bluuebunny/crossref_metadata_2025 huggingface dataset:
Characterization of Strain Fields Around Weld Defects
Authors: Chavez S. A. , Deason V. A.
Published: October 2009

Moire interferometry is used as an alternate technique to resistance strain gages in finding full-field, local strain response of weldments to applied loads. The principles of moire interferometry and the experimental set-up are explained. Data from the two techniques are compared, with no major discrepancies. The strain field around a surface defect is analyzed using moire data. It is concluded that the moire technique is useful for obtaining full-field strain data in welds.
Fracture Modes and Low Cycle Biaxial Fatigue Life at Elevated Temperature
Authors: Sakane M. , Ohnami M. , Sawada M.
Published: October 2009

This paper describes the crack growth direction in biaxial low cycle fatigue under combined axial and torsional stresses in hollow cylindrical specimens of type 304 stainless steel at 923 K in air. Three types of crack are identified, namely macrocrack greater than 1 mm in length, subcracks between 0.1 mm and 1.0 mm in length, and microcracks less than 0.1 mm in length. The macrocrack direction as well as that of the subcrack depends on the principal strain ratio but the microcrack is mode I for all the principal strain ranges tested. The connection of the three types of crack is discussed in relation to the surface oxidation. Typical strain stress and criteria for the biaxial low cycle fatigue failure are applied to the experimental data and their applicability is discussed.
Thermodynamic Characterization of Microcrack Dependent Material Response Properties
Authors: Stout R. B.
Published: October 2009

Available experimental data from uniaxial tests are analyzed to estimate values for parameters of a microcrack dependent model of material response. The experimental data on microcrack density evolution during uniaxial deformation were obtained with small-angle X-ray scattering techniques on polymer specimens. The parameters of the microcrack dependent model are the opening and size of the microcracks, a thermodynamic potential for microcrack kinetics that describes energy conditions for microcrack creation, and coefficients in a nonlinear Onsager type relationship to describe rate kinetics of microcrack creation. The Onsager relationship contains a nonequilibrium thermodynamic measure that is the work done per microcrack created minus the thermodynamic energy per microcrack created. Deformation stability concepts of microcrack dependent material response are discussed in terms of mechanical stability, thermodynamic stability, and global or system stability of the uniaxial test.
Redundant Deformation Factor Evaluation Through the Stress-Strain Curves Superposition Method in Round Section Bar Drawing—Experimental Results
Authors: Cetlin P. R. , Marcos J. L. N.
Published: October 2009

Based on a previous literature analysis of the stress-strain curves superposition method for the evaluation of the redundant deformation factor φ, an experimental program is proposed and carried out for SAE 1018 steel. The method is applied for tensile and compressive testing, and for multiple and single passes up to 30 percent logarithmic strains. For single passes, results for tensile testing were reasonably in accordance with those in the literature. For multiple passes, work hardening was higher for 2 or 3 passes than for 1 pass, contrarily to results for Copper in the literature. Compression testing should not be used for φ evaluation if one wants to obtain φ values similar to those in the literature.
Experimental Verification of the Similarity of Dynamic Compaction Processes of a Copper Powder Medium in Dies of Elementary Shapes
Authors: Miyagi Kiyohiro , Sano Yukio , Hayashi Takuo
Published: October 2009

The similarity of dynamic compaction processes was investigated theoretically and predicted in our previous report, where powder media in a die were assumed to be of a simple type, and the punch and plug to be rigid bodies. The predictions were based on a set of one-dimensional equations and a set of nondimensionalized one-dimensional equations. The objective of this study is to examine the similarity experimentally and to present the results of compaction experiments in order to verify the existence predicted. The experiments were carried out on a copper powder medium in dies having inner cross-section in elementary shapes such as circle, square and triangle. The pressure of the medium at a point contacting the end of the plug, the density distribution and mean density of the green compacts were measured in the experiment. From the analysis of the experimental data the validity of the dynamic similarity theory was demonstrated and the similarity was verified to exist despite the differences in size and shape between the dies used, which implies that the copper powder medium in the dies of elementary shapes is of a simple type. Relations between the density and the shape coefficients showed that the density reached maximum as the coefficients decreased approaching a certain point with a decreasing influence of the die wall friction, while past that point, contrary to the prediction by the theory, it began to decrease due to an increasing influence of the elastic deformation of the punch and plug.
The Influence of Microstructure on Tensile Properties of an Aluminum-Lithium Alloy
Authors: Srivatsan T. S. , Meyers C. W.
Published: October 2009

The double ligament tensile (DLT) test was used to evaluate the tensile properties and anisotropy of a lithium-containing aluminum alloy in the three orthogonal directions of the wrought ingot metallurgical plate. In order to minimize uncertainties associated with results obtained from this test comparisons are made with results obtained from the conventional tensile test. Variation in tensile properties with direction of stressing are discussed in terms of the specific role of specimen size and configuration, and intrinsic microstructural features.
A Finite Element Study of Flat Rolling
Authors: Hwu Yhu-Jen , Lenard J. G.
Published: October 2009

