共查询到20条相似文献，搜索用时 296 毫秒
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《浙江大学学报(A卷英文版)》2021,(11)
目的:在材料高速冲击结构物的过程中引起的应力波往往在材料中向边界逐渐传播,并在传统固定或自由边界处反射回材料内部,造成结构物附件的应力场和接触力数值的扰动。本文旨在在物质点法模拟中实现吸收边界的应用,在模型边界处吸收材料中的应力波,减少其反射及其对中心区域的干扰。创新点:1.对不同条件处的边界分别采用黏壶和阻尼层的吸收边界,优化边界处应力波的吸收效果;2.建立物质点法分析模型,对吸收边界的效果进行量化评估。方法:1.在边界网格节点上采用黏壶吸收边界,并通过数学推导,确定不同时刻对节点处速度的调整量,以实现对应力波的充分吸收;2.在距离边界一定距离的厚度内,设置阻尼层,对材料瞬态速度进行一定程度的调整,使其达到所需的稳态值,即对应力波完成吸收;3.采用物质点法建立一维压缩、海底滑坡冲击管线和管线贯入模型,对吸收边界的使用效果进行评估,并对两种吸收边界的使用场景进行分析。结论:1.黏壶吸收边界通过对波动方程的推导,使其在自由边界处的使用更加灵活;2.阻尼层吸收边界需要在计算区域外侧设置一定厚度的阻尼层,且阻尼值不宜过大;3.在一定条件下,两种吸收边界组合使用可以优化对应力波的吸收。 相似文献
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目的：本文旨在探讨不同尺度颗粒形貌特征对于砂土应力-应变以及能量耗散行为的影响。方法：1.通过同步X射线计算断层扫描实验,提取高精度的真实颗粒形貌,并通过三维点云表征;2.通过基于球谐分析的主成分分析方法,构建不同尺度下颗粒形貌的突变与衰减;3.通过离散单元法仿真,模拟不同形貌试件的三轴剪切过程,并进一步讨论不同尺度颗粒形貌对于颗粒材料应力-应变以及能量耗散行为的影响。结论：1.通过比较较松散和较密实的试件,发现对于较松散试件,颗粒形貌对颗粒材料的初始刚度、应力-应变、体积应变和摩擦能量耗散等响应的影响更为明显;2.对于不同尺度下的颗粒形貌,局部圆度较长径比对颗粒材料宏观响应的影响更大;3.颗粒材料的能量耗散行为由颗粒形貌和初始孔隙率共同决定。 相似文献
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建立了一种基于广义梁理论(GBT)的非线性显式动力梁有限元模型,该模型可用于等截面薄壁钢构件的冲击响应模拟.考虑冲击加载时的应变率强化及绝热升温引起的热软化效应,当前模型采用了一种修正的Cowper-Symonds率相关本构模型.用GBT截面变形模态构建单元截面位移场,因此新模型可考虑构件截面的畸变、屈曲及任意的翘曲剪切等局部效应.此外,用三次非均匀B样条基函数拟合各个GBT截面变形模态的幅值函数.用Kirchhoff薄板假设构造弯曲相关位移场.用Green-Lagrange应变张量和PK2应力分别描述材料点的应变和应力,假设各材料点处于平面应力状态.为了验证所提模型的有效性,给出了3组薄壁构件的冲击分析算例,将当前模型的结果和壳有限元(Ls-Dyna)分析结果进行了对比,结果表明:当前模型和壳有限元模型的位移解和应力解具有等效精度,但所提模型的计算效率更高,并具备更好的结构明晰性. 相似文献
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基于《自密实混凝土应用技术规程》(JGJ/T 283-2012)推荐的配合比设计方法,采用地方材料,成功配制出了强度等级为C50-C60的自密实高性能混凝土。在此基础上,进一步试验研究所配制的自密实高性能混凝土的单轴受压应力-应变曲线,重点考察自密实高性能混凝土的应力-应变曲线特征、峰值应变和泊松比等。研究结果为自密实高性能混凝土的实际应用提供了一定的参考依据。 相似文献
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《浙江大学学报(A卷英文版)》2019,(2)
目的:功能梯度准晶材料有助于减缓层合板界面处的应力集中现象,提高层间粘接强度,从而提升层合板表面的耐磨性。本文旨在建立功能梯度压电准晶层合板的力学模型,并研究功能梯度变化和叠放顺序对层合板的影响。创新点:1.首次将状态向量法推广到功能梯度压电准晶板的分析中;2.假设功能梯度函数的变化形式为幂函数和指数函数;3.在准晶层中观察到声子场应力和电势的不敏感点。方法:1.通过联立三大基本方程,推导出准晶板的状态方程,并求解该微分方程,得到单层准晶板的解析解;2.通过引入功能梯度函数,使解析解中的描述各材料特性的值能够沿厚度方向呈现梯度变化;3.采用传递矩阵法,求出多层准晶板的解析解;4.通过仿真模拟,将所得结果与已有文献进行对比,验证所提方法的可行性和有效性。结论:1.准晶层合板中的功能梯度效应随着梯度参数的增加而增大,且材料参数的变化对声子场、相位子场以及电场的响应均产生影响。2.在功能梯度效应下,从准晶层中观察到了声子场应力和电势的不敏感点。3.与准晶作为中间层相比,准晶作为表层时机械载荷引起的位移响应更小。研究结果可以为压电准晶元器件的设计提供理论参考。 相似文献
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冲击碰撞试验台在中应变率压缩试验中的应用 总被引：1，自引：0，他引：1
《实验室研究与探索》2015,(9)
选用以脉冲加速度作为激励的垂直冲击碰撞试验台进行中应变率压缩试验。针对缓冲材料在中应变率1~500 s-1的应力-应变曲线,介绍了垂直冲击碰撞试验台的工作原理,推导了缓冲材料试件的应力-应变曲线与输入脉冲加速度之间的关系。以常见的蜂窝纸板的动态压缩试验作为例子。试验表明,蜂窝纸板在动态压缩时的应力-应变曲线明显不同于在准静态压缩时的结果,同时证实了利用垂直冲击碰撞测试缓冲材料的中应变率压缩试验时,具有操作简单与易控制的优点。 相似文献
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《浙江大学学报(A卷英文版)》2017,(11)
