Effects Of External Constraints Research Articles

Synergistical influence of internal expansion and external constraint on demolition efficiency of soundless chemical demolition method for concrete structures

Soundless chemical demolition (SCD) holds significant promise in building demolition engineering due to its safety, eco-friendliness, and flexibility, while insufficient understanding of the damage to concrete structure using this method hinders its application, which requires further research. This study investigated the damage of concrete structure caused by the soundless chemical demolition agent from the perspective of internal expansion and external constraint. The two parameters were controlled by adjusting the hole diameter, spacing and specimen size in the experiment and finite element simulation. Experiment results showed that the cracking time of concrete blocks shortened with increased internal expansion or decreased external constraint. The damage of blocks varied between the double-hole, unidirectional single-hole and multidirectional single-hole pattern with the increase of inter-hole constraint. Further, the damage range and level of blocks damaged in the unidirectional single-hole pattern were almost 45 % and 50 % lower than those of blocks damaged in other patterns, respectively, indicating that enhancing the synergy of adjacent holes or weakening the around-hole constraint can significantly improve the damage of concrete blocks. For the blocks damaged in the same pattern, internal expansion played a significant role in the damage range and level, while the effect of external constraint was not obvious. In addition, a hole parameter design method was established based on the comprehensive analysis of the synergy between external constraint and internal expansion, which was verified by the experiment of concrete shear walls. This work provides a new solution for the efficient demolition of concrete structure based on SCD.

Effects of Welded Pipe-cutting on the Residual Stress Re-Distribution and Engineering Critical Assessment

Welded rolled up steel pipe plates undergo more roundness deformation than seamless pipes. The main reason is that the existing residual stress after welding was re-distributed by the cutting process. The objective of this research is to investigate the effect of the constraint on the cutting process through finite element analysis (FEA) to minimize deformation. To include the effect of the cutting simulation, the external constraint was used as the mechanical restraint, and a welded pipe without constraints was used for comparison purposes. The results show that the cutting deformation and residual stress were both significantly reduced under the effect of external constraints. Moreover, the method of reducing conservatism in engineering critical assessment (ECA) was proposed using residual stress re-distribution.

Mitigation of residual stress and deformation induced by TIG welding in thin-walled pipes through external constraint

Thin-walled pipes have been widely used in chemical facilities and propulsion structures, where the distortion problem induced by welding fabrication is common and prominent, deteriorating assembly accuracy and even reducing load-bearing capacity. External constraint has shown great capacity to control the residual stresses and welding deformation. The objective of this research is to investigate the effect of constraint on welding process in thin-walled 304 stainless steel pipes through experiments and numerical simulation. To include the clamping effect in the welding simulation, the external constraint was modeled as the additional heat dissipation and mechanical restraint. The seam welded pipes with and without constraints were both modeled for comparison purpose. Good agreement was obtained between numerical modeling and measurements in both pipes. The results show that the welding deformation and residual stresses are both obviously reduced under the effect of external constraint, which was found to work mainly in the cooling process by generating more tensile plastic strain so as to reduce the shrinkage force in both axial and hoop directions. The maximum distortion is observed on the middle section of constrained pipe and on the end sections in the unconstrained one, which is caused by the combined effect of bending direction on the circumference and shrinkage force in the axial direction according to the inherent strain analysis. Moreover, the analysis of welding deformation mode reveals that the inward bending induced by hoop constraint contributes to the dimensional accuracy of the pipe ends under axial shrinkage forces. Parametric simulation analysis of the external constraint strategy was performed, and the results showed that reducing the constraint distance was the most effective way to mitigate welding distortion in seam welded pipes.

Data-driven stochastic modelling of zebrafish locomotion.

In this work, we develop a data-driven modelling framework to reproduce the locomotion of fish in a confined environment. Specifically, we highlight the primary characteristics of the motion of individual zebrafish (Danio rerio), and study how these can be suitably encapsulated within a mathematical framework utilising a limited number of calibrated model parameters. Using data captured from individual zebrafish via automated visual tracking, we develop a model using stochastic differential equations and describe fish as a self propelled particle moving in a plane. Based on recent experimental evidence of the importance of speed regulation in social behaviour, we extend stochastic models of fish locomotion by introducing experimentally-derived processes describing dynamic speed regulation. Salient metrics are defined which are then used to calibrate key parameters of coupled stochastic differential equations, describing both speed and angular speed of swimming fish. The effects of external constraints are also included, based on experimentally observed responses. Understanding the spontaneous dynamics of zebrafish using a bottom-up, purely data-driven approach is expected to yield a modelling framework for quantitative investigation of individual behaviour in the presence of various external constraints or biological assays.Electronic supplementary materialThe online version of this article (doi:10.1007/s00285-014-0843-2) contains supplementary material, which is available to authorized users.

