bluuebunny/crossref_metadata_2025 huggingface dataset:
Finite Element Analyses of Real-Time Stability Control in Sheet Forming Processes
Authors: Sim H. B. , Boyce M. C.
Published: April 2008

Sheet metal forming processes involve the plastic deformation of a sheet of material into a desired shape. In practice, the uncontrolled variation of boundary and material conditions have made the continual reproducibility of a sheet forming process a very difficult operation. Recently, real-time control schemes based on simplified models of “average” in-process stresses and/or strains have provided a repeatability of end product quality in terms of final shape, failure modes, and/or material state. The success of these control schemes have warranted a more detailed investigation into the complete physics of the deformation process. This study takes one such operation, the axisymmetric cup-forming process, and conducts an off-line detailed analysis using the finite element method in order to obtain information on the state of the material during the deformation process. In our analysis, actual closed-loop feedback control laws which have previously been applied in experiments have been numerically simulated with a novel method of modifying the boundary conditions based on current conditions. This has lead to further understanding of the role of the control law in optimizing draw failure height. Our further investigation and analysis directly incorporates the predicted localized nature of failure of this process into the feedback loop and has lead to the construction of an improved control algorithm which has the potential of dramatically increasing the failure height and which can be used in on-line control of the process. The study clearly demonstrates the utility and power of using off-line detailed analyses which incorporate closed-loop feedback laws to obtain a better understanding of the physics of the deformations which occur during processing, and thereby greatly improve upon the algorithms which are used for real time control of forming or other processing.
Effect of Yield Surface Curvature on Local Necking in Biaxially Stretched Sheets in Porous Materials
Authors: Yan Xiangqiao
Published: April 2008

In this paper, a recently proposed material model (Sun model) that is based on the lower bound approach of plasticity is extended by introducing a family of dilatant plasticity theories. The yield surfaces change by a combination of isotropic expansion and kinematic translation. The sensitivity of the local necking predictions in biaxially stretched sheets to the curvature of the yield surface in porous materials is addressed. The results of the present analysis obtained by using four material models, the isotropic hardening version of Sun, the kinematic hardening version suggested in this paper, the Gurson model, and the Mear and Hutchinson model, indicate that the local necking predictions are highly sensitive to the curvature of the yield surface, and the predictions given by the kinematic hardening model are more reasonable for local necking analysis than those by the isotropic hardening model.
A Coupled Finite Element Model of Thermo-Elastic-Plastic Large Deformation for Orthogonal Cutting
Authors: Lin Z. C. , Lin S. Y.
Published: April 2008

In this paper, a coupled model of the thermo-elastic-plastic material under large deformation for orthogonal cutting is constructed. A chip separation criterion based on the critical value of the strain energy density is introduced into the analytical model. A scheme of twin node processing and a concept of loading/unloading are also presented for chip formation. The flow stress is taken as a function of strain, strain rate and temperature in order to reflect realistic behavior in metal cutting. The cutting tool is incrementally advanced forward from an incipient stage of tool-workpiece engagement to a steady state of chip formation. The finite difference method is adopted to determine the temperature distribution within the chip and tool, and a finite element method, which is based on the thermo-elastic-plastic large deformation model, is used to simulate the entire metal cutting process. Finally, the chip geometry, residual stresses in the machined surface, temperature distributions within the chip and tool, and tool forces are obtained by simulation. The calculated cutting forces agree quite well with the experimental results. It has also been verified that the chip separation criterion value based on the strain energy density is a material constant and is independent of uncut chip thickness.
Crack Closure and Propagation Studies to Determine the Effects of Simple Load Interaction
Authors: Chand Satish
Published: April 2008

Crack closure and fatigue crack growth experiments were performed on centrally notched specimens of 6063-T6 Al-alloy under single overload and block loading conditions. Using crack closure data, values of effective stress range ratio (U) were found. Assuming that the crack closure phenomenon is responsible for transient behavior of fatigue crack growth rate (FCGR), the FCGR behavior during load interaction was predicted using a constant amplitude crack propagation description in conjunction with the experimentally measured U-values. On comparing predicted FCGR with those found experimentally, it was observed that the predicted FCGR always agrees with the trend of experimental FCGR behavior and provides either exact or conservative estimates of the FCGR.
Transient Creep Strain of a Fiber-Reinforced Metal-Matrix Composite Under Transverse Loading
Authors: Wang Y. M. , Weng G. J.
Published: April 2008

