Showing papers in "International Journal of Materials and Structural Integrity in 2010"

Approach on thermoelectricity reliability of board-level backplane based on the orthogonal experiment design

Abstract: The objective of this paper is to provide a systematic investigation to orthogonal experiment design of backplane. The thermoelectricity reliability is systematically investigated by using mixed orthogonal array L9 (3, 4) based on orthogonal experimental design. The experiment results show that the wire width and wire pitch have a significant impact on the thermoelectricity reliability of the backplane, while the wire thickness has an unobtrusive effect. A finite element model of backplane is established based on a sample structure. The results show that the maximum stress occurred in the copper wire, which connected with FR-4 and the polyimide.

Wireless and embedded nanotechnology-based systems for structural integrity monitoring of civil structures: a feasibility study

Abstract: Civil structures are prone to continuous and uncontrollable damage processes during their designed service life span. These damage processes are attributed to poor maintenance and aging. To improve safety, a continuous monitoring system is needed. Several inspections methods are available for evaluating the condition of civil structures; however, they are typically employed infrequently due to high cost and time constraints. In this paper, the feasibility of using wireless and embedded nanotechnology-based systems for monitoring of civil structures is presented. As a proof of concept, two types of wireless devices were fabricated and evaluated through a research program to determine if their wireless signals can be used to monitor the integrity of concrete structures. These devices are MEMS sensors designed to monitor temperature and moisture inside concrete material and long gauge nanotube sensors for crack detection. The wireless response of the embedded devices was evaluated and the results are presented herein.

On the relationship of microstructure properties of asphalt mixtures to their constitutive behaviour

Abstract: Asphalt mixtures are composite materials that consist of asphalt binder, air voids and aggregate particles that vary by orders of magnitude in size Most constitutive models of asphalt mixtures are formulated based on macroscopic measurements However, little effort has been spent in the past in determining the relevance of these macroscopic measurements to actual material response at the microstructural level This paper presents an overview of a viscoelastic-viscoplastic model for asphalt mixtures that was developed previously by the authors The model's parameters were obtained in this paper by analysing triaxial repeated creep and recovery tests conducted at different confining and axial stresses The microstructure characteristics of asphalt mixtures were determined by measuring aggregate physical characteristics, three-dimensional orientations of aggregates and air void distribution The relationships of model's parameters with these microstructure characteristics are discussed in this paper The results are used to draw conclusions in regard to the influence of microstructure characteristics on asphalt mixture response in terms of hardening, softening and dilation These results have also provided insight in regard to the suitability of some of the macroscopic measurements in reflecting the actual changes in the material microstructure during deformation

Two-scale modelling of effects of microstructure and thermomechanical properties on dynamic performance of an aluminium alloy

Abstract: Influences of microstructure and properties of an aluminium alloy on resistance to dynamic perforation are predicted using a decoupled multiscale modelling approach. At the scale of individual grains, a crystal plasticity model is developed accounting for finite elastic and plastic deformations, thermal softening and energy storage mechanisms linked to microscopic residual stress fields induced by line defects and second-phase particles. An averaging scheme is invoked to compute macroscopic stress-deformation responses corresponding to various microstructures. The results of the averaging process motivate choices of parameters entering a macroscopic plasticity model, with different parameter sets corresponding to different microstructures. This macroscopic model, with various parameter sets, is in turn used to simulate impact and perforation of a thin plate of the aluminium alloy by a cylindrical projectile. The results provide quantitative assessments of possible benefits of texturing, insertion of strengthening and energy storage mechanisms and enhancement of ductility on performance of the alloy.

Dislocation-based model for predicting size-scale effects on the micro and nano indentation hardness of metallic materials

Abstract: In micro- and nano-indentation tests for evaluating strength and stiffness properties of engineering materials, a commonly observed phenomenon is the dependence of material properties on the indent size, also known as indentation size effect (ISE). The objective of the present work is to formulate a micro-mechanical based model based on dislocation mechanics for predicting ISE from conical or pyramidal (Berkovich and Vickers) indenters and to compare it with the most widely used Nix-Gao model. The key idea proposed here while deriving the model is a non-linear coupling between the geometrically necessary dislocations (GNDs) and the statistically stored dislocations (SSDs) that eventually allows it to simultaneously predict ISE from both micro- and nano-indentations tests on a wide range of metallic materials while the Nix-Gao model fails to do so. The work also presents a method for identifying the length scale parameter from micro- and nano-indentation experiments and also correlates it with the spacing between dislocations and thus gives a physical interpretation of the material intrinsic length scale.

