The Role of Fibre Length on the Fatigue Failure of Injection-Moulded Composites at Elevated Temperatures under a Range of Axial Loading Conditions

Trevor Sabiston,Waqas Muhammad,Carlos Engler-Pinto,Bin Li,Jidong Kang

doi:10.3390/jcs6020038

Abstract

The effect of fibre length distribution on the fatigue behaviour of an injection-moulded PA66 carbon fibre composite is investigated. Two materials, short carbon fibre with a mean length of 100 microns, and long carbon fibre with a mean length of 580 microns, are subjected to fully reversed fatigue loading at room temperature and three stress ratios at 120 °C. The fatigue results are compared, and fracture surfaces are analyzed to determine the differing failure modes between the materials and loading conditions. At 120 °C, the fibre length has a significant effect on the fatigue behaviour with order of magnitudes of different fatigue life for a given stress amplitude during tensile fatigue loading. Under tensile loading, fatigue failure initates as fibre matrix debonding with pits present due to end effects in the short carbon fibre material. Under compression–compression loading, the fatigue life is matrix-dominated and should be treated as a maximum stress failure. Under this loading, a smooth crack propagates across the sample with buckling as the final failure mode.

Highlights

The fibre length distribution (FLD) has an impact on the cost of the feedstock, and it is of interest to evaluate the impact of the FLD on the resulting temperature-dependent fatigue behaviour
For the short carbon fibre (SCF) material, there is a 57.7% reduction in strength from room temperature to 120 ◦ C. These results demonstrate the temperature dependence on the mechanical properties of the injection-moulded PA66 composite material
The room temperature fracture surfaces are presented in Figure 6; the samples were selected to have one with shorter fatigue life and one with longer fatigue life to contrast similarities and differences in the observed failure mode

Summary

Introduction

Many studies have been conducted on the fatigue life of injection-moulded composites for high production applications [4]. Another major consideration of automakers is the cost of the products and weighing the expense of different materials and manufacturing technologies versus the benefits in terms of reduced energy consumption. For injection-moulded composites, the temperature, fibre length, and fibre orientation are known to affect the resulting material properties. The effect of fibre length distribution (FLD) on the fatigue performance of a commercially available carbon fibre PA66 injection moulding feedstock is evaluated. The FLD has an impact on the cost of the feedstock, and it is of interest to evaluate the impact of the FLD on the resulting temperature-dependent fatigue behaviour

Methods

Results

Discussion

Conclusion