bluuebunny/crossref_metadata_2025 huggingface dataset:
Influence of Fiber-matrix Interphase on the Long-term Behavior of Graphite/ Epoxy Composites
Authors: Subramanian S , Elmore JS , Stinchcomb WW , Reifsnider KL
Published: March 2009

A systematic experimental study was conducted to examine the influence of fiber surface treatment and sizing on the formation of fiber-matrix interphase and its effects on the fatigue performance of (0,903)s cross-ply laminates. Three material systems having the same Apollo graphite fibers and HC 9106-3 toughened epoxy matrix, but with different fiber surface treatments and sizings, were used in this study. The presence of different interphases in these materials was confirmed using dynamic mechanical analysis techniques. Fatigue tests at R = 0.1 and 10-Hz frequency were conducted at various load levels to characterize the long-term behavior. Stiffness reduction, penetrant enhanced X-ray radiography, and scanning electron microscopy techniques were used to monitor damage progression.

Results indicate that the presence of different interphase regions in these materials can be identified using the dynamic mechanical analyzer. The nature of the interphase region has significant effect on the long-term behavior of cross-ply laminates. The polyvinylpyrrolidone (PVP) sized, 100% surface-treated, 810 O laminates have longer fatigue lives at higher load levels and shorter fatigue lives at lower load levels compared to the epoxy-sized, 100% surface-treated, 810 A laminates. The 200% surface-treated, epoxy-sized, 820 A laminates have longer life compared to the other two materials systems, at all three load levels. The damage mechanisms and failure modes in cross-ply laminates under long-term loading are significantly influenced by the nature of the fiber-matrix interphase. The 810 O material exhibits greater damage and stiffness reduction than the other two materials. The epoxy-sized 810 A and 820 A systems exhibit a brittle stress concentration controlled failure, while the PVP-sized 810 O system exhibits a global strain controlled failure.
Analysis of Test Methods for Characterizing Skin/Stringer Debonding Failures in Reinforced Composite Panels
Authors: Minguet PJ , O'Brien TK
Published: March 2009

A simple test specimen configuration is proposed to evaluate the bond strength between a skin and secondarily bonded or co-cured stringer or frame when the dominant loading in the skin is flexure along the edge of the frame. The specimen consists of a flange bonded onto a skin, loaded either in a three- or four-point bending test fixture. Two configurations for the flange termination were examined, either square-ended or with a 20° taper. Observations show that failure initiates at the tip of the frame flange, either in the adhesive or in the topmost skin ply. Loads at which failure initiates were recorded, as well as the load at which a delamination propagates along the skin/flange interface. Detailed finite element models were built to examine the stress distribution in that critical area. Two failure modes were considered, failure in the adhesive material due to maximum tensile stress and formation of transverse cracks in the skin topmost ply due to maximum transverse principal tensile stress. When applying the experimentally measured failure initiation loads onto the finite element models, results show that the calculated transverse stress in the top skin ply is very close to the transverse strength of a unidirectional tape ply for all the configurations tested. Results also show that the stress levels in the adhesive are almost identical for all the configurations tested.
Analysis of Mode III Delamination Fracture Testing Using a Midplane Edge Crack Torsion Specimen
Authors: Li J , Wang Y
Published: March 2009

A shear deformation theory is used to analyze the edge crack torsion (ECT) specimen for Mode III interlaminar fracture testing. The theory is based on an assumed displacement field and the principle of virtue work. Mode II interference due to bending-twist coupling in general symmetric laminates is identified. The effects of free-edge delamination on the torsional stiffness and total strain energy release rate of a family of symmetric laminates containing 0, 90, and ±45 layers are studied. Favorable layups for the Mode III interlaminar fracture toughness characterization are recommended. Effective procedures for the determination of minimum torsional stiffness to initiate Mode III delaminations are established.
Analysis of Woven and Braided Fabric-Reinforced Composites
Authors: Naik RA
Published: March 2009

A general purpose micromechanics analysis that discretely models the yarn architecture within the textile repeating unit cell was developed to predict overall, three-dimensional, thermal, and mechanical properties. This analytical technique was implemented in a user-friendly, personal computer-based, windows-compatible code called Textile Composite Analysis for Design (TEXCAD). TEXCAD was used to analyze plain, 5-harness satin, and 8-harness satin weave composites along with two-dimensional (2-D) braided and 2 × 2, 2-D triaxial braided composites. The calculated overall stiffnesses correlated well with available three-dimensional (3-D) finite element results and test data for both the woven and the braided composites. Parametric studies were performed to investigate the effects of yarn size on the yarn crimp and the overall thermal and mechanical constants for plain weave composites. The effects of braid angle were investigated for the 2-D braided composites. Finally, the effects of fiber volume fraction on the yarn undulations and the thermal and mechanical properties of 2 × 2, 2-D triaxial braided composites were also investigated.
Design and Evaluation of Three Methods for Testing Extension-Twist-Coupled Laminates
Authors: Hooke DA , Armanios EA
Published: March 2009

Elastically tailored composite laminates are those laminates that have been designed with specifically tailored stiffness parameters. These parameters can be sized to give an out-of-plane response to in-plane loading, resulting in deformation modes not found in conventional homogeneous materials.

Three different methods of testing extension-twist-coupled specimens are discussed. The benefits and limitations of each of the methods are highlighted. Quantitative results for each of the testing methods using a hygrothermally stable specimen are shown and compared to determine the applicability and suitability of each of the methods.

A comparison of data with predictions from a shear deformation sublaminate plate theory and finite element method (FEM) is presented.
The Accelerated Development of Standards for Environmental Data Collection
Authors: Johnson AI
Published: March 2009

There has been an increasing need for uniformly high quality basic data for making decisions related to the regulation of wastes and the protection of the environment, especially the quantity and quality of the nation's water resources. Hundreds of Federal and non-Federal agencies have recognized the need for high-quality standards that provide greater comparability, compatibility, and usability of all types of environmental data. The wide use of computerized data banks, also has accelerated the need for stored data of known quality.

Federal co-operation in the development of standard methods was initiated in the early 1970's through the U.S. Geological Survey's Office of Water Data Coordination. As a result of a co-ordinated effort of Federal agencies, with review by a group of non-Federal representatives, a “National Handbook of Recommended Methods for Water Data Acquisition” was produced. This handbook contained many ASTM existing standards and made recommendations for many others that could be developed by a variety of ASTM committees.

As the needs increased for high-quality data, and more regulatory and quality assurance requirements were developed, the need for consensus-type standards also increased. As a result, during the past several years joint efforts by the EPA, U.S. Geological Survey, and U.S. Navy have resulted in a funding process whereby highly accelerated development has been made possible by ASTM for a wide variety of standard methods, practices, guides, and terminology. The process of developing such standards in relation to a variety of water resources, waste management, and environmental problems are described.
A Common Sense Sampling Strategy to Expedite Hazardous Waste Site Cleanup
Authors: Soloyanis SC
Published: March 2009

A common criticism of the remedial investigation/feasibility study process at Comprehensive Environmental Response, Compensation and Liability Act (CERCLA) sites is that too much time and money are spent studying the problem before remediation can be started. A factor leading to this perception may be that the timing, type, and spacing of soil and groundwater sampling at these sites are inappropriate. The purpose of this paper is to propose a 3-step sampling strategy for quickly obtaining sufficient information to make remediation decisions and thus reducing overall characterization costs. The significant element in the strategy is that most of the expensive, time-consuming sampling and analyses using permanent monitoring devices are reserved for the end of the 3-step process as confirmation of the conceptual site model developed as a result of the investigation.

Step 1 is to identify the presence and source of contamination. Sample collection methods for this step should be nonintrusive or minimally intrusive; few permanent monitoring devices should be installed; and field screening analytical methods should be emphasized. The resulting data are used to assess the potential for risk to human health and the environment and identify potential pathways and barriers to migration that are the focus of subsequent investigation.

Step 2 is to delineate the contaminant source and determine contaminant fate and transport. Many samples may be collected at discrete intervals (both lateral and vertical), using temporary devices. The resulting geochemical and geotechnical data are used to determine feasibility of remediation and identify presumptive remedies.

Step 3 is to quantify risk and determine cleanup goals. Permanent monitoring devices should be installed if long-term monitoring will be necessary. The resulting data are used to document the presence of contaminants above background or regulatory criteria.
Use of the Hydropunch for Groundwater Plume Delineation: A Case Study
Authors: Kraemer CA , Penn WE , Busa MD
Published: March 2009

Historic groundwater investigations at a 300-acre manufacturing facility in Connecticut indicated that solvent and metal contaminated groundwater was migrating off site. To preliminarily investigate off-site groundwater contamination, the collection of discrete-interval groundwater samples using a HydroPunch was attempted in twenty soil borings. The borings were located along three transects perpendicular to the general direction of groundwater flow: 1) three soil borings were located near groundwater monitoring well clusters along the downgradient facility boundary, 2) ten soil borings were located along a road at the approximate midpoint between the facility boundary and a nearby river, and 3) seven soil borings were located along the banks of the river. At each soil boring, collection of the first HydroPunch sample was attempted at ten feet below the water table; sample attempts continued at 3-meter (10-ft) intervals until refusal. Samples were analyzed for volatile organic compounds and selected metals.

Geologic materials significantly influenced the sampling program success. In the fine-grained, floodplain deposits, samples could not be collected from five of the seven soil borings, with limited sampling success in the other two borings. At the two other transects, the collected sample volumes varied significantly, dependent upon the physical characteristics of the sampled materials. Analytical results from the HydroPunch samples collected along the middle transect clearly defined the horizontal extent of solvent contamination. The vertical extent of groundwater contamination was not as well characterized, because of the anisotropic nature of the aquifer materials.
Cone Penetrometer Testing for Characterization and Sampling of Soil and Groundwater
Authors: Edelman SH , Holguin AR
Published: March 2009

Cone penetrometer testing (CPT) is an alternative method to drilling for subsurface characterization of hazardous materials release sites. CPT provides higher quality data at lower cost and with fewer health and safety concerns than conventional drilling. CPT basically consists of pushing a cone-tipped, steel rod into the subsurface soils at a constant velocity and measuring the stresses used for automatic determination of soil types. CPT with concurrent measurement of pore pressure is used for determining hydraulic head and other parameters.

Several methods for in situ screening of subsurface contaminants have been added to CPT equipment, including vapor sampling, laser induced fluorescence (LIF), and pore water resistivity. CPT is also used for “direct push” sampling of soil and groundwater and for installation of small diameter “well points.”

CPT can be used with an assessment strategy that parallels that of conventional drilling; however, the in situ testing capabilities of CPT lend themselves to a more comprehensive assessment strategy that minimizes soil and groundwater sampling. A case study illustrates this comprehensive assessment strategy.
The Multiport Sampler: An Innovative Sampling Technology
Authors: Leavell DA , Malone PG , Lee LT
Published: March 2009

The Multiport Sampler (MPS) was developed to overcome current cone penetrometer sampling limitations. The MPS was specifically designed to obtain multiple fluid (gas, vapor, and/or liquid) samples during a single penetration while minimizing sample cross-contamination from each sampling cycle. The MPS consists of a series of vertically stacked sampling modules that are independently operated from the surface. As the cone penetrometer is advanced to the desired sampling depth, a module is selectively opened to allow soil pore fluid to be drawn through a sidewall port. Fluid samples may be either analyzed during the penetration event using equipment on the surface or collected inside the penetrometer for subsequent analysis. The MPS has been used only to sample vapors from soils contaminated with chlorinated organic solvents to determine the relative concentration of the contaminants in different soil strata.
Accelerating Remedial Investigations at Closing Air Force Installations
Authors: Attebery CW
Published: March 2009

The Air Force, in coordination with the Environmental Protection Agency and state environmental regulatory agencies, is attempting to expedite the transfer of federal land to the public. The Air Force has implemented four programmatic and technical initiatives focused on streamlining environmental sampling strategies and decision-making processes to accelerate remedial investigations at a limited number of closing Air Force installations. The success of these initiatives may result in standardization of remedial investigation environmental sampling strategies and decision-making processes for the Air Force.
Estimation of Volatile Organic Compound Concentrations in the Vadose Zone: A Case Study Using Soil Gas and Soil Sample Results
Authors: Sextro RK
Published: March 2009

Obtaining defensible and conservative estimates of the nature, extent and concentration of volatile organic compounds (VOCs) in the vadose zone is extremely important when formulating the conceptual model of the site, when performing risk assessments, for estimating contaminant mass, for assessing remedial alternatives, for selecting target areas for cleanup, and/or for making no further action/investigation decisions. Studies have shown that soil gas analytical results provide both a more complete indication of the VOCs present and a higher estimate of their respective concentrations in the vadose zone than the analysis of soil samples alone. For the past several years deep downhole (to 30+ meters) soil gas sampling and analysis has been performed by various consultants during remedial investigations (RIs) and remedial actions (RAs) of the vadose zone at McClellan Air Force Base. A number of these soil gas results have been confirmed by the concurrent collection and analysis (for VOCs) of soil samples (preserved by either refrigeration to 4 degrees centigrade or refrigeration combined with methanol preservation). The use of this VOC sampling and analysis strategy has resulted in the optimization of VOC sampling and analysis procedures, in a better understanding of the relationship between the concentration of VOCs in soil gas and in the soil, and in a more accurate and comprehensive conceptual model for VOC contamination in the vadose zone. The paper will present the methodologies used by the various consultants for sample collection, preservation, and in the analysis of soil gas and soil samples, present the results of a focused QC study on soil gas sampling and analysis, and discuss the correlation between the soil gas and soil matrix analytical results. The current and future strategies for the sampling, analysis, and estimation of VOCs in the vadose zone during RIs and RAs will also be presented.
Methods of Determining in Situ Oxygen Profiles in the Vadose Zone of Granular Soils
Authors: DeGroot DJ , Lutenegger AJ , Panton JG , Ostendorf DW , Pollock SJ
Published: March 2009