Based on the combination of Mori-Tanaka’s mean-field concept and Luo-Weng’s solution of a three-phase cylindrically concentric solid, a local-field theory is developed to study the evolution of stress distribution in the ductile matrix and the time-dependent creep strain of a fiber-reinforced metal-matrix composite. Due to the nonlinear stress dependence in the creep rate and the highly heterogeneous nature of the transverse deformation, this local theory is shown to provide a more accurate estimate for the overall transverse creep of the composite than the simpler meanfield theory (the difference between the two however is not significant in the axial tensile creep). The disclosed transverse stress field in the matrix is truly heterogeneous, with the 45 deg region exhibiting a substantially higher effective stress than the 0 deg and 90 deg regions. The stress in the higher stress region is found to decrease continuously; it is passed on to the fibers and thereby serves as an important creep-strengthening mechanism for the composite. The interfacial tensile stress at the pole, which is the highest stress point around the interface, is seen to grow continuously and becomes a potential site for a later creep debonding. The developed micromechanical theory is finally applied to predict the transverse tensile creepstrain of a Borsic/aluminum composite, and the result is found to be in close agreement with the test data.
Modeling Complex Behavior of Metals by the “State-Kinetic Coupling Theory”
Authors: Lemaitre Jean , Marquis Didier
Published: April 2008

After introducing internal variables related to different mechanisms involved in the behavior of materials, two types of couplings are introduced in order to determine the state and dissipation potentials from which the constitutive equations are derived.
Dominant Creep Failure Process in Tensile Components
Authors: Hsia K. J. , Argon A. S. , Parks D. M.
Published: April 2008

The competing effects of failure by net section stress rupture and failure due to crack growth in creeping structural alloys have been investigated to determine the dominant failure process under various constant load service conditions. Two sets of experimental information were utilized: times to failure by quasi-homogeneous damage accumulation represented by Larson-Miller master curves, and creep crack growth rate information correlated either with C* for creep-ductile materials or with K for creep-brittle materials. A criterion, phrased in terms of the applied stress, temperature and initial crack length, has been established to justify the rate-determining fracture process. A number of materials, ranging from ductile materials such as Type 304 stainless steel, IN800H and low alloy steels obeying C*-controlled crack growth, to brittle materials such as Ni-based superalloys obeying K-controlled crack growth, have been studied. Both the configurations of infinite bodies and finitesize specimens were considered. The results show that for those materials where crack growth is C*-controlled, eventual failure is governed by quasi-homogeneous creep damage accumulation; whereas, for the materials with K-controlled crack growth, creep crack growth is likely to govern the final failure of engineering structures.
Impact Properties of a Laminated Composite Based on Ultrahigh Carbon Steel and a Ni-Si-Steel
Authors: Lee S. , Wadsworth J. , Sherby O. D.
Published: April 2008

A laminated composite consisting of an ultrahigh carbon steel (UHCS) and an 8Ni-2Si iron interleaf material can be selectively heat treated without carbon diffusion between adjacent layers. This desirable attribute leads to a low ductile-brittle transition temperature (DBTT) of about 163K ( − 110°C) after selective heat treatment. This result is a consequence of notch blunting from the presence of the sharp interlayer boundary and the tough interleaf material. Based on Charpy notch impact results of selectively heat-treated UHCS composites containing 8Ni-2Si iron and other interleaf materials, it is concluded that the DBTT is principally a function of the notch-toughness of the interleaf material.
A Creep-Fatigue-Oxidation Microcrack Propagation Model for Thermomechanical Fatigue
Authors: Miller M. P. , McDowell D. L. , Oehmke R. L. T.
Published: April 2008

A high temperature fatigue (HTF) life prediction model is developed based on the concept of microcrack propagation. The model is used to correlate isothermal HTF and thermomechanical fatigue (TMF) life for the Ni-base superalloy MAR-M247. The mechanical strain versus temperature relationships for the TMF tests include in-phase, out-of-phase, and a counter-clockwise diamond history. The proposed model explicitly accounts for damage from all three HTF damage mechanisms: fatigue, oxidation, and creep. The fatigue and oxidation components are correlated using the ΔJ parameter with an additional time dependence included in the oxidation term. The creep component is correlated using a stress power release rate-type parameter, Cˆ. In this paper, we focus on application of a model to HTF and TMF of Ni-base superalloys. However, the basic model features may well apply to other classes of metallic materials.
A Bounding Surface Theory for Cyclic Thermoplasticity
Authors: McDowell D. L.
Published: April 2008

A nonisothermal, rate and time independent generalization of nonlinear kinematic hardening theory for cyclic plasticity is introduced. The model includes decomposition of backstress and of isotropic hardening between the yield surface radius and the backstress amplitude. A purely temperature dependent component of yield surface radius is assumed in addition to an isotropic hardening component. Issues of thermoplastic material stability and temperature history independence are clearly distinguished and addressed via implications of temperature rate terms. Correlations are reported for OFHC copper subjected to thermomechanical cyclic loading.
On the Analysis of Distortion and Residual Stress in Carburized Steels
Authors: Henriksen M. , Larson D. B. , Van Tyne C. J.
Published: April 2008

