FE-model for Titanium alloy (Ti-6Al-4V) cutting based on the identification of limiting shear stress at tool-chip interface

Modeling of metal cutting has proved to be particularly complex, especially for tool-chip interface. The present work is mainly aimed to investigate the limiting shear stress at this interface in the case of Titanium alloy (Ti-6Al-4V) dry cutting based on a FE-model. It is first shown that the surface limiting shear stress was linked to the contact pressure and the coefficient of friction (CoF). A relationship between CoF and the limiting shear stress was given, and the effect of the temperature on the limiting shear stress was also considered. After that, an orthogonal cutting model was developed with an improved friction model through the user subroutine VFRIC in Abaqus/Explicit software. The numerical results obtained were compared with experimental data gathered from literature and a good overall agreement was found. Finally, the effects of cutting speed, CoF and tool-rake angle on chip morphologies were analyzed.     

Optimization of Resource Allocation and Leveling Using Genetic Algorithms

Resource allocation and leveling are among the top challenges in project management. Due to the complexity of projects, resource allocation and leveling have been dealt with as two distinct subproblems solved mainly using heuristic procedures that cannot guarantee optimum solutions. In this paper, improvements are proposed to resource allocation and leveling heuristics, and the Genetic Algorithms (GAs) technique is used to search for near-optimum solution, considering both aspects simultaneously. In the improved heuristics, random priorities are introduced into selected tasks and their impact on the schedule is monitored. The GA procedure then searches for an optimum set of tasks' priorities that produces shorter project duration and better-leveled resource profiles. One major advantage of the procedure is its simple applicability within commercial project management software systems to improve their performance. With a widely used system as an example, a macro program is written to automate the GA procedure. A case study is presented and several experiments conducted to demonstrate the multiobjective benefit of the procedure and outline future extensions.     

Identification of design motifs with pattern matching algorithms

Design patterns are important in software maintenance because they help in understanding and re-engineering systems. They propose design motifs, solutions to recurring design problems. The identification of occurrences of design motifs in large systems consists of identifying classes whose structure and organization match exactly or approximately the structure and organization of classes as suggested by the motif. We adapt two classical approximate string matching algorithms based on automata simulation and bit-vector processing to efficiently identify exact and approximate occurrences of motifs. We then carry out two case studies to show the performance, precision, and recall of our algorithms. In the first case study, we assess the performance of our algorithms on seven medium-to-large systems. In the second case study, we compare our approach with three existing approaches (an explanation-based constraint approach, a metric-enhanced explanation-based constraint approach, and a similarity scoring approach) by applying the algorithms on three small-to-medium size systems, JHotDraw, Juzzle, and QuickUML. Our studies show that approximate string matching based on bit-vector processing provides efficient algorithms to identify design motifs.     

Electrooptic modulation of multilongitudinal mode laser diodes: Demonstration at 850 nm with simultaneous data transmission by coherence multiplexing

An electrooptic modulation method based on signal coding through optical delays larger than the source coherence length is described. The method is illustrated with the simultaneous transmission of several signals by path-difference multiplexing. In this method, the signals are coded as a sequence of optical delays introduced by a series of electrooptic modulators working as delay lines. Decoding is carried out by temporal correlation performed by another sequence of optical delays introduced by birefringent plates, and matched to those used at the emission process. The permissible delays are shown to be ruled by the source coherence length and by the number of laser modes.     

Factors contributing to early age shrinkage cracking of slag concretes subjected to 7-days moist curing

The objective of this study was to investigate all the factors contributing to early age shrinkage cracking in concrete, namely, shrinkage, tensile creep, tensile elastic modulus, tensile strength of concretes, and to study the effect of slag as a binder on these factors. The above-mentioned factors were measured in early age concretes made with 0, 35, 50 and 65% level replacement of ordinary Portland cement by slag. All the concretes studied were moist cured for 7-days. It was found that, at lower slag replacement levels (0, 35 and 50%), the tensile strength decreased with increasing slag replacement. However, this is more than compensated by decreasing tensile elastic modulus and shrinkage. There was no significant change found in tensile creep with the changing slag levels. The study shows that the influence of the tensile elastic modulus is a major consideration for early age cracking of slag concretes.     

