bluuebunny/crossref_metadata_2025 huggingface dataset:
The Effect of Aggregate Gradation on the Creep Response of Asphalt Mixtures and Pavement Rutting Estimates
Authors: Matthews JM , Monismith CL
Published: March 2009

The objective of this paper is to determine the influence of aggregate grading on asphalt mixture performance in rutting on heavy duty highways. For this purpose, the Hveem stabilometer method and simple creep tests (unconfined) were utilized. In both methods, Watsonville granite aggregate and AR 4000 and AR 8000 asphalts were used to cast specimens by kneading compaction. Two types of aggregate gradations were used: (1) California standard 0.5 inch (13 mm) maximum size, medium gradation and (2) California standard 0.5 inch (13 mm) maximum size, coarse gradation. The rut depths were predicted for a total of 15 cases, consisting of 4 temperature conditions, 2 aggregate gradations and 2 asphalts. The conclusions drawn, from the results of both methods of measuring performance (stabilometer and creep tests), were that (i) the medium graded mixtures provided significantly better performance in rutting than the coarse graded mixtures, and (2) temperature has more influence on rutting than the aggregate grading.
Deformation of Building Sealants Due to Movement During Cure
Authors: Brower JR
Published: March 2009

State-of-the-art testing of chemically cured building sealants movement capabilities is performed after sealants are fully cured. Field experience has shown that either immediate failures or premature sealant failures can and do occur as a result of joint movement during cure and the subsequent deformation of the installed sealant profiles. This paper discusses the effects of temperature cycling, panel size, sealant cure characteristics, joint spacing, building orientation, etc. Also included are suggestions for minimizing the effects of movement during the cure of the sealant.

The paper is nonproprietary and stresses the need for understanding of the problems and the need for development of tests and standard practices by ASTM and our industry associates
The Effect of Building Joint Movements on Outdoor Performance of Sealants During Their Cure
Authors: Matsumoto Y
Published: March 2009

Due to changes in environmental conditions, such as temperature, building joints move continuously. Accordingly, sealants in joints are subjected to such movements from the time of application. Failures of sealant in joints, such as cracking, breakage, and deformation, particularly those which occur in the short period of time after a sealant has been applied, may be caused by the movement of joints during the sealant curing. Up to the present, various research and testing methods in building material standards do not focus on performance against these failures. To study the relation between failure of sealants and the movement of joints, a testing apparatus was designed and dynamic outdoor exposure tests were conducted of various kinds of sealants. Failure of sealant attributable to joint movement during curing was found to occur in four patterns. These findings correspond to sealant failures actually observed in buildings in service.
Shear Component of a Structural Sealant Glazing Joint
Authors: Klosowski JM , Wong A
Published: March 2009

Thermal change loads in structural glazing should be of great concern to all and are every bit as important as the usually quoted tension loads imposed from the wind. Strong winds are an infrequent event in most areas of the country and the maximum wind load is approached infrequently. Thermal changes are daily events, and large thermal changes happen often. This paper discusses the proper way to calculate the forces on the sealant from thermal change and proper design considerations to accommodate the expected thermal changes.
Fatigue Life Prediction Under Thermal-Mechanical Loading in a Nickel-Base Superalloy
Authors: Rémy L , Bernard H , Malpertu JL , Rezai-Aria F
Published: March 2009

Thermal-mechanical fatigue of IN-100, a cast nickel base superalloy, was previously shown to involve mainly early crack growth using either bare or aluminized specimens. This crack growth was found to be controlled by interdendritic oxidation. A model for engineering life to crack initiation is thus proposed to describe this microcrack growth phase using local stresses in a microstructural volume element at the crack tip. The identification of damage equations involves fatigue crack growth data on compact tension (CT) specimens, interdendritic oxidation kinetics measurements and fatigue crack growth on CT specimens that have been embrittled by previous oxidation at high temperature. The application of this model to life prediction is shown for low cycle fatigue and thermal-mechanical fatigue specimens of bare and coated specimens as well as for thermal shock experiments.
Modeling of Thermomechanical Fatigue Damage in Coated Alloys
Authors: Kadioglu Y , Sehitoglu H
Published: March 2009

A life prediction model that determines the contribution of fatigue, creep and environmental damage to failure was developed for an aluminide coated nickel-based superalloy, Mar-M247. In the first phase of the study, isothermal (IF) and thermomechanical fatigue (TMF) experiments were conducted to investigate the experimental damage mechanisms. In the second phase, an analytical technique was advanced to compute the stress fields due to a surface inclusion in a half-space where the inclusion simulates the oxide spike. The technique is based on Eshelby's equivalent inclusion method and elucidates the mismatch in elastic moduli and thermal expansion coefficients of the matrix and the oxide spike on local strain fields. The fatigue life results of several experiments, along with the local stress-strain field in the vicinity of an oxide spike, were employed to define the model constants. Life prediction bounds are established corresponding to short-time coating protection, where the coating provides inconsiderable protection to substrate, and long-time coating protection, where the coating provides appreciable protection to the substrate. For in-phase loading, since the failure is governed by creep damage, the nature of coating protection did not influence the fatigue lives. The out-of-phase predictions corresponding to short-time coating protection and the experimental data coincided as the maximum temperature increased in the experiments, confirming that the coating provides unsubstantial protection at higher temperatures.
Analysis of Thermomechanical Cyclic behavior of Unidirectional Metal Matrix Composites
Authors: Coker D , Ashbaugh NE , Nicholas T
Published: March 2009

