蜂窝铝异面压缩变形的有限元分析

考虑蜂窝铝结构细部特征,建立了基于壳单元的有限元模型,利用壳单元模型研究了蜂窝铝的异面压缩特性,验证了蜂窝铝壳单元模型的有效性。利用PAM-CRASH材料库中的41号材料建立蜂窝铝实体有限元模型,由壳单元模型推导计算材料本构关系中的各项参数。对蜂窝铝实体单元模型进行分析,通过将壳单元与实体单元模型进行对比,获得了应力-应变曲线和能量吸收曲线,发现可以利用实体单元模型替代壳单元模型,进行蜂窝铝异面压缩变形的有限元分析。仿真计算结果表明,相较于考虑蜂窝铝结构细部特征的壳单元模型,蜂窝铝实体单元模型计算规模更小,能够大幅缩短计算时间,提高计算效率。     

基于壳单元的侧碰移动可变形壁障研究

采用壳单元技术,参照蜂窝铝的真实窝孔结构,建立基于壳单元的侧碰移动可变形壁障(Moving deformable barrier,MDB)有限元模型;针对1∶1尺寸建模导致模型规模过大的问题,进行窝孔及单元尺寸等比例扩大,将单元规模缩减到原来的1/5;应用静态异面压缩仿真,对单元厚度与压缩强度进行参数化研究,合理匹配窝孔及单元尺寸扩大之后的单元厚度,确保模型缩放前后的静态压缩力学性能达到一致;针对动态试验压缩强度大于静态试验的现象,采用简易气囊模拟MDB窝孔中空气受压缩的率效应;结合侧碰试验中的蜂窝铝失效现象,设置铝箔的材料失效以及铝箔、前面板之间粘胶的材料失效;对所建立的壳单元MDB模型进行零部件级别与整车级别的试验验证,结果表明壳单元MDB模型具有很高的精度。     

基于Pamcrash的蜂窝铝异面压缩仿真与验证

为了得到与实验一致性较好的蜂窝铝有限元模型,利用Hypermesh和Pamcrash软件联合仿真,以软件材料库中105号壳单元为基础,建立了蜂窝铝模型,模拟蜂窝铝异面匀速压缩过程;通对比触发力、平台力、吸能量和压实应变,验证仿真模型。对比结果表明,仿真模型与实验试件的主要变形模式相同,仿真数据与实验数据吻合。在考察蜂窝铝异面压缩吸能能力的情况下,所建立的蜂窝铝有限元模型能够代替实验试件,进行研究与设计。     

蜂窝夹层结构拉脱破坏的有限元分析

采用有限元模拟方法分析了蜂窝夹层结构拉脱破坏的机理,并通过试验对其进行了验证。结果表明:使用Usdfld定义的失效模型能够准确地预测蜂窝夹层结构的失效过程;在加载过程中,对整个结构的失效起决定作用的是与灌封胶接触部位的蜂窝材料的剪切失效破坏,蜂窝芯材剪切失效破坏导致了材料的形变突增,最后影响周边的复合材料面板发生基体失效破坏,整个失效过程基本不发生纤维拉伸失效;模拟结果与试验结果比较吻合。     

湿热环境下含脱粘损伤蜂窝夹芯材料弯曲性能研究

通过使用三明治夹芯等效理论将蜂窝芯层等效为均匀连续的实体单元,将湿热环境中的湿应力等效为热应力,建立湿热环境下的蜂窝夹芯材料本构方程,以改进Hashin准则与Besant准则作为蜂窝夹芯材料的失效判据,并通过编写VUMAT子程序实现.采用Cohesive单元模拟面板与芯层间的连接方式建立湿热环境下蜂窝夹芯板的有限元模型,研究湿热环境对蜂窝夹芯材料弯曲性能的影响.切除某些Cohesive区域模拟面板与芯层脱粘现象并计算脱粘损伤对材料性能的影响,对比边缘脱粘与内部脱粘研究脱粘位置对蜂窝夹芯材料弯曲性能的影响.结果表明湿热环境降低了材料的极限承载能力,脱粘现象会加速面板与芯层分离,脱粘位置影响材料的损伤扩展性能,降低材料的弯曲强度.     

