Increase Of Solution Time Research Articles

Forging process of a new type high-performance P/M turbine disk superalloy

The hot forging deformation experiments of a new type high performance powder metallurgy (P/M) turbine disk superalloy FGH98 I has been performed under the conditions of the deformation temperatures of 1050-1100°C and strain rates of 0.0003∼0.01 s-1, and then with subsequent subsolvus and supersolvus heat treatments for 0.25-1h. The results show that FGH98 I alloy exhibits the desired thermoplastic response under the testing conditions. The forging flow stress increases with increasing strain rate and decreasing temperature. The mean grain size of as-forged FGH98 I varies between 6.0μm and 8.0μm, and only slightly coarsens with the increasing temperature and decreasing strain rate. The mean grain size of the subsolvus heat treated specimens varies between 8.6μm and 24μm, slowly coarsens with increasing solution time, and moderately coarsens with increasing temperature and decreasing strain rate. The mean grain size under supersolvus heat treated varies between 10μm and 46μm, obviously coarsens with increasing temperature and solution time, and coarsens with decreasing strain rate. The above results can be used for optimizing the practical forging process of FGH98 I disk alloy.

Influence of Heat Treatment on the Microstructure and Property of Mg-Nd-Gd-Zn-Zr Alloy

Abstract The influence of heat treatment process on the microstructure and property of Mg-Nd-Gd-Zn-Zr magnesium alloy was studied. The results show that, with the increase of the solid solution temperature, the grains of the alloy grow obviously and its elongation rate is decreased, but the residual second phase in grain boundary reduces, and the fracture mode of the alloy changes from a combination of second-phase fracture and trans-grain fracture to the trans-grain cleavage fracture; with the increase of solution time, the change of the tensile strength is not evident and the elongation rate is increased, but oxidation extent tends to increasing; the double-stage ageing process can improve the elongation rate, but the tensile strength is lowered to some extent.

Effect of Solution Treatment on Microstructure and Mechanical Properties of ZL114A Alloy

By using the universal mechanical testing machine and electric microscope, the effect of solution parameters on the mechanical properties of ZL114A aluminum alloy has been studied. The experimental results lead to the following conclusions. With the increase of solution temperature, the eutectic silicon gradually become round, and the roundness of solution at 550°C/10h is good. The tensile strength and hardness will increase, and the elongation rate will rise and then drop when the solution temperature increases. Along with the increase of solution time, the tensile strength and hardness will increase and then decrease, however, the elongation rate has been rising. When the water temperature is below 40°C, the satisfied mechanical properties can be got. The optimal solution temperature and time are 540±5°C/10h and the water temperature is below 40°C.

Dissolution of Al2Cu phase in non-modified and Sr modified 319 type alloys

This study investigates the effects of solution heat treatment on dissolution of the Al2Cu phase in non-modified and 150 ppm Sr modified 319 type alloys. Experimental and industrial 319 alloys containing different Mg levels (0, 0·3 and 0·6 wt-%) were used for this purpose. Electron probe microanalysis (EPMA) in conjunction with energy dispersive X-ray (EDX) analysis was used to monitor the distribution of Cu in the matrix and to measure the undissolved Al2Cu phase. In as cast 319 alloys, copper segregates at the dendrite boundaries. The addition of Mg and Sr may cause this segregation to deteriorate. After heat treatment, the copper begins to distribute more evenly across the dendrite as well as in the matrix. The amount of Cu dissolved in the matrix increases with increasing solution time and temperatures, reaching a maximum for the 490°C/8 h solution heat treatment. The dissolution process of eutectic and block like Al2Cu was also investigated.

