A cantilever beam method for evaluating Young’s modulus and Poisson’s ratio of thermal spray coatings

Young’s modulus and Poisson’s ratio for thermal spray coatings are needed to evaluate properties and characteristics of thermal spray coatings such as residual stresses, fracture toughness, and fatigue crack growth rates. It is difficult to evaluate Young’s modulus and Poisson’s ratio of thermal spray coatings be-cause coatings are usually thin and attached to a thicker and much stiffer substrate. Under loading, the substrate restricts the coating from deforming. Since coatings are used while bonded to a substrate, it is desirable to have a procedure to evaluate Young’s modulus and Poisson’s ratio in situ. The cantilever beam method to evaluate the Young’s modulus and Poisson’s ratio of thermal spray coat-ings is presented. The method uses strain gages located on the coating and substrate surfaces. A series of increasing loads is applied to the end of the cantilever beam. The moment at the gaged section is calcu-lated. Using a laminated plate bending theory, the Young’s modulus and Poisson’s ratio are inferred based on a least squares fit of the equilibrium equations. The method is verified by comparing predicted values of Young’s modulus and Poisson’s ratio with reference values from a three-dimensional finite ele-ment analysis of the thermal spray coated cantilever beam. The sensitivity of the method is examined with respect to the accuracy of measured quantities such as strain gage readings, specimen dimensions, ap-plied bending moment, and substrate mechanical properties. The method is applied to evaluate the Young’s modulus and Poisson’s ratio of four thermal spray coatings of industrial importance.     

Tight-binding bond order potential a forces for atomistic simulations

The formalism of a new bond order potential is described in detail, including very recent developments-most notably the implementation of a numerically stable recursive algorithm for obtaining the coefficients of the many-atom expansion. This tight-binding Green’s function method is efficient, the computer time scaling linearly with number of atoms. Technical notes on the proof of the central results and on handling the integration of Green’s functions are attached.     

Anodic behavior of β- and γ-phases of In-Ga alloys in chloride solutions

Anodic polarization curves of indium, tin, and β and γ phases of the In-Sn system in acidic chloride solutions, as well as the partial currents of In and Sn dissolution, the potential (E), and the degree of the alloy’s surface enrichment in tin as the functions of the time of anodic-polarization of β- and γ-phases are analyzed. It is shown that tin, which accumulates on the alloy’s surface, enters into a phase transition with indium producing new phases of high Sn content. Their formation is attributed to reaching the critical Sn concentration in a superficial layer of the dissolving phase. The study is supported by the Russian Foundation for Basic Research (project no. 99-03-32478a).     

On predicting forming limits using hill’s yield criteria

The analysis of localized necking is strongly dependent on the yield function. To predict forming limits, therefore, numerous yield criteria have been postulated to characterize the plastic deformation of sheet materials. Among them Hill’s 1948 and the fourth form of 1979 yield criteria are the most commonly used. A new yield criterion was proposed by Hill in 1993. It uses five independent and easily obtainable material parameters, which makes it flexible in representing the shape of the yield locus for different materials. The present investigation compares these three yield criteria in forming limit predictions based on both the Marciniak and Kuczynski (M-K) approach and the bifurcation analysis. It is observed that the M-K analysis based on Hill’s 1993 yield criterion provides forming limit predictions in agreement with experimental data. The bifurcation analysis based on Hill’s 1948 yield criterion also provides an acceptable prediction of forming limits for aluminum, although they are slightly higher. All three yield criteria are found to provide acceptable predictions for aluminum-killed (AK) steel based on the M-K method. For brass, only the prediction based on the M-K method and Hill’s 1993 yield criterion is close to the trend of experimental data.     

The influence of a water extract of horse chestnut fruit on the corrosion of St3 steel in water

The process of low-carbon steel’s corrosion in water on the addition of a water extract of horse chestnut fruit by gravimetric, electrochemical, and physical-chemical methods, namely, UV and IR spectroscopy and X-ray analysis, was investigated. It was shown that the extraction time and the additives’ concentration appreciably decreased the steel’s corrosion rate to a value of 6.4. The protection degree is estimated to be 84%. A possible mechanism of the inhibition’s action was proposed.     