碳纤维增强环氧树脂基复合材料圆管轴向压溃分层失效仿真

为了模拟单向碳纤维增强复合材料圆管的压溃失效形式及吸能特性,对圆管进行轴向压溃试验,获得圆管的压溃失效形式及压溃载荷-位移曲线。采用单层壳单元模型进行压溃仿真,确定MAT54材料模型中非试验可测量参数。建立多层壳单元模型,基于Tiebreak接触模拟分层失效,研究网格划分尺寸及壳单元层数对压溃失效形式的影响,通过与试验结果对比验证所建立模型的准确性。研究表明参数YCFAC和SOFT影响压溃载荷-位移曲线的峰值载荷和平均压溃载荷。网格尺寸和壳单元层数影响圆管的失效形式,网格尺寸越小,分层失效和基体开裂现象越明显。随着壳单元层数增加,初始峰值载荷呈递减趋势,所需计算时间呈指数型增长趋势。综合考虑计算成本和预测准确性,采用4层壳单元模型能够准确预测碳纤维圆管的轴向压溃性能和分层失效。     

负泊松比蜂窝动态压溃行为的有限元模拟

采用有限元数值模拟方法,研究了负泊松比蜂窝在不同冲击速度下的变形模式和能量吸收等动力学响应特性。数值模拟结果表明,在动态冲击下,负泊松比行为的产生机制与静态加载下一致,仍为孔壁的内凹和旋转,同时解释了交错排布的三角形和正方形蜂窝在中低速冲击下所表现出的缩颈现象。此外,数值模拟结果还使我们对二维负泊松比多孔材料的动态力学性能和能量吸收性能有了一定的认识,也为进一步研究三维负泊松比泡沫材料的冲击行为奠定了基础。     

金属板料冲压成形的数值模拟

本文采用有限元动力显式算法模拟金属板料冲压成形的加工过程。四结点蜕化壳单元和刚体壳单元分别用来建立权和模具的有限元模型;更新Ｌａｇｒａｎｇｅ法和速率型本构关系被用来处理板料变形中的大应变和大转动;材料模型采用塑性各向异性屈服与等向强化模型;通过主从面模型定义板料和模具的接触,接触算法采用运动约束法,摩擦力用库仓定律计算;并利用动力松弛法对回弹过程进行了计算。模拟结果和实际零件比较,证明模型合理,算法稳定,结果可靠,具有良好的应用价值。     

第三代超高强钢QP1180硬化与失效行为研究

超高强钢材料是当前汽车上应用最广泛的轻量化材料,精确预测其在整车碰撞过程中的失效风险是目前行业内面临的主要挑战。以第三代超高强钢QP1180为研究对象,采用修正的幂函数硬化模型(MPL模型)来描述变n值类材料的硬化行为,并采用液压胀形方法来验证不同硬化模型外推准确性。设计了5种不同应力状态加载工况,通过DIC测量方法获得了QP1180材料在试验加载工况下断裂极限应变,基于试验数据完成了MMC断裂极限准则参数拟合,通过优化方法完成GISSMO损伤模型参数识别,并进一步设计了帽型梁特征件三点弯曲试验来验证失效特性表征结果。结果表明,MPL硬化模型直接外推预测精度明显优于Swift与H-S模型,更适用于QP1180材料;在复杂非线性应变路径下,GISSMO损伤模型可以较好预测材料的失效行为。     

基于多折叠单元理论的蜂窝纸板面外压缩数值模拟

通过原纸拉伸试验获取蜂窝纸板的材料参数，建立蜂窝纸板的有限元简化模型(Y单元模型),采用有限元方法对该模型进行准静态加速压缩模拟，并与蜂窝纸板的面外准静态压缩试验结果进行对比；采用该模拟方法研究蜂窝孔边长、纸板厚度和胞壁厚度对Y单元折叠模式的影响。结果表明：Y单元模型经准静态加速压缩模拟得到的形貌与试验结果相吻合，压缩应力-应变曲线中平台应力的模拟结果与试验结果的相对误差为3.87%,验证了该模型的可靠性；不同规格的Y单元模型在压缩后共出现3种折叠模式，蜂窝孔边长和纸板厚度是影响Y单元折叠模式的2个关键因素。1/2蜂窝孔边长与一次折叠褶皱波长的比值会影响Y单元的一次折叠模式，而双层胞壁与单层胞壁的厚度差是导致多折叠模式发生的主要原因。     

