缀板式钢管混凝土组合柱框架有限元分析

为研究缀板式方钢管混凝土组合柱框架的抗震耗能能力,基于三榀框架试验所验证的有限元模型,在不改变材料本构及各不同构件的参数设置,采用ABAQUS有限元软件建立不同构造形式的框架模型,通过有限元软件得到框架的应力云图及荷载-位移曲线,研究框架在低周水平往复荷载作用下滞回性能。模拟结果表明,不同构造形式下框架钢梁发生了屈曲扭转、底部柱子在大位移时发生压弯、肋板连接处所受应力较大,破坏机制符合强柱弱梁,具有良好的滞回性能,为以后实际工程中提供可参考依据。     

Influence of longitudinal structural connectivity on seismic performance of three-hinged precast arch culverts

The hinge type of precast concrete arch culvert was introduced to Japan from France in the 1990s in consideration of the saving of labor, shortening of the construction period, and high quality control of the concrete members. However, due to the 2011 off the Pacific Coast of Tohoku Earthquake (March 11, 2011), the three-hinged precast arch culverts that had been constructed in Japan at the beginning of the period when precast arch culverts were firstly introduced, suffered damage, which spoiled their serviceability. According to the extent of the damage and the type of culverts that were damaged, the longitudinal structural connectivity of the culverts was assumed to be one of the possible reasons for the reported damage mechanism. Therefore, the objective of this paper was to clarify how strongly the longitudinal structural connectivity influenced the longitudinal seismic behavior of the three-hinged arch culverts. To achieve this objective, an elasto-plastic finite element analysis was conducted with an analytical model that could capture the characteristics of the damaged culverts. Simultaneously, a penalty method with the bi-linear spring model was applied as a solution to the contact-impact problems of the precast segmental arch members. As a result, it was found that the weaker longitudinal structural connectivity in the damaged culverts allowed the torsional displacements of the arch members to induce critical damage to the arch members, namely, edge defects in the arch crown and concrete foundation. The numerical results proved the unignorable influence of the longitudinal structural connection on the possible damage to three-hinged arch culverts.     

Critical length of encased stone columns

Encased stone columns are vertical inclusions in soft soils formed by gravel wrapped usually with a geotextile. Their critical length is the one where further lengthening of the column provides a negligible improvement and it is therefore not effective to build columns longer than it. This paper aims to obtain common values of the critical length using simplified two-dimensional axisymmetric and full three-dimensional finite element analyses. A uniform soft soil layer with a linear elastic perfectly plastic behaviour is considered for the sake of simplicity. For the studied cases, the critical column length is around 1.3–2.5 times the footing diameter for encased stone columns, and slightly lower for ordinary stone columns, namely around 1.1–1.9. The critical length of the encasement is found to be slightly lower than the critical column length. The value of the critical column length is related to the extent of plastic deformation and that may be used to decide the column length in the design phase without the need of parametric analyses. As a first approximation, a general value of the critical column length of 2 and 2.5 times the footing diameter may be considered for ordinary and encased stone columns, respectively.     

Load performance analysis of three‐pad fixing pad aerodynamic journal bearings with parabolic grooves

Three‐pad fixing pad aerodynamic journal bearings (TPFPAJBs) have been widely used in precision instruments due to their low friction, high stability and non‐pollution. In order to improve the load performance of TPFPAJBs, parabolic grooves are opened in the bearing pad surfaces. By opening parabolic grooves in various bearing pad surfaces, the effects of the orientation angle, distance, width and depth of the grooves on the load performance of micro‐grooved TPFPAJBs can be investigated. The numerical results show that the location of the micro‐grooved bearing pads can greatly affect the load performance of micro‐grooved TPFPAJBs. When the given bearing pad surface is grooved, the effects of the bearing number and width‐to‐diameter ratio on the load performance of micro‐grooved TPFPAJBs can be studied. The bearing number and width‐to‐diameter ratio are observed to have significant influences on the load performance of micro‐grooved TPFPAJBs. Copyright © 2015 John Wiley & Sons, Ltd.     

