Experimental and numerical verification of transient spatial temperature distribution in thick-walled pressure components

The aim of this work is to present a method to determine the transient-state spatial temperature distribution in a cylindrical component. The presented method involves solving the inverse heat conduction problem based on the Finite volume method (FVM). This approach enables determination of transient-state temperature fields with boundary conditions known on one surface of the component only. The proposed method is verified using the laboratory installation located at the Cracow University of Technology. The main components of the laboratory stand are, among others, a steam outlet header and a steam boiler. During the experiment, the steam header is heated up abruptly from the inside by contact with dry saturated steam. The spatial transient-state temperature distribution within the steam outlet header is determined using the proposed method, which is based on temperature measurements made by 19 thermocouples located on the outer surface of the component. The temperature histories in three selected nodes are compared with the measurement results obtained from thermocouples located inside the component wall. The exact location of the thermocouples corresponds to the nodal position at selected control volumes. Moreover, the Ansys Mechanical APDL software is used to verify calculations and experimental data. A transient- state simulation is performed. The temperature histories at the inner and outer surfaces are set as the model boundary conditions. In order to enable verification of the temperature measurements, the component discrete model includes nodes at appropriate locations. An error analysis is performed between calculated and measured temperature values. The results obtained from the numerical and experimental validation demonstrate fully satisfactory agreement. Additionally, a stress analysis of the outlet header is performed in the Ansys software based on the transient-state temperature distribution within the steam outlet header. The method proposed in this paper is a convenient and accurate tool for monitoring working conditions of the power boiler thick-walled components.     

Experimental study on mechanical behaviors of injection molded PC/PMMA blends

Journal of Mechanical Science and Technology - Mechanical property is one of the quite important factors of optical articles. Most of pure plastics materials are rarely found to have both high...     

薄壁半管注塑件熔体填充分析与结构优化

针对半管注塑件填充不平衡问题,采用增加导流结构的方法来优化聚合物熔体在型腔中的流动状态,并据此改进了注塑件的结构设计。运用Moldflow软件对注塑件进行填充过程仿真分析,结果表明,将熔体填充仿真分析与注塑件结构优化设计紧密结合,能有效避免可能出现的注塑成型问题,可以缩短模具研发周期,提高制件成型的效率和质量。     

注塑模具瞬态温度仿真研究

以变径管注塑模具为例,采用ANSYS软件进行瞬态热分析,对模具和塑件的冷却过程进行仿真。该方法能够直观显示模具和塑件在各个时刻的瞬态温度分布,可检验冷却效果,为保压周期的的确定和模具优化设计打下基础。     

Experimental and numerical analyses of the pressure distribution in electrochemical machining

Measurements have been made of the pressure distribution of the electrolyte solution flowing along the inter-electrode gap during electrochemical machining. A theoretical model for the pressure distribution, which takes into account the growth of the hydrogen gas layer along the cathode electrode, is proposed. A method of solution of the model, based on optimisation techniques, is discussed.The experimental results and the theoretical model are correlated in terms of the variation of the interelectrode gap, thereby providing a prediction of the pressure distribution together with values for gas void fraction index, the slope of the gas bubble layer and the friction factor.A comparison of the measured and predicted pressure variation is presented. Numerical values for the above parameters are then discussed in the light of other observations of the process.     

Experimental and numerical study of the temperature field during creep feed grinding

In this study, commercially pure titanium sheets (American Society for Testing and Materials grade?2) were welded by resistance spot welding at various welding parameters. The welded joints were subjected to tensile-shearing tests in order to determine the strength values. In addition, the hardness and microstructural examinations were carried out in order to examine the influence of welding parameters on the welded joints. The experimental results showed that increasing electrode force, welding current and welding time increased the tensile-shearing strength of the welded specimens. Hardness measurement results indicated that welding nugget had the highest hardness and this was followed by the heat-affected zone and the base metal. Microstructural examinations showed the growth of the weld nugget grains with increasing heat input. Besides, due to plastic deformation during the welding process, twins were formed and at the same time twins increased with increasing electrode force, welding current and welding time.     