Minimal Realization of Linear Graph Models for Multi-physics Systems

An engineering system may consist of several different types of components,belonging to such physical"domains"as mechanical,electrical,fluid,and thermal.It is t...     

Quantum Cooperative Robotics and Autonomy

The intersection of Quantum Technologies and Robotics Autonomy is explored in the present paper.The two areas are brought together in establishing an interdisci...     

考虑进油孔有限长滑动轴承油膜力的近似解析解

针对具有进油孔的有限长滑动轴承油膜力求解问题,采用变分原理和分离变量法,求得了有限长滑动轴承油膜压力分布的近似解析表达式。将油膜压力分布的近似解析表达式在油膜存在区域上进行积分,即得到了油膜力。将提出的计算有限长滑动轴承油膜力方法与无限长轴承模型、有限元方法的计算结果进行了比较,发现了提出的方法与有限元方法的计算结果很接近。最后,研究了进油孔位置和进油压力对油膜存在区域、油膜力等的影响,研究结果表明进油孔位置和进油压力对油膜存在区域和油膜力有较大的影响。     

Fifth International Summer School on Screw-Theory Based Methods in Robotics

正3-11 September,2014University of Bologna,Bologna,Italy www.summerscrews.org summerscrews2014.ing.unibo.it SUMMER 20SCREWS 14In 2014,our screw-theory school comes to the world's oldest university.In early September,Summer Screws'14 will gather six experts in the application of screw theory in robotics and up to 40 participants at the University of Bologna,Bologna,Italy.The school will teach attendees how to apply existing methods and empower them to develop new ones in their own research.The basic theoretical notions will be introduced in a rigorous manner,emphasizing examples,applications,and exercises.Scholarships are available.     

三绕组变压器的双绕组等效建模及在Matpower中的应用

针对实际电网存在着大量的三绕组变压器,但国际上一些著名商业软件,如BPA仿真软件、Matpower这一权威潮流计算开源软件,均只提供双绕组变压器模型,限制了其在具有三绕组变压器的电力系统中的应用的问题,潮流计算是自主开发的电力系统各种应用软件的核心模块,因此依托国际权威开源程序进行二次开发,是一种较好的选择。对Matpower要求的数据格式进行了归纳,对变压器的一般的等值电路及带理想变压器的等值电路和带标幺值的等值电路进行了分析研究,提出了三绕组变压器转换为双绕组等效模型的建模方法,使得原先只适应双绕组变压器的潮流计算软件可以适用于三绕组变压器电网的潮流计算;最后以Matpower软件为例进行了案例计算,并用PSASP仿真软件进行对比验证。研究结果证明,所提出的建模方法是有效的。     

On the Relation of Load to Average Gap in the Contact Between Surfaces with Longitudinal Roughness

A computer simulation model for the contact between longitudinally-oriented rough surfaces has been formulated. This model closely duplicates the actual surf ace contact deformation behavior by taking into account the elastic interactions between the asperities. There were no assumptions made about the shapes, or any deformation behavior of the asperities, except for their obeying the laws of elasticity. The plastic deformations on the high asperity peaks were taken into account by setting a ceiling on their contact pressures at the material hardness value. The simulations used real surface profiles which were digitized from unworn circumferentially ground steel surfaces. Each pair of these profiles was mathematically combined to form an equivalent rough profile pressing against an infinitely rigid flat and having the appropriately adjusted elastic modulus. A total of 28 different pairs of profiles were used in the simulations. Each contacting pair was subjected to 30 different load levels and the local contact pressures and deformations were calculated. The contact simulations yielded some important mathematical relationships between parameters, such as the real area of contact, average gap, and average asperity load through statistical curve fitting. Two analytical functions were generated to relate the average load to average gap and the real area of contact to load.     

