复合材料层压板低速冲击损伤的有限元模拟

基于复合材料层压板的低速冲击试验,建立一套“铺层-界面-铺层”的复合材料层压板在低速冲击载荷作用下的有限元模型.通过VUMAT子程序建立复合材料铺层的本构关系,采用应力描述的失效判据来判断层内的各种损伤,并结合相应的刚度折减方案对失效单元进行刚度折减.模型中在相邻两铺层间加入cohesive单元,用来模拟层间界面.     

铝/碳纤维复合材料保险杠轻量化设计

对保险杠进行轻量化设计,并保证碰撞安全性,用铝/碳纤维复合材料替换原保险杠防撞梁钢质材料。分别对保险杠各部分厚度及碳纤维铺层角度进行了设计,确定了铝合金和碳纤维的厚度,探讨了铝合金和碳纤维板的厚度对碰撞性能的影响,通过采用对碳纤维铺层角度优化的方法提高碰撞安全性。通过拉丁超立方采样得到的试验样本,用移动最小二乘法建立近似模型并验证其精度,利用多目标遗传算法对近似模型寻优,确定了碳纤维最佳铺层角度,得到优化后铝/碳纤维复合材料保险杠防撞梁。与原钢质材料的保险杠相比,优化后铝/碳纤维复合材料保险杠质量减轻了36.497%,且满足碰撞安全性要求。     

泡沫夹层复合材料与复合材料层合板低速冲击性能的比较

采用[0°]8,[0°,90°]2s方式铺成的碳纤维增强环氧树脂预浸料作为泡沫夹层复合材料的面板,PMI(聚甲基丙烯酰亚胺)泡沫作为芯材,制得泡沫夹层复合材料(12mm厚);采用相同预浸料和[0°]16,[0°,90°]4s的铺层方式制备了复合材料层合板(2mm厚),对比研究了两种复合材料的低速冲击性能。结果表明:无论是泡沫夹层复合材料还是复合材料层合板,正交铺层结构比单向铺层结构的冲击载荷峰值高,冲击损伤程度小,抗冲击能力好;在两种铺层方式下,泡沫夹层复合材料的抗冲击能力明显优于复合材料层合板的。     

碳纤维复合材料层合板三点弯曲损伤仿真研究

研究碳纤维复合材料在弯曲载荷作用下的失效形式与损伤过程,以预测材料抗外力损伤性能,指导碳纤维复合材料车身结构设计。进行碳纤维复合材料性能试验和三点弯曲试验,获得材料力学性能参数。建立基于Tiebreak算法的碳纤维复合材料层合板三点弯曲有限元模型,与试验对比验证模型的有效性。研究单元划分方式和Tiebreak接触层设置方式对仿真结果的影响规律,实现碳纤维复合材料分层破坏和纤维断裂的复杂失效及弯曲大变形损伤过程模拟。研究结果表明,计算精度与Tiebreak接触层设置相关,层合板弯曲变形的层间裂纹和层内裂纹扩展速度不同且相互影响。     

碳纤维复合材料假脚冲击与压缩强度试验*

碳纤维复合材料已成功应用于假肢领域产品的开发,然而其对冲击载荷比较敏感,受冲击后其强度将会大幅下降。针对一种新型碳纤维复合材料假脚,开展自由落体冲击试验及冲击后压缩强度试验,分析不同铺层参数、不同冲击吸收能量等因素对其冲击损伤及剩余强度的影响规律。结果表明,对于碳纤维复合材料假脚的U形结构件,不同铺层参数对其冲击损伤影响显著,且随着0°铺层含量的增加,试件的冲击损伤面积越来越小,外观损伤越来越轻;随着冲击吸收能量的增加,碳纤维结构件的冲击损伤面积明显增大,剩余压缩强度逐渐降低。对于碳纤维复合材料假脚结构件,在0~16 J的低能冲击范围内,冲击吸收能量与其剩余压缩强度近似呈线性关系。随着0°铺层含量的增加,碳纤维复合材料结构件的剩余压缩强度逐渐提高。     