Experimental and numerical study of the load distribution in a ball-screw system

In this work, load distribution on ball-screw systems (BSS) is determined by experimental techniques. Two optical techniques are used: photoelasticity for stress-field measurement and the mark-tracking method for displacement-field determination. In parallel to the experimental study, finite element method (FEM) and analytical solutions are used to calculate the loads applied on each ball of the BSS. Experimental results are used to validate the choice of boundary conditions and contact conditions between ball-screw and ball-nut in the FEM solution. The validation criterion is the correspondence between numerical and experimental fringes representing the differences of principal stresses. In addition to the study of load distribution, this paper presents the influence of the angle of contact direction on the stress distribution in BSS.     

Experimental analysis and numerical simulation of sintered micro-fluidic devices using powder hot embossing process

For the past 2 years, interest in manufacturing technologies based on micro-fluidic systems has been continuously increasing. Today, micro-fluidic systems are used in numerous biomedical and pharmaceutical applications. Micro-fluidics cannot be thought about separately without advances in micro- and nano-fabrication. Investigations based on experiments, finite element modelling and simulations of powder hot embossing process (PHE) were performed to optimise the sintering step and processing parameters of micro-fluidic components. The model pertaining to thermo-elasto-viscoplastic behaviour was identified for 316L stainless steel powders. In this regard, different material properties such as sintering stress, bulk, and shearing viscosities were identified by inverse analysis from present dilatometer measurements using beam-bending and free sintering tests. The identification of materials was performed for various powder volume loadings and kinetic rates for different 316L elaborated feedstock, and the parameters were obtained as functions of relative density. The initial inhomogeneity due to the PHE process has been taken into account in the sintering simulation, as it affects the final shrinkage of the sintered components. The solid-state sintering simulations were investigated for various final sintering temperatures and kinetic rates to obtain high and homogeneous relative density distributions, achieve isotropic shrinkage and optimise the sintering process parameters. The numerical simulations were realised based on the identified parameters on a 3D micro-structured specimen with an associated rectangular plate support elaborated by PHE; this allowed a comparison between the numerical predictions and the experimental results for the sintering stage. The finite element simulation results of the sintering stage with a micro-fluidic structured component at a high final temperature (1360 °C) are in excellent agreement with the results of the experiments. The comparison of the simulation and experimental results validated the identified and implemented physical model and proposed methodologies.     

Experimental and direct numerical analysis of hard-disk drive

The purpose of this paper is to study methods for enhancing the reliability and performance of hard-disk drives (HDD) because it is essential for improving recording density, speed of data access, and output signal. This study also investigates various techniques that can be used for head/disk contact detection. The acoustic emission (AE) and friction signal characteristics were observed with respect to the durability of the head/disk interface (HDI) under various operating conditions using a contact start-stop (CSS) test. In addition, to study the influence of surface topography on the stiction performance of the HDI, a modified and polished laser pump was proposed and CSS investigations were accomplished. Moreover, the static and dynamic properties of an HDD air slider were studied using a finite element method (FEM).     

Experimental evaluation and simulation of volumetric shrinkage and warpage on polymeric composite short natural fibers reinforced injection molded

A polymeric natural fiber-reinforced composite is developed by extrusion and injection molding process. The shrinkage and warpage of high-density polyethylene reinforced with short natural fibers of Guadua angustifolia Kunth are analyzed by experimental measurements and computer simulations. Autodesk Moldflow® and Solid Works® are employed to simulate both volumetric shrinkage and warpage of injected parts at different configurations: 0 wt.%, 20 wt.%, 30 wt.% and 40 wt.% reinforcing on shrinkage and warpage behavior of polymer composite. Become evident the restrictive effect of reinforcing on the volumetric shrinkage and warpage of injected parts. The results indicate that volumetric shrinkage of natural composite is reduced up to 58% with fiber increasing, whereas the warpage shows a reduction form 79% to 86% with major fiber content. These results suggest that it is a highly beneficial use of natural fibers to improve the assembly properties of polymeric natural fiber-reinforced composites.     

