Abstract
Mechanical properties of fibre reinforced composites are primarily dependent on those of fibres. Fibre properties are used for estimating the damage and strength behaviour of composite materials and structures. Tensile strength of fibres is commonly determined by single fibre tensile tests, which is challenging and is prone to measurement errors. In this study, different possible sources of errors due to experimental limitations in the fibre testing process were identified. Their effect on fibre tensile strength was analytically modelled. This model was used to evaluate the uncertainty in experimentally determined fibre strength. A sensitivity analysis was conducted to rank the relative significance of input quantities on the calculated fibre strength. Since composite models require fibre properties determined at very small gauge lengths, the results of the sensitivity analysis were extrapolated to determine critical parameters for tests done at those small gauge lengths of a few millimetres. It was shown that, for sufficiently long fibres, their strength depends mainly on the diameter and failure force; however, for shorter gauge lengths, the effects of misalignment become very significant. The knowledge of uncertainty would be useful in estimating the reliability of the predictions made by composite strength models on the damage and failure behaviour of composite materials and structures. Minimising the influence of critical parameters on fibre strength would help in designing improved single fibre testing systems capable of determining fibre strength more accurately.
Highlights
Fibre reinforced composite materials are ideal to be used for structural applications in the automotive and aerospace industry due to their lightweight and high specific strength
Their effect on fibre tensile strength was analytically modelled. This model was used to statistically evaluate the uncertainties in experimentally determined fibre strength. When such a set of fibre tensile strength data is represented with the help of a statistical function, these uncertainties in individual fibre strength values are propagated into the resulting function, and add uncertainty to the parameters of the statistical distribution function
Since fibre strength data are used as an input in composite strength models for predicting the material and structural behaviour, the predictions they make would be unreliable
Summary
Fibre reinforced composite materials are ideal to be used for structural applications in the automotive and aerospace industry due to their lightweight and high specific strength. The properties of fibres are used as an input in composite strength models for evaluating the damage and failure behaviour of composite materials and structures [5]. The very small cross-section of fibres make them very delicate to handle leading to a very challenging and cumbersome process of fibre specimen preparation and testing [6]. These challenges significantly affect the accuracy of the prepared specimen and may lead to inaccurate fibre strength measurements [7,8]
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