复合材料层合板低速冲击后压缩破坏的数值模拟

采用软化夹杂法来模拟低速冲击后层合板的压缩破坏。笔者用ABAQUS软件建立冲击损伤的有限元模型,模型将损伤区等效成一个圆形的软化夹杂,研究了不同的损伤深度对冲击后剩余压缩强度的影响;分析了层合板在压缩过程中,各单层的载荷分配情况;并且模拟了复合材料层合板从损伤开始到完全失去承载能力的压缩破坏全过程。计算结果表明:复合材料层合板冲击后的压缩破坏,损伤最早发生在冲击损伤区周围的±45°铺层,主要发生基体压缩损伤;在压缩载荷下,0°铺层主要的损伤形式是纤维的屈曲;90°铺层发生的主要损伤形式也是基体压缩损伤,但损伤的面积较小。     

碳纤维复合材料防撞梁的设计与分析

对某款乘用车的碳纤维复合材料防撞梁进行了研究。对碳纤维铺层进行了设计,通过有限元建模、施加边界条件与载荷,对碳纤维复合材料防撞梁的应力、变形与应力失效因数进行了分析,并对不同碳纤维铺层铺设角度进行了对比。通过设计与分析,使碳纤维复合材料防撞梁在满足要求的前提下,相比铝合金防撞梁质量减轻31.4%。     

层合板低速冲击损伤的数值模拟

为了分析复合材料层合板在冲击载荷作用下,层合板的损伤演化发展情况,结合采用单元失效技术和铺层刚度退化技术建立层合板低速冲击的三维有限元分析模型。在该模型中,当有限元模型中的单元发生某种冲击失效形式时,定义该单元发生部分失效,并将其刚度适当的退化。计算发现冲击背面容易产生基体开裂,并由此导致分层发生,而且靠近冲击背面的界面所产生的分层面积要较靠近冲击正面的界面的分层面积要大;随着冲击能量的增大,分层面积也增大;当冲击能量很高时,铺层内会出现纤维断裂,同时在层合板的边界处也容易出现损伤,计算结果和试验结果吻合。     

不同铺层转角T700/E44 复合材料拉伸强度有限元分析

碳纤维复合材料的失效行为与复合材料内部的应力状态有关,不同铺层转角的单向碳纤维复合材料层合板的性能具有明显差异。文中利用HyperWorks 商用有限元软件建立了T700/E44 复合材料层合板拉伸模型,基于Chang-Chang 复合材料失效模型对不同铺层转角复合材料层合板的 X 向及 Y 向拉伸性能进行了数值模拟分析。研究结果表明,复合材料层合板以45° 铺层转角对称结构层合时,复合材料有着最佳的综合拉伸性能。这对高性能雷达中复合材料部件的铺层结构设计具有重要的指导意义。     

复合材料缠绕压力容器冲击损伤分析

基于复合材料经典层合板理论和冲击动力学理论,采用Chang -Chang损伤准则对受低速冲击后的复合材料缠绕层进行损伤判定,并进行相应的刚度折减,分析复合材料纤维缠绕压力容器在冲击载荷作用下的动态响应和损伤状况.结合动力松弛法分析冲击能量对不同工作压力下复合材料缠绕压力容器抗冲击性能的影响,并对压力容器不同部位的抗冲击敏感性进行了相应研究,预测出压力容器的缠绕层损伤特征和最不利的冲击位置.     

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...     

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.     

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.     

Application of Feature Extraction through Convolution Neural Networks and SVM Classifier for Robust Grading of Apples

This paper proposes a novel grading method of apples,in an automated grading device that uses convolutional neural networks to extract the size,color,texture,an...     

分布动态载荷识别的抗噪处理

针对正交多项式频域法在用多种响应对矩形薄板进行载荷识别中抗噪性较差的问题,综合运用平均法、矩阵预处理和奇异值截断法等方法对之进行改善,并引入空间映射的思想,将该方法的应用范围拓展为复杂的模型.利用仿真算例,证实了该方法具有较好的抗噪性.     