Experimental analysis and numerical modeling using lisa-ddb hybrid breakup model of direct injected gasoline spray

This paper presents the effect of injection pressure on the atomization characteristics of high-pressure injector in a direct injection gasoline engine both experimentally and numerically. The atomization characteristics such as mean droplet size, mean velocity, and velocity distribution were measured by phase Doppler particle analyzer. The spray development, spray penetration, and global spray structure were visualized using a laser sheet method. In order to investigate the atomization process in more detail, the calculations with the LISA-DDB hybrid model were performed. The results provide the effect of injection pressure on the macroscopic and microscopic behaviors such as spray development, spray penetration, mean droplet size, and mean velocity distribution. It is revealed that the accuracy of prediction is promoted by using the LISA-DDB hybrid breakup model, comparing to the original LISA model or TAB model alone. And the characteristics of the primary and secondary breakups have been investigated by numerical approach.     

Effects of molding conditions on injection molded direct joining using a metal with nano-structured surface

Injection molded direct joining (IMDJ) is one of the metal-plastic direct joining processes and is based on a combination of a special surface treatment of a metal piece and an insert molding. This study employed a chemical processing as the special surface treatment to form nano-structures on the metal piece. We investigated relationship between joining strengths and molding conditions; we focused on pressure of a mold cavity and injection speed as molding conditions in this work. To evaluate the IMDJ samples processed under various molding conditions, we carried out tensile-shear tests. Then we compared the results of the tests to discuss how much each condition variation affected the joining strength. From the discussion, we found an interesting effect of the injection speed, which is unique to the IMDJ using a metal piece with nano-structures. The findings of this study will promote a better understanding of the IMDJ.     

Influence of molding conditions on the shrinkage and roundness of injection molded parts

During the plastic injection molding process, one of the biggest challenges is shrinkage which deteriorates the quality of produced parts. To control and reduce this defect, the essential way is to perfectly determine the variables like molding parameters. In this study, the effects of molding parameters including packing pressure, melt temperature, and cooling time on shrinkage and roundness have been investigated experimentally. Also, the relationship among initial molding parameters, the cavity pressure, and mold temperature was investigated. The results of this experimental study and analysis fulfill various requirements of plastic injection molding and clarify the relationship between molding conditions and the overall quality of produced parts. This study illustrated that packing pressure and melt temperature are dominant factors which determine the quality of parts.     

Understanding the structure of table-type dolmens using numerical analysis

Computer-aided methods are used extensively to analyze archaeological images. This data can then be used to make mappings and provide greater structural understanding of archaeological objects of interest. This paper details a numerical analysis of a typical Korean dolmen, performed in order to enhance our understanding of its structure in terms of force/pressure, strain/stress, and fatigue damage. The advanced engineering tools “ABAQUS” and “Nastran” are employed to analyze force/pressure, deformation/strain/stress relations, and the overall distribution of stress and damage, respectively. This structural analysis was performed for various geometrical configurations such as offset distances of the top stone, inclined angles of the supporting stones, and varying shapes of dolmens. This analysis shows that dolmens having vertically-erected supporting stones are most stable. With the help of this parametric study using idealized models, two real existing models were applied to analyze and predict damage to the table-type dolmens. The accuracy of the numerical predictions shows that this kind of analysis has great potential to be the method of choice for structural understanding of such objects. If run in parallel with the sensing techniques currently used, it could greatly aid in the conservation of archaeological objects.     