This paper describes seven different methods evaluated to determine in situ oxygen profiles in the vadose zone at a site consisting of granular soils. The techniques investigated included both permanent installations (four) and rapid deployment drive probes (three). The soil and ground water conditions at the site are first described followed by details of the design, deployment and sampling for each method. Typical oxygen profile results obtained from the different methods are presented and compared based on their ease of deployment, efficiency, repeatability, and reliability. Based on the results of this study, the most reliable and consistent sampler types tested were two of the permanent installation designs. The ease of construction and relatively low material costs of these particular methods, combined with their simplicity, relative quickness and accuracy of sampling make them superior to the others tested. The rapid deployment drive probe methods were prone to errors due to short circuiting, damage during deployment or sampling difficulties. However, when care was taken to minimize these factors, some of these methods also produced reliable and consistent results.
Use of Phased Approach to Sampling Soil and Sediment for Site Characterization at the Pantex Plant in Amarillo, Texas
Authors: Lazowski DD
Published: March 2009

In this study, the phased approach is used to expedite collection of data and information about the site. The approach consists of sampling soils and sediments at a variety of locations, using applicable sampling devices. The validated analytical measurements acquired from sampling is entered into a database. This data then can be applied in a geographical information system (GIS). Further analysis of material can be reduced and saved in the database. The chain-of-custody records throughout the phased approach ensures careful and accurate documentation.
Sample Preparation Techniques for Filtration Testing of Fly Ash with Nonwoven Geotextiles
Authors: Gabr MA , Akram MH
Published: March 2009

A laboratory investigation was conducted to evaluate the applicability of five preparation techniques of fly ash/geotextile specimens for the gradient ratio (GR) test (ASTM D 5101-90). These techniques included the current ASTM method, a modified ASTM method, a vibro-prep technique, a dry preparation, and slurry method. Using the ASTM method for preparation, measured specific discharge and GR across the fly ash-geotextile systems were 8.0×10-4 cm/sec and 1.25, respectively. However, during the placement of the fly ash in the permeameter some intrusion of the particles into the geotextile openings took place. A technique for placing fly ash in the permeameter was modified after ASTM D5101. Using this modified method, the specific discharge and GR were measured to be 6.8x10-4 cm/sec and 0.80, respectively. The specimens prepared using the slurry method exhibited a relatively stable behavior. The specific discharge had an average value of 2.5×10-4 cm/sec after 600 hours of testing. The GR decreased from 1.52 to 1.37 during this period. The extent of piping under different testing conditions was quantified in this investigation. The specimens prepared using dry method exhibited an unsteady behavior and piping was observed to be dominant. Although piping of fine particles through the geotextile system was less than the suggested limit of 0.25 g/cm2 for soils, it is proposed that in the case of fly ash specimens with geotextile, stable systems should be categorized as those with piping rate less than 0.03 g/cm2.
Current Forgings and their Properties for Steam Generator of Nuclear Plant
Authors: Tsukada H , Suzuki K , Kusuhashi M , Sato I
Published: March 2009

Current steel forgings for steam generator (SG) of PWR plant are reviewed in the aspect of design and material improvement. The following three items are introduced.

1. The use of integral type steel forgings for the fabrication of steam generator enhances the structural integrity and makes easier fabrication and inspection including in-service inspection [1]. The following examples of current integral type forgings developed by the Japan Steel Works, Ltd. (JSW) are introduced (1)Primary head integrated with nozzles, manways and supports (2)Steam drum head integrated with nozzle and handhole (3)Conical shell integrated with cylindrical sections and handholes

2. In order to decrease the weight of steam generator, the high strength materials such as SA508, C1.3a steel have been adopted in some cases. The properties of this steel are introduced and the chemistry and heat treatment condition are discussed.

3. As one of the methods to minimize the macro- and micro-segregations, the use of vacuum carbon deoxidization (VCD), i.e. deoxidization of steel by gaseous CO reaction, with addition of Al for grain refining was investigated. The properties of SA508, C1.3 steels with Low Si content are compared with those of conventional one.
The Optimization of Mechanical Properties for Nuclear Transportation Casks in ASTM A350 LF5
Authors: Price S , Honeyman GA
Published: March 2009

Transport flasks are required for the movement of spent nuclear fuel. Due to their nature of operation, it is necessary that these flasks are produced from forged steels with exceptional toughness properties. The material specification generally cited for flask manufacture is ASTM A350 Grade LF5 Class 1, a carbon-manganese-nickel alloy. The range of chemical analysis permitted by this specification is very broad and it is the responsibility of the material manufacturer to select a composition within this range which will satisfy all the mechanical property requirements, and to ensure safe and reliable performance.

