Showing papers in "Journal of Testing and Evaluation in 1994"

Instructions for a New Method of Inclusion Rating and Correlations with the Fatigue Limit

Abstract: Many inclusion rating methods already exist [1–6], some of which have been adopted as the standards for particular countries or industries. However, with the existing methods, it is difficult to evaluate the relationship between the fatigue limit and the type, size, or distribution of the inclusions. Recent works have shown that inclusions behave as small defects and that the quantitative effect on the fatigue strength can be assessed from an evaluation of the square root of the projected area of the largest inclusion, on a plane perpendicular to the maximum principal stress direction. This parameter, designated √areamax, contained in a definite volume, can be evaluated using the statistics of extremes of the inclusion distribution.

The use of fatigue specimens precracked in compression for measuring threshold values and crack growth

Abstract: Precracks generated in purely compressive cycles permit a determination of threshold values ΔKth and crack growth curves with increasing load amplitude only. They also permit to measure the effective threshold ΔKeff th and the dependence of ΔKth on crack length. The production of such precracks is also discussed.

Numerical analysis of plasticity effects in the hole-drilling residual stress measurement

Abstract: The aim of this work was to analyze the effect of plasticity on residual stress measurement when the through thickness center-hole technique is used. The study investigated the effect of the most important loading, measuring, and material parameters, i.e., the residual stress intensity, the ratio between the principal residual stresses, the orientation of the strain-gage rusette with reference to the residual stress principal directions, the yield strength, and the strain hardening characteristics of the material. By means of a finite element simulation of the measurements, the errors that are usually produced by the direct use of ASTM E 837 (Test Method for Determining Residual Stresses by the Hole-Drilling Strain Gage Method) for the elaboration of the rosette strain gage readings was firstly determined by considering large enough ranges of the above-mentioned parameters to represent many conditions of practical concern. Afterwards it was shown that, at least within the limit of validity of the model, a considerable reduction of those errors can be obtained by using the proposed analytical procedure for elaborating the readings of a classical these elements strain-gage rosette. Moreover, the use of a new type of rosette with four radially oriented strain gages was proposed which could lead to further improvement of the measurement accuracy in any considered condition.

Effects of Load-Distributed Width on Split Tension of Unnotched and Notched Cylindrical Specimens

Abstract: Unnotched and notched cylinders in split tension are analyzed. The load-distributed width has been shown to affect the stress and displacement distributions. Based on finite element analysis, linear elastic fracture mechanics (LEFM) formulas for the stress intensity factor KI, crack mouth opening displacement (CMOD), and the crack opening displacement (COD) profile for the split tension of notched cylinders are first provided in terms of load-distributed width as well as load magnitude, specimen size, and notch length. A formula expressing the effect of load-distributed width on maximum tensile stress in an unnotched cylinder is also provided.

Behavior of Asphalt Concrete Mixtures in Triaxial Compression

Abstract: The triaxial compression test is one of the most common standard tests for determining the stress-strain behavior and strength parameters of soils under drained and undrained conditions. The use of the test method in asphaltic mixtures is less well known and seldom practiced. This paper describes the use of the triaxial compression test for asphaltic mixtures for determining their engineering properties such as the friction angle φ, the cohesion, c, and the elastic compression modulus, E. Effects of test temperatures, strain rate, and confining pressures on the compressive behavior of asphalt concrete were studied. The results showed that the friction angle is primarily a function of aggregate friction and interlocking, being independent of test temperature and strain rate. The cohesion, on the other hand, is largely dependent on the binder and fines mixture being sensitive to both test temperature and strain rate changes. The confining pressures have no influence on c and φ, but have significant influence on the compression modulus. E. The tests can be conducted at controlled temperatures, constant strain-rate, and confining pressures so as to allow the determination of the basic engineering stress-strain and strength properties of these materials under controlled environmental conditions. Using these properties, a constitutive plasticity model based on the Drucker-Prager yield condition can then be applied in an axisymmetric finite element model to describe the mechanical behavior of the asphaltic material in triaxial compression. Analysis shows that the plasticity model is able to describe the stress-strain behavior of the triaxial specimen to failure, predicting both the failure strain and the failure stress fairly accurately. Comparison of analysis with measured lateral deformation at failure also show good agreement. Thus it seems that a simple idealized elastic-perfectly-plastic constitutive model, whose parameters can be determined from a triaxial compression test at constant strain-rate, is adequate to describe the behavior of asphaltic mixtures, loaded in compression to failure.

