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Transcript of Hole Drilling Techniques - National Physical...
BCA Structural Materials Workshop – 12th September 2000
Residual Stress in Context. How to Choose a Technique
Hole Drilling Techniques
Jerry LordThe NPL Materials Centre
BCA Structural Materials Workshop – 12th September 2000
Breakdown of PresentationBreakdown of Presentation
n Introduction and Background
n Basic Hole Drilling Technique
n Recent Developments
n Examples
n Summary
n NPL Project on Residual Stress
BCA Structural Materials Workