Abstract :
macrodescription of the nonlinear behavior of a heterogen under compression, as
given by the central function : CT= EEG, employs the Gaussian term G, which expresses the stochastic
character of the heterogen’s atrophy through microcracking and comprises two critical parameters :
the limiting strain of elasticity (atrophy threshold)-c,,. and the scattering factor-d. It does not,
however. involve parameters of the microcracking mechanisms. As for the models of local lateral
tension and microrupture, they are based on the gradients in Poisson’s ratio and elastic moduli of
the heterogen‘s components and are not related to the parameters of the heterogen in macro.
Linkage of the micro and macro models was effected by generalization of the gradient micromechanisms.
It showed that the strength of a brittle solid in compression is a function of its
resistance to microrupture and of the gradient factor. Despite the fact that longitudinal compression
creates the gradient strains, it is shown that the two critical macroparameters, E, and d, are affected
(m a probabilistic way) by two critical lateral strains : the minimal limiting strain of microrupture--
I:,: and the strain of the mode (the maximum) of the pdf of the heterogen’s resistance to microrupture--$.
To check the obtained models. the linkage between the strength of concrete in tension and
compression was analyzed. It was found that their ratio reflects the gradient factor in the heterogen.
The decrease in Poisson gradient with increasing strength can explain the faster increase in the
compressive strength versus the tensile one. The obtained results confirm an old idea that the
properties of a heterogen in tension represent its fundamental characteristics.
In the light of the obtained models the failure of concrete in the Brazilian test seems not to be
another type of tensile failure, but a distinct kind of degeneration of the heterogen due to gradient
lateral strains induced through the strips under compression. 111 1997 Elsevier Science Ltd.
