Interface Flaws Research Articles

Delamination resistance of thermal barrier coatings containing embedded ductile layers

Micromechanical models are developed to explore the effect of embedded metal layers upon thermal cycling delamination failure of thermal barrier coatings (TBCs) driven by thickening of a thermally grown oxide (TGO). The effects of reductions in the steady-state (i.e. maximum) energy release rate (ERR) controlling debonding from large interface flaws and decreases in the thickening kinetics of TGO are investigated. The models are used to quantify the dependence of the ERR and delamination lifetime upon the geometry and constitutive properties of metal/TBC/TGO multilayers. Combinations of multilayer properties are identified which maximize the increase in delamination lifetime. It is found that even in the absence of TGO growth rate effects, the delamination lifetime of TBC systems with weak TGO/bond coat interfaces can be more than doubled by replacing 10–20% of the ceramic TBC layer with a metal whose ambient temperature yield stress is in the ∼100–200MPa range.

Evaluating Design Principles for Temporality in Information Technology for Crisis Management

This work evaluates a set of design principles for temporality in crisis management information systems by reflecting on the design principles based on two national crisis management information systems. Interviews were used as data collection method where: crisis managers discussed how the interface supports the design principles, crisis managers demonstrated common tasks in the system, and information from past crisis management activities was used as an indication of how the system is used in actual crisis management. The evaluation indicates that the design principles: 1) can be used to identify interface flaws, 2) can be a foundation for discussing temporality in design, and 3) can be used to explore temporality in general, including temporality found in: work tasks, the crisis context, and the interaction between crisis manager and information system. In addition, the evaluation suggests two new design principles as a complement to the original six principles.

Mode I stress intensity factor estimate for a half-penny shaped crack in a trilayer structure by reduction to a bilayer model

The stress intensity factor (SIF) of a half-penny shaped crack normal to the interface in the top layer of a three-layer bonded structure is obtained by the finite element method for a wide range of parameters. To obtain a simple estimate of the SIF, the method of reduction of an idealized cracked trilayer domain to that of a corresponding bilayer domain has been introduced based on the notion of an equivalent homogeneous material substitution for the two bottom layers. The results obtained are utilized in estimating the SIF of a small crack at the interface in a trilayer structure subjected to an indentation load based on the stress calculations in a corresponding uncracked structure. The simplification method may be useful in predicting brittle failure initiating from interfacial flaws in layered structural components with complex geometries that would normally require extensive computational modeling.

On Failure Mechanisms in Flip Chip Assembly—Part 1: Short-Time Scale Wave Motion

The demand for higher clock speed and larger current magnitude in high-performance flip chip packaging configurations of small footprint has raised the concern over rapid thermal transients and large thermal spatial gradients that could severely compromise package performance. This paper explores coupled electrical-thermal-mechanical multiphysics to evaluate the concern and to establish the knowledge base necessary for improving flip chip reliability. It is found that within the first few hundreds of nanoseconds after power-on, there are fast-attenuating, dispersive stress waves of extremely high frequency propagating in the package. The concepts of high cycle fatigue, power density, and joint time-frequency analysis are employed to characterize the waves along with the various damage modes resulting from the propagation of these short-lived dynamical disturbances in bulk materials and along bimaterial interfaces. A qualitative measure for failure is developed to evaluate the extent of damage inflicted by short-time wave motion. Damages identified in this study are in agreement with physical failure modes commonly seen in industry, thus implying that micron scale cracks or interfacial adhesion flaws initiated at the short-time scale would be further propagated by the coefficient of thermal expansion induced thermal stresses at the long-time scale and result in eventual electrical disruptions.

Arbitrary 3D flaws in electromagnetothermoelastic composites under coupled multiplefields

The arbitrary 3D flaws in fully electromagnetothermoelastic coupled multiphase composites(EMTE-CMCs) under extended electromagnetothermoelastic coupled loads are turned intoa set of extended hypersingular integral equations. Analytical solutions for the extendedsingular stresses, the extended stress intensity factors and the extended energy release ratenear the crack fronts are provided. A numerical method is put forward in which theextended displacement discontinuities are approximated by the product of basic densityfunctions and polynomials. In addition, the relationships between the extended stressintensity factors and the shapes of cracks, the distance between two interface flaws, theproperties of the materials and the electromagnetoelastic coupling effects arediscussed. The effects of flaw orientation, interaction and shielding are analyzed.