This paper appraises the accuracy with which distortion and residual stress can be predicted in carburized and quenched gear steels. An experimental sample is heattreated such that a nonsymmetric carbon profile results. During quenching, the strip develops longitudinal transformation strains that result in amplified transverse deflections, similar to those of thin bimetallic strips. Deformations in carburized SAE 4023 and SAE 4620 alloys are compared with finite element predictions. The finite element procedure is based on an elastic-plastic yield surface which includes dependence on temperature. The analysis uses property data published and used by others. Some, but not all, of the predicted distortions agree with experiments; the study shows that distortions are quite sensitive to small variations in constitutive parameters. The paper includes recommendations for practitioners using finite element procedures for prediction of residual stress.
Consideration of Phase Transformations in the Study of Shear Bands in a Dynamically Loaded Steel Block
Authors: Zhu Z. G. , Batra R. C.
Published: April 2008

We study plane strain thermomechanical deformations of a square block made of steel, and model a material defect in it by a rigid non-heat-conducting ellipsoidal inclusion located at the center of the block. The boundaries of the block are presumed to be thermally insulated, and its top and bottom surfaces compressed vertically at a prescribed rate. The loading pulse is assumed to be made up of three parts; an initial segment in which the speed increases from zero to the steady value, the steady part, and the third part in which the speed decreases gradually to zero and is maintained at zero subsequently. In the undeformed state, the specimen is assumed to be fully annealed, isotropic, and its microstructure to be a mixture of coarse ferrite and cementite. A material point is presumed to start transforming into austenite once its temperature exceeds the transformation temperature; the rate of transformation is controlled by a simple kinetic equation. Proper account is taken of the latent heat required for the transformation, the associated volume change, and the variation in the thermophysicalproperties. The complete thermomechanical problem is analyzed during the loading and unloading phase till all of the body points have essentially come to rest, and the energy equation is solved subsequently. It is found that the austenite is quenched rapidly enough by the surrounding material for it to be converted into martensite rather than pearlite or a mixture of pearlite and martensite.
An Analysis of the Thin-Walled Torsion Specimen
Authors: White C. S.
Published: April 2008

A detailed finite element analysis has been conducted of the thin-walled torsion specimen. This specimen, when properly gripped, provides an approximation to the simple shear deformation field. Variations through the thickness of the specimen are small for the shear stress but can be large for the axial normal stress. Plastic deformation extends into the shoulder region requiring a correction factor to be used when converting the applied twist at the grips to average shear strain across the gauge section. This correction factor can be numerically quantified and used in data reduction.
Cyclic Stress-Strain Behavior and Low-Cycle Fatigue of Ti 6-4 at 260°C
Authors: Bui-Quoc T. , Gomuc R. , Biron A.
Published: April 2008

Low-cycle fatigue tests on Ti 6-4 (Ti-6Al-4V) have been carried out at 260°C under strain-controlled conditions with constant strain amplitude and increasing multistep strain levels. The results of constant strain amplitude tests were used to establish the fatigue diagram whereas the multistep tests were examined to assess the cyclic stress-strain behavior in comparison with the conventional stress-strain curve. Most of the tests were carried out under zero-to-tension conditions in the intermediatecycle range (Nf ≃ 3 x 103 to 105 cycles). The effect of prior strain cycling on the tensile properties was also investigated. The experimental data is discussed together with theoretical evaluations. In addition, microstructural examinations of the rupture surfaces have been made to show evidence on the type of crack initiation sites and on the crack propagation modes at different strain levels.
Use of the Shadow Optical Method of Caustics to Predict Fatigue Crack Growth in Compression
Authors: Leftheris B. P. , Papazian J. M.
Published: April 2008

The shadow optical method of caustics has been applied to the measurement of the bulging out of the surface of aluminum alloy 7075-T6 in the vicinity of a blunt notch in a single edge notch tensile sample after a compression overload and during compression fatigue. The size and shape of the caustic were found to be sensitive functions of the amount of elastic and plastic strain in the vicinity of the notch. Examination of the caustic during application and after release of the overload shows the elastic zone to be larger and more circular than the plastic zone, as predicted. A crack was propagated through the plastic zone using only far-field cyclic compression loading: the crack was self-arresting at the edge of the elasticplastic boundary created by the initial compression overload. The size of the plastic zone as measured by the caustic was found to agree with the maximum length of the crack. The actual surface profile in the vicinity of the notch was measured and its shape was used along with geometrical arguments to develop a model for interpretation of the caustics results. These results indicate that the caustics technique can be used to detect the presence of a plastic zone at the tip of a notch after a compressive overload, and that the size of this zone as measured by caustics is approximately equal to the size as determined by subsequent fatigue crack propagation.
Characterization of Fatigue Behavior in Cross-Ply Laminate of SCS-6/Ti-15-3 Metal Matrix Composite at Elevated Temperature
Authors: Mall S. , Portner B.
Published: April 2008

A study was conducted to investigate the fatigue behavior of a cross-ply, [0/90]2s, laminate of silicon fiber reinforced titanium matrix composite, SCS-6/Ti-15-3 at an elevated temperature of 427°C. Two sets of tests, at frequencies 0.02 and 2 Hz, were run at different stress levels. Fatigue damage initiation and growth patterns were dependent on the specific test conditions of frequency and stress level. Microscopic analysis of the fatigued specimens revealed matrix failure mechanisms ranging from ductile failure to cleavage fracture. The results of this study showed that temperature and frequency, as well as stress levels, are important design considerations for this composite in fatigue loading applications.
On the Mechanism of Plastic Deformation Induced Surface Roughness
Authors: Dai Y. Z. , Chiang F. P.
Published: April 2008

