Stress is defined as the force per unit area of a material while Tensile means the material is under tension.Tensile stress is the ratio of the stretching force to the cross-sectional area.The maximum stress a material can stand before it breaks is called the breaking stress or ultimate tensile stress.This is an important concept in engineering, especially in the fields of material science, mechanical engineering and structural engineering.
σ=F/A
where,
Units of σ : Nm2 .However, stress has its own SI unit, called the pascal. 1 pascal (symbol Pa) is equal to 1 N/m2. In Imperial units, stress is measured in pound-force per square inch, which is often shortened to "psi". The dimension of stress is the same as that of pressure.
Tensile forces is determined by the requirement that total fractional changes in length,Thermal expansion plus elastic strain must be zero.F/A is positive in case of decrease in temperature since change in temperature becomes negative.
In cases where change in temperature tends to increase in temperature of the body then F and F/A becomes negative, corresponding development of to compressive force and strength.
Finally stress which is is positive with decrease in temperature is Tensile stree and stress which is negative with increase in temperature is Compressive stress.