PSI - Issue 20

A.K. Kychkin et al. / Procedia Structural Integrity 20 (2019) 198–205 A.K.Kychkin et al. / Structural Integrity Procedia 00 (2019) 000 – 000

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chemical transformations connected with post hardening of the epoxy matrix, resulting from high solar activity in Yakutsk in summer. Here, the role of atmospheric moisture is insignificant.

Table 2.Comparative test data on buckling of samples.

Regulation norms and documents for tests TU standard 296-00120994511-04

, MPa Initial state

BPA type

After exposure 28 month

After exposure 51 month

Rods 6 mm in diameter Rods 8 mm in diameter

1022,6 975,4

1215 1050

1220 1150

Table 3. Results of comparative tests for axial tension.

Regulation norms and documents for tests

Initial state

After 20 month.

After 51 month.

BPA type

Е, GPa

Е, GPa

Е, GPa

, MPa

, MPa

, MPa

Rods 6 mm

53,2

1120,1

52,7

1205,8

53,5

1275,1

GOST standard 31938-2012

Rods 8 mm

50,8

1003,4

51,2

1077,6

51,8

1080,78

According to results of strength and deformability tests using tension testing machines, destruction of initial samples starts, as a rule, with a rupture of the braided thread forming a periodic profile. Then, follows the rupture of separate fibers in the surface layer of the effective area of the sample, and more intensive destruction of fibers over the rod perimeter with centripetal propagation occurs. Here, the load growth stops, and rupture of the rod occurs, forming wisps. The characteristic type of destruction is given in Fig. 2 (a). In samples after exposure, destruction starts with chipping of the surface layer of the rod, followed by rupture of braided thread and further viscous brittle fracture in the effective area of the sample (Fig. 2 (b)). The conducted mechanical tests evidence that destruction of the samples during exposure starts with deterioration of the surface layer of composite rods, thus, the greater the diameter of the samples under study, the higher strength properties after exposure under the conditions of Yakutsk.

Fig. 2. Nature of destruction: a) type of destruction of the initial sample, b) type of destruction after 28 months of exposure c) a type of destruction after 51 months of exposure