PSI - Issue 32

A.S. Smirnov et al. / Procedia Structural Integrity 32 (2021) 321–325 A.S. Smirnov et.al./ Structural Integrity Procedia 00 (2021) 000–000

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In order to record possible structural changes in the composite during heating, dilatometric analysis was made using a Linseis L75VD1400C vertical dilatometer with an α -Al 2 O 3 pusher in the air environment. The measurement repeatability error of the dilatometer is ±150 nm. For the study, 20-mm long specimens were cut in the directions of [0°] and [90°] in the plane of the material and heated from room temperature to 150 °C at a rate of 3 °C/min. Figure 5 shows fiberglass elongation as a function of temperature during the first and second heating of the specimen. The data in Fig. 5 show that, as the test specimens are heated to 150 ºC, the linear dimensions change nonmonotonically. A more intense change in linear dimensions of the fiberglass is observed at temperatures of up to 110 ºC, and then the increment in the linear dimensions slows down with increasing temperature. This behavior of the material is probably due to a change in the matrix structure at a temperature above 110 º С. At the same time, the matrix structure does not recover its initial state during cooling, this being manifested in a significantly altered temperature dependence of specimen elongation during reheating. The obtained result of the irreversible rearrangement of the fiberglass matrix structure at a temperature of 150 º С can explain the reason for the lower strength properties of the composite at a temperature of 140 °C after reaching a load of followed by an interdeformation pause. Most likely, the rearrangement of the structure is affected not only by temperature, but also by the applied external stress and the time that the polymer needs to rearrange its structure after the load is removed. The irreversibility of the structural rearrangement of the composite matrix at a temperature of about 140 °C is demonstrated by the dilatometric tests.

Fig. 4. The fracture pattern of the fiberglass specimen under loading perpendicular to the sheet plane.

Fig. 5. Dilatometric diagram of fiberglass cut in the directions of [0°] (a) and [90°] (b) under heating at a constant rate: gray – the first heating; yellow – reheating.