Simple model for consolidation of metal matrix coated SiC fibre composites

Abstract

A simple approach to modelling the consolidation of matrix coated fibre composites is presented. It employs an existing porous material constitutive model for monolithic materials. It is argued that in the consolidation of metal coated SiC fibres, the deformation primarily occurs in an outer layer of the fibre coating, and the internal core remains undeformed, largely because of the generally hydrostatic compressive loading, and because of the incompressible nature of the material in creep. The consolidation process is therefore not vastly different to that occurs for monolithic metal fibres, and similar equations can therefore be used for the composite consolidation. The constitutive equations have been implemented into general purpose non-linear finite element software within a large deformation formulation by means of two different user subroutines, one providing a general implementation, and the other a cpu time efficient approach. The manufacture and testing of SiC continuous fibre, Ti-6Al-4V metal matrix composite specimens is described and the results of the tests compared with the model calculations, showing that good agreement can be achieved with a simple model. The dependence of volume fraction of fibres and temperature can be introduced empirically through the specification of just two material constants. The model is therefore useful in the development of consolidation processes.     

Effect of dynamic strain aging on fatigue crack growth behaviour of reactor pressure vessel steels

Abstract

Fatigue tests under constant amplitude load were conducted on compact tension specimens of SA533B3 steels with four levels of sulphur content at different temperatures. A modified capacitance type crack opening displacement (COD) gauge was shown to be suitable for fatigue crack length measurement at high temperatures. Test results obtained with different measurement techniques show good consistency. The observation that the Young's moduli measured at a strain rate of 4 × 10^?3 s^?1 for the SA533B3 steels at 150 and 300°C do not decrease with increasing temperature seems to be related to the presence of dynamic strain aging. The fatigue crack growth rates at 150 and 300°C are about two and half times slower than those tested at 400°C because dynamic strain aging prevails at 150 and 300°C. Fractographic examination results suggest that inclusions embedded in secondary cracks enhanced the fatigue crack initiation rather than the fatigue crack growth.     

Corrosion resistance of AA2219 aluminium alloy: electrochemical polarisation and impedance study

Abstract

The addition of copper increases the strength of aluminium, but decreases the localised corrosion resistance of the metal to seawater as the copper containing intermetallics exhibit different electrochemical properties from the matrix. The main requirement of corrosion resistance could be met through the surface modification by removing the copper rich phase. The present work involves investigations of the influence of prior copper removal treatment on the pitting and general corrosion resistance of AA2219 alloy containing a high copper content in different initial thermal tempers. Significant improvement in the pitting and general corrosion resistance after surface copper removal treatment was evident from the results of electrochemical polarisation and the impedance tests. Attempts were also was made to modify the surface further, with a conversion layer of cerium as an alternative to the chromate coating.     

Characteristics of intermediate temperature dynamic embrittlement of age hardenable copper-chromium alloys

Abstract

Copper-chromium alloys exhibit a severe intermediate temperature loss in ductility during uniaxial tensile loading that has the characteristics of dynamic embrittlement. The dynamic embrittlement is characterised by intergranular fracture caused by stress induced ingress of sulphur to the grain boundaries followed by decohesion.     

DELPHI中动态链接库调用之剖析

本文系统介绍了动态链接库(DYNAMICLINKLIBRARY,简称DLL)的基本概念和对DLL的实现原理进行剖析,使我们对DLL文件的内部结构有一个全面的认识,并通过实例描述如何在DELPHI通过编程实现动态链接库调用过程。     

Dynamic and stable reconfiguration of self-reconfigurable planar parallel robots

This paper discusses dynamic and stable reconfigurations of self-reconfigurable planar parallel robots that can be done by coupling and decoupling of two underactuated robots on a horizontal plane. The limbs of the parallel robots are 2R open kinematic chains with their second joints unactuated. Two types of self-reconfigurable parallel robots are considered. One is formed by two limbs, and the other is by a limb and an underactuated robot consisting of two limbs and a platform. Uncertainty singularities enable them to self-reconfigure without additional actuators at their coupling mechanism. In this paper, we propose dynamic contact motion control to move them from an initial contact configuration to an uncertainty singular configuration while maintaining their contact. This paper also considers dynamic stability at their uncertainty singularities as equilibrium and shows that there exist geometrically stable configurations without feedback control, which are useful for decoupling. Experiments with real robots are carried out to verify the effectiveness of the dynamic contact motion control and stability analysis.     

Dynamic perception after visually guided grasping by a human-like autonomous robot

We will explore dynamic perception following the visually guided grasping of several objects by a human-like autonomous robot. This competency serves for object categorization. Physical interaction with the hand-held object gives the neural network of the robot the rich, coherent and multi-modal sensory input. Multi-layered self-organizing maps are designed and examined in static and dynamic conditions. The results of the tests in the former condition show its capability of robust categorization against noise. The network also shows better performance than a single-layered map does. In the latter condition we focus on shaking behavior by moving only the forearm of the robot. In some combinations of grasping style and shaking radius the network is capable of categorizing two objects robustly. The results show that the network capability to achieve the task largely depends on how to grasp and how to move the objects. These results together with a preliminary simulation are promising toward the self-organization of a high degree of autonomous dynamic object categorization.     

Real-time zero moment point compensation method using null motion for mobile manipulators

This paper presents a method to deal with the dynamic stability for a mobile manipulator. Although the system has static stability, manipulation on the moving base or mobile locomotion with a manipulator may cause the system to turn over due to dynamics, so the controller of a mobile manipulator is carefully designed. In this paper, to define the dynamic stability for a mobile manipulator, the zero moment point (ZMP) is used. ZMP is a very useful measure of the dynamic stability. However, if the degrees of freedom of the system are large, the calculation algorithm is very complicated. So, to simplify the calculation algorithm, we define ZMP using the iterative Newton–Euler formulation. Next, a unified approach for the two subsystems, i.e., mobile and manipulator, is formulated using a redundant scheme. To conserve the dynamic stability of the system in real-time, we define the performance index for the redundant system using ZMP. Then, the redundancy resolution problem for optimizing the proposed performance index is solved using the null motion optimization. Finally, the performance of the proposed method is demonstrated by simulation.     

Developing predictive tools for friction stir weld quality assessment

Abstract

This research programme explores predictive tools that assess friction stir weld quality in aluminium alloys through dynamic characterisation. The study focuses on the correlations between dynamic interrogations measures of friction stir welded panels with the weld energy, as welded mechanical properties and the microstructure. 7136-T76 aluminium extrusions were joined at unique weld energies, and to characterise and identify the friction stir welds through non-destructive techniques, theoretical modelling and lab scale dynamic testing were conducted to establish the correlation between the weld energy and the associated spectral characteristics of the beam (natural frequencies/mode shapes). In this non-destructive evaluation study, the modal parameters were measured and were correlated with the friction stir weld microstructure and the physical parameters of the welded components, such as axial and flexural rigidities. The viability of weld parameter identification and weld quality assessment of friction stir welding beams using dynamic interrogation techniques is demonstrated.