bluuebunny/crossref_metadata_2025 huggingface dataset:
Measurement of Contact Pressure in Metal Forming by Pressure Sensitive Film
Authors: Mori K. , Osakada K. , Fukuda M.
Published: October 2009

A simple method is presented for measuring the distribution of tool contact pressure in metal forming by using a pressure sensitive film which detects the contact pressure from the change in color density. In the method, a sufficiently hard sheet metal compared to the workpiece is inserted between the workpiece and the pressure sensitive film in order to eliminate the influence of frictional shear stress at the tool-workpiece interface on the measured result. Since the maximum pressure which can be determined by the film is 150MPa, lead is used as a workpiece material. Distributions of tool contact pressure are measured in upsetting of cylindrical billets, in free forging of plates of various shapes, and also in backward extrusion of a can. The measured distributions agree well with those computed by the rigid-plastic finite element method.
Process Modeling of Orthogonal Cutting by the Rigid-Plastic Finite Element Method
Authors: Iwata K. , Osakada K. , Terasaka Y.
Published: October 2009

A numerical modeling method for plane strain orthogonal cutting in steady state is developed on the basis of the rigid-plastic finite element method. The methods for determining the material and frictional properties to be used in the model are discussed. The shape of chip, i.e., the thickness and curl, distributions of stress and strain are calculated. Fracture of chip is predicted by combining the present model with the criteria of ductile fracture. The simulated results agree well with the results obtained by the microscale cutting experiment carried out within a scanning electron microscope.
Surface Integrity in Machining Solution-Treated and Aged 2024-Aluminum Alloy, Using Natural and Controlled Contact Length Tools. Part II—Lubricated Conditions
Authors: Bailey J. A. , Elkhabeery M. M.
Published: October 2009

The effects of cutting speed, chip-tool contact length, and tool surface finish on the surface integrity of solution-treated and aged 2024-aluminum alloy, that is machined under lubricated orthogonal conditions are investigated. The surface region of machined workpieces is examined using a variety of diagnostic techniques. In addition, tool forces are measured and the cutting geometry is determined. The results show that a variety of geometrical surface features are generated that contribute to the natural surface roughness, and that a plastically deformed surface region is generated that contains variations in hardness, microstructure, and residual plastic strain. The results are interpreted in terms of the type of chip produced, the mechanics and thermodynamics of the cutting process and the lubricating action of cutting fluids. When the results of the investigation are compared with similar results derived under nonlubricated conditions, it is found that at low cutting speeds application of a lubricant produces a reduction in tool forces, power consumption, surface roughness, surface defects, and subsurface deformation, whereas at high cutting speeds application of a lubricant has little influence on the cutting process.
The Fatigue Behavior of Nickel, Monel, and Selected Superalloys, Tested in Liquid Mercury and Air; A Comparison
Authors: Price C. E. , Good J. K.
Published: October 2009

The fatigue lifetimes and fractography were compared for nickel and typical nickel base alloys of the Monel, Inconel, and Incoloy series, tested at room temperature in alternating tension in the environments of air and liquid mercury. It was found that the fatigue life was always less in mercury and that a different fracture mode resulted. The alloys Nickel 200, Inconel 600, Incoloy 800, and Incoloy 825 that did not show intergranular fractures in the slow strain-rate tensile tests, did so under fatigue testing. A generalized crack propagation sequence in mercury was identified beginning with intergranular cracking but transferring eventually to transgranular modes.
JIc Determination of Five Cast Steels at Room Temperature and −45°C (−50°F)
Authors: Chung J. H. , Stephens R. I.
Published: October 2009

JIc tests using the multiple specimen procedure described in ASTM standard E813 were conducted at room temperature and −45°C (−50°F) with five common carbon or low alloy cast steels, viz., 0030, 0050A, C-Mn, Mn-Mo, and 8630. Specimen thickness was 25.4 mm (1 in.). Valid JIc values were obtained with four of the cast steels at room temperature and only two of the cast steels at −45°C (−50°F). Only Jcl (Jcleavage) values were obtained with the four other tests due to unstable brittle or cleavage fracture. Valid JIc values were obtained if the test temperature was above the mid-point temperature of the Charpy V notch energy transition region as measured along the temperature axis. Conservative estimates of KIc were calculated from JIc test results and a preliminary empirical equation involving KIc and Sy at room temperature and upper shelf CVN energy was suggested for cast steels. Room temperature JIc values were higher for the three tempered martensitic cast steels than for the two ferritic-pearlitic cast steels.
Modeling of the Plastic Behavior of Inhomogeneous Media
Authors: Berveiller M. , Zaoui A.
Published: October 2009

The general method which work for the case of linear properties are taken as a pattern for the derivation of the local total strain rate field of an inhomogeneous material (such as a polycrystal, a composite, or multiphase material) submitted to a uniform macroscopic elastic-plastic strain rate; the localization procedure leads to an integral equation, the solution of which is shown to yield the overall behavior. This method allows to locate within a common framework all the classical approaches, namely Taylor’s, Lin’s ones, the self-consistent scheme…and to suggest possible extensions. Some significant results are reported, concerning strain-hardening, yield stress, and texture devolopment of FCC polycrystals, according to simplified, one-site self-consistent model.
A Self-Consistent Analysis of the Stiffening Effect of Rigid Inclusions on a Power-Law Material
Authors: Duva J. M.
Published: October 2009