Forgemasters Steel and Engineering Limited have experience in the manufacture of large high integrity fuel element flask forgings which extend over several decades. This experience and involvement in international standards in USA, Europe and Japan has facilitated the development of an optimised analysis with a low carbon content, nickel levels towards the top end of the allowed range, a deliberate aluminium addition to control grain size and strictly controlled residual element levels. The resultant steel has excellent low temperature impact properties which greatly exceed the requirements of the specification This analysis is now being adopted for the manufacture of all current transport flasks.
A New Model for Calculating Maximum Blow Force of Die-Forging Hammer
Authors: Li Y , Yang K , Ni Z
Published: March 2009

The blow procedure of a die-forging hammer is analysed theoretically taking account of the elastic deformation of the cushion under the anvil block, and the new formulae for calculating the maximum blow force are deduced from a new model proposed in the paper. The results calculated by the formulae agree well with experimental data. Thus, the formulae and the results provide a basis for designing and using die-forging hammers properly.
High Strength 12% Cr Heat Resisting Steel for High Temperature Steam Turbine Blade
Authors: Ishii R , Tsuda Y , Yamada M
Published: March 2009

The factors to attain the high creep rupture strength for 12% chromium ferritic steels were studied. Large amount of Laves phase and high content of solute elements during creep were important to maintain the creep resistance, and the degradation correspond to the recovery of matrix. Based on these studies, the chemical composition of 10.5Cr-2.5W-1Co-0.2Re-VMoNbNB steel with large amount of Laves phase and high solute tungsten content was determined for the new blade material. The producibility of this steel were verified with 2 ton ESR ingots which were successfully manufactured by various industrial processes. The mechanical properties of the trial bars were sufficient to be applicable to the blade, especially the creep rupture strength was very higher than that of HCr-1Mo-1W-VNbN steel being used. In near future, this new steel will be applied to commercial power plants with steam condition of 593‡C or higher as the blade material.
Hydrogen and Flaking after 40 Years of Vacuum Degassing
Authors: Steiner JE , Murphy EL , Williams RD
Published: March 2009

Background on the early urgent push for hydrogen control, primarily in heavy rotor forgings, as a result of the rotor failures of the mid 50's, is presented in a brief retrospective. Recent experience with the several degassing processes, their efficiency and costs in terms of safety treatment, delayed deliveries and claim losses is covered. Industry concern with hydrogen analysis of vacuum degassed steel solid product is discussed with regard to end customer need, justification and reliability of analysis, with the increasingly wide-spread use of the ladle refining furnace, some producers are reporting hydrogen problems with low sulfur vacuum degassed steels. Interaction among several factors possibly related to this phenomenon is discussed.
International Business, Codes, and Material Specifications
Authors: Gold M
Published: March 2009

The nature of the business environment of large forging manufacturers and users has changed significantly in the twelve years since the first ASTM forging symposium. The largely domestic nuclear market has become a global fossil and petrochemical market. Further, the primary market is on the other side of the world from North America. To participate in this market, original equipment manufacturers are required to form joint ventures, with manufacturers in customer's countries, just to obtain market access. This has a significant effect on how their businesses operate, on the construction codes to which they design and build equipment, and on material sources and materials specifications they are required to use to be competitive. There will also be significant changes required in ASME construction codes and ASTM materials specifications, if North American manufacturers are to continue to use these and still compete effectively.
Assessment of Corrosion of Steel in Concrete Structures by Magnetic Based NDE Techniques
Authors: Ghorbanpoor A , Shi S
Published: March 2009

Corrosion damage of steel in concrete structures is a major concern. NDE techniques based on variations in induced magnetic fields due to loss of steel have been shown to be an effective tool. This paper includes results from laboratory investigation, field tests, and numerical analysis based on this concept. Test specimens included reinforcing bars and prestressing cables with simulated flaws as well as flaws from real corrosion. Variations in the magnetic field were recorded as electrical signals that were characterized to aid in the detection of corrosion and evaluation of the condition of steel in concrete. It was found that the amplitude of the signals could be related to the extent of the corrosion. Loss of cross sectional area in bars and cables of approximately 3 percent could be detected by the technique. The results of a finite element analysis yielded a good agreement with those from the experiment. The technique offers significant capabilities for field assessment of the condition of steel in concrete structures.
Common Problems at the Interface Between Masonry Drainage Walls and Windows
Authors: Krogstad NV , Weber RA , Johnson DK
Published: March 2009

An often overlooked area in masonry wall construction is the interface between masonry walls and windows. Interior water leakage, water staining, peeling paint, condensation, mold and mildew can result from deficiencies at this interface. The causes of these problems include water bridging across cavities to interior surfaces, water penetrating failed sealant joints, air from the masonry cavity contacting window jambs, air or moisture moving from the interior into wall cavities and components of the wall system forming thermal bridges. This paper reviews considerations for detailing the interface between masonry walls and windows and offers suggested methods for different window configurations. The authors have developed interface details to address the problems identified during their investigations of hundreds of building failures. The window opening configurations reviewed by the authors include horizontal ribbon windows, shallow and deeply recessed punched windows and vertical strip windows. Continuous flashings at the heads and sills of the wall openings and seals across drainage cavities at jambs prevent water and air leakage. Multi-component or thermally broken flashings prevent thermal bridges between interior and exterior surfaces.
The Effect of Freezing and Thawing on the Flexural Bond Strength of Masonry
Authors: Walker D
Published: March 2009

This investigation determined the effect of freezing and thawing on mortar bond strengths. Comparisons were made of a Type S portland cement-lime mortar without an air entraining agent and a companion mortar of the same cement-lime proportions with a purposefully added air entraining agent. The UBC Mortar Cement Test Method UBC 21-20, (formerly UBC 24-30) was used to construct prisms and test the mortar joints for flexural bond strengths. A series of six prisms were made for each mortar type, using the UBC standard concrete brick. Four sets of prisms for each mortar were made corresponding to: a control set (no freeze-thaw treatment), and prism sets for 5, 10 and 25 freeze-thaw cycles.