Effect of external constraint on the characteristics and behavior of the plasma plume during high-power CO2 laser welding

Laser-induced plasma has been one of the hotspots of high-power CO2 laser welding for many years. A novel method was proposed to suppress the plasma plume through external constraints, which resulted in more stable welding process and slightly increased penetration depth. Based on high-speed camera and image processing technology, it was demonstrated that the expansion of plasma plume both in height and width was suppressed by a pair of water-cooled copper blocks laid near laser incident point along the direction of seam. Besides its intensity and size, the dynamical behavior of plasma plume under spatial constraint was observed and analyzed by the characteristic parameters. The constraint mechanism and influence of the spacing between the two copper blocks was discussed. Results showed that external constraint was effective to suppress plasma plume, stabilize welding process, and to increase weld penetration for high-power CO2 laser welding.

Strong dependency of lithium diffusion on mechanical constraints in high-capacity Li-ion battery electrodes

The effect of external constraints on Li diffusion in high-capacity Li-ion battery electrodes is investigated using a coupled finite deformation theory. It is found that thin-film electrodes on rigid substrates experience much slower diffusion rates compared with free-standing films with the same material properties and geometric dimensions. More importantly, the study reveals that mechanical driving forces tend to retard diffusion in highly-constrained thin films when lithiation-induced softening is considered, in contrast to the fact that mechanical driving forces always enhance diffusion when deformation is fully elastic. The results provide further proof that nano-particles are a better design option for nextgeneration alloy-based electrodes compared with thin films.

Toward a more realistic prediction of peri‐prosthetic micromotions

The finite element (FE) method has become a common tool to evaluate peri-prosthetic micromotions in cementless total hip arthroplasty. Often, only the peak joint load and a selected number of muscle loads are applied to determine micromotions. Furthermore, the applied external constraints are simplified (diaphyseal fixation), resulting in a non-physiological situation. In this study, a scaled musculoskeletal model was used to extract a full set of muscle and hip joint loads occurring during a walking cycle. These loads were applied incrementally to an FE model to analyze micromotions. The relation between micromotions and external loads was investigated, and how micromotions during a full loading cycle compared to those calculated when applying a peak load only. Finally, the effect of external constraints was analyzed (full model vs. diaphyseal fixation and reduced number of muscle loads). Relatively large micromotions were found during the swing phase when the hip joint forces were relatively low. Maximal micromotions, however, did concur with the peak hip joint force. Applying only a peak joint force resulted in peak micromotions similar to those found when full walking cycle loads were applied. The magnitude and direction of the micromotions depended on the applied muscle loads, but not on external constraints.

Effect of External Constraint on the Index of Myocardial Performance in a Canine Model of Left Ventricular Dysfunction

With left ventricular (LV) dysfunction, it is not clear how alterations in external constraint influence the index of myocardial performance (IMP). We have previously demonstrated that pericardial constraint is a factor in the production of the restrictive filling pattern. We hypothesized that altering pericardial constraint by changing intracardiac volume or removing the pericardium would produce similar directional changes in LV ejection time (LVET) and isovolumic relaxation time (IRT) resulting in minimal IMP changes. We studied 13 canines with chronic moderate LV dysfunction. LV pressures, transmitral and transaortic Doppler were obtained prior to and following pericardiectomy (PECT) with alterations of intracardiac volume, using inferior vena caval occlusion (IVCO) and volume loading. With an intact pericardium, IVCO reduced LV size, LV end diastolic pressure (LVEDP), and increased deceleration time (all P < 0.05) but did not affect IMP. Volume loading increased LV size, LVEDP, and shortened deceleration time (all P < 0.05). LVET and IRT lengthened (P < 0.05), and IMP declined (0.58 +/- 0.24 to 0.52 +/- 0.13, P < 0.05). Following PECT, IVCO reduced LV volumes and LVEDP (P < 0.05), but did not change IMP. Volume loading increased LV size, stroke volume, and LVEDP (all P < 0.05). IMP declined (0.57 +/- 0.13 vs 0.51 +/- 0.14, P < 0.05) due to an increase in both LVET and IRT (P < 0.05). Comparison of stages prior to and following PECT revealed an increased LVET and stroke volume (P < 0.05) but a similar IMP. Increases in intracardiac volume associated with elevated LVEDP resulted in reduced IMPs. Pericardiectomy increases LV volumes, stroke volume, and LVET but did not influence IMP.

Micromechanical Modeling of Stress Evolution Induced During Cure in a Particle-Filled Electronic Packaging Polymer

Particle-filled polymers are widely used in electronic industries. From microscale view, cure-induced residual stress can be generated not only by the external constraints but also by the constraint effect among the particles. In this paper, a three-dimensional micromechanical finite element method (FEM) model has been setup for a silica particle filled epoxy. In the micromechanical model, the epoxy matrix is modeled with a previously developed cure-dependent viscoelastic constitutive model, whereas the silica particles are modeled as elastic with high stiffness. Cure shrinkage is applied to the matrix as an initial strain for each time increment. The cure-dependent viscoelastic properties were obtained from shear and tension-compression dynamical mechanical analysis measurements. Cure shrinkage and reaction kinetics were characterized with online density measurement and differential scanning calorimeter measurements, respectively. In order to simulate a partly constrained object, the micromechanical model is coupled with a macromodel FEM analysis. The displacements from the macromodel are used as boundary conditions for the micromodel. The effect of external constraints on the generation of the micro stresses is studied by using the boundary conditions related to different external constrained states.

