body to cold body. If I need a reverse of this, I have to add some work. System operation: 1. We are having the FREON as refrigerant in the vapor cycle cooling system. It has a boiling point of 4°C. 2. At the receiver I am having high pressure, ...
Get more »

Smoke detection system in Aircraft

By -
Image
What are the methods to find smoke prevailing in aircraft? Explain with neat sketches. For smoke, fire is main reason. In some cases it may not be. However pure air just contains 78% of nitrogen, 21% of oxygen and 1% rest of other gases. When there is fire in the aircraft the air will be dirt since carbon monoxide or carbon dioxide presents. There are four effective ways to identify the smoke. Light detection Light Refraction Ionization Solid state semiconductor Light detection type: We all know photo voltaic cell converts light energy into electrical energy. The pure light rays will be fall on photo voltaic panel and produces some electrical energy at normal.  When the area is surrounded by smoke the intensity of light rays falling on the panel gets differ. From that we get alarm. Light Refraction type smoke detector: Here a certain mass of air is taken for smoke detection by use of fan. Source of light is the Electric bulb. It is made to ...
Get more »