目的:奥氏体不锈钢(ASS)在深冷压力容器中应用广泛。ASS较高的应变硬化特性有助于其产生应变强化。在应变强化过程中,保载时间是影响材料最终变形量的关键参数。基于室温蠕变应变弛豫理论,本文旨在提出一种S30408深冷压力容器应变强化过程中的保载时间预测方法。创新点:1.根据室温蠕变应变弛豫理论,保载过程即为材料在室温蠕变中应变速率逐渐减缓、材料结构逐渐稳定的过程;本文据此获得了保载时间的计算模型。2.结合材料试验与容器试验,将计算模型中涉及的多个微观变量转换为唯一宏观变量——圆柱壳上的最大环向应力,可为常规工业生产提供定量的、具有实际可操作性的技术支持。方法:1.根据室温蠕变应变弛豫理论,建立蠕变本构关系,得出保载时间计算模型。2.通过材料试验,考虑实际生产中的特定条件,将保载时间计算模型的多个微观变量简化为唯一宏观变量。3.通过在多个工业规模的容器上进行实验,比较验证所提计算方法的可靠性。结论:1.室温蠕变应变弛豫理论可以用于描述应变强化保载过程中的材料变化。2.容器保载时长,即材料应变弛豫时长,与其所承受的最大应力有关。3.所提出的保载时间计算方法可以为容器保载时间提供可靠预测;其平均绝对误差为7.53%,且绝大部分情况下偏于保守。 相似文献
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《东南大学学报》2020,(2)
建立了黏弹性功能梯度(FG) Timoshenko微梁的尺寸依赖连续模型,其材料参数沿轴向随幂律变化.为研究微梁的尺寸效应,利用修正偶应力理论和Kelvin-Voigt黏弹性模型将材料的黏性项纳入应力和偶应力张量的偏离分量中;结合Timoshenko梁理论导出了应变、曲率、应力和偶应力的分量;基于哈密顿原理,给出了任意截面形状的微梁在任意荷载作用下的控制微分方程和边界条件.然后,以点荷载作用下的简支微梁为例,研究了尺寸效应、功能梯度效应、泊松效应以及截面形状对黏弹性微梁力学行为的影响.结果表明:当微梁尺寸足够小时,其转角、正应力和偶应力的尺寸效应明显;当微梁尺寸足够大时,微梁的功能梯度效应较为明显;此外,泊松比对尺寸效应影响较大,梁截面形状也是影响微梁力学性能的重要因素. 相似文献
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A new oxidation kinetics model is established for high-temperature oxidation. We assume that the interface reaction is fast enough and the oxidation rate is controlled by diffusion process at high temperature. By introducing the growth stress gradient we modify the classical oxidation parabolic law. The modified factor of the oxidation rate constant is a function of growth strain, environment oxygen concentration, and temperature. The modeling results show that the stress gradient effect on the oxidation rate cannot be ignored. Growth strain will dominate whether the stress gradient effect promotes or slows down the oxidation process. The stress gradient effect becomes weaker at higher temperature. This effect is amplified at higher concentrations of environmental oxygen. Applied mechanical loads do not affect the oxidation rate. This model is available for high temperature oxidation of metals and alloys. 相似文献
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以聚氨酯泡沫为试样,建立了多孔介质水平燃料床阴燃的二维两相流数学模型.模型包括燃料吸热热解、燃料放热氧化及焦炭的放热氧化3个反应过程.通过有限单元法对聚氨脂泡沫的阴燃控制方程进行离散,并采用数值分析软件包FEMLAB进行计算求解.数值模拟了来流速度为0.28 cm/s时燃料阴燃的温度分布和固体成分(燃料泡沫、炭粒和灰分)的变化,其中阴燃传播平均速度为0.0214cm/s,阴燃最高温度平均为644.67K;固体成分的变化曲线明显的将填充床分成4个区域:未燃区、燃料热解氧化区、焦炭氧化区及燃料燃尽区.同时,模拟研究了来流速度及燃料特性参数(导热率、比热、密度、孔隙直径等)对阴燃传播特性的影响.结果表明:阴燃速度和阴燃温度随着来流速度的增大基本上呈线性增长;燃料密度对阴燃传播影响最大;对于孔径较大的多孔介质燃料,模型中要考虑辐射的影响.模拟数据与实验数据进行了对比,结果基本吻合. 相似文献
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钢桥面环氧沥青铺装的界面行为 总被引：2，自引：0，他引：2
通过引入一个新参数膜劲度,在部分共同作用原理的基础上,建立了描述钢桥面环氧沥青混凝土铺装复合梁在负弯矩作用下的界面行为模型,用以分析钢-环氧沥青混凝土之间的界面滑移与应变.推导了弹性工作状态下复合梁的界面滑移与应变的表达式,编制了数值计算程序并用2根复合梁进行了校核.然后采用该程序分析了界面滑移与应变沿复合梁纵向的分布特征,以及铺装层中的最大拉应力、层间剪应力对材料参数的敏感性.结果表明,界面效应削弱了钢桥面铺装复合梁的整体抗弯刚度;中低温条件下,采用劲度更大的粘结层材料有利于改善沥青铺装层的受力;粘结层的损伤累积将加剧沥青铺装层的破坏. 相似文献