Using an Eulerian formulation, a finite element solution for the flat rolling problem is presented. Calculations are performed to establish the effects of roll deformation and of the variation of the coefficient of friction in the roll gap on the predictive capabilities of the model. Comparison to the data of Al-Salehi et al. (1973) and Shida and Awazuhara (1973) indicates that the differences between measurements and calculations decrease when the above-mentioned effects are accounted for.
Transient Thermal Load Effects on Coatings Bonded to Cylindrical Substrates and Containing Circumferential Cracks
Authors: Kokini K. , Hornack T. R.
Published: October 2009

The effect of a transient thermal load on a coating which is bonded to a cylindrical substrate is analyzed using fracture mechanics by considering the presence of a circumferential edge crack normal to the inner boundary of the coating. The solution is obtained using the finite element method and is compared to the exact solution of the problem. The analysis is then used to show that smaller heat transfer rates at the boundary result in smaller stress intensity factors. For three different materials combinations, including two ceramic coatings on metal, the nondimensional stress intensity factor has a similar magnitude for short crack lengths, but varies appreciably as the crack length becomes longer. It is also determined that inner coatings result in smaller or comparable stress intensity factors than thicker ones.
Interfacial Stress Singularities at Free Edge of Hybrid Metal Matrix Composites
Authors: Lau C. W. , Delale F.
Published: October 2009

Novel hybrid-matrix composites with alternating metallic matrices of different plastic flow resistance offer excellent potential for a superior strength and toughness combination than traditional monomatrix composites. The local stress concentrations in this class of composites can be controlled by proper tailoring of the metal matrices. The free edge accentuated stress state which govern inter-matrix interfacial cracking in such hybrid metal matrix composites has been solved. Determined through asymptotic expansion and numerical methods, the local decohesion stress, σθθ, is found to be always positive for far field tensile loading. The power of the stress singularity is found to depend on the ratio of the plastic resistances of the two matrix metals. A larger difference in resistance to onset of plastic flow between the two matrix metals leads to stronger stress singularity. The work hardening behavior of the matrices also affects the power of the stress singularity. At the limit, the interfacial stress becomes nonsingular for non-workhardening matrices. Detailed results of both the power of the stress singularity, and its angular variation have been determined for a range of matrix combinations.
A Modified Universal Slopes Equation for Estimation of Fatigue Characteristics of Metals
Authors: Muralidharan U. , Manson S. S.
Published: October 2009

Using extensive data on forty-seven materials including steels, aluminum, and titanium alloys, a new equation has been derived for estimating fatigue properties from simple tensile data at the temperature of interest in the sub-creep range. Compared to the Universal Slopes Equation previously proposed by Manson and Hirschberg, the new equation provides predictions that agree more closely with the measured fatigue properties over the entire life range. The earlier Universal Slopes Equation now in common use involves only ductility in the estimation of the plastic line whereas the improved equation involves both tensile strength and ductility in the estimation of the plastic line. A new equation was also derived for a large class of materials suitable for use in the cryogenic temperature range (ten different structural alloys and metals tested at liquid helium and liquid nitrogen temperatures). Here, as in the original Universal Slopes Equation, the plastic line did not require a tensile strength term. Although new constants were derived for the cryogenic range, the final predictions provided about the same degree of accuracy as the original Universal Slopes Equation.
Microcracking in Polycrystalline Solids
Authors: Laws N. , Brockenbrough J. R.
Published: October 2009

A polycrystalline brittle solid may undergo grain boundary micro-cracking due to residual stresses or applied load. This paper contains some results pertaining to the loss of macroscopic stiffness of such solids when all micro-cracks are open and when some may be closed and be subject to frictional sliding. Two specific models are investigated: first micro-cracking on the grain boundaries of a regular hexagonal array, second, micro-cracks which are randomly located and oriented. It is shown that for many purposes the two models give identical results. The paper concludes with some analysis of the possible toughening due to process zone micro-cracking at the tip of a macroscopic crack. It is found that toughening can only occur if the saturation crack density is very large.
Surface Displacement Analysis of the Transformed Zone in Magnesia Partially Stabilized Zirconia
Authors: Cox B. N. , Marshall D. B. , Kouris D. , Mura T.
Published: October 2009

The utility of surface displacement measurements as a source of quantitative information about subsurface plastic deformation is illustrated by analysis of the transformed zone in magnesia partially stabilized zirconia (Mg-PSZ). The surface displacements are derived from partial fringe analysis of optical interference micrographs. Their interpretation is based on analytical and numerical calculations of the surface displacements generated by a transforming semi-ellipsoidal in-homogeneity at the surface of a half-space. Inhomogeneous transformed zones, i.e., those possessing nonuniform distributions of transformation strain, are modeled as linear sums of nested, uniformly transforming semi-ellipsoids. It is found that the transformed zones around either through cracks or small, surface-breaking cracks in Mg-PSZ are indeed inhomogeneous. The degree of transformation is near the maximum possible only within a few microns of the crack plane. It falls away linearly or faster as the distance from the crack plane increases. Qualitative evidence suggests furthermore that significant net shear transformation persists near the crack plane. These conclusions are consistent with phase analysis using Raman spectroscopy.
Analysis of Transient Heat Conduction in Complex Shaped Composite Materials
Authors: Nomura Seiichi , Haji-Sheikh A.
Published: October 2009

