Modeling the thermal shock induced cracking in ceramics

Prediction of surface cracking in ceramics due to quenching is performed numerically using either the coupled criterion or a cohesive zone model. Under such a thermal shock, a network of short cracks with minimal spacing between them initiate and propagate until some of them stop while the others continue propagating. The numerical implementation consists of a periodic array of cracks modeled by a representative volume element. It allows crack initiation, simultaneous propagation and period doubling to be predicted. The investigation of the crack period doubling allows a precise determination of the optimal crack spacing, which decreases with an increasing thermal shock amplitude. The predicted crack spacing results are in agreement with experimental measurements.     

Phase-change regulation criterion based on size-dependent lattice distortion rate and born theory for VO2 nanomaterials

Vanadium dioxide (VO₂) is a promising thermally induced phase transition material because of the abrupt changes in electrical and optical properties. However, the high phase transition temperature of VO₂ and its unspecified modulation relationship need to be resolved urgently. Herein, we proposed a simple and precise regulation criterion for VO₂ materials based on size-dependent lattice distortion rate and Born theory. The results indicated that the application of a tensile stress changed the elastic properties of the VO₂, which promoted VO₂ phase transition, and regulated the phase transition temperature. Moreover, the specific modulation relationship between the stress and phase transition temperature of VO₂ was confirmed experimentally. These results show that our criterion provides theoretical guidance to regulate VO₂ thermally induced phase transition materials.     

车载空调控制器的新型按键旋钮溃缩设计

本文针对乘用车内部凸出物的法规要求对车载空调控制器的旋钮按键溃缩进行了研究和设计，描述了这种新型旋钮按键溃缩设计相对于目前常用的方案在成本、空间、可靠性等方面的优势。根据实际设计结果表明，本文所应用的新型旋钮按键溃缩设计能在成本与空间有限的情况下可靠的满足法规对乘用车内部凸出物的要求，为乘用车内部凸出物溃缩方案提供了新方向，值得我们推广应用。     

An ignition criterion for combustible solids integrating surface temperature and heating rate

Surface ignition temperature has been widely used as an ignition criterion for the piloted ignition of common combustible solids. However, experimental observations have shown that the surface temperature of a solid at ignition varies with external heat flux. In addition, if the external heat flux is smaller than the critical heat flux for ignition, the solid will not ignite while the actual surface temperature may be higher than the defined surface ignition temperature. To overcome these limitations and maintain the simplicity of the surface ignition temperature criterion, a new ignition criterion integrating heating rate and surface temperature is proposed, developed, and validated. Predictions based on the new criterion compare well with experimental results on piloted ignition of a thermoplastic material (black PMMA), a thermoset composite material (E‐glass fiber reinforced polyester composite) and a cellulosic material (Red Oak) subjected to different heat flux levels. Potential factors affecting the accuracy and predictive capability of the new heating rate‐related ignition temperature criterion are discussed. The method and associated procedures to construct the heating rate‐related temperature ignition criterion can be used to obtain the same ignition criterion for other combustible solids. Copyright © 2014 John Wiley & Sons, Ltd.     

Prediction of hot tearing susceptibility of direct chill casting of AA6111 alloys via finite element simulations

To predict hot tearing susceptibility (HTS) during solidification and improve the quality of Al alloy castings, constitutive equations for AA6111 alloys were developed using a direct finite element (FE) method. A hot tearing model was established for direct chill (DC) casting of industrial AA6111 alloys via coupling FE model and hot tearing criterion. By applying this model to real manufacture processes, the effects of casting speed, bottom cooling, secondary cooling, and geometric variations on the HTS were revealed. The results show that the HTS of the billet increases as the speed and billet radius increase, while it reduces as the interfacial heat transfer coefficient at the bottom or secondary water-cooling rate increases. This model shows the capabilities of incorporating maximum pore fraction in simulating hot tearing initiation, which will have a significant impact on optimizing casting conditions and chemistry for minimizing HTS and thus controlling the casting quality.     

方形剪力墙雷达塔爆破拆除技术

为了拆除复杂环境下一座高耸、方形、薄壁、钢筋混凝土剪力墙雷达塔,采用"化墙为柱"的爆破方法。利用机械预拆除、开设定向窗确保倒塌方向准确;利用多重近体防护和建土堤,防止爆破飞石和触地振动;利用对后部支撑墙体偏心爆破和两侧圆弧状支撑,防止出现强烈后坐现象。爆破后雷达塔按照设计倒塌,达到了预期效果。对类似工程具有一定的参考意义。     

茅台酒厂26层剪力墙结构大楼爆破拆除

根据茅台酒厂钟楼的结构特性、周围环境特点及爆破要求,分析该栋26层高楼的爆破拆除控制要点,采用了单向三折叠的爆破方案。通过爆破方法预先拆除切口内部分剪力墙,有效地降低爆破总药量;通过切口间开设铰链,使大楼在空中充分解体,减小了塌落体的触地块度,从而降低了触地冲击;采用胶皮网覆盖和敷设减振带等防护措施,有效地控制了爆破飞石及触地振动。结合高速摄影对钟楼倒塌后坐造成排污管及排污沟破坏的原因进行了分析,可为类似工程提供参考。