In today's market, the global competition has put manufacturing businesses in great pressures to respond rapidly to dynamic variations in demand patterns across products and changing product mixes. To achieve substantial responsiveness, the manufacturing activities associated with production planning and control must be integrated dynamically, efficiently and cost-effectively. This paper presents an iterative agent bidding mechanism, which performs dynamic integration of process planning and production scheduling to generate optimised process plans and schedules in response to dynamic changes in the market and production environment. The iterative bidding procedure is carried out based on currency-like metrics in which all operations (e.g. machining processes) to be performed are assigned with virtual currency values, and resource agents bid for the operations if the costs incurred for performing them are lower than the currency values. The currency values are adjusted iteratively and resource agents re-bid for the operations based on the new set of currency values until the total production cost is minimised. A simulated annealing optimisation technique is employed to optimise the currency values iteratively. The feasibility of the proposed methodology has been validated using a test case and results obtained have proven the method outperforming non-agent based methods.
Fatigue cracks initiated from fastener holes are common in aircraft structures. Implementation of effective structural health monitoring (SHM) system to detect or monitor fatigue cracks near fastener holes is desired for realizing condition-based maintenance with improved aircraft safety at reduced cost. In this work, direct-write piezoelectric ultrasonic transducers were used for monitoring crack near fastener hole. Made of poly (vinylidenefluoride-co-trifluoroethylene) [P(VDF-TrFE)] film and annular array electrodes, the direct-write piezoelectric ultrasonic transducers were both directly coated and patterned around the fastener holes. A novel ring-design using annular array electrodes with small footprint was proposed to detect fatigue crack initiated in the vicinity of a fastener hole using pulse-echo and pitch-catch methods. The ring-design direct-write piezoelectric ultrasonic transducers were designed to operate with Lamb wave modes at 1.5 MHz. A numerical simulation study was conducted to investigate the interaction of Lamb wave modes with the fatigue crack. Experimental ultrasonic testing was performed with signal gates determined using wavelet analysis. Fatigue crack detection was demonstrated using an energy ratio method by comparing energy parameter of gated ultrasonic signal with baseline signal. Using the pulse-echo method, the direction of the fatigue crack was able to be determined. The pitch-catch method was found to have higher sensitivity in fatigue crack detection but could not determine the direction of the fatigue crack. These transducers made of thin films promise high conformability even on curved surface and around irregular objects with limited space, compared to conventional discrete ultrasonic transducers. The analysis and results showed that the ring-design direct-write piezoelectric ultrasonic transducers have great potential for fastener hole SHM.
A major reason why structural health monitoring (SHM) has still not come into the successful application is the lack of being able to describe the resulting cost advantages SHM might have when being implemented on components of an engineering system. This paper provides an idea how the maintenance process of a mechanical system such as an aircraft can be simulated by using a commercial software tool named ARENA. The procedure allows the different structural components to be inspected along the critical path of an optimised maintenance process to be identified. The critical components are then assessed in terms of SHM implementation and the solution is fed back into the maintenance process simulation. The original and the modified processes are finally compared in terms of duration and cost with the objective to enhance aircraft operability. The procedure is illustrated on the basis of different aerospace applications.
Knowledge on the life span of the riveting dies used in the automotive industry is sparse. It is often the case that only when faulty products are produced are workers aware that their tool needs to be changed. This is of course costly both in terms of time and money. Responding to this challenge, this paper proposes a methodology which integrates wear and stress analysis to quantify the life of a riveting die. Experiments are carried out to measure the applied load required to split a rivet. The obtained results (i.e. force curves) are used to validate the wear mechanisms of the die observed using scanning electron microscopy. Sliding, impact, and adhesive wears are observed on the riveting die after a certain number of riveting cycles. The stress distribution on the die during riveting is simulated using a finite element (FE) approach. In order to confirm the accuracy of the FE model, the experimental force results are compared with the ones produced from FE simulation. The maximum and minimum von Mises' stresses generated from the FE model are input into a Goodman diagram and an S-N curve to compute the life of the riveting die. It is found that the riveting die is predicted to run for 4 980 000 cycles before failure.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.