bluuebunny/crossref_metadata_2025_split huggingface dataset:
Effects of Notch Geometry and Moisture on Fracture Strength of Carbon/Epoxy and Carbon/Bismaleimide Laminates
Authors: Underwood JH , Burch IA , Bandyopadhyay S 
Published: March 2009

Composite panels of various ply orientations and 1 to 2 mm thickness were tested in tension with a center notch to determine the translaminar fracture toughness and in bending with no notch to determine the bulk flexural strength and modulus. Carbon/epoxy panels with a variety of notch lengths and widths were subjected to laboratory air conditions before testing. Carbon/bismaleimide panels with one basic notch configuration were tested in three pretest exposure conditions: laboratory air, a 400-h exposure in a controlled moisture chamber, and a 4000 h exposure in a natural tropical environment.
The tests were performed to investigate the following effects on fracture and mechanical properties and on micro and macrofailure mechanisms of the laminates.
(a) Effects of notch width and length and ply orientation on translaminar fracture toughness were studied in 0/90 and 0/±60 carbon/epoxy laminates, including effects of notches produced by ballistic penetration.
(b) Effects of extended exposure to moisture and sunlight on fracture and mechanical properties were studied in various 0/90 layups of carbon/bismaleimide laminates. A direct comparison of controlled chamber and natural tropical moisture effects was made for two materials.
(c) The load-deflection macrobehavior of notched panels was noted and analyzed. Linear-elastic and J-integral analyses were used to determine critical values of stress intensity factor, K, at the onset of self-similar translaminar fracture. A simple splitting model was used to describe the interlaminar failure that competed with and often prevented the translaminar fracture.
(d) Scanning electron microscope fractography was used to investigate and contrast the microfailure mechanisms of the laminates. The differences in micromechanisms between carbon/epoxy and carbon/bismaleimide were related to differences in the macrofracture behavior of the materials.
Analysis was performed of the test procedures for determination of fracture toughness and flexural strength and modulus. The method used for fracture toughness and associated K, J, and displacement expressions were proposed for more general use in measuring translaminar fracture toughness of composites. Use of the four-point bending test for flexural strength and modulus revealed an error that can occur in this type of test that is not fully addressed in ASTM Test Methods for Flexural Properties of Unreinforced and Reinforced Plastics and Electrical Insulating Materials (D 790-86).
Fatigue Crack Growth in a Unidirectional SCS-6/Ti-15-3 Composite
Authors: Kantzos P , Telesman J , Ghosn L 
Published: March 2009

An investigation was conducted to characterize and model the fatigue crack growth (FCG) behavior of a SCS-6/Ti-15-3 metal matrix composite. Part of the study was conducted using a fatigue loading stage mounted inside a scanning electron microscope (SEM). This unique facility allowed high magnification viewing of the composite fatigue processes and measurement of the near crack tip displacements. The unidirectional composite was tested in the [0]8 (that is, longitudinal) and [90]8 (that is, transverse) orientations. For comparison purposes, unreinforced matrix material produced by the identical process as the reinforced material was also tested.
The results of the study reveal that the fatigue crack growth behavior of the composite is a function of specimen geometry, fiber orientation, and the interaction of local stress fields with the highly anisotropic composite. In the case of [0]8 oriented single edge notch (SEN) specimens and [90]8 oriented compact tension (CT) specimens, the crack growth was normal to the loading direction. However, for the [0]8 CT specimens, the crack grew mostly parallel to the loading and the fiber direction.
The unusual fatigue behavior of the [0]8 CT specimens was attributed to the specimen geometry and the associated high tensile bending stresses perpendicular to the fiber direction. These stresses resulted in preferential cracking in the weak interface region perpendicular to the fiber direction. The interface region, and in particular the carbon coating surrounding the fiber, proved to be the composite's weakest link.
In the [0]8 SEN, the crack growth was confined to the matrix, leaving behind unbroken fibers that bridged the cracked surfaces. As the crack grew longer, more fibers bridged the crack resulting in a progressive decrease in the crack growth rates and eventual crack arrest. The actual near-crack-tip displacement measurements were used in a proposed formulation for a bridging-corrected effective crack driving force, ΔKeff. This parameter was able to account for most of the experienced bridging and correlated the [0]8 SEN fatigue crack growth data reasonably well.
An Investigation of the Effects of Temperature on the Impact Behavior and Residual Tensile Strength of an ARamid Aluminum Laminate (ARALL-2 Laminate)
Authors: Lee TC , Wilson DA 
Published: March 2009