This paper addresses a generalized analytical procedure for transient heat conduction in composite materials of two- and three-dimensional finite region. The Galerkin method is employed to obtain temperature field in closed form with the utilization of symbolic algebra software such as REDUCE or MACSYMA. It is found from illustrative examples that the proposed method yields accurate and effective predictions of temperature fields for which purely numerical methods such as finite element or finite difference are not suitable.
Thermo-Viscoelastic Response of Graphite/Epoxy Composites
Authors: Lin Kuen Y. , Hwang I. H.
Published: October 2009

The thermo-viscoleastic behavior of composite materials is studied analytically using a special finite-element formulation. Numerical results on stress and deformation histories are obtained for both unnotched and notched graphite/epoxy composites subjected to mechanical and thermal spectrum loads. The results indicate that time-dependent effects are important in composites with matrix-dominated layup orientations. Such effects also strongly depend on the specific environment condition and load spectrum applied.
Nonlinear Vibration of Laminated Composite Plates in Hygrothermal Environments
Authors: Gandhi Mukesh V. , Usman Mohammad , Chao Luping
Published: October 2009

This paper addresses the phenomena of nonlinear vibration of moderately thick laminated composite plates in hygrothermal environments. The shear-deformable plate theory is modified to account for midplane stretching due to large deflections, large rotations, and dimensional and constitutive changes due to moisture-induced swelling effects and temperature-induced expansions and contractions. The in-plane hygrothermal dimensional changes are accounted for by introducing fictitious forces and moments, and the hygrothermal dimensional changes along the thickness of the plate are explicitly incorporated in the assumed form of the deformation field. The free vibration of a cantilevered laminated composite beam in hygrothermal environments is discussed as an illustrative example to demonstrate the applicability of the proposed methodology. It is anticipated that this work will be significantly relevant to applications in the defense, aerospace and manufacturing environments, where severe variations in the moisture and temperature conditions may be encountered.
Degradation of Graphite-Epoxy Due to Electron Radiation
Authors: Herakovich C. T. , Fox D. J. , Sykes G. F.
Published: October 2009

Experimental results are presented showing that electron irradiation has a variable effect on the properties of graphite-epoxy depending upon the test temperature and the property of interest. In general, compression properties are improved at cold temperature and degraded at elevated temperature. With the exception of some moduli, tensile and shear properties are degraded at both cold and elevated temperatures. Electron irradiation lowers the glass transition temperature of graphite/epoxy significantly. Property degradation of irradiated materials at the elevated temperature is associated with the reduction in Tg. It is shown that a [0] compression strength test is the most sensitive test for exhibiting the effects of electron irradiation. Results from tests on neat resin also show that the bulk matrix is degraded after irradiation and that the correlation between resin and composite response is good.
Hygroscopic Effects in Aramid Fiber/Epoxy Composite
Authors: Hahn H. T. , Kim K. S.
Published: October 2009

Hygroscopic effects in aramid fiber composites are assessed semi-empirically using a combination of micromechanics models and experimental data. It is pointed out that the in situ moisture concentration of the fiber should be known as it affects diffusional as well as expansional properties. The micromechanics models for moisture absorption indicate that the in situ moisture concentration is lower than the bulk value. The interfacial radial stress can be tensile in wet unidirectional composites, and ply cracks are shown to increase moisture diffusion in laminates.
The Effect of Hygrothermal Histories on Matrix Cracking in Fiber Reinforced Laminates
Authors: Rothschilds R. J. , Ilcewicz L. B. , Nordin P. , Applegate S. H.
Published: October 2009

Environmental factors that affect matrix cracking in composite laminates include temperature, moisture content, and hygrothermal history. Matrix cracking in laminates exposed to aircraft environments was modelled using a fracture mechanics approach based on strain energy release rates. Residual stress relaxation due to hygrothermal history was found to alter the static mechanical strain necessary to cause matrix cracking in experiments. Depending on material type and hygrothermal history, this effect was shown to either increase or decrease the resistance to matrix cracking. Close agreement between predicted and measured strains at the onset of matrix cracking was obtained using a modification to the fracture mechanics approach. Viscoelastic stress relaxation was modelled as shifts in the stress free temperature. This approach seems feasible providing that matrix crack growth is an elastic phenomena. Matrix crack growth in laminates subjected to creep loads and severe environments may require the development of viscoelastic failure criteria.
Hygrothermal and Strain Rate Effects on Properties of Graphite/Epoxy Composites
Authors: Daniel I. M. , Yaniv G. , Peimanidis G.
Published: October 2009

