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In this work, we study the deformation behavior in amorphous/crystalline metallic composites (A/C-MCs) through nanoindentation experiments and molecular dynamic (MD) simulations. The atomic deformation processes in both crystalline (C-) and amorphous (A-) phases near the amorphous-crystalline interface (ACI) are investigated and correlated with the material’s overall constitutive behavior at the microscale. Our major findings are (i) the ACIs enable a co-deformation of the A- and C-phases through “stiffening” the soft phases but “softening” the stiff phases in A/C-MCs through different micro-mechanisms; (ii) there exists an ACI-induced transition zone with a thickness of ~ 10 nm; (iii) the strong coupling between shear transformation zones (STZs) and dislocations can be quantified through carefully designed indentation experiments and simulations; and (iv) the nanoscale MD-simulation-predicted mechanisms can be mapped to the “pop-in” or “excursion” events on the force–indentation depth curves extracted from microscale experiments, although there is a length-scale gap in between.

Statistical fractal characteristics are examined for polymer-based interfaces. Interfacial fracture behavior is modulated via exposure to varying levels of chemical contaminant concentration so as not to affect the initial interface roughness. The results of 1D height–height correlation analysis show a strong correlation between the interfacial fracture toughness and the resulting fracture surface roughness, and a toughness-independent roughness exponent; $$\beta \approx$$ 0.35 ± 0.04, which is the slope of the self-affine domain. The cut-off length scale of the self-affinity is found to scale with interface toughness, and equal the combined length scales of interfacial cohesive length and plastic zone size within the adhesive layer. The reported statistical characteristics of interfacial fracture surfaces is among the first to show the quantitative inter-correlation between interfacial adhesion and the resulting fracture surface roughness. With additional examination of other systems, the observed correlations have the potential to assess the interfacial fracture toughness for a wide range of polymer-based interfaces.

Ductile alloys fail in corrosive environments by intergranular stress corrosion cracking, through interactions between mechanical and chemical processes that are not yet understood. We investigate formation and mechanical effects of metal defects produced by grain boundary corrosion of low-alloy pipeline steel, at conditions of high susceptibility to stress corrosion cracking in the absence of hydrogen evolution. Nanoindentation measurements show local softening near corroded grain boundaries, indicated by significantly reduced critical loads for dislocation nucleation. Molecular dynamics simulations of nanoindentation of bulk iron showed that metal vacancies and not interstitial hydrogen atoms explain the observed critical load reduction. Both the dislocation activation volume and dislocation activation energy for vacancy-charged samples are found to be nearly one-half of that for a hydrogen charged samples. Quantitative agreement with experimentally measured indentation response was found for vacancy concentrations equivalent to the bulk silicon concentration in the steel, suggesting that vacancies originate from oxidation of reactive silicon solute atoms at grain boundaries. The results help explain the chemical mechanism of formation of vacancy defects that may participate in grain boundary degradation in the absence of hydrogen embrittlement environment.

An amorphous/crystalline metallic composite (A/C-MC) integrates metallic glass with crystalline metals in one system. The amorphous-crystalline interface (ACI) in A/C-MCs under deformation absorbs dislocations and may fundamentally change the dilemma that the strength comes at the expense of the ductility of a material. However, the development of such materials is still at a trial and error stage due to the lack of a clear-cut understanding on how the amorphous component become instable when a dislocation-mediated plasticity flows into the glassy phases. To meet this need, here we focus on gaining the physical insights into the dislocation-ACI reaction in A/C-MCs through atomistic simulations. We have (i) digitally resembled an interface structure close to that in experiments by annealing melted metallic glasses at cooling rates as low as ∼ 104 K/s; (ii) correlated the dislocation absorption events with the activation of shear transformation zones (STZs) in A/C-MCs under a plastic shear; (iii) identified the mechanisms responsible for a continuous dislocation absorption-induced instability in glassy phases; (iv) calibrated a set of constitutive relations, kinetic rules, and model parameters that can be used in an effective temperature concept-based STZ theories at the continuum level; and (v) characterized the local stress states ahead of the instability band and lay the macroscopic-level glass instability criterion on a firm atomistic basis. Our major findings are: (a) there exists a nanoscale structure transition at the ACI when the cooling rate in the atomistic simulations is reduced to an experimentally-comparable level; (b) the number of atoms participating in the STZs exponentially increases with the number of dislocations arriving at the ACI at an early stage of the dislocation-ACI reaction, but is linearly proportional to the number of absorbed dislocations at a later stage; (c) the dislocation absorption-induced instability in metallic glasses occurs through a three-stage process, i.e., the activation of STZs in the region between icosahedral (ICO) clusters, the coalescence of newly formed STZs, and then the breakdown of ICOs; (d) the model parameters in the continuum-level constitutive relations and kinetic rules are found to be sensitive to cooling rates; and (e) the local stress states ahead of the instability band in glassy phases map surprisingly well with the Mohr-Coulomb criterion regardless of the applied stress at the macroscopic level. The gained knowledge may provide a pathway of connecting the atomistic deformation physics of an A/C-MC with its overall mechanical performance, which is currently difficult to achieve in laboratory experiments.