An approximate constitutive relation is derived for a power-law viscous material stiffened by rigid spherical inclusions using a differential self-consistent analysis. This approach consists of two parts: the formulation of a self-consistent differential equation, and the solution of an associated kernel problem, a nonlinear boundary value problem for an isolated inclusion in an infinite power-law viscous matrix.
A Micromechanical Basis for Constitutive Equations With Internal State Variables
Authors: Hart E. W.
Published: October 2009

A micromechanical model based on the glide and interaction of dislocations is developed to rationalize some of the phenomenological features of inelastic deformation. An origin for an internal stress is explicitly stated. The relation among the applied stress, the internal stress, and the glide friction stress is derived. The internal stress is shown to be linearly proportional to a stored anelastic strain. The micromechanical model is shown to provide a detailed basis for the state variable constitutive relations proposed by Hart.
An Experimental Investigation of Yield Surfaces and Loading Surfaces of Pure Aluminum With Stress-Controlled and Strain-Controlled Paths of Loading
Authors: Phillips Aris , Lu Wei-yang
Published: October 2009

Tension-torsion tests with a computer controlled servohydraulic testing machine are reported. Yield surfaces were obtained during a load controlled path, which includes combined stress creep, as well as during a strain controlled path, which includes combined stress relaxation. These surfaces and their relation to the corresponding loading surfaces is discussed. The development of plastic strain increments and their relation to the yield surfaces and loading surfaces is also discussed.
The Anisotropic Deformation of Yield Surfaces
Authors: Eisenberg M. A. , Yen Chian-Fong
Published: October 2009

Extensive experimental evidence indicates that yield surfaces exhibit significant anisotropic hardening. Subsequent yield surfaces are both translated and deformed in stress space. A viscoplasticity theory which describes anisotropic hardening by using a Lagrangian deformation mapping of the elastic domain is applied to the quantitative modelling of observed yield surface deformation of 1100-0 aluminum subject to non-proportional loading in tension-torsion space.
Analysis of Stress Response to Various Strain-Paths in Axial-Torsional Deformation of Metals
Authors: Wu Han C. , Yao Jen-Che
Published: October 2009

The stress response to various axial-torsional strain paths is discussed. The modified endochronic plasticity theory, which is formulated based on plastic-strain is used for theoretical analysis. In a sensitivity study, it is shown that a substantial amount of change in the stress response is induced by a small perturbation on the plastic-strain path. Of this change a significant amount is due to perturbation in the direction of the plastic-strain path. Several stepwise strain paths, both total-strain and plastic-strain paths, are also included in the investigation. It has been found that, when the number of steps is increased to infinity such that the strain path converges to a straight line corresponding to an in-phase path, the stress response to such a path is wildly fluctuating in the stress space if the path is a plastic-strain path, and the stress response converges to that of the in-phase path if the path is a total-strain path.
Creep Experiments Under Nonproportional Loadings With Stress Reversals for 2618 Aluminum
Authors: Ding J. L. , Findley W. N.
Published: October 2009

Experiments on creep of 2618-T61 aluminum under nonproportional loading steps combined with shear stress reversals, are reported. Compared to previous work, the stress levels, under which nonproportional loading steps were performed, were relatively low in the current work. In addition to the features of the material responses under nonproportional loadings such as anisotropy induced by creep strain, synergistic effects on creep and creep recovery, more findings related to stress reversals were a cyclic softening effect. The effect of shear stress reversal on tension creep was not significant because of the low stress levels. Isotropic strain hardening, kinematic hardening and independent strain hardening theories were evaluated. An auxiliary rule was developed for the isotropic and independent strain hardening approaches to extend the capabilities of the theories. Creep under stress reversals predicted by the kinematic flow rule was well described at low stresses but was too exagerated at high stress levels.
Constitutive Modeling of Dissipative Solids for Postcritical Behavior and Fracture
Authors: Perzyna Piotr
Published: October 2009

The paper aims at the description of the postcritical behavior and fracture of dissipative solids during tensile test. The ductile fracture is understood as the final stage of the necking process and is preceded by the nucleation and growth of voids mostly due to plastic deformations and yield stress state and by the linkage of voids. An elastic-viscoplastic model of solids with internal imperfections parameter interpreted as the void volume fraction is postulated. Elastic-plastic response of the matetrial is also discussed. The material functions and constants are determined based on available mechanical test data as well as on metallurgical observation results. The theory of ductile fracture based on the evolution of internal imperfections is presented. Influence of different effects is examined and synergetic nature of fracture phenomenon is investigated. The criterion of fracture is deduced. The initial-boundary-value problem is discussed.
Solid Phase Sheet Forming of Thermoplastics—Part II: Large Deformation Post-Yield Behavior of Plastics
Authors: Nied H. F. , Stokes V. K.
Published: October 2009