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A number of finite element simulations were performed to analyze the in-plane crushing behaviour of aluminium honeycombs and the results are presented and discussed. The simulations include both X1 and X2 cases. All the analyses are quasi-static, and can be divided into three groups, which are designed to investigate the effects of cell size, foil thickness and yield stress of the foil material, respectively, on the structural response of honeycombs. The result indicates that these factors can significantly affect the plateau stresses of honeycomb cellular structures in both directions, and the plateau stresses in X2 direction are slightly smaller than those in X1 direction. The simulation results were further compared with published theoretical predictions and show higher values. The difference was then analyzed and a new expression for the plateau stress of honeycombs was suggested. 相似文献
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ZHU Feng ZHAO Longmao LU Guoxing 《天津大学学报(英文版)》2006,12(B09):142-146
A number of finite element simulations were performed to analyze the in-plane crushing behaviour of aluminium honeycombs and the results are presented and discussed. The simulations include both X1 and X2 cases. All the analyses are quasi-static, and can be divided into three groups, which are designed to investigate the effects of cell size, foil thickness and yield stress of the foil material, respectively, on the structural response of honeycombs. The result indicates that these factors can significantly affect the plateau stresses of honeycomb cellular structures in both directions, and the plateau stresses in X2 direction are slightly smaller than those in X1 direction. The simulation results were further compared with published theoretical predictions and show higher values. The difference was then analyzed and a new expression for the Plateau stress of honeycombs was suggested. 相似文献
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An analytical model for straight hemming was developed based on minimum energy method to study the effect of flanging die
corner radius on hemming qualities. In order to calculate plastic strain and strain energy more exactly, the neutral layer
of specimen corner after hemming is assumed to be a half ellipse with its major semi-axis unknown. Isotropic hardening rule
is adopted to describe bending and reverse bending processes neglecting Bauschinger effect. The model takes into account the
material property parameters in order to satisfy a wide application range of different materials. Specimen profile, creepage/growing
(roll-in/roll-out) and maximum equivalent strain are predicted, which are greatly influenced by the flanging die corner radius.
