Numerical methods to simulate softening and fracture of concrete

The tensile fracture of concrete is as a rule regarded as brittle. Concrete has no yield behaviour of the type found in metals. Its tensile stress-strain diagram is nearly linear up to the maximum point, whereupon it immediately starts to descend. In spite of this concrete however can be said to have a considerable toughness. This toughness causes the fracture process zone in front of a growing crack to be of the order of 100–200 mm or even longer [1], i.e. much longer than what is normally found for metals. Because of these long fracture process zones linear elastic fracture mechanics (LEFM) can as a rule not be applied to concrete. On the other hand those methods which have been developed to take into account yielding within the non-linear zone for metals cannot be applied directly to concrete, as concrete does not yield in the way metals do. The toughness of concrete has to do with the softening, i.e. the existence of a descending branch in the stress-deformation diagram. This chapter describes the possibility of analysing the tensile fracture and fracture mechanics of concrete by means of methods based on the softening behaviour. The starting point will therefore be the softening properties of concrete in a simple tension test.