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曲线梁桥在地震作用下产生的不规则平面旋转位移使得应用碰撞单元法计算曲线梁体碰撞效应存在一定的局限性,为了探讨曲线梁桥地震碰撞效应的非均匀分布规律,提出了采用显式动力接触算法计算曲线梁桥地震碰撞效应的数值模拟方法,并分析曲线连续梁桥碰撞效应引起的主梁、挡块和桥墩的冲击地震反应特点。结果表明,主梁与桥台胸墙的碰撞作用限制了主梁的切向位移,使得固定墩墩底弯矩小于不考虑碰撞时的墩底弯矩。碰撞后梁端截面顶板正应力和曲线内外侧挡块径向应力的分布严重不均匀,梁端截面悬臂翼缘的正应力明显小于腹板间顶板的正应力,曲线外侧挡块的径向应力显著大于内侧挡块的径向应力。地震碰撞作用使得主梁的最大拉应力和压应力通常会发生在梁体曲线的内外侧。这为合理解释曲线连续梁桥在强震下的碰撞破坏震害现象提供了理论指导。 相似文献
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针对隔震连续梁桥纵桥向主梁与桥台碰撞问题,以一联三跨混凝土隔震连续梁桥作为算例,采用ABAQUS建立了考虑混凝土材料损伤及三维接触碰撞的有限元模型。在此基础上,应用显式积分算法分析了纵桥向地震作用下隔震连续梁桥的碰撞响应,探究了伸缩缝间隙以及支座屈服位移对碰撞响应的影响。研究结果表明:采用三维有限元模型计算得到的碰撞持时与应力波理论得到的结果吻合较好;随着碰撞的发生,混凝土材料损伤积累,碰撞持时有增加的趋势。增大伸缩缝间隙将减小碰撞次数的发生,但对最大碰撞力的影响趋势不明显;随着支座屈服位移的增加,碰撞次数显著减小,但最大碰撞力变化不大。 相似文献
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考虑材料非线性和应变率相关性等因素的影响,运用LS_DYNA非线性有限元软件对RC梁横向低速冲击试验进行了数值模拟,从动态损伤扩展、冲击能量转化等方面研究了RC梁的冲击响应过程和破坏机理。结果表明:RC梁的冲击响应过程可分为局部响应、整体响应和回弹变形三个阶段;RC梁的损伤主要发生在局部响应阶段,梁体变形主要发生在整体响应阶段;局部响应阶段的冲击力完全由梁体惯性力平衡,整体响应阶段的变形模式和截面弯矩分布与刚塑性模型基本相同;受拉钢筋变形耗能是RC梁最主要的冲击耗能机制。 相似文献
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提出了一种基于应力波因子的金属材料表面塑性损伤检测方法。将AZ31镁铝合金试件加载到不同的拉伸载荷后,利用Ritec SNAP非线性超声测试系统激发和接收Rayleigh表面波,通过实验测试在不同载荷作用后基于应力波因子的声学非线性系数与应力的关系。研究结果表明,当加载应力接近材料的屈服极限时,基于应力波因子的声学非线性系数随着应力的增加明显增大,因此可以利用基于应力波因子的声学非线性系数对金属材料表面的塑性损伤进行非线性超声无损评价。 相似文献
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通过分析“九寨沟地震”作用下现场实测的高速铁路桥梁结构(距离震中约195km)动力响应特征及地震预警时间,并将地震和动车作用下的实测数据进行时域和频域对比,得出:地震S波作用下桥梁结构动力响应快速增大,最大值约为P 波作用下的2?5倍;桥址处“异地震前预警”时间约为50s,“现地地震P 波预警”时间约为15s;地震作用下桥梁结构以高墩的低频、整体横向振动为主,横向振动数值大于竖向;地震作用下墩顶横向振幅最大值是动车作用下的43倍,梁体竖向振幅与桥梁跨度呈正相关;动车组列车作用下的梁体横向和竖向加速度均大于地震作用;对比地震发生前后的桥梁自振特性、竖向刚度、振动参数,表明桥梁结构工作状态无异常变化。 相似文献
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为了研究AD95陶瓷在冲击加载下的动态力学性能与损伤机理,采用仿真软件AUTODYN模拟了一维应力与一维应变状态下材料不同失效与破碎模式,获得了完整的损伤历程.结果表明,在一维应力波作用下,材料内部损伤以及裂纹扩展始于圆柱试样端部的应力集中,在陶瓷整体被瞬间压垮前,试样仍具有承载能力.平面冲击波作用时,试样在低于Hugoniot弹性极限下出现了两个相向传播的破坏面.由于应力波的相互作用以及材料本身抗拉强度不足,试样内同时产生了明显的层裂现象. 相似文献
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利用应力波特征能够有效识别材料结构中内部缺陷及其分布形式,为了将工艺载荷作为应力波激励源对预成型体内部缺陷进行识别,应首先研究铺丝过程中工艺参数对应力波传播特征的影响,以确定应力传感器的放置位置。本文采用有限元方法构建了铺丝过程热力耦合模型,分析了应力波特征参数与工艺参数之间的关系,并进行了实验验证。为了从微观能量角度解释工艺参数对应力波特征的影响规律,采用分子动力学方法,建立了预浸丝界面的分子模型,并计算出总能量、纤维表面能、基体内能等能量参数,识别和评价了不同工艺参数作用下的应力波驱动能量及其贡献比,以揭示工艺参数对应力波特征的能量作用机制。结果表明,以基体内能作为驱动能量的侧向应力波与工艺参数的关系明显,在不同工艺参数施载下,内部缺陷的形成对该波形的作用易于识别,该结论可作为应力传感器放置位置的参考依据。 相似文献
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为研究行波效应下高速铁路连续梁桥与无缝线路的非线性互制作用,采用带刚臂的梁单元模拟梁体,用非线性杆单元模拟梁轨间的互制作用,建立了考虑纵向和竖向地震动行波效应的梁轨相互作用模型。以我国沪昆线上某(60+100+60)m连续梁桥为算例,分析了轨道结构对梁体和墩台地震响应的影响,研究了纵向和竖向行波效应下钢轨和墩台的受力特点。研究表明:轨道的存在可提高系统基频,降低连续梁桥地震响应;但在地震动的行波效应下,钢轨纵向力最大值可达一致激励下的1.2倍;减小线路纵向阻力,增加桥墩刚度可减小地震作用下的钢轨应力;在检算钢轨时,还应累计竖向行波效应对钢轨受力的影响。 相似文献
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Photostriction is the superposition of a photovoltaic and piezoelectric effects. In this study, photostrictive effects in the perovskite (Pb, La) (Zr, Ti)O3 were investigated as a function of B-site impurity doping. Donor doping was found to reduce both the grain size and room-temperature dielectric constant, influencing photovoltaic response. WO3 and Ta2O5 doping increase the photovoltaic response, but do not significantly affect the piezoelectric effect in this material. Maximum photostriction is obtained for samples with 0.4 at% WO3 doped or 1 at% Ta2O5 doped PLZT 相似文献
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AbstractThe temperature effects on the intensity profile, self-deflection process, and stability of (1 + 1)-dimensional steady-state bright solitons resulting from both the linear and quadratic electro-optic effects are comprehensively analyzed. Moreover, three physical factors, i.e. diffusion effect, dark irradiance, and the dielectric constant, have been investigated through the theoretical analysis to determine which one dominates the temperature dependence of intensity profile and self-deflection of bright solitons. It is also found that the incident beam evolves into stable bright solitons in the vicinity of initial temperature, but oscillates or even collapses when the crystal temperature deviates significantly from the initial temperature. 相似文献