Using Surface Deflection for Detection of Interface Damage Between Pavement Layers

ABSTRACT In order to detect interface flaws between bituminous and hydraulic layers of composite pavements, three-dimensional finite element simulations of the deflection under a standard axle load were carried out. The pavement layers are considered as linear elastic and the interface behaviour follows three different hypotheses: perfectly bonded, perfectly smooth and frictional. The load is moved above the flaw and the deflection curve of the pavement surface is registered. The first derivative of this last and the curvature radius are calculated numerically. Different measurement modes under moving loads are considered using either pavement fixed or vehicle fixed sensors during the measurement recording. The presence of an interface flaw does not affect significantly the deflection curve. Inversely, the first derivative of the deflection curve and the curvature radius beneath the wheel load provide suitable indicator of the flaw presence and extension.

A combined integral transform asymptotic expansion method for the characterization of interface flaws through pulsed infrared thermography

This work is devoted to the non-destructive evaluation of materials using stimulated infrared thermography. The proposed approach provides simple analytical solutions to evaluate the lateral extent, and the thickness of a plane flaw in a three-dimensional (3D) heat transfer configuration. It is based on the application of a Laplace transform on the time variable t, then a double Fourier transform on the space variables x and y. Reduction of the models is obtained through an asymptotic expansion method. This mathematical formalism leads to the construction of explicit relationships that are very convenient for quantitative inversion. An experimental validation of the inversion procedures is performed on calibrated carbon-epoxy laminates. A particular attention is dedicated in the second part of this work to the experimental analysis of the impact of the definition of the experimental thermal contrast and the sane (i.e., non-defective) area on the inverted parameters. The analysis is carried out through a comparison between two classical definitions of the thermal contrast and a new method, the DAC contrast, developed recently by our team. The impact of a hyper parameter of the inversion procedures (i.e., the Laplace variable) is also analyzed. Both analyses are illustrated through an experiment aiming to estimate the depths of some calibrated flaws in a CFRP laminate.

Scattering of ultrasonic waves by defective adhesion interfaces in submerged laminated plates

We present an analytical-numerical method to simulate time-harmonic ultrasonic scattering from nonhomogeneous adhesive defects in anisotropic elastic laminates. To that end, we combine the quasistatic approximation (QSA) with a very high-order (tens or hundreds of terms) regular perturbation series to allow modeling of nonuniform interfacial flaws. To evaluate each term in the perturbation series, we use a recursive algorithm based on the invariant imbedding method. It is applicable to solve wave propagation problems in arbitrarily anisotropic layered plates and it is stable for high frequencies. We demonstrate examples of convergence and divergence of the perturbation series, and validate the method against the exact solution of plane wave reflection from a layered plate immersed in water. We present a further example of scattering of a Gaussian beam by an inhomogeneous interfacial flaw in the layered plate. We discuss how results of our simulations can be used to indicate the frequencies and angles of incidence where scattering from potential defects is strongest. These parameters, presumably, offer the best potential for flaw characterization.

Static and dynamic mechanical damage mechanisms in TiC-1080 steel cermets

Mechanical damage mechanisms in TiC-1080 steel cermets were characterized by transmission electron microscopy. Quasi-static failure occurs by blunting of interfacial flaws, and by interfacial cracking, with subsequent propagation into the steel matrix. Dynamic loading induces an additional failure mechanism of transgranular TiC cracking without extension to the steel matrix.

In‐Situ Fiberized Poly(ethylene terephthalate) as a Reinforcement to Poly(propylene) Matrix

AbstractThe reinforced poly(propylene) (PP)/poly(ethylene terephthalate) (PET) in‐situ fiberized composites were prepared by extrusion‐drawing‐injection molding. The influences of PET weight fraction (fw) on the PET fiberization, phase morphology, and mechanical properties of the composites, together with their functional mechanisms were studied by contrast to the normal‐blended materials without drawing. The results show that as the fw rises from 0 to 20%, the number of PET fibers increases, whereas their diameter and dispersity decrease till fw = 15% and then increase, and the number of remained PET particles tends to rise. These changes of PET fiberization and phase morphology with fw were attributed to the consequence of the combined actions of breakup, coalescence, and deformation of the PET dispersed phase in the PP matrix during the extrusion drawing. Correspondingly, the tensile strength (σt) and Young's modulus (E) of the in‐situ composites increase till fw = 15% and then decrease, with maximum gains of σt and E of about 20 and 70% relative to the neat PP, respectively. This σt/fw relation was ascribed to the counterbalanced result between the reinforcing effect of the dispersed phase on matrix and the interfacial flaw effect of two immiscible phases, while the E/fw relation was considered as a representation of the rigidizing effect of the fibers on the matrix being controlled by both their number and diameter.In‐situ PET fibres (PET/PP = 85/15) in an as‐drawn filament.magnified imageIn‐situ PET fibres (PET/PP = 85/15) in an as‐drawn filament.