An analytical tool is developed to determine the three-dimensional stress state in a unidirectional composite subjected to axial loading and changes in temperature. A finite difference method is used to analyze a representative volume element of the composite which consists of concentric cylinders. The constituents are assumed to be elastic-plastic materials having temperature dependent properties. An iterative technique using the Prandtl-Reuss flow rule to determine incremental plastic strains is implemented in a computer code capable of predicting the axisymmetric triaxial stresses in a composite under thermomechanical fatigue (TMF) loading conditions. The model is verified with finite element method calculations for the problem of thermal residual stresses resulting from cool-down from the processing temperature. Results for several TMF loading conditions are compared with experimental data and 1-D predictions for a SCS-6 silicon carbide fiber and Ti-24Al-11Nb matrix composite. Significant differences are noted between results based on 1-D and 3-D approximations to the stress state in a composite and are discussed in detail.
Thermomechanical Fatigue of the Austenitic Stainless Steel AISI 304L
Authors: Zauter R , Petry F , Christ H-J , Mughrabi H
Published: March 2009

The isothermal and thermomechanical fatigue (TMF) behavior of the austenitic stainless steel AISI 304L has been studied in plastic strain control between room temperature and 1073K at a plastic strain amplitude of Δεpl/2 = 0.5% in vacuum. The isothermal fatigue experiments showed a maximum of the stress amplitude connected with a change of the dislocation slip mode towards planar glide in an intermediate temperature region between about 550K and 800K as a result of dynamic strain ageing processes. The stress amplitudes in TMF tests are strongly influenced by the maximum temperature. When the maximum temperature lies below 873K and the temperature intervals extend over the full range of dynamic strain ageing, the stress amplitudes are very similar to the maximum values under isothermal conditions. With increasing maximum temperature, dynamic recovery by dislocation climb gains importance and the stress amplitudes decrease. When the maximum temperature of the TMF cycling exceeds a limit of about 1000K, dynamic recrystallization is observed. The numbers of cycles to fracture depend strongly on the phase between temperature and plastic strain. In particular, during in-phase cycling with a maximum temperature of 923K and higher, early failure occurs due to creep damage during the tensile half cycle. At maximum temperatures lower than 823K, the absence of creep phenomena results in similar cycle numbers to fracture in out-of-phase and inphase tests, respectively.
Thermomechanical Fatigue of Turbo-Engine Blade Superalloys
Authors: Guedou JY , Honnorat Y
Published: March 2009

A thermomechanical fatigue (TMF) facility has been developed in the Snecma Materials Laboratory to characterize the mechanical behavior and the damaging processes of blade superalloys under realistic loading conditions. Three nickel-base superalloys have been investigated using a reference TMF cycle representative of blade leading edge. Stabilized stress-strain loops exhibit greater plastic strains and higher stress amplitudes for an equiaxed alloy IN-100, mainly due to elastic anisotropy of the directionally solidifed DS-200 and AM1 single crystal alloys. The application of a viscoplastic constitutive model shows a good correlation between calculation and experiment for DS-200 and AM1 but indicates that the IN-100 model coefficients need improvement.

The TMF lives are much more important for the two oriented alloys (that is, AM1 and DS-200) as compared with the equiaxed IN-100, as in isothermal LCF conditions, but a correlation between TMF and LCF lives cannot be easily proposed and depends upon the material considered. The damaging mechanisms have been investigated on single crystal failed specimens, and compressive loads at high temperature play an important role in the damaging process. A continuous damage model delivered good predictions for TMF lives on equiaxed alloy specimens. Nevertheless, the application of such a model to structure calculations must take into account possible effects of crystallographic anisotropy in the case of directionally solidified (DS) and single crystal alloys.
Proposed Framework for Thermomechanical Fatigue (TMF) Life Prediction of Metal Matrix Composites (MMCs)
Authors: Halford GR , Lerch BA , Saltsman JF , Arya VK
Published: March 2009

