Papers by Keyword: Shrinkage

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Authors: H. Maupas, Jean-Louis Chermant
Authors: A.A.A.P. Silva, A.S. Rodrigues, R.X. Freitas, S.E.N. Cury, I.V.F. Suhett, C. Santos
Abstract: In this work, the effect of pressure and direction of compression in the shrinkage and flatness of ZrO2-(Y2O3) dental ceramics were studied. Samples (40x15x15mm) were uniaxial cold pressed at different pressures ranging from 10MPa to 160MPa, and then pre-sintered for further cutting. For comparison, samples were also isostatically cold pressed at 300MPa. The pre-sintered samples were cut longitudinally and transversely to the direction of compression, with final thickness of 1mm. Then the samples were ground and polished, and measured with a micrometer at different positions of the sample. After the measurements, the samples were sintered at 1530C-120 min, and again measures. The results indicate the effect of pressure decline in considerable amounts, up to pressures of about 80MPa. Above this value the differences in shrinkage and warpage are insignificant when compared to isostatically pressed samples.
Authors: Kritkaew Somton, Kannigar Dateraksa, Ryan C. McCuiston
Abstract: The relationship between granule property, pressed green density and shrinkage of 92% alumina spray dried granules were studied for both simple and complex shapes. Two types of granules, the in-house granule (A) and the commercial granule (B), was observed morphology using microscopy and liquid immersion techniques. Examination of the granules showed that granule A have several undesirable features; agglomeration, hollow granules and non-spherical granules where granule B showed them to be unagglomerated and spherical. The mixture A and B were conducted to study the particle size distribution (PSD) and compared with Dinger-Funks ideal PSD. The result showed that granule mixture A: B 100:0 had closest PSD curve fitted but had lowest tapping and pressed green density than 70:30 and 30:70 mixtures. This is because the agglomerated shape in granule mixture 100:0 caused air gap in between granule contact resulting in low tap density. The specific fracture strengths of the granules can affect to the densification of green ceramic during pressing. Low pressed green density affected to a high amount of shrinkage during sintering and leading to small grain growth after sintered. The simple and complex shape follows the same trend in shrinkage.
Authors: Luis Costa, Maria Clara Cramez, A.J. Pontes
Abstract: Warpage and poor dimensional stability of rotomoulded products are two of the main obstacles to the use of this technique in the production of engineering parts. The knowledge of the effect of the processing conditions on the shrinkage of rotomoulded parts will allow overcoming some of the restrictions of this process. In the present work the influence of the processing conditions on the development of shrinkage and warpage of rotomoulded parts was studied. The moulding of the parts was performed using a rotational moulding machine build at the University of Minho. The shrinkage and the warpage of the moulded parts were assessed using 3D MMC (3D measuring Machine Control) equipment, and understanding the microstructural development.
Authors: Yan Ying Li, Yong Sheng Zhang
Abstract: To test the temperature stress and deformation of the major platform in Nanjing Olympic Sports Center, 8 shrinkage members and 3 creep members were poured on the worksite for comparison analysis. With finite elements analysis, gliding rubber supporters were used on all the pillar tops. The floor stress would be in a constant compressive stress with pre-stress and post-cast-span. This method makes the appearance and developments of structure cracks under effective control. Under temperature changes, the buildings were ensured not to have damageable cracks. This project was passed with super quality.
Authors: S. Ragunath, R. Gokulan, K. Letcham
Abstract: The aim of this investigation is to study the use of the water soluble polyethylene glycol as self-curing agent. The function of self-curing agents is to reduce the water evaporation from concrete and hence they increase the water retention capacity of concrete compared to the conventionally cured concrete.The use of self-curing admixtures is very important from the point of view that saving of water is a necessity everyday (each one cubic meter of concrete requires 3m3 of water for a construction, most of which is used for curing). In this study, compressive strength and split tensile strength of concrete containing self-curing agent is investigated and compared with that of conventionally cured concrete.It is experimentally found by the authors that the concrete cast with polyethylene glycol as self-curing agent is stronger than that obtained by sprinkler curing as well as by immersion curing. In this project, foundry sand is replaced as a fine aggregate. It is also tested with conventional concrete and self curing concrete with 5% and 10% replacement of foundary sand which has been tested for compressive strength and split tensile strength for 7days and 28 days of curing and their results are compared. The compressive strength by 13.62%, 18.83% and 22.43%when compared to the Con mix at the age of 7 days and also 5.40%, 8.90% and 14.16% at the age of 28 days. Mixtures WSPG and WSPG with FS enhanced their tensile strength by 14.50%, 16.36% and 20.82% when compared to the Con mix at the age of 7 days and also 4.30%,8.15% and 12.90% at the age of 28 days.
