Axial Shrinkages Research Articles

Hybrid infrared with hot air drying of Pisang‐Awak banana: Kinetics and shrinkage quality

AbstractThe purpose of this study was to develop the prototype drying system for drying the Pisang‐Awak (PA) banana. It was designed and implemented to study the drying kinetics in each drying mode: hot air drying (HA), infrared drying (IR), and hybrid drying (Hy). The experimental results were fit with simulation results from the finite element method (FEM). Two statistical parameters, the coefficient of determination and the root mean square error , were used to assess the fit between experimental results and simulation results, and their respective ranges were 0.960–0.997 and 0.014–0.050. For PA banana drying the most suitable drying mode is hybrid, combining 1.5 m/s flow of hot air and IR heating at 60°C drying temperature. The axial and radial shrinkages of PA banana were the largest in Hy mode at 60°C, namely 18.2 and 27.3%, respectively, and this choice gave the best/lowest specific energy consumption (SEC) for drying performance and the best final dried PA banana.Practical ApplicationsThe understanding of the drying kinetics and shrinkage properties of the dried PA banana is important for the choice of drying process because these reflect the quality of the dried product and help an engineer to design the drying system. Therefore, the empirical mathematical modeling of the drying process serves a crucial role in the food industry sector. These results can be used to quantify temperature and moisture content as functions of drying time to monitor the drying process of PA banana, saving energy and time.

Effect of geometry and green density on the anisotropic sintering shrinkage of axisymmetric iron parts

ABSTRACTSintering shrinkage of prior cold compacted iron rings with different geometry (height to wall thickness ratio) and green density in the 6.5–7.3 g/cm3 range was investigated. It displays a minimum at an intermediate green density. Axial, tangential and radial shrinkages are different, due to the gradients of green density along the axial and the radial directions. Therefore, the effect of height on shrinkage and its anisotropy is the result of their effect on the stress distribution in the green parts during cold compaction, and the resulting green density and deformation experienced by the powder. Anisotropy decreases on increasing shrinkage.

Microwave sinter forging of alumina powder

Microwave sintering under load is expected to be a promising technique to process ceramics with fine microstructure. This paper presents a new setup allowing sinter forging ceramic compacts in a 2.45GHz single-mode microwave cavity. This setup has the following features: maximum temperature of 1600°C, heating rate between 1 and 250°Cmin−1, maximum stress of 50MPa applied upon an 8mm diameter sample. A specific protocol has been defined to calibrate the pyrometer used to measure the sample temperature. Alpha-alumina compacts have been microwave sinter forged under various stresses in the range 0–30MPa. The results are compared to those obtained in a conventional furnace under 0, 4 and 8MPa. Final axial and radial shrinkages are identical with the two techniques. The final relative density of the material is not affected by load and is equal to 0.94 and 0.96 in microwave sinter forging and conventional sinter forging, respectively. Two assumptions are proposed to explain this difference: a microwave effect and a temperature discrepancy. Finally the load does not significantly affect grain growth.

A new method to measure the polymerization shrinkage kinetics of composites using a particle tracking method with computer vision

Objectives The aim of this study was to develop a new method to measure the polymerization shrinkage of light cured composites and to evaluate the overall utility and significance of the technique. Methods An optical instrument to measure the linear polymerization shrinkage of composites without directly contacting the specimen was developed using a particle tracking method with computer vision. The measurement system consisted of a CCD color video camera, a lens, an image storage device, and image processing and analysis software. The shrinkage kinetics of a commercial silorane-based composite (P90) and two conventional methacrylate-based composites (Z250 and a flowable Z350) were investigated and compared with the data measured using the “bonded disc method”. Results The linear shrinkage of the composites was 0.33–1.41%. The shrinkage value was lowest for the silorane-based (P90) composite and highest for the flowable Z350 composite. The estimated volume shrinkages of the materials were comparable to the axial shrinkages measured with the bonded disc method. Significance The new instrument was able to measure the true linear shrinkage of composites without sensitivity to the specimen geometry and the viscosity of the material. Therefore, this instrument can be used to characterize the shrinkage kinetics for a wide range of commercial and experimental visible-light-cure materials in relation to the composition and chemistry.

Patient-specific artery shrinkage and 3D zero-stress state in multi-component 3D FSI models for carotid atherosclerotic plaques based on in vivo MRI data.

Image-based computational models for atherosclerotic plaques have been developed to perform mechanical analysis to quantify critical flow and stress/strain conditions related to plaque rupture which often leads directly to heart attack or stroke. An important modeling issue is how to determine zero stress state from in vivo plaque geometries. This paper presents a method to quantify human carotid artery axial and inner circumferential shrinkages by using patient-specific ex vivo and in vivo MRI images. A shrink-stretch process based on patient-specific in vivo plaque morphology and shrinkage data was introduced to shrink the in vivo geometry first to find the zero-stress state (opening angle was ignored to reduce the complexity), and then stretch and pressurize to recover the in vivo plaque geometry with computed initial stress, strain, flow pressure and velocity conditions. Effects of the shrink-stretch process on plaque stress/strain distributions were demonstrated based on patient-specific data using 3D models with fluid-structure interactions (FSI). The average artery axial and inner circumferential shrinkages were 25% and 7.9%, respectively, based on a data set obtained from 10 patients. Maximum values of maximum principal stress and strain increased 349.8% and 249% respectively with 33% axial stretch. Influence of inner circumferential shrinkage (7.9%) was not very noticeable under 33% axial stretch, but became more noticeable under smaller axial stretch. Our results indicated that accurate knowledge of artery shrinkages and the shrink-stretch process will considerably improve the accuracy of computational predictions made based on results from those in vivo MRI-based FSI models.