Each freeze-thaw cycle consisted of water saturation, draining, freezing for 12 h, and thawing at room temperature. Flexural bond strength data were obtained from 30 joints per prism set, in accordance with ASTM C1072 test method.

Results of this study indicate that air entrainment accelerates the loss of flexural bond strength of masonry composites when exposed to water saturated freeze-thaw conditions. Mortar freeze-thaw durability is not equivalent to masonry freeze-thaw durability, because there are mortar to masonry unit interfaces in masonry composites, and this is a significant weak link in masonry durability.
Fiber-Matrix Micromechanics and Microstructural Observations Under Tensile and Cyclic Loading
Authors: Davidson DL
Published: March 2009

A technique is described for measuring the displacements in fibers due to loading the composite. Fiber access was obtained by removing only very small pieces of the matrix, thereby minimizing the change in residual stresses. Fiber stresses were obtained near a hole, a slit, and a fatigue crack. It was found that fibers slipped within the matrix at a stress of 2 to 2.6 GPa near both the hole and slit; after cyclic loading the specimen with a hole, fiber stress at slip increased to 2.6 to 3.6 GPa. Fiber stresses bridging the wake of a fatigue crack were found to be approximately constant. The models used to compute a stress intensity factor at the tip of a bridged fatigue crack are reviewed, and it is shown that those assuming a constant fiber stress gave the best results.
The Role of Frictional Sliding in Transverse Failure of a Titanium Aluminide Composite
Authors: Marshall DB , Morris WL , Cox BN , Kouris DA
Published: March 2009

Circumferential frictional sliding between the matrix and fibers in a titanium aluminide matrix composite has been measured during transverse loading using a displacement mapping method based on differential image analysis. Sliding was detected over all of the interface before initiation of the cracks that eventually caused failure. The results are compared with recent analytical solutions for the interfacial stresses that account for near-neighbor fiber interactions. The location at which sliding initiated coincided with the predicted position of maximum shear stress, while the calculated magnitude of the shear stress when sliding began was equal to the previously measured resistance to frictional sliding in the longitudinal direction. The results indicate that circumferential sliding has a strong influence on the local stress concentrations that lead to failure.
Issues Related to Prediction of Residual Stresses in Titanium Alloy Matrix Composites
Authors: Rangaswamy P , Jayaraman N
Published: March 2009

Recently, a detailed study of residual stresses on the as-processed SCS-6/Ti-24Al-11Nb [0]8 composite, and SCS-6/Beta-21S composites in unidirectional [0]4, cross-ply [0/90]s, and quasi-isotropic [0/±45/90]s layups has been completed. In this study, residual stresses have been measured using X-ray diffraction (sin2ψ) technique. We have shown that the use of conventional unit cell models consisting of a quarter fiber surrounded by the matrix material to predict residual stresses for verification of experimental results is inadequate. Such models have predicted successfully the stresses at the fiber-matrix interface. However, experimental work to measure residual stresses have always been on surfaces far away from the interface region.

In this paper, the approach taken in extending the conventional unit cell model to the concept of multifiber models to predict average stresses are presented. In this process, several modeling issues have been identified. These issues are (1) use of conventional unit models for prediction of average surface residual stresses, (2) effect of orientation of the sub-surface plies on the residual stresses in the surface ply, (3) residual stresses in the interior plies, and (4) constituent material properties.
High Temperature/High Frequency Fatigue Crack Growth in Titanium Metal Matrix Composites
Authors: Zheng D , Ghonem H
Published: March 2009