A unidirectional graphite/epoxy material was characterized at strain rates ranging from 5 × 10−6 to 5 s−1 under various hygrothermal conditions. A time-temperature-moisture equivalence principle was applied to obtain master curves for the longitudinal, transverse and in-plane shear moduli and corresponding strengths and ultimate strains of the unidirectional graphite/epoxy. It was found that, except for the longitudinal modulus which shows a slight increase with strain rate, temperature and moisture, all other longitudinal properties in general remain unchanged. All matrix dominated properties, i.e., transverse and intralaminar properties, decrease with increasing temperature and moisture content for a fixed strain rate. The transverse and in-plane shear moduli increase with strain rate. Transverse ultimate properties show a trend reversal with a local maximum. The in-plane shear strength increases noticeably, but the ultimate shear strain decreases slightly with strain rate. The time-temperature-moisture shift function is expressed as a function of two variables, temperature and moisture, allowing interchangeability of the three parameters, time, temperature and moisture content.
Temperature-Dependent Dynamic Mechanical Properties of Polymeric Laminated Beams
Authors: Lee C. Y. , Thompson B. S. , Gandhi M. V.
Published: October 2009

Polymeric composite laminates are being increasingly employed to fabricate parts which must be designed to operate successfully in dynamic mechanical environments under various temperatures. Current computer-aided design tools are, however, generally restricted to the modeling of these materials at ambient room temperatures. In order to develop a set of experimental data for evaluating the predictive capabilities of new computer-aided design tools for predicting the elastodynamic response of engineering structural components operating under different temperature regimes, an experimental program was undertaken to study the elastodynamic response of E-glass/Epon cantilever specimens and AS-4 graphite/Epon cantilever specimens subjected to discrete ambient temperatures in the range of −10°F to 300°F at a constant relative humidity of 75 percent. Design charts demonstrating the variation of damping and the dynamic longitudinal elastic modulus were then plotted as a function of temperature for these specimens.
Mechanical Properties of Discontinuous SiC Reinforced Aluminum Composites at Elevated Temperatures
Authors: Nieh T. G. , Xia K. , Langdon T. G.
Published: October 2009

High temperature mechanical properties of discontinuous, whisker and particulate, SiC reinforced aluminum composites, including 2124 and 6061 alloy matrices, are reviewed. It is shown that the behavior of these composites is similar to conventional oxide dispersion strengthened alloys. Namely, they exhibit a low strain rate senstivity and a high apparent activation energy for creep deformation. Despite the fact that the addition of SiC significantly improves the mechanical properties of aluminum at room temperature, the mechanical strength of the composite at elevated temperatures is dominated by the strength of the aluminum matrix This is because the SiC dispersoids are, in general, too coarse and they are not effective barriers for dislocation motion. It is also demonstrated that SiC particulate composites are less creep resistant than SiC whisker composites.
Thermally Induced Twist in Graphite-Epoxy Tubes
Authors: Hyer M. W. , Rousseau C. Q. , Tompkins S. S.
Published: October 2009

This paper discusses an analytical and experimental study to investigate the thermally induced twist in laminated angle-ply graphite-epoxy tubes. Attention is focused on balanced laminates which, contrary to intuition, exhibit twist when the temperature is changed. The twisting is due to the fact that in tube a lamina with a + Φ orientation and a lamina with a − Φ orientation must be at slightly different radial positions. The lamina with the greater radial position determines the sense of the twist. Classical lamination theory does not predict this phenomenon and so a more sophisticated theory must be employed. This paper outlines such a theory, which is based on a generalized plane deformation elasticity analysis, and presents experimental data to confirm the predictions of the theory. A brief description of the experimental apparatus and procedure used to measure twist is presented.
Effects of Thermal Cycling on Properties of Carbon Fiber/Aluminum Composites
Authors: Kyono Tetsuyuki , Kuroda Etsuro , Kitamura Atsushi , Mori Tsutomu , Taya Minoru
Published: October 2009

Effects of thermal cycling on mechanical properties such as longitudinal tensile strength, interlaminar shear strength and work of fracture of carbon fiber/aluminum composites have been investigated. The composite specimens fabricated by a squeeze casting technique were thermally cycled in fluidized baths between room temperature and various temperatures (250, 300, and 350° C) for up to 1000 cycles. The cross sections and fracture surfaces were examined to clarify the degradation mechanism. Significant degradation of the mechanical properties by thermal cycling was observed in untreated carbon fiber/aluminum composites whereas much less degradation in surface treated carbon fiber/aluminum composites. Microscopic observations and short beam shear tests have indicated that the degradation of mechanical properties is caused by debonding at the fiber/matrix interface. The fiber/matrix interface for surface treated fiber was more resistant to debonding. It is concluded that thermal cycling damage of carbon fiber/aluminum composites can be minimized by increasing their fiber/matrix bond strengths.
Thermal Stresses and Thermal Expansion Coefficients of Short Fiber Composites With Sliding Interfaces
Authors: Jasiuk I. , Mura T. , Tsuchida E.
Published: October 2009