The plastic deformation induced surface roughening mechanism of aluminum sheets is experimentally investigated. Specimens used in the study have grain sizes varying from tens of microns to millimeters. The roughnesses of the specimens’ free surfaces are measured during plastic deformation by means of a mechanical stylus type profilometer with a tip radius of 5 microns. Observations show that plastic deformation roughens a free surface mainly by introducing slip bands within individual grains and relative rotation among grains. The average grain rotation and grain size are found to be the dominant contributor to the surface vertical characteristics such as the root-mean-square roughness. The surface horizontal characteristic such as the correlation length is found to be mainly determined by the average grain size. Based on the observations and some analysis, a model is advanced for the explanation of the phenomenon that the root-mean-square roughness is proportional to the magnitude of plastic deformation and average grain size.
Modeling Welding by Surface Heating
Authors: Sheng I. C. , Chen Y.
Published: April 2008

A mathematical model has been developed in describing the temperature distribution, the flow of the molten fluid and the stress field in the solid during welding. In modeling the properties of the material during welding, the solid phase is assumed to behave as a thermoviscoplastic solid obeying Bodner-Partom/Walker type constitutive equation, whereas the fluid phase as a thermoviscous incompressible fluid. Three regions exist: pure solid, pure fluid, and the transition (solid-fluid mixture). In the formulation of the boundary value problem, the energy equation is coupled to the equation of motion through the terms of mechanical work and the latent heat of the phases, whereas the equations of motion of the solid and the fluid are decoupled. Appropriate thermal and traction boundary conditions are detailed in the text. Phase transformation activities during cooling are monitored by CCT diagram and Avrami equation. An arbitrary Lagrangian and Eulerian method is used to accommodate the kinematic description of both the solid and the fluid phases. A representative plane perpendicular to the moving heat source is analyzed. Results of sample calculations are presented to show the temperature and the stress evolution in time. Residual stress and microstructure patterns are presented.
Test Machine and Control System Interactions in the Evaluation of Rate-Dependent Metal Flow
Authors: Brown S. B. , Dave V. R.
Published: April 2008

Although rate-change experiments are essential for characterizing rate-dependent flow, certain nonobvious aspects of test machine dynamic response and control system strategies can distort rate-change data. These distortions are large enough to cause rate-change experiments to characterize the test system dynamic response instead of the test material’s rate dependence. We demonstrate that both relaxation and strain rate change experiments exhibit this potential distortion of test data. Investigators performing these experiments must therefore examine control error carefully to assure that the experiments are valid. We demonstrate that the standard PID control modes normally used in servocontrolled mechanical test equipment will generate error. Either P or PD control modes are more appropriate for rate-change experiments.
Compression Failure in Reduced Adhesion Fiber Laminates
Authors: Swanson Stephen R. , Colvin Glenn E.
Published: April 2008

The compressive strength of fiber composites is of key interest in many strength critical composite structures, due to the generally lower failure values relative to tension dominated stress states. The general understanding of the factors that control compression failure is quite rudimentary, and as a consequence strength controlled design of practical structures loaded in compression can not be accomplished on a rational basis at present. In recent work it has been shown that the compressive strength of the principal load carrying axial plies is markedly affected by the adjacent plies in the laminate. A micro-mechanics model for compression failure of laminates has been formulated that attempts to explain the observed behavior. In the present work a further verification of the model is presented by means of a comparison with experiments performed on laminates with specially treated fiber-matrix interphases. In addition to control specimens using fibers with standard surface treatment, tests were carried out on laminates in which the fibers were treated with a release agent to reduce fiber-matrix adhesion. The specimens with reduced fiber adhesion showed a loss of strength of up to 75 percent, indicating the effects of loss of matrix support. The results show that the model explains a number of important features of the experiments, and thus gives insight into compression failure of laminates.
Role of Crack Wake Toughening on Elevated Temperature Crack Growth in a Fiber Reinforced Ceramic Composite
Authors: Nair Shantikumar V. , Gwo Tsung-Ju
Published: April 2008

Theoretical models were developed to predict the nature of the elevated temperature failure behavior in composites containing bridged cracks both for the case where crack front creep is absent (brittle regime) and for the case where a frontal creep process zone is present (ductile regime). The nature of the thermally activated time-dependent bridging of matrix cracks was first briefly reviewed from an earlier study and then applied to the case where crack front creep was present. Stable crack growth was predicted both in the presence and absence of crack front creep after an initial delay period, or initiation, which depends on crack size and wake parameters, such as, fiber diameter, volume fraction and interface properties. The dependence of the initiation time and crack growth rates on flaw size and wake parameters as well as on composite microstructure was derived both for the presence and absence of crack front creep. The implications of the results for elevated temperature composite component design are discussed.
Stable Crack Growth in Ceramics at Ambient and Elevated Temperatures
Authors: Pastor J. Y. , LLorca J. , Planas J. , Elices M.
Published: April 2008

