PSI - Issue 18

D.A. Bondarchuk et al. / Procedia Structural Integrity 18 (2019) 353–367 D.A. Bondarchuk, B.N.Fedulov, A.N. Fedorenko/ Structural Integrity Procedia 00 (2019) 000 – 000

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The fracture pattern is different for two cases. In case of ignoring residual stresses there is no distinctive cracking along the fibers of the layers oriented along the direction of the load. A visual and X-ray analysis of samples with a single-axis tension, provided by Tinô and Aquino (2004) , Gyekenyesi (2019), Tarpani et al. (2006), Shen et al. (2017), showed the presence of intense cracking in the binder (Fig.9 a and Fig.9 b).

(a)

(b)

ε=0,95%

Gauge length marker

Load direction

AE transducer

Fig. 9. (a) the formation of cracks in the matrix with longitudinal tension in the sample 0 0 /90 0 ;(b) X-ray of cracks in the sample with [0 4 0 /90 4 0 ] layup under unidirectional loading.

6. Conclusions In current research, an extensive numerical investigation of stress concentration phenomena near the free edge of AS4/8552-1 carbon-epoxy multilayered composite was provided. The problem was solved for plane strain case for composite specimen with [0 0 /90 0 ] lay-up and perfect straight cut along the fiber direction after curing. The behavior of the material during manufacturing and distribution of locked-in stresses was studied using developed program that was implemented in Abaqus software. Based on simulation results it can be concluded that maximum stresses in specimen are close to the ultimate one. However, the maximum stresses after cut are concentrated in a small area around 10 microns near the free edge. According to data provided in the product data sheet for epoxy matrix 8552, transversal tensile strength for prepreg AS4/8552 is 81 MPa. The maximum stress for samples after polymerization before cut is 52.7 MPa and for samples after cut the stress values reach 68 MPa. The out of plane stress (σ 33 ) after cut is 48MPa. Thus, the values for stresses are essential and cannot be ignored in consequent stress analysis. The possible failure mechanism of composite is matrix mode fail. Possible delamination of the composite occurs because of normal margin and not connected with the shift of the layers. Such effects cannot be seen using shell elements for modeling. As a result of modelling the loading of the composite up to failure with consideration of the residual stresses, it is shown that tension leads to cracking of the matrix in layers where the orientation of the reinforcement coincides with the direction of the load application. At the same time, when ignoring residual stresses, the appearance of such defects is not observed. This research shows that residual stresses affect both the strength of the material and the mode of failure.