The framework of a mechanics of materials model is proposed for thermomechanical fatigue (TMF) life prediction of unidirectional, continuous-fiber metal matrix composites (MMCs). Axially loaded MMC test samples are analyzed as structural components whose fatigue lives are governed by local stress-strain conditions resulting from combined interactions of the matrix, interfacial layer, and fiber constituents. The metallic matrix is identified as the vehicle for tracking fatigue crack initiation and propagation. The proposed framework has three major elements. First, TMF flow and failure characteristics of in situ matrix material are approximated from tests of unreinforced matrix material, and matrix TMF life prediction equations are numerically calibrated. The macrocrack initiation fatigue life of the matrix material is divided into microcrack initiation and microcrack propagation phases. Second, the influencing factors created by the presence of fibers and interfaces are analyzed, characterized, and documented in equation form. Some of the influences act on the microcrack initiation portion of the matrix fatigue life, others on the microcrack propagation life, while some affect both. Influencing factors include coefficient of thermal expansion mismatch strains, residual (mean) stresses, multiaxial stress states, off-axis fibers, internal stress concentrations, multiple initiation sites, nonuniform fiber spacing, fiber debonding, interfacial layers and cracking, fractured fibers, fiber deflections of crack fronts, fiber bridging of matrix cracks, and internal oxidation along internal interfaces. Equations exist for some, but not all, of the currently identified influencing factors. The third element is the inclusion of overriding influences such as maximum tensile strain limits of brittle fibers that could cause local fractures and ensuing catastrophic failure of surrounding matrix material. Some experimental data exist for assessing the veracity of the proposed framework.
Residual Life Assessment of Pump Casing Considering Thermal Fatigue Crack Propagation
Authors: Sakon T , Masaharu F , Sada T
Published: March 2009

Thermal fatigue crack propagation is the main concern on the life assessment of the boiler feed-water circulation pump casings under cyclic operation. This paper describes the experimental and analytical studies on the thermal fatigue crack growth behavior, and the remaining life prediction of the casings.

First, it was confirmed by low-cycle fatigue test that the propagation behavior of surface cracks accompanied with the coalescence could be estimated by the da/dN-ΔJ relationship for long cracks. Secondly, the simplified J-integral estimation method for the thermal stress problem was discussed based on some bench mark calculations. Finally, the crack growth behavior in the casings was estimated and the results were compared with the field inspection data. Good agreement was found between them and, hence, these type of pump casings had adequate remaining lives to the final failure.
Structural Problems in Search of Fracture Mechanics Solutions
Authors: Barsom JM
Published: March 2009

This second Jerry L. Swedlow Memorial Lecture presents a few significant developments in fracture mechanics that occurred over the past 25 years and some unresolved problems relating to materials and design and to technology transfer and education. Examples of some accomplishments and problems needing solutions are presented in areas of fracture toughness, including elastic, elastic-plastic and short cracks, and of environmental effects.

Professor Jerry L. Swedlow was an educator and a researcher who devoted his career to the transfer of technology to his students and to scientists and engineers. Thus, the lecture appropriately concludes with a few observations, needs, and recommendations concerning technology transfer.
Crack Initiation Under Generalized Plane-Strain Conditions
Authors: Shum DKM , Merkle JG
Published: March 2009

A method for estimating the decrease in crack-initiation toughness, from a reference plane-strain value, due to positive straining along the crack front of a circumferential flaw in a reactor pressure vessel, is presented in this study. This method relates crack initiation under generalized plane-strain conditions with material failure at points within a distance of a few crack-tip-opening displacements ahead of a crack front, and involves the formulation of a micro-mechanical crack-initiation model. While this study is intended to address concerns regarding the effects of positive out-of-plane straining on ductile crack initiation, the approach adopted in this work can be extended in a straightforward fashion to examine conditions of macroscopic cleavage crack initiation. Provided single-parameter dominance of near-tip fields exists in the flawed structure, results from this study could be used to examine the appropriateness of applying plane-strain fracture toughness to the evaluation of circumferential flaws, in particular to those in ring-forged vessels that have no longitudinal welds. In addition, results from this study could also be applied toward the analysis of the effects of thermal streaming on the fracture resistance of circumferentially oriented flaws in a pressure vessel.
Experimental Relationship Between Equivalent Plastic Strain and Constraint for Crack Initiation
Authors: Reuter WG , Lloyd WR , Williamson RL , Smith JA , Epstein JS
Published: March 2009

The applicability of fracture mechanics data generated from standard fracture toughness specimens in predicting structural integrity is often a concern. For elastic-plastic conditions, a second parameter identified as “constraint” (hydrostatic stress divided by the equivalent stress) is being used to link different specimen/flaw configurations, thus providing a mechanism for using data generated from standard fracture toughness specimens to predict structural integrity. Much of the literature is concerned with the difference in constraint between specimens and a structure, while little effort is being given to investigating the sensitivity of the crack initiation process to constraint for a given material. This paper presents experimental results relating crack initiation processes to constraint for a ferritic steel and an aluminum-based alloy.
A Comparison of Weibull and βIcAnalyses of Transition Range Data
Authors: McCabe DE
Published: March 2009

Specimen size effects on KJc data scatter in the transition range of fracture toughness have been explained by extremal (weakest link) statistics. In this investigation, compact specimens of A533 Grade B steel were tested in sizes ranging from ½TC(T) to 4TC(T) with sufficient replication to obtain good three-parameter Weibull characterization of data distributions. The optimum fitting parameters for an assumed Weibull slope of four were calculated. Extremal statistics analysis was applied to the ½TC(T) data to predict median KJc values for 1TC(T), 2TC(T), and 4TC(T) specimens. The distributions from experimentally developed 1TC(T), 2TC(T), and 4TC(T) data tended to confirm the predictions. However, the extremal prediction model does not work well at lower-shelf toughness. At -150°C, the extremal model predicts a specimen size effect where in reality there is no size effect.

