PSI - Issue 32

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

322

2

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

determination of the physical and mechanical properties of polymer composite materials and the study of thermomechanical effects on their fracture mechanisms and deformation behavior in a wide temperature range are relevant for determining the operating ability of aircraft structural elements under conditions of high temperatures. The goal of this study is to determine the influence of the deformation-temperature-time factor on the mechanical properties. 2. Research methodology and results The object of the study is a cross-reinforced laminated fibrous ten-layer fiberglass sheet with [0/90]n schemes of laying reinforcing layers (Fig. 1).

Fig. 1. Fiberglass lay-up (a); an image of the fiberglass along (b) and across (c) the direction of laying.

The effect of temperature and time on changes in the mechanical properties of the fiberglass was studied on the basis of dilatometric analysis and compression tests in a universal device designed at the Institute of Engineering Science, Ural Branch of the Russian Academy of Sciences. Compression was performed in the direction perpendicular to the plane of the fiberglass sheet. The effect of temperature and time on the changes in mechanical properties was tested as follows. First, fracture stress was determined at the test temperature. Then, at the same temperature, the specimens were loaded to 90% of the fracture stress and held under load for 5 seconds (Fig. 2). After that, the load was removed, the specimens were immediately loaded to fracture, and the value of the fracture stress was determined. In order to define the effect of the pause on the change in the properties, the specimens, as in the first case, were loaded to 90% of the fracture stress, held under load for 5 s, unloaded, and then held for 30 min at the test temperature. Thereafter, the specimens were loaded to fracture and the value of the fracture stress was determined (Fig. 2). These experiments were performed at temperatures of 70, 110, and 140 °C. At least six experiments with interdeformation pauses and at least six experiments without interdeformation pauses were made for each temperature.