The paper analyzes thermal stresses and effective thermal expansion coefficients of the composites in which the fiber-matrix interface is allowed to slip. Thermal stresses are evaluated by introducing an eigenstrain in the fibers, which corresponds to the strain due to the mismatch of thermal expansion coefficients. For simplicity, the effect of friction is neglected. Boussinesq-Papkovich displacement potential method is used in the analysis. Then, the results for a single sliding fiber are used to predict the average thermal expansion coefficients of the composite containing finite concentration of fibers. It is observed that sliding at the fiber-matrix interface causes higher stress concentrations and affects significantly the average coefficients of thermal expansion of the composite.
Elastoplastic Plane Strain Analysis of Stresses and Strains at the Notch Root
Authors: Glinka G. , Ott W. , Nowack H.
Published: October 2009

For the evaluation of the local elastoplastic strains and stresses at the notch root suitable approximation formulas of sufficient accuracy are often used. In the present study the “equivalent strain energy density” concept for elastic-plastic notch strain-stress analysis has been developed. It was found that the evaluation of the strain energy density in the notch tip plastic zones does not require any input data other than the material stress-strain relation and the elastic stress concentration factor. The concept was verified on the basis of the results obtained from plane strain elastic-plastic finite element analysis using the material model after Mro´z. Comparison of the two sets of results revealed satisfactory accuracy of the equivalent strain energy concept. It was also shown that all stress and strain components in the notch tip can be calculated by complementing the method with Hencky’s equations. Neuber-based calculations were also included in the study. It was found that the energy concept was superior to Neuber’s rule, especially in the presence of high inelastic strains in the notch tip.
Creep-Fatigue Fracture of Dissimilar Metal Electron Beam Welded Joints at Elevated Temperature
Authors: Okazaki M. , Mutoh Y. , Yamaguchi M.
Published: October 2009

Creep-fatigue tests of dissimilar-metal electron beam welded joints between A387 Gr.22 ferritic low-alloy steel and AISI 405 ferritic stainless steel were carried out under strain-controlled cycling at a temperature of 873 K. It was found that the creep-fatigue life of a dissimilar metal welded joint was significantly shorter than those of its base metals. This resulted from the strain concentration on the AISI 405 side (with the lower deformation resistance.) It was also found that the hardness distribution was one of the important measures by which the local strain distribution was reflected. Furthermore, a simple prediction method for the creep-fatigue life of dissimilar metal welded joints was proposed based on the creep-fatigue life properties of its base metals by applying the strain range partitioning approach. The predicted lives were in good agreement with the experimental results.
Environmental Effects on Fatigue Crack Initiation in 2.25 Cr-1 Mo Steel and 316L Stainless Steel
Authors: Mathews V. K. , Gross T. S.
Published: October 2009

Blunt notch fatigue crack initiation tests for Type A387 2.25 Cr-1 Mo steel and 316L stainless steel were performed in air at room temperature, in silicone oil at room temperature, in V-131B coal process solvent at 100°C, and in chlorine-modified V-131B coal process solvent at 100°C. For both steels the most damaging environment was room temperature air. The number of cycles to initiate a crack were almost identical in the coal process solvent and the silicone oil for the Type A-387 steel. These two environments resulted in the longest crack initiation lifetime for the Type A-387 steel. The crack initiation lifetime for the Type A-387 steel in the chlorine modified V-131 B coal process solvent was roughly a factor of five less than the lifetime in the silicone oil and the unmodified coal process solvent. The crack initiation lifetime for the Type A-387 steel in room temperature air was a factor of 30 less than the lifetime in the silicone oil or the unmodified coal process solvent. The improvement of the crack initiation lifetime for the Type A-387 steel in the unmodified coal process solvent and the silicone oil is attributed to protection of the material from embrittlement from room temperature air. The decrease in crack initiation lifetime in the chlorine modified coal process solvent indicates that chlorine can be an active embrittling agent in the coal process solvent. The crack initiation lifetime for 316L stainless steel was longest in the silicone oil. The lifetime decreased somewhat in the unmodified coal process solvent with a further decrease for the chlorine modified coal solvent. The crack initiation lifetime in air was an order of magnitude lower than the lifetime in the silicone oil. The silicone oil and the coal process solvent apparently protected the 316L stainless from the embrittlement in air. However, the coal process solvent is not entirely inert as in the case of Type A-387 steel. The chlorine is an active embrittling agent for the 316L stainless steel in the coal process solvent.
Electrical Potential Drop and Notch Opening Displacement Methods for Detecting High Temperature Low Cycle Fatigue Cracks of Circumferential Notched Specimens
Authors: Sakane Masao , Ohnami Masateru
Published: October 2009

This paper assesses the accuracy of the crack initiation detection methods for type 304 SS circumferential notched specimens subjected to strain and stress controlled low cycle fatigue loads at 873 K in air. The methods examined were DC potential drop method (PDM) and the maximum stress criterion in the strain controlled test while they were DC potential drop method and the minimum notch opening displacement method (NOD) in the stress controlled test. The DC potential method and the minimum notch opening displacement method were proved to have a sufficient accuracy for the detection of crack initiation while the maximum stress criterion has less accuracy. The crack length detection based on DC potential drop method is also discussed.
Relationship Between Workhardening Characteristics, Shape and Instability of Hydroformed Thin Shells
Authors: Shang H. M. , Shit S. K. , Tay C. J.
Published: October 2009

