Hill Engineering recently published new research detailing our efforts to quantify uncertainty for slitting method
residual stress measurements. This new approach provides a more accurate estimate of the measurement uncertainty associated with the slitting method, which is very helpful for probabilistic performance assessments. The paper is titled An Uncertainty Estimator for Slitting Method Residual Stress Measurements Including the Influence of Regularization and appears in Experimental Mechanics. The abstract text is available here along with a link to the publication.
This paper describes the development of a new uncertainty estimator for slitting method residual stress measurements. The new uncertainty estimator accounts for uncertainty in the regularization-based smoothing included in the residual stress calculation procedure, which is called regularization uncertainty. The work describes a means to quantify regularization uncertainty and then, in the context of a numerical experiment, compares estimated uncertainty to known errors. The paper further compares a first order uncertainty estimate, established by a repeatability experiment, to the new uncertainty estimator and finds good correlation between the two estimates of precision. Furthermore, the work establishes a procedure for automated determination of the regularization parameter value that minimizes total uncertainty. In summary, the work shows that uncertainty in the regularization parameter is a significant contributor to the total uncertainty in slitting method measurements and that the new uncertainty estimator provides a reasonable estimate of single measurement uncertainty.
If you are interested, the full publication is available here.
Hill Engineering recently contributed to a publication related to residual stress measurement in additive manufacturing (AM) test specimens titled, Elastic Residual Strain and Stress Measurements and Corresponding Part Deflections of 3D Additive Manufacturing Builds of IN625 AM‑Bench Artifacts Using Neutron Diffraction, Synchrotron X‑Ray Diffraction, and Contour Method. The work was performed under the NIST AM-Bench program in collaboration with researchers from NIST, Los Alamos National Laboratory, University of California Davis, and Cornell High Energy Synchrotron Source. The abstract text is available here along with a link to the publication. Continue reading Additive Manufacturing Benchmark Publication
Hill Engineering, answering strong demand for its residual stress measurement services, would like to announce our agreement with VEQTER, Ltd to license the Deep-Hole Drilling (DHD) technology. VEQTER, along with the University of Bristol, aided in the development of the DHD technique, and have practiced the technology for over 25 years. With this agreement, VEQTER will provide Hill Engineering with the equipment, technology, and support to deliver state-of-the-art DHD measurements within the North and South American Continents. Continue reading Hill Engineering announces agreement with VEQTER for Deep-Hole Drilling technology
Hill Engineering is proud to support the USAF and their objective to advance damage tolerance analysis methods through the Engineered Residual Stress Implementation (ERSI) workshop. At this year’s ERSI meeting (September 12-13), Hill Engineering will meet with other stakeholders in the USAF aircraft community to review progress over the past year towards implementation of engineered residual stress in the USAF fleet. Continue reading Engineered Residual Stress Implementation workshop
As a follow-up to our previous post about additive manufacturing (AM) we wanted to highlight some other activities in the additive manufacturing space.
One such activity that Hill Engineering has been involved in is the NIST AM-Bench program. AM-Bench is developing a continuing series of controlled benchmark tests with two initial goals: 1) to allow modelers to test their simulations against rigorous, highly controlled additive manufacturing benchmark test data, and 2) to encourage additive manufacturing practitioners to develop novel mitigation strategies for challenging build scenarios. As part of this program, Hill Engineering has been working in collaboration with UC Davis to support residual stress measurement activities using the contour method. Continue reading Additive Manufacturing Benchmark Test Series
Additive manufacturing (AM) is a manufacturing process that deposits material in a controlled manner to build three-dimensional part geometry (bit by bit). This is in contrast to traditional manufacturing processes where material is cut or removed (i.e., subtracted) from the raw stock to create the intended part shape. The potential for additive manufacturing to significantly improve the economics and performance of manufactured parts for certain applications has made it a popular topic. However, since most additive manufacturing processes are highly thermal (e.g., material is deposited in a melted form and solidifies into the desired shape) significant residual stresses can develop. Hill Engineering has been working with many collaborators to better understand the influence of these processes on residual stress. Continue reading Residual stress in additive manufacturing
Residual stresses exist in most materials and structures. Processes like forging, rolling, extruding, quenching, additive manufacturing, machining, and welding can cause residual stresses to develop. These stresses can influence the way that materials perform (e.g., fatigue, fracture, distortion, and corrosion). There are many different residual stress measurement techniques available to quantify residual stresses. The following are some examples of common measurement techniques. Continue reading Residual stress measurement techniques
The contour method, which is based upon solid mechanics, determines residual stress through an experiment that involves carefully cutting a specimen into two pieces and measuring the resulting deformation due to residual stress redistribution. The measured displacement data are used to compute residual stresses through an analysis that involves a finite element model of the specimen. As part of the analysis, the measured deformation is imposed as a set of displacement boundary conditions on the model. The finite element model accounts for the stiffness of the material and part geometry to provide a unique result. The output is a two-dimensional map of residual stress normal to the measurement plane. The contour method is particularly useful for complex, spatially varying residual stress fields that are difficult (or slow) to map using conventional point wise measurement techniques. For example, the complex spatial variations of residual stress typical of welds are well-characterized using the contour method. A basic measurement procedure is provided along with comments about potential alternate approaches, with references for further reading.