This paper examines the phenomenology of the large strain, post-yield behavior of the three thermoplastics—polycarbonate, polybutylene terephthalate and polyetherimide—from the point of view of the sheet forming process. A photographic technique is utilized to measure the large nonhomogeneous strains observed in polymers. This technique makes possible the mapping of the strain field for flat specimens in the form of strain contours. Amorphous polymers polycarbonate and polyetherimide are shown to behave differently from semicrystalline polybutylene terephthalate. All three polymers are shown to neck in a stable manner, with the necked regions undergoing very large strains. The mechanical properties of the necked/drawn polymer are shown to be substantially different from the properties of the virgin polymer.
A Theoretical Derivation of the Similarity of Dynamic Compaction Processes of Powder Media in Dies
Authors: Sano Yukio
Published: October 2009

Multiple shock compactions of powder media within a die with a rigid punch are theoretically investigated. First, similarity of dynamic compaction processes for a powder medium of a simple type is exhibited through nondimensionalized one-dimensional equations. The similarity is established after determination of three parameters, i.e., the ratio S* of the lateral surface to the cross-sectional area of the medium, the ratio M* of the mass of the punch to that of the powder medium filled in the die, and the compaction energy per unit powder volume e. The similarity indicates that the particle velocity, specific volume and pressure have the same variation with respect to nondimensional time at all points in the medium with various cross-sections and initial lengths so long as S* is kept fixed at a certain value, i.e., at the same proportional nondimensional point in the medium. The density distributions of the green compacts are necessarily identical, and so is the mean density in all compactions. Second, it is shown in one of the nondimensionalized equations that wall frictional influence in a compaction where S* → 0 is not present, while the wall frictional influence is extremely large when S* is very large, which implies that the mean densities of the compacts are larger in compactions with smaller S*. Two types of compactions can be obtained for any powder medium because the equation used is applicable to any medium.
A Finite Element Modelling of Embrittlement in Composite Liquid Phase Sintered Heavy Alloys
Authors: Rittel D. , Roman I. , Bercovier M.
Published: October 2009

Sintered tungsten base heavy alloys made of tungsten grains embedded in a nickel rich matrix can possess low room temperature ductility that may be improved by subsequent heat treatment. The sintering thermal cycle was simulated by a finite element procedure, and it was found that the vast differences in thermal and elastic properties of the microstructural components result in significant residual interfacial strains upon cooling to ambient temperature. These strains may contribute significantly to the low room temperature ductility of this class of liquid phase sintered alloys and should be relieved in order to improve ductility.
Measurement of Residual Hoop Stresses in Cylinders Using the Compliance Method
Authors: Cheng Weili , Finnie Iain
Published: October 2009

A method is proposed for measurement of the hoop stress in an axisymmetric residual stress field in cylinders in which the axial stress is independent of the axial coordinate. The method involves measuring strains at the outside surface while an axial crack is cut progressively from the outside. Experimental results are presented for two short cylindrical rings cut from a long quenched cylinder. Good general agreement is obtained with X-ray and hole drilling measurements of residual stresses.
A Three-Dimensional Finite Element Evaluation of a Destructive Experimental Method for Determining Through-Thickness Residual Stresses in Girth Welded Pipes
Authors: Rybicki E. F. , Shadley J. R.
Published: October 2009

The accuracy of a destructive, experimental method for the evaluation of through-thickness residual stress distributions is investigated. The application of the method is to a welded pipe that has been subjected to a residual stress improvement process. The residual stress improvement process introduces gradients in the stress distribution. The question of interest is how well the back-computation method used to interpret the experimental data represents the residual stress distribution for this type of stress profile. To address this question, a finite element model was used to provide a reference stress solution for comparison with the back-computation results of the experimental method. Three-dimensional finite element stress analyses were also conducted to simulate the cutting steps of the destructive laboratory procedure. The residual stress distributions obtained by the back-computation procedure were then compared with the reference stress solutions provided by the finite element model. The comparisons show agreement and indicate that good results can be expected from the experimental method when it is applied to a pipe that has been subjected to a residual stress improvement process, provided that the axial gradient of stress is not too large.
Tensile Fracture Loci for Brittle Materials Containing Spherical Voids
Authors: Shaw M. C. , Avery J. P.
Published: October 2009

When very brittle materials are subjected to a complex state of stress they fail by maximum intensified tensile stress criterion first introduced by Griffith [1]. Nominal applied stresses are intensified by defects present in all real materials. It appears that defects controlling the strength of brittle materials are of two types—open ones characterized by circular voids found in sintered materials such as tungsten carbide and thin, essentially closed ones found in brittle polyphase rock such as granite. This paper is concerned with the extension of a very simple two dimensional theory for circular voids [3] to the three dimensional case involving spherical voids. While the fracture locus for the two dimensional case represents a conservative approximation sufficient for most engineering applications, the three dimension solution is necessary to give detailed result for cases involving near hydrostatic tension or compression.
The Determination of Stress-Strain Curves of Thin Layers Using Indentation Tests
Authors: Tangena A. G. , Hurkx G. A. M.
Published: October 2009