Another model that has potential for dealing with data scatter effects in the transition range is the Irwin βc-βIc relationship. This model uses breakdown in constraint as the argument for specimen size effects and suggests that data sets can be transposed from one size to another by operating on each individual datum with the following equation KIc=KJcβIc/βc

Both models predict about the same distributions for specimens larger than 1TC(T), and only the extremal statistical model can predict correctly the smaller specimen distribution. With the βc-βIc relationship, the limitation appears to be that βc ⩽ π must not be exceeded. Therefore, both the statistical and βIc models have limitations for their use. This study explores these limitations and makes specimen size requirement recommendations on KJc data.
The Conditions at Ductile Fracture in Tension Tests
Authors: Dexter RJ , Roy S
Published: March 2009

The geometry dependence of several potential criteria for the onset of ductile fracture in tension tests was investigated for a modern tremethylcyclopentanone (TMCP) line pipe steel using an experimental/numerical approach. Large-strain finite-element simulations were used to estimate the state of stress and strain in highly instrumented notched and smooth tension tests of various geometries. The softening effect of void growth became significant only after the specimens had undergone extensive necking and had lost most of their load-carrying capacity. Therefore, for this steel, a practical fracture criterion can be based on the conditions at the onset of significant void growth, eliminating the need for void-growth modeling. At the onset of significant void growth, the maximum principal strain, the effective strain, and the strain energy density were independent of the tension-test geometry.
Evaluation of Dynamic Fracture Toughness Using the Normalization Method
Authors: Herrera R , Carcagno G , de Vedia LA
Published: March 2009

This paper presents a simple technique to determine dynamic J-R curves from a single, precracked Charpy-type specimen by means of an instrumented Charpy testing machine. This technique is based on the normalization method proposed originally by Landes and Herrera. This method eliminates the need for crack length monitoring that makes it particularly suitable under dynamic loading conditions.

The method used to generate J-R curves consisted of conducting precracked Charpy tests using a stop block. This simple device allows interruption of the test before the specimen is completely broken, furnishing the two calibration points necessary for applying the normalization method. J-R curves obtained with the normalization method were compared with values calculated following the multiple specimen technique.
Asymptotic Analysis of Steady-State Crack Extension of Combined Modes I and III in Elastic-Plastic Materials with Linear Hardening
Authors: Yuan H , Cornec A
Published: March 2009

In this paper, asymptotic crack-tip fields of steady-state crack extension in materials with linear plastic hardening under combined in-plane (Mode I) and anti-plane shear (Mode III) loading conditions are investigated. Only the power singularity form of the in-plane and the anti-plane shear stresses is assumed, and the coupled differential equations are solved by means of the perturbation method. The governing equations of the asymptotic crack-tip field are formulated from two groups of angular functions: one for the in-plane mode and the other for the anti-plane shear mode. All stresses and deformations are of variable-separable forms of r and ϑ that represent the polar coordinates centered at the actual crack tip. Perturbation solutions of the governing equations have been carried out. The perturbation solutions predict that, regardless of the mixity of the crack-tip fields and strain-hardening, the in-plane stresses under the combined Mode I and Mode III loading conditions are generally more singular than the anti-plane shear stresses. The anti-plane shear stresses perturbed from the plane-strain Mode I field lose their singularity for small strain hardening, whereas the angular variation of stresses perturbed from the plane-stress Mode I behaves quite similarly to the pure Mode III solution. An obvious deviation between the perturbed and the unperturbed solutions can be observed under combined plane-strain and anti-plane Mode III loading conditions, but not under the plane-stress and Mode III conditions. The results imply that there exist no uniformly singular crack-tip fields under combined in-plane Mode I and anti-plane Mode III loading conditions.
Stress Intensity Factor Solutions for Partial Elliptical Surface Cracks in Cylindrical Shafts
Authors: Chen K-L , Kuo A-Y , Shvarts S
Published: March 2009

Pump shaft cracking has become an emergent issue recently in power industry. Prediction of residual life for a cracked shaft relies on accurate stress intensity factor calculations. Because of the three-dimensional nature of the cracked shaft problem, it is prohibitively expensive to obtain a complete stress intensity factor solutions library with three-dimensional finite-element method.

The expensive task of performing the three-dimensional fracture analyses can be alleviated by using an alternating analytical procedure. The alternating analytical procedure utilizes two analytical solutions: (a) the solution for an elliptical crack embedded in an infinite domain and (b) the solution for an infinitely long, uncracked cylinder subjected to arbitrary surface loadings. Because no finite-element mesh is required in the alternating analytical technique, the efforts to accomplish this study has been reduced significantly.