A novel experimental configuration was devised to monitor the deformation mechanisms in metallic glasses at the microscopic scale. The experiment is comprised of a wedge like cylindrical indenter while monitoring the evolution of the associated plastic zone, and crack initiation and propagation by a microscopic digital image correlation system. A new algorithm is developed to measure the localized shear strain with the shear band, which found to be in excess of several thousand percent. The deformation within the band and outside the band were resolved and showed very intricate cooperative interactions. The measurements and in-situ observations shed lights on the micromechanisms of deformation in BMG alloys.

This study explores the effect of environmental contamination level on mode-I failure and fracture surface evolution of adhesively bonded composite joints. We examined a common adhesive/adherend material system (Hysol EA9394/Hexcel IM7-G/8552) exposed to a typical aviation hydraulic fluid (MIL-PRF-87257) at varying contaminant concentrations . The macroscopic bond line fracture toughness measurement by double cantilever beam test exhibited a progressive deterioration with increasing contaminant concentration. Even a trace level (3 µg/cm 2 ) resulted in a 15% reduction of average bond line strength and 30% drop in bond line toughness. An Arrhenius-type correlation between interface toughness and contaminant concentration was observed, with potential to predict the bond line toughness deterioration level. Increasing the contaminant concentration changed the fracture surface morphology from ductile-to-brittle failure mode, driven by diminished plasticity within the adhesive layer . Finite element method employing cohesive surfaces was also utilized to rationalize the experimentally observed trends. The combined experimental and numerical results suggest that the bond line contamination deteriorates the interfacial toughness through two mechanisms: (i) weakening the interfacial bonding strength, and thereby reducing the intrinsic interfacial toughness, and (ii) shielding the plastic energy dissipation within the adhesive layer, and leading to a reduction in the overall effective bond line toughness.

In this study, both finite element analysis (FEA) and experimental observations were used to investigate the single CBN grain wear in high-speed grinding of Inconel 718 superalloy. The wear characteristics for each grinding pass were numerically assessed utilizing the tensile and compressive strength limits of the cutting grain. Additionally, stress distribution within the grain, chip formation and grinding force evolution during multiple passes were investigated. The combined experimental and numerical results show that the CBN grain wear has two major modes: the macro fracture on the grain top surface propagating from the rake surface, and the micro fracture near the cutting edges. The resultant tensile stress is the main factor inducing grain wear. The cutting edges will be under self-sharpening due to the grain wear. With multiple micro cutting edges engaged in grinding process, the limited material removal region was divided into different sliding, ploughing and cutting dominant regions. Overall, the ratio of material elements removed by a cutting process ranges from 80% to 20%, and continue to decrease during the grinding process. With a stronger effect of the cutting process, larger fluctuation of the grinding force will commence, however its average value remains below that with stronger sliding and ploughing process characteristics.

Pipeline steels are vulnerable to stress corrosion cracking (SCC) during intergranular corrosion (IGC) at potentials of active dissolution in moderately alkaline carbonate-bicarbonate solutions. Morphology evolution accompanying IGC has not been fully described, despite the relevance of the corrosion geometry to crack initiation. The present article reports a characterization of concurrent morphology and mechanical stress development during the initial stages of IGC of X70 steel in sodium bicarbonate solution, in the potential range of high SCC susceptibility. Morphology was revealed by scanning electron microscope examination of cross sections through the IGC layer, and stress evolution was monitored by curvature interferometry. At potentials in the range of SCC susceptibility, IGC creates triangular wedges of porous corrosion product centered at grain boundary triple junctions. The wedge shape indicates a higher corrosion rate at the grain boundary compared to the grain surfaces. Compressive stress is generated during IGC due to internal oxidation on grain surfaces forming a thin compact corrosion product layer. Polarization at a potential below the SCC range resulted in selective grain dissolution with no internal corrosion product or compressive stress increase. Silicon solute atoms are selectively oxidized into the compact grain boundary corrosion product film.