A method is presented for estimating the plastic part of stress-strain curves of metal coatings, using a Brinell indentation test. The accuracy of the stress-strain curves obtained in this way is tested by using these curves in a finite element calculation and comparing the calculated results with results from experiments. Stress-strain curves are given for galvanic layers such as citrate Au, Co-Au, sulfamate Ni and also for solid annealed pure Au.
Laser Heat Treatment of Cast Irons—Optimization of Process Variables, Part II
Authors: Molian P. A. , Mathur A. K.
Published: October 2009

ASTM class 40 gray and 80-55-06 ductile cast irons were surface heat-treated by a 1.2-kW, CO2 laser to study the effects of square and oscillating-gaussian beam modes on case depth, coverage rate, distortion, hardness, and microstructure. The results were compared with that of ring and gaussian beam modes, which were described in Part I. Square and oscillating beams maximized case depth and coverage rate, while ring and gaussian beams minimized distortion. Hardness and microstructure of heat-treated layers were unaffected by the beam mode. For given laser parameters, ductile iron always exhibited larger case depth and coverage rate than gray iron because of the lower thermal diffusivity. Experimental data and theoretical models indicated that thermal response of a material to laser power cannot be described by a simple function as given by heat conduction models and that the best correlating factor for case depth is P/V (P is laser power, V is scan rate).
Sheet Metal Forming Limits Under Complex Strain Paths Using Void Growth and Coalescence Model
Authors: Rao U. S. , Chaturvedi R. C.
Published: October 2009

It is well established that ductile fracture occurs by nucleation, growth and coalescence of voids. Several models have been developed to predict limits under constant strain ratio paths considering void inhomogeneity and void growth. In this paper the void growth and coalescence model developed by Rao and Chaturvedi for predicting forming limits under constant strain ratio paths, has been extended for predicting forming limits under two stage strain paths. The predicted results have been compared with experimental results of Ishigaki and analyzed.
A New Workability Criterion for Ductile Metals
Authors: Vujovic V. , Shabaik A. H.
Published: October 2009

The forming limit curves are important aids in determining the extent of deformation a material can be subjected to during a forming process. In this paper a forming limit criterion for bulk metalworking processes, based on the magnitude of the hydrostatic component and the effective stress of the state of stress, is proposed. The determination of the forming limit curve by means of three simple tests, namely, tension, compression, and torsion tests, is presented.
Investigation of Endochronic Constitutive Equation Subject to Plastic Strain-Controlled Axial-Torsional Deformation
Authors: Wu Han C. , Yao J. C. , Chu S. C.
Published: October 2009

Plastic-strain controlled test is investigated both experimentally and theoretically. The plastic-strain control is feasible by means of computer-aided material test system. Theoretical study is made by use of the modified endochronic theory in which plastic strain is employed to define intrinsic time. Three in-phase plastic-strain paths (a pure axial path, a pure torsional path and an axial-torsional in-phase path) and two out-of-phase plastic-strain paths (small and large perturbations from the axial-torsional in-phase path) are studied. It is shown that the theory and experiment have good agreement. Furthermore, both experimental and theoretical results show that strain-hardening is enhanced by out-of-phase loading.
The Coefficient of Thermal Expansion of a Super Invar-Ta16W18O94 Composite
Authors: Chu C. N. , Saka N. , Suh N. P.
Published: October 2009

The coefficient of thermal expansion (CTE) of a hot pressed Ta16W18O94 which was produced from Ta2O5 and WO3 powders was found to be −1.52×10−6 K−1 in the temperature range 180–330 K. Using the Ta16W18O94 and Super Invar powders, 50:50 volume percent metal-ceramic composites were made by the powder metallurgy techniques. When the mixture of constituent powders was hot pressed at 1123 K for 10 minutes, a CTE of 1.1 × 10−6 K−1 was obtained in the temperature range 140–420 K.
Macro-Mechanical Analysis for Symmetric and Asymmetric Fully Plastic Crack Growth
Authors: Kardomateas G. A.
Published: October 2009

Asymmetries like welds or shoulders, may eliminate one of the two shear zones of symmetrically fully plastic cracked parts and thus give crack propagation along the remaining active slip band through pre-strained material instead of through the relatively unstrained region between two shear bands of the symmetric case. One thus expects a reduced ductility in the single shear band asymmetric case. A macro-mechanical analysis provides a physical basis for explaining the development of deformation in both geometries, as observed from tests on several alloys. The asymmetric case is approximated as Mode II shearing, with the crack extension occurring by sliding off along a single slip plane and fracture. In the symmetric Mode I case, the crack is assumed to extend by alternating shear on two symmetric slip planes and fracture.
Delamination Fracture Toughness of Graphite and Aramid Epoxy Composites
Authors: Saghizadeh H. , Dharan C. K. H.
Published: October 2009