Determining asphalt concrete properties via the impact resonant method

Abstract: Various publications have demonstrated that the results from the resilient modulus test (see ASTM D 4123, Method for Indirect Tension Test for Resilient Modulus of Bituminous Mixtures) display a wide range of variability. Considering this, an alternate testing method that produced more consistent results with a simpler test setup was pursued. A standardized vibrational test procedure for Portland cement concrete (ASTM C 215, Test Method for Fundamental Transverse, Longitudinal, and Torsional Frequencies of Concrete Specimens) was modified to measure the material properties of asphalt concrete. The impact resonant method provided three separate, independent tests, two measuring the elastic modulus and one the shear modulus. Poisson's ratio was obtained by comparing moduli results. Unlike the semi-nondestructive nature of the resilient modulus test, the impact resonant method was a true non-destructive test. The method also allowed for a possible laboratory link to nondestructive analysis of in-situ pavement. Experimental test results demonstrated that the impact resonant method provided precise and reproducible results. Further experiments revealed that the impact resonant method could detect different magnitudes of microcrack healing.

Estimation of young's modulus and of hardness by ultra-low load hardness tests with a vickers indenter

Abstract: The evaluation of the elastic-plastic properties of a material by using an ultra-low load hardness test requires a geometrical calibration that must take into account the imperfect form of the diamond indenter. In the present work, the Vickers indenter offset of the microindentation equipment was estimated using differently heat-treated steel samples. To this end, the dimensions of the indentations have been evaluated by two different methods: optical measurement of the diagonals and direct measurement of the penetration depth during the test. The elastic-plastic properties are then calculated from the analysis of the penetration depth/indentation load curves. The Young's modulus values determined for the different high-speed steel samples were very similar and close to the literature value for steel if the appropriate corrections are performed. The hardness values decrease when the determination procedure includes the geometrical correction of the indenter offset, and still further when using the total correction obtained by means of optical measurements of the indenter diagonal. Variation of the hardness values with the applied load is much less when the corrections are carried out.

A fractographic technique for the estimation of initiation fracture toughness JIC for ductile materials

Abstract: A single specimen fractographic technique based on critical stretch zone width measurements is suggested for the estimation of fracture toughness (JIc) for highly ductile materials. The salient feature of this technique is that it overcomes the problem of fatigue precracking and is able to predict the fracture toughness of a material using a blunt notch specimen. Fracture toughness tests on commercially pure Armco iron, nickel, and aluminum as well as Al-Mn based austenitic stainless steel and En28 steel were carried out to validate the method.

Back-face strain compliance and electrical-potential crack length calibrations for the disk-shaped compact-tension DC(T) specimen

Abstract: Back-face strain compliance and electrical-potential crack length calibrations have been experimentally determined for the disk-shaped compact-tension DC(T) specimen. Finite-element modeling was used to ascertain the back-face strain distribution at several crack lengths to determine the significance of inconsistent gage placement. The numerical solutions demonstrated good agreement with experiment, especially at smaller crack lengths when the back-face strain gradients are minimal. It is concluded that precise gage placement is only critical when the crack tip closely approaches the back of the test specimen.

A Suggested Test Procedure to Measure Mixed Mode I–III Fracture Toughness of Brittle Materials

Abstract: This article describes a test procedure to measure mixed mode I–III fracture toughness. The traditional compact tension specimen geometry is modified to include an angled crack slot. This angle is varied to produce various mode I/mode III ratios. A further modification to the specimen design involving two crack fronts in a triple “pantleg” configuration that can produce near-mode III loading at the crack tip is also described. Together, these two specimens can be used to test the entire spectrum of combined mode I–III. Results of mixed mode fracture tests on 2034 aluminum alloys using these specimens are presented. A three-dimensional (3-D) finite element model of the modified compact specimen to validate the analytical procedure is also described. Angular correction factors for the mixed mode case are also presented. The results indicate the feasibility of developing a new standard test method to measure mixed mode fracture toughness in macroscopically brittle metallic materials.

