# US 11,906,488 B2 · Systems and methods for analysis of material properties of components and structures using machining processes to enable stress relief in the material under test

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- Number: US 11,906,488 B2
- Document ID: US11906488B2
- Status: Granted
- Kind: B2
- Application number: 17/841,652
- Filed: 2022-06-15
- Published: 2022-12-01
- Granted: 2024-02-20
- Earliest claimed: 2017-11-29
- Assignees: Hill Engineering, Inc.
- Applicants: Hill Engineering, LLC
- Inventors: Adrian T. DeWald; Michael R. Hill; Eric Summer; Brett Watanabe; Teresa Wong
- Web page: https://patentgrep.com/patent/US11906488B2

## CPC

- G01N 3/58: Investigating machinability by cutting tools; Investigating the cutting ability of tools
- G01B 7/18: {using change in resistance}
- G01B 11/16: for measuring the deformation in a solid, e.g. optical strain gauge
- G01B 11/161: {by interferometric means}
- G01L 5/0047: {measuring forces due to residual stresses}
- G01N 3/066: {with electrical indicating or recording means}
- G01N 3/068: {with optical indicating or recording means}
- G01N 2203/0053: Cutting or drilling tools
- G01N 2203/0647: Image analysis
- G01N 2203/0676: Force, weight, load, energy, speed or acceleration
- G01N: INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES (measuring or testing apparatus or processes other than immunoassay, involving enzymes or microorganisms C12M, C12Q)
- G01B: MEASURING LENGTH, THICKNESS OR SIMILAR LINEAR DIMENSIONS; MEASURING ANGLES; MEASURING AREAS; MEASURING IRREGULARITIES OF SURFACES OR CONTOURS
- G01L: MEASURING FORCE, STRESS, TORQUE, WORK, MECHANICAL POWER, MECHANICAL EFFICIENCY, OR FLUID PRESSURE (weighing G01G)

## Abstract

Analysis of residual stress in materials is often done in static conditions in a laboratory. Accurate systems and methods for performing these analyses in a dynamic, non-laboratory environment are notoriously difficult and can be very inaccurate. A method using a portable, field deployable apparatus having greater accuracy than currently available is disclosed whereby accurate and repeatable residual stress analysis may be implemented in non-laboratory environments leading to greatly improved diagnostics, maintenance and life limit prediction.

## Claims

### Claim 1

A method for measuring residual surface stress in a component under test having one or more strain gauges mounted along predetermined axes and operationally coupled to a strain measurement system which generates an output proportional to changes in strain as a stress state of the component under test is changed, the method comprising: locating a machining appliance and the component under test in appropriate relative positions so that cuts are made into a surface of the component under test (CUT); probing a surface proximate to a region of the intended cuts and mapping a surface profile of the region; locating a point determined by placement of the one or more strain gauges near which material is to be removed from the CUT so that pre-existing residual surface stress at the point is altered; machining a feature starting at the point, and at a predetermined angle relative to the surface based on the mapped surface profile, wherein the machining includes a plurality of light cuts without introducing additional surface stress from the machining, so that residual surface stress in an area proximate to the feature is interrupted from a bulk of the CUT, and wherein the predetermined angle is maintained throughout the feature during the machining and based on the mapped surface profile; and measuring a change in surface strain resulting from the machining for use in calculating residual surface stress of the CUT.

### Claim 2 (depends on 1)

The method of claim 1 wherein the surface profile of the region is recorded.

### Claim 3 (depends on 1)

The method of claim 1 wherein the probing includes probing using a linear variable differential transducer.

### Claim 4 (depends on 1)

The method of claim 1 wherein the probing includes probing using an optically enabled and digitally encoded probe.

### Claim 5 (depends on 4)

The method of claim 4 wherein the optical probe is a camera.

### Claim 6 (depends on 5)

The method of claim 5 wherein the camera is an autofocusing camera.

### Claim 7 (depends on 1)

The method of claim 1 wherein the feature is an annulus surrounding the strain measurement component.

### Claim 8 (depends on 1)

The method of claim 1 wherein the feature is a slot cut alongside the strain measurement component.

### Claim 9 (depends on 1)

The method of claim 1 wherein the measurement system includes a Wheatstone bridge.

### Claim 10 (depends on 1)

The method of claim 1 wherein measuring the change in strain includes—an optical system using a light source and one or more detectors.

### Claim 11 (depends on 10)

The method of claim 10 wherein the light source is selectable to be monochromatic or polychromatic.