The delamination fracture toughness of graphite and aramid-epoxy composite laminates was determined as a function of loading rate for unidirectional and woven reinforcements. In addition, the in-situ fracture toughness of the epoxy matrix was obtained by determining the crack energy release rate during the delamination fracture of thin epoxy films. The fracture surfaces were investigated using scanning electron microscopy. The results show that increasing the loading rate and the use of woven reinforcements increase the fracture toughness. A model was used to estimate the relative contributions from the fiber-matrix interface and the matrix to the overall delamination crack energy release rate.
New Measuring Method of Axisymmetric Three-Dimensional Residual Stresses Using Inherent Strains as Parameters
Authors: Ueda Yukio , Fukuda Keiji , Kim You Chul
Published: October 2009

For the measurement of axisymmetric three-dimensional residual stresses, Sachs’ method is often used. The accuracy of this method is not high when even small errors are contained in observed strains. In 1975, the authors presented a new approach for the measurement of residual stresses in which inherent strains (the source of residual stresses) are dealt with as parameters and formulated a basic theory using the finite element method. In this paper, based on the new approach, a basic theory for the measurement of axisymmetric three-dimensional residual stresses is developed and a practical procedure of measurement is presented. This method is applied to determine the residual stresses in a quenched shaft and its reliability and practicability are also demonstrated.
Shear Plastic Stress-Strain Relation Obtained From Torque-Twist Data
Authors: Batdorf S. B. , Ko Robert W. C.
Published: October 2009

A standard technique for finding the shear stress-strain relation of a material employs a torsion test on a solid circular cylinder. It is shown that the exact solution is easily obtained as a correction to the sometimes-used quasielastic approximation. The solution is extended to the case of hollow cylinders. The analysis is shown to be applicable also to the case where a constant axial stress is present, and to a special case of planar isotropic materials.
Thermal Expansion Behavior of Alloyed Pearlitic Flake Graphite Cast Irons
Authors: Rukadikar M. C. , Reddy G. P.
Published: October 2009

Precise understanding of thermal expansion behavior of flake graphite cast irons is essential to know the thermal fatigue resistance of these irons when used for elevated temperature application like diesel engine components, ingot moulds, hot mill rolls, glass moulds, dies, etc. Twenty-three pearlitic flake graphite irons having identical base compositions (levels of sulfur, manganese, phosphorus, dissolved gases, and trace elements) having two levels of carbon (3.93 percent and 3.00 percent) and alloyed with elements such as molybdenum, vanadium, chromium, tin, nickel, copper, antimony, and aluminum were produced by carburizing steel scrap in an electric melting furnace. Thermal expansion behavior of all these irons were studied with the help of a dilatometer to determine the influence of graphite morphology and chemical composition. It is seen from the results that thermal contraction of flake graphite irons follows a different path during cooling than the thermal expansion path followed during heating. Further increase in graphitic carbon and coarseness of graphite tend to lower the coefficient of thermal expansion. Additions like molybdenum/copper at high level help in reducing thermal expansion; higher content of tin/antimony/aluminum/silicon tend to increase it while chromium/nickel/copper at low level have no effect. The present investigation has thus provided information regarding thermal expansion/contraction behavior of twenty-three flake graphite irons having almost all commonly used alloying elements.
Modeling Internal Stresses in the Nonelastic Deformation of Metals
Authors: Lowe T. C. , Miller A. K.
Published: October 2009

The roles of short range and long range internal stresses during nonelastic deformation have been postulated and explored using the MATMOD-4V deformation model. New microstructural variables have been introduced in MATMOD-4V which represent the effects of internal stresses upon deformation. Simulations for aluminum have been performed to demonstrate improved capability to represent small strain deformation behavior and dynamic recovery. Comparisons are made between experimental data and computer predictions of microplastic straining and cyclic deformation.
Optimum Working Conditions in Thick Walled Cylinders
Authors: Naga S. A. R.
Published: October 2009

Although thick walled cylinders subjected to both pressure difference and internal heat flow can be found in many engineering applications, optimizing for maximum material utilization is still needed. Hence, the present work presents a close insight into stress analysis and optimization of both thick walled impermeable and permeable cylinders under the combined effect of temperature and pressure gradients.
Interaction of Mixed Mode Loading on Cyclic Debonding in Adhesively Bonded Composite Joints
Authors: Mall S. , Rezaizadeh M. A. , Gurumurthy R.
Published: October 2009

A combined experimental and analytical investigation of an adhesively bonded composite joint was conducted to characterize the fracture mode dependence of cyclic debonding. The system studied consisted of graphite/epoxy adherends bonded with EC 3445 adhesive. Several types of specimens were tested which provided the cyclic debond growth rate measurements under various load conditions: mode I, mixed mode I and II, and almost mode II. This study showed that the total strain-energy-release rate was the governing factor for cyclic debonding.
Static Mechanical Performance of Composite Elliptic Springs
Authors: Mallick P. K.
Published: October 2009

Composite elliptic spring is a new concept as an application of fiber reinforced plastics in automotive suspensions. It functions in the same vertical deflection mode and packaging space as a steel coil spring and has the potential of saving as much as 50 percent by weight over a steel spring. The unique feature of the elliptic spring is that the fibers are utilized in tension instead of shear, thus avoiding the inherent weakness of a composite material in a coiled configuration. Several elliptic spring elements can be mounted in series to obtain the desired spring rate. In this paper, mechanical performance and failure analysis of composite elliptic springs under static loads are presented. Both thick and thin walled elliptic spring elements constructed from unidirectional E-glass fiber reinforced epoxy tapes were tested in static compression. Interlaminar shear failure is the primary failure mode in these springs. Both failure load and spring rate depend on the thickness of the spring. Joining of spring elements by bolts is also investigated.
Fracture Analysis of Notched Composites
Authors: Delale F.
Published: October 2009

