PSI - Issue 59

Serhii Drobyshynets et al. / Procedia Structural Integrity 59 (2024) 601–608 Serhii Drobyshynets et al./ Structural Integrity Procedia 00 (2019) 000 – 000

603 3

  cyc n n 1

 u n W W

(1)

Low-cycle fatigue has been sufficiently studied for metal materials with clearly defined areas of elastic and elastic-plastic work (mild steels, aluminium alloys, etc.). For such materials, the following relationship is used (Coffin and Tavernelli (1959), Manson (1953))



  2 (1 ) W a u

  

  



n





(2)

a cyc

In formula (2)  and  are the approximation parameters between stresses and plastic strains in the form

 

 

pl ,

(3)

The approximation of the low-cycle fatigue curves of concrete can be written in the form of a fractional power function (Babych and Krus (1999))

q cyc

1

n



1  

,

p



, b cyc

q cyc

n

(4) The transformed structure of dependence (4) is similar to the analytical criterion of formula (2). The parameter p can be determined from equation (4), by taking n  , i.e. p = 1 - cr b cyc ,  . The parameter q is determined by taking into account the energy hypothesis (Martin (1961))

R  1 2 

q



,



R

(5) where R  is the elasticity coefficient of concrete in the region of significant plastic deformation. The method for determining the parameter q is given in (Babych and Krus (1999)). 3. Methodology of experimental studies

In order to verify the acceptability of formula (4) for steel fibre reinforced concrete, experiments were carried out in the laboratory of the Department of Building and Civil Engineering of Lutsk National Technical University to study the mechanical characteristics of steel fibre-reinforced concrete and determine the low-cycle fatigue of this material. Prisms measuring 15x15x60 cm were tested, made in wooden cassette moulds in three samples with horizontal mixing. Portland cement grade 500 and quartz sand with a particle size distribution of 2.4 were used for the concrete matrix. The steel fibres were made from used ropes, with a wire diameter of 1 mm and a length of 80 mm. The fibres were not profiled. The percentage of reinforcement by volume was 1.5 %. They were washed twice in petrol to clean the fibres from fuel oil. The mixture for the experimental specimens in the composition of 1:2 with a water-cement ratio of 0.4 (by