Wear-related fatigue in a wire rope failure

Abstract: The fatigue failure of a nonrotating wire rope used on a skip hoist in an underground mine has been studied as part of the ongoing research by the U.S. Bureau of Mines into haulage and materials handling hazards in mines. Correlation of individual wire failures within two segments of the failed rope were used to gain an understanding of the progression of degradation leading to rope failure. Wire failures occurred predominantly at locations of wear between adjacent strands. These interstrand wear sites are identifiable by a large reduction in diameter; however, reduction in area is not responsible for the location of failure. Fractography revealed crack initiation sites to be located opposite the characteristic wear site or at other less noticeable wear sites. The primary failure mechanism of individual wires within the rope is believed to be a function of contact stress at the interstrand wear sites. Axially loading and unloading the rope produces high compressive stresses at the contact sites, which in turn produce large alternating tensile stresses on the opposite side of the wire. This mechanism has been termed “contact stress-accelerated fatigue.” This mechanism and the affiliated wear pattern both are consequences of interstrand contact.

Numerical Assessment of the Dynamic Tension Test Using the Split Hopkinson Bar

Abstract: An experimental and numerical analysis of tension tests in the Hopkinson bar is made to assess the suitability of this method to characterize materials in tensile conditions at strain rates about 1000/s. The stress and strain fields that appear in the specimen are analyzed by the finite element method. This mathematical simulation of the test allows a check of the hypotheses normally used in obtaining results: equilibrium situation and uniform strain distribution in the specimen. The simulation process also provides some criteria to design the experimental setup and the specimen geometry for the best agreement with the ideal situation. Finally, because of the usual assumption regarding the uniformity of the strain distribution in the specimen may not be valid, some corrections are suggested to obtain reliable material properties from direct test results in different situations.

Proposed Test Method for Dynamic, Properties of Connections Assembled with Mechanical Fasteners

Abstract: A new test procedure for connections assembled with mechanical fasteners is presented. The procedure provides information on cyclic and dynamic characteristies that will allow the relative performance of connections manufactured with different materials to be directly compared. An equivalent energy elastic-perfectly plastic system is defined that allows comparison of initial stiffness, yield load, and ductility on an equivalent basis. The hysteretic and equivalent viscous damping are also determined to provide information on the energy dissipation characteristics of the connection. Adoption of this test procedure will provide information that will allow engineers and architects to evaluate the performance of competing materials with direct comparisons. It will also provide uniform data from which revisions to the model building codes and design specifications for each material can be made on an equivalent basis.

International Aviation Security Research and Development

Abstract: A discussion of the research and development activities with the U.S. Federal Aviation Administration (FAA) related to aviation security, based on the principles of (1) denying access; (2) weapons/explosives detection; (3) human factors; and (4) aircraft hardening, is presented.

Comparative Studies of Yarn and Fabric Friction

Abstract: A comparison of the magnitudes of yarn-to-yarn and fabric-to-fabric friction is made. It is shown that yarn friction measured on a capstan (cylindrical) surface is significantly greater than that measured on a flat surface. The greater magnitude of the coefficient of friction in a capstan assembly is ascribed to the effects of experimental variables such as capstan radius, angle of lap, and input tension. The coefficient of friction of fabrics is also shown to be greater than that of their component yarns. Yarns with higher frictional properties yield fabrics whose frictional properties are also higher.