In this study the problem of part-through cracks emanating from a central notch in a composite laminate is considered. The composite laminate is modeled as an orthotropic plate and along the branches, it is assumed that the stresses are carried by the fibers only. The stresses along the uncracked portions are assumed to be proportional to the crack opening displacement at that point. After formulating the branched crack problem, the model is applied to a (±45 deg)2s composite laminate. The stress concentration factors for the fibers are computed for various values of the spring constant K. Sample results showing the crack opening displacement are also displayed in the figures.
Hygrothermal Damage in Graphite/Epoxy Laminates
Authors: Hahn H. T.
Published: October 2009

The use of micromechanics equations for moisture diffusivity shows that the in situ diffusivity is slightly lower than the bulk diffusivity for matrix resins, thereby indicating absence of any matrix damage in virgin composites. When exposed to hygrothermal environments, however, composites undergo degradation which manifests itself in anomalous moisture diffusion behavior and reduced structural performance. The hygrothermal degradation is the result of matrix plasticization, microvoid formation, and microcracking. The time dependence of plasticization as well as the tensile stress resulting from steep moisture gradient is responsible for the damage induced by thermal spiking of wet composites. Swelling of neat resins is frequently less than predicted by the volume additivity. A simple micromechanics analysis provides a good estimate of composite swelling strain from resin properties. The bilinearity and the hysteresis observed in relations between swelling and moisture content are attributed to the existence of a threshold moisture concentration below which swelling is negligible. Relaxation of residual stresses is a long-term process under nonhostile environments. However, it is accelerated considerably around and above the glass transition temperature. The fast stress relaxation can change the transverse ply stress from compressive to tensile after thermal spiking, thereby inducing ply cracking and accelerating the subsequent moisture absorption. How residual stresses can affect ply cracking and delamination is shown through a fracture mechanics analysis.
Validation of Advanced Composite Thermal Stress Analysis Methods
Authors: Crose J. G. , Holman R. L. , Pagano N. J.
Published: October 2009

The thermal stress analysis of thermally degrading tape wound phenolic composites in rocket nozzles is complicated by the extreme variation of properties with temperature, combined with steep temperature gradients on the order of 50,000° F/in. This study applied two very different numerical approaches to the same problem of predicting thermal stresses in a moderately thick conical frustum. One method uses a variational theorem derived by Reissner while the other applies the classical finite element method based on minimization of the total potential energy. The good agreement of the two methods appears to validate the results and an extensive convergence study is presented that identifies the magnitude of errors in the finite element method as a function of element density. A modification to the finite element method to account for intra-element material property variation is shown to improve the convergence of the procedure.
Impact Energy Absorption of Continuous Fiber Composite Tubes
Authors: Schmueser D. W. , Wickliffe L. E.
Published: October 2009

This paper presents the results of an impact testing program that was conducted to characterize the energy absorption and failure characteristics of selected composite material systems and to compare the results with aluminum and steel. Composite tube specimens were constructed using graphite/epoxy (Gr/Ep), Kevlar/epoxy (K/Ep), and glass/epoxy (Gl/Ep) prepreg tape and were autoclave cured. Vertical impact and static compression tests were performed on 56 tubes. Tests results for energy absorption varied significantly as a function of lay-up angle and material type. In general, the Gr/Ep tubes had specific energy absorption values that were greater than those for K/Ep and Gl/Ep tubes having the same ply construction. Angle-ply Gr/Ep and K/Ep tubes had specific energy absorption values that were greater than those for 1024 steel tubes. Gr/Ep and Gl/Ep angle-ply tubes exhibited brittle failure modes consisting of fiber splitting and ply delamination, whereas the K/Ep angle-ply tubes collapsed in an accordian buckling mode similar to that obtained for metal tubes.
Fatigue Crack Propagation in 2090 Aluminum-Lithium Alloy: Effect of Compression Overload Cycles
Authors: Yu W. , Ritchie R. O.
Published: October 2009

Fatigue crack propagation behavior has been examined in a commercial 12.7 mm thick plate of Al-Cu-Li-Zr alloy, 2090, with specific emphasis on the effect of single compression overload cycles. Based on low load ratio experiments on cracks arrested at the fatigue threshold (ΔKTH), it is found that crack growth at ΔKTH can be promoted through the application of periodic compression cycles, of magnitude two times the peak tensile load. Similar to 2124 and 7150 aluminum alloys, such compression-induced crack growth at the threshold decelerates progressively until the crack re-arrests, consistent with the reduction and subsequent re-generation of crack closure. The compressive loads required to cause such behavior, however, are far smaller in the 2090 alloy. Such diminished resistance of aluminum-lithium alloys to compression cycles is discussed in terms their enhanced “extrinsic” crack growth resistance from crack path deflection and resultant crack closure, and the reduction in the closure from the compaction of fracture surface asperities by moderate compressive stresses.
The Effect of Sheet Thickness on Near-Threshold Fatigue Crack Propagation and Oxide and Roughness-Induced Crack Closure
Authors: Tokaji K. , Ando Z. , Nagae K.
Published: October 2009

