Cycle fatigue weakens a structure. Poisson’s ratio is a sensitive indicator of cycle fatigue. The amount of fatigue is proportional to the severity of an abnormality, such as a crack, delamination or other imperfection. Our prior work confirms that direct estimates of Poisson’s ratio by Cornu’s method must be identical for all antinodes of a mode shape of a homogeneous, thin, hinged–hinged beam. Therefore, if a direct estimate at any antinode was found to be significantly different from the other estimates at the other antinodes, then that would simultaneously indicate fatigue and identify the location of the abnormality. We use simulations of Besselograms and apply Cornu’s method to directly estimate Poisson’s ratio at all antinodes of a beam. We transform finite element simulations of the out-of-plane bending displacements of mode shapes by simulating time-average scanning digital holography. We show that amount of disagreement between the direct estimation Poisson’s ratio and the true value of Poisson’s ratio depends on the ratio of the distance between nodes of a mode shape divided by the width of the beam. We call this distance between the nodes of a mode shape the ‘Span’. We then define a unified expression for predicting the simulated direct estimate given the true value of Poisson’s ratio and the Span-to-Width ratio. Next, we invert the unified expression, which enables us to use the Span-to-Width ratio and simulated direct estimates of Poisson’s ratio as the independent variables to compute the adjusted value of Poisson’s ratio. We find that our inverse expression makes it possible to obtain an estimate of Poisson’s ratio that is within ±2% of the true value for thin hinged–hinged beams and plates that have a Span-to-Width ratio greater than 1. We also find that if the material is known to have a Poisson’s ratio greater than zero, which can be assessed by our previous statement, then we can extend our confidence to Span-to-Width ratios greater than 0.1. That was the lower limit of our testing. Finally, we show how to use direct estimates of Poisson’s ratio to statistically detect and localize an abnormality along a hinged–hinged plate or beam. We believe that our combination of Cornu’s method and time-averaging could eventually offer the ability to directly estimate Poisson’s ratio from hinged–hinged beams and plates as well as to unambiguously monitor cycle fatigue for changes in effective material properties, predict time-to-failure, and do so without contact.

This research extends a method for direct estimation of Poisson's ratio from mode shapes of plates with hinged-hinged boundary conditions to include combinations of clamped and free boundary conditions. Using finite element simulations, we observe the effects of boundary conditions on the estimate of Poisson's ratio using the combination of Time-Average Scanning Digital Holography and Cornu's method. First, we introduce the abstraction of the span-to-width ratio to an effective antinode region. This abstraction enables us to extend the direct estimation technique to plates with various boundary conditions. Second, for long and thin enough plates, the effects of boundary conditions become negligible and Cornu's method is sufficient for direct estimation of the true value of Poisson's ratio from an out-of-plane bending mode shape. We note that for many situations, the necessary plate dimensions could be a limitation. Therefore, as a third concept, we discuss the behavior of the direct estimate of Poisson's ratio with respect to each type of boundary condition. Ultimately, this research initiates a path forward for a common processing technique for making a direct estimate of Poisson's ratio across different types of opposing boundary conditions for thin plates.

The incremental hole-drilling method is widely used in residual stress depth distribution analysis. However, two specific difficulties with the generalization of the incremental method exist, including the consideration of the sample thickness and residual stress states close to the local material's yield strength. The stress concentration effect of the hole can lead to plastic deformation in the vicinity of the hole, which results in an overestimation of residual stresses. Typically, the effect of the component's thickness and the plasticity effects are analyzed separately and correction approaches are proposed. In the current paper, we analyze the combined effects of plasticity and thickness on residual stress analysis using the incremental hole-drilling method. A systematic study was performed on steel samples with (i) isotropic and (ii) anisotropic elastic and elasto-plastic material behavior with varying thicknesses ranging between 1 mm and 4 mm. Electronic speckle pattern interferometry (ESPI) hole-drilling experiments were conducted on beam samples loaded using a 4-point bending fixture. Finite element simulations were conducted to gain insight into the effects of incremental hole-drilling. The results indicate that reducing the component's thickness increases the plastic deformation in the vicinity of the hole and results in significant stress deviations. Thin components bend during hole-drilling as a result of the loss of stiffness, which amplifies the plasticity effect.

