Hole drilling is a measurement technique used to determine near surface residual stresses and has been codified in ASTM E837-20. In ASTM E837-20, the minimum allowable distance to a free edge is prescribed as 1.5 times the gauge circle diameter.
Objective
This work examines the effect arising from the distance from a free edge on a hole drilling measurement and provides an approach to determine residual stress for measurements where the edge distance is closer than that currently permitted by ASTM E837-20.
Methods
Numerical experiments were performed to understand how the compliance matrices change when the distance from a hole drilling measurement to a free edge varies. In addition, a series of hole drilling measurements were performed
at various distances from a free edge using a shot peened aluminum plate with a nominally equibiaxial stress state to demonstrate the approach.
Results
The numerical experiments determined that the use of corrected compliance matrices is appropriate when the edge distance is as small as 0.35 times the gauge circle diameter. Physical measurements supported the use of custom compliance matrices for a given free edge distance and specimen thicknesses.
Hill Engineering is committed to providing high-quality residual stress measurement data to its customers, both in our laboratory and on-site. Our Residual Stress Field Team is equipped with the same knowledge and expertise as our laboratory team to meet the challenge of performing residual stress measurements in the field.
Our Residual Stress Field Team has the experience necessary to tailor each measurement approach to meet the unique needs of the customer and bring our world-class residual stress measurement capabilities to the place it matters most – the operational environment. Challenging measurement access, complex geometry, and applications requiring rapid turn time are just a few situations where our team and equipment excel, allowing us to assess both near-surface and bulk residual stress in components that are delicate, large, or otherwise unable to be sent to our laboratory for in-house testing.
Hill Engineering’s Residual Stress Field Team can perform testing on-site for components that are too large to ship to our laboratory
From a quality control perspective, measurements performed in the field allow customers to get a detailed glimpse of their manufacturing process, as measurements can be carried out shortly before or after a critical step, such as heat treatment, all without having the component leaving the manufacturing line, saving time for the customer.
On-site measurements and services that are available through our field team include:
The Hill Engineering Residual Stress Field Team, with its ability to perform on-site residual stress measurements, is just one of the ways we offer flexible, precise, and high-quality residual stress testing to our customers. Their mobility, coupled with advanced technology, ensures that the science of engineering is not confined to laboratories but can thrive in real-world environments where innovation truly takes flight.
If you have any questions about the capabilities of our Residual Stress Field Team and how it can help your project, please contact us.
TrueSlot® is an innovative technique for measuring near-surface residual stress that is more reliable than conventional techniques.
TrueSlot® is a residual stress measurement technique for generating a profile of residual stress versus depth from the material surface. The stress computation is similar to slitting but offers more sensitivity near the surface due to the proximity of the strain gage.
Additionally, TrueSlot® is globally less invasive than slitting because the volume of removed material is localized to the surface and does not typically extend through most of the specimen thickness.
A model of a completed TrueSlot® method measurement.
The physical application of TrueSlot® is like hole drilling, however instead of a shallow hole being milled into the body of a specimen containing residual stress, the material removed is a shallow slot. The strain released with each incremental slot depth is measured near the slot using a strain gage.
TrueSlot® is useful for
Production quality control applications
Applications requiring in-field measurements with portable equipment
Near-surface residual stress determination
Parts with large or complex geometry
Applications with challenging measurement access
Applications requiring rapid turn time
TrueSlot® was found to have better repeatability when compared with conventional x-ray diffraction.
Results from the method repeatability study which found TrueSlot® to be a more repeatable measurement method than XRD
Are you working on a project with a tight deadline? We’re here to help!
Hill Engineering offers expedited residual stress measurement services (ExpressRS®). With ExpressRS®, our customers can expect the same level of high-quality residual stress measurement results within an accelerated delivery time – typically less than 1 week for most jobs and next day service is available in select cases. When our customers choose ExpressRS®, their project is given priority in our measurement laboratory queue to help meet tighter deadlines without sacrificing quality.
The DART system performing an automated hole drilling residual stress measurement.
Hill Engineering is a global leader in residual stress measurements. We believe every materials engineer, designer, and manager should have solid data upon which they can make sound decisions. Our broad range of best-in-class measurement capabilities ensures that we can tailor our approach to your specific project needs.
The following residual stress measurement techniques are available through ExpressRS®:
A completed ring core measurement – one of the residual stress measurement techniques available through Express RS.
Hill Engineering has the expertise to address issues arising in materials, manufacturing, and design engineering, with unique capabilities in residual stress measurement, material testing, service life assessment, and mechanical design. Our laboratory maintains an active ISO 17025 accreditation.
ExpressRS® gives our customers access to this expertise with urgency. If you have any questions or are interested in utilizing our rapid-results service, please contact us for more information.
Strain gages are devices used to measure strain on the surface of an object. These strain measurements can be used to infer the amount of stress induced on the object, as is done with many types of residual stress measurements.
Additionally, strain gages can be used to measure things such as aircraft wing deflection, bridge cable creep, and tensile testing for material properties, making them an ideal tool for in-field measurements.
Strain gages come in many shapes and sizes and can measure strain in a single direction or in multiple directions, depending on the goal of the experiment. Strain gages can be used on a wide variety of materials under many conditions, such as in extreme temperatures or underwater.
Hill Engineering has extensive experience with strain gage application and can help design the experiment needed to reach your project’s goals. Strain gage application can be performed in our laboratory or at your site, to your specifications.
