Development of a non-destructive evaluation system for mass timber panels

The use of timber in construction originated with timber framing methods then transitioning to mass timber construction in the last decade. Locally in Australia the impacts of the COVID-19 pandemic have also outlined the societal demand to move from concrete and steel structures to more sustainable and environmentally friendly buildings. Reported by the Wood Solutions (2021), timber sales had seen a drastic increase compared to previous years putting pressure on processors to meet the demand set by the current construction boom. Mass timber construction uses intelligent design practices to layer, laminate and/ or fasten timber products to create a light-weight and environmentally friendly structure. With the continued increase in demand for these mass timber products, manufacturers of these materials will be met with pressure to ensure high levels of quality are being maintained. Of the serviceability requirements, the mechanical properties are one of the key design parameters considered. While these properties are commonly quantified through static test methods, this testing provides an accurate representation of the material tested. These static experiments are time consuming, costly to conduct and destructive. Non-destructive evaluation (NDE) techniques are often equally precise in determining the material properties in a rapid, and accurate alternative to static testing for beams and boards. These rapid evaluation techniques have been adopted by industry as a time saving quality assurance (QA) method in board processing. Several international attempts have been made to develop an NDE system for use by mass panel manufacturers as a QA tool. Although no such system has focused on the industry implementation requirements. This study aims to investigate the experimental parameters involved in NDE of mass timber panel systems. The system developed through this study will focus on the experimental requirements of a QA system that is to be used in conjunction with a theoretical model. The model has been developed in collaboration with researchers from the Department of Agriculture and Fisheries (DAF) and Centre for International Research Agricultural Development and (CIRAD). The information presented in this thesis can be separated into four main parts. Part one (section 3) presents the signal specific section of the research. This section involves the program development using LabVIEW to create a signal acquisition and postprocessing system for conducting the dynamic vibration experiments. As part of the initial stages of the research, gaining an understanding for the applicable methods of digital signal processing (DSP) were identified as an important factor. The resolution of the acquired signal is a major contributor to the NDE testing approaches accuracy. The acquisition of these signals are a result of the hardware, software, and experimental method. The signal measurement is an important phase of the research. Part two of this thesis reports on the experimental setup requirements for conducting the dynamic vibration tests (section 4). A series of boundary conditions for supporting the mass timber panels were selected for investigation. These setups were evaluated for their repeatability in regard to measured vibrational response, accuracy when compared with an orthotropic model of a thin plate with similar properties to the test material, and the practical considerations for industries appetite towards the nominated conditions (in-line application). Part three of the thesis investigates the effects of the finite element analysis (FEA) structure used to simulate a CLT panel (section 5). This component of the study was to investigate cross laminated timber (CLT) panels to evaluate whether there are inaccuracies in assuming the product responds to impulse as a solid plate element. CLT is a layered panel consisting of laminated boards bonded face to face with no bonding between boards edgewise, therefore introducing discontinuities or gaps. This section of the study compares a number of modelling parameters against experimental modal analysis results to identify potential accuracy increases to be had in considering a higher degree of detail in the structure and design of the FEA. Part four of this thesis presents experimental and theoretical test data obtained from imposing the testing method expanded on through previous sections on a series of mass timber panels (section 6). Materials were sourced with a focus to evaluate a range of sizes and different thicknesses to provide a robust proof of concept testing system for measuring mechanical performance of mass timber panel products. After vibratory testing of the large scale panels static testing was conducted to evaluate the products elastic moduli (MoE) and shear (G) properties to validate the NDE system.