The main objective of this investigation was to determine the effects of temperature on the impact behavior of ARALL-2 laminate. Post-impact studies included the assessment of localized damage and the determination of residual tensile strength. Longitudinal specimens (0° fiber orientation) were subjected to impact damage at temperatures of -29, 24, 66, 93, 121, and 138°C (-20, 75, 150, 200, 250, and 280°F) using an instrumented pendulum impact testing system and then loaded in tension to failure. Damage assessment included ultrasonic C-scanning of the impact areas and a scanning electron microscope (SEM) analysis.
The effects of temperature on the impact response of ARALL-2 were made apparent through the behavior of the aluminum layers. Impact damage and, consequently, residual tensile strength were found to vary considerably with temperature. The 24°C (75°F) impacts produced the least amount of internal damage, displayed the longest backsurface cracks, and absorbed the greatest amount of energy. As the impact temperature increased, the internal damage area increased and the energy absorbed decreased. Backsurface cracks decreased with increasing temperature, disappearing altogether at 93°C (200°F) and above.
A maximum tensile strength reduction of 41% occurred for the specimens impacted at 24°C (75°F). Accordingly, the residual tensile strength increased with increasing impact temperature. Since the tensile load was carried primarily by the fibers, this indicated that as temperature increased, fewer fibers experienced breakage. The -29°C (-20°F) impact specimens deviated from these trends. This was attributed to the behavior of the metal adhesive. Less localized deformation occurred, and more unbroken fibers remained to bridge the crack, thus contributing to the residual tensile strength.
Flame Penetration Test for Protective Clothing in Oxygen
Authors: Sanders J , Currie JL 
Published: March 2009

There are a plethora of test methods for assessing the flammability of flame resistant fabric materials. However, there is no suitable test method to assess the relative levels of protection provided by flame resistant clothing materials to personnel who may be subjected to the effects of an ignition in an oxygen system or equipment. BOC Limited has developed a flame penetration test which simulates the severe conditions that exist during an ignition event in oxygen. The test has been used to rank candidate materials in order of their resistance to flame and metal impingement.
The test is comparatively simple. The test apparatus consists of a horizontally mounted oxygen-acetylene welding torch. The torch is mounted in front of the textile specimen which is vertically mounted in a metal frame. Between the specimen and torch is a sheet of mild steel which is used to provide molten metal splashes. Several flame retardant materials were evaluated by the test including FirotexR, NomexR, PanotexR, FlamretR, KermelR, and ProbanR. ProbanR had the highest ranking in the test. Other parameters evaluated were the effect of washing the material and ageing of the material to assess their effects on test results. Further development of the test method will be undertaken in particular on repeatability and reproducibility of results.
Recommended Changes in ASTM Test Methods D2512-82 and G86-84 for Oxygen-Compatibility Mechanical Impact Tests on Metals
Authors: McColskey JD , Reed RP , Simon NJ , Bransford JW 
Published: March 2009

A cooperative test program to assess the oxygen compatibility of aluminum-lithium alloys with NASA White Sands Test Facility (WSTF), NASA Marshall Space Flight Center (MSFC), and the National Institute of Standards and Technology (NIST) led to the assessment of the mechanical impact test by NIST. There were substantially different variations in test parameters between the test laboratories; some of these led to significant variability in the actual energy absorbed by the specimens. Therefore, test results varied widely.
To reduce the large disparities in interlaboratory test results, a number of changes are recommended in the current ASTM test standards.
Oxygen Compatibility of High-Surface-Area Materials
Authors: Dunbobbin BR , Hansel JG , Werley BL 
Published: March 2009

High-surface-area metallic structured packings are finding increasing use in the cryogenic distillation of air. An experimental program was performed to determine the oxygen compatibility of selected metals under the high-surface-area-to-volume ratios and adiabatic conditions encountered in commercial use.
Under some conditions brass packing unexpectedly had a higher relative flammability than aluminum, which is contrary to reported test results using metal rods and strips. This is due, we believe, to the specific geometric and adiabatic configuration of the packing material which appears to enhance the propagation of combustion in brass. Aluminum flammability in gaseous oxygen has been shown to be very dependent upon argon dilution and, in the presence of liquid oxygen, strong energy releases have been observed, similar to those experienced with aluminum powder and liquid oxygen. Copper was found to be nonpropagating in all tested oxygen purities.
These findings suggest that results from oxygen compatibility tests on rods and strips cannot be used reliably for ranking the suitability of materials in high-surface-area-to-volume ratio and adiabatic configurations.
Use of Computer Analysis to Predict and Reduce Liquid Hammer Forces in High Pressure, High Flow Liquid Oxygen Systems
Authors: deQuay L , Scheuermann PE 
Published: March 2009