Cracked shafts under tensile, bending, and torsional loads are studied in this paper. K solutions for a wide range of crack geometries are presented. The K solutions can be applied in shaft residual life studies.
Development of Fatigue Life Prediction Program for Multiple Surface Cracks
Authors: Kim Y-J , Choy Y-S , Lee J-H
Published: March 2009

The objective of this paper is to develop a computational model and a software for predicting the fatigue propagation of collinear multiple surface cracks under constant-amplitude and variable-amplitude loading. After examining fatigue crack growth rate data for compact tension (CT) specimens and single surface crack specimens, an empirical equation is proposed for the prediction of fatigue life in a multiple surface crack geometry. The accuracy of the proposed model is verified using a life prediction computer program. The predictions are compared with the results from several case studies to check the accuracy of the proposed model and to verify the usefulness of the developed program. Good agreement is observed between the numerical results based on the proposed model and the published experimental data.
Investigating the Near-Tip Fracture Behavior and Damage Characteristics in a Particulate Composite Material
Authors: Liu C-T
Published: March 2009

In this study, the local fracture behavior and damage state near the crack tip in a particulate composite material were investigated through the use of precracked sheet specimens. The specimens were subjected to a simple incremental strain history at room temperature. During the test, a high-energy real-time X-ray system was used to record the X-ray data and the fracture process near the crack-tip region. The experimental data were analyzed and the results are discussed.
Effect of Fiber-Matrix Debonding on Notched Strength of Titanium Metal-Matrix Composites
Authors: Bigelow CA , Johnson WS
Published: March 2009

Two specimen configurations of a [0/90]2s SCS-6/Ti-15-3 laminate were tested and analyzed: a center-hole (CH) specimen and a double-edge-notched (DEN) specimen. The two specimen configurations failed at similar stress levels in spite of the large difference in the stress concentration factors for the two geometries. Microscopic examinations of the failure surfaces indicated more fiber-matrix debonding at the notch tip in the DEN specimen than in the CH specimen. Based on the experimental results, it was hypothesized that the radial stresses that developed at the fiber-matrix interface ahead of the notch tip in the DEN specimen caused fiber-matrix debonding in the 0° plies, thus lowering the stress concentration in the DEN specimen to a level comparable to that of the CH specimen.

Two analytical techniques, a three-dimensional finite-element analysis and a macro-micro-mechanical analysis, were used to predict the overall stress-deformation behavior and the notch-tip fiber-matrix interface stresses in both configurations. The micromechanical analysis predicted radial stresses next to the notch in the DEN configuration that were nearly seven times as large as those predicted for the CH configuration. The overall stress-deformation response of both configurations was predicted accurately when debonding of the 90° plies was included. Predictions of the axial stress in the notch-tip 0° fiber correlated well with the specimen static strength when fiber-matrix debonding of 0° plies was included for the DEN specimen. The results shown indicate that a first fiber failure criteria based on the axial stress in the first intact 0° fiber can predict the static strength of notched specimens when interfacial damage is modeled.
Evolution of Notch-Tip Damage in Metal-Matrix Composites During Static Loading
Authors: Bakuckas JG , Awerbuch J , Tan T-M , Lau ACW
Published: March 2009

The evolution of notch-tip damage during static loading in center-notched unidirectional boron/aluminum and silicon carbide/titanium composites was characterized through a two-prong investigation involving experiments and analysis. The effects of heat treatment on the failure process in boron/aluminum were addressed. In the experimental phase, the notch-tip damage initiation and progression was monitored and recorded in real time through a high-magnification (× 150) closed-circuit television system, acoustic emission, and load-deformation responses. Fracture surface morphologies were examined via a scanning electron microscope in order to identify the microfailure mechanisms.

In the analytical phase, a numerical technique was employed to predict the failure process in the materials studied without specifying the crack path a priori. The predictions elucidated the failure mechanisms and their interaction in the evolution of damage ahead of an existing crack. Correlations were made with experimental results in terms of the observed failure process and load-deformation responses. Good agreement was obtained between the observed failure process and predictions. The computational predictions captured the salient features in the observed failure processes.