基于MELTAC-N平台的核电厂安全级DCS环网研究与测试

针对工程实践中环网通讯相关问题的处理缺乏理论基础及国产化安全级DCS平台的开发缺乏成熟经验借鉴问题,对基于MELTAC-N平台核电厂安全级DCS环网的软硬件实现进行了研究。提出了安全级DCS环网双环网冗余设计、光切换开关设计等硬件设计方法,以及以RPR协议为基础,采用全数据收发策略的软件设计方法。在CPR1000安全级DCS平台上对安全级DCS环网的可靠性及实时性进行了评价,并进行了容错能力、响应时间及响应时间稳定性测试验证实验。结果表明,基于MELTAC-N平台安全级DCS环网软硬件设计具有较好的容错能力及响应时间稳定性。     

Short-Term Relay Quality Prediction Algorithm Based on Long and Short-Term Memory

The fraction defective of semi-finished products is predicted to optimize the process of relay production lines, by which production quality and productivity ar...     

End-to-End Multiview Gesture Recognition for Autonomous Car Parking System

The use of hand gestures can be the most intuitive human-machine interaction medium.The early approaches for hand gesture recognition used device-based methods....     

The laboratory simulation of abrasive wear

Abrasive wear has long been recognised as one of the most potentially serious tribological problems facing the operators of many types of plant and machinery; several industrial surveys have indicated that wear by abrasion can be responsible for more than 50% of unscheduled machine and plant stoppages. Locating the operating point of a tribological contact in an appropriate operational ‚map’︁ can provide a useful guide to the likely nature and origins of the surface degradation experienced in use, though care must be exercised in choosing the most suitable parameters for the axes of the plot. Laboratory testing of materials and simulations of machine contacts are carried out for a number of purposes; at one level for the very practical aims of ranking candidate materials or surface hardening treatments in order of their wear resistance, or in an attempt to predict wear lives under field conditions. More fundamentally, tests may be aimed at elucidating the essential physical mechanisms of surface damage and loss, with the longer term aim of building an analytical and predictive model of the wear process itself. In many cases, component surface damage is brought about by the ingress of hard, particulate matter into machine bearing or sealing clearances. These may be running dry although, more usually, a lubricant or service fluid is present at the interface. A number of standardised wear test geometries and procedures have been established for both two- and three-body wear situations, and these are briefly described. Although abrasive wear is often modelled as following an ‚Archard’︁ equation (i.e. a linear increase in material loss with both load and time, and an inverse dependence on specimen hardness) both industrial experience and laboratory tests of particularly lubricated contacts show that this is not always the case: increasing the hardness differential in an abrasively contaminated lubricated pair may not always reduce the rate of damage to the harder surface.     

ANGULAR DISTORTION ALLOWABLE VALUE AND ASSESS METHOD OF WELD ON COKE TOWER

A graph as the new engineering method for estimate the safety of bulging deformation of coke tower is proposed. Through stresses analysis of circumferential weld of coke tower and comparing the stresses produced by pressure with heat stress of steady state, residual stress, bending stress produced by both itself weight and wind loads, it showed that the stresses produced by pressure on the angle distortion are the main factor of equivalent stress of the combined stress. After comparing four kinds of stress controlling conditions, the relation to stress with depth of angular distortion, grade of curvature of angular distortion and half of region of angular distortion has been inferred. Graph of deformation allowable value of coke tower for different condition by angular distortion and half of region of angular distortion has been plotted. The five steps for its engineering use have been explained. The lighter the grade of curvature is, the larger of bulge allowance, may be, and the bigger of depth of angular distortion may pose too. For the coke tower with a popular structure of Dg 5 400 mm×28 mm, the result by graph is nearly more than the result of two formulas formed by other research, the error is less than 7.0%. But, the graph can be easily applied to different size of angular distortion.