The Instrumented Indentation Study of HVOF-Sprayed Hardmetal Coatings

Elastic-plastic properties, namely, hardness and Young’s modulus, of four HVOF-sprayed hardmetal coatings were measured by instrumented indentation using Oliver-Pharr method Nanoindenter XP MTS with a continuous stiffness measurement (CSM) module. The results show that with sufficient number of CSM measurements, one can distinguish between indents made in the hard particles and indents made in the binder material. This can be accomplished by analyzing the plots of hardness and Young’s modulus versus load (or versus indentation depth). Further development of the dependence curves enables the load (or indentation depth) to be set to correspond to the point of transition from a single structure component to the composite material and to determine the properties of both. Comparison of results of CSM measurement with the results of single indentation measurement at a defined load reveals a new perspective on the origin of the indentation size effect in hardmetal coatings. The measurements show that the increase in both the hardness and Young’s modulus with decreasing load is caused mainly by the predominant influence of hard particles in the coatings.     

Understanding of Vibration Stress Relief with Computation Modeling

A finite element model was developed to predict weld residual stress and simulate the vibratory stress relief. Both resonant and nonresonant vibration stress relief were studied to better understand the mechanism of vibration stress relief. The effect of process parameters, vibration amplitude and frequency, of vibration stress relief on weld residual stress reduction was investigated with the developed model. It was found that both resonant and nonresonant vibration stress relief can relieve weld residual stresses. For the nonresonant vibration, the stress reduction strongly depends on the vibration’s amplitude. For the resonant vibration, the vibration’s frequency is essential to stress relief. The vibration’s frequency should be close to the structure’s natural frequency for the desired vibration mode.     

Kid geniuses: Fame,fortune, and science fairs

Conclusion In the Jersey City School District, science students are stars—the STS winners and their teacher were showered with gifts from school officials and even given jackets with school letters that are usually worn by athletes. Andrew Yeager, who is director of stem cell transplantation at the University of Pittsburgh Medical Center, would like to see similar attention showered on all scientists. “When we think about how much professional sports figures make, I’m trying to figure out, are we a better country, a better world because of ... people beating Babe Ruth’s record? Don’t get me wrong, I enjoy watching sports and going to games, but shouldn’t we be identifying and shouldn’t we be encouraging accomplishments in things that, maybe not immediately but over time are going to lead to a better world? Better health, better living conditions, newer materials, newer technologies. Isn’t it right, isn’t it appropriate that we should seek out, identify, reward, and encourage the passion for and accomplishment in science and technology?” At least within the world of STS, Siemens Westinghouse, and ISEF, Yearger’s dream is a reality. Maureen Byko is managing editor of JOM.     

Mechanical Properties and Microstructure of VPS and HVOF CoNiCrAlY Coatings

In this study, high velocity oxy-fuel (HVOF) and vacuum plasma spraying (VPS) coatings were sprayed using a Praxair (CO-210-24) CoNiCrAlY powder. Free-standing coatings underwent vacuum annealing at different temperatures for times of up to 840 h. Feedstock powder, and as-sprayed and annealed coatings, were characterized by scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), and x-ray diffraction (XRD). The hardness and Young’s modulus of the as-sprayed and the annealed HVOF and VPS coatings were measured, including the determination of Young’s moduli of the individual phases via nanoindentation and measurements of Young’s moduli of coatings at temperatures up to 500 °C. The Eshelby inclusion model was employed to investigate the effect of microstructure on the coatings’ mechanical properties. The sensitivity of the mechanical properties to microstructural details was confirmed. Young’s modulus was constant up to ~200 °C, and then decreased with increasing measurement temperature. The annealing process increased Young’s modulus because of a combination of decreased porosity and β volume fraction. Oxide stringers in the HVOF coating maintained its higher hardness than the VPS coating, even after annealing.     