An evaluation of several techniques for measuring air-void content in asphalt concrete specimens

Abstract: Precise and accurate measurement of air-void content is critical to the evaluation of asphalt-aggregate mix specimens taken in the field or compacted in the laboratory. It is an integral part of the performance-based testing and analysis methods developed by the Strategic Highway Research Program Contract A-003A (SHRP A-003A). Standard methods for drying specimens after coring and/or cutting from a larger compacted mass, and for measuring bulk specific gravity present problems for testing of the same specimen using equipment developed by SHRP A-003A, or whenever the specimen must be fixed to the testing equipment by means of an adhesive. This paper presents a comparison of the standard methods of air-void content measurement, measurement of bulk specific gravity using unsealed specimens and using specimen sealed with paraffin wax (ASTM D 1188, Test Method for Bulk Specific Gravity and Density of Compacted Bituminous Mixtures Using Paraffin-Coated Specimens), with three alternative methods for sealing the specimen: dusting with zinc stearate powder, wrapping with a waxy elastic paper called Parafilm™ (American National Can), and covering with a rubber membrane. The results indicate that each of the methods produces different measured air-void contents. The waxy elastic paper results were closest to those obtained from specimens sealed with paraffin, and it is suggested that this is a suitable alternative to paraffin wax when the specimens have smooth (cut/cored) surfaces and are to be tested for performance afterward. The use of an air gun to dry specimens after coring and/or cutting was compared with the standard oven-drying method (ASTM D 2728, Practice for Paving Uses and Application Temperatures for Road Tars). It was found that the use of a 210 kPa (30 psi) air gun produced similar results to those found with the standard method and was nondestructive, thus allowing further testing of the specimen.

Back Face Strain Calibration for Crack Length Measurements

Abstract: A new calibration of back face strain (BFS) versus crack length a was developed. The calibration incorporates crack closure effects and is based upon a least squares multiple curvilinear regression analysis using seven specimens. Fatigue crack growth took place over a range of crack length to width ratios a/W from 0.2 to 0.8. The information was obtained under constant change in stress intensity factor ΔK using compact fractures toughness specimens of 2024-T351 aluminum alloy. In addition, two segular fatigue life crack propagation test conditions were used in the analysis database. The calibration function A*(a/W) is presented in a tubular form as well as in a polynomial equation format. The physical crack length was measured on both surfaces and later, after fracture, corrections of crack length were made for both curvature and plastic zone size. No effect of ΔK and specimen thickness on the calibration behavior was found to occur. The calibration equation was checked against crack lengths during fatigue crack growth behavior of both HSLA steel and mechanically alloyed aluminum materials and was found to be accurate.

Data Acquisition and Analysis of Tensile Properties for Metal Matrix Composites

Abstract: Problems arise when existing standard tension tests are used for the measurements of the properties of metal matrix composites (MMCs), largely because the elastic limits in these materials are low due to intrinsic residual stresses. A new and validated data acquisition and analysis system has been developed to provide reference data for comparison with the results of two U.K. interlaboratory exercises on the tension test method for MMCs. Particular attention is paid to assessing an automatic system for calculating Young's modulus from the input data and using plots of secant or tangent modulus against stress or strain to present information on properties in a clear and succinct manner, and to methods for validating the software. The results of both interlaboratory exercises, on different types of MMCs, showed that the analysis system produced the smallest deviation from the mean.

Effects of Sample and Test Variables on Electrical Wire Insulation Flammability

Abstract: A new test method has been adopted to evaluate the flammability of electrical wire insulation materials. In this test, wire insulation is exposed to an external ignition source while the electrical conductor is internally heated by an electric current. The repeatability of the test and the effects of wire gage and insulation thickness, internal wire temperature, and sample orientation on the wire insulation flammability were evaluated. Experimental results showed that the new test is a practical and repeatable method for evaluating flammability of wire insulation materials.

Introduction to the Sixth International Civil Aviation Security Conference (AVSEC'93)

Abstract: This introduction is provided as an overview of the papers included in this section of the Journal and to provide a context for reviewing these papers for the regular readers of the Journal. The Federal Aviation Administration (FAA) entered into a partnership with ASTM (Committee F-12 on Security Systems and Equipment) to conduct the Sixth International Civil Aviation Security Conference (AVSEC'93), held on 26–28 October 1993 in Washington, DC. The objective of this conference was to provide a forum for government, the aviation industry, and security service providers to exchange insights on solutions to the global challenge of providing safe and secure air travel.

