Hill Engineering’s DART issued second US patent!

Hill Engineering has been recently issued its second US patent for the DART™ measurement system. This updated device offers improved residual stress measurements within small-diameter pipe applications, allowing for more accurate analysis in both in-laboratory and non-laboratory settings.

Continue reading Hill Engineering’s DART issued second US patent!

TrueSlot® – near surface residual stress measurement

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 solid model block with a long but thin slot cut out of the top.
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.

A plot with depth and repeatability as the axis and two lines of data, one red, the other black. For most depths, the red line is higher than the black, signifying that XRD is less repeatable than slotting.
Results from the method repeatability study which found TrueSlot® to be a more repeatable measurement method than XRD

You can read about our repeatability study here.

TrueSlot® measurements are performed using our DARTTM system for automated residual stress measurement.

ExpressRS® – expedited residual stress results

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.

A close-up image of the DART system completing a hole drilling residual stress measurement.
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 ring cut into an aluminum surface circumscribing a green strain gage with thin wires attached.
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 Gaging Services

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 gage
Photograph of a uniaxial strain gage

Zoomed in image of a uniaxial strain gage grid
Zoomed in image of a uniaxial strain gage grid

A photograph of a pile of various strain gages
A photograph of a pile of various strain gages

New case study: Residual Stress

The heart of work at Hill Engineering has everything to do with residual stress. That’s why we thought it was about time we published a case study giving a general overview of what residual stress is, and why it is so important for designers and manufacturers to consider.

Continue reading New case study: Residual Stress

Residual Stress

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 slim metal coupon with a fracture surface showing a crack growth area shaped like ripples from a source location.
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.

A construction worker wearing a yellow hard hat crouched over a grid of metal rebar.
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.

The methods we employ are as follows:

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.