Evaluation of a detailed radiation heat transfer model in a high temperature reactor systems simulation model

Radiation heat transfer is a major mode of heat transfer in high temperature gas-cooled reactors (HTRs) because of the high operating temperatures. It is, however, a difficult phenomenon to calculate in full detail due to its geometrical complexity. One has to use either a numerical method or complex analytical view factor formulae. Except the difficulty of view factor calculation, a vast number of calculation elements are required to consider all interacting surfaces around a cavity. A common approximation in systems simulation codes is to connect only directly opposing surfaces with a view factor of one. The accuracy of this approximation was investigated with a finite volume, two-dimensional axial-symmetric reactor model implemented in the systems simulation code Flownex. A detailed radiation model was developed and also implemented in the Flownex reactor model. This paper also describes the analytical formulae for view factor calculation in this detailed radiation heat transfer model. The HTR-10 and the 268 MW version of the PBMR were used as case studies in which Loss-of-Flow events without SCRAM were simulated. In these simulations, the time to reach recriticality was used as an indicator of heat removal effectiveness. With the HTR-10, other non-linear phenomena in the reactor core constrained the solution process, so that the number of radiation elements had no effect on solution time, while with the 268 MW PBMR DLOFC, the use of a detailed radiation model increased solution time with 30%. With both the HTR-10 and the PBMR, the radiation model had negligible effect on the total heat resistance from the reactor, as indicated by the time elapsed until recriticality. For system simulation codes that focus on transient response of a plant, it is not considered worthwhile to use a detailed radiation model, as the gain in accuracy does not justify the increased solution time or the implementation and verification effort.

Development of a genetic algorithm for component placement sequence optimization in printed circuit board assembly

This paper describes the development and evaluation of a custom application exploring the use of genetic algorithms (GA) to solve a component placement sequencing problem for printed circuit board (PCB) assembly. In the assembly of PCB’s, the component placement process is often the bottleneck, and the equipment to complete component placement is often the largest capital investment. The number of components placed on a PCB can range from few to hundreds. As a result, developing an application to determine an optimal or near-optimal placement sequence can translate into reduced cycle times for the overall assembly process and reduced assembly costs. A custom application was developed to evaluate the effectiveness of using GA’s to solve the component placement sequencing problem. A designed experiment was used to determine the best representation and crossover type, crossover rate, and mutation rate to use in solving a component sequencing problem for a PCB consisting of 10 components being placed on a single-headed placement machine. Three different representations (path, ordinal, and adjacency) and six appropriate crossover types (partially mapped, ordered, cycle, classical, alternating edges, and heuristic) were evaluated at three different mutation rates and at 11 crossover rates. Two algorithm response variables, the total distance traveled by the placement head and the algorithm solution efficiency (measured as number of generations and algorithm solution time) were used to evaluate the different GA applications. The combination of representation and crossover type along with mutation rate were found to be the most significant parameters in the algorithm design. In particular, path representation with order crossover was found to produce the best solution as measured by the total distance traveled as well as the solution generation efficiency. Increasing the mutation rate led to slightly improved solutions in terms of head travel, but also resulted in increased solution time.

Research on Solution and Aging Treatment of Mg-7Zn-3Al Alloy

Effect of solution and aging treatment on the microstructure of Mg-7Zn-3Al alloy is studied by using optical microscopy, scanning electron microscopy, X-ray diffraction, transmission electron microscopy and quantitative image analysis. The results show that the as-aged microstructure is composed of α-Mg matrix, grain boundary τ (Mg32(Al,Zn)49 ) phase, and fine dispersed τ particles inside the grain. The solution degree has significant effects on the formation, morphology, and size of the grain boundary τ phase. The volume fraction and the size of the undissolved eutectic τ phase decrease with the increase of solution time treated at 325°C. Through sufficient solution treatment, discontinuous eutectic τ phase retains fine strip morphology after aging, in contrast to the microstructure in sample undergone insufficient solution which manifests as-cast feature, while at the same time nano-sized particles precipitate out from the matrix. The precipitates display paralleled short bar, having certain orientation relationship with the matrix.

Microstructure of AZ91D in Different Treatment Conditions

The microstructures of magnesium alloy AZ91D in as-cast, solid solution and aging conditions were studied by optical, scanning electron and transmission electronic microscopes. The relationship between microstructure and the microhardness was analyzed. It has been found that the microhardness in the matrix varied slightly with the increasing solution time, but increased quickly with the aging time. The difference of the microhardness between the matrix and the second phase in as-cast condition is larger than that in T6 aging condition, because the aluminum-zinc-magnesium (poor) phase existed in the as-cast condition.