Testing Techniques for Measurement of Bulk Modulus

Abstract: The objective of this study was to examine prospective tests for determining the bulk modulus of elastomers used in the construction of elastomeric bearings. Because elastomeric materials are nearly incompressible, relatively slight volume changes are experienced during isotropic compression, sizably governing the accuracy of test measurements. For this reason major topics of interest are equipment calibration, test repeatability, and error accountability. Test methods explored included use of a deformation jacket, a fluid displacement volume change measurement device, and load ram displacement for measurement of volume change. For verification of test methods specimens of Adeprene were tested. Results from all test methods were found to be suitably, but not equally, repeatable. Considering ease of operation, and acceptability of errors, the load ram method is found to be superior compared to other methods investigated.

Physiologic Challenges Induced by Participation in Ice Hockey—Implications for Training

Abstract: Training programs for ice hockey players have two fundamental objectives; namely, to optimize performance and to minimize the risk of injury. The design of efficient and successful programs to meet these purposes depends on a careful analysis of the physiological demands of the game and the environment in which it is played. Moreover, if the program is to meet individual needs, the physical and physiological status of the player must be considered. Ice hockey is a demanding sport that involves the recruitment of essentially all of the skeletal muscles of the body in order to perform the diverse skills of the game. These skills are performed over various ranges of movement, at various velocities and loads, and usually involve several large muscles acting synergistically. Moreover the extended nature of the game, performed over three periods, results in numerous repetitions of each task. Collectively, the repeated performance of these tasks impose extreme demands on respiratory, cardiovascular, neural, muscular, metabolic, and thermoregulatory systems of the body. The physiological demands may be further exaggerated given the protective equipment that is worn and the fact that abnormally high temperatures and humidities may be present. Proper preparation can only be realized by exposing the participant to progressive routines designed to systematically challenge each of the physiologic systems in a manner appropriate to game conditions.

Determining the Potential Drop Calibration of a Fatigue Crack Growth Specimen Subject to Limited Experimental Observations

Abstract: Six separate calibration techniques are applied to potential drop (PD) and crack length data from 23 experimental datasets. Five of the techniques use limited experimental input gained during precracking and after test completion to derive the coefficients associated with the calibrations. The datasets include SE(B) and M(T) specimens, fatigue crack growth (FCG) tests and foil analog simulations as well as various aluminum alloys and steel. A comparison of the calibration techniques is undertaken in terms of crack length and the subsequent effect on stress intensity factor errors. The best calibration techniques using two PD and crack length data pairs are the two-point modified and post-test corrected Johnson's equation. Using these methods, 21 of the 23 tests satisfy a criterion based on an acceptable ±2% mean variation in stress intensity factor. If a statistical assessment of the data is made, only 30 to 35% of the tests satisfy this criterion. Finally, the crack length prediction errors that result from the different calibrations can typically cause a 15 to 30% variation in FCG rate da/dN at a given ΔK level. This difference is found to be primarily due to errors in the ΔK calculation.

Security Technologies and Techniques: Airport Security Systems

Abstract: A description of pertinent text and figures from the revised Chapter 6, “Technologies and Techniques of Security,” of the ICAO security manual is provided.

Bond Tests of Fiberglass-Reinforced Plastic Bars in Concrete

Abstract: Fiberglass Reinforced Plastic (FRP) bars for concrete reinforcement have been commercially available for several years. The main advantage of such bar relative to the conventional steel reinforcing bars is their resistance to corrosion. The reinforced plastic bars are slightly different from the conventional steel bars both geometrically and mechanically. Thus, research is needed to understand their behavior and to be able to use them in concrete reinforcement with adequate reliability. Bond strength of reinforced plastic bars in concrete is one of the mechanical and behavioral differences with the steel bars. This paper presents the results of pullout and beam tests conducted to determine the bond stress-slip behavior of FRP bars in concrete.