An experimental study was conducted to examine the effects of high temperature/high frequency loading on the crack growth behavior in titanium composites. Fatigue crack growth tests were performed on the unidirectional SM 1240/TIMETAL-21S composite in air environment at three different temperatures: 24, 500, and 650⪤gC with a loading frequency of 10 Hz and a stress ratio of 0.1. Tests were also carried out in vacuum and on aged specimens. In all the tests, the crack length was measured continuously while the crack opening displacement (COD) was measured at discrete positions along the crack length. Results show that, at all temperatures, the crack progresses in two sequential stages; a stage in which the crack growth rate decreases as the crack length increases followed by a stage characterized by an accelerated crack growth rate. The first stage corresponds to a crack-bridging condition and is the focus of the analysis in this paper. In additional to COD measurements, the microstructural features associated with the fracture process during this stage was examined by scanning electron microscopy with emphasis being placed on the matrix crack morphology, debonding location, temperature, and environmental influences on the fiber coatings. An analytical procedure, employing concepts of the theory of fracture mechanics and micromechanics analysis of the stress state along bridging fibers, was applied in order to calculate the fiber-bridging stress, the frictional shear stress, and the effective stress intensity factor. Results of this work suggest that the fiber-bridging stress and the frictional shear stress are variables along the crack length and are test temperature dependents. Furthermore, it was concluded that both the crack-tip opening displacement and the effective stress intensity factor can be used as measurements of the crack-tip driving force in the crack-bridging stage. Based on the experimental and analytical results collected in this study, a bridging damage mechanism under the loading condition specified here is suggested. This mechanism argues that the effect of temperature on the high frequency crack growth process is established through the temperature-related modification of the frictional shear stress and the resulting adjustment of the internal stress state in the debonded regions of the bridging fibers.
A Fully Associative, Nonlinear Kinematic, Unified Viscoplastic Model for Titanium-Based Matrices
Authors: Arnold SM , Saleeb AF , Castelli MG
Published: March 2009

Specific forms for both the Gibb's and complementary dissipation potentials are chosen such that a complete (that is, fully associative) potential-based multiaxial, unified viscoplastic model is obtained. This model possess one tensorial internal state variable that is associated with dislocation substructure, with an evolutionary law that has nonlinear kinematic hardening, and both thermal- and strain-induced recovery mechanisms. A unique aspect of the present model is the inclusion of nonlinear hardening through the use of a compliance operator, derived from the Gibb's potential, in the evolution law for the back stress. This nonlinear tensorial operator is significant in that it allows both the flow and evolutionary laws to be fully associative (and therefore easily integrated) and greatly influences the multiaxial response under nonproportional loading paths. In addition to this nonlinear compliance operator, a new, consistent, potential-preserving, internal strain unloading criterion has been introduced to prevent abnormalities in the predicted stress-strain curves that are present with nonlinear hardening formulations during unloading and reversed loading of the external variables. Specification of an experimental program for the complete determination of the material functions and parameters for characterizing a metallic matrix, for example, TIMETAL 21S, is given. The experiments utilized are tensile, creep, and step-creep tests. Finally, a comparison of this model and a commonly used Bodner-Partom model is made on the basis of predictive accuracy and numerical efficiency.
Inelastic Deformation of Titanium Matrix Composites Under Multiaxial Loading
Authors: Lissenden CJ , Herakovich CT , Pindera M-J
Published: March 2009

A theoretical model capable of predicting the thermomechanical response of continuously reinforced, titanium matrix composite (TMC) laminates, subjected to multiaxial loading has been developed. The model is based on micromechanics and employs classical lamination theory to determine inelastic response. The constitutive relationships for each lamina are determined from a micromechanics analysis that is performed numerically using the finite element method. Matrix viscoplasticity, thermal stresses, and damage to the fiber/ matrix interfacial zone are explicitly included in the model.

The representative cell of the micromechanical model is considered to be in a state of generalized plane strain, enabling a quasi two-dimensional analysis to be performed. Constant strain triangular elements are formulated with elasto-viscoplastic constitutive equations. Interfacial debonding is incorporated into the model through interface elements that are based on a constitutive model that includes normal and tangential debonding.

Theoretical predictions are compared with the results of an experimental program conducted on SCS-6/Ti-15-3 unidirectional, [04], and angle-ply, [±45]s, tubular specimens. Multiaxial loading included increments of axial tension, compression, torque, and internal pressure. Loadings were chosen in an effort to distinguish inelastic deformation due to damage from matrix plasticity and separate time-dependent effects from time-independent effects. Results show that fiber/matrix debonding can be a major factor in the effective stress-strain response and that significant room temperature creep can occur at relatively low applied stress levels.
Prediction of Matrix Fatigue Crack Initiation from Notches in Titanium Matrix Composites
Authors: Herrmann DJ , Ward GT , Lawson EJ , Hillberry BM
Published: March 2009

Fatigue crack initiation from notches in titanium matrix composites (TMCs) is of interest in the design of TMC structures. A model is presented for predicting the fatigue crack initiation life of longitudinal, transverse, and symmetric cross-ply laminates using the strain-life behavior of the matrix material. The effective strain parameter, Δεeff, proposed by Hillberry and Johnson is used to account for the residual stress state imposed during composite processing. Since the effective strain parameter requires knowledge of the local residual and applied strain in the matrix, methods for calculating these strains are developed. Model predictions were verified with crack initiation tests of [0]4, [90]4, and [0/90]s SCS-6/TIMETAL 21S center-hole specimens at room temperature and [04/¯90]s SCS-6/Ti-15-3 center-hole specimens at 300 and 550°C.
Matrix Fatigue Cracking in α2 Titanium Matrix Composites for Hypersonic Applications
Authors: Gabb TP , Gayda J
Published: March 2009