某外能源自动机迟发火故障损伤分析

为分析迟发火故障对于外能源自动机造成的危害,建立该自动机闭锁击发时的3 维模型。针对不同开闩 时机,基于接触有限元理论建立某自动机炮闩机构的非线性结构动力学模型,采用显式时间积分方法仿真模拟击发 过程,分析自动机迟发火状态下主要部件的应力和失效情况,获得膛压作用下危险截面的应力变化和弹壳破坏情况。 研究结果表明：闭锁齿齿根处与接触面发生破坏,弹壳底部发生断裂,不同延迟时间下自动机损伤程度不同,迟发 火故障损伤分析与试验结果一致,可为迟发火保险机构设计提供依据。     

紫外非线性光学晶体分子设计

紫外非线性光学晶体对全固态激光器的发展起着举足轻重的作用,对性能优秀的紫外非线性光学晶体的探索是光电功能材料领域的研究热点.如何在种类繁多的晶体材料中高效地搜索并获得结构优化的紫外非线性光学晶体,是当前该领域研究的关键问题.对非线性光学材料构效关系研究的发展历史进行了回顾,重点介绍了阴离子基团理论以及第一性原理方法在新型紫外非线性光学材料探索中的重要应用.材料计算模拟方法不仅能够较准确地预测紫外非线性光学晶体的关键光学参数,并可以定量和直观地分析其与晶体结构特征之间的内在关系.通过将理论模拟与结构搜索、化学合成、粉末倍频效应测试、单晶生长等实验手段紧密结合,建立了快速高效的非线性光学材料分子设计专家系统.具体的科研数据及成果显示,发展和完善这一基于分子工程学基础的专家系统,将能加快非线性光学晶体的研究步伐,提升其自主创新水平.     

铝合金薄壁波纹板充液成形工艺研究

目的解决航空铝合金薄壁波纹板爆炸成形工艺成形效率低且成形质量差的问题。方法提出了3种充液成形工艺方案,利用有限元分析软件对3种成形方案进行了对比分析,并且对最优方案进行了试验验证。结果有限元分析结果显示,双面加压充液成形方法能够使零件的各部分变形均匀,避免了在充液成形过程中因摩擦力作用导致的局部变形过大产生的开裂,有效地提高了材料的成形能力。结论双面加压充液成形方法能够成形出轮廓精度高、表面质量好的铝合金薄壁波纹板。     

前基板和后基板共模模锻成形研究

目的针对前基板和后基板共模模锻成形进行研究。方法通过分析前基板和后基板模锻工艺性,并将相同或相近形状、尺寸、精度、功能类别和材料牌号等要素,按成组技术合并同类项等方法,实现共模模锻成形,为优化模锻工艺和优化锻模设计提供有力的理论与实践支持。结果前基板和后基板共模模锻成形的模锻工艺性好,可有效扬长避短传统模锻工艺和锻模设计的优缺点。结论前基板和后基板共模模锻成形达到了优质、高效和低耗的效果。     

大断面收缩率楔横轧成形工艺改进

目的研究大断面收缩率一次轧制成形的可行性,降低材料利用率。方法以某型号变速箱二轴为研究对象,将原来的二次楔轧制改为一次楔轧制,用有限元软件对改进前后工艺进行模拟分析,获得了等效应变、应力场分布和轧制力矩的变化。结果模拟结果表明,一次楔轧制变速箱二轴是可行的,料头尺寸得到了减小。一次楔轧制的端头的应力小于极限应力,没有产生缩颈等缺陷。结论改进后的工艺切实可行,节省了材料,而且方便了模具的加工制造。     

基于有限元法的轮毂成形工艺对比

目的对比某型号轮毂成形的工艺方案。方法对轮毂在不同条件下的成形过程进行了数值模拟和实验研究,分析成形工艺对应力分布、应变分布、金属流动速度场、成形载荷及内部组织的影响。结果坯料在800℃下采用闭式模锻所需成形载荷小,模具结构较简单,内部组织为粒状珠光体,力学性能优于其他2种方案下的内部组织魏氏体。结论闭塞式挤压和闭式模锻成形等效应力、等效应变、金属流动速度场、成形载荷及内部组织各不相同。模拟结果可以指导实际生产中工艺方案的选择。