双掺玄武岩纤维和陶砂对混凝土收缩开裂性能的影响

通过干燥收缩、塑形收缩和圆环开裂试验,研究了双掺玄武岩纤维和陶砂混凝土的抗收缩开裂性。试验结果表明,单掺玄武岩纤维可增大混凝土收缩开裂趋势;长度6mm、18mm和30mm的纤维,其干缩应变相比基准混凝土分别增大了5%、17%和22%;双掺玄武岩纤维和陶砂可降低混凝土收缩开裂趋势;陶砂掺量为10%时,可明显降低混凝土收缩开裂性,陶砂掺量继续增加(20%和30%),混凝土收缩开裂趋势增加。     

原料组成对砂浆抗裂性能的影响研究

砂浆的收缩率和柔韧性严重影响着砂浆的抗裂性能,本文借助正交实验方法,研究了配制砂浆的原料组成与砂浆收缩率及柔韧性的关系,可为砂浆的合理配制提供理论依据。     

Shrinkage, vitamin C degradation and aroma losses during infra-red drying of apple slices

The goal of this study was to determine the effect of drying temperature on the shrinkage, ascorbic acid (vitamin C) degradation and aroma retention of apples. Apple samples were found to shrink continuously until a water content value of 2 kg/kg d.b. The degradation of ascorbic acid followed a pseudo-first-order reaction and the degradation rate constant increased when temperature increased from 40 to 70 °C. The loss of aroma volatiles increased with temperature and drying time.     

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.