INTEGRAL EQUATION METHOD＇S APPLICATION IN HOLE-EDGE STRESS OF COMPOSITE MATERIAL PLATE WITH DIFFERENT SHAPED HOLES

The strength of composite plate with different hole-shapes is always one of the most important but complicated issues in the application of the composite material. The holes will lead to mutations and discontinuity to the structure. So the hole-edge stress concentration is always a serious phenomenon. And the phenomenon makes the structure strength decrease very quickly to form dangerous weak points. Most partial damage begins from these weak points. According to the complex variable functions theory, the accurate boundary condition of composite plate with different hole-shapes is founded by conformal mapping method to settle the boundary condition problem of complex hole-shapes. Composite plate with commonly hole-shapes in engineering is studied by several complex variable stress fimction. The boundary integral equations are founded based on exact boundary conditions. Then the exact hole-edge stress analytic solution of composite plate with rectangle holes and wing manholes is resolved. Both of offset axis loadings and its influences on the stress concentration coefficient of the hole-edge are discussed. And comparisons of different loads along various offset axis on the hole-edge stress distribution of orthotropic plate with rectangle hole or wing manhole are made. It can be concluded that hole-edge with continuous variable curvatures might help to decrease the stress concentration coefficient; and smaller angle of outer load and fiber can decrease the stress peak value.     

INDUSTRIAL ENGINEERING AND VISUALISATION-A PRODUCT DEVELOPMENT PERSPECTIVE

Taking the actual project of teaching and researching process for example, the relationship between the industrial engineering and product development is discussed. And use the novel visualization technology to support the industrial engineering and product development. How to use the new computer modeling and simulating technologies to support the product development and industrial engineering, is introduced especially. The support includes both domestic products and industrial systems. The visualization and computer technologies take a very important role in some system or multi-direction modeling, those technologies mentioned above can help the industrial engineers study the effect of design on the whole life circle, including the producing steps. So the engineers can avoid making the wrong decision which may cause bad effects on the whole industrial engineering.     

电站锅炉模糊风险评价方法研究与应用

针对电站锅炉风险等级评价问题,将模糊综合评价技术应用到电站锅炉风险等级评价中。开展了电站锅炉失效影响因素及模糊评价因素的重要程度分析,建立了一套科学合理适于在线评价的电站锅炉风险评价体系,提出了模糊综合评价技术与改进的模糊层次分析法相结合的模糊风险评价方法,利用改进的模糊层次分析法计算了指标体系中各层指标权重。对某一台电站锅炉的实际运行工况影响子因素进行了模糊风险评价,采用模糊合成算子进行模糊综合运算得到电了站锅炉运行工况影响子因素的评价向量。研究结果表明:电站锅炉的运行工况影响子因素的风险评价等级为第6级,失效可能性等级为小,该电站锅炉运行工况良好。     

Non-monotonic material contrast in scanning ion and scanning electron images

30 keV Ga⁺ focused ion beam induced secondary electron (iSE) imaging was used to determine the relative contrast between several materials. The iSE signal compared from C, Si, Al, Ti, Cr, Ni, Cu, Mo, Ag, and W metal layers does not decrease with an increase in target atomic number Z₂, and shows a non-monotonic relationship between contrast and Z₂. The non-monotonic relationship is attributed to periodic fluctuations of the stopping power and sputter yield inherent to the ion–solid interactions. In addition, material contrast from electron-induced secondary electron (eSE) and backscattered electron (BSE) images using scanning electron microscopy (SEM) also shows non-monotonic contrast as a function of Z₂, following the periodic behavior of the stopping power for electron–solid interactions. A comparison of the iSE and eSE results shows similar relative contrast between the metal layers, and not complementary contrast as conventionally understood. These similarities in the contrast behavior can be attributed to similarities in the periodic and non-monotonic function defined by incident particle–solid interaction theory.