The mechanical polishing is one of the critical microfabrication processes in semiconductor and a host of other critical industries. There has been a great effort in consumable development (pads, slurries, etc.) to improve the overall polishing efficiency and resulting surface quality. In this study, we explored a unique composite polishing wheel with integration of magnetorheological elastomers (MREs). The proposed design aims to control local contact area and contact pressure during fine polishing process and thereby control the material removal rate with precise adjustment of the magnetic field. Two (Two MRE microstructure) MRE, isotropic and chain structured orthotropic, materials were included in the design. The feasibility of the designed wheel and the workpiece-wheel contact characteristics were tested under compression loading. An experimental setup was designed to apply vertical and horizontal magnetic fields. Digital image correlation technique was utilized to measure the local in-plane strain field around contact region. It was found that addition of MRE inserts can alter the local stress field around the contact area, resulting in a strong modulation with up to three-fold increase of both the contact area and the local pressure distribution. Finite element analysis highlighted the intricate role of the MRE inserts in modulating the local strain field around the contact area, and thereby inducing a concurrent increase in both the contact area and the local pressure distribution under the same nominal macroscopic applied load. The observed demand modulation of the contact pressure is anticipated to have a marked effect on the polishing process and the resulting surface quality.

High-strength low-alloy steels used for oil and gas pipelines are vulnerable to intergranular stress corrosion cracking in moderately alkaline soils. The mechanism of corrosion-induced embrittlement under such conditions is not yet understood. Nanoindentation was used to detect localized degradation of mechanical properties near internal grain boundaries of X-70 steel undergoing intergranular corrosion at active dissolution potentials at pH 8.2. The measurements identified a one-micron thick mechanically-degraded layer with 25% reduced hardness near corroded grain boundaries. It is suggested that the corrosion process may introduce an active softening agent, possibly non-equilibrium lattice vacancies generated by oxidation. Keywords: Intergranular corrosion, Dissolution-induced degradation, Stress corrosion cracking, Grain boundary softening, Nanoindentation

A model is presented for intergranular corrosion (IGC) of nonsensitized low-carbon pipeline steels, in which enhanced grain boundary (GB) oxidation is enhanced by vacancies produced by oxidation of reactive Si atoms. Evidence for vacancy injection at corroding GBs had been provided by recent nanoindentation measurements. Model calculations of IGC evolution controlled by lattice vacancy diffusion are compared to experimental measurements. Realistic dihedral angles of corroded GB grooves are predicted based on a vacancy diffusivity within the range of values expected for bcc iron. The calculations rationalize observations of sharpening of GB grooves with time during corrosion exposures, and show that vacancy diffusion quantitatively accounts for enhancement of IGC by reactive solute atoms, without invoking solute segregation or precipitation at GBs.

Wear and life expectancy of a nickel-electroplated monolayer of cubic boron nitride grinding wheels are characterized based on the wheel surface topological evolution, observed after grinding Inconel 718 super-alloys. The wheel is for surface or cylindrical grinding, and having 250 mm diameter, 10 mm thickness and B40/50 coarse grit size. A unique grit-workpiece interaction process, leading to a non-uniform spatial distribution of the grit wear has been identified. Largest grits have been observed to pullout rapidly, resulting in load redistribution to their surroundings, and leading to the attritious and fracture wear phase. The detailed analysis showed that the stresses on the cutting grits arising from the thermal shock are 3–5 folds those arising from mechanical cutting forces, and reach an order of magnitude differences for the high efficiency deep grinding (HEDG) process. It is also found that the grit wear rate is primarily dependent on the workpiece feed rate rather than the grinding wheel speed. The total wheel life is then constructed as the sum of pullout life (Phase-I) and attritious and fracture wear life (Phase-II). Model predictions for the total wheel life compare well to the experimental observations. This facilitates comparisons of different types of grinding configurations and design space exploration. As an example, the HEDG process is compared to a regular high speed grinding, and it is observed that HEDG configuration can deliver much higher material removal for the same amount of wheel wear.

Matrix-variate distributions can intuitively model the dependence structure of matrix-valued observations that arise in applications with multivariate time series, spatio-temporal or repeated measures. This paper develops an Expectation-Maximization algorithm for discriminant analysis and classification with matrix-variate $t$-distributions. The methodology shows promise on simulated datasets or when applied to the forensic matching of fractured surfaces or the classification of functional Magnetic Resonance, satellite or hand gestures images., Comment: 12 pages, 7 figures

