Showing papers in "Journal of Testing and Evaluation in 1986"

An Ultrasonic Method for Determining Axial Stress in Bolts

Abstract: An ultrasonic technique for determining the axial stress within a bolt was developed and experimentally verified. The technique uses time-of-flight measurements of both shear and longitudinal waves propagating along the axis of a bolt along with the material parameters to calculate the stress acting on the bolt. One significant advantage of the technique is that an independent measurement of neither the original nor present length is required. Experimental results suggest that the method may be usable for fasteners which have experienced a small amount of plastic deformation.

A Method for Determining Conservative Fatigue Threshold While Avoiding Crack Closure

Abstract: The low-rate fatigue properties of a mild steel are obtained on small compact-type (CT) specimens while avoiding crack closure. These properties are similar to those of butt-welded joints obtained at a much lower stress ratio in the range −1 to 0.5. This is a result of the existence of tensile residual stress at the crack tip of the welded joint which prevents crack closure even at low stress ratios. It is concluded that the most conservative fatigue crack propagation properties, including fatigue threshold values, can be easily obtained by confirming that the results are the same for CT specimens tested at different terminal stress ratios using a ΔK decreasing method which avoids crack closure.

Evaluation of the Effect of Contact-Time When Measuring Floor Slip Resistance

Abstract: To test the slip resistance of shoe and floor materials, the Horizontal pull Slipmeter (HPS) is normally placed on a smooth floor surface and then connected to a capstan which applies force to overcome friction. This normal procedure was compared with a laboratory modification of the normal HPS operation: the meter was placed on the floor at the same time the capstan began applying the lateral force. Results from 1360 measurements involving 17 shoe-sole materials and two floor materials, wet and dry, were as follows: (1) differences in time of contact between shoe sole and floor materials affected the slip resistance for some materials, and (2) dry leather materials were most consistently and substantially affected, whereas other affected materials showed relatively small differences. Previous researchers have shown dry leather to be generally less slip resistant than other shoe-sole materials. Results from this evaluation study may be used in support of these previous findings.

Modified Lever System for Constant-Stress Compressive Creep Machine

Abstract: A simple mechanical system for keeping constant applied stress during the course of a creep test is proposed. The system uses the forced movement of load and is especially suitable for compressive creep testing. Verification in practical implementation has shown that the tolerance in the stress constancy is better than ±1.5% up to a strain of 30%.

Determination of fracture toughness by CTOD resistance curve method

Abstract: Fracture toughness δi of AISI 4340 steel in the hardened and tempered condition has been determined by the multiple-specimen CTOD (crack tip opening displacement) resistance curve method This fracture toughness δi value has been compared with the JIc fracture toughness also obtained by the multiple-specimen JR curve technique The investigation also examines the effect of specimen size, thickness, and width on δi and δR curve behavior The effect of these parameters on the constraint factor m in the J-δ relationship has also been examined Compact tension specimens with TL orientation were used All specimens satisfied ASTM E 813 standard size requirements This investigation demonstrates that Jδi values obtained by the CTOD resistance curve method are similar to JIc values obtained from the J-integral resistance curve method The specimen thickness has no significant influence on δi or δR curve behavior On the other hand, specimen width has a distinct influence on constraint factor m and δR curve behavior

On the Determination of Crack Initiation Using Standard Test Methods

Abstract: The results presented in this paper were obtained by participation in an ASTM experimental round-robin exercise. The roundrobin was aimed at verifying the appropriateness of ASTM Draft Test Method for Crack Tip Opening Displacement (CTOD) Testing. It was demonstrated that the Draft Method is suitable for determining initiation values of CTOD and that more unequivocal values are obtained if the crack length is measured as the average of ten instead of three individual values distributed over the specimen thickness. This is consistent with the recent revision of the Draft Method.

A Microcomputer-Based System for the High-Speed Compression Test by the Split Hopkinson Pressure Bar Technique

Abstract: A microcomputer-based system has been developed for the high-speed compression test by the split Hopkinson pressure bar technique. The present test system enables one to obtain reliable dynamic stress-strain data for materials for a very short period. The range of strain rates achieved by the test system is approximately 102 to 2 × 103 s−1 depending on the strength of the material and the impact velocity of a striker bar. The accuracy of the entire test system is checked directly by comparing the static and dynamic test results for a strain-rate insensitive material. Test results are presented for tough pitch copper and two aluminum alloys.

