Faculty of Engineering

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Subject: search.filters.subject.Simulation

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    Simulation of ionomer membrane fatigue under mechanical and hygrothermal loading conditions
    (Elsevier, 2015-04-01) Khorasany, R. M. H; Kjeang, E; Wang, G. G; Rajapakse, R. K. N. D
    Understanding the fatigue lifetime of common perfluorosulfonic acid (PFSA) ionomer membranes under fluctuating hygrothermal conditions is essential for the development of durable fuel cell technologies. For this purpose, a finite element based fatigue lifetime prediction model is developed based on an elastic–plastic constitutive model combined with a Smith-Watson-Topper (SWT) fatigue formulation. The model is validated against previously reported experimental results for a membrane under cyclic mechanical loadings. The validated model is then utilized to investigate the membrane fatigue lifetime in ex-situ applications under cyclic humidity and temperature conditions. The simulations suggest that the membrane fatigue lifetime is shorter under fluctuating humidity loadings than for temperature loadings. Additionally, the membrane fatigue lifetime is found to be more sensitive to the amplitude of the strain oscillations than to the mean strain under hygrothermal cycling. Most notably, the model predicts that simultaneous humidity and temperature cycling can exacerbate the fatigue process and reduce the fatigue lifetime by several orders of magnitude compared to isolated humidity or temperature cycling. The combination of measured mechanical fatigue data and the present numerical model provides a useful toolkit for analysis of membrane fatigue due to hygrothermal variations, which can be costly and time-consuming when addressed experimentally.
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    PublicationOpen Access
    An improved approach to line balancing for garment manufacturing
    (Faculty of Management Studies and Commerce, University of Sri Jayewardenepura, 2016-06-01) Wickramasekara, A. N; Perera, H. S. C
    Production managers in the apparel industry frequently face the issue of being unable to complete the orders at the scheduled time. One of the reasons for this issue is the unavailability of a Line Balancing procedure that could encompass the stochastic nature of the sewing process, which is manifested through the likes of variability of sewing times, machine breakdowns, correcting defective products, and operator breakings such as for changing bobbins and drinking water. The objective of this research is to introduce a diverse approach to Line Balancing through giving due consideration to the stochastic nature of the process. The improved approach was developed through case study approach. Having selected a sewing line in an apparel factory, the process times of operations, major random events and the times elapsed between random events were recorded. Then the whole production cycle was simulated using ARENA software. By attempting and analysing different scenarios, a different approach for line balancing was introduced. The initial steps of the algorithm developed includes: collecting processing times and necessary information on manufacturing process, fitting standard probability distributions to both value added and non-value added activities, developing the precedence diagram, developing an initial algorithm for balancing a production line and finally, making necessary adjustments to the algorithm analyzing different scenarios. In order to check the validity of the algorithm, a production line was balanced for two different daily production targets. Thus, the application of proposed algorithm to balance the production line reduces the gap between the expected production target and the real achievement.