During the advanced and final development phases of rocket engine component and subsystem testing failures are very likely to occur from time to time. To minimize or prevent damage or destruction to the components and to the test facility itself, high pressure oxygen supplied must be cut off rapidly on the order of 100 to 400 milliseconds. However, rapid cutoff of liquid oxygen, as well as, other liquids and high pressure gases can impart large pressure surges and hammer forces. For liquid and gaseous oxygen this phenomenon can initiate ignition and subsequent destruction of test articles as well as facility piping systems.
An additional concern is the use of liquid oxygen pressure and flow control valves required to operate these type of facilities. Pressure differentials across valves and induced turbulence and flow separation must be understood and analyzed during facility design.
Oxygen Compatibility of Materials and Equipment for the Vulcain European Rocket Engine
Authors: de Monicault J-M , Garceau P , Vagnard G 
Published: March 2009

Under the aegis of the European Space Agency (ESA) and under the responsibility of the French Centre National d'Etudes Spatiales (CNES), the “Société Européenne de Propulsion” (S.E.P.) has developed systems including the engines of the three stages of the Ariane European launchers for twenty years. Several engine simplement a large use of cryogenic propellants, including liquid an gaseous oxygen.
The selection of materials for propulsion components operating in an oxygen environment — valves, pumps, transducers, etc. — requires a strict methodology.
On Vulcain, the main engine of Ariane V launcher for the Hermes space shuttle, SEP, as prime contractor, has developed a working method in coordination with its 27 European project partners to select and test materials.
We will present the application of this method for the gas generator valves of the Vulcain engine: • material choice according to foreseen risks, • laboratory choice and testing procedure (L'AIR LIQUIDE), • results and conclusions.(1) Manager, Raw Materials and Process Research Société Européenne de Propulsion - Materials and Testing Laboratory VERNON, FRANCE (2) Leader Engineer, Vulcain gas generator valves Société Européenne de Propulsion - Design Department VERNON, FRANCE (3) L'Air Liquide - Manager Center - Operational Development Division - Technology and Testing Center - LE BLANC MESNIL, FRANCE
Pavement Condition Index — Remaining Service Life
Authors: Baladi GY , Novak EC , Kuo WH 
Published: March 2009

The issues and the setting of common engineering criteria to establish threshold values for a better calculation of the pavement distress indices and Remaining Service Life (RSL) are presented. Benefits derived from the use of RSL such as simplifying the Pavement Management System (PMS), computational procedures, improving communication between the various PMS users, and increasing the PMS capability are also included. Within the framework of a PMS, most State Highway Agencies (SHAs) collect pavement condition data to calculate pavement distress indices. Because pavement condition data is the basis for all PMS analysis, the values of the pavement indices are typically prioritized and the highest priority is placed on eliminating most deficiencies. Examination of this effort has indicated that the method is deficient and that the RSL is a better pavement condition index.
Common pavement distress indices deficiencies were found to be related to basing the indices on a single variable (pavement condition at the time of the survey). The rate of the pavement deterioration is not included in the calculation of the indices. In order to eliminate the common deficiencies, it was found that the pavement indices must be based on pavement performance which consists of two variables, surface condition and the rate of deterioration.
Laboratory and Field Studies of Polyolefin and Latex Modifiers for Asphalt Mixtures
Authors: Newcomb DE , Stroup-Gardiner M , Epps JA 
Published: March 2009

A five-year study was performed to investigate the behavior of asphalt mixtures containing plastic and latex modifiers. The plastics were functionalized polyolefins; high meltflow index acrylic acid copolymers that were used in a pelletized form. The styrene-butadiene rubber latex was supplied as an emulsion. These materials were used separately and in combinations with each other to change the characteristics of asphalt mixtures. The research included laboratory experiments to characterize the materials and field projects in five locations to ascertain their performance. Field projects of flexible pavement overlays were constructed in Alabama, Maine, Michigan, Idaho, and Texas. This paper presents some of the significant findings made during the course of the five-year effort.
Mixture variables which were examined in the laboratory included asphalt grade, modifier type, and modifier concentration. Mixture preparation was investigated with respect to the order of addition of the components and compaction temperature. Laboratory results showed that the effectiveness of these modifiers was very dependent upon the source of the asphalt used in the mixtures. The order of addition of ingredients was found to be important for latex modified mixtures, and was not as significant in mixtures containing latex and polyolefins. The concentration of modifier changed the mixture behavior only up to levels of about 10 percent by weight of total binder. Compaction temperature had a profound effect on the resilient modulus of the mixtures.
The field projects were built in climates ranging from hot and wet in Alabama to cold and dry in Idaho. Control sections of conventional mixtures were placed along with sections of modified mixtures. The mixtures containing latex only as a modifier showed problems during construction. These problems were confined to the mixtures sticking in the dump trucks and the workability through the paver. There were considerable differences noted between the results from behind-the-paver construction samples and test results from the inplace materials. The modifiers seemed to provide more mixture stiffness at higher temperatures which possibly indicated a greater resistance to permanent deformation, while maintaining about the same characteristics as conventional mixtures at low temperatures.
Performance of Polymer Modified Asphalt Mixes in Kentucky
Authors: Fleckenstein LJ , Mahboub K , Allen DL 
Published: March 2009