A computerized test system for thermal-mechanical fatigue crack growth

Abstract: A computerized testing system to measure fatigue crack growth under thermal-mechanical fatigue conditions is described. Built around a servohydraulic machine, the system is capable of a push-pull test under stress-controlled or strain-controlled conditions in the temperature range of 25 to 1050 C. Temperature and mechanical strain are independently controlled by the closed-loop system to simulate the complex inservice strain-temperature relationship. A d-c electrical potential method is used to measure crack growth rates. The correction procedure of the potential signal to take into account powerline and RF-induced noises and thermal changes is described. It is shown that the potential drop technique can be used for physical mechanism studies and for modelling crack tip processes.

Poisson's Ratio As Determined for Elastic and Plastic Deformation and for Monotonic and Cyclic Loading—Part I: Critical Review

Abstract: Poisson's ratio is defined strictly on the assumption that the material is homogeneous. In applications of Poisson's ratio to mechanical problems, this assumption can be overlooked. To check whether the assumption applies to monotonic and cyclic loading, we review measurements of Poisson's ratio, or rather the ratio of diametral strain to axial strain. Such measurements are quite rare for cyclic deformation. However, they show that the ratio of diametral strain to axial strain can differ from values expected on the basis of traditional values of Poisson's ratio for elastic and plastic deformation. The technical consequences of this difference are indicated.

Investigation of Dynamic JId for Alloy Steel Weldments Using the Split Hopkinson Bar

Abstract: The fracture toughness parameter JId, under dynamic loading conditions, was determined for weldments of HY80 and QT28 alloy steels using a split Hopkinson bar technique. JId was obtained for the fusion zone, the heat-affected zone, and the base metal for these steels as a function of temperature in the range of −80 to 25°C and at loading rates of ˙K = 106 MPa√m s−1. Wedge loaded compact tension specimens were loaded in a split Hopkinson bar. The onset of stable crack growth was determined by using a strain gage that was attached ahead of a fatigue crack. The results show that, at −80°C, fracture with limited stable crack growth takes place, while for all other testing conditions considerable ductility precedes fracture of these alloys.

An Empirical Model for Predicting Performance of Fire-Resistive Coatings in Wood Construction

Abstract: Currently used fire-retardant coatings for wood products reduce flame spread; they are not designed specifically to provide fire resistance. Fire-resistive coatings designed for steel and foam plastics generally are not recommended for wood. However, these fire-resistive coatings have been tested for their ability to improve the fire resistance of plywood. We have developed an empirical model for predicting the fire-resistance performance of fire-resistive-coated wood based on these small nonload-bearing fire-resistance tests. The equations in the model provide estimates for the times to reach either a temperature rise of 139°C or a temperature of 288°C. Using these equations, various applications for fire-resistive coatings in wood construction were examined. Applications considered include thermal barriers, walls, floors, large timber members, and doors. Predictions using the model compared favorably with the very limited experimental data available in the literature. Additional research is needed before use of fire-resistive coatings in wood construction can be realized.

Erosion by Solid-Particle Impacts: A Testing Update

Abstract: A workshop on erosion by solid particles focused attention on the status of applicable testing technologies. ASTM Standard G 76-83, in which erodent particles are entrained in gas jets, was reviewed, and procedural variations based on it were described and discussed. Among the factors considered were cratering, particle fluxes, particle feeding, and the characteristics of nozzles, specimen surfaces, and erodent particles. Many effects of the foregoing factors are not yet fully understood. Jet-type erosion tests such as ASTM G 76 cannot simulate all practical circumstances in which erosion by solid particles occurs. Therefore the development of additional standardized testing procedures is needed. Two alternatives, slinger-type testing and wind-tunnel testing, with potential for further development were described.

Fatigue Crack Growth Threshold and Crack Opening of a Mild Steel

Abstract: The effects of stress ratio, compressive peak stress, and cold rolling on the threshold stress intensity and crack closure level of a mild steel (SAE 1010) were investigated. As the stress ratio and the magnitude of the compressive peak stress were increased, the threshold level decreased linearly. The threshold stress intensity also decreased linearly as the yield strength was increased by cold rolling. Crack opening measurements showed that the measured threshold is composed of two parts: an intrinsic threshold stress intensity range, ΔKin, and an opening stress intensity, ΔKop. The opening stress intensity decreased with increasing magnitude of the compressive peak stress. The intrinsic threshold stress intensity range was not significantly affected by the compressive peak stress. Severe cold rolling decreased the opening stress in the near threshold region to near zero. In a constant amplitude load-controlled test, the ratio of the opening stress intensity to the maximum stress intensity decreased as the maximum stress intensity (crack length) increased, and no crack closure could be observed when the net stress approached the yield strength of the material.