In this paper, a pattern is observed which relates the stress-strain curve of sheet materials to the shape and instability of hydroformed axisymmetrical thin shells. According to this pattern, prolate shells are obtained when the effective strain at the pole has a value within the linear (or almost linear) portion of the stress-strain curve; while oblate shells are obtained when the polar effective strain is at the curved portion of the stress-strain curve. With the aid of Ludwik and Hollomon equations, a family of stress-strain curves of various n-values is constructed and the curves are divided into four zones which indicate the shape of shells and its evolution with deformation, the transition point toward instability and the onset of instability. From the fracture strain of a given material during hydroforming, the observed pattern also indicates whether or not instability is present.
Elasto-Plastic Analysis of the Peel Test for Thin Film Adhesion
Authors: Kim Kyung-Suk , Kim Junglhl
Published: October 2009

Analyses have been made to extract the objective interfacial fracture toughness from the peel strength of very thin metallic films. An elastoplastic bending model of the adherend film has been employed in the analyses applying the fracture mechanics concept of steady-state interfacial crack growth. The analytic result finally shown is a universal peel diagram where the objective interfacial fracture toughness is readily readable when the peel strength is known. Experimental results for Cu films on Si and polyimide substrate systems with a Cr interface are also presented.
Fracture Toughness Variations in Alloy 718
Authors: Mills W. J. , Blackburn L. D.
Published: October 2009

Heat-to-heat and product-form variations in the JIc fracture toughness of Alloy 718 were examined at 24°C, 427°C, and 538°C using the multiple-specimen JR-curve method. Five different material heats along with three product forms from one of the heats were tested in the conventional heat-treatment condition. Statistical analysis revealed only two significantly different JIc levels of 48 kJ/m2 and 74 kJ/m2 for these materials. These two mean JIc levels were independent of temperature. A minimum-expected JIc level based on a tolerance interval bracketing 90 percent of the lower JIc population at a 95 percent confidence level was evaluated as 33 kJ/m2. Coarse δ precipitates controlled the fracture properties by initiating secondary dimples that pre-empted continued growth of primary dimples nucleated by broken carbide inclusions.
Corrosion Fatigue Crack Growth of Steels in Various Environments
Authors: Alawi H. , Ragab A. , Shaban M.
Published: October 2009

Corrosion fatigue crack growth of three steels namely: AISI C1018, AISI 4340, and Stainless 17-7PH is studied in various environments. Testing medias include natural sea water, polluted sea water from an industrial site, drinking water produced from desalination process, and laboratory environments. Results obtained for the three steels are consistent in showing that polluted sea water is the most aggressive environment followed by low bicarbonate and alkalinity drinking water, then natural sea water. An attempt is made to explain this extraordinary aggressiveness of the polluted sea water and drinking water.
Simulation of Surface Grinding
Authors: Li Y. Y. , Chen Y.
Published: October 2009

The objective in this research is to develop a mathematical model which simulates the grinding process and predicts the transient temperature field and the stresses generated in the workpiece due to the forces applied and the heat produced by the grinding wheel. It also predicts the residual stress and the microstructure. The model considers the fully coupled thermomechanical field equations, with coupling through the dilatational work, the plastic work, the heat release during phase transformation and the heat generated by the grinding wheel in the energy equation. Computations were performed for a workpiece in plane strain. The model calculates the temperature, stress, microstructure fields and elastic/plastic regions of the workpiece during grinding. Different downfeeds of the grinding wheel were considered. The results show a good qualitative agreement with experiment.
Frequency and Hold-Time Effects on Low Cycle Fatigue Life of Notched Specimens at Elevated Temperature
Authors: Sakane Masao , Ohnami Masateru , Awaya Teruyoshi , Shirafuji Nakao
Published: October 2009

This paper describes the frequency and hold-time effects on high temperature low cycle fatigue for round notched specimens. Unnotched and notched specimens having different elastic stress concentration factors were fatigued under triangular and trapezoidal stress waves at frequencies ranging from 5 Hz to 0.0001 Hz at 873 K. The three specific fracture characteristics were observed: cycle dependent, time dependent, and cycle-time dependent. The respective notch sensitivity occurred in the respective fracture regime. The fatigue life of notched specimens was predicted from the elastic-plastic-creep cyclic FEM analysis using the linear damage rule and the strain range partitioning rule. Both the life prediction methods predicted the creep-fatigue life within almost a factor of two scatter band.
On a Class of Kinematic Hardening Rules for Nonproportional Cyclic Plasticity
Authors: Moosbrugger J. C. , McDowell D. L.
Published: October 2009

