Interfacial reaction mode and its influence on tensile strength in laser joining Al alloy to Ti alloy

Abstract

In order to obtain a robust dissimilar joint of Al/Ti alloys, a filler wire of Al–12 wt-%Si and 45° V shape groove on the base metal were used during CO₂ laser welding. Heat input had evident influence on the interfacial reaction mode. It was found that a dissolution mode for low heat input and a melting mode for high heat input exist at the joint interface, which was analysed from thermodynamic point of view. Tensile strength of the joints in the dissolution mode reached as high as 296 MPa, which was significantly higher than that in the melting mode.     

Surface characterization and adhesion of black-oxide-coated copper substrate: effect of surface hardening processes

The effects of surface-hardening processes on the changes in surface characteristics and adhesion of black copper oxide substrate with epoxy resins are studied. Various techniques, namely SEM, XPS, AFM, XRD, Auger electron spectroscopy, contact angle goniometry, D-SIMS and RBS, were used to identify the changes in surface characteristics. Dense, fibrillar cupric oxide crystals characterized the as-deposited oxide coating with high surface roughness. The surface-hardening process flattened and consolidated the fibrils without changing the compositional and thermodynamic characteristics of the coated surface. The surface-hardening process reduced the total thickness of copper oxide by approximately 50–150 nm. The reduction in oxide thickness was not a predominant factor for the reduced bond strength of the surface-hardened coating. The bond strengths of both the as-deposited and surface-hardened black oxide coatings increased with oxidation time, until saturation at about 120–150 s. For the as-deposited oxide coating, mechanical interlocking, high wettability and resistance to surface contamination are the three major sources for improved adhesion, amongst which the enhanced mechanical interlocking provided by the fibrillar cupric oxide is the most important. Surface hardening reduced the efficiency of mechanical interlocking mechanism. There was close functional dependence between the button-shear strength and surface characteristics, such as surface roughness, coating thickness and surface free energy.     

Effect of weld nugget size on overload failure mode of resistance spot welds

Abstract

In the present paper, effects of welding current, welding time, electrode pressure and holding time on the weld nugget size were studied. A failure mechanism was proposed to describe both interfacial and pullout failure modes. This mechanism was confirmed by SEM investigations. In the light of this mechanism, the effect of welding parameters on static weld strength and failure mode was studied. Then, an analytical model was proposed to predict failure mode and to estimate minimum nugget diameter (critical diameter) to ensure pullout failure mode in shear tensile test. On the contrary to existing industrial standards, in this model, critical nugget diameter is attributed to metallurgical characterisation of material (weld nugget hardness to failure location hardness ratio), in addition to sheet thickness. For a given sheet thickness, decreasing H_WN/H_FL increases interfacial failure mode tendency. The results of this model were compared with experimental data and also with the literature.     

Failure mode transition and mechanical properties of similar and dissimilar resistance spot welds of DP600 and low carbon steels

Abstract

The present work addresses the microstructure and mechanical properties of similar and dissimilar resistance spot welds of low carbon steel (LCS) and dual phase steel (DP600). Correlations between the critical fusion zone size required to ensure pullout failure mode, the weld microstructure and the weld hardness characteristics were developed. Dissimilar DP600/LCS spot welds exhibit the lowest tendency to fail in interfacial failure mode. Effects of weld physical attributes and weld microstructure on the peak load and energy absorption of similar and dissimilar DP600/LCS resistance spot welds are analysed.     

31—THE HANDLE AND BENDING BEHAVIOUR OF FABRIC LAMINATES

Certain aspects of the handle of fabric laminates are related to properties of the component fabrics. Particular attention is paid to a theoretical prediction of the bending stiffness of a laminate from the bending and tensile properties of its components. This theoretical stiffness is a minimum value; if, in practice, the observed stiffness is much greater than this, it may generally be assumed that excess of adhesive or of melted foam is the cause. The paper also reports work on other features of the bending behaviour, such as the degree of recovery from bending, and on the shearing behaviour. The work is concluded by a brief study of some faulty laminates.     

16—THE EFFECTS OF HEAT-SETTING ON THE GEOMETRY AND SHEAR BEHAVIOUR OF DACRON POLYESTER-FIBRE AND NYLON FABRICS

An account is given of an investigation of the effects of temperature and tension during heat-treatment on the geometrical configuration and shear behaviour of spun-Dacron polyester-fibre and spun-nylon fabrics. The shear curve is analysed at various stages of deformation, and the jamming effect resulting from heat-setting is demonstrated. The contribution of fabric geometry to shear behaviour is discussed.     

Mode filters and their effectiveness for enhancing colour images

Abstract

Mode filters are less well known than median filters: this is because they are more difficult to implement, and their detailed specification turns out to be less straightforward. However, early success using the 'truncated median filter' implementation suggested that further investigation of their performance would be worthwhile. In particular, performance with colour images was a vital concern which needed to be addressed. In addition, there were questions about the shape and size distortions that this type of filter might be subject to. All these aspects are covered in the present paper. On the one hand, it is shown that performance with colour images is impressive, not merely with regard to the earlier image enhancement application but also for the purpose of noise elimination. On the other hand, the edge shifting properties of this type of filter are similar to those of the median filter, and the mode filter offers no particular advantage in this respect.     

Factors affecting mechanical properties of resistance spot welds

Abstract

The present paper addresses the factors governing the mechanical performance of low carbon resistance spot welds. Correlations among the process parameters (welding current, welding time, electrode force and holding time), physical spot weld attributes and mechanical performance are analysed. Peak load and energy absorption of spot welds during the tensile shear test are used to describe spot welds performance. It is shown that weld nugget size, electrode indentation, failure mode and strength/ductility of the failure location are the main factors affecting peak load and energy absorption of spot welds.     

Simulation and Optimization of Wiped-Film Poly-Ethylene Terephthalate (PET) Reactor Using Multiobjective Differential Evolution (MODE)

The multiobjective differential evolution (MODE), which is an extension of the Differential Evolution (DE), is applied to solve the multiobjective optimization problem (MOOP) of wet film Poly-Ethylene Terephthalate (PET) reactor considering minimization of acid end group and vinyl end group as the main objectives. The objective function is modified to solve five different possible cases. The results show that a Pareto set (a set of equally good solutions) is obtained for the cases when two of the parameters (residence time of the polymeric reaction mass, θ, and the speed of the wiped-film agitator, N) are considered as decision variables, unlike a unique solution obtained using Nondominated Sorting Genetic Algorithm (NSGA). The Pareto optimal front provides wide-ranging optimal sets of operating conditions. And an appropriate set of operating conditions can be selected based on the requirements of the user.     

低信噪比下线性/非线性调频信号距离超分辨

本文研究了应用高分辨阵列处理算法实现雷达距离超分辨问题。利用我们提出的针对线性／非线性调频（ＬＦ ／ＮＬＦＭ）信号的降噪算法,提高了回波信号的有效信噪比（ＳＮＲ）。通过将ＭＯＤＥ算法拓展到色噪声环境中,基于频域处理解决了不同目标速度接近时造成的目标回波强相关甚至相干给超分辨处理带来的困难。计算机模拟表明,本文方法可在低ＳＮＲ下实现多目标的距离超分辨估计,并克服了现有方法在ＳＮＲ门限、回波相干性、计算量等方面的限制。