Experimental facilities were designed and hemming experiments were undertaken. The predicted results of the present analytical
model were compared to experimental data as well as finite element (FE) simulation results. It was confirmed that they are
in good agreement, and the model can be used to evaluate whether the material used as an outer panel for hemming is appropriate
and to optimize process parameters when the material used for hemming is changed. 相似文献
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In recent years, much attention has been devoted to the design and operation of bearings made of elastic metal plastic (EMP). The surface of the bearing bush is covered by a layer of polymer PTFE(polytetrafluoroethylene). The physical performances of the polymer are quite different from that of metal. It can reduce friction because of its lower surface energy, and it is more difficult for the fluid to be adhered. Consequently, the slip will exist at the oil-bush interface. The journal bearings made of this material are researched in this article. Through test, the existence of slip is proven and the equation of the slip velocity for the EMP journal bearing is established when shear stress up to a certain value. Thus, the classical Reynolds equation is modified. The lubrication mechanism is analyzed by some simulation results. 相似文献
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本文建立了热残余应力分析的数学模型，采用数值方法对陶瓷涂层材料的热残余应力进行了分析，得出了金属基底的弹性性能、过渡层的厚度和陶瓷涂层的孔隙率对热残余应力的影响，为含FGM的陶瓷涂层材料的优化提供了一种理论分析方法。 相似文献
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本文采用量子化学AM1半经验的方法对卤代环氧酮化合物进行了优化计算。并比较了在环的相同位置,氢原子同时被两个氯原子取代、两个溴原子取代、分别被氯和溴原子取代三种情况下同分异构体的分子结构、分子能量、电荷密度和分子前线轨道能级,给出了各分子的相对反应活性和相对稳定性。结果表明,标题物为反式的椅式几何构型。本文研究有助于环氧有机化物的结构、性能研究,并为在实验室获得该高能密度材料化合物提供理论指导。 相似文献
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Terrorist attacks using improvised explosive devices (IED) can result in unreinforced ma-sonry (URM) wall collapse. Protecting URM wall from IED attack is very complicated. An effective solution to mitigate blast effects on URM wall is to retrofit URM walls with metallic foam sheets to absorb blast energy. However, mitigation of blast effects on metallic foam protected URM walls is currently in their infancy in the world. In this paper, numerical models are used to simulate the per-formance of aluminum foam protected URM walls subjected to blast loads. A distinctive model, in which mortar and brick units of masonry are discritized individually, is used to model the perform-ance of masonry and the contact between the masonry and steel face-sheet of aluminum foam is modelled using the interface element model. The aluminum foam is modelled by a nonlinear elas-toplastic material model. The material models for masonry, aluminum foam and interface are then coded into a finite element program LS-DYNA3D to perform the numerical calculations of response and damage of aluminum foam protected URM walls under airblast loads. Discussion is made on the effectiveness of the aluminum foam protected system for URM wall against blast loads. 相似文献