Notch-tip damage progression was quite different in the various materials studied. A complex state of damage developed in the vicinity of the notch-tip consisting of several dominant failure mechanisms. The various failure mechanisms were identified, and the development of the notch-tip damage zones was determined.
Experimental Verification of a New Two-Parameter Fracture Model
Authors: Richardson DE , Goree JG
Published: March 2009

This paper presents an experimental verification of a new two-parameter fracture model based on the equivalent remote biaxial stresses (ERBS) developed by the authors. A detailed comparison is made between the new theory and the constant, KIc, approach of linear elastic fracture mechanics (LEFM). Fracture is predicted through a failure curve representing the change in a variable fracture toughness, Kc, with the ERBS ratio, B. The nonsingular term, T, in the series expansion of the near crack-tip transverse stress is included in the model. Experimental results for polymethyl methacrylate (PMMA) show that the theory can account for the effects of geometry on fracture toughness as well as indicate the initiation of crack branching. It is shown that the new criterion predicts failure for PMMA with a 95% confidence zone that is nearly three times smaller than that of the LEFM KIc approach.
Near-Tip Behavior of Particulate Composite Material Containing Cracks at Ambient and Elevated Temperatures
Authors: Smith CW , Wang L , Mouille H , Liu C-T
Published: March 2009

After briefly reviewing the results of a series of constant head rate tests on center-cracked “biaxial” test specimens of a particulate composite at room temperature, a second test series utilizing edge-cracked “biaxial” specimens of a particulate composite with a different particulate gradation at ambient and elevated temperatures and low and moderately high head rates is discussed. Results show different near-tip mechanisms for crack opening and growth for the two materials and, while changes in head rate and temperature produced quantitative differences in near-tip fields of displacement and strain for both materials, they did not affect the basic near-tip mechanisms of each material qualitatively.
Probabilistic Fracture Mechanics Evaluation of Local Brittle Zones in HSLA-80 Steel Weldments
Authors: Eiselstein LE , Harris DO , Scoonover TM , Rau CA
Published: March 2009

The engineering significance of local brittle zones in multipass, HSLA-80 steel weldments that might be subjected to large strains (such as the straining that occurs during explosive bulge testing) was evaluated through the use of probabilistic fracture mechanics. The heat-affected zone of HSLA-80 was modeled as containing only two distinct types of material along the fusion line, local brittle zones, and the gaps between them. The local brittle zones have a lower toughness than gap material, and both have toughness properties that are lower than those of the base plate. The model calculated the failure probability of weldments as they are plastically strained to various levels by simulating the growth of preexisting crack-like weld defects that are distributed along the fusion line and within the weld metal. Failure was considered to occur if weld defects link up and grow through the entire plate thickness. The model incorporates the statistical variation of the toughness for the base metal, weld metal, local brittle zones, and gap materials to model the tearing resistance along the fracture path. The probabilistic fracture mechanics modeling of typical HSLA-80 weldments indicates that the distribution and toughness of local brittle zones and gaps have a small effect on the failure probability at large plastic strains typical of explosive bulge tests. The calculated failure probabilities agree with a limited number of actual explosive bulge tests. At the large strain levels considered, the simulations showed that the failure probabilities are nearly equal to the existence probability of welding defects.
A New Device for Evaluating Load-Transfer In Geosynthetic Reinforced Soils
Authors: Whittle AJ , Larson DG , Germaine JT , Abramento M
Published: March 2009

Although geosynthetics are often used in soil reinforcement applications, there are currently no methods for estimating reliably the stresses within the reinforcements at working load levels. This paper summarizes the design of a new laboratory device, referred to as the Automated Plane Strain Reinforcement (APSR) cell, which measures the maximum tensile stress that develops at the center of a single planar inclusion due to shearing of the surrounding soil. The cell can accomodate a wide range of reinforcing materials and can be equiped with additional instrumentation to measure the distribution of strains and/or stresses with inclusions of half-lengths up to 450mm. Test data, obtained for an instrumented steel sheet inclusion embedded in Ticino sand, demonstrate the capabilities of the APSR cell for measuring load-transfer at working load levels. Simple closed form solutions based on shear lag analysis describe accurately the tensile stresses measured in the elastic steel sheet inclusion. The new device provides the capability to compare load-transfer characteristics for different classes of geosynthetic reinforcing materials.
Laboratory Testing of Modular Masonry Concrete Block-Geogrid Facing Connections
Authors: Bathurst RJ , Simac MR
Published: March 2009

This paper describes a laboratory apparatus and test procedure that was developed by the authors to quantify the mechanical behavior of the connection between mortarless modular concrete block units and geogrid reinforcement materials. The paper illustrates that the tests should be carried out with 1-m wide samples of geogrid reinforcement in order to account for the influence of block joints and surface geometry irregularities that occur along the length of typical geogrid-reinforced concrete block walls. This paper gives recommendations for a 20 ram/min rate of loading. The interpretation of connection strength and efficiency for modular block-geogrid reinforcement connection systems is related to conventional index strengths that are routinely reported in the literature based on the ASTM D 4595 method of test.
Evaluation of Shear Strength and Dilatancy Behavior of Reinforced Soil from Direct Shear Tests
Authors: Bauer GE , Zhao Y
Published: March 2009

In order to evaluate the shear strength and dilatancy behavior of coarse granular soils reinforced with geogrid a large direct shear apparatus (1000×1000×940 mm) was built. A series of shear tests were carried out to study the effect of geogrid orientation and soil volume changes on shear strength. A numerical model is proposed to calculate the shear strength increase. This is verified by the experimental results. Tensile strains in the geogrid can also be calculated using this model.
Pullout Resistance and Load-Slip Response of Mechanically Damaged Geogrids
Authors: Razaqpur AG , Bauer GE , Halim AOA , Zhao Y
Published: March 2009