Experimental and numerical analysis of velocity distribution in a compound meandering channel with double layered rigid vegetated flood plains

Vegetation is one of the major topographic features that is encountered along and across the margins and flood plains of many rivers systems. This vegetation creates a most complex flow mechanism in the compound river bed channels; therefore, a detailed analysis is required to observe the flow and vegetation interactions to understand the hydrodynamic aspects in the river systems. This paper studies the effect of double-layered rigid vegetation in a meandering channel on the flow characteristics at two relative depth conditions, of 0.34, 0.45 which creates an alternate emergent and submerged flow situation. The three-dimensional velocity distribution was captured using micro-ADV. The concept of two relative depth conditions allowed us to capture record and classify the velocity zones between the short and tall vegetation. Compared to the flow in the main channel, flood plains registered relatively lower velocity values due to the resistance offered by the vegetation along the flood plains, which consequently led to the increase in main channel flow velocities. Velocities compared to the non-vegetated meandering channels; the highest velocity readings were recorded at the centerline of the main channel. Numerical analysis was also conducted using the CFD codes in fluent. The vegetation geometry is modelled as cylindrical dowels of diameter 10 mm and two-variable heights of 7.5 cm and 15 cm at two relative depth flow conditions. The experimental results were numerically compared using the k-ϵ model along with grid sensitivity tests. The final simulated numerical results were found to be close and in good agreement with experimental values.     

Experimental analysis of emission reduction by the split injection strategy using close post injection with a double-row nozzle in heavy EGR conditions

As EURO-6 regulations will be enforced in 2014, simultaneous reduction of NO_x and PM emissions becomes an important issue in recent diesel engine research. New combustion concepts, such as LTDC and pHCCI, have been introduced to overcome the NO_x and PM trade-off relation. However, these novel combustion concepts are usually implemented with a high EGR rate and by advancing the main injection timing which cause high CO and THC emissions along with poor fuel consumption due to low combustion efficiency. Therefore, the split injection strategy, which was consisted of applying post injection close to the main injection, was carried out in this experiment. Specifically, two different nozzles — a 7-hole conventional nozzle and a 12-hole double-row nozzle — were evaluated to determine the effects of nozzle configurations on engine-out emissions. The result shows that CO emission was reduced by the close post injection strategy regardless of the nozzle configuration. However, THC and PM emissions were reduced only when the 12-hole double-row nozzle was used. Thus, the use of close post injection with the 12-hole double-row nozzle could increase the combustion efficiency in heavy EGR conditions.     

Experimental and numerical study of piston thermal management using piston cooling jet

This research investigates the effects of piston cooling jet (PCJ) on the temperature and heat transfer of a piston. A numerical model was developed by using the computational fluid dynamic approach in which the fluid and solid domains of the piston were coupled in a three-dimensional space. Two-phase flow of oil and air was also simulated. This method was used to analyze the effects of oil velocity and piston position on the heat transfer coefficient at the bottom of the piston as the new outcomes of this study. For the experiment, combustion heat flux on the piston was simulated in a test rig, and numerical results were validated. The results showed a linear relation between the oil jet velocity and the average of heat transfer coefficient at the bottom of the piston, and a periodic correlation between the piston’s vertical position and the average of heat transfer coefficient. The average of the piston crown temperature could be reduced to about 70 K by using the PCJ system, but this cooling method could create 50 K temperature gradient in the piston.     

Measurement of temperature distribution in machining using IR photography

A review of various techniques employed in measuring cutting temperatures is presented and it is pointed out that the method of IR photography is certainly better than other techniques for the accurate measurement of the temperature distribution in the cutting region. The thermal sensitivity of high speed IR film has increased significantly in the past two decades. It is now possible to use IR photography for measuring cutting temperatures without preheating the workpiece and the cutting tool.Temperature measurements in the surface region of annealed 18% Ni maraging steel were made at cutting speeds of 80 and 160 ft min^?1. It was observed that the temperature is very high at the surface and decreases with depth beneath the surface. The cutting temperature increases with an increase in the wear land or dullness of the tool.