This is a composite with two different materials and sections with a size of 50mm x 50mm x 50mm. Uniaxial displacement loading is given and stress strain curve is obtained in two methods as shown. Looks like Both methods gives similar results. 

I want to know whether these two methods are equivalent and why? (In first method sum the RF2 values of bottom nodes and combine it with a displacement from a top node and convert it to stress and strain. Second method is combining Volume averaged stress and strain over whole model. Volume average is calculated by the given equation by using stress component of integration points and volume of integration point)

Abaqus ​​​​​​​