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This paper presents results of experimental and numerical modeling of ductile fracture and failure of elements made of S235JR steel subjected to static tension. The prediction of failure was generally based on the stress modified critical strain (SMCS) model. The numerical simulations were performed using the Gurson-Tvergaard-Needleman (GTN) model, which takes into consideration the material structure. The approach applied in this study was based on the computational cells with microstructurally based length scales. The cell size and initial porosity were determined through microstructural examinations of S235JR steel. The parameters of the GTN model for S235JR steel were established on the basis of the microstructural analysis and the numerical modeling of tensile strength tests. As a result, it was possible to determine the SMCS failure criterion to predict ductile fracture for S235JR steel. [ABSTRACT FROM AUTHOR]

The paper focuses on the design of a robust H-infinity attitude controller for an unmanned small-scale helicopter. To take into account the salient nonlinearities, a model with six-degrees-of-freedom nonlinear dynamics and some linear approximation of the aerodynamic parts are used when extracting a linear model and performing simulations to check the performance of the designed controller. To design a robust H-infinity controller, an augmented plant is constructed by adjusting several weighting functions. Then, a robust controller is synthesized utilizing the augmented system with the weighting functions and H-infinity control methodology. Using computer simulation it is shown that the H-infinity controller works well when applied to the nonlinear model even though it is designed using a linear model approximation. Through frequency response analysis, it is shown that the proposed controller can overcome more than half of the uncertainty variations around a nominal point at the input side. The time-domain simulation with the nonlinear model demonstrates that the proposed controller is very robust in relation to the uncertainties, as was expected, overcoming large gain uncertainties and time delay in each input channel. The analysis and simulation results also show that the control system satisfies the Level 1 handling requirements, as defined in Aeronautical Design Standard ADS-33E-PRF. [ABSTRACT FROM AUTHOR]

Operational performance in residential construction production systems is assessed based on measures such as average house-completion time, number of houses under construction, lead time, and customer service. These systems, however, are prone to nonuniformity and interruptions caused by a wide range of variables such as inclement weather conditions, accidents at worksites, fluctuations in demand for houses, and rework. The availability and capacity of resources therefore are not the sole measures for evaluating construction production systems capacity, especially when rework is involved. The writers' aim is to investigate the effects of rework timeframe and frequency/length on tangible performance measures. Different call-back timeframes for rework and their impact on house-completion times are modeled and analyzed. Volume home-building was chosen as the industry sector studied in the research reported in this paper because it is a data-rich environment. The writers designed several experiments to model on time, late, and early call-back timeframes in the presence of rework with different length and frequency. Both mathematical modeling and discrete-event simulation were then used to compare and contrast outputs. The measurements showed that the average completion time is shorter in systems interrupted by frequent but short rework. In other words, a smaller downstream buffer between processes is required to avoid work starvation than those systems affected by infrequent but long interruptions. Early call-backs for rework can significantly increase the number of house completions over the long run. This indicates that there is an opportunity for the mass house-building sector to improve work practice and project delivery by effectively managing rework and its related variables. The research reported in this paper builds on the current body-of-knowledge by applying even-flow production theory to the analysis of rework in the residential construction sector, with the intention of ensuring minimal disruption to construction production process and improving productivity. [ABSTRACT FROM AUTHOR]

Microwave heating is a potential method for mitigating dust issues and creating solid regolith structures, such as landing pads, on the moon, Mars, and other extraterrestrial bodies. The advantage of using microwave heating is that regolith has the potential to be directly heated in situ. A computational model was developed that predicts the heating behavior of a lunar simulant, JSC-1A, using various methods for applying microwave energy. The efficiency of microwave heating depends on the properties of the materials. Dielectric properties are used to characterize a material's microwave behavior, which is temperature and frequency dependent. Obtaining a variety of actual regolith samples for dielectric characterization can be challenging, which is why simulants and computational models were developed. This work used lunar simulant JSC-1A for dielectric characterization, microwave-processing studies, and computational modeling, inasmuch as this simulant is available in large quantities and has been extensively studied. The dielectric properties of JSC-1AC (a coarse sizing of JSC-1A) were previously measured at 2.45 GHz as a function of temperature up to the melting point. Only room-temperature measurements were available for actual lunar regolith, which were comparable with JSC-1AC at low temperatures. An experimental design and a computational model were developed to study surface-only heating using microwaves on a deep bed of powder. Heating was performed in a 2.45-GHz, 6-kW microwave chamber, in an argon atmosphere to avoid oxidative changes to the simulant powder on heating. The use of microwaves for surface-only heating on deep beds of simulant powder was demonstrated. Modeling used finite-element and finite-difference methods to calculate the electromagnetic and thermal heat development, using the dielectric properties of JSC-1A. The heating patterns obtained from the computer model were compared with microwave-heating experiments. The model was adjusted to achieve close approximations of JSC-1A microwave heating using different heating scenarios. The geometry of heating patterns and range of temperature agreement between the model and experimental methods demonstrated a good representation of JSC-1A microwave-surface heating. [ABSTRACT FROM AUTHOR]