Quasi-static, stable crack propagation tests in ceramics are presented. The tests are performed using a recently developed technique in which the crack mouth opening displacement (CMOD) is continuously monitored during the test by means of a laser extensometer, and this signal is employed to control a servo-hydraulic testing machine. The advantages of such tests to characterize the fracture behavior of ceramics at high temperature are described, and the technique is used to study the fracture behavior of an ytria-partially stabilized zirconia ceramic at ambient and elevated temperatures.
Finite Element Simulations of Fiber Pull-Out
Authors: Povirk G. L. , Needleman A.
Published: April 2008

Fiber pull-out is simulated through a quasi-static analysis of a circular elastic cylinder with a rigid cylindrical fiber embedded in its center. The interface between the fiber and the matrix is characterized in terms of a rate dependent internal variable friction constitutive relation. The analysis is carried out in two steps; one simulating the residual stresses that develop while cooling the cylinder from its processing temperature and the other simulating the mechanical response during fiber pull-out. Depending on parameter values, fiber pull-out can occur smoothly or a stick-slip instability can occur. Numerical simulations of fiber pull-out are presented that explore the effects of loading device stiffness, loading rate, and friction law parameters on the predicted behavior. For example, the amplitude of the load fluctuations during stick-slip was found to decrease as the rate of pull-out increased.
Toughening Mechanisms in Quasi-Brittle Materials
Authors: Shah S. P. , Ouyang C.
Published: April 2008

Fracture processes in cement-based materials are characterized by a large-scale fracture process zone, localization of deformation, and strain softening. Many studies have been conducted to understand the toughening mechanisms of such quasi-brittle materials and to theoretically model their nonlinear response. This paper summarizes two innovative experimental techniques which are being developed at the ACBM Center to better define the fracture process zone in cement-based materials. A brief summary is also given of two types of theoretical approaches which attempt to simulate some of the observed nonlinear fracture response of these materials.
An Evaluation of Gurson’s Theory of Dilatational Plasticity
Authors: Lee B. J. , Mear M. E.
Published: April 2008

Gurson’s constitutive theory for the plastic deformation of porous metals is specialized to small deformations of power-law solids containing a dilute concentration of voids, and the resulting incremental relations are integrated for proportional stress histories to obtain a total relation between stress and strain. The predictions of the theory are then evaluated by comparing them with accurate numerical results for spherical voids obtained by Lee and Mear (1992). The modification of Gurson’s theory proposed by Tvergaard (1982) is also discussed.
A Simple and Efficient Multiaxial Fatigue Damage Model for Engineering Applications of Macro-Crack Initiation
Authors: Chaudonneret Madeleine
Published: April 2008

This paper is devoted to the presentation of a multiaxial fatigue damage model, derived from Chaboche’s uniaxial formulation. Fit for use in the entire range of crack initiation life, it takes a number of different effects into account, including mean-stress influence and cumulative damage under nonperiodic proportional and nonproportional loadings. Its identification and integration is described, and it is shown as a simple but efficient engineering tool. Several examples, taken from different authors allows us to validate this kind of model.
Fatigue of AZ91E-T6 Cast Magnesium Alloy
Authors: Goodenberger D. L. , Stephens R. I.
Published: April 2008

The purpose of this research was to obtain room temperature fatigue behavior of AZ91E-T6 cast magnesium alloy and to determine if commonly used models that depict fatigue behavior are applicable to this cast alloy. Axial strain-controlled fatigue behavior using cylindrical specimens were employed to determine low cycle fatigue behavior with strain ratios R = εmin/εmax = 0, −1, and −2. The conventional log-log total strain low cycle fatigue model properly represented the R = −1 axial fatigue data. Significant mean stress relaxation occurred for all R = 0 and −2 axial fatigue tests. However, for the smaller strain amplitude tests with R = 0, sufficient mean stresses were retained such that fatigue life was reduced. The mean strains/stresses had little influence on the cyclic stress-strain curve which exhibited cyclic strain hardening. Mean stress effects were analyzed using the Morrow, SWT and Lorenzo-Laird models and similar, but oftentimes nonconservative, calculations resulted. Region I and II fatigue crack growth behavior was determined using C(T) speciments with load ratios R = Pmin/Pmax = 0.05 and 0.5. Values of ΔKth and (ΔKth)eff were less than 1.5 MPa m and the Paris equation slopes were between 3.3 and 3.9. Quasi-cleavage was predominant for both fatigue crack growth and final fracture regions. The commonly used low cycle fatigue and fatigue crack growth models appear to reasonably represent most of the results with this AZ91E-T6 cast magnesium alloy.
Strip Yield Analysis for Multiple Cracked Sheet With Riveted Stiffeners
Authors: Nishimura T.
Published: April 2008

