Rt Horstman

Impact Three-Point Bend Testing for Notched and Precracked Specimens

Testing and data analysis procedures developed from a recently completed fracture toughness testing program on ferritic nuclear pressure vessel steels are presented. These procedures describe the measurement of dynamic fracture toughness at stress intensification rates near 105 MPa√m/s using instrumented impact testing of three-point bend specimens. These procedures have been submitted to several ASTM task groups, and it is hoped that these guidelines will be incorporated into current and future interlaboratory activities eventually leading to a standard method for testing.

Evaluation of the J Integral for the Compact Specimen

Methods for determining the J integral from an experimental load versus load point displacement curve for the compact specimen are discussed. The original analysis by Merkle and Corten, which accounted for the tension component in the compact specimen, is presented along with a simplified version (of the analysis) that is shown to be essentially equivalent to the original formulation. Based on experimental results from Landes, Walker, and Clarke, a further simplified expression is recommended as the best expression to use for determining J for the compact specimen.

Generalized Application of Neuber's Rule

An analysis is presented concerning problems of correct application of approximation formulas such as Neubers rule for the case of inelastic net section behavior of notched members. The rules developed allow a generalized consideration of elastic-plastic net section behavior for any type of loading and notch geometry. The analysis is illustrated by discussion of experimental and calculated load-notch strain curves of different specimens.

Contextual Effects in Category Ratings

In sensory evaluations of consumer products, panels of observers often use ratings on category scales to assess differences in the sensory characteristics of products. However, use of rating scales, especially by naive observers, is prone to several biases that may act to distort such judgments. Observers learn about the range and distribution of sensory values for a given characteristics, and then adjust their judgments of that characteristic so that a full range of the available categories are assigned, and so that the categories are assigned with roughly equal frequency. Unless trained and given a constant frame of reference, observers use category scales as relative, not absolute, scales of judgment, adjusting their internal strandards based upon the recent contexts within which a product was presented.

Relationships Between Low-Cycle Fatigue and Fatigue Crack Growth Rate Properties

A fracture mechanics model is developed to describe crack growth in a low cycle fatigue test specimen. The model involves a J integral analysis and a growth rate hypothesis in terms of ΔJ. A relationship for low cycle fatigue is derived that has strain energy density as the controlling variable. This relationship reduces to well-known low cycle fatigue equations in terms of elastic and plastic strains for the limiting conditions of fully elastic and fully plastic strain fields. These equations in turn define relationships between the material properties commonly employed to describe low cycle fatigue and fatigue crack growth rate data. The latter are used to demonstrate the facility of predicting fatigue crack growth rate curves from standard low cycle fatigue properties.

Frequency, Stress Ratio, and Potential Effects on Fatigue Crack Growth of HY130 Steel in Salt Water

Fatigue crack growth rates over wide ranges of stress intensities (from threshold to nearly critical stress intensity) were measured on HY130 steel in 3.5% sodium chloride aqueous solution at several cyclic frequencies, stress ratios, and potentials. The growth rates are compared with reference data measured in laboratory air. The growth rate curves for both environments can be approximated by two linear sections converging at low stress intensity ranges to the same threshold, which depends only on the stress ratio. The upper parts of the lines with lower slopes converge again to the point where maximum stress intensity approaches its terminal value. As a result, the maximum environmental acceleration of crack growth appears at intermediate stress intensities, and it increases with decreasing frequency and potential. Data indicate a relatively low susceptibility of HY130 steel to corrosion fatigue. With increasing stress ratio R the fatigue crack growth threshold is shifted to lower stress intensity ranges by the same amount in both air and salt water environments. The effect of R on growth rate can be introduced into a power law expression.

A CONSTANT TENSILE STRESS CREEP TESTING MACHINE

A new constant tensile stress creep testing machine is described. The machine makes it possible to keep the stress constant within 0.1% up to a strain 0.45, assuming the volume of the specimen does not change during the test. The cam profile has been solved for specimen gage lengths of 50.0, 35.0, and 25.0 mm. The static counterbalance of the loading system ensures its high sensitivity, which, together with the minimizing of frictional forces, offers the possibility for the tensile stress to be accurately defined. Erratum to this paper appears in 4(4)

Comparisons of Fracture Toughness Measurements by the Short Rod and ASTM Standard Method of Test for Plane-Strain Fracture Toughness of Metallic Materials (E 399-78)

A multilaboratory blind comparison testing program evaluated the accuracy of the short rod method of measuring the fracture toughness of metallic materials. Valid comparisons between values measured according to ASTM Standard Method of Test for Plane-Strain Fracture Toughness of Metallic Materials (E 399-78) and values of the plane-strain critical stress intensity factor as measured by the short rod method of fracture toughness measurement (KIcSR) were obtained for several steels, aluminum alloys, and titanium. The KIcSR values measured by the short rod method were consistently low, averaging 6% below the measurements according to ASTM Standard Method E 399. A 4% adjustment in the short rod calibration constant that had been previously evaluated only to ±7% brings the two sets of measurements into very good agreement. The short rod method thus appears to be a viable alternative for measuring the fracture toughness of metallic materials.

A Screening Bioassay Using Daphnia pulex for Refinery Wastes Discharged into Freshwater

A simple method using unsophisticated equipment is suggested for on-site toxicity testing of refinery effluents. This method will provide an inexpensive means of identifying problem materials and establishing priorities for coping with these materials. An arbitrary reference mixture, containing six common constituents of refinery wastewaters, was used for static toxicity tests on 15 species of freshwater invertebrates and 3 species of fish. Daphnia pulex was selected for further testing because it was the most sensitive of the animals tested, relatively inexpensive and easy to maintain, and a potential fish-food organism. If the reference mixture were representative of a refinery effluent, the Daphnia bioassay would be sufficiently sensitive to give reliable results within 48 h, whereas a fish bioassay would show no toxicity even after 96 h. To assess the suitability of the Daphnia bioassay, tests were conducted by personnel at six petroleum refineries. Duplicate tests were in agreement. Results of tests using actual refinery effluents ranged from no toxicity after 96 h to a mean lethal concentration of 1.2% effluent after 48 h. The data presented show that the method was reproducible and that refinery personnel were able to perform the bioassay. Potential problems and advantages of the method are discussed.

Effects of Stress Ratio on Fatigue Crack Growth Rates in X70 Pipeline Steel in Air and Saltwater

Fatigue crack growth rates in an X70 pipeline steel were measured over a wide range of stress intensities in laboratory air and in 3.5% sodium chloride solution under free corrosion and cathodic (coupled to zinc) potentials. The effects of stress ratio in all these environments and of cyclic frequency in the sodium chloride solution were studied. The results are compared with fatigue crack growth rates measured previously in lower strength X65 steel. The stress ratio strongly influences the fatigue crack growth thresholds and close-to-threshold growth rates. With increasing stress intensity range, the stress ratio effect decreases similarly in both air and aqueous environments. The lower cyclic frequency enhances corrosion fatigue crack growth rates at intermediate stress intensity ranges, as was observed earlier in X65 steel.