Applicability of the crack tip element analysis for damage prediction of composite T-joints

The expanding application of polymeric composite materials in the Aerospace industry has led to the extension of its application to other industries such as the marine industry. A typical joint between the hull and bulkhead used in a monocoque structure is known as a T-joint. It consists of composite overlaminates over a shaped fillet to allow the transmission of direct and membrane shear stresses. The CTE (crack tip element) method offers the capability to provide accurate results with minimum computational resources. It is also an excellent damage prediction tool for composite laminates where oscillatory singularity exists at the crack tip. This paper describes the application of the CTE method for damage prediction of the T-joint. Issues involved in the current modeling approach and recommended solutions are discussed.     

Modelling of microstructure evolution during hot rolling of AA5083 using an internal state variable approach integrated into an FE model

Hot rolling, a critical process in the manufacturing of aluminum sheet products, can significantly impact the final properties of the cold rolled sheet. In this research, a mathematical model was developed to predict the through-thickness thermal and deformation history of a sheet undergoing single stand hot rolling using the commercial finite element (FE) package, ABAQUS^™. A physically based internal state variable microstructure model has been incorporated into the FE simulation for an AA5083 aluminum alloy to predict the evolution of the material stored energy and the subsequent recrystallization after deformation is complete. The microstructure predictions were validated against experimental measurements conducted using the Corus pilot scale rolling facility in IJmuiden, the Netherlands for an AA5083 aluminum alloy. The model was able to predict the fraction recrystallized as well as the recrystallized grain size reasonably well under a range of industrially relevant hot deformation conditions. A sensitivity analysis was carried out to determine the influence of changing the material constants in the microstructure model and deformation conditions on the predicted recrystallization behaviour. The analysis showed that the entry temperature was the most sensitive process parameter causing significant changes in the predicted driving force for recrystallization, nucleation density, fraction recrystallized, and recrystallized grain size.     

Structure characterization of switched Ag – metal oxide contact materials

The structural changes of several Ag ‐ metal oxide composites during switching operations were investigated. During the switching operation the contact material is melting and for a short moment (ca.10 ms) the metal oxide particles will be floating in the liquid silver resulting in structural changes. These processes affect the switching performance of contact materials and shall be described in this work. The low hardness of the Ag‐matrix requires careful sample preparation in order to avoid preparation artifacts and to reveal the actual structural features. This was achieved by a final step, in which the polished surface was ion beam etched. The samples will be analyzed by stereography, light microscopy, field emission scanning electron microscopy (FE‐SEM) and electron back scatter diffraction (EBSD). It was found that the structure of a switched material can be divided into four category regions: Firstly, the bulk material, secondly, a very small heat affected zone, thirdly, a broad fusion zone and finally, the surface layer. The fusion zone is characterized by large columnar grains, increasing porosity and oxide agglomeration towards the surface. These structural phenomena can only be revealed by ion beam etching, as will be illustrated by examples of selected contact material.     

Numerical study on the deformation behaviors of the flexible die forming by using viscoplastic pressure-carrying medium

The flexible die forming (FDF) of sheet metal with the aid of viscoplastic pressure-carrying medium (VPCM) is one of the advanced forming technologies for forming complex sheet metal components with large plastic deformation. The technology has been used in industries by employing different VPCMs, the epistemological understanding of the deformation and process behaviors of this process, however, has not yet been fully addressed. In this paper, numerical study is conducted to look into the deformation behaviors of this process by explicit 3D-FE simulation under the ABAQUS platform, in which the counter pressure variations of VPCM is applied via user subroutine VDLOAD and the ductile fracture criterion is implemented by using VUMAT. Three case study parts, viz., barrel, conic and parabolic parts with large Limit Drawing Ratio (LDR) are studied. The comparison between the conventional deep drawing (CDD) and VPCM-based FDF is conducted in terms of wall-thickness reduction, hydrostatic pressure, principal stress distribution and damage factor. The uniqueness and the deformation behaviors of the VPCM-based FDF are then highlighted. The simulation results show that the higher VPCM pressure could result in the higher hydrostatic pressure throughout the process and further resist wall thinning and prevent fracture of the sheet metal. The formability is thus increased significantly.     

