Destruction of fiberglass plastics by mechanoluminescence

Abstract

The objective of the present work was to determine the laws governing the destruction of a unidirectionally reinforced glass fiber plastic when stretched in the direction of reinforcement and to detect the initial stage of destruction of tubular fiberglass specimens in the plane stressed state by means of mechanoluminescence. The tests were carried out with rectangular flat specimens made of unidirectionally reinforced fiberglass plastic, tubular specimens made of fiberglass plastic, and with the individual components of this composite: ED-10 epoxy resin and RBMN-10-1680 glass fibers. The plane specimens had the shape of a "shovel" (dumbbell) with a cross section of the working section of 5 x 0.5 mm and a total length of 130 mm. The cross section of the working section of specimens made of epoxy resin was 6 x 1 mm. Stress--strain diagram (d11 -- E11) were obtained simultaneously with a record of the photoemission pulses by stretching of the specimens. Loads were applied by means of a special machine. An experimental procedure has been proposed in [3] for the testing of tubular specimens in the individual types of plane stressed state: stretching, compression, and internal pressure. In the present work the fiberglass tubular specimens were tested by stretcbing, compression, torsion, and combinations thereof. The tests were carried out on specimens with longitudinal-transversal winding (Fig. i). The working section of the specimens consisted of tbree layers. Tbe layers were arranged as follows: the first layer in the direction of the axis 2, the second layer in the direction of axis i, and tbe third layer in the direction of axis 2. The wall thickness ~ of the specimen was i.i mm. VM86 glass fibers were used as the reinforcing fibers and ED-10 epoxy resin as the binder. The experiments were carried out on the MTS testing machine with programmed control, using an algorithm in FORTRAN--BASIC. This test ar ~ rangement allowed us to apply a load to the beam in the stress space in a plane stressed state and to record the test data. A total of 15 specimens made of fiberglass plastic, i0 specimens made of epoxy resin, 5 specimens consisting of glass fibers, and 21 tubular specimens were tested. The intensity of mechanoluminescence was measured by photon counting. The block scheme of the measuring equipment is shown in Fig. 2. The specimens were placed into a light-tight chamber. The body of the PEM photoreceiver was placed as closely to the specimen as possible, which was cooled by running water with a temperature of 15~ The dark background count was 5  0.4 pulses/sec. The electromechanical shutter S was installed between the chamber and the body. A specially selected exemplar of a FEU-79 photoelectron multiplier was used as the photoreceiver. The output pulses were amplified by means of the pulse amplifier K. The amplified photoelectron pulses were separated and standardized by means of an integral discriminator D. The pulses were counted by means of the 43-48 electron-counting meter F. The control module C counted the light cycles and started the frequency meter at the start of each cycle. The pulses were integrated over 1 sec. The test results were recorded on a PDS-021 two-coordinate (x, y) recorder, by converting the digital information to tbe analog form by means of two digital--analog converters DAC.