Effects of Heat Treatment on Microstructure and Mechanical Properties of Rolled AM50+xCa Magnesium Alloys

Effects of solution and aging treatment on microstructure and mechanical properties of rolled AM50+xCa alloys(x=0, 1, 2 wt. %) were studied. The results indicated that, with increasing solution time i, the secondary phase Mg17Al12 was dissolved into the Mg matrix and Al2Ca became thinner and shorter, then gradually broken and spheroidized.With an increase of aging time, Mg17Al12 precipitated from the Mg matrix in the form of particles and Al2Ca changed a little. After solution treatment, hardness and tensile properties of the alloy’s decreased. After the aging treatment, the alloy’s hardness increased first and decreased later while the tensile properties increased little. The solution and aging treatment can increase the ductility of AM50 and AM50+1Ca alloys. For AM50+2Ca alloy, the ductility increased after solid solution treatment and decreased after aging treatment.

A methodology for controlled empirical investigation of membership continuity and change in GDSS groups

Controlled laboratory experiments using monetary rewards tied directly to performance are detailed and illustrated, as part of a methodology for investigating how membership continuity and change affect group meeting performance, solution time, and productivity. Performance-based rewards were structured to induce subject attendance and to prompt subjects to contribute their best effort. A key element of our methodology is the ability to successfully conduct longitudinal studies. We illustrate the methodology in an example study of groups of size three and groups of size five. Experiments are carefully monitored and controlled as a means to begin development of a set of consistent and comparable investigations, of groups of differing sizes and differing levels of membership continuity and change. The initial experiments yielded results formally verifying that membership continuity produces better meeting outcomes (increased performance and productivity, and decreased solution time) while membership change produced the exact opposite (decreased performance and productivity, and increased solution time). Drawing from philosophy of science, we emphasize the importance of carefully checking and verifying in a longitudinal study even what some might suggest as “obvious.”

Scheduling using tabu search methods with intensification and diversification

After spending five years in Medical School, physician students have to complete additional study including several interships before becoming full members of their professional guild. In this paper, we deal with the annual scheduling of internships taking into account the supervision capacities of the hospitals. The problem is modeled as an assignment-type problem. Several variants of Tabu Search procedures including intensification and diversification strategies are proposed and tested to deal with this problem. The numerical results indicate that the solution quality can be improved using intensification and diversification, at the expense of increasing solution time. Scope and purposeAfter spending five years in Medical School, future physicians have to complete additional study including several internships before becoming full members of their professional guild. The number of internships to be completed, their subject area, and their length depend on the student specialization. In this paper, we analyze the problem faced by the medical school each year to specify the schedule for each student's internships. For each of his internships, a student specifies preferences about its time period and the location. The objective function is to maximize the overall satisfaction of the students. The constraints correspond to the bounds (lower and upper) on the number of students that the hospitals are ready to supervise for each type of internships and for each period of the year. The problem is formulated as an assignment-type problem. To deal with this problem, we propose several variants of local search heuristic procedures including strategies to intensify the search in specific region of the feasible domain (intensification), and others to search the whole feasible domain more extensively (diversification). These variants are tested and compared to establish the tradeoff between solution time and solution quality.

