In this research, applicability of electrochemical technology in removing nitrogenous compounds from solid waste landfill leachate was examined. Novel cathode material was developed at laboratory by introducing a Cu layer on Al substrate (Cu/Al). Al and mild steel (MS) anodes were investigated for the efficiency in removing nitrogenous compounds from actual leachate samples collected from two open dump sites. Al anode showed better performances due to the effect of better electrocoagulation at Al surface compared to that at MS anode surface. Efficiency studies were carried out at a current density of 20 mA/cm 2 and at reaction duration of 6 h. Efficiency of removing nitrate-N using Al anode and developed Cu/Al cathode was around 90%. However, for raw leachate, total nitrogen (TN) removal efficiency was only around 30%. This is due to low ammonium-N removal as a result of low oxidation ability of Al. In addition to the removal of nitrogenous compounds, reactor showed about 30% removal of total organic carbon. Subsequently, raw leachate was diluted four times, to simulate pre-treated leachate. The diluted leachate was treated and around 88% removal of TN was achieved. Therefore, it can be said that the reactor would be good as a secondary or tertiary treatment step in a leachate treatment plant.
Technology gaps exist for design and certification of bonded repair of large composite structures under multiaxial loading. They are 1) consideration of delamination failure without including the matrix cracking-induced stress concentration at a ply interface; 2) use of test data from a simple geometry for the failure prediction of a complex repaired configuration with a multiaxial stress state and spatial variation of the local stress ratio; 3) pre-assumed failure modes without including the multiaxial stress state-driven damage initiation and progression; and 4) lack of a rational modeling approach for the damage evaluation of a full-scale structure to balance the computational efficiency and solution accuracy. Our primary goal of this study is to extend our modeling capability for a bonded composite structure subjected to multiaxial loading and to demonstrate a global-local modeling capability for the high-fidelity damage evaluation at a critical location of a full-scale composite wing section. Multiaxial tests for a scarf repaired component are performed via the bi-axial cruciform apparatus while a capability demonstration is conducted using the strain survey test of a full-scale wing section via the developed test rig. After verification of the global response prediction, the developed global-local modeling strategy is used to evaluate the damage progression at a critical location with a detected initial defect.
This paper presents the characterization of bearing failure mechanisms in composite joints with countersunk bolt by applying an X-ray Computed Tomography (XCT) technique and a developed bearing failure model to build the physical mechanisms into the framework of continuum damage mechanics (CDM) in our composite bolted and bonded analysis tool for Abaqus (CB2ATA). The high-fidelity XCT was explored for the detection and characterization of bearing failure in bolted composite components without removing the fastener, which could introduce significant scatter in XCT scan due to its high density, compared with lightweight carbon fiber reinforced polymer (CFRP) composite laminates. A static bearing model was also developed for the damaged material response in the bearing region based on a micromechanics analysis in the longitudinal and transverse directions. In this study, single shear bearing (SSB) tests was firstly executed with XCT scan, and then progressive failure analyses were performed to explore the effects of bolt failure on the interaction of the intra- and inter-ply damages. The predicted load-displacement response was compared with experimental measurement, and the simulated failure patterns were compared with the XCT images. A new design was proposed using the enhanced analysis tool to achieve a dominant bearing failure mechanism on the basis of the current SSB test.
To investigate the failure mechanism in composite bolted joints, an in-situ X-Ray computed tomography (XCT) technique was developed and single shear bearing (SSB) tests were performed with quasi-isotropic layup. High-fidelity XCT was explored for the detection and characterization of bearing failure in bolted composite components without removing the fastener. A novel load frame was also introduced for in-situ XCT scan and a preliminary scan was performed. A micro-macro coupling modeling approach was proposed on the basis of continuum damage mechanics (CDM) method and a static bearing model, which was based on micromechanics analysis to consider the residual stress after fiber kinking and matrix cracking under compression in the bearing region. The SSB specimens were modified using a larger bolt diameter to avoid bolt failure and achieve extensive bearing failure. The developed modeling approach was verified using SSB test data by comparing the predicted load displacement response with experimental measurement and the failure patterns obtained from XCT scanning images.
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