Young’s modulus and fatigue behavior of plasma-sprayed alumina coatings

The fatigue behavior and Young’s modulus of plasma-sprayed gray alumina on low-carbon steel substrates were investigated. The investigation of the properties of composites that were defined as “coating-substrate” composites included measurements of the microhardness profile, the residual stress on the top of the coating, and the residual stress profile in the substrate. Fatigue samples were periodically loaded as a cantilever beam on a special testing machine. Failed samples were observed with a scanning electron microscope to determine the failure processes in the coating. The Young’s modulus of the coating was measured by the four-point bending method. Samples were tested both in tension and compression under low (300 N) and high (800 N) loads. The authors’ experiments revealed that the average fatigue lives of coated specimens were nearly two times longer than those of the uncoated specimens. The measurements of Young’s modulus of the coating yielded values that varied between 27 and 53 GPa, with an average value of 43 GPa. Loading in tension caused a decrease in the Young’s modulus of the coating, while loading in compression led to an increase in Young’s modulus. The increase in the lifetime of coated samples was likely due to compressive residual stresses in the substrate, originating during the spray process. The failure of the coating was due to several processes, among which the most important were splat cracking, splat debonding, and the coalescence of cracks through the voids in the coating.     

Synergistic inhibition between Schiff’s bases and sulfate ion on corrosion of aluminium in sulfuric acid

The effect of Schiff’s bases alone and Schiff’s bases with additive Na₂SO₄ on the corrosion of aluminium in H₂SO₄ have been investigated by using weight loss method. The present study revealed that aluminium in H₂SO₄ has been more efficiently inhibited by Schiff’s bases in the presence of additive Na₂SO₄ than Schiff’s bases alone due to the synergistic effect between Schiff’s bases and Na₂SO₄. Inhibition efficiency was found maximum upto 95.02% for aluminium in H₂SO₄ by Schiff’s bases in presence of additive NaNa₂SO₄. The adsorption of inhibitor accords with the Langmuir adsorption isotherm. Results obtained in both the cases indicate the dependence of inhibition efficiencies on the concentration of Schiff’s bases, additive Na₂SO₄ and also on the concentration of H₂SO₄ solution. The results show the increasing trends of inhibition efficiency with the concentration. The article is published in the original.     

Measurement of dynamic young’s modulus for molybdenum disilicide/pentatitanium trisilicide

The PUCOT (piezoelectric ultrasonic composite oscillator technique) has been used to measure the temperature dependence of dynamic Young’s modulus of molybdenum disilicide (M0S12) reinforced with 10, 30, and 50% volume fraction of pentatitanium trisilicide (Ti₅Si₃). The temperature ranges were room temperature to 600 °C for the 30 and 50 % specimens, and room temperature to 880 °C for the 10 % specimens. In all cases, the values of Young’s modulus decreased linearly with increasing temperature, although at different rates. A graph of Young’s modulus versus composition was used to estimate the value of Young’s modulus for MoSi₂. The value obtained (385 GPa) was in excellent agreement with the value of 388 GPa quoted in the literature.     

Fracture of Open-Cell Nickel Foams Under Quasi-Static Tensile Loading

Open-cell nickel foams with average pore size of 600 μm have been subjected to room temperature tensile tests to explore their tensile properties. Using a state of the art extensometer of noncontact type, foam properties as ultimate tensile strength, yield strength, and the Young’s modulus (E) have been measured accurately. The reason behind the usage of this kind of extensometer is to avoid completely any minor deformation that might be caused by the attachment of conventional extensometer to the sample’s surface prior to testing. The function of this extensometer is based on the usage of a laser (CCD) camera that detects and records the dimensional changes as soon as the load is applied. A series of cyclic loading-unloading tests was performed to determine the foam’s Young’s modulus. The fracture behavior of foam cells was observed to be ductile. Complete separation of struts or cell walls took place successively by necking.     

Production engineering for self-organizing complex systems

Today’s models in production engineering are mainly based on quasi-stationary design assumptions. With increasing dynamics, models reflecting the nonlinear characteristics of production are becoming increasingly relevant. Several approaches have been formulated to design self-organizing systems, leading to good results with regards to the efficiency in which dynamics are mastered by local interaction of a system’s entities. While in self-organization a system’s characteristics emerge bottom-up, effectiveness is designed into a system by an analytical, top-down design approach. The paper discusses how a target oriented analytical design approach can be combined with the concept of self-organization and shows its application and impact on practical examples.     