Synthesis and characterisation of sodium trititanate whisker surface Cd(II) ion-imprinted polymer and selective solid-phase extraction of cadmium

Abstract: A new surface ion-imprinted polymer (IIP) was synthesised with sodium trititanate whisker in the presence of Cd(II), chitosan (CTS) and γ-glycidoxypropyl trimethoxysilane (KH-560). The prepared surface IIP was characterised by using FTIR, UV, XRD and SEM. A batch of adsorption experiments were performed to evaluate the adsorption behaviour of Cd(II) using inductively coupled plasma atomic emission spectrometry (ICP-AES). The effects of solution pH and sorbent amount on the extraction of Cd(II) from aqueous solutions were studied. The adsorption kinetics and adsorption isotherm were also obtained. The Langmuir isotherm can fit the experimental equilibrium data. Under the optimum conditions, the value of the adsorption was above 99%, and the maximum adsorption capacity was 52.34 mg/g. In accordance with the parameters distribution coefficient (Kd) and selectivity coefficient (K), the selectivity for Cd (II) of the prepared imprinted polymer was higher than non-imprinted polymer. Finally, the reuse of imprinted sorbent was discussed and showed that it could be reused nine times with about 5.0%-6.0% regeneration loss. The detection limit of 0.024 μg/mL−1 with the relative standard deviation (RSD) of 1.74% (C = 1.0 μg/mL−1, n = 13) of this method was obtained.

On the differences of dynamic localisations between different types of metals

Abstract: This paper presents a numerical study of inelastic localisations in metals after utilising a thermodynamically consistent framework of viscoplastic formulation implemented into a commercial finite element code. The significance of using physically-based flow stress relations, instead of empirical relations, is examined by considering three microstructure-based constitutive equations developed previously for three different crystal types of metals. The same numerical values of material constants are used with a range of loading initial temperatures and velocity impacts. Differences of dynamic localisations between three body-centred cubic metals (niobium, tantalum and vanadium), one fcc metal (OFHC copper) and one hcp metal (titanium) are illustrated and discussed through studying the initiation and propagation of necking and shear bands in a circular bar and simple tension plane strain problems, respectively. Moreover, the effect of initial temperatures and strain rates on dynamic localisations is also scrutinised. Objective results using different mesh configurations are verified as a result of including viscosity in the constitutive models.

Preparation and mechanical property test on Cu/Cr bilayer film

Abstract: The Cu/Cr bilayer film was deposited by RF magnetron sputtering. The elastic modulus and the hardness of the bilayer film were tested by using nanoindenter. The results show that the elastic modulus and the hardness of the bilayer film are different at the difference maximum depth hmax. In the meantime, the result shows the elastic modulus and the hardness of the bilayer film are lower than both of the Cr film and the Cu film. But the hardness is closer to the Cu film. It shows the Cu film has a great influence on the hardness of the Cu/Cr bilayer film.

The effect of atomic force microscope probe size on indentation tests simulated using realistic surface forces

Abstract: The effects of the size and shape of an indenter tip used in a nanoscale indentation test (such as with an atomic force microscope) are studied using realistic, finite-range surface forces to describe the contact and extended-range interaction of the indenter and sample. Sphero-conical indenters with tips ranging from sharp-pointed to very rounded tips (similar to spherical tips) are studied. A continuum Lennard-Jones adhesion potential and a Poisson-Boltzmann exponential repulsion law are used to study adhesive and repulsive-only interactions, respectively. The size of the tip affects the qualitative response for an adhesive surface force potential, with increasingly rounded tips exhibiting a more pronounced jump into contact and a greater overall adhesion. The effects of tip size are less pronounced for pure repulsion.

Dynamic properties analysis and test of SMT printed circuit board assembly

Abstract: In this paper, a SMT-PCB assembly is manufactured with different packaging forms and material parameters. A finite element model is established for analysing the basic dynamic property of the sample based on some simplified treatments in the modelling. In the meantime, the experimental test is developed to test the dynamic response of the SMT-PCB assembly. The comparison between the experimental test and simulation can illustrate the validity of the test and of the modelling method. It builds a basis for future investigation such as fatigue life estimation and structural optimisation for improving the working characteristics. Finally, some suggestions on how to optimise the chip layout and improve its reliability also are discussed.