Historically, Kentucky has been synonymous with coal. This is because Kentucky produces 160 million tons of coal per year. This translates into relatively heavy volumes of coal-haul truck traffic moving on public highways. Excessive load and tire pressure are common problems in Kentucky.
In response to these severe truck traffic conditions, the Kentucky Department of Highways in conjunction with the Kentucky Transportation Center developed an experimental program to evaluate effectiveness of modified asphalt systems that are available in the market. This paper deals with two projects that were designed to study polymer modified asphalts.
Polymer modified asphalts are claimed to: (a) reduce thermal cracking, usually associated with low temperatures and (b) reduce rutting, usually associated with high temperatures and heavy loads. Kentucky's unique environment conditions provided the opportunity to test these claims.
Chemical Characterization of Cross-Linked Polyurethane Films
Authors: van der Ven LGJ , van Houwelingen GDB , Lamping RR 
Published: March 2009

The chemical composition and the physical properties of two-component polyurethane coatings are influenced by the curing conditions, viz. relative humidity and temperature. Apart from the formation of urethane, carbon dioxide can be released by hydrolysis of the isocyanate groups, leading to the formation of urea groups.
Chemical-analytical methods have been developed to characterize cross-linked polyurethane coatings based on hydroxy-functional acrylic resins and trifunctional isocyanates. Spectroscopic and wet chemical methods as well as carbon dioxide measurements were applied. Quantitative data were obtained on the content of isocyanate, hydroxyl, and amino groups and on urethane and urea cross-links.
The influence of the curing temperature, relative humidity, and type of hydroxyl groups on the network structure has been investigated. The relative humidity influences the composition of the coating cured at ambient temperature. During curing at elevated temperatures, the relative humidity hardly affects the chemical structure of the film. However, during storage after baking, urea groups are formed.
Failure Analysis of Applied Coatings
Authors: Tator KB , Weldon DG 
Published: March 2009

When protective coatings are properly formulated and applied, they are usually expected to last ten years or more with periodic maintenance. However, occasionally, premature failure occurs, with expensive cost ramifications. The investigation of a field coating failure is considerably different than routine paint analysis, even though the same laboratory equipment is used. Instead, a forensic analysis technique is required, which relies heavily on background information, field sampling and observations, and laboratory testing and analysis.
This paper will describe how one coating consulting company conducts the field and laboratory investigation of coating failures. The structure of failure analysis will be illustrated by three different failures. The first failure involves an alkyd applied over concrete; the second failure involves the delamination of a urethane topcoat from an epoxy primer; and the third failure involves the cohesive failure of an inorganic zinc-rich primer topcoated with a vinyl system.
A Framework for Quantifying Crack Tip Constraint
Authors: Shih CF , O'Dowd NP , Kirk MT 
Published: March 2009

The terms high and low constraint have been loosely used to distinguish different levels of near tip stress triaxiality in different crack geometries. In this paper, a precise measure of crack tip constraint is provided through a stress triaxiality parameter Q. It is shown that the J-integral and Q are sufficient to characterize the full range of near-tip fracture states. Within this framework J and Q have distinct roles: J sets the size scale over which large stresses and strains develop, while Q scales the near-tip stress distribution relative to a reference high triaxiality state. Specifically, negative (positive) Q values mean that the hydrostatic stress ahead of the crack is reduced (increased) by Qσ0 from the plane strain reference distribution.
The evolution of near-tip constraint as plastic flow progresses from small-scale yielding to fully yielded conditions is examined. It is shown that the Q parameter adequately characterizes the full range of near-tip constraint states in several crack geometries. Through-thickness deformation and stress conditions affect near-tip triaxiality. Stress triaxiality near a three-dimensional crack front is measured by pointwise values of Q.
The J-Q theory provides a framework that allows the toughness locus to be measured and utilized in engineering applications. A method for evaluating Q in fully yielded crack geometries and a scheme to interpolate for Q over the entire range of yielding are presented. Extension of the J-Q theory to creep crack growth is discussed in the concluding section.
Constraint and Toughness Parameterized by T
Authors: Hancock JW , Reuter WG , Parks DM 
Published: March 2009

A series of cracked specimen configurations have been tested to correlate the geometry dependence of crack tip constraint and fracture toughness in full plasticity. Specimens with through cracks included a range of edge-cracked bend bars, compact tension specimens, and center-cracked panels. Surface-cracked panels were tested in tension to produce resistance curves.
The geometry dependence of ductile crack extension in plane strain has been correlated with crack tip constraint as parameterized by the T stress, which indicates the nature of the development of higher order terms in the nonlinear asymptotic crack tip expansion.