Effect of stress and Youngs modulus

When a solid is subjected to a stress, it generally experiences a strain which, if pursued, could cause the material to fracture. The applied stress is measured in newtons per square meter. 

A solid, therefore, is characterized by its modulus of longitudinal elasticity, known as Young s modulus, defined by  

If we start at O and arrive at a point between O and A (a point marking the start of a lesser increase of the curve), and we slowly decrease the stress, the strain deereases in accordance with the same Hooke curve. We then say that we are in the domain of elastic deformation. When the stress returns to zero, the sample returns to its initial length. The load at point A is called the elastic limit. 

When we reach a point R, the test-tube breaks. The corresponding stress is called the fracture limit. 

The different characteristics of the curves in Figiue 1.2 vary greatly from one material to another. Hence, for example, the fracture load is much greater for steel than for concrete, which has pitifril traction resistance - this is why steel rods are used in reinforced concrete. 

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