Characteristics of fatigue crack propagation have been investigated in a low carbon steel and a high tensile strength steel to evaluate the effect of sheet thickness. Crack propagation data are generated over a wide range of growth rates, from 10−8 to 10−3 mm/cycle, for load ratios of 0.05 and 0.70 at room temperature in laboratory air. Particular emphasis is placed on behavior at near-threshold growth rates. Near-threshold fatigue crack propagation behavior is found to show a marked sensitivity to sheet thickness, and near-threshold growth rates decrease and threshold values increase with increasing sheet thickness. Oxide and roughness-induced crack closure models are proposed as a mechanism for the effect of sheet thickness on near-threshold fatigue crack propagation. It is also shown that the requirement for specimen thickness recommended by ASTM, W/20≤B≤W/4, is not always valid for near-threshold fatigue crack propagation.
Modeling of the Hydroforming of Sheet Materials Clamped With Varying Blank Holding Loads
Authors: Shang H. M. , Chau F. S. , Lee K. H. , Tay C. J. , Toh S. L.
Published: October 2009

During hydroforming of sheet materials into axisymmetrical shells, varying the blank holding load causes a change in the draw-in condition of the flange, and hence deformation. By assuming the shell surface to be spherical and the infeeding material to be unstretched and uniformly distributed along the shell surface, a simple model is developed to describe the effect of blank holding load on the deformation of aluminum, brass and copper specimens. In this model, the size of the die shoulder radius is also considered; and the workhardening characteristic of sheet metal is linearized by the use of a suitable strain measure derived from the experimental curve. It is observed that the theoretical results compare well with experimental results.
Local Crack-Tip Strain Concept for Fatigue Crack Initiation and Propagation
Authors: Shimada Heihachi , Furuya Yasubumi
Published: October 2009

The existence of the unified local strain field where we can substantially combine the two fatigue stages, crack initiation and propagation, was experimentally confirmed. Using the fine-grid-method, the changes of local notch-root or crack-tip strain and these histories were investigated until the small elemental block of material was broken by crack initiation and propagation. It became clear that the crack-tip strain behavior and its fracture process showed the similarity with local strain damage accumulation on crack initiation process. Especially, when the local strain history in the “elemental size, ρ*” adjacent to the crack-tip was taken into account, very good agreement of two stages could be obtained, ρ* depended on the kind of material. Based on this result, we have proposed a new idea termed “local crack-tip strain concept” that has the possibility for more simple, one parameter approach for future fatigue life analysis. It qualitatively differs from the currently used macroscopic, two parameters approach by combining the gross-strain (Δεtotal) fatigue life curve and fracture mechanics parameter (ΔK).
Influence of Cathodic and Internal Trapped Hydrogen on Fatigue Crack Growth in a NiCrMoV Structural Steel
Authors: Barbangelo A.
Published: October 2009

Fatigue crack propagation has been investigated in a NiCrMoV structural steel in air or in electrolytic hydrogen charging environments. The behavior of this steel containing internal trapped hydrogen absorbed during the steelmaking processes was also considered. Hydrogen, both internal and adsorbed by the environment, causes accelerated crack growth over the entire stress-intensity factor range. As the loading conditions are varied, two different damage mechanisms, triggered by hydrogen, are observed, and are separated by a transition zone where the fatigue crack growth rate is constant. The results of the fatigue tests and of a fractographic analysis suggest that the phenomenon is controlled by the stress distribution at the crack tip, and that a transition occurs when the cyclic plastic zone size at the crack tip is larger than the prior austenite grain size.
Effects of an Artificial Small Defect on Torsional Fatigue Strength of Steels
Authors: Endo Masahiro , Murakami Yukitaka
Published: October 2009

In order to elucidate the effect of small defects on the torsional fatigue strength of steels, reversed torsion tests were carried out on the 0.46 percent C steel specimens containing a small hole. The hole diameter ranges from 40 to 500μm. The fatigue behaviors on the specimen surface and near the hole were observed with the aid of a microscope. The torsional fatigue strength of steels containing small holes can be predicted from the results of rotating bending fatigue test by considering the threshold condition for crack propagation.
Direct Measurement of Temperature in High Speed Torsion Tests
Authors: Woodward R. L. , Baxter B. J. , Pattie S. D. , Coleman J. A.
Published: October 2009

A method of directly measuring the temperature rise during high speed torsion tests is described. The test sample is formed by welding two materials of similar mechanical properties but different thermoelectric characteristics and ensuring, by reducing the section, that the gauge length includes the thermocouple junction. A number of tests were conducted using the nickel base thermocouple alloys Nicrosil and Nisil (I.S.A. Type N). The temperature rise observed during uniform deformation agrees with that expected from simple thermomechanical calculations. Void growth and coalescence lead to a strain concentration and ductile fracture which is accompanied by a more significant temperature rise.
Infrared Thermographic Flaw Detection in Composite Laminates
Authors: McLaughlin P. V. , Mirchandani M. G. , Ciekurs P. V.
Published: October 2009

