It occurs when an object becomes curved due to a curling force (moment) and it ends or when an object is supported as it ends and loaded in the middle. The greater the pressure the farther the object will bend. Every object is different but all can only be bent to a certain point before they break. If a beam bends the top is squeezed together and the bottom is pulled apart.The compression stress would be greatest along the top of the beam and the tension is greatest right at the bottom edge of the beam. This can change depending on where the beam and supported and where the load is.