Laser shock deforming and induced microstructure evolution of austenitic stainless steel sheet

Abstract: The black paint coated austenitic stainless steel sheet ASTM-204L was laser shock deformed by the Nd:YAG laser with the 1,054 nm output wave length and the 20 ns short pulse, when tap water was used as the confinement regime. The macro-deformation of the sheets was examined and the laser induced microstructures' evolution was observed and analysed with the thermo-field emission scanning electron microscope. The experimental results indicate that the plasma detonation wave acted on the sheets' surface upon laser shocking can produce designed deformation when the laser facular is 7 mm dia., the energy density 2 GW cm−2. The microscopic morphology observation reveals that condensed plasma becomes a magma-like shell, which effectively guarantees the shocking effects of the laser beam due to the ethyl-silicate black paint coating and the confinement stratum. The macroscopic deformation mechanism belongs to the uniform plastic deformation in the thickness limit of the test material; however, in the microscopic mechanism, the twin deformation, slipping and stacking faults in austenite grains become dominant. The material grain boundaries have a negative effect on the plastic deformation of steel sheets upon laser shock processing.

Modelling size effects in micro/nano-systems by including interfacial effects in a gradient plasticity framework

Abstract: The effect of the material microstructural interfaces increases as the surface-to-volume ratio increases. It is shown in this work that interfacial effects have a profound impact on the scale-dependent plasticity encountered in micro/nano-systems. This is achieved by developing a physically-based higher-order gradient-dependent plasticity theory that enforces microscopic boundary conditions at interfaces and free surfaces. These non-standard boundary conditions relate the micro traction stress at the interface to the interfacial energy. Application of the proposed framework to size effects in biaxial tension of a thin-film on an elastic substrate is presented. Three film-interface conditions are modelled: soft, intermediate, and hard interfaces.

Lengthscale-dependent modelling of ductile failure in metallic microstructures

Abstract: The purpose of the current work is the application of a recent extension (Reusch et al., 2003a, 2003b) of the Gurson-Needleman-Tvergaard (GTN) model (e.g., Needleman and Tvergaard, 1984) to the simulation of ductile damage and failure processes in metal matrix composites at the microstructural level. The extended model is based on the treatment of void coalescence as a lengthscale-dependent process. In particular, we compare the predictions of the (local) with GTN model with those of the lengthscale-dependent extension for ductile crack initiation in ideal and real Al-SiC metal matrix microstructures. As shown by the current results for metal matrix composites and as expected, the simulation results based on the local GTN model for both the structural response and predicted crack path at the microstructural level in metal matrix composites are strongly mesh-dependent. On the other hand, those based on the current lengthscale-dependent void-coalescence modelling approach are mesh-independent. This correlates with the fact that, in contrast to the local approach, the predictions of the lengthscale-dependent approach for the crack propagation path in the real Al-SiC metal matrix composite microstucture considered here agree well with the experimentally-determined path.

A review on graph isomorphism identification of mechanism kinematic chain for intelligent and digital manufacturing

Abstract: The graph theory is an important method to achieve conceptual design for mechanism. During the process of kinematic structures enumeration using graph theory, isomorphism identification of graphs is an NP-complete problem. So, the graph isomorphism identification is a crucial problem in mechanism creative design. In this paper, some recent literatures are introduced to demonstrate some method to solve this NP-hard problem. These approaches are all proved to be effective in some cases. The purpose of this paper is to provide references and helps for researchers.

Modelling and controlling of critical dimension in semiconductor manufacturing

Abstract: As critical dimension (CD) in semiconductor device is always shrinking, it brings us many difficulties to control it. Since lithography and etch are all pivotal steps of CD, it is critical to identify, manage and minimise the major sources of variation of lithography and etch in the presence of different disturbances. Therefore, in this paper, two linear model predictive controllers (LMPCs) are formulated – the lithography CD controller and the etch CD controller on the basis of presenting a comprehensive study of the advantages and disadvantages of current methods of controlling of CD. The lithography CD controller manipulates multiple inputs – dose and focus, the etch CD controller manipulates etch time and Kalman filtering technologies are used to estimate state variables. The simulations of the two CD controllers designed are performed considering different types of disturbances and a comparison of performance of LMPCs and exponentially weighted moving average (EWMA) is presented. The results show that there is a significant reduction of the effect of the disturbances on CD and the two controllers are flexible and robust controllers with superior control ability to control CD.