Residual stress (RS) is often implicated in the failure of parts or assemblies, but there has not been any quantification or statistics collected on RS induced failures. Using the ASM Failure Analysis Database™, 147 individual case histories of failure analysis involving residual stress were identified and categorized based on various criteria. Information about the type of failure, material, processing, severity, date and other pertinent facts were extracted from the failure write-ups and the statistics on date of publication, material type, and failure type are compiled here. This information is used in conjunction with other compiled information on residual stress induced failures to estimate the impact of various residual stress induced problems in manufacturing and industry.

This paper describes measurements of residual stress in thin slices removed from the wall of a pressurizer safety/relief nozzle, which is a cylindrical welded component found in a nuclear power pressurized water reactor. Because the slices comprise a cross-section through a dissimilar metal weld that joins the low-alloy steel pressurizer to a stainless steel safe-end, the residual stress measurements are difficult. Typical welds have large grains and preferred orientations, along with chemical and phase gradients, that challenge diffraction techniques using neutron or x-ray beams. Welds also contain spatial gradients of residual stress that challenge mechanical release techniques like contour, slitting, and hole drilling. Therefore, the paper describes the application of, and compares the results from, three applicable residual stress measurement techniques: slitting, electronic speckle pattern interferometry hole drilling, and neutron diffraction. The results of slitting and neutron diffraction are in rough agreement, while the results from hole drilling are significantly different. An uncertainty analysis shows that slitting results had the smallest uncertainty, followed by hole drilling, and that neutron diffraction results had large uncertainty, particularly in the weld.

the material prior to annealing and the duration and temperature of the annealing process. In general, the HIP procedure significantly reduces the dislocation density, but the final state of the clad plate, both texture and dislocation density, depends strongly on the final processing step of the fuel foil. In contrast, the residual stresses in the clad fuel plate do not depend strongly on the final processing step of the bare foil prior to HIP bonding. Rather, the residual stresses are dominated by the thermal expansion mismatch of the constituent materials of the fuel plate.

The interface bonds are critical to in-reactor performance for a high density monolithic plate fuel system which uses low enriched uranium 10wt% molybdenum foils corolled with Zr and clad with 6061Al. Stresses induced during reactor shutdown have been identified as a source of concern for that integrity. Because of the post-reactor radioactivity, those residual stresses will have to be measured in a shielded nuclear radiation containment chamber or “hot cell” with remote handling of specimens and instrumentation, which limits measurement options. This study tested options for stress measurements by using surrogate fuel plates, such as with depleted uranium, but using only hot-cell appropriate equipment. Several measurements were performed using the incremental slitting method (a.k.a. crack compliance) but, for hot cell use, using a milling cutter instead of wire EDM for making the cut and a displacement sensor instead of a strain gauge. Measurements were also performed using incremental hole drilling using an interferometry system instead of strain gauges. For both measurement techniques, special data reduction development was required in order to handle discontinuities in the stress profiles across the layers. The results were encouraging, and the slitting method is now being implemented for use in a hot cell.

Multiple measurements using the hole drilling method were made in samples with a "known" state of residual stress. Drilling parameters were independently varied (bit rotation speed, bit diameter, and hole depth) to determine the effect on accuracy and repeatability. The study showed that accurate results can be achieved without ultra-high drill rotation speeds and that, in aluminum and stainless steel, speeds over 5 krpm and 10 krpm (respectively) were sufficient. Inaccuracies were evident in the stainless steel at speeds below 10 krpm and were attributed to non-circular holes, which may have been the result of bit vibration. There were no significant trends associated with altering the hole depth and only a slight trend associated with bit diameter variation.