Derivation of temperature and pressure from submillimetric limb observations

We demonstrate the feasibility of retrieval of temperature and pressure profiles from spaceborne limb-sounding spectroscopic measurements in the submillimetric region. Whether these profiles can be retrieved determines whether a submillimetric instrument can be self-sufficient as far as the atmospheric model is concerned or whether complementary sensors in other spectral regions, dedicated to temperature and pressure measurements, are needed. Molecular-oxygen transitions are selected for the purpose of temperature and pressure retrieval on the basis of realistic observational parameters. We use a mathematical model of the retrieval process to evaluate the information content of the spectral features and to study the trade-off between the uncertainty of the retrieved profiles and their vertical resolution. It is shown that, using only one oxygen transition and without any constraint, one can achieve uncertainties of 5% for both temperature and pressure from 10 to approximately 40 km of altitude with a vertical resolution of 3 km; above 40 km the vertical resolution needs to be degraded to limit the uncertainties. The possibility of exploiting a priori information is discussed, as well as the effects of external constraints that can be used to improve the quality of the retrieved profiles. The sources of systematic error that need to be considered for the compilation of the total error budget are also evaluated.

Optimisation of Monitor Weighting Factors for the Estimation of Effective Dose Equivalent from External Photon Exposures

A procedure is proposed for using front and back personnel monitors for the estimation of effective dose equivalent HE from external photon irradiation. The optimised model calls for weighing the front monitor derived estimate of HE by 0.7 and the back monitor HE estimate by 0.3. In order to arrive at these weights, published coefficients for the conversion of physical and operational quantities to HE were used in simulations of HE, and published conversion coefficients for the conversion of phantom calibrated dosemeters were used to simulate idealised dosemeter based quantities. Radiation exposures were modelled as mixtures of anteroposterior (AP) and postero-anterior (PA) photon irradiations for which the AP variable was drawn randomly from normal or uniform distributions having mean values of 0 to 100% AP exposure. The results show that for a wide range of photon energy and randomly varying (i.e. 'uncertain') irradiation geometries, both the accuracy improves and uncertainty in HE estimation is minimised using the two-dosemeter approach compared to a single monitor. The described approach is applicable for a wide variety of exposure scenarios in which the energy and geometry of irradiation are uncertain. In addition, the approach provides a method for testing the effects of external constraints, such as regulatory limits, on the uncertainty and accuracy of monitor based estimates of H E .

Career Orientations in Women from Rural and Urban Backgrounds

This study examines career orientations in women from rural and urban backgrounds, using a longitudinal data set collected over a period of 10 years, from 1973-1982. When first contacted, respondents were 18 years of age. The final data collection in 1982 resulted in a sample of some 1300 women. The longitudinal data was analyzed using LISREL structural equation modeling and was guided by a theoretical framework developed by Krumboltz (1981), which focuses on the process of decision-making. The theory attempts to explain how educational and occupational preferences and skills are acquired and how selections of courses, occupations and fields of work are made and identifies the interactions of genetic factors, environmental conditions, learning experiences, cognitive and emotional responses, and performance skills that produce movement along one career path or another. Results from the study found that there were some differences between women of contrasting geographic background over the secondary school-early career development stage. Noticeably larger differences occurred in values found for rural women in the effect of external constraints on early work satisfaction, the stability of work satisfaction, the effect of work satisfaction on occupational interest and the effect of parental status on career orientation

The optimal rate of industrialization in developed and developing centrally-planned economies: A general equilibrium approach

The investment policies of Czechoslovakia and Romania are examined by means of counterfactual experiments employing econometric models of these countries. Alternative investment policies considered are: (1) an increase in aggregate investment with unchanged sectoral distribution; (2) a shift in investment from other sectors to manufacturing; and (3) a shift in investment from manufacturing to services. For Czechoslovakia policy (2) is deemed superior to the historical pattern of investment and to the other two hypothetical policies, while for Romania policy (3) is best. The general equilibrium evaluation of development policies shows the conflicts among planners' goals in setting investment policy and the effect of external constraints, such as the availability of food and raw material imports, on planners' ability to implement desirable strategies.

Thermal stability and crystallization of metallic glasses

Investigations into the annealing behaviour of metallic glasses are reviewed. The low-temperature structural relaxations and the temper-embrittlement phenomena are discussed briefly. The author then reviews current knowledge on the crystallization behaviour of glassy metals, including the compositional dependence of stability against crystallization, crystallization morphologies, crystallization kinetics, and the effect of external constraints on crystallization. Some areas for future research are suggested.