The role of flaw geometry in thin film delamination from two-dimensional interface flaws along free edges

Delamination from planar interface edge flaws between a thin film and a semi-infinite substrate is examined to determine the roles of flaw width and depth relative to the film thickness. The flaws have curved and straight sections, and the crack front intersects the free edge at a right angle. Three-dimensional finite element models are used to extract local energy release rates and mode-mixity angles along the entire crack front. This paper focuses the crack dimensions required to reach steady state, wherein energy release rates are independent of flaw dimensions along the entire crack front. Results indicate that moderate elastic mismatch, although affecting mode mixity, plays a small role in determining the crack aspect ratios required to reach steady state. For wide cracks, the energy release rate for crack advance into the film interior approaches the plane-strain steady-state value when the half-width of the crack is approximately four times its depth (for cracks whose depths is several times the film thickness). For narrow cracks, the energy release rate near the free edge is significantly greater than the plane-strain steady-state result, and reaches a steady state when the depth approximately 10 times its width (for widths several time the film thickness). The results imply that delamination from wide cracks is reasonably accurately predicted via plane-strain analyses. Conversely, two-dimensional models are incapable of accurately predicting delamination from narrow cracks, which have a tendency to widen into flaws with more balanced aspect ratios (i.e. without growth in the depth direction).

SH-wave diffraction by an interfacial flaw in monoclinic bimaterials

A system of incident, reflected and transmitted plane SH-waves is diffracted by an interface flaw in two dissimilar linearly elastic anisotropic half-spaces. The half-space solids have single planes of material symmetry. These coincide, but the two sets of principal material axes in the common plane have arbitrary orientations with respect to each other and to the interface. Exact transient solutions show the effects of material properties and orientation. Increasing the degree of non-orthotropy causes the maximum and minimum shear wave speeds in each solid to deviate more from the isotropic limit. For a non-orthotropic/isotropic bimaterial, this also causes the dynamic stress intensity factor to decrease, and the factor always falls below the factor value arising for a homogeneous solid with properties identical to those of the isotropic constituent.

Rapid Mode III Interface Flaw Extension: Dissimilar Anisotropic Solids with Largely Arbitrary Orientations of their Principal Material Axes

Two half-spaces are rigidly bonded along a semi-infinite portion of their interface, but separated by a vanishingly-thin flaw along its remainder. They consist of dissimilar elastic solids with single planes of material symmetry. The symmetry planes coincide, but principal material axes of the two solids in the common plane are of arbitrary orientation with respect to each other, and to the interface. Anti-plane shear forces moving on the flaw surfaces are assumed to create steady-state interface flaw extension; flaw and forces move at the same constant speed. Exact solutions for any constant speed show that the interface shear wave speed in each solid is sensitive to material properties and principal axis orientation. The subsonic case is studied in more detail, and the energy dissipation rate is extracted. Calculations when one solid is isotropic show its sensitivity to non-orthotropy and to ratios of the shear moduli and mass densities.

Modeling of 3D transversely piezoelectric and elastic bimaterials using the boundary element method

This paper presents a numerical model for three-dimensional transversely isotropic bimaterials based on the boundary element formulation. The point force solutions expressed in a united-form for distinct eigenvalues are studied for transversely isotropic piezoelectricity and pure elasticity. A boundary integral formulation is implemented for the modeling of two-phase materials. In this study, the stress distributions are computed for a near interface flaw. The influences of the shape and location of the flaw on the the stress concentration are examined. The accuracy of the numerical procedures is validated through selected example problems and comparison studies.

Delamination of Thin Films From Two-Dimensional Interface Flaws at Corners and Edges

This paper details the mechanics governing delamination of thin films driven by thermal expansion mismatch from two-dimensional interface flaws. Two scenarios are considered: (i) the edge of the film is concurrent with the edge of the substrate and (ii) the substrate extends past the edge of the film. Fully three-dimensional finite element models are used to analyze semi-circular interface flaws (along the edge) or quarter-circle interface flaws (at the corner of the film) for both scenarios. Results are presented for energy release rates and mode-mixity along two-dimensional crack fronts. For all cases considered, the crack driving force very close to the intersection of the crack front and the edge of the film is substantially larger than that for the interior portions of the crack front. For a given flaw size, the energy release rate along the entire front is higher when the substrate extends past the end of the film. The stress intensity factors are mixed-mode along the entire crack front; the predictions illustrate that the mode III component comprises a substantial contribution to the crack driving force over a significant part of the crack front. The implications of the results on film delamination is discussed in terms of critical flaw sizes, crack front profiles and the influence of the intersection singularity.