Pullout tests were conducted on 30 pre-damaged specimens of a uniaxial and a biaxial polyester geogrid to determine the effect of damage on their pullout resistance and end displacement. The specimens were embedded in crushed aggregates and subjected to surcharge loads of 14 kPa and 20 kPa. The results showed that substantial damage in the tested specimens could reduce their maximum pullout force by up to 33% and their pullout stiffness by 50%, where pullout stiffness is defined by the ratio of the maximum pullout force to the corresponding slip (KN/mm). For moderate amounts of damage, the reduction was in the order of 10% to 14%. These results suggest that the present safety factors for installation damage (1.1 to 3.0) may be applicable to pullout resistance, but they may need to be modified for controlling displacements in geogrids.
Testing for Biological Deterioration of Geosynthetics in Soil Reinforcement and Stabilization
Authors: Bright DG
Published: March 2009

Over the past decade, critical earthen structures have been designed to incorporate geosynthetics. To facilitate proper design and assure long-term stability, it is necessary to know the susceptibility of these geosynthetics to biological deterioration. The perception is that the polymers and their additives used in geosynthetics are not susceptible to biological degradation. However, the literature clearly shows that some polymers and common additives are susceptible. Through mutation, microorganisms can develop specificity towards a host material. Biocides exhibit specificity and limited effectiveness. Unfortunately, current test methods are quite inadequate, for many reasons, in assessing the biological stability of the geosynthetics on the market today. A alternative test protocol circumvents these shortcomings and accounts for synergistic effects, heretofore ignored. A means of predicting long-term stability through superposition principles is suggested.
Stability Analysis of Thick-Section Composite Cylinders Under Hydrostatic Pressure Including Three-Dimensional Effects and Nonlinear Material Response
Authors: Bonanni DL
Published: March 2009

Recent studies of thick-section laminated composite materials and structures have suggested that there is a need for three-dimensional (3-D) structural analysis methods which include the nonlinear material response of the constituents. The work described in this paper integrates a 3-D micromechanics-based nonlinear constitutive model for laminated composite materials into 3-D structural analyses performed with the ABAQUS general purpose finite element code. The nonlinear model and its incorporation into ABAQUS are described. The method is demonstrated through 3-D stability analyses of thick, unstiffened AS4/3501-6 carbon/epoxy circular cylinders under external hydrostatic pressure. The results of two-dimensional (2-D) shell finite element analyses of these cylinders are also presented for comparison. The cylinders analyzed are geometrically identical and are subjected to the same loading and boundary conditions. Five different ply layups are considered, including cross-ply, quasi-isotropic, and [±45°]. Modeling the nonlinear material response is found to reduce the predicted cylinder collapse load by up to 50% when layers oriented at ±45° to the cylinder axis are present in the laminate. The role of material nonlinearity in the plane of the laminate versus through-thickness nonlinearity is discussed for the cylinders analyzed.
Application of a New Micromechanics-Based Homogenization Technique for Nonlinear Compression of Thick-Section Laminates
Authors: Pecknold DA , Rahman S
Published: March 2009

A simple micromechanics-based material model for nonlinear analysis of thick-section laminated composites is presented. The model, which has been incorporated in a finite element package, provides constitutive information for the laminate at a material point (Gaussian integration point) in a standard displacement-based isoparametric 3-D or thick-shell finite element. This integrated approach allows the use of micromechanics-based criteria for detection of failure, including compression kink banding, in the analysis of a composite structure or structural component. A nonlinear elastic power-law model is used to reflect matrix shear softening; simple maximum stress criteria are used for detection of failure in constituent phases; and the tangent shear modulus of the matrix phase (determined as a function of load level during the nonlinear stress analysis of the composite) is used in the Hahn-Williams criterion to detect compression kink banding. Numerical procedures are used to redistribute the load in damaged regions. Detailed comparisons with published numerical and experimental results are presented, including: elastic modulus predictions for a graphite/epoxy lamina; nonlinear response of unidirectional boron/epoxy laminae and laminates with various stacking sequences; and nonlinear response of a notched graphite/epoxy laminate in compression.
A Shear Deflection Theory for Analysis of End Plugs for External Pressure Tests of Composite Cylinders
Authors: Blake HW , Starbuck JM
Published: March 2009

A shell theory, based on the Donnell approximation with modifications to include transverse shear deformations, is applied to the analysis of contoured end plugs for external pressure tests of composite cylinders. Solutions are derived for constant radius and linear taper end plugs. The effect of finite shear stiffness on stresses and end plug contact length is determined and results compared with earlier shell solutions based on bending deformations only. Computed stress values for finite and infinite shear stiffness are compared for a graphite composite cylinder. Results indicate that the effect of shear deformations is large for transverse shear stiffness values typical of composite cylinders. The effects are evident in both results for stresses and contact length. Solutions which neglect shear effects underestimate the contact length and overestimate the maximum stresses. Further conclusions are drawn as to the preferred plug contour for reducing the end effect.
The Effect of Assembly Fit-Up Gaps on the Compression Response of Thick-Section Carbon/Epoxy Composites
Authors: Camponeschi ET , Bohlmann RE , Hall J , Carr TT
Published: March 2009