Determination of Fracture Toughness for Brittle Nonmetallic Materials at the Subcritical Crack Growth Stage

Abstract: In addition to the KIc characteristics of such brittle materials as glass-like and ceramic ones, it is proposed to determine the values of KIo and KIi, corresponding to the crack onset and the beginning of the accelerated stage of its subcritical growth. An experimental method has been developed: to grow a given edge crack in a flat specimen, to determine the values of KIo and KIi by loading this specimen in transverse compression and then, in the course of eccentric tension (wedging) of the same specimen, to evaluate the KIc characteristics. The validity of the KIo, KIi and KIc values obtained for glass and polymethyl methacrylate (PMMA) is confirmed by their comparison with the data published.

Direct Modeling of Concrete Block Masonry Under Shear and In-Plane Tension

Abstract: A better understanding of the complex behavior of masonry structures is necessary to embrace the more appropriate concept of ultimate strength design. Owing to the prohibitive cost of full-scale testing of masonry systems, a more economical method utilizing direct modeling techniques is proposed. It is the objective of this study to evaluate the use of direct modeling of ungrouted and grouted block masonry under shear and in-plane tension. A total of 62 quarter-scale model shear and tension specimens were tested, and the results were compared with similar prototype test results. The study includes the effect of mortar strength, grout strength, and load orientation on the assemblage mode of failure and ultimate strength. Correlations between model and prototype results are performed. Excellent correlations were obtained for mode of failure and the overall effects of different parameters. It is concluded that direct modeling is feasible and is capable of predicting the behavior of masonry. Deviations from prototype strength results were observed that are attributed to size effect of aggregate, imperfections in unit geometry, and higher strength values of model blocks.

R -Curve Round-Robin Program for ASTM Recommended Practice for R -Curve Determination (E 561)

Abstract: A round-robin program sponsored by ASTM Task Group E24.01.02 on Crack Growth Resistance Curves was conducted to establish guidelines on variability for a Precision and Accuracy statement for ASTM Recommended Practice for R-Curve Determination (E 561). Two high strength aluminum alloys were tested by seven participants using the compact configuration specimen. The results of these tests are summarized herein, and a Precision and Accuracy section given along with variability at four levels of effective crack growth.

Linear Elastic Fracture Mechanics Applied to an Adhesive Spar—Wingskin Joint

Abstract: When utilizing adhesive bonding in structures where a failure might have serious consequences, one is generally interested in the possibility of determining the sensitivity of the bond strength to certain types of bond imperfections. It is well known that most adhesive bonds will contain defects such as voids, regions with no or poor bonding, and microcracks. When such defects are located in regions with alternating stresses of sufficiently high amplitude, they might grow to form macrocracks. To investigate how the static strength of an adhesive spar—wingskin joint is affected by the presence of two straight edge cracks in the interface between the adhesive and the spar flange and located symmetrically with respect to the spar center line, experiments were performed for different crack sizes. Specimens were loaded by a tensile force acting along the spar center line in order to simulate the effect of fuel pressure. To find out whether the usual linear elastic fracture mechanics (LEFM) assumption of a critical elastic energy release rate value at onset of fracture applied in this case also, the elastic energy release rate was calculated analytically by use of a simple beam model and numerically by use of the finite element method (FEM). The following conclusions were drawn for the specific geometry considered: 1. For crack lengths below 4 mm, the joint was critical with respect to interlaminar separation in the spar flange. 2. For crack lengths above 4 mm, the joint was critical with respect to debonding. 3. The critical energy release rate was approximately constant for crack lengths in the interval of 4 to 15 mm. The influence of the radius in the connection between the spar web and spar flange and the elasticity modulus of the elastic insert in the same region was investigated numerically. From this it was concluded that: 4. For cracks larger than about 10 mm the joint will become more crack sensitive with increasing radius, whereas it will be almost unaffected by changes in the insert elasticity modulus.