Residual stress measurement techniques can be categorized as either relaxation or diffraction methods. Practitioners often advocate a particular category and sometimes a specific technique (hole drilling, contour, XRD, neutron, etc) based on their experience or capability rather than using the best technique for the particular application. This paper considers some of the implications from applying this “drunkard’s search” or “streetlight” approach by examining examples where the critical stress could be hidden from both relaxation and diffraction measurements. A better approach to planning residual stress measurements would begin with a detailed consideration of why the stresses should be measured and how the results will be used. Only then can the most appropriate measurement plan be developed. Since a single measurement technique cannot reveal the full state of stress, especially in challenging parts, the use of multiple measurement types often provides the most useful information to customers.

Time-of-flight neutron diffraction, contour method, and surface hole drilling residual stress measurements were conducted at Los Alamos National Lab (LANL) on a lab sized plate specimen (P4) from phase 1 of the joint U.S. Nuclear Regulatory Commission and Electric Power Research Institute Weld Residual Stress (NRC/EPRI WRS) program. The specimen was fabricated from a 304L stainless steel plate containing a seven pass alloy 82 groove weld, restrained during welding and removed from the restraint for residual stress characterization. This paper presents neutron diffraction and contour method results, and compares these experimental stress measurements to a WRS finite element (FE) model. Finally, details are provided on the procedure used to calculate the residual stress distribution in the restrained or as welded condition in order to allow comparison to other residual stress data collected as part of phase 1 of the WRS program.

A novel dual-axis ESPI hole-drilling residual stress measurement method is presented. The method enables the evaluation of all the in-plane normal stress components with similar response to measurement errors, significantly lower than with single-axis measurements. A numerical method is described that takes advantage of, and compactly handles, the additional optical data that are available from the second measurement axis. Experimental tests were conducted on a calibrated specimen to demonstrate the proposed method, and the results supported theoretical expectations.

The traditional contour method maps a single component of residual stress by cutting a body carefully in two and measuring the contour of the cut surface. The cut also exposes previously inaccessible regions of the body to residual stress measurement using a variety of other techniques, but the stresses have been changed by the relaxation after cutting. In this paper, it is shown that superposition of stresses measured post-cutting with results from the contour method analysis can determine the original (pre-cut) residual stresses. The general superposition theory using Bueckner’s principle is developed and limitations are discussed. The procedure is experimentally demonstrated by determining the triaxial residual stress state on a cross section plane. The 2024-T351 aluminum alloy test specimen was a disk plastically indented to produce multiaxial residual stresses. After cutting the disk in half, the stresses on the cut surface of one half were determined with X-ray diffraction and with hole drilling on the other half. To determine the original residual stresses, the measured surface stresses were superimposed with the change stress calculated by the contour method. Within uncertainty, the results agreed with neutron diffraction measurements taken on an uncut disk.

The intergranular thermal residual stresses in texture-free solid polycrystalline beryllium were determined by comparison of crystallographic lattice parameters in solid and powder samples measured by neutron diffraction during cooling from 800 °C. The internal stresses are not significantly different from zero >575 °C and increase nearly linearly <525 °C. At room temperature, the c axis of an average grain is under ∼200 MPa of compressive internal stress, and the a axis is under 100 MPa of tensile stress. For comparison, the stresses have also been calculated using an Eshelby-type polycrystalline model. The measurements and calculations agree very well when temperature dependence of elastic constants is accounted for, and no plastic relaxation is allowed in the model.

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Electronic Speckle Pattern Interferometry (ESPI) is used to measure the vibration mode shapes of circular and bandsaws. A video camera views a vibrating sawblade that is illuminated by a laser light. The image within the camera is mixed with a reference light to create an interference pattern. The reference phase is stepped by 180 degrees using a piezoelectric actuator before measuring each successive image. Subtraction of the successive images gives a contour view of the vibration mode of the sawblade. The technique is noncontacting and displays vibration mode shapes in real-time. It has the advantage over the classical Chladni method because it avoids the need to spread a powder over the sawblade surface and because it can also identify low-frequency vibrations.