Research performed to develop thermography as a routine rapid flaw detection tool for large composite structures is presented. The externally applied thermal field (EATF) technique is described whereby surface cracks or sub-surface impact damage creates detectable surface temperature perturbations when heated. EATF thermographic procedures and flaw detection capabilities in multidirectional and unidirectional graphite and glass fiber composites are described. The method’s advantages and limitations are outlined.
An Analysis of Drawbeads in Sheet Metal Forming: Part II—Experimental Verification
Authors: Maker B. , Samanta S. K. , Grab G. , Triantafyllidis N.
Published: October 2009

This paper presents experimental results obtained for a variety of drawbeads typical of automotive applications, and compares the results with those obtained from the numerical model presented in the first part of this work (Triantafyllidis et al., 1986). The deformation process is divided into two phases: the “locking/clamping” phase as the binder closes to form the sheet around the drawbead, and the “pulling” phase as the panel is formed, causing the material to be drawn through the bead. Metals considered are SKDQ steel, aluminum, and brass. Dry and lubricated conditions are investigated. Good correlations between model and experiment are obtained for strain distributions over the sheet and excellent agreement is observed in the binder clamping forces. Using a Coulomb friction law in the model, horizontal restraining forces are compared to experimental results. The model is shown to accurately predict the influence of variations in material, geometry, and friction conditions. However, the correlation between the model and experiment is not as good in two cases: as the punch (male bead) reaches the “locked” condition, and in the initial stages of “pulling” deformation. Reasons for the discrepancies are discussed.
The Correlation Between the Residual Stresses of ABS Terpolymers and Injection Molding Conditions
Authors: Chiu Cheng Ping , Hsieh Min Chin
Published: October 2009

Residual stresses (R.S.) in a microcomputer-controlled injection molded ABS terpolymers have been determined. The layer-removal method and the microscopic measurement techniques were used to evaluate the stresses in these molded articles. The relationship between the R.S. and the processing parameters such as injection pressure, holding pressure, holding time, injection rate, and mold temperature was studied. Experimental results indicated that, at the higher injection rates (>10g/s), the R.S. are compressive in the surface layer and tensile in the interior; however, at the lower injection rates (<10g/s), the residual stresses are tensile in the surface layer and compressive in the interior. The results also indicated that the higher the injection rate, the lower the residual stresses; the compressive residual stresses increased in proportion to the increase of holding pressure; the residual stresses could be decreased by keeping a higher mold temperature; the longer the holding time, the higher the compressive R.S. and the lower the tensile R.S.
Fatigue Characteristics of Laser Surface-Hardened Cast Irons
Authors: Molian P. A.
Published: October 2009

Contrary to expectations, laser surface heat treatment has a deleterious effect on the fatigue performance of pearlitic gray and ductile cast irons. A 1.2 kW, continuous wave, CO2 gas laser, operating in square beam mode, was employed to heat-treat the surfaces of standard fatigue specimens. Rotational-bending fatigue tests were then conducted on untreated (as-cast) and laser treated specimens. Results indicated that the effect on fatigue behavior of case depth, microstructure and hardness of laser-hardened surface layers were opposite to that observed in carbon and low alloy steels. A fracture model based on the presence of graphite, residual stresses, and strain-induced transformation is postulated to explain the adverse effect of laser hardening of cast irons.
The Influence of Displacement Rate on Environmentally Assisted Cracking of Precracked Ductile Steel Specimens
Authors: Mayville R. A. , Warren T. J. , Hilton P. D.
Published: October 2009

Sustained load and rising displacement tests were performed on precracked specimens to investigate the environmentally assisted cracking (EAC) behavior of AISI 4340, σ0 = 1095 MPA (159 ksi), in flowing synthetic seawater. J-R resistance curves were generated in environment over four orders of magnitude in displacement rate and KIJ (from JIC) from the slowest test was found to agree closely with the KIEAC (KISCC) value determined from cantilever beam tests. Crack velocity data from the slowest rising displacement test and constant stroke—decreasing KI—tests fall on the same line suggesting that there is a unique a˙-KI curve for EAC in this system. A method is suggested to determine the displacement rate needed to obtain a good estimate of KIEAC from a rising displacement test.
Relation Between Cyclic Creep and Pure Creep on Copper
Authors: Ishikawa H.
Published: October 2009

The behavior of a pure copper subject to pure creep and cyclic creep under imposed load is examined at room temperature, and at 200°C, 300°C, and 400°C to show the relation between these two kinds of phenomena. Plots of observed strain, not against number of cycles, but against time are available for the direct comparison between cyclic creep and pure creep. This unified treatment shows that the instantaneous strain affects the succeeding mechanism of both pure creep and cyclic creep. As the result, these two kinds of phenomena are essentially identified, and pure creep could be regarded as the extreme aspect of cyclic creep.