Use of X-Ray Diffraction with the Gaussian Curve Method to Evaluate the Hardening in Quenched Steels

Abstract: An X-ray diffraction line will broaden considerably when steels transform to martensite on quenching Slack quenched steels contain a mixed martensite and fine pearlite structure which produces an anomalous diffraction line profile with a sharp peak superimposed on a broad base The sharpness of the diffraction line peak can be measured by using a constant of the Gaussian curve fitted to the peak This constant (denoted GCP) for completely hardened steels increases with increasing carbon content up to 07 wt% carbon At higher carbon contents, the GCP becomes almost constant Also, the GCP increases with increasing hardness along a single curve independently of carbon content The GCP for the slack quenched steels is smaller than that for the completely hardened steels Extent of hardening of the slack quenched steels having a sharp diffraction line peak can be evaluated rapidly and nondestructively by comparing their GCP value with that for the completely hardened steels

Evaluation of plane-stress fracture testing methods

Abstract: ASTM Recommended Practice for R-Curve Determination (E 561) allows the use of either center cracked or compact specimens for determination of R-curves and Kc. A round-robin program to establish a Precision and Accuracy statement for ASTM E 561 was recently conducted on compact specimens. This paper presents R-curves and Kc data for two materials as determined from both specimen types. A discussion of the results is included.

Fracture Mechanics Evaluation of Irradiation Embrittlement in Reactor Vessel Steels Based on the Rate Process Concept

Abstract: A new evaluation procedure for the critical fracture toughness (KIc, KId) from Charpy-V impact absorbed energy is presented. The strain-rate/temperature effect on the cleavage-controlled fracture toughness transition is first explained by applying the concept of a stress-dependent rate process for fracture initiation. The expression described in terms of the Charpy-V energy ratio, Cv-us/Cv, for fracture toughness under a constant strain rate is newly derived. The feasibility of the new procedure for evaluating the irradiation embrittlement of reactor pressure vessel steel, such as SA533B-1, is here verified utilizing the data for both unirradiated and irradiated materials in the literature. Another method for the determination of coefficients in the new expression from the Cv-fitting curve is also presented.

Using an Impact Device with Sliding Drop Collar for In Situ Evaluation of Compressive Strength of Insulating Cellular Concrete

Abstract: This paper describes the efforts of the Central Building Laboratory of the Standards Institute of Israel to develop a relatively simple method for in situ nondestructive evaluation of the compressive strength of lightweight cellular concrete used for thermal insulation of roofs. The idea of the developed impact device with sliding drop collar is similar in principal to the well-known soil test method of drop-weight penetration, ordinarily used for field determination of compacted soil density. Test results show that the depth of penetration is influenced by two main parameters: compressive strength of the concrete and its density. If the unit weight of the cellular concrete is known or predetermined, its compressive strength can be estimated by means of the impact device with a sufficient degree of accuracy. Thus the drop-collar penetrometer may find useful application in in situ quality control of lightweight cellular insulating concretes.

Analysis of Service Failures in Thermoplastic Pressure Piping Water Systems

Abstract: Investigators into failures of installed thermoplastic water piping systems often do not have sufficient knowledge of the types or classes of failure and their causes to make a proper analysis of problems in this area because of the newness of thermoplastic piping. The authors, who have had extensive detailed and long-term experience in this field (40 and 28 years respectively), decided it would be helpful to users, manufacturers, installers, piping engineers, code officials, and other interested parties if a concise treatment of this topic was presented. The types or classes of failure found in thermoplastic water piping systems are burst, damaged pipe and/or fittings, and leaking joints. The causes of these failures are improper system design, overpressurization, use of materials not intended for manufacture of piping components, non-standard materials, contaminated materials, improper manufacture, improper handling, faulty installation, poor joints, and the installed system being damaged by third parties. These topics are discussed in detail. A list of publications that describe procedures and recommendations to reduce failures in service is given.

Effect of Axial Compression

Abstract: The beneficial effects of work hardening have been long known to, and appreciated by, the steel industry and have been accepted as a step in the same direction as heat treatment. Because of the obvious difficulty with buckling, however, so far only the tension mode and the transverse compression mode have been commonly used (e.g., pipe expanders for tension, and cold-rolling, cold-drawing for transverse compression). Treatment stresses in the tension method are restricted to stresses less than the ultimate strength of the material. Compression loads can be many times that of the ultimate tensile strength of the material.

