Raymond E. Schramm

Stacking fault energies of fcc Fe--Ni alloys by x-ray diffraction line profile analysis

The stacking fault energies of the fee alloy series Fe-28 Ni to pure Ni were investigated using X-ray diffraction line profile analysis. A minimum stacking fault energy of about 70 mJ/m2 occurs at the approximate composition of Fe-40 pct Ni. From this point, the lower nickel alloys rapidly increase to a very high stacking fault energy, estimated to be 200 mJ/m2, while the energies of the high Ni alloys rise linearly to the Ni value of 214 mJ/m2. Anomalous reductions of the lattice parameter after cold work were found for the low nickel alloys; this was interpreted as evidence for Fe3Ni ordering and corrections to the stacking fault energy were made.

Mechanical, thermal, and electrical properties of selected polymers

Abstract An extensive compilation has been completed on the mechanical, thermal, and electrical properties of six commercially available polymers. These data are discussed and summarized here as a function of temperature, radiation, and frequency. A brief description and characterization of each polymer is included.

Ultrasonic measurement of stress in railroad wheels

The equipment described here generates ultrasonic shear waves using an electromagnetic-acoustic transducer. Precise measurement of the velocity of two orthogonally polarized signals determines the birefringence and allows the calculation of stress. It is necessary to account for the effect of metallurgical texture which can contribute to the birefringence and appear as moderate stress. This system sends a signal through the thickness of a railroad wheel rim, digitizes the first echo, locks onto a cycle, and calculates the time when it crosses zero amplitude. Signal averaging yields the arrival time of a signal at about 90 μs with a standard deviation of 2–4 ns. In screening the residual stress in the rims of cast-steel railroad wheels, this system has a total error of ≈±60 MPa; most of this is due to variability of the texture measured in several stress-relieved blocks cut from wheels. The initial measurements were on wheels in which the manufacture had induced known levels of thermal damage. Results from...

Safety assessment of railroad wheels by residual stress measurements

Residual stresses in railroad wheels may change from compressive to tensile; this change could lead to wheel failure. The current US regulation calls for the measurement of discoloration indicating heating that may lead to unsafe stress. Quantitative measurement by ultrasonic methods is an attractive alternative, since stress causes small changes in sound velocity. We did an extensive series of measurements on ten cast-steel wheels. Two different ultrasonic instruments gave comparable results. Destructive evaluation of stress in three wheels showed a good correlation with the ultrasonic measurements. This suggests a reliable method and a field-usable instrument for quantitative nondestructive inspection.

Emats for Roll-By Crack Inspection of Railroad Wheels

Railroad safety depends on many factors. The integrity of the wheels on rolling stock is one that is subject to nondestructive evaluation. For some years, ultrasonic testing has been applied to the detection of cracks in wheel treads, with particular attention to automatic, in-rail, roll-by methods. We have begun constructing a system aimed at using relatively low frequency Rayleigh waves generated by electromagnetic-acoustic transducers (EMATs). The current design uses a permanent magnet to maintain a compact structure and minimize the size of the pocket machined into the rail. Measurements thus far indicate a responsiveness, even to small flaws. With the development of a signal processing and analysis system, field tests should soon be possible.

GAS-COUPLED, PULSE-ECHO ULTRASONIC CRACK DETECTION AND THICKNESS GAGING

Ultrasonic inspection is a standard method to assess the integrity of large-diameter oil pipelines. However, similar methods applied to natural-gas pipelines present a considerably greater challenge; gas is a poor coupling agent for the probing ultrasonic signals between the transducer and the pipe wall. Natural gas exhibits a very low specific acoustic impedance (300 Rayls for methane at atmospheric pressure) compared to oil (1.5 MRayls and higher). Consequently, large ultrasonic-signal transmission losses occur at the transducer/gas and pipe-wall/gas interfaces. To circumvent this obstacle, past exploratory developments included the use of a liquid-filled wheel [1], electromagnetic-acoustic-transducer (EMAT) [2], and liquid-slug technologies [3]. While prototypes of high-speed, in-line inspection systems employing such principles do exist, all exhibit serious operational shortcomings that prevent widespread commercial exploitation.

NONCONTACT ULTRASONIC INSPECTION OF TRAIN RAILS FOR STRESS

This paper discusses acoustic techniques to quantify stress, the construction of transducers, and initial measurements on a short test section of railroad track. Our goal is to develop instrumentation useful for nondestructive testing during field inspection for potentially dangerous conditions, such as those generated by thermal stress. The application of unconventional noncontact transducers (EMATs) takes advantage of minimal surface preparation and the elimination of fluid couplants. This approach depends on precise (1 part in 104) timing of signal arrival. Elastic changes caused by stress generate very small, but detectable velocity changes. However, other factors, notably changes in metallurgical texture, may similarly alter the velocity. First tests on a rail section under applied compressive loading showed a sensitivity comparable to that seen with conventional piezoelectric transducers. If an all-EMAT system proves practical, it should be possible to design an automated device to scan at reasonable speeds.

Sizing Canted Flaws in Weldments Using Low-Frequency Emats

Techniques for detecting and sizing flaws with electromagnetic-acoustic transducers (EMATs), previously used successfully for normal planar flaws, were applied to canted flaws in steel plates. Comparisons were made between metallographic and ultrasonic measurements on specially prepared welds. Results indicated a high probability of detecting canted flaws (> 0.5-mm deep) with EMATs. The EMAT sizing was highly repeatable and, for the most part, very accurate. Some, as yet unexplained, inaccuracies did show up, however, in some weld sections. There is a possibility that the calibration curve may be more complex for canted flaws than for normal flaws.

EMAT/Synthetic Aperture Approach to Thick-Weld Inspection

Rapid advances in automated welding and increased demands for reliable weld-quality inspection tools have created a need for new ultrasonic inspection systems. In particular, new systems capable of operation at elevated temperatures and rapid scan rates are in demand in fully and semi-automated welding applications to complement radiographic and conventional ultrasonic inspection techniques. In such applications, radiography is fundamentally limited because of its inability to detect and dimension most sharp flaws, and possible health hazards. On the other hand, conventional ultrasonic techniques are limited because they tend to be difficult to automate, require fluid couplants, and are often operator-dependent.

Gas-Coupled Ultrasonics for High-Pressure Pipeline Inspection

Ultrasonic pigs (Fig. 1) frequently inspect large-diameter oil pipelines so there is considerable expertise for using the ambient liquid to couple sound into the steel walls. We set out to show feasibility and determine obstacles when using compressed gas as the sound couplant. The main obstruction to inspecting natural gas pipelines with ultrasonics is that the specific acoustic impedance of gas is many orders of magnitude smaller than that of oil and other liquids used as coupling agents. In oil, an impedance of about 1.5 MRayls allows reasonable energy transfer into steel at 46 MRayls. However, in methane the impedance is only about 300 Rayls at atmospheric pressure. In the past, it seemed that such a mismatch, along with sound attenuation in the gas, would preclude using the gas as the coupling agent. Instead, considerable resources went into alternative approaches: liquid-filled wheel probes,1 electromagnetic-acoustic transducers (EMATs),2 and liquid slugs.3 While prototypes of high-speed, in-line inspection systems employing such principles now exist, all exhibit serious operational shortcomings that prevent widespread commercial exploitation. We addressed this problem with gas-coupled ultrasonics and took advantage of recent improvements in ultrasonic puiser, receiver, and piezoelectric-transducer technologies. High-pressure gas exhibits both little propagation loss and a greatly increased specific acoustic impedance. We have already demonstrated concept feasibility.4 Our present focus here is some of the physical factors influencing practicality.