This study explores the probable correlation between degradation in bond line fracture toughness and the changes in the measurable mechanical properties of the adhesive layer due to environmental contamination in adhesively bonded composite structures. Nanoindentation technique is utilized to measure the adhesive Young’s modulus and hardness. The proposed framework utilizes the large scale bridging of interfacial fracture proposed by Tvergaard and Hutchinson (Philos Mag A 70(4):641–656, 1994), for considering the significant contribution of plasticity on the macroscopic bond line fracture toughness. A typical adhesive-adherend material system (EA9394/Hexcel IM7-G/8552) exposed to different contaminants at the same concentration is examined. Hardness measurements showed two distinct effects of contamination on the adhesive material; namely (1) softening and (2) hardening depending on the class of contaminants. In addition, macroscopic mode-I fracture toughness is independently measured by double cantilever beam test. Finite element method employing cohesive zone method is used to rationalize the experimental results and the prospective scaling-laws. The combined experimental results of macroscopic properties and the numerical results of the interfacial properties showed the role of contamination in reducing the plastic dissipation within the bond line and the macroscopic deterioration of the bond line effective fracture toughness. The results showed the existence of a correlation similar to Tvergaard and Hutchinson’s results. However, the results suggest a scaling between the interfacial cohesive fracture toughness and the measurable flow stress. The scaling correlation has the potential to be utilized in assessing the relative trend between different contaminants. While the proposed scaling is verified for a common adhesive-adherend system in aerospace industry, with additional examination of other systems, the proposed scaling law might facilitate the utilization of the perceived non-destructively evaluated indentation hardness to serve as an indicator for the bond line macroscopic fracture toughness.

Paired polishing process (PPP) is a variant of the chemical mechanical polishing process which facilitates defect mitigation via minimization of maximum force as well as effective planarization via profile driven determination of force gradient. The present embodiment of PPP machine employs two polishing wheels, radially spanning the wafer surface on a counter-gimbaled base. The PPP machine is deployed to experimentally investigate the role of the process parameters on the surface roughness evolution, and the effective material removal rate. Two sets of copper and aluminum blanket layers were polished under a range of applied down force, polishing wheel speed and transverse feed rate to examine the scalability of the process parameters for different material constants. The experimental measurements along with the topological details of the polishing pad have been utilized to develop a mechanistic model of the process. The model employs the soft wheel-workpiece macroscopic contact, the polishing wheel roughness and its amplification to the local contact pressure, the kinematics of abrasive grits at the local scale, and the collective contribution of these individual micro-events to induce an effective material removal rate at the macroscale. The model shows the dependence of the material removal on the ratio of wheel rotational to feed speed for the PPP process, in a form of an asymptote that is scaled by the surface hardness of each material. The PPP machine exploits this insight and utilizes an oblique grinding technique that obviates the traditional trade-off between MRR and planarization efficiency.

A new planarization method, chemical mechanical paired grinding (CMPG), is developed by combining strengths of grinding and polishing while avoiding their weaknesses. Surface waviness, a key performance index, is significantly influenced by the induced obliqueness ratio (transverse feed velocity to polishing/grinding wheel velocity) of the CMPG process. The window of planarized wavelengths expanded significantly with increasing obliqueness ratio, while MRR could be enhanced by adjusting rotational speeds of the wheel pair. This endows CMPG with global planarization capabilities, while potentially obviating the MRR vs. planarization efficiency trade-off typical of either fixed abrasive grinding of free abrasive CMP processes.

Inspired by the toughening mechanism of double-network (DN) hydrogels, a soft composite consisting of a fabric mesh and VHB tape layers was fabricated. The composite was as stiff as the fabric mesh, and as stretchable as the VHB tape. At certain compositions, the composite was significantly stronger and tougher than the base materials. The extensibility and toughness of the composite can be attributed to a damage delocalization mechanism similar to that of the DN gels. In the partially damaged regions, the fabric mesh fragmented into small islands, surrounded by the highly stretched VHB tapes. Accommodated by the finite sliding at the interface, the large deformation of the composite is highly non-affine. Just as the DN gels, the coexistence of the partially damaged and intact regions resulted in a stable necking in the composite when subjected to uniaxial tension. The propagation of the necking zone corresponded to a plateau on the stress-stretch curve. During cyclic loading, the composite also exhibited stress hysteresis with almost recoverable strain, similar to that in a DN gel. To rationalize these observations and to better understand the underlying physical mechanism, a simple 1D model has been developed for the damage evolution process in the composite. The predictions of the model have achieved good agreement with the measured properties of the composite of various compositions. Furthermore, the composite itself may also be regarded as a macroscopic model when studying the properties and toughening mechanism of the DN gels.

The Preston equation suggests interoperability of material removal rate (MRR) by either pressure or velocity. Traditionally, planarization is pursued by pressure control. A novel velocity control strategy for a single step on a blanket wafer is recently proposed. The effectiveness of both strategies on patterned wafers is numerically investigated here, using the MIT Mask layout. Superiority is observed to be pattern dependent, scaling with MRR and material choice. However, improved quality at feature scale induces deterioration at the die scale. Scratch generation propensity, which is a micro- or even nano-scale phenomenon, is typically invariant to macro-level control strategies. A mixed control strategy produces better results in terms of finish quality and productivity, by attaining the targeted local and global planarization in less polishing time, compared to individual strategies.