Two surface theories for rate-independent plasticity have previously been shown to offer superior correlative capability in modeling material response under non-proportional loading. In this study, a class of kinematic hardening rules characterized by a decomposition of the total kinematic hardening variable is discussed. The concept of generalized image point hardening in conjunction with mulitple loading surface interpretations is presented. The ability of this class of rules to correlate experimental data from stable nonproportional cycling of Type 304 stainless steel at room temperature is examined. In addition, the proper framework for inclusion of isotropic hardening for this class of models is discussed.
Effects of Extremes of Hardness and Mean Stress on Fatigue of AISI 4340 Steel in Bending and Torsion
Authors: Findley W. N.
Published: October 2009

Experiments are reported for fatigue tests in bending and in torsion at hardness levels from fully annealed to fully hard and super quenched. Results indicate a linear relation between fatigue strength and Brinell hardness. The relation between bending and torsion and the effects of mean stress and size are also examined.
J-Integral Analysis of the Compact Tension Specimen
Authors: Zahoor A.
Published: October 2009

A J-integral solution is presented for the compact tension specimen. The solution allows analysis for crack lengths greater than 20 percent of the specimen width. Unlike previous solutions that were based on the assumptions of full ligament yielding, deeply cracked specimen, or limit load, this paper derives a J solution that does not require such assumptions. Solutions are presented for both the deformation theory J and modified J, JM. These solutions are suitable for J-resistance curve development. A relationship between the plastic and the elastic η factor is presented. A comparison of the present solution with earlier solutions indicates that the J for those solutions is underestimated for a/W below 0.5. Numerical results show that Jd and JM resistance curves are closer than previously obtained. A criterion for extrapolating J-resistance curve is proposed. A relationship for scaling load-displacement curves suitable for key curve analysis is also presented.
Characterization of Prepreg Tow Carbon/Epoxy Laminates
Authors: Swanson S. R. , Toombes G. R.
Published: October 2009

Resin systems used in wet filament winding differ from those used in prepreg laminates. However it is possible to use the resins from prepreg systems in filament winding by using prepreg tows. A characterization study was carried out to investigate the matrix dominated properties of filament wound systems using AS4/3501-6 carbon/epoxy. This 3501-6 resin system is normally used in layed up prepreg laminates. The tests used were torsion combined with axial tension and compression of thin-walled tubes. The results showed the shear and cross fiber properties to be similar to those seen in layed up prepreg systems, and considerably higher than obtained with usual wet filament winding resins. Additional tests were performed on [±45]2s filament wound cylinders. Shear properties from these tests agreed well with the torsion tests at low stress levels, but were quite different at high stresses due to microcracking and state of stress effects.
A Model for Abrasive-Waterjet (AWJ) Machining
Authors: Hashish Mohamed
Published: October 2009

Ultrahigh-pressure abrasive-waterjets (AWJs) are being developed as net shape and near-net-shape machining tools for hard-to-machine materials. These tools offer significant advantages over existing techniques, including technical, economical, environmental, and safety concerns. Predicting the cutting results, however, is a difficult task and a major effort in this development process. This paper presents a model for predicting the depth of cut of abrasive-waterjets in different metals. This new model is based on an improved model of erosion by solid particle impact, which is also presented. The erosion model accounts for the physical and geometrical characteristics of the eroding particle and results in a velocity exponent of 2.5, which is in agreement with erosion data in the literature. The erosion model is used with a kinematic jet-solid penetration model to yield expressions for depths of cut according to different modes of erosion along the cutting kerf. This kinematic model was developed previously through visualization of the cutting process. The depth of cut consists of two parts: one due to a cutting wear mode at shallow angles of impact, and the other due to a deformation wear mode at large angles of impact. The predictions of the AWJ cutting model are checked against a large database of cutting results for a wide range of parameters and metal types. Materials are characterized by two properties: the dynamic flow stress, and the threshold particle velocity. The dynamic flow stress used in the erosion model was found to correlate with a typical modulus of elasticity for metals. The threshold particle velocity was determined by best fitting the model to the experimental results. Model predictions agree well with experimental results, with correlation coefficients of over 0.9 for many of the metals considered in this study.
Dynamic Equilibrium Constitutive Relations of Copper Powder Within Dies Subjected to Mutliple Shock Compactions
Authors: Sano Yukio , Miyagi Kiyohiro , Tokushima Koji
Published: October 2009

An approximate dynamic equilibrium pressure p-specific volume V relation exists for porous materials of a simple type undergoing mutliple shock compaction processes. A copper powder medium in dies is assumed to be of such a type, and the relation is constructed when the medium is compacted by a punch. It is given by an expression in the form of p=(V−Vi)/[b{Vi(1−a)−V}], where Vi, a and b are the material constants. These constants are estimated by matching the computational and experimental results obtained for the mean green density of the medium. Similarly, a dynamic equilibrium lateral pressure p1-specific volume V relation is also estimated for the medium after being given by p1=αp2+βp for ρ<3430 kg/m3, where α and β are the material constants and ρ is the density, while p1=0.5(Vsolid/V)νp+c for ρ≧3430 kg/m3, where Vsolid is the specific volume of solid copper, ν the material constant, and the contant c continuously connects the lateral pressures of the above two equations at ρ=3430 kg/m3. The compaction processes analyzed using the estimated relations agree favorably with the powder particle movement and shock wave front paths from experiments, suggesting the validity of the simple type assumption and that of the estimated relationships.
Changes in State Variables at Elevated Temperatures
Authors: Sehitoglu Huseyin
Published: October 2009

