PSI - Issue 18

Ekaterina M. Zubova et al. / Procedia Structural Integrity 18 (2019) 843–848 Zubova et al./ Structural Integrity Procedia 00 (2019) 000–000

847

5

In addition, for each sample we plotted charts comparing the load corresponding to the initial AE emission (crack initiation load) and the maximum load (breaking load) (Fig. 4). Further, calculated the ratio of the crack initiation load to the breaking load. The average value of this ratio for the three samples in all groups are presented in Table 2. It should be noted that the ratio of crack initial load to breaking load for 3D reinforced samples is lower than for layered ones. As a result of mechanical tests on uniaxial tension, the longitudinal, shear, and transverse strain fields were estimated. It is noted that at the early deformation stage at the moment of appearance of the first acoustic emission signals no damage was detected on the surface of composite samples, that may indicate the formation of internal defects and failure processes in the grip area. The characteristic longitudinal, transverse, and shear strain fields, which correspond to the moment of defect initiation in the specimen, are given below for an example (Fig.5).

Table 2. Ratio of crack initial load to breaking load for samples in tensile tests Samples group Type 1 Type 2 Type 3

Type 4

% of maximum load

12,95

8,64

35,5

31,7

ε xy , %

ε xy , %

ε yy , %

0,38

0,02

0,001

0,25

0,01

-0,012

0,13

-0,01

-0,025

0

-0,02

-0,038

Fig. 5. Illustration of inhomogeneous fields components of strain at the time of damage initiation in the sample

Conclusions A series of mechanical tensile tests of CFRP (samples obtained by 3D weaving, layered samples) was carried out in simultaneously by the using acoustic emission technique and digital image correlation technique. New experimental data were obtained (the maximum load, the crack initiation load, fields of displacements and strain at the initial stage of loading). The crack initiation load was determining by using the AE technique as the load at which a jump occurred in the distribution of the energy parameter of the AE. It is revealed that the ratio of the crack initiation load to the breaking load for 3D reinforced plastics is lower than for laminated plastics. Acknowledgements The reported study was funded by RFBR according to the research project № 18-31-00452.