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乳胶渗透蒸发膜分离醇水混合物 总被引:1,自引:0,他引:1
以苯乙烯、丙烯酸丁酯为单体进行乳液聚合,将聚合获得的乳胶直接浇铸制备出乳胶膜.将该膜用于水-乙醇混合物的渗透蒸发分离,优先透水,渗透通量为50一450g/(m2·h),分离因子为80~260.考察了乳胶膜的选择性及料液浓度对乳胶膜分离性能的影响.研究了塑化效应和耦合效应对组分渗透的影响,发现在乳胶膜中,乙醇的存在有利于水的渗透,而水的存在会阻止乙醇的渗透. 相似文献
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We report the observation of self-focusing effects in organic photorefractive films based on a carbazole derivative and sensitizer 2,4,7-trinitro-9-fluorenone at 632.8 nm wavelength without applying a biased field, owing to the orientationally enhanced photorefractive nonlinearity caused by photopolymerization of the carbazole derivative. The experiment was repeated in three samples with different sensitizer doping percentages and similar phenomena were observed. 相似文献
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Surface effect aero-hydrodynamics, as one of the influencing factors in the design and operation of wing-in-ground effect
vehicles, is briefly illustrated. Some important issues are discussed. These include high lift/drag configuration, power augmented
ram, flight stability and control and wind-wave effects on aerodynamics. 相似文献
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Richa Pandey Gaurav Vats Jae Yun Chris R. Bowen Anita W. Y. Ho‐Baillie Jan Seidel Keith Tobias Butler Sang Il Seok 《Advanced materials (Deerfield Beach, Fla.)》2019,31(43)
An insight into the analogies, state‐of‐the‐art technologies, concepts, and prospects under the umbrella of perovskite materials (both inorganic–organic hybrid halide perovskites and ferroelectric perovskites) for future multifunctional energy conversion and storage devices is provided. Often, these are considered entirely different branches of research; however, considering them simultaneously and holistically can provide several new opportunities. Recent advancements have highlighted the potential of hybrid perovskites for high‐efficiency solar cells. The intrinsic polar properties of these materials, including the potential for ferroelectricity, provide additional possibilities for simultaneously exploiting several energy conversion mechanisms such as the piezoelectric, pyroelectric, and thermoelectric effect and electrical energy storage. The presence of these phenomena can support the performance of perovskite solar cells. The energy conversion using these effects (piezo‐, pyro‐, and thermoelectric effect) can also be enhanced by a change in the light intensity. Thus, there lies a range of possibilities for tuning the structural, electronic, optical, and magnetic properties of perovskites to simultaneously harvest energy using more than one mechanism to realize an improved efficiency. This requires a basic understanding of concepts, mechanisms, corresponding material properties, and the underlying physics involved with these effects. 相似文献
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S. Bouzgarrou Na. Sghaier M.M. Ben Salem A. Souifi A. Kalboussi 《Materials science & engineering. C, Materials for biological applications》2008,28(5-6):676-679
The aim of this work is to study the origin of parasitic effects observed on the output characteristics of InAlAs/InGaAs/InP HEMTs with various buffer layers. Ids − Vds measurements as a function of the temperature have first been performed. Several anomalies were observed such as kink and hysteresis effects. C-DLTS measurements have also been performed. From the obtained results, we have established a strong correlation between parasitic effects observed on the output characteristics and deep levels located near the buffer layer interface. 相似文献