The effect of consistency, specimen geometry and adhesion on the axial polymerization shrinkage measurement of light cured composites

Objectives This study investigated the effect of the consistency, specimen geometry and adhesion on the measurements of axial polymerization shrinkage of light cured composite resins using an axial shrinkage-measuring device. Methods Four commercially available composites were examined: an anterior posterior hybrid composite Z100, a posterior packable composite P60 and two flowable composites, Filtek flow and Tetric flow. The axial polymerization shrinkage of the composites was determined using a ‘bonded disc method’ and ‘non-bonded’ free shrinkage method at varying C-factors by altering the specimen geometry. These measured axial shrinkages were compared with the free volumetric shrinkages. The consistency of the composites was also compared using a squeeze test. Results Using the non-bonded method, the axial shrinkage was approximately one third of the true volumetric shrinkage as a result of isotropic contraction. However, in the bonded disc method, the axial shrinkage increased up to the volumetric shrinkage by anisotropic contraction as the bonded surface increased. The axial shrinkage increased with the increasing C-factor. It approached the true volumetric shrinkage and reached a plateau at near a C-factor of 5–6. However, in flowable composites, a lower level of axial shrinkage was measured by the compensational radial flow. Significance When estimating the volumetric shrinkage from the axial shrinkage measured using the bonded disc method, the C-factor of the specimen should be higher than 5 and the consistency of the composite is also an important factor that needs to be considered.

Constitutive behaviour of WC–Co materials with different grain size sintered under load

The deformation during sintering under an applied uniaxial load was investigated experimentally for two WC–Co cemented carbides with different grain size. The lower applied loads changed only the relative magnitude of axial and radial shrinkages, whereas the higher loads also affected the volumetric strain. Local maxima in shrinkage rate were found at relative densities close to 0.8 for all sintering conditions. The constitutive parameters uniaxial viscosity, Poisson’s ratio and sintering stress were empirically modelled as functions of temperature and relative density.

Determination of internal stresses during sintering of dispersion reinforced glass matrix composites

This paper presents a procedure for estimating the internal stresses that develop during sintering of glass matrix composite materials containing hard second phase inclusions. The experimental data are obtained by the heating microscopy technique, that allows the measurement of axial and radial shrinkages during sintering of powder compacts. With this experimental information sintering kinetics parameters are readily obtained, which can be used to determine the internal stresses that develop during sintering, normalized by the sintering pressure. Data on glass matrix composites containing spherical rigid ceramic inclusions are presented. More experimental data are needed, however, for testing the described procedure and for validating existing theoretical models for the sintering of glass composites containing rigid inclusions.

Thorium oxide: Calcination, compaction and sintering

Calcination of thorium oxalate in hydrogen is found to yield black powder — a mixture of carbon and thorium oxide. Reheating in air eliminated the carbon and resulted in white ThO 2 powder. Optimum compaction pressure has been suggested to be that at which axial and diametral sintering shrinkages of a cylindrical pellet are equal. The effects of the additives MgO and Nb 2O 5 and the effect of furnace atmosphere on the sinterability of ThO 2 have been investigated and the interdependence of additive and atmosphere has been brought out. 0.25 mol% of Nb 2O 5 in ThO 2 lowers the sintering temperature in air from 1600–1700°C to 1150–1200°C. Air sintering of niobia added thoria thus provides an economical alternative to conventional hydrogen sintering. A novel thermal etching technique has been used to reveal the microstructure of sintered thoria.

Viscous Sintering under a Uniaxial Load

An analysis is presented for viscous sintering under a uniaxial load; numerical results are presented for compressive loads. The load increases the axial contraction rate, hut counteracts the radial contraction rate. When the load is similar in magnitude to the capillary stress driving sintering, the radius remains essentially constant as the body densifies. Following a suggestion by Bordia, the viscosity and sintering kinetics can be determined in one experiment by measuring the axial and radial shrinkages simultaneously.

Neutron Irradiation Effects on Carbon and Graphite Cloths and Fibers

A series of cloth and fiber samples were irradiated to fluences of 3.5, 7.3, and 10 x 10/sup 21/ cm/sup -2/ at 470/sup 0/C. Dimensional changes of the fibers in the radial direction ranged from -19% to +33% and in the axial direction from -18% to -27%, roughly ten times greater than dimensional changes found for typical nuclear graphites. Despite these large dimensional changes, all but one of the 2-dimensional cloths remained essentially unchanged in overall physical appearance. The 3-dimensional cloths, on the other hand, deteriorated apparently because these types of weaves were less able to accommodate the large axial fiber shrinkages.

Sintering processes in metal-glass materials

1. The results are presented of an investigation into the reaction of glass with metal, and it is shown that glass activates shrinkage processes during the sintering of metal-glass materials. 2. A study was made of the influence of sintering temperature on shrinkage; it is demonstrated that the ratio of axial and radial shrinkages increases with increasing glass content, and is a complex function of sintering temperature. 3. It is shown that similar features characterize sintering in the presence of a glass phase irrespective of whether sintering is carried out in theα- orγ-phase regions. Differences in the extent of shrinkage are due to the influence of the glass phase, particularly at large amounts of the latter. 4. During the sintering of metal-glass materials, greater shrinkage is exhibited by materials containing acid glasses.