TRUE STRESS VS ENGINEERING STRESS EXPLAINED !!!

Stress is defined as the resistance force acing per unit cross section area of the body. It is also defined as the ratio of applied load to the cross section area of the body.It is an internal property of the material.True stress and Engineering stresses are a bit different. 

Let us take the example of tensile test.Before doing the tension test we have to determine the length and diameter of the specimen and we assume these parameters remain constant throughout the whole experiment. So when we calculate the stress by the formula-

 Stress= Force/Area

we actually calculate the stresses (corresponding to different strains) for the given value of diameter which we have calculated in the beginning of experiment. These stresses are called Engineering Stresses.but as we do the experiment we observe a phenomenon called necking and till now we have been neglecting any such necking which takes place. So let's see what happens when there is necking.

So, As we can see as the bar is subjected to tensile forces just like what happens in a tension test experiment and after certain instant a neck like region forms. This shows the cross-section of the specimen has changed as the experiment proceeds further.

Hence whatever we  will get the stresses now will be different from the ones we got when we we assumed the cross-section remained constant. These stresses are called TRUE STRESSES. True stresses are thus force divided by the area of the section at that instant.

(It should be noted that only after the necking starts there is a considerable change in the cross-section and thus the variation between the two stresses becomes more prominent).

INDUSTRIAL HELMET COLOUR CODE EXPLAINED !!!

You might have seen various employees of a factory wearing a hard hat of different color!!Let's understand the meaning of this color code!

Hard hats are made from hardened plastic and, as such, they have an expiry date because plastic deteriorates over time.  This means that they will need to be replaced periodically so it’s important that you check the expiry date on any hard hat that you use.  A hard hat’s service life starts when it is first used and that date should be recorded on the hat in indelible pen.  The maximum time for replacing a hard hat is five years, but it should be checked regularly for signs of wear or damage.  The hard hat suspension should be replaced on an annual basis – they’re widely available from work gear outlets.

Hard hats come in a range of colours, all of which are significant as it allows workers on site to identify who is who and what type of work they are undertaking.

KNOW THE MEANING OF A/F ON NUMBER PLATE IN NEW VEHICLES !!!!

A/F stands for Applied For. This was a previous notation on the newly bought number plates of the vehicles. Every vehicle needs to be registered under the Motor Vehicle Act 1989.

Yes,it's illegal to drive with an A/F plate in India and can attract heavy fine and even car can be bonded. Every car that rolls off the showroom now gets either a temporary number or a permanent number according to the state.

The Central Motor Vehicles Rules (CMVR) do not allow driving a vehicle without registration. To drive a vehicle even with the `A/F' (Applied For) status is an offence. "It is a misconception that people can drive with an A/F tag,"