VICONOPT - Program for exact vibration and buckling analysis or design of prismatic plate assemblies

ASUMMARY is given of key features of the computer program VICONOPT,1 which covers prismatic assemblies of anisotropic plates exactly for buckling and vibration analysis and also for design subject to buckling constraints. Contents VICONOPT (VIpasa with CONstraints and OPTimization) is a 23,000 line Fortran 77 computer program that incorporates the earlier programs VIPASA2 and VICON.3 It covers any prismatic assembly of anisotropic plates and Fig. 1 shows typical cross sections. Each plate can carry any combination of NL, NT9 and Ns, the longitudinally invariant in-plane forces per unit length of plate edge shown in Fig. 1. VICONOPT performs analysis or optimum design. The analysis includes calculation of critical buckling load factors, or undamped natural frequencies, and mode shapes. VIPASA uses the stiffness matrix method based on exact flat plate theory with Winkler foundations. It also uses an algorithm that guarantees convergence on all required eigenvalues and permits the user to employ nested (to any level) substructuring very concisely and flexibly to reduce solution times, data preparation, and computer memory usage. The mode of buckling or vibration is assumed to vary sinusoidally in the longitudinal direction x> with the displacement amplitudes u, v, w, and ^ shown in Fig. 1 and with computations being repeated for a user specified set of half-waveleng ths X. Plate bending and membrane behaviors are uncoupled and the bending and in-plane stiffness matrices D and A are respectively fully populated and orthotropic, which treats balanced symmetric laminates. The global stiffness matrix becomes complex when anisotropy or shear loading are present, thus, increasing solution time. The nodal lines of zero displacement are straight and in the y direction if all plates are orthotropic with Ns = 0, and so satisfy simply supported end conditions. Otherwise, solutions only approximate such end conditions and become excessively conservative as A approaches L Dead load values of NL, NT9 and Ns are permitted for both buckling and vibration problems. In the former case they are additional to live load values that are factored until buckling occurs. Plate loadings may be given as data, although NL is usually calculated from the total longitudinal load on the panel or

A single-branch implicit enumeration algorithm for zero-one programs with geometrical constraints

This paper presents an algorithm for solving a class of mathematical programming problems that arise in connection with optimizing recovery from air base attacks. The problems are formulated as zero-one programs with geometrical constraints associated with quasirandom arrangements of circular craters imposed on taxiways. It is shown that efficient, computer-based enumerative methods may be employed successfully in the absence of algebraic representations for the constraints. The computational efficiency of the algorithm is characterized empirically using samples of randomly generated test problems. Rapid increase in solution time with growth in problem size is noted. A simple but effective means of decomposition to additive subproblems is described to help avoid long solution time. Finally, directions of current related research are given.

The continuous cooling transformation behaviour of zirconium-niobium-oxygen alloys

The continuous cooling transformation behaviour of zirconium alloys containing up to 5 at% niobium and 3 at% (5300 ppm) oxygen has been examined using thermal analysis and metallographic techniques. Two types of reactions were found; nucleation and growth reactions which showed the familiar C-curve kinetics, and the athermal martensite reaction. The nucleation and growth reactions were identified as the formation of α-zirconium at the β-grain boundaries and the transformation βzr → αZr+βNb throughout the grains. Increasing niobium content lowered the temperature and increased the time required to obtain the thermal arrests. Increasing oxygen raised the temperature of both reactions and caused grain boundary nucleation to occur sooner and nucleation within the grains to occur later. The martensite start temperature was not affected by oxygen but decreased linearly with niobium content. Clustering of solute atoms within the β-phase has been suggested by other workers. The results show that this must be an equilibrium condition. Clusters will not disperse with increased solution time as previously proposed.

Effect of word length on anagram solution time

Ten Ss were presented with 80 anagrams, which varied in length from three to 10 letters. The cumulative distribution of solution times for each number of letters was fitted by the equation for an hyperbola. This equation had two empirical constants: L, the limiting percentage of solutions, which was approached asymptotically with increasing time; and R, a constant inversely related to the rate at which the limit was approached. In general, both the limit and the rate of approach decreased as anagram length increased. The time required to solve a given percentage of anagrams increased with anagram length, but the increase in solution time did not keep pace with the progressively larger increments in the number of different letter arrangements made possible by each additional letter. In fact, the increment in solution time produced by each additional letter became smaller when anagram length exceeded six letters. Two properties of the English language may have facilitated solution of the longer anagrams: the occurrence of familiar suffixes in words longer than six letters, and the decreasing number of words of a given length above six or seven letters.