Strain gage application is useful for:
Applications requiring in-field measurements with portable equipment
Measuring strain in multiple directions
Parts in every shape and size – nothing is too big or too small
Measuring residual stress
If you’re interested in how we apply a strain gage to a simple specimen, watch our video:
Photograph of a uniaxial strain gageZoomed in image of a uniaxial strain gage gridA photograph of a pile of various strain gages
Residual stress is the stress present in a material in the absence of externally applied loading. These stresses can often form during manufacturing, and are typically an unintentional byproduct of a manufacturing process. Residual stresses can be caused by a number of factors, including plastic deformations, temperature cycles, or phase transformations.
Residual stresses can positively or negatively affect a product’s performance, which makes them a vital consideration for any critical design component. Often, structures are designed with considerable safety factors, in which case the effects of residual stress can be ignored, but as we push for higher performing structures that operate closer to the cutting-edge of technology, factors like residual stress can be the difference between successful performance and structural failure.
Positive values of residual stress are referred to as tensile, meaning the material is being pulled or stretched. Unintended tensile residual stresses can cause undesirable results, including cracking and failure. If tensile stresses induced by manufacturing processes are not taken into account, these can lead to premature failure.
A fatigue crack that grew from a countersunk fastener hole.
Negative values of residual stress are referred to as compressive, meaning the material is being pushed together. These kinds of residual stresses can improve the performance of fatigue-critical components. Surface treatment processes like shot peening and laser shock peening intentionally introduce compressive stress in select locations at the material surface to make products perform better. For instance, introducing compressive residual stress can toughen brittle materials such as glass in smartphone screens or pre-stressed concrete used in city infrastructure.
Rebar is often used to negatively pre-stress concrete in order to prevent cracking.
Overall, the residual stress on any given plane in a material must be in equilibrium, but there can be local regions with tensile or compressive stress. Below is our Residual Stress 101 vlog, which highlights the information above.
Residual stress engineering involves the practice of manipulating residual stresses in order to maximize the usability and lifespan of manufactured components.
Through residual stress measurement techniques, Hill Engineering is capable of quantifying the internal stresses in a material, to better inform design decisions. We are the industry leader in Contour Method measurements and provide the same level of precision and accountability in a broad range of other residual stress measurement methods.
Hill Engineering is a trusted source for a wide range of measurement capabilities. For more information about residual stresses or any of the residual stress measurement techniques we employ at Hill Engineering, feel free to contact us.
This paper assesses the accuracy of fatigue crack growth (FCG) predictions for high-strength aluminum samples containing residual stress (RS) and complex two-dimensional cracks subjected to constant amplitude load. FCG predictions use linear-elastic, multi-point fracture mechanics. A first prediction includes RS estimated by the model described in Part 1; a second prediction includes RS measured by the contour method. FCG test data show a significant influence of RS. Ignoring the RS results in a +60% error in predicted FCG life (non-conservative). Including RS improves predictions of crack growth significantly (errors better than +26% (estimated RS) and -14% (measured RS)).
The objective of this paper is to validate a measurement-driven, model-based approach to estimate residual stress (RS) in samples machined from quenched aluminum stock. Model input is derived from measurement of RS in the parent stock. Validation is performed for prismatic T-sections removed from bars at different locations. We find RS predicted agrees with RS measured, by contour and neutron diffraction methods, with root-mean-square model-measurement difference of 22 MPa. Follow-on work (in Part 2) applies the RS estimation to samples representative of aircraft structures and examines the effects of RS on fatigue crack growth in the RS-bearing samples.
There are various experimental measurement techniques used to measure residual stress and this work describes one such method, the slotting method, and its application to measure near surface residual stresses. This work examines its application to macro-scale specimens. A series of numerical experiments were performed to understand the size required to assume that the specimen is infinitely large, namely the thickness, width, and height. To assess measurement repeatability, 12 slotting measurements were performed in a shot peened aluminum plate. The numerical experiments determined the specimen should have a thickness greater than or equal to 21.6 mm (0.85 in), a total specimen width (normal to the slot length) greater than or equal to 44.5 mm (1.75 in), and total height (parallel to the slot) greater than or equal to 38.1 mm (1.5 in) for the specimen to be assumed to be infinite. Slotting measurement repeatability was found to have a maximum repeatability standard deviation of 30 MPa at the surface that decays rapidly to 5 MPa at a depth of 0.3 mm from the surface. Comparison x-ray diffraction measurements were performed. Infinite plate dimensions and slot length were determined as well as measurement repeatability. Slotting was shown to have significantly better repeatability than X-ray diffraction with layer removal for this application.
Residual stress spatial mapping has been developed using various measurement methods, one such method comprising a multiplicity of one-dimensional slitting method measurements combined to form a two-dimensional (2D) map. However, an open question is how to best distribute the individual slitting measurements for 2D mapping. This paper investigates the efficacy of different strategies for laying out the individual slitting measurements when mapping in-plane residual stress in thin stainless steel slices removed from a larger dissimilar metal weld. Three different measurement layouts are assessed: independent measurements on nominally identical specimens (i.e., one slitting measurement per specimen, with many specimens), repeatedly bisecting a single slice, and making nominally sequential measurements from one side of the specimen towards the other side of the specimen. Additional comparison measurements are made using neutron diffraction. The work shows little difference between the independent and bisecting slitting measurement layouts, and some differences with the sequential measurements. There is good general agreement between neutron diffraction measurement data and the data from the independent and bisecting layouts. This work suggests that when using slitting to create a 2D map of in-plane residual stress, a cutting layout that repeatedly bisects the specimen works well, requires a small number of specimens, and avoids potential errors from geometric asymmetry or measurement sequence.