The compressive response of thick, quasi-isotropic, AS4/3501-6 laminates with geometric anomalies was investigated theoretically and experimentally. The specimens considered were rectilinear with nominal dimensions of 254 mm (10 in.) long, by 102 mm (4 in.) wide, by 29.9 mm (0.78 in.) thick. The anomalies were designed to simulate expected fit-up clearance conditions resulting from normal manufacturing tolerances in the sphere joint regions of the DARPA Man-Rated Demonstration Article. Tests were conducted both with unfilled fit-up gaps and with fit-up gaps filled with a polymer shimming material (Hysol EQ9394). Strains were monitored in the specimen gage sections and in regions of high strain concentration resulting from the manufacturing anomalies. Measured strains correlated well with predicted strains from an ABAQUS finite element analysis. For all test cases the specimens were able to withstand strains due to the anomalies when gage section strain reached 7000 με. One specimen with no anomalies was tested to failure in uniaxial compression and failed in the gage section at 614 MPa (89.0 ksi) and 13 500 με, which is equivalent to autoclave-cured, thin-section composite failure strains for this material system and layup.
Compression Response of a Fatigue-Loaded Composite Hip Prosthesis
Authors: Liao K , Lee SS , Reifsnider KL
Published: March 2009

The compression-compression fatigue behavior of a kind of hip prosthesis made from laminated fiber-reinforced polymeric composite material under biaxial loading was investigated. Specimens were cyclically tested at 59, 69, and 84% of the compressive quasi-static ultimate load. X-ray radiography and a surface replication method were used to record fatigue damage development. Specimens were sectioned after cyclic tests and examined under microscope and scanning electronic microscope for details of surface-related damage features. It was found that the critical damage modes in the neck and mid-stem region of the prosthesis were matrix cracking along fiber directions and microbuckling-type damage in major load-carrying plies, respectively. Occurrences of these different damage modes were attributed to changing stress states, structural geometry, and boundary conditions along the prosthesis. Also, different failure modes were observed among the specimens, which were attributed to the difference in applied load levels.
Compression-Compression Fatigue of a Stitched Uniwoven Graphite/Epoxy Composite
Authors: Vandermey NE , Masters JE , Poe CC , Morris DH
Published: March 2009

Stitched uniwoven graphite/epoxy laminates show great promise as a damage-tolerant composite material which is easily fabricated into large net-shaped parts and structures. They also offer the potential of being less costly than other damage-tolerant systems such as toughened matrix composites. Work to date with stitched uniweaves has included evaluations of static properties and damage tolerance as measured by impact resistance, compression after impact, and delamination propagation [1-7]. This paper focuses on experimental characterization of the fatigue response of stitched uniweave composite materials.

The performance of a stitched uniweave material system with an underlying AS4/3501-6 quasi-isotropic lay-up subjected to compression-compression fatigue loading was investigated. In addition, the material's strength and modulus were measured in a limited static compression study. Performance of unnotched specimens having stitch rows at either 0 or 90° to the loading direction was compared. Specimen performances were generally the same regardless of stitch orientation.

Special attention was given to the effects of stitching-related manufacturing defects. The stitches locally compacted the surface layers; microcracks were also evident along the length of the stitches. Damage evaluation techniques included monitoring stiffness and residual compressive strength, X-ray radiography, and edge replication. It was found that the manufacturing defect of inclined stitches had an adverse effect on material performance but only under low-cycle, high-load fatigue conditions. The microcracks did not generally initiate damage or propagate during the compression-compression cycling. The compression failure mode was transverse shear for all specimens, both in static compression and fatigue cycling tests.

Finally, manufacturing advances have improved material performance compared to previously evaluated stitched systems.
Compressive Static and Fatigue Loading of Continuous Fiber-Reinforced Composites
Authors: Schulte K
Published: March 2009

The compressive static and fatigue behavior of continuous fiber-reinforced composites has not yet been studied to a generally satisfactory state. The present investigation will contribute to the knowledge in compressive testing of polymer and metal matrix composites. As buckling is a major problem under compressive loading and is dependent on matrix properties, special attention has been given to determine experimentally the compressive strength of the neat matrix. A special test figure was designed. Fatigue tests were performed at different stress ratios of R = σmin/σmax = 0.1, -1, -0.55, and 10. Two different types of fibers were used in the study: the intermediate modulus fiber T800 and the high-tenacity fiber T300, both with the BMI/resin system 5245c from BASF-Narmco. Finally, the compressive response of metal matrix composites was studied using Al2O3 fiber-reinforced aluminum.