<Emphasis Type="Italic">SpaceShipOne</Emphasis>, the ansari X prize,and the materials of the civilian space race

Conclusion Gregg Maryniak of the X Prize Foundation believes the benefits of the contest will not end when Scaled Composites deposits its $10 million prize in the corporate account. “The reason we put this prize on the table was to ultimately lower the cost of access to space, which has huge societal benefits,” Maryniak said. “We’re surrounded by an ocean of resources that is literally unlimited.” Many of the low-budget Ansari X Prize contenders have visions of a better world where space travel is affordable and accessible-they hope for new sources of energy or water, access to minerals unavailable on earth, speedy medical responses worldwide, and improved telecommunications, for starters. All of these are well in the future, and some may be unrealistic. But James Clark, executive director of World Technology Network, believes the Ansari X Prize extended an invitation to imagine that was long overdue. “The absence of these competitions was in many ways depressing,” he said. “It’s probably better that people are dreaming big again than not.” Maureen Byko is managing editor of JOM. Editor’s Note: A hypertext-enhanced version of this article is available on-line at www.tms.org/pubs/journals/JOM/0411/Byko-0411.html     

Structural properties in flame quenched Cu−9Al−4.5Ni−4.5Fe alloy

The flame quenching process has been employed to modify the surfaces of a commercial marine propeller material, aluminum bronze alloy (Cu−9Al−5Ni−5Fe), and the material’s microstructure and hardness properties have been studied. The thermal history was accurately monitored during the process at various surface temperatures and holding times. XRD and EDX analyses have shown that aboveT _β temperature the microstructure consisting of α and κ phases changes into α and β’ martensite due to an eutectoid reaction of α+β→κ and a martensitic transformation of β→β’. The β’ martensite phase formed has a face-centered cubic (FCC) crystal structure with typical twinned structure. The hardness of the flame-quenched layer having the α+β’ structure is similar to or lower than that of the α+κ structure, depending highly on the size and distribution of β’ and κ phases. It is noted that the sliding wear resistance of the flame-quenched layer is enhanced with the formation of β’ martensite.     

Australian accreditation for engineers—Part II

Conclusion Efforts have been made to ensure that AusIMM’s CPS approach is generally compatible with the corresponding schemes of other relevant Australian professional institutes as well as those practiced in other areas of the world, particularly in North America and Europe. Time will tell if suitable arrangements can be negotiated with overseas bodies to allow mutual recognition of each others’ registration, which should facilitate global working opportunities. Editor’s Note: The first part of this article appears in the January 1997 issue on pages 22–23. M.J. Lawrence is 1999 president elect of the Australasian Institute of Mining and Metallurgy and managing director of Minval Associates Pty Limited, Sydney, Australia.     

Dynamic Young’s modulus and internal friction in polycrystalline copper

An attempt has been made to measure the temperature dependence of dynamic Young’s modulus together with the related variation of internal friction in polycrystalline copper. A mechanical spectroscopy study was employed using a standard servo hydraulic fatigue testing machine equipped with a scanning laser extensometer. Dynamic Young’s modulus and internal friction were measured over a temperature range of 298 to 873 K at very low frequencies of 0.1, 0.05, and 0.01 Hz. One internal friction peak was observed over the ranges 450 to 700 K, together with marked decreases in the dynamic Young’s modulus in the same temperature range. From a quantitative analysis of the experimental data with the relaxation strength, relaxation time, and activation energy, it is concluded that the peak phenomenon is due to grain-boundary sliding relaxation.     

A new approach to determine the wear coefficient for wear prediction of sheet metal forming tools

Accounting for the increase of wear in metal forming tools, it is eminent to have detailed information about the tool lifetime already during the tool design. With the wear simulation tool REDSY—developed at the Institute of Metal Forming and Casting—tool wear can be simulated qualitatively and quantitatively for sheet metal forming processes. The calculations are based on Archard’s wear model, a model using contact mechanics to describe the wear behavior. In this project, a new approach to determine the wear coefficient has been developed using a simple cylindrical cup deep drawing experiment for the wear measurements. Several tool and sheet material combinations were analyzed using a five-stage progressive die tool in a precision automatic punching press in order to achieve a high wear volume in a short period of time. The wear coefficient for the respective material combination could be determined combining the experimental results with simulation. This method is verified by comparing the wear simulation results with actual measurements. This project was funded by Germany’s Bundesministerium für Wirtschaft und Arbeit (BMWA) over Arbeitsgemeinschaft industrieller Forschungsvereinigungen “Otto von Guericke” e.V. (AiF). Project code: AiF14291N.