Single crystal sapphire substrates with high quality surface finish and integrity significantly enhance performance and reliability of various microelectronics and LED devices. Traditional Chemical Mechanical Polishing necessitates highly alkaline slurries or ultra-hard abrasives owing to sapphire's ultra-high hardness and chemical inertness. Such trade-off is obviated by utilizing an atmospheric pressure plasma (in He–H 2 O mixture) for chemical action, facilitating higher material removal rate at neutral pH by buffing alone, without abrasives. Plasma induced surface modification is studied by nanoindentation. A 2× improvement in MRR is achieved, and 40× projected. Effects of plasma parameters and polishing conditions on planarization effectiveness are discussed.

This study explores the effect of environmental contamination on the interfacial toughness and strength of polymer-based interfaces. Double cantilever beam, end-notched flexure, and single lap joint tests are utilized to examine the contaminated bond line behavior under different fracture modes. A typical adhesive/adherend material system exposed to a common aviation hydraulic fluid at varying contamination concentrations is examined. The mode-I fracture tests reveal a significant degradation in mode-I fracture toughness and strength with increasing contaminant concentration, whereas mode-II fracture properties are found to be insensitive to the contamination level. To the contrary, single lap joint shear strength exhibits an enhancement with increasing contaminant concentration. Such contradictory result can be attributed to nucleation vs. propagation of interfacial cracks. Contamination weakens the interfacial bonding and thereby reduces the interfacial adhesion while shielding plastic dissipation within the bond line. Whereas, contamination also reduces the plastic flow stress of the bond line and thereby increases local plastic dissipation in the SLJ geometry.

The principals of interfacial fracture mechanics and modified Gibbs adsorption equation are utilized to provide a predictive correlation for the macroscopic (effective) fracture toughness of polymer-based adhesive interfaces, exposed to varying level of contaminant concentration. The macroscopic fracture toughness measurement by double cantilever beam test exhibits a progressive deterioration with the increase of the contaminant surface concentration. The associated variation of fracture surface morphology exhibits ductile-to-brittle failure transition, caused by the contamination-induced suppression of plastic deformation within the adhesive layer. The corresponding intrinsic interfacial surface energy is extracted by finite-element simulation, employing surface-based cohesive elements. The modified Gibbs adsorption equation is utilized to correlate the contamination-induced degradation of the interfacial surface energy as a function of contaminant surface concentration. Interfacial fracture mechanics principals are applied to extend the correlation to the macroscopic fracture toughness of the interface. With additional examination of other systems, the proposed correlation may provide the basis for nondestructive evaluation of bond line integrity, exposed to different levels of contaminant.

In situ surface roughness measurements are used to elucidate size effects on plastic deformation mechanisms in free-standing Cu films with a fine microstructure. Spectral analysis of the surface roughness distribution showed the competing influences of microstructure- and free surface-induced effects on strength and ductility. The measurements show that the free-surface effect on intergranular interactions underlies the reduction in strength and ductility seen with thickness reduction. We find that while microstructure refinement increases film strength, it also serves to limit ductility.

This study explores a probable correlation between the degradation of bond line toughness in adhesively bonded joints and the degradation/changes in measurable mechanical properties of the adhesive layer by indentation hardness due to contamination. The proposed framework utilizes the large scale bridging of interfacial fracture proposed by Tvergaard and Hutchinson (Philos Mag A 70:641–656, 1994). A typical adhesive/adherend material system (EA9394/Hexcel IM7-G/8552) exposed to different contaminants at the same concentration was examined. Nano indentation technique, considered as a non-destructive testing methodology compared to the bond line thickness, was utilized to measure the adhesive mechanical properties. In addition, macroscopic mode-I fracture toughness was independently measured by double cantilever beam test. Finite element method employing cohesive zone method was used to rationalize the experimental results and the prospective scaling-laws. The combined experimental results of macroscopic properties and the numerical results of the interfacial properties suggest a scaling between the interfacial cohesive fracture toughness and the measurable flow stress. While the proposed scaling is verified to a common adhesive-adherend system in aerospace industry, with additional examination of other systems, the proposed scaling law facilitates the utilization of the non-destructively evaluated indentation hardness to serve as an indicator for the bond line macroscopic fracture toughness.

Stress Corrosion Cracking (SCC) is a cracking process observed in metals under tensile stress and corrosive environment. It has been reported as one of the major failure modes in high strength steel pipelines over few decades. This study aims to characterize sub-surface damage, which leads to near surface mechanical property changes during the initiation stage of SCC. The quasi-static and dynamic nano indentation technique, were utilized to resolve the mechanical property variation in the near-surface region. The measurements indicated significant softening and modulus reduction near the grain boundaries. Such findings could further elucidate the underlying deformation mechanisms during the early stage of SCC as a function of degradation level.