Evaluation and Carbon Fiber Reinforced Polymer Strengthening of Existing Garage: Case Study

The concrete-repair fiber reinforced polymer technology emerged in the United States during the past 10 years. Since 1995, carbon fiber reinforced polymer (CFRP) has been applied to strengthen concrete decks of a troubled posttensioned garage in Atlanta. During the construction of the garage, design deficiencies were found. A remedial repair, involving heavily?reinforced, 7.6 cm (3 in.) thick Gunite (Shotcrete) beams, applied to the underside of the slab between drop panels in the east-west (E-W) direction, was developed in 1984. Since then, delamination of Gunite beams and other structural problems repeatedly occurred. Epoxy injection and other limited repairs were done over the years in an attempt to remediate the problems. In 2000, due to the growing delamination concerns, backed up with nondestructive impact-echo testing results, and due to the newest set of structural analyses that showed additional design deficiencies, Simpson Gumpertz & Heger developed a new and comprehensive remedial program. The first phase of this program included an in-depth mechanical in?situ load test program to study the strength and stiffness performance of the existing typical slab spans, including the effects of Gunite beams, the loss of Gunite beams due to delamination, and the CFRP?strengthing of spans. The tests showed that the CFRP repair of E-W spans with delaminated Gunite beams is warranted and that it performs well. The performance of the existing typical spans in the north-south direction was found to be acceptable without any repairs. Further monitoring of the performance of Gunite beams is required, and additional CFRP strengthening will be done periodically. In addition, structural deficiencies of the typical second-level end bays were repaired using additional steel framing supports.     

Life-Cycle Cost Analysis using Deterministic and Stochastic Methods: Conflicting Results

Life-cycle cost analysis is an essential approach to differentiating alternative rehabilitation strategies for steel bridge paint systems. An economic analysis (EA), which is a deterministic method, and the Markov decision process (MDP), which is a stochastic method, were used to carry out the life-cycle cost analysis. These analyses were applied to data from two state Departments of Transportation. The deterioration curves for steel bridge paint condition rating against age were constructed. Different rehabilitation scenarios were proposed for steel bridge paint. The EA and the MDP were used to analyze and differentiate among the proposed rehabilitation scenarios. The results of the EA were different from those of MDP for the two data sets. MDP favored the “do nothing” scenario until the end of paint life and then a complete repainting. EA indicated that the scenario “do spot repairs at state 3 of the paint life” and repeat that until the end of the bridge life was superior. The results were analyzed to determine the reason for the conflict.     

In search of a stable urban regime for Montreal: issues and challenges in metropolitan development

As with many major North American urban areas since the 1960s, Montreal has faced contextual changes that have brought to the fore the question of its development. However, because of its history and the uncertainties linked with Quebec's constitutional future, attempts to stimulate its development have required certain compromises, often with unexpected results. In order to evaluate the performance of coalitions formed with the objective of meeting the challenges associated with urban and metropolitan development, we have drawn upon the concept of urban regimes. Focusing specifically on Montreal, we ask whether it is possible to transpose urban regime analyses that consider both structural and cultural factors specific to local organized forces. Revealing though they might be, these analyses nevertheless possess certain limitations, notably the underestimation of the weight and increasing importance of players and forces occurring on a metropolitan scale. This is particularly true in the case of Montreal.     

Synthesis and thermal cure of high molecular weight polybenzoxazine precursors and the properties of the thermosets

High molecular weight polybenzoxazine precursors have been synthesized from aromatic or aliphatic diamine and bisphenol-A with paraformaldehyde. The precursors were obtained as soluble white powder. Molecular weight was estimated from the size exclusion chromatography to be several thousands. The structure of the precursors was confirmed by IR, ¹H NMR and elemental analysis, indicating the presence of cyclic benzoxazine structure. The ratio of the ring-closed benzoxazine structure and the ring-opened structure in the high molecular weight precursor was estimated from ¹H NMR spectrum and also from the exotherm of DSC, showing that the ratio of the ring-closed benzoxazine structure was 77–98%. The precursor solution was cast on glass plate, giving transparent and self-standing precursor films, which was thermally cured up to 240 °C to give brown transparent polybenzoxazine films. The toughness of the crosslinked polybenzoxazine films from the high molecular weight precursors was greatly enhanced compared with the cured film from the typical low molecular weight monomer. Tensile measurement of the polybenzoxazine films revealed that polybenzoxazine from aromatic diamine exhibited the highest strength and modulus. While, polybenzoxazine from longer aliphatic diamine had higher elongation at break. The viscoelastic analyses showed that the glass transition temperature of the polybenzoxazines derived from the high molecular weight precursors were as high as 238–260 °C. Additionally, these novel polybenzoxazine thermosets showed excellent thermal stability.