An elasto-plastic analysis is conducted based upon a strip yield model for analyzing multiple cracks in a sheet reinforced with riveted stiffeners. Using the basic solution of a single crack and taking unknown fictitious surface tractions and fastener forces, Fredholm integral equations are formulated from the equilibrium condition along multiple cracks in the sheet. In addition compatibility equations of displacements are formulated among the sheet, fasteners and stiffeners. Based upon no stress singularity at the fictitious crack tips, these equations are iteratively solved as a single system of equations. Then the unknown fictitious surface tractions, fastener forces, and plastic zone sizes ahead of the crack tips are determined. The crack tip opening displacements for a multiple cracked sheet with riveted stiffeners are determined from the derived fictitious surface tractions and plastic zone sizes. Four example calculations and predictions are presented.
Prediction of Residual Stresses in Butt Welded Plates Using Inherent Strains
Authors: Ueda Y. , Yuan M. G.
Published: April 2008

The source of residual stresses in the vicinity of a weld may be expressed in terms of inherent strains. The characteristics of the inherent strain distributions in butt welds are investigated. It is found that the patterns vary little with changes in the welding conditions and sizes of the welded plates. With some assumptions, simple formulas are derived for the distribution and magnitude of inherent strain in a butt weld. A method of predicting the residual stress in a butt-welded plate using the characteristics of inherent strain distributions is presented. The validity of the method is confirmed by thermal elasto-plastic analysis using the finite element method (FEM).
Computational Model of Flame-Cutting
Authors: Lindgren L. E. , Carlestam A. , Jonsson M.
Published: April 2008

A computational model for simulation of flame-cutting has been developed. Two different cutting conditions are compared with respect to the residual stresses. The first case is a plate cut at room temperature and the other is the cutting of a preheated plate. The model depends on measured micro-structure to estimate the required heat input. The model is verified by comparing the calculations for the preheated plate with experimentally obtained residual stresses. Lower residual stresses in the preheated plate prevents subsequent cracking.
Fabrication of W-1%ThO2 Reinforced Fe-25Cr-8Al-0.5Y Superalloy Matrix Composite
Authors: Armstrong W. , Ramulu M. , Taya M.
Published: April 2008

Four different aligned W-1%ThO2 reinforced Fe-25Cr-8Al-0.5Y matrix fiber reinforced superalloy [FRS] material billets were produced by powder metallurgical processing. Three materials differed only in reinforcing fiber aspect ratio, while one material included a small diameter, misoriented Al2O3 hybrid reinforcement. Tensile and thermal cycling specimens were fabricated from the composite billets by using abrasive waterjet and turning processes. Finally the specimens were protected from high temperature oxidation by a FeCrAlY thermal spray coating. Metallurgical and mechanical properties were evaluated and discussed.
Thermal Fatigue of Composites: Ultrasonic and SEM Evaluations
Authors: Forsyth D. S. , Kasap S. O. , Wacker I. , Yannacopoulos S.
Published: April 2008

Results are presented on the evaluation of thermal fatigue in three fiber reinforced polymer composites, using ultrasonic techniques and scanning electron microscopy. The composites examined were (a) continuous carbon fibers in a vinylester matrix (b) continuous aramid fibers in a vinylester matrix and (c) randomly oriented aramid fibers in a polyphenylene matrix. Specimens of these composites were subjected to thermal fatigue by thermal cycling from −25°C to 75°C. Changes in ultrasonic attenuation and velocity were monitored during thermal cycling, and scanning electron microscopy was used to qualitatively evaluate any damage. It was observed that ultrasonic attenuation is sensitive to thermal fatigue, increasing with increasing number of thermal cycles. SEM evaluations showed that the primary damage due to thermal fatigue is due to fiber-matrix debonding.
Fractography of an Axle Which Broke Under Combined Bending Impact and Torsion
Authors: Johnson Alan A.
Published: April 2008

An automobile rear axle broke at the differential end when the vehicle collided with a tree at about 35 m.p.h. The fracture surfaces exhibited features characteristic of both bending impact and torsional overload. It was concluded that the fracture started as a bending impact when the frontal collision forced the entire drive system rearward. The fracture was completed by torsional overload when the drive system locked and the wheel continued to turn.
Measurement of Near Surface Residual Stresses Using Electric Discharge Wire Machining
Authors: Cheng W. , Finnie I. , Gremaud M. , Prime M. B.
Published: April 2008

In previous work it has been shown that near surface residual stresses may be deduced from surface strains produced by making a cut of progressively increasing depth. The process of electric discharge wire machining (EDWM), by providing very narrow cuts, greatly improves the ability of the method to resolve a stress gradient near the surface. However, the EDWM process may also introduce residual stresses. In the present work a model for estimating the influence of EDWM is presented, and a procedure for eliminating its effect on residual stress measurement is developed. Experimental results validate the theoretical approach.
Cumulative Damage Behavior of Anisotropic Al-6061-T6 as a Function of Axial-Torsional Loading Mode Sequence
Authors: Lin Hong , Nayeb-Hashemi Hamid , Berg Charles A.
Published: April 2008