Crack closure state is a controlling parameter in Vibrothermographpy testing as well as other Non-Destructive Evaluation (NDE) techniques. The closure phenomenon reduces probability of detection (POD) by reducing the effective crack size. For this reason, understanding and quantifying closure has implications in the field of NDE. Cracks grown under fatigue have unpredictable and diffcult to quantify closure states. We propose a simple model to quantify crack closure and measure residual stress. The analysis is limited to the case of 1D residual loading of a through crack. Extensions can be made to the more applicable semi-elliptical surface crack. This model is introduced to replace the model previously suggested by Renshaw [1]. The model is applied to thermal data taken on rectangular test specimens with fatigue cracks.

A multi-physics model encompassing chemical dissolution and mechanical abrasion effects in CMP is developed. This augments a previously developed multi-scale model accounting for both pad response and slurry behavior evolution. The augmented model is utilized to predict scratch propensity in a CMP process. The pad response delineates the interplay between the local particle level deformation and the cell level bending of the pad. The slurry agglomerates in the diffusion limited agglomeration (DLA) or reaction limited agglomeration (RLA) regime. Various nano-scale slurry properties significantly influence the spatial and temporal modulation of the material removal rate (MRR) and scratch generation characteristics. The model predictions are first validated against experimental observations. A parametric study is then undertaken. Such physically based models can be utilized to optimize slurry and pad designs to control the depth of generated scratches and their frequency of occurrence per unit area.

The interfacial fracture toughness and the adhesion strength of two dissimilar materials are governed by the diffusion interfacial thickness and its mechanical characteristics. A new testing methodology is implemented here to estimate the actual interfacial thickness from a series of nanoindentations across the interface, under the same applied load, with tip radius and indentation depth many times larger than the interface thickness. The bimaterial system used is a semicrystalline polymer interface of isotactic polypropylene and linear low-density polyethylene. The laminate is prepared under a range of diffusion temperature to yield diffusion interfaces of 0 to 50 nm. A numerical relationship is developed using two-dimensional (2D) finite element simulation to correlate the true interfacial thickness, measured by transmission electron microscopy, with the experimentally estimated apparent interfacial thickness, derived from the transition domain of a series of indents across the interface. A range of material-pairs property combinations are examined for Young’s modulus ratio E1/E2 = 1 to 3, yield strength ratio σY1/σY2 = 1 to 2.5, and interfacial thickness of 0 to 100 nm. The proposed methodology and the numerically calibrated relationship are in good agreement with the true interfacial thickness.

A multi-scale model encompassing pad response and slurry behavior is developed to predict scratch propensity in a chemical mechanical planarization (CMP) process. The pad response delineates the interplay between the local particle level deformation and the cell level bending of the pad. The slurry agglomerates in the diffusion limited agglomeration (DLA) or reaction limited agglomeration (RLA) regime. Various nano-scale slurry properties significantly influence the spatial and temporal modulation of the material removal rate (MRR) and scratch generation characteristics. The model predictions are first validated against experimental observations. A parametric study is then undertaken. Such physically based models can be utilized to optimize slurry and pad designs to control the depth of generated scratches and their frequency of occurrence per unit area.

This article reports on the in situ observations of deformation behavior of a metallic glass under a wedge-like cylindrical indenter. The experimental observations for various indenter radii provide information on both macroscopic and microscopic details of the deformation. The deformation zones developed under indenters with different radii that were found to be self-similar and in agreement with the predictions of continuum finite-element simulation with pressure-dependent yielding. There are two types of shear bands being identified beneath the indenter. A set of primary bands is identified as evolving with the process zone front and presents an included angle of 78–80°. The other set of bands evolves at a later stage of loading within the originally formed ones but with a consistently higher included angle of around 87°. Despite the richness of the shear-band details, the macroscopic trends, the force-indentation depth response, and the extent of deformation zones are well captured for this constrained deformation mode by the continuum models that address the onset of yielding only.

The wear of Cubic Boron Nitride (CBN) grinding wheel directly affects the workpiece surface integrity and tolerances. This paper summarizes a combined experimental-modeling framework for CBN grinding wheel life expectancy utilized in both cylindrical and surface grinding. The presented fatigue type model is based on grit pullout mechanism and the associated state of damage percolation. The unique grit-workpiece interaction process leads to a non-uniform spatial distribution of the grit wear. The life expectancy model can be described as a function of the process parameters, grinding wheel geometry and topology, workpiece material properties, etc. The developed modeling framework will greatly enhance the understanding of electroplated CBN grinding wheel wear mechanism.Copyright © 2015 by ASME