The objective of this work was to understand matrix cracking mechanisms in a unidirectional α2 titanium matrix composite (TMC) in possible hypersonic applications. A [0]8 SCS-6/Ti-24Al-11Nb (atomic %) TMC was first subjected to a variety of simple isothermal and nonisothermal fatigue cycles to evaluate the damage mechanisms in simple conditions. A modified ascent mission cycle test was then performed to evaluate the combined effects of loading modes. This cycle mixes mechanical cycling at 150 and 483°C, sustained loads, and a slow thermal cycle to 815°C. At low cyclic stresses and strains more common in hypersonic applications, environment-assisted surface cracking limited fatigue resistance. This damage mechanism was most acute for out-of-phase nonisothermal cycles having extended cycle periods and the ascent mission cycle. A simple linear fraction damage model was employed to help understand this damage mechanism. Time-dependent environmental damage was found to strongly influence out-of-phase and mission life, with mechanical cycling damage due to the combination of external loading and CTE mismatch stresses playing a smaller role. The mechanical cycling and sustained loads in the mission cycle also had a smaller role.
Characterization of Damage Progression in SCS-6/TIMETAL 21S [0]4 Under Thermomechanical Fatigue Loading
Authors: Castelli MG
Published: March 2009

A detailed experimental investigation was performed at a single maximum cyclic stress (σmax) level to physically characterize the progression of thermomechanical fatigue (TMF) damage in continuously reinforced [0°] SCS-6/TIMETAL 21S, a titanium matrix composite. In-phase (IP) and out-of-phase (OP) loadings were investigated at σmax = 1000 MPa with a temperature cycle from 150 to 650°C. Damage progression, in terms of macroscopic property degradation, was experimentally quantified through an advanced TMF test methodology that incorporates explicit measurements of the isothermal static moduli at the TMF temperature extremes and the coefficient of thermal expansion (CTE) as functions of the TMF cycles. Detailed characterization of the physical damage progression at the micro-structural level was performed by interrupting multiple TMF tests at various stages of mechanical property degradation and analyzing the microstructure through extensive destructive metallography. Further, the extent of damage was also quantified through residual static strength measurements. Results indicated that damage initiation occurred very early in cyclic life (N < 0.1 Nf) for both the IP and OP TMF loadings. IP TMF damage was found to be dominated by fiber breakage with a physical damage progression in the microstructure that was difficult to quantify. OP TMF loadings produced matrix cracking exclusively associated with surface initiations. Here, damage progression was easily distinguished in terms of both the number of cracks and their relative inward progressions toward the outer fiber rows with increased cycling. The point at which the leading cracks reached the outer fiber rows (when localized fiber/matrix debonding and matrix crack bridging occurred) appeared to be reflected in the macroscopic property degradation curves.
Fatigue Maps for Titanium Matrix Composites
Authors: Zok FW , Connell SJ , Du Z-Z
Published: March 2009

The present article attempts to bring together many of the observations and measurements pertaining to fatigue cracking and fracture of unidirectional titanium matrix composites at ambient temperature into a fatigue fracture map. The map identifies the regimes in which various mechanisms operate, allowing fatigue life predictions to be made. The map is constructed using micromechanical models that incorporate crack bridging. The article also demonstrates the utility of the models in describing the experimental data for one specific composite system.
Simulation of Fatigue Behavior of High Temperature Metal Matrix Composites
Authors: Tong MT , Singhal SN , Chamis CC , Murthy PLN
Published: March 2009

A generalized relatively new approach is described for the computational simulation of fatigue behavior of high temperature metal matrix composites (HT-MMCs). This theory is embedded in a specialty-purpose computer code. The effectiveness of the computer code to predict the fatigue behavior of HT-MMCs is demonstrated by applying it to a silicon-fiber/titanium-matrix HT-MMC. Comparative results are shown for mechanical fatigue, thermal fatigue, thermomechanical (in-phase and out-of-phase) fatigue, as well as the effects of oxidizing environments on fatigue life. These results show that the new approach reproduces available experimental data remarkably well.
Life Prediction for Bridged Fatigue Cracks
Authors: Cox BN
Published: March 2009

The growth rates of matrix fatigue cracks bridged by sliding fibers are now commonly predicted by models based on the micromechanics of frictional interfaces. However, there exist many reasons, both theoretical and experimental, for suspecting that the most popular micromechanical models are probably wrong in detail in the context of fatigue cracks. Furthermore, a review of crack growth data reveals that the validity of the micromechanics-based predictive model has never been tested and may never be tested. In this paper, two alternative approaches are suggested to the engineering problem of predicting the growth rates of bridged cracks without explicit recourse to micromechanics. Instead, it is shown that the material properties required to analyze bridging effects can be deduced directly from crack growth data. Some experiments are proposed to test the validity of the approach.