Gradient-enriched linear-elastic tip stresses to perform the highcycle fatigue assessment of notched plain concrete

C Bagni,L Susmel,H Askes

doi:10.3221/igf-esis.33.14

Abstract

Gradient Elasticity (GE) allows the stress analysis to be performed by taking into account the size of the dominant source of microstructural heterogeneity via a suitable length scale parameter. This is done by simply assuming that the material under investigation obeys a linear-elastic constitutive law, albeit equipped with additional spatial strain gradients. From a practical point of view, the most important implication of this modus operandi is that gradient-enriched linear-elastic stresses at the notch tips are always finite, this holding true also in the presence of sharp stress risers (such as cracks). In the present investigation, the accuracy of two different GE based design strategies was checked against a number of experimental results generated by testing, under cyclic four-point bending, plain concrete samples containing different geometrical features. The high level of accuracy which was obtained by directly using gradient-enriched linear-elastic notch stresses strongly supports the idea that GE is a powerful tool suitable for designing notched concrete components against high-cycle fatigue. This result is very promising also because the required stress analysis can directly be performed by using standard Finite Element (FE) solvers.

Highlights

I n the civil infrastructure sector, concrete is the most commonly used material
The aim of the present investigation is to check whether linear-elastic gradient-enriched notch tip stresses are successful in performing the high-cycle fatigue assessment of notched plain concrete
These diagrams clearly prove that the use of the gradient-enriched notch tip stresses determined by taking l equal to the average inter-aggregate distance resulted in highly accurate estimates

Summary

INTRODUCTION

I n the civil infrastructure sector, concrete is the most commonly used material This explains the reason why the problem of optimising the static assessment of concrete has been studied by the international scientific community for decades. It has to be highlighted that, apart from three isolated investigations [3,4,5], no effort has been made so far to devise and validate (through appropriate experimental investigations) specific techniques capable of modelling the detrimental effect of notches on the overall fatigue strength of plain concrete In this setting, the aim of the present investigation is to check whether linear-elastic gradient-enriched notch tip stresses are successful in performing the high-cycle fatigue assessment of notched plain concrete.

FUNDAMENTALS OF GRADIENT ELASTICITY

NTB u

EXPERIMENTAL INVESTIGATION

Specimen ID

Blunt Intermediate

CONCLUSIONS