This paper reports on the experimental examination of the deformation characteristics near a crack tip in a cyclically work-hardened copper single crystal using a 2D surface scans with nano-indentation. The experimental methodology enables the characterization of the primary deformation field near a crack tip via the modulation of the imposed secondary deformation field by a nano-indentation. In a heavily deformed 4-point bend specimen, the measurements showed an existence of an asymptotic field around the crack tip at a distance of R P 2.5J/r0. The measurements also showed the qualitative details of toughness evolution within the high-gradient deformation field around the crack tip. The nature of dislocation distribution (i.e. statistically distributed vs. distributions necessitated by geometry) around the crack tip is quantified. The measurements indicate the dominance of the geometrically necessary dislocation within the finite deformation zone ahead of the tip up to a distance of R � 3J/r0. Thereafter, it is confined in radial rays coinciding with the sector boundaries around the crack tip. These measurements elucidate the origin of the inhomogeneous hardening and the size dependent macroscopic response close to crack tip. � 2006 Elsevier Ltd. All rights reserved.

An experimental methodology was developed which is simple and yet accurately elucidates the stress-state dependency of the deformation behavior of metallic glasses or similar amorphous systems. The methodology includes in situ observations of the evolution of the deformation behavior of metallic glasses under a cylindrical indenter. The set-up not only collects information on the load–displacement response of the system to the deformation, but also resolves the much-needed information on the temporal and spatial evolution of the shear bands. By employing various indenter radii, the critical shear stress for the nucleation of the shear bands is obtained. Experimental results for a zirconium based metallic glass where found to be consistently independent of the indenter radius and in close agreement with the uniaxial yield values.

A Ti:Sapphire (IR 800-nm) femtosecond (fs) pulsed laser was used to ablate a sputtering grade of silicon carbide (SiC) in an ultra-high vacuum chamber. The laser-induced plasma species were then driven and grown to form 3C-SiC films of about 1 μm thick on single crystal silicon wafers at 20 °C (room temperature) and 500 °C. Scanning electron microscopy, atomic force microscopy, X-ray photoelectron microscopy, X-ray diffraction and nanoindentation were used to characterize the structure, composition, thickness and properties of the SiC films. Results of the femtosecond-pulse laser deposited (fs-PLD) films were compared with those obtained by atmospheric pressure chemical vapor deposition (APCVD) and nanosecond-pulse laser (excimer laser at 248-nm) deposition (ns-PLD). The distinctive features of fs-PLD films are their extremely smooth surfaces, stoichiometry, amorphous structure and low defect density compared to APCVD films, along with better film quality and higher growth rates than ns-PLD films. In addition to film growth studies, a SiC microgripper (to grab 20-μm-sized objects) was micromachined by use of the fs-pulsed laser to demonstrate the utility of ultra-short PLD in SiC-device fabrication.

A scratch intersection based material removal mechanism for CMP processes is proposed in this paper. The experimentally observed deformation pattern by SEM and the trends of the measured force profiles (Che et al., 2003) reveal that, for an isolated shallow scratch, the material is mainly plowed sideway along the track of the abrasive particle with no net material removal. However, it is observed that material is detached close to the intersection zone of two scratches. Motivated by this observation, it is speculated that the deformation mechanism changes from ploughing mode to shear-segmentation mode as the abrasive particle approaches the intersection of two scratches under small indentation depth for ductile metals. The proposed mechanistic material removal rate (MRR) model yields Preston constant similar to those observed experimentally for CMP processes. The proposed model also reveals that the nature of the slurry-pad interaction mechanism, and its associated force partitioning mechanism, is important for determining the variation of MRR with particle size and concentration. It is observed that under relatively soft pads, small particles and low particle concentration, the pad undergoes local deformation, yielding an increased MRR with increasing particle size and concentration. At the other extreme, the intact walls of the surface cells and the connecting cell walls between the surface pores deform globally, resembling a beam or a plate, and a decreasing trend in MRR is observed with increasing particle size and concentration. The predicted MRR trends are compared to existing experimental observations.

The notch strengthening effect is studied experimentally in closed cell aluminum foams. The limit loads, net section strength were found for a set of double-edge-notched (DEN) and single-edge-notched (SEN) specimens loaded in compression. In addition, the evolution of the deformation is monitored through a digital image correlation procedure. The influence of independently varying the net section width, b. and the crack length to width ratio, a/W is examined. The DEN specimens showed notch-strengthening behavior, while the SEN specimens were found to be notch-insensitive. From the plastic deformation measurements the dominant deformation mode for the SEN specimens was found to be a crushing/twinning mode. The constraint imposed on this twinning mode by the DEN geometry leads to the observed notch-strengthening behavior. A phenomenological model is developed to ratiorialize the observed strength enhancement for the DEN-specimens, featuring a dependence on the ligament width to cell size ratio, b/d. (C) 2004 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

A combined experimental and modeling approach has been devised to understand the material removal mechanism during abrasion of ductile copper discs. First, single grit scratch intersection experiments are conducted at the micro-scale (with 1-30 μm depth of cut). This is followed by FEM analysis. Then a simple analytical model is developed, and the model prediction is verified against experimental observations and results from numerical simulations. A characteristic material detachment length is correlated between experimental observations and model predictions. The insights gained from this exercise may be used to develop a mechanistic model of material removal in chemical mechanical polishing (CMP) of ductile materials.

