熔模铸钢件缩孔(松)的防止

结合生产实例，系统阐述了防止熔模铸钢件缩孔（松）的主要措施：其一是转移，即将缩孔由铸件中转移到浇注补缩系统中；其二是分散，即将缩孔分散成许多细微的缩松。     

木质装饰材料干缩湿胀性对家具拼口的影响

随着装饰业、家具制造业的强劲发展,对于木质材料干缩湿胀性研究尤为重要,企业渴望得到解决木质材料干缩湿胀性的技术。本文在分析了大量文献的基础上,简述了国内外木质材料干缩湿胀性的研究成果,并提出了一些对家具制造具有实用价值的措施。     

Failure of a Cast Aluminum Engine Head in a High Performance Application

The investigation described in this article examined a cast aluminum head used in a high performance (drag racing) application. These engine heads had been failing within a few seconds of startup. A sample head was examined to determine the cause. Visual inspection found two cracks on the exhaust side of the head. One crack initiated at the bottom of a spark plug well. The head was then sectioned for metallographic examination and fracture analysis. Metallographic examination revealed a large number of shrinkage pores throughout the casting. The fracture surface intersected many of these shrinkage pores. A significantly sized pore was located near the bottom of the suspect spark plug well near a stress-concentrating feature. This pore acted as the crack-initiating defect, which caused the engine head to fail.     

Eight-year exploration of shrinkage in high-performance concrete

In this paper, an experimental and analytical exploration on the effect of water-binder ratio (w/b), silica fume and age on autogenous, carbonation, drying and total shrinkage of high-performance concrete (HPC) is outlined. Eight types of HPC were studied. Carbonation, internal relative humidity (RH) and strength were studied on specimens from the same batch of HPC that was used in the studies of shrinkage. The results indicate fairly good correlation between carbonation, shrinkage, w/b and RH. The type and amount of silica fume affected shrinkage.     

Evolution of the capillary network in a reactive powder concrete during hydration process

Ultrasonic waves in echographic mode, combined with autogenous shrinkage measurements, were used to study the evolution of the capillary network of reactive powder concrete (RPC) from the time after the mixing. Two characteristic porous classes have been identified: the first, between 10 and 20 nm, begins when the material reaches its solid hyperstatic state, and the second about 1 or 2 nm. The first class is associated with the porous space between the C-S-H hydrate clusters and the second with the internal porosity of the hydrate. The evolution of the active capillary radius as a function of the degree of hydration allows us to understand the strong interaction between the capillary network size and the chemical activity given by the dissipated calorimetric power curve. Indeed, the maximum point of the chemical activity marks the transition of the first class of pores to the second one. Finally, measurements of electrical conductivity through RPC samples show that after the maximum of the dissipated power, the curve of this electrical conductivity presents the same evolution as the capillary radius. As the electrical conductivity clearly depends on the evolution of the capillary network, the similarity between the results confirms our analysis in pore classes.     

Prediction of cracking within early-age concrete due to thermal, drying and creep behavior

To predict potential early-age cracking after concrete placing, a numerical simulation procedure has been completed based on a micromechanical model and empirical formulas on the property development of young concrete. The numerical model could account for the effects of hydration, moisture transport and creep. Environmental influences, such as removal of formworks, curing conditions and variations of surrounding temperature and relative humidity, have been investigated. In calculating stress field with age caused by these synthetic physical-mechanical processes, three-dimensional finite element and finite difference (3D-FE-FD) methods are combined together.     

Mixture-proportioning of high-performance concrete

The paper presents a new approach to design concrete mixtures. It is based upon a set of models relating composition and engineering properties of concrete, to be implemented into software, linked with a material database. The principles underlying the various models are summarized, most of which focus on the granular structure of fresh/hardened concrete. A global approach to concrete is promoted, where performance specifications can be formulated in terms of fresh concrete (yield stress, plastic viscosity, slump and air content), hardening concrete (adiabatic temperature rise and autogenous shrinkage) and hardened concrete (compressive strength at any age, tensile strength, elastic modulus, creep and shrinkage). This approach is illustrated through the design of a special high-shrinkage high-performance concrete (HPC) for road application. To date, durability is lacking in the model and requires further research.     

圆筒形铸件缩松缩孔的产生原因及解决方法

针对圆筒形铸铁辊体冒口端面产生的缩松、缩孔缺陷，进行了举例说明、系统分析，找到了缺陷产生的原因及影响因素。通过解决措施的应用与实施，有效地克服了圆筒形辊体铸件冒口端面产生的缩松、缩孔缺陷，同时应用到其它大型圆筒形铸件中，都得到了良好效果。     

How to study drying shrinkage microcracking in cement-based materials using optical and scanning electron microscopy?

Three different ‘destructive’ microscopy methods were tested on their ability to show drying shrinkage microcracks on a specimen cross-section. The first two were methods in which the microcracks were impregnated with a fluorescent epoxy and examined with fluorescence microscopy. In one method, the impregnation was applied before making the cross-section and in the other after making the cross-section. In the third method, the sample was kept wet constantly and examined in an environmental scanning electron microscope (ESEM). It was concluded that the method in which the dried specimen was impregnated before making the cross-section was the most reliable method to record drying shrinkage microcracks. With this method, it was possible to impregnate the complete drying shrinkage microcrack pattern in the studied cement-based materials from the surface, and there was no risk of recording microcracks introduced by sample preparation.     

采用RFR-GA算法的薄壁注塑件质量多目标优化

汽车内饰件可由注塑加工获得,但成型过程中塑件产生的翘曲、体积收缩较大,针对该问题,以某汽车薄壁注塑件为例,研究了其注塑工艺参数的优化方法。通过以注塑过程中的最小翘曲和最小体积收缩率为目标函数,以注塑温度、模具温度、注射压力、保压压力、保压时间以及冷却时间等参数作为设计变量,构建了多目标全局优化模型。利用Moldflow软件结合正交试验获得的试验结果训练随机森林回归模型,采用遗传算法对多目标模型进行全局寻优,获得最佳成型工艺参数,即对其成型缺陷进行了优化。结果表明,所提出的优化方法能够得到全局最优解,并同时优化了该汽车薄壁注塑件的翘曲和体积收缩率。将得到的最佳成型工艺参数进行Moldflow试验,可知翘曲和体积收缩率分别优化了74.6%和42.7%。将获得的最佳注塑成型工艺参数进行生产验证,结果表明生产出的薄壁汽车件成型质量较好,满足生产要求。