Interpretive report on the sensitization of type 304 stainless steel

Abstract: When Type 304 stainless steel is sensitized by a thermal treatment in the range of 400 to 850°C, intergranular attack will occur upon subsequent exposure to certain media. Interest in the sensitization behavior of Type 304 has been rekindled by the recurrent problem of pipe cracking in boiling water reactors, and the subject is of major importance to the electric power utility industry. In many practical situations, such as welding, sensitization is best studied by continuous cooling through the sensitizing temperature range wherein the variables are the peak temperature reached and the cooling rate in contrast to temperature and time of the isothermal hold which has been the customary practice. This report will focus on the importance of continuous cooling sensitization in certain heats of Type 304 with changing section size. A review of the test methods that assess intergranular corrosion and the effort to quantify degree of sensitization upon Jominy testing of bar, strip, and pin specimens or Gleeble-type testing of small rods will be presented. The major influence of carbon content and the effects of other elements will be discussed along with material remedies and suggestions for future work.

A Modified Metallographic Method to Detect Sensitization in Type 316 Stainless Steel

Abstract: For detecting susceptibility to intergranular corrosion (IGC) in austenitic stainless steels, ASTM Recommended Practices for Detecting Susceptibility to Intergranular Attack in Austenitic Stainless Steels (A 262), Practice A (metallographic test), serves as a screening test. Alloys showing “step” or “dual” structures are considered to have passed the test. When a “ditch” structure is obtained, the material needs further testing by one of the immersion tests (Practices B, C, D, or E). It has been observed that the electro-etching parameters of Practice A are rather severe, leading to the development of “ditch” structures in nonsensitized materials which are not susceptible to IGC. A modified etching technique has been developed in which nonsensitized samples of Type 316 stainless steel as detected by Practice E show step structure or no structure at all; ditch structure is developed only in the cases of samples heat treated close to or within the sensitization range. Use of this technique could result in a reduction of the number of specimens that must be tested by one of the other practices in ASTM A 262.

Bibliography on clean glass: supplement I

Abstract: This bibliography supplements an earlier bibliography on clean glass(Journal of testing and Evaluation, Vol. 5, No. 1, Jan. 1977, pp. 53–57) by extending coverage of the literature from 1973 through 1984. Coupled with the recommendations included in ASTM Practice for Designing a Process for Cleaning Technical Glasses (C912), the list of references, organized into five categories for ready access, should provide a useful up-to-date base for rationally designing a cleaning process.

A Better Way to Present Results from a Least-Squares Fit to Experimental Data: An Example from Microhardness Testing

Abstract: Fitting a straight line to data using the least-squares method is very often the method of choice when presenting experimental results. When there are a number of sets of data, each with its fitted line, it can be difficult at first to appreciate the meaning of the results. Also, parameters calculated from least-squares fits are often quoted without estimates of accuracy, even when the original data contain considerable scatter. A method is described here that aids the assimilation of a number of least-squares fits and takes full account of estimates of accuracy.

References and conference proceedings towards the understanding of fracture mechanics

Abstract: A list of books, reports, periodicals, and conference proceedings, as well as individual papers, centered on specific aspects of fracture phenomenon has been compiled by the ASTM Committee E-24 on Fracture Testing. A list of basic references includes the articles on the development of fracture toughness, evaluation of stress intensity factors, fatigue crack growth, fracture testing, fracture of brittle materials, and fractography. Special attention is given to the references on application of fracture mechanics to new designs and on reevaluation of failed designs, many of them concerned with naval and aircraft structures.

Development of a Constant- K Specimen for Materials Testing

Abstract: A study is presented of a constant stress intensity factor specimen comprising four circular cutouts. The results of fatigue crack growth tests, compliance measurements, and a finite element formulation show that minor modifications to a center cracked tension specimen lead to constancy in the stress intensity factor as a function of crack length. The basic geometry can also be repeated in a stacked configuration in order to test multiple cracks in a single setup.

Factors affecting results of chemotaxis inhibition tests with protozoa

Abstract: Several factors were examined with respect to their influence on the attraction of protozoa towards yeast extract and on the inhibitory effect of cadmium on chemoattraction. These included: density of protozoa (numbers per volume), age of cultures, axenic and bacterized cultures, and starvation period before testing. A marine species, Miamiensis avidus, and a strain of Tetrahymena isolated from a local river, were tested separately. Two-fold increases in density of Miamiensis resulted in a three-fold increase in numbers attracted, whereas Tetrahymena resulted in a two-fold decrease in numbers attracted. However, inhibition by cadmium was not altered by using different densities. At 250 and 500 protozoa/25 μL, Tetrahymena was inhibited 87.8 ± 5.2 (average of four replicates ± 1 SD) and 89.0 ± 2.6%, respectively; at 117 and