Studies of structure cracking and fracture strength of E-glass fibres using acoustic emission.

An Acoustic Emission (AE) technique has been developed to permit the determination of the strength distribution of E-glass fibre strands containing as many as 4,000 filaments. This technique is novel in that it allows fast data acquisition and provides the accurate load, location and time of fracture of each filament. The design also permits the strand to be exposed to various environmental conditions during Acoustic Emission, monitoring. A range of statistical data including the fracture strength and AE signal parameters can be extracted. Software has been developed for the evaluation of the large number of collected data during a traction test and for the graphical presentation of the AE signal parameters in two and three dimensions. The final test package thus allows automatic testing and provides the analyst with an overall picture of the real strength distribution of fibres in a strand. The application of the technique to study the effects of sample size (number of filaments) and of sample length of a commercial roll of E-glass fibres has shown significant variation in the bundle strength and Weibull parameters. Samples were also tested across the width of the strand and significant variations in these parameters were again found. These results show that it is essential to test a complete strand of filaments for accurate evaluation of strength distribution. The complete strand tests (of 4,000 filaments) have shown the true characteristic of the flaw distribution in a strand and have provided concrete evidence of the existence of a bimodal flaw population. The existence of two flaw distributions was not evident in tests conducted on single filaments or bundles containing small numbers of filaments reported elsewhere. Complementary results confirming the two flaw distributions have been obtained from the study of AE signal parameters and fracture surfaces using a Scanning Electron Microscope. A laboratory simulation of the impregnation-pultrusion process for the production of E-glass fibre reinforced composites has been established. Using the developed measurement system E-glass strands have been tested at elevated temperature, in the presence of an inert atmosphere, whilst subjected to various conditions of friction and in combinations of these test conditions. The results obtained have indicated a significant variation in the strength of fibre strands tested under these process conditions. In general elevated temperature and friction both cause a reduction in strength, a decrease in Weibull modulus and an increase in the coefficient of variability. For example at 20 degrees C the maximum load carrying capacity of the strand in the absence of friction is l,040N and in the presence of friction at 20 degrees fibre-roller contact angle it is reduced to 910N. The strand strength at 300 degrees C in the absence of friction is reduced to 800N and in the presence of friction at 20 degrees fibre-roller contact angle it is further reduced to 630N. The strand strength is drastically reduced to 450N at 300 degrees C and 40 degrees fibre-roller contact angle. The results obtained from the AE signal parameters and fractography of the fractured fibres under various test conditions give independent confirmation of these reductions in strength. In seeking an explanation of this reduction in strength Fourier Transform Infra-red Spectroscopy, Thermogravametric analysis and the physical appearance of the strand were studied. It is established that degradation of the size (coating) of the fibres takes place in the temperature range 170 degrees C - 330 degrees C. The unprotected fibres are more prone to damage and the subsequent structural changes in the material give rise to a reduction in strength. The information obtained during signal analyses of the AE waveform in the time and frequency domains have provided insight into the micro-mechanical changes which occur in the material during fibre fracture. One example is that the rise time of the AE signals increases as the sample temperature is raised indicating a reduction in the "brittleness" of the material. The results obtained in this investigation have been related to the impregnation-pultrusion process in order to increase the knowledge of the processability of the fibres used in the manufacture of composite materials. It has also been established that the AE technique is useful in an on-line production monitoring role.

Grantor dc:publisher.institution

Robert Gordon University

Year dc:date.issued

1994

Author dc:creator

• Jihan, Sha

Advisor dc:contributor.advisor

• A.M. Siddiqui, M.A.S. Sweet, S. Jones and R. Bailey

• Acoustic emission (AE)
• E-glass fibre strands
• Strength distribution
• Fracture identification
• Weibull modulus
• Bimodal flaw population
• Scanning electron microscope
• Fourier transform infra-red spectroscopy
• Thermogravametric analysis
• Impregnation-pultrusion

Language dc:language

en

Identifier

oai:rgu-repository.worktribe.com:2807419
https://doi.org/10.48526/rgu-wt-2807419

OAI identifier oai:identifier

oai:rgu-repository.worktribe.com:2807419