Void nucleation on intentionally added defects in Al interconnects

Void nucleation in passivated aluminum interconnects was studied using high voltage scanning electron microscopy. To test theories about stress-induced and electromigration void nucleation, Ar ions were implanted into Al specimens. The Ar atoms precipitated and formed bubbles that served as nucleation sites with high surface energy. In the implanted samples, voids formed away from the interconnect sidewalls, in contrast to voids in ordinary passivated Al interconnects. The evolution of the void volume was also affected by the reduction in the nucleation barrier. These results strongly support the theory of void nucleation on interface flaws in Al interconnects.

Void nucleation in metal interconnects: Combined effects of interface flaws and crystallographic slip

A micromechanical model of void nucleation in passivated metal interconnection lines is proposed. The model is based on the evolution of stress and strain fields in a two-dimensional model system, obtained from numerical modeling. Interface flaws in the form of debond between the metal and the surrounding dielectric are assumed to exist. A unique pattern of shear stress resolved on the slip systems in the metal line, due to the presence of pre-existing debond, is found. A dislocation slip model is constructed in accordance with the shear mode. The mechanism of crystallographic slip is such that lateral thinning of the metal line at the debond region together with the slip step produced at the edges of debond lead to a net transport of atoms away from the debond area, and a physical void is thus formed. The significance and implications of this proposed micromechanism are discussed.

A spring model for the simulation of the propagation of ultrasonic pulses through imperfect contact interfaces

A spring model for the simulation of the propagation of ultrasonic pulses in arbitrarily complex heterogeneous media is proposed in the framework of the local interaction simulation approach (LISA). The algorithm used allows us to include heuristically additional local interaction mechanisms. In particular, the problem of propagation of pulses across imperfect contact interfaces is considered. A contact quality tensor, which is expected to be connected, although not necessarily in a trivial way, to the bond quality, is introduced directly into the model in order to treat interface flaws, such as delaminations and/or slipping bonds. To demonstrate the applicability of the technique, which is particularly suitable for parallel processing, a few examples of numerical simulation of pulse propagation in media with various kinds of imperfections are presented.

Effect of Substrate Orientation, Roughness, and Film Deposition Mode on the Tensile Strength and Toughness of Niobium–Sapphire Interfaces

The strength and toughness of interfaces between sputter‐deposited polycrystalline niobium films and sapphire substrates with basal and prismatic orientations were measured. The effect of deposition parameters and substrate roughness on these interface properties also was investigated. Substrates of polycrystalline alumina with two different surface morphologies were chosen for studying the effect of interface roughness. The interface strength was measured using a previously developed laser spallation experiment in which a laser‐generated compressive stress pulse in the substrate, upon reflection into a tensile stress pulse from the coating's free surface, pulls the interface apart. The interface toughness was obtained using a controlled delamination technique, in which a residually stressed loading layer was used to buckle the underlying test layer from its substrate. The energy balance in the prebuckeled and postbuckled states provided a direct measure of the interface toughness. These values were independently obtained by another experiment in which well‐characterized, artificially generated, interfacial flaws were loaded using a stress pulse in the laser spallation assembly. The coating's free surface velocity upon crack initiation was related to the critical energy release rate via a numerical simulation. The results of the two toughness experiments conformed to each other and related fairly well to the independently obtained strength measurements.

Void Nucleation in Passivated Interconnect Lines: Effects of Site Geometries, Interfaces, and Interface Flaws

Stress driven nucleation of voids in passivated aluminum interconnect lines is analyzed within the context of classical nucleation theory. A discussion of sources of tensile stress in such lines leads to an upper limit of 2 GPa. Calculations suggest that even at this high stress, nucleation rates are far too low to account for observed rates of voiding. Void formation at a circular defect at the line/passivation interface is then considered. In this case, a flaw on the order of nanometers in size may develop into a void under the imposed stress. These results strongly suggest that void nucleation in aluminum interconnect lines can be controlled by eliminating defects in the line/passivation interface.