Thermal and mechanical properties of cellular polystyrene and polyurethane insulation materials aged on a flat roof in hot-dry climate

Abstract: Cellular polymers, which have been increasingly used for thermal insulation of external walls and roofs since the 1970s, degrade in some cases. The heat transmission of a cellular polymer insulator, the k value, is predominantly dependent on the heat conduction of the air or gas remaining in the cells. An insulator may be aged and start transmitting more energy due to replacement of cell content with different gases or moisture or both, changes in size, softening and creeping under pressure and heat, or penetration of water or mineral particles into cells, or a combination thereof. The solid face also degrades due to ultraviolet light, heat and atmospheric oxygen. A research project was carried out from January 1988 to December 1991 to investigate the performance of flat roofs, waterproofing, and thermal insulation materials in the hot-dry climatic region of Saudi Arabia. In this context a field station was built and operated for weathering of roofing and insulation materials and for monitoring the surface and the inner temperatures of the applied roof systems. Basically, two types of cellular polymer, expanded polystyrene and foamed polyurethane, were installed on the roof of the station for insulation. Specimens taken from the fresh, stored, and weatheredmore » polystyrene and polyurethane foams were tested to evaluate them according to the selected properties of thermal conductivity, compressive strength at relative deformation, and dimensional stability at elevated temperature. The test results were compared with the requirements presented in the literature and the standard specifications.« less

Uniaxial Tensile Strength of Cementitious Composites

Abstract: A brief review of various methods of measuring the uniaxial tensile strength of cementitious composites is presented. The pros and cons of these methods are described. Common problems associated with the traditional uniaxial tension testing techniques exist, and these problems arise from two areas: (1) stress concentration at gripping and (2) misalignment. These testing artifacts can significantly influence the test results, producing measurements that underestimate the intrinsic strength of the material. A novel approach for testing cementitious composites in tension is described. The test uses cylindrical bar specimens 9.5 mm in diameter and 120 mm in length. The specimens are fractured in a hydraulic chamber which allows specimen self-alignment. The advantages of using the technique are minimization of misalignment and stress concentration, larger specimen volume under stress, and determination of initiation of fracture. The tensile strength values obtained using the hydraulic tension test technique are compared to those obtained by the traditional uniaxial tension tests. The average tensile strength of bigger size specimens, such as 16 mm in diameter and 120 mm in length, was predicted using the application of Weibull theory. Furthermore, these specimens were also tested using the hydraulic tension testing technique. The data show that the predicted values obtained using the application of Weibull theory compare well with the experimental values obtained by the novel teasion testing technique.

Numerical model of primary creep deformation in a novel double shear specimen

Abstract: Three-dimensional finite element calculations were performed for primary creep deformation in a novel double shear specimen. Two characteristic creep behaviors were considered: one in which the stress exponent, n, is equal to 3 and another in which n is equal to 5. Both models resulted in a quasi-stationary stress state in which the principal stresses change only slightly with time while the von Mises effective stress and principal facet stress reach essentially constant values. The uniformity of this quasi-stationary stress state throughout the gage section indicates that it may be used to characterize the overall stresses driving creep deformation and damage.

Development of an improved compression specimen geometry for unreinforced polymers

Abstract: One of the recommended compression specimen geometries for plastics in ASTM D 695, Test Method for Compressive Properties of Rigid Plastics, is a straight-sided cylinder or prism. This end-loaded specimen tends to barrel at high strains. Additionally, if modulus is desired, the standard suggests that the specimen have extra length to avoid end constraints. Therefore, compression specimens for modulus can fail at a different stress level than compression specimens for strength. To overcome these problems, a compression specimen with a gage section of reduced area which is end-loaded but side supported was developed. Additional experimental observations of the thermosetting polymer of interest included a nonlinear compressive stress-compressive strain response which required a parabolic constitutive relationship to model, an observation of a significant anelastic material response, and a material response termed anelastic buckling. These observations of material behavior had not previously been observed.

Effect of composition of El-lajjun oil shale on its calorific value

Abstract: A geochemical analysis of El-lajjun oil shale in Jordan was carried out. It was found that El-lajjun oil shale consists of the following groups: organic matter, biogenic calcite and apatite, detrital clay minerals, and quartz. The calorific values of 100 samples of shale were determined. The effect of bore depth, calcium carbonate, organic carbon, and sulfur content on the calorific values were studied. Results were well correlated by the following equation Calorific value = 352,44 ( CaCO 3 ) - 0.066 ( S ) 0.257 ( C org ) 1.141 with correlation coefficient of 0.983 and with an average standard error of 2.63%.