A novel experimental configuration was devised to measure the evolution of the deformation field and the corresponding toughness in solder joints for microelectronic packaging. The utilized material system comprised a ductile layer of tin-based solder encapsulated within relatively hard copper shoulders. The experimental configuration provided pure shear state within the constrained solder layer. Different Pb/Sn compositions were tested with grain size approaching the film thickness. The in-plane strain distribution within the joint thickness was measured by a microscopic digital image correlation system. The toughness evolution within such highly gradient deformation field was monitored qualitatively through a two-dimensional surface scan with a nanoindentor. The measurements showed a highly inhomogeneous deformation field within the film with discreet shear bands of concentrated strain. The localized shear bands showed long-range correlations of the order 2–3 grain diameters. A size-dependent macroscopic response on the layer thickness was observed. However, the corresponding film thickness was approximately 100–1000 times larger than those predicted by nonlocal continuum theories and discreet dislocation.

Molecular dynamics simulations of the nanometric cutting of single-crystal copper were performed with the embedded atom method. The nature of material removal, chip formation, material defects and frictional forces were simulated. Nanometric cutting was found to comprise two steps: material removal as the tool machines the top surface, followed by relaxation of the work material to a low defect configuration, after the tool or abrasive particle has passed over the machined region. During nanometric cutting there is a local region of higher temperature and stress below the tool, for large cutting speeds. Relaxation anneals this excess energy and leads to lower dislocation work material. At high cutting speeds (180 m s−1), the machined surface is rough but the work material is dislocation free after the large excess energy has annealed the work material. At lower cutting speeds (1.8– 18 m s−1), the machined surface is smooth, with dislocations remaining in the substrate, and there is only a small excess temperature in the work material after machining. The size of the chip grows with increasing cutting speed.

The role of a porous pad in controlling material-removal rate (MRR) during the chemical-mechanical planarization (CMP) process has been studied numerically. The numerical results are used to develop a phenomenological model that correlates the forces on each individual abrasive particle to the applied nominal pressure. The model provides a physical explanation for the experimentally observed domains of pressure-dependent MRR, where the pad deformation controls the load sharing between active-abrasive particles and direct pad-wafer contact. The predicted correlations between MRR and slurry characteristics, i.e., particle size and concentration, are in agreement with experimentally measured trends reported by Ouma1 and Izumitani2.

The wear rate of a grinding wheel directly affects the workpiece surface integrity and tolerances. This paper summarizes a combined experimental-modeling framework for life cycle prediction of an electroplated Cubic Boron Nitride (CBN) grinding wheel, typically utilized in nickel-based superalloy grinding. The paper presents an experimental framework to facilitate the formulation of a micro-mechanics based modeling framework. The presented work investigates the topological evolution of the grinding wheel surface and mechanisms of grit failure via depth profiling, digital microscopy and scanning electron microscopy. The results are used to elucidate the statistical evolution of the grinding wheel surface. Different modes of grit failure, including grit attritious wear, fracture and pull out haven been identified. The analysis of the surface topological features indicates a unique grit activation process, leading to a non-uniform spatial distribution of the grit wear. Additionally, single grit pull out experiment has been conducted to assess the residual strength of the grit-wheel interface and the associated state of damage percolation. The experimental results can be utilized in developing a life expectancy model for the CBN grinding wheel to assess the grit mean time to failure as well as grit surface topological evolution as a function of the process parameters.Copyright © 2014 by ASME

By combining the field-stiffening effect of magnetorheological (MR) elastomers and the Euler buckling mechanism, we developed a brush-like magneto-active structure with highly tuneable stiffness. When the applied mechanical load is within a certain range, the effective stiffness of the structure can be tuned by several orders of magnitude with the applied magnetic field. The performance of the structure and its dependence on various synthesis parameters, such as the curing field and filler concentration, were investigated experimentally. It is found that the increase in the critical load for buckling is more than the contribution from the stiffening of the MR elastomer. To unravel the relationship between the stiffness increase and the applied field, a theoretical model with coupled mechanical deformation and magnetic field is established. The prediction of the model agrees well with experimental results. The theory may also be used to model the behaviour of other similar materials, such as MR gels. The MR brush developed in this research holds promise for potential applications in smart structures or devices that require mechanical stiffness to be tuneable in a relatively large range. As the amplification mechanism is independent of the base material, it could be used in conjunction with emerging MR materials for further enhanced performance.