Neural network prediction of physical property changes of dried carrot as a function of fractal dimension and moisture content

The relationship between microstructural and physical properties of dried foods is difficult to quantify. This study uses artificial neural network analysis (ANN) to predict shrinkage and rehydration of dried carrots, based on inputs of moisture content and normalized fractal dimension analysis (ΔD/D₀) of the cell wall structure. Several drying techniques were used including conventional hot air (HAD), low pressure superheated steam (LPSSD), and freeze drying (FD). Dried carrot sections were examined by light microscopy and the fractal dimension (D) determined using a box counting technique. Optimized ANN models were developed for HAD, LPSSD, HAD + LPSSD, and HAD + LPSSD + FD, based on 1–10 hidden layers and neurons per hidden layer. ANN models were then tested against an independent dataset. Measured values of shrinkage and rehydration were predicted with an R² > 0.95 in all cases.     

Influence of sintering temperature on the shrinkage and geometrical characteristics of steel parts produced by powder metallurgy

The dimensional and geometrical characteristics of Charpy bars produced with two different steels were investigated to evaluate the effect of increasing the sintering temperature from 1120 °C (conventional sintering temperature) up to 1350 °C. The problem was approached from the Geometric Dimensioning and Tolerancing (GD&T) point of view, referring to the standard ASME Y14.5 (2009). The dimensional and geometrical characteristics were evaluated using a Coordinate Measuring Machine (CMM), measuring the surfaces by scanning mode. The work highlights that the increase in the sintering temperature, aimed at improving the mechanical properties, does not prevent the main benefit of this technology, i.e., the possibility of producing parts with good dimensional and geometrical precision. Moreover, a methodology establishing the measurement procedures and data processing, to be used in future work for the characterisation of more complex shapes, was defined.     

铁型覆砂球墨铸铁件凝固模拟及收缩缺陷预测

建立了铁型覆砂铸造凝固过程模拟的数学模型.采用动态膨胀收缩法(DECAM)和K*G/R判据预测球墨铸铁件的收缩缺陷,对球墨铸铁四缸曲轴新产品进行了模拟计算,根据模拟结果对原有工艺方案进行了改进,并在实际生产中得到了合格的铸件.结果表明,对铁型覆砂球墨铸铁件进行数值模拟和工艺优化,有助于提高铸件质量,缩短试制周期,降低工装费用.     

The effect of wollastonite incorporation on the linear firing shrinkage and flexural strength of dental aluminous core ceramics: A preliminary study

The aim of this study is to evaluate the effect of wollastonite (CaSiO3) material on the linear firing shrinkage and flexural strength of dental aluminous core porcelain. Twenty five specimens were prepared in a manner that each five of them contained 0%, 2%, 3%, 4%, and 5% wollastonite by weight. The linear firing shrinkage values were determined according to the formula given in the standard ANSI/ADA (American National Standards Institute/American Dental Association) 69 and the flexural strength of the specimens was evaluated using 3-point bending test. The results of this study showed that addition of wollastonite reduced the linear firing shrinkage and increased the flexural strength of dental aluminous core porcelain. The highest reduction (approx. 20%) in the linear firing shrinkage was obtained by the addition of 5% wollastonite. Kruskal–Wallis test found a statistically significant difference among the mean linear firing shrinkage values of the porcelain groups at the 95% confidence level (p < 0.05). Mann Whitney U statistical test was performed to demonstrate which porcelain groups show statistically significant difference. In spite of achieving 30% increase in the flexural strength by the addition of 2% wollastonite, no statistically significant difference was found among the mean flexural strength values of the porcelain groups (p > 0.05).     

Flexural performance of fiber-reinforced ultra lightweight cement composites with low fiber content

This paper presents an experimental study on flexural performance of ultra lightweight cement composites (ULCC) with 0.5 vol% fibers. Low density of the ULCC is achieved by using cenospheres from coal-fired power plants as micro aggregates. Effects of shrinkage reducing admixture (SRA) and fiber types on compressive strength and flexural performance of the ULCC are investigated. ULCC with density of 1474 kg/m³, compressive strengths of 68.2 MPa, flexural strength of 8 MPa, and deflection hardening behavior can be produced. Such good performance could be attributed primarily to the SRA which reduced entrapped air in paste matrix and densified fiber–matrix interface. The improvement on the flexural performance of the ULCC depends on fibers used and bond between fibers and matrix. Improvement of the flexural performance of the steel fiber (coated with brass) reinforced ULCC due to the densification effect by SRA was more significant than that of the PE fiber reinforced ULCC.     

Pyrolysis of large wood particles: a study of shrinkage importance in simulations

Shrinkage models have been developed and included in a model for the pyrolysis of large wood particles. Shrinkage is modelled in three different ways: uniform shrinkage, shrinking shell and shrinking cylinders. These models and a reference model without shrinkage are compared with experimental data for mass loss versus time during pyrolysis of birch cylinders at different temperatures. In the experiments a wood particle was introduced into a pyrolysis furnace held at constant temperature. The particle mass and volume were recorded using a balance and a video camera. Uniform shrinkage slows down the pyrolysis whereas shrinking shell and cylinder models enhance the pyrolysis rate. The effect was sufficiently small to be neglected given the uncertainty about some wood physical properties.     

大型整体铸钢轧辊无流浇注工艺研究

在浇注辊身长径比≥2．5时，辊身易出现探伤超标，冒颈缩孔、疏松等品质缺陷。为解决此问题，采取无流浇注工艺，以实现整个浇注过程的顺序凝固，减少上述品质缺陷的发生几率，从而提高产品的内在品质。     

Birch wood particle shrinkage during rapid pyrolysis

A study of the shrinkage of cubic (∼5 mm) birch wood particles during pyrolysis is presented. The particles were rapidly injected into a preheated furnace with a constant temperature in the range 350-900°C. The size of the particles in longitudinal, tangential and radial directions was measured until no further mass loss occurs. The volume shrinkage was found to be 45-70% and the shrinkage in the different directions 5-25, 25-40 and 15-40% for longitudinal, tangential and radial directions, respectively. Longitudinal shrinkage commenced after about 60% mass loss and is not strongly dependent on heating rate or on cellulose chain scission. A maximum shrinkage was found for tangential and radial directions at 400 and 500-700°C, respectively, and above these temperatures the shrinkage decreases. The char yield decreases and the char structure becomes more deranged with increasing temperature. Empirical models of shrinkage as a function of conversion are presented.     

Maturation of fresh cement paste within 1- to 10-m-large formworks

The objective of this research was to examine the maturation of early-aged cement paste through the survey of the evolutions of the total lateral pressure exerted by cement paste against formworks and of the pore water pressure. The experimental device was specially developed for this purpose. Three types of cement paste mixtures with a water/cement (W/C) ratio of 0.30, 0.36 and 0.45, respectively, have been tested. In addition, temperature and setting kinetics were also examined. The results have shown that the kinetics of the pore water pressure and the total lateral pressure were strongly affected by the W/C ratio, the vibration and the level of stress, to which the fresh cement paste is subjected. The confrontation of these results with the theory currently available as regards setting of cement makes it possible to identify the physicomechanical phenomena, which occur within formworks.