Material characterization of timber utility poles using experimental approaches

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Utility poles made of timber are a significant part of Australia’s infrastructure for power distribution and communication networks. Wood as a natural material deteriorates under the influence of environmental conditions such as weathering, fungus and insect attack which results in a reduction of the strength of the poles. Determining soundness and the remaining strength of timber utility poles in service is crucial in order to maintain a reliable and secure power network. This thesis presents an investigation of using static and dynamic material testing approaches to determine material properties and detecting internal damage of timber utility poles from two hardwood eucalyptus tree species, i.e. Spotted Gum and Tallowwood. The comparative study of static and dynamic tests based on the wave transmission time or time of flight (TOF) is necessary for the development of novel non-destructive testing (NDT) techniques for the health assessment of in-situ utility poles. In order to develop accurate non-destructive models, knowledge of the orthotropic material properties is necessary. In open literatures, comparative studies on orthotropic material properties are scarce to find for most eucalyptus species used for utility poles. Typically, material properties are only available in the longitudinal (i.e. along main wood fibre) direction, and most international standards cover only details on material testing in such direction with no coherent or comprehensive guidelines being given for the testing of the other two secondary directions (radial and tangential) of timber. TOF measurements were conducted by several researchers for a number of timber species, however non on high density woods such as the investigated eucalyptus species. Based the full set of material properties (Modulus of Elasticity and Poisson’s ratios) of two new utility poles determined with static tests in all three orthotropic directions (longitudinally, radially and tangentially), the dynamic tests were calibrated and used for the non-destructive material characterization and internal damage detection. The tests were also conducted taking into account varying moisture contents and different grain angles as they occur in the field. Ultimately, an orthotropic numerical model was created to simulate the experimental damage detection case which could be used to simulate further damage cases. The results revealed that the formulas used for the dynamic material characterization must be adjusted for the investigated species. The numerical model was capable of simulating the experimental case and predicting the TOF for damaged poles. The method has potential for the prediction of internal damage of eucalyptus timber poles in the field.
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