Two types of low cycle fatigue tests were conducted along two principal orthotropic directions of an orthotropic Al-6061-T6 plate in strain control at room temperature: (1) reference fatigue tests under three loading conditions: push-pull, torsion, and combined push-pull/torsion in-phase; (2) sequential fatigue tests in which different sequences of push-pull and torsion were performed. Fatigue cracking behavior was observed during all of the fatigue tests. Shear cracking dominated the damage of the material. Anisotropic constitutive relations of the material were used in the evaluation of several multiaxial fatigue damage models. The predictive capabilities of these models were assessed based on the results of reference fatigue tests. The damage accumulation behavior of the material was found to depend on the sequence of the loading mode. For the sequence of torsion then push-pull, the damage summation was greater than unity. However, for the sequence of push-pull then torsion, the damage accumulation was near unity as predicted by the linear damage rule. A nonlinear damage accumulation rule could represent the results of the sequential fatigue tests.
On the Modeling of Nonproportional Cyclic Plasticity of Waspaloy
Authors: Abdul-Latif A. , Clavel M. , Ferney V. , Saanouni K.
Published: April 2008

The isotropic hardening is known to play an effective role in the overhardening of materials under nonproportional cyclic loading. However, the behavior of the two states of Waspaloy (namely overaged and underaged states) under these loading conditions, shows that the kinematic hardening has also a considerable role in the overhardening. Experimental tests were carried out on these two states under various proportional and nonproportional cyclic loading conditions at room temperature. The effect of loading paths on micro-mechanisms of deformation was studied. From a microstructural point of view, it was shown that the deformation modes (quantitatively and qualitatively) depend on the loading path and the heat treatment. A constitutive model is proposed to describe the effect of overhardening, under the nonproportional loading conditions, on the kinematic hardening. The predicted responses are in good agreement with experimental results.
Fatigue Behavior of a 22Cr-20Ni-18Co-Fe Alloy at Elevated Temperatures
Authors: Krukemyer T. H. , Fatemi A. , Swindeman R. W.
Published: April 2008

An experimental investigation was conducted on Haynes Alloy 556 to study the fatigue behavior of the material at elevated temperatures. Fatigue tests were run at constant temperatures ranging from room temperature to 871°C with strain ranges from 0.265 to 1.5 percent resulting in lives between 102 and 106 cycles. Cyclic deformation properties were evaluated based on the fatigue data. Three fatigue life models were evaluated for their ability to predict the isothermal fatigue lives of the material. These included the Ostergren, Frequency Separation and Stress-Strain-Time models. Strengths and weaknesses of each model are discussed based on the experimental results.
The Combined Effects of Notches and Microstructure on the Performance of Medium Carbon Steel Breakaway Couplings
Authors: Henkel D. P. , Pense A. W.
Published: April 2008

Combined effects of notches and microstructure on the structural performance of medium carbon steel breakaway couplings were discussed. Property troughs commonly associated with tempered martensite embrittlement were characterized as a function of temper for AISI 4130 and 4140 steel couplings. It was observed that a circumferential notch could change the fracture mode from ductile to brittle with no change in tempering condition. Notch-strengthening, a second significant effect, was also observed in similar couplings with an average strength increase of thirty percent. A critical assessment was made of the AASHTO specifications on breakaway couplings used for highway structures and of their interpretation by individual states.
High Temperature Multiaxial Low Cycle Fatigue of Cruciform Specimen
Authors: Itoh Takamoto , Sakane Masao , Ohnami Masateru
Published: April 2008

This paper describes high temperature multiaxial low cycle fatigue lives of type SUS304 stainless steel and 1Cr-1Mo-1/4V steel cruciform specimens at 923K and 823K in air. Strain controlled multiaxial low cycle fatigue tests were carried out using cruciform specimens at the principal strain ratios between −1 and 1. The principal strain ratio had a significant effect on low cycle fatigue lives. Fatigue lives drastically decreased as the principal strain ratio increased. Multiaxial low cycle faitgue strain parameters were applied to the experimental data and the applicability of the parameters was discussed. The equivalent strain based on crack opening displacement (COD strain) developed in the paper and Γ* —plane parameter successfully predicted multiaxial low cycle fatigue lives. The crack morphology was also extensively discussed from not only the surface crack direction but also the crack inclination into the specimen.
Effective Thermomechanical Behavior of Plain-Weave Fabric-Reinforced Composites Using Homogenization Theory
Authors: Dasgupta A. , Bhandarkar S. M.
Published: April 2008

