PSI - Issue 48

Mirza Manjgo et al. / Procedia Structural Integrity 48 (2023) 161–168 Manjgo et al / Structural Integrity Procedia 00 (2023) 000 – 000

162

2

Cracks are one of the most dangerous damages that can occur during exploitation of a certain part. Therefore, determination of the material’s properties which infl uence crack formation and propagation is very important. By knowing the mechanical properties of the material, it is possible to determine the sensitivity of individual parts of the structure to the formation of cracks. Fracture mechanics, through theoretical and experimental analysis of the behaviour of bodies with a crack, has opened new possibilities in ensuring the safety of structures [4]. As for the other materials, knowledge of fracture mechanics parameters is of crucial importance also for the use of armour steels [5]. Therefore, the goal of this investigation was to obtain the resistance curve towards the crack, the R -curve, that is, the J - ∆ a dependence, which represents the values of the J integral for uniform increments of the crack ∆ a . Beside the other basic mechanical tests also the instrumented Charpy test was done. Instrumented Charpy test allows to split the total measured energy into the fraction required for the creation and the fraction required for the propagation of the crack. Thereby, a better understanding of the materials resistance to crack formation and propagation is facilitated, which is very important for understanding the behaviour of materials in anti-ballistic protection. 2. Material SA500 steel, produced in the Slovenian steelworks Acroni Jesenice, was used for the experimental work. It belongs to the group of steels for anti-ballistic protection, ultra-high strength, high hardness and good ductility. Its function is to repel the bullet, deform the bullet, absorb the energy of the bullet or a combination of all three effects [1]. The chemical composition of the tested steel is given in Table 1, and the basic mechanical properties are given in Table 2.

Table 1. Chemical composition of SA500 steel [6]. All values are in max. %

Mo 0.5

B

C

Si

Mn 1.2

P

S

Cr

Ni

0.30

1.0

0.02

0.003

0.8

0.6

0.004

Table 2. Typical mechanical properties SA500 steel [6]

Hardness HB

Tensile strength R m [MPa]

Elongation A 5 [%]

Impact energy CVN [J]

Yield strength R p0,2 [MPa]

at - 40⁰C

480-530

1200

1700

10

35

3. Experimental For the experimental tests, mechanical tests were carried out to determine the properties of resistivity and deformation of the base material: strength, hardness, elasticity, plasticity, and impact energy.

3.1. Tensile test

The tensile test is defined by the EN ISO 6892 – method A [7]. The test was carried out on an electromechanical machine Smithweld 1405. Two test pieces were tested (Figure 1). Results of the tests are shown in Table 3.

Figure 1. Geometry of the tensile specimen