燃料电池轿车变速器齿轮强度分析及疲劳寿命计算

燃料电池轿车变速器齿轮由于其工况的特殊性,在齿轮材料、齿轮强度和疲劳寿命上都有很高的要求。论文建立了燃料电池轿车变速器齿轮的三维模型,然后应用有限元法,结合变速器实际载荷特性工况对齿轮的强度进行了仿真计算,最后根据强度计算结果,应用齿轮有限寿命设计理论和方法对齿轮的疲劳寿命进行了计算。     

客车概念设计中的结构优化有限元分析

以实例客车为对象,在客车车身结构概念设计阶段,建立以参数化几何模型为基础的有限元简化分析模型.以提高车身的扭转刚度、降低车身骨架的自重为目标,应用ANSYS软件,对早期结构方案进行了优化分析应用研究.研究表明,方法和结果完全可以用来进行早期结构分析和方案评价.     

氧化的碳化硅颗粒增强铝-镁基复合材料的界面微结构特征

通过FE－SEM（Field Emission-Scanning Electron Microscopy)和TEM（Transmission Electron Microscopy)研究了经高温氧化后的SiC颗粒增强铝镁基复合材料的界面微结构特征。研究表明碳化硅的氧化能够有效抑制铝对碳化硅的侵蚀,其润湿性,基体合金中的Mg与SiC表面的氧化层SiO2极易反应,根据基体合金中Mg的含量形成纳米尺度的MgO或MgAl2O4。     

Topology synthesis of large‐displacement compliant mechanisms

This paper describes the use of topology optimization as a synthesis tool for the design of large‐displacement compliant mechanisms. An objective function for the synthesis of large‐displacement mechanisms is proposed together with a formulation for synthesis of path‐generating compliant mechanisms. The responses of the compliant mechanisms are modelled using a total Lagrangian finite element formulation, the sensitivity analysis is performed using the adjoint method and the optimization problem is solved using the method of moving asymptotes. Procedures to circumvent some numerical problems are discussed. Copyright © 2001 John Wiley & Sons, Ltd.     

Mechanical Properties of Pineapple Leaf Fiber Reinforced Epoxy Infused with Silicon Carbide Micro Particles

Natural fiber composite materials are finding applications in the manufacturing of the nonstructural parts in different areas of aerospace, automobiles…etc. In this study, the effect of addition of silicon carbide (SiC) particles on the mechanical properties of the pineapple leaf fiber (PALF)-reinforced polymer composite is examined using a two-step approach. Finite element analysis was performed to characterize the properties of the equivalent epoxy/SiC matrix. Then, using the equivalent matrix properties, the hybrid composite with the PALF fiber is characterized. It was observed that the infusion of the particles has increased the shear properties of the fiber reinforced composite material significantly.     

Behavior and strength of headed stud shear connectors in ultra-high performance concrete of composite bridges

This study presents an experimental and numerical investigation on the static behavior of headed stud shear connectors in ultra-high performance concrete (UHPC) of composite bridges. Four push-out specimens were tested. It was found that no cracking, crushing or splitting was observed on the concrete slab, indicating that UHPC slab exhibited good performance and could resist the high force transferred from the headed studs. The numerical and experimental results indicated that the shear capacity is supposed to be composed of two parts stud shank shear contribution and concrete wedge block shear contribution. The stiffness increment of a stud in UHPC was at least 60% higher than that in normal strength concrete. Even if the stud height was reduced from 6d to 2d, there was no reduction in the shear strength of a stud. Short stud shear connectors with an aspect ratio as small as 2 could develop full strength in UHPC slabs. An empirical load-slip equation taking into account stud diameter was proposed to predict the load-slip response of a stud. The reliability and accuracy of the proposed load-slip equation was verified by the experimental and numerical load-slip curves.