PSI - Issue 50

N. Mullahmetov Maksim et al. / Procedia Structural Integrity 50 (2023) 200–205 Mullahmetov Maksim N. et al./ Structural Integrity Procedia 00 (2022) 000 – 000

201

2

1. Introduction Composite materials have a set of properties and features that distinguish them from traditional structural materials and open up wide opportunities both for improving existing multifunctional structures and for developing new structures and technological processes. [V.V. Vasiliev et al (1990)]. Stress concentration is often present in structures due to the nature of their operation, damage, or any geometric factors (holes, fillets, grooves, etc.) [Lobanov D. S et al (2019), J. Awerbuch et al (1985), Strungar, E. et all]. There are various approaches to account for this phenomenon. A prime example of this is the Critical Distance Theory (TCD) [D. Taylor et al 2007, J. M. Whitney et al (1974), B. Gillham et al (2021)]. The TCD method is essentially a linear elastic fracture mechanics (LEFM) approach and as such is based on elastic stress analysis. 2. Materials and methods To predict the strength properties of composites, two methods of the theory of critical distances were used: linear and point. The idea is that a critical volume of material must be subjected to critical stress for failure to occur. The theory is presented in two review monographs [J. M. Whitney et al (1974), ]. The critical distance is a constant that depends on the material. The theory of critical distances, in fact, is an approach of linear elastic fracture mechanics and is based on the analysis of elastic stresses in the vicinity of a notch. The stress at the characteristic point or the average stress along the characteristic line near the notch is taken into account. Fracture is predicted to occur if the stress range at a point (or averaged over a line) is equal to the stress causing failure in a simple sample (without a concentrator). By type of topology, the approach can be categorized as shown in fig. 1.

Fig. 1. Linear and point method of the theory of critical distances.

Point method:

σ eff = σ 0 = σ y (Ɵ = 0, ρ = L/2).

Line method:

1 2 0 

  d ρ , σ θ ρ 0 

L

σ σ eff

 

y

0

2

L