### Claim 12 (depends on 1)

The method of claim 1 wherein the strain measurement system includes an optical system using a camera and performing digital image correlation to determine the strain change.

### Claim 13 (depends on 1)

The method of claim 1 wherein the mapped profile is used to adjust the machining of the feature based on the profile of the surface of the CUT.

### Claim 14 (depends on 1)

The method of claim 1 wherein probing location calibration is achieved by using a particular feature present on the CUT.

### Claim 15 (depends on 1)

The method of claim 1 wherein the probing include probing using a mechanical contact probe.

### Claim 16 (depends on 1)

The method of claim 1 further comprising probing to measure depth of the cuts.

### Claim 17 (depends on 1)

The method of claim 1 wherein the machined feature is a slot, and wherein cut depth of the plurality of cuts is consistent throughout the slot and is based on the mapped profile.

### Claim 18

An appliance for use in residual surface stress analysis of a component under test (CUT), the appliance comprising:
a motion platform having two or more mutually orthogonal axes of motion;
a drive mechanism for each motion axis coupled to a control system;
a profiling probe for probing a surface proximate to a region of the intended light cuts and mapping a surface profile of the region;
a machining tool coupled to the control system, wherein the tool is configured to machine a plurality of light cuts in a component under test (CUT) to produce a machined feature at a predetermined angle relative to the surface based on the mapped surface profile without introducing additional surface residual stress from the machining of the plurality of light cuts, so that residual surface stress in an area proximate to the machined feature is interrupted from a bulk of the CUT, wherein the predetermined angle is maintained throughout the feature during the machining and wherein the predetermined angle is based on the mapped surface profile; and
wherein the control system includes a processor and interface enabling measurement of a change in surface strain resulting from the machining for use in calculating residual surface stress of the CUT.

### Claim 19 (depends on 18)

The system of claim 18 having a reticule for measuring distance at the viewing area.

### Claim 20 (depends on 18)

The system of claim 18 wherein the reticule is generated electronically and overlaid on a displayed image.

### Claim 21 (depends on 18)

The system of claim 18 wherein a hood is fitted to a lens of the camera includes one or more selectable light sources for illuminating the viewing area with monochromatic or polychromatic.

### Claim 22 (depends on 18)

The system of claim 18 wherein having a probe station to allow automatic connection to a strain gauge or an array of gauges.

### Claim 23 (depends on 18)

The system of claim 18 wherein the machined feature is a slot, and wherein cut depth of the plurality of cuts is consistent throughout the slot and is based on the mapped surface profile.

### Claim 24 (depends on 18)

The system of claim 18 wherein the machined feature includes one or more optional shapes corresponding to preprogrammed operations conditioned on the entry of dimensional data.

### Claim 25 (depends on 24)

The system of claim 24 wherein the one or more optional shapes include a hole, an annulus, a slot, a slit, an ellipse, a rectangle, or a plus sign.

### Claim 26 (depends on 18)

The system of claim 18 wherein adjustable feet are provided for angular adjustment of the cutting tool relative to the area to be machined.

### Claim 27 (depends on 18)

The system of claim 18 wherein the mapped surface profile is used to adjust or direct the drive mechanism to enable the machined feature to be adjusted based on the profile of a surface of the CUT.

### Claim 28 (depends on 18)

The system of claim 18 wherein the machining tool includes a high speed motor fitted with a collet or chuck assembly for holding a drilling, milling or cutting tool.

### Claim 29 (depends on 18)

The system of claim 18 wherein the machined feature includes at least two steps along a vertical axis.

### Claim 30 (depends on 18)

The appliance of claim 18 wherein the profile of the region is recorded.

### Claim 31 (depends on 18)

The appliance of claim 18 wherein the probe includes a linear variable differential transducer.

### Claim 32 (depends on 18)

The appliance of claim 18 wherein the probe includes an optically enabled and digitally encoded probe.

### Claim 33 (depends on 32)

The appliance of claim 32 wherein the optical probe is a camera.

### Claim 34 (depends on 33)

The apparatus of claim 33 wherein the camera is an autofocusing camera.

### Claim 35 (depends on 18)

The appliance of claim 18 wherein probing location calibration is achieved by using a particular feature present on the CUT.

### Claim 36 (depends on 18)

The appliance of claim 18 wherein the probe includes a mechanical contact probe.

### Claim 37 (depends on 18)

The appliance of claim 18 wherein the probe is used to measure depth of the cuts.