Two state variables, strength and internal (back) stress, were determined during cyclic deformation by rapid unloading-reloading experiments. The experiments were performed at different temperatures and strain rates, Considerable increases in strength at low temperatures (20°C–300°C) due to cyclic deformation and due to strain aging were measured. The variation of internal stresses at elevated temperatures (600°C) with strain rate was identified. Regions of high back stress rates were established on stress-back stress diagrams. High strain rates during unload-reload excursions are needed to minimize changes in back stress during measurements. The results (state variables) and the stress-strain response were compared to predictions based on a unified constitutive model. The capabilities of the model under cyclic loading, decrease in strength at high temperatures due to spheroidization, and increase in strength due to strain aging at lower temperatures, were found to be satisfactory. The extension of the unloading-reloading technique to multiaxial loading is outlined.
Material Characterization for Metal-Cutting Force Modeling
Authors: Stephensen D. A.
Published: October 2009

Widely applicable machining simulation programs require reliable cutting force estimates, which currently can be obtained only from process-dependent machinability databases. The greatest obstacle to developing a more basic, efficient approach is a lack of understanding of material yield and frictional behavior under the unique deformation and frictional conditions of cutting. This paper describes a systematic method of specifying yield stress and friction properties needed as inputs to process-independent cutting force models. Statistically designed end turning tests are used to generate cutting force and chip thickness data for a mild steel and an aluminum alloy over a wide range of cutting conditions. Empirical models are fit for the cutting force and model-independent material parameters such as the tool-chip friction coefficient and shear stress on the shear plane. Common material yield behavior assumptions are examined in light of correlations between these parameters. Results show no physically meaningful correlation between geometric shear stress and strain measures, a weak correlation between geometric stress and strain rate measures, and a strong correlation between material properties and input variables such as cutting speed and rake angle. An upper bound model is used to fit four- and five-parameter polynomial strain-rate sensitive constitutive equations to the data. Drilling torques calculated using this model and an empirical turning force model agree reasonably well with measured values for the same material combination, indicating that end turning test results can be used to estimate mean loads in a more complicated process.
Pressure Effects in Abrasive-Waterjet (AWJ) Machining
Authors: Hashish Mohamed
Published: October 2009

Abrasive-waterjets (AWJs) are formed by mixing high-pressure (up to 400 MPa) waterjets (0.1 to 1 mm in diameter) with abrasive particles in mixing tubes with typical 1/d ratios of 50 to 100. The pressure of the waterjet influences the overall performance of the abrasive-waterjet cutting system through operational and phenomenological effects. Higher pressures result in lower hydraulic efficiency, more frequent maintenance, high wear rates of mixing tubes, and fragmentation of particles before they exit the nozzle. However, with high pressures, deeper cuts can be obtained and higher traverse speeds can be used. Consequently, the hydraulic power is best utilized at an optimum pressure, which is a function of all other parameters as well as the application criteria. This paper presents data and analyses on the effect of pressure on nozzle operational characteristics, i.e., jet spreading characteristics, abrasive particle fragmentation, suction capability, wear of mixing tubes, and mixing efficiency. The effect of pressure on the parameters of cutting performance is discussed with example data. These parameters are depth of cut, specific area generation, maximum cutting traverse rate, surface waviness, and cost of cutting. Optimal pressure examples presented in this study indicate that pressures over 240 MPa are required for efficient abrasive-waterjet performance in metal cutting.
An Experimental Verification of the Hemispherical Cup Puckering Problem
Authors: Donoghue M. , Stevenson R. , Kwon Y. J. , Triantafyllidis N.
Published: October 2009

In this work is presented an experimental study of the hemispherical cup puckering test. This investigation is motivated by some theoretical as well as by some practical reasons which are elaborated upon in the introduction. After a brief outline of the analytical model and the corresponding numerical solution technique, the presentation continues with a description of the experimental procedure. A comparison between the experimental and the theoretical results is given next followed by a critical discussion.
Notch Effect in Biaxial Low Cycle Fatigue at Elevated Temperatures
Authors: Umeda H. , Sakane M. , Ohnami M.
Published: October 2009

This paper describes the notch effect in biaxial low cycle fatigue of an austenitic stainless steel SUS 304 at 873K in air. Mises’ equivalent stress controlled fatigue tests were carried out for the three kinds of round notched specimens in push-pull/torsion biaxial stress states. Cracks emanated at the notch root were measured by a d.c. potential drop method. Reduction in the fatigue life due to the notch was most significant in the reversed torsion test in comparison with the push-pull and combined push-pull/reversed torsion tests. The conventional fatigue life prediction methods, i.e., the Neuber’s rule, the Stowell’s method, and the Koe’s method, were applied to the experimental data and the accuracy of the prediction methods were discussed.