A micromechanical analysis is presented to obtain the effective macroscale orthotropic thermomechanical behavior of plain-weave fabric reinforced laminated composites based on a two-scale asymptotic homogenization theory. The model is based on the properties of the constituents and an accurate, three-dimensional simulation of the weave microarchitecture, and is used for predicting the thermomechanical behavior of glass-epoxy (FR-4) woven-fabric laminates typically used by the electronics industry in Multilayered Printed Wiring Boards (MLBs). Parametric studies are conducted to examine the effect of varying fiber volume fractions on constitutive properties. Nonlinear constitutive behavior due to matrix nonlinearity and post-damage behavior due to transverse yarn failure under in-plane uniaxial loads is then investigated. Numerical results obtained from the model show good agreement with experimental values and with data from the literature. This model may be utilized by material designers to design and manufacture fabric reinforced composites with tailored effective properties such as elastic moduli, shear moduli, Poisson’s ratio, and coefficients of thermal expansion.
Creep, Stress Relaxation and Biaxial Ratchetting of Type 304 Stainless Steel After Cyclic Preloading
Authors: Ishikawa Hiromasa , Sasaki Katsuhiko
Published: April 2008

A series of tests for creep, stress relaxation, and biaxial ratchetting of type 304 stainless steel after cyclic preloading were carried out to investigate their interaction. The interesting fact was pointed out that back stress in cyclic plasticity played an important role to describe creep, relaxation, and biaxial ratchetting following cyclic preloading. Then, the test results showed that the material behavior due to creep after cyclic preloading could be represented by the modified Bailey-Norton law with stress levels evaluated from the current center of the yield surface, i.e., back stress which was determined by the hybrid constitutive model for cyclic plasticity proposed by the authors. In addition, biaxial ratchetting of axial strain induced by cyclic shear straining after cyclic preloading was expressed by the shear stress amplitude, the number of cycle and the axial stress level from the current center.
A Constitutive Model for Anisotropic Creep Deformation
Authors: Kawai M.
Published: April 2008

Anisotropic creep behavior of polycrystalline metals under repeated stress changes is modeled from a phenomenological point of view. The creep model consists of basic constitutive equations (BCE) and an auxiliary hardening rule (AUX) to enhance the predictive capability of the BCE. The BCE is characterized by a kinematic hardening variable which is defined as the sum of two component variables; one represents the back stress and the other a flow resistance in the opposite direction of the stress deviator. The AUX is governed by a memory region in which only the evolution of the back stress takes place. The validity of the creep model is discussed on the basis of simulations for multiaxial nonproportional repeated creep of type 304 stainless steel at 650°C.
Holographic Inspection of Plates Containing Areas of Localized Thickness Variation
Authors: Shang H. M. , Lwin M. , Tay T. E.
Published: April 2008

Circular plates, under unknown clamping conditions and containing simulated defects in the form of circular localized thinning or thickening, are inspected by double-exposure holography. With an incremental uniform pressure applied between exposures, eccentric defects are readily revealed from the distinct irregular fringe patterns. In the case of central circular defects, however, the absence of distinct irregular fringe patterns does not enable easy visual detection of the defects. The simple method of analysis described in this paper, based on the fact that the displacement in a defective plate differs from that in a defect-free plate, allows easy deduction of central and eccentric defects from the fringe patterns. Furthermore, this method enables identification of the type of defect (localized thinning or thickening), the extent of thickness variation, as well as an accurate estimation of the location and size of the defect.
Experimental Characterization of the Elastic-Plastic Strain Fields at the Crack Tip Due to Cyclic Loading
Authors: Ranganathan N. , Jendoubi K. , Merah N.
Published: April 2008

Some mechanical components cease to function satisfactorily, failing either under excessive elastic deformation or extensive plastic yielding. In the case of constrained plastification, the researcher is faced with some difficulties in evaluating plastic and elastic-plastic strain behavior near the crack tip. In the present study local strains are measured by microstrain gages, mounted near the crack tip on CT specimens made from the high strength aluminum alloy 2024-T351 under cyclic loading at constant ΔK. The behavior and the evolution of the elastic-plastic zone are studied as a function of the stress ratio R, the thickness of the specimen and the level of ΔK. The experimental results are compared with those given by numerical and theoretical analyses based on the concepts of linear elastic fracture mechanics (LEFM).
Thermally Induced Fields in Electroelastic Composite Materials: Average Fields and Effective Behavior
Authors: Dunn M. L.
Published: April 2008

The average thermally induced electroelastic fields and the effective thermal expansion and pyroelectric coefficients of two-phase composite materials are obtained by applying the Mori-Tanaka mean-field theory to the coupled response of electroelastic composites through a field superposition scheme. Results are obtained for composites reinforced by ellipsoidal piezoelectric and pyroelectric inhomogeneities and thus are applicable to a wide range of microstructural geometry including lamina, spherical particle, and continuous fiber reinforcement. The results are shown to obey the recently derived Levin-type equations relating the effective thermal expansion and pyroelectric coefficients of a two-phase composite to those of the constituents and the electroelastic moduli of the constituents and the composite. The analysis is developed in a matrix formulation convenient for numerical computation in which the electroelastic (elastic, piezoelectric, and dielectric) moduli are represented by a 9×9 matrix and the thermal expansion and pyroelectric coefficients by a 9×1 column vector. A limited parametric study is performed to illustrate the interesting behavior exhibited by some typical composite microstructures. Finally, analytical predictions are examined in light of existing experimental observations.