Papers by Keyword: Repair

Abstract: The repair welding of aluminium alloy 6082T6 with two fillers 4043 and 5356 were studied by using MIG welding process with pulse current at frequency 5 Hz. After that, macrostructure and microstructure were investigated and the density of porosity and testing of mechanical properties were determined. The results found that the density of new weld was less than repair weld. The results of mechanical tests showed that the new weld were better than the repair weld.

Abstract: The purpose of this study is to reveal the effects of the modification of the sheet of Polypropylene (PP) with fine glass fibers for repair of the Carbon Fiber Reinforced Thermo Plastics (CFRTP) on the recover ratio of degraded mechanical properties of damaged CFRTP after impact bending. Impact damaged specimen was repaired by inserting tiny melted sheet of PP modified with fine glass fibers to be assimilated with PP matrix around the surface of damaged area. Model specimens having cut reinforcements were prepared for compressive buckling tests to investigate the effect of the modification on mechanical behaviors under compressive stress due to the impact bending. The recovering ratio defined as the ratio of compressive buckling strength of damaged model specimen to that of un-damaged specimen was investigated. The recovering ratio of model specimen after the repair was about 49% when the unmodified PP sheet was used to repair. On the other hand, when the weight content rate of fine glass fibers was 2.0wt%, about 73% of recovering ratio was successfully obtained. The appropriate condition of the weight content rate was shown for repairing the damaged part of the CFRTP used in this study.

Abstract: A rapid repair and retrofitting technique for reinforced concrete (rc) Chinese existing bridges damaged by a strong earthquake, is proposed and tested. These bridges were designed according to Chinese codes [1] [2] [3] but with insufficient transversal steel reinforcement. The damaged rebar and concrete parts were replaced by new bar systems and concrete cast respectively. Finally, a C-FRP wrapping was applied to increase the insufficient shear strength and to guarantee the necessary ductility in plastic hinge. This repair technique is an upgrade of the one tested with very good results during a previous experimental research [4] on bridge designed according to old Italian code [5] without proper seismic details. A new bar system assures that plastic dissipation is distributed in plastic hinge only. Some pier specimens (in scale 1:6) were built with and without the new bar systems. These specimens were tested by cyclic tests at Fuzhou University lab (China) to evaluate the effectiveness of the intervention.

Abstract: Concrete sewage systems can be severely damaged when attacked by biogenic sulfide corrosion. While minor aggressive exposures can be accounted by using a high sulfate resistant cement, higher concentrations of acid (pH 3.5) require the sealing and protection of concrete surfaces. Throughout the decades, polymer concrete (PC) has been used in sewage systems due to its high acid resistance. However, it has been limited to newly constructed pipes and manholes as well as local repair. In cooperation with Massenberg GmbH, the Institute of Building Materials Research of RWTH Aachen University developed a new way of applying PC for the rehabilitation of damaged concrete surfaces of sewage systems; by dry spraying an epoxy mortar on concrete, layers with an average thickness of 20 mm on vertical and overhead surfaces were successfully produced. The dry sprayed PC was examined for its overall performance such as strength, adhesion, thermal expansion, and wear. A special focus has been put on the diffusion properties and the durability in an acidic environment. Based on these positive laboratory results, a first practical application in a waste water structure is currently underway.

Abstract: The repair welding of aluminum alloy 5083 was studied using Gas Metal Arc welding (GMAW) process. The effect of heat cycles from welding was investigated in some details. Butt joints of 6 mm and 3 mm thick were welded with 5356 filler metal. Then weld was removed by grinding and repeatedly welded again for 2 times. After each repair weld, the weld was assessed by macrostructure, microstructure and mechanical tests. The results revealed porosities of all weld samples. The repair welds indicated lower tensile strength compared with the new welds. In addition, all tensile strengths were much lower than the base metal. All samples were fractured at the weld metal.

Abstract: This paper presents a case of repair practice for a concrete bridge that was classified as imminent failure condition. The bridge is slab-type with an equal span of 10 meters long. Each pier is built up of six driven concrete piles. Over 30 years, critical deterioration occurred to concrete pier columns with many severe corrosion spots on reinforcing bars. A concept of section replacement was used to develop a repair technique to remove an entire body of deteriorated materials and restore with selected new materials, was used to develop a repair method. The method involved several stages of works that included: site investigation, damage inspections; work area preparation and installation of temporary structure; material replacement; and work completion. The lesson learned from repair practice suggests the number of key success factors to complete the task safely and cost effectively in a timely way.

Abstract: Airborne VOR receiver receive the reference phase signal and variable phase signal which transmitted by VOR ground station. Obtain the aircraft QDR relative to the ground station by compare the phase difference. The indicator indicates the orientation information. For the pilot to determine the location of the plane and guide the aircraft. This paper briefly describes the working principle of the VOR receiver system, and put forward the method of troubleshooting and repair, testing process.

Abstract: In this paper, three bio-mineralization mechanisms were proposed to repair cement-based materials cracks. The common feature is that the three are all induced by bacterial. A type of bacterial which can decompose urea and release carbonate ions could be applied to repair micro cracks on concrete surface when combining calcium ions. But what need to be noted is that the way of repairing cracks is passive. Some alkaliphilic bacterial spores could be added to concrete when casted and two different types of bacterial were used to realize the function of self-healing. The sources of carbonate ions made them different, the one release carbonate dioxide through its own cellular respiration, the other could transfer carbon dioxide in air to bicarbonate. Coefficient of capillary suction, apparent water permeation coefficient and area repairing rate were applied to characterize the repairing effectiveness. The tests results were that all three bio-mineralization mechanisms showed excellent repair effect to small cracks formed at early ages. When the bacteria were immobilized by ceramsite, the self-healing effect could be improved for the cracks formed at late ages.

Abstract: The paper analyses the manufacturability and difficulties in weld repairs of the electroslag casting red copper crucible with bent axle, work out the relevant measure. It is proved by experiment that large red copper product can be perfectly repairs by use suitable welding procedure.

Abstract: Under the bad environment, high polymer wear-resistant material has more superior erosion wear resistant performance than metal. It can replace wear-resistant metal material partly. In this paper, high polymer wear-resistant coat has been prepared with the epoxy resin, low molecular polyamide, nanoAl₂O₃ coupling agent. The shear strength and wear resistant test has been carried out under different elements content, and the test curve of coat is given. The results are analyzed. By the experiment result, the optimum coat formula is: low molecular polyamide content is 60% relative to E – 51; and the content of MoS₂ is 12%. The result shows that the coat erosion wear resistance is 9 times of 45# steel under the best recipe. The coat is used to repair a worn mortar pump impeller, and the effect is obvious.