Authors: Abul B.M. Saifullah, Syed H. Masood
Abstract: In an injection moulded part, warpage is the distortion caused by non-uniform shrinkage within the plastic part. When looking critically at the causes of warpage, it is found that several key parameters of the moulding process have some effect on the warpage. However, the two major categories that contribute to warpage include the part design and the mould design. In mould design, the gate location, runner/gate system and cooling system design are the major factors affecting not only the warpage and part quality but also the injection moulding cycle time. This paper presents an investigation of using different cooling system configuration on warpage and shrinkage of an industrial plastic part with the aim of determining which cooling configuration will provide minimum warpage and cycle time. As conventional injection mould cooling design is based on straight drilling, it limits the geometric complexity of the cooling design, especially curved shape cooling channels. Nowadays, new technology of advanced rapid tooling based on solid freeform fabrications can be been used to provide conformal cooling channels in injection moulds. In this paper, several type of cooling channels are analysed to compare the performance in terms of warpage and shrinkage and to determine which configuration is suitable for minimizing warpage. Autodesk Moldflow Insight (AMI) simulation software is applied to examine the results of the cooling performances and warpage analysis.
Authors: Yin Fang Jiang, Yi He, Yu Zhong He, Xiao Ming Qian, Yu Huang
Abstract: Shrinkage porosity defects occurring in ring groove underside the pin hole of aluminum piston are strongly influenced by the time-varying temperature profiles inside the solidifying casting. By adopting the finite element analysis software PROCAST and combining with production practice, the gating system which has open-cycle ring feeding channel in the bottom of the piston was compared with conventional techniques; the influence of opening angle of ring feeding channel and different process parameters on shrinkage distribution was researched. The results show the gating system with open-cycle ring feeding channel can satisfy progressive solidification and effectively eliminate the shrinkage in ring groove underside piston pin hole, and can greatly reduce the riser size and improve casting yield; the opening angle influences shrinkage distribution and can be adjusted to achieve effective feeding; shrinkage size is influenced by pouring temperature and casting speed which have less effect on shrinkage distribution. The system of ring feeding channel is adopted, the opening angle and process parameters are adjusted, all which can effectively eliminate shrinkage in the bottom of the piston, improve casting yield and process rate.
Authors: Yun Feng Li, Rong Qiang Du, Fan Ying Kong
Abstract: The early-age shrinkage cracking of concrete plays an important role to the accelerated deterioration and shortening the service life of concrete structures. Modern concretes are more sensitive to cracking immediately after setting, which is due to material characteristics (lower water/binder ratio and higher cement content) and external environmental fluctuations (humidity and temperature change). Determination of concrete free shrinkage is the basis of shrinkage cracking research. Analytical models of the autogenous shrinkage and drying shrinkage are established in this paper. The calculated results agree well with the experimental results.
Authors: Vojtěch Kolínský, Jan L. Vítek
Abstract: The paper deals with evaluation of experimental data collected during the Oparno arch bridge construction and with subsequent analysis of the construction process and long-term behavior with regard to rheological properties of concrete. The Oparno valley bridge is composed of two separate concrete arch structures with spans of 135 metres (this is currently the second longest span of concrete arch bridge in the Czech Republic). It was built using cantilever casting technology with temporary cable-stays and auxiliary pylons. The data recorded for this study include detailed geodetic measurement of the bridge structure during construction, along with measured strains and temperatures in the arches. Most of the data was measured during the bridge construction in 2008 and 2009. Data significant for long term behavior of structure are still being collected. Verification of different concrete material models and their suitability for design of arch bridges built by free cantilevering will be a main result of the analysis. On the basis of a detailed comparison of numerical results and measured deflections, strains and temperatures, it is possible to quantify the impact of rheological properties of the material (or their individual input parameters) on the resulting structural behavior. Unlike previous research, the examined structure is made of reinforced concrete (not prestressed) and consists of compact solid section and in the final state it is mainly in compression.
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