Xuming Su

Unidirectional glass fiber reinforced polymer (GFRP) composite insulators are widely used in extra-high voltage (EHV) and ultra-high voltage (UHV) transmission lines due to their outstanding electrical and mechanical performance. However, the accurate prediction of the critical buckling load is crucial to satisfy the high reliability requirement under complex operations. In this paper, an improved Perry–Robertson theory to predict the critical buckling loads of GFRP composite insulators with different slenderness is proposed. Firstly, initial imperfection is expressed as a function of the insulator strut length, which enables the critical load to be formulated as a function of slenderness explicitly. It also allows for convenient comparisons with other theories, such as Euler and Johnson’s, and easy calibration with the magnitude of initial imperfections. Secondly, the nonlinear material behavior of the GFRP composite insulator strut, resulting from changes in glass fiber orientation in relation to the loading direction during buckling, is considered to further enhance the prediction accuracy. The predicted results with current theory were validated through compression tests of GFRP composite insulators with solid and hollow struts and different slenderness and boundary conditions, which shows an accuracy of over 85%. Thus, the proposed improved Perry–Robertson theory can be also applied in other fiber-reinforced composite buckling analyses.

A closed die forging process was developed to successfully forge an automotive suspension component from AZ80 Mg at a variety of different forging temperatures (300 °C, 450 °C). The properties of the forged component were compared and contrasted with other research works on forged AZ80 Mg at both an intermediate forging and full-scale component forging level. The monotonic response, as well as the stress and strain-controlled fatigue behaviours, were characterized for the forged materials. Stress, strain and energy-based fatigue data were used as a basis for comparison of the durability performance. The effects of the starting material, forging temperature, forging geometry/configuration were all studied and aided in developing a deeper understanding of the process-structure-properties relationship. In general, there is a larger improvement in the material properties due to forging with cast base material as the microstructural modification which enhances both the strength and ductility is more pronounced. In general, the optimum fatigue properties were achieved by using extruded base-material and forging using a closed-die process at higher strain rates and lower temperatures. The merits and drawbacks of various fatigue damage parameters (FDP’s) were investigated for predicting the fatigue behaviour of die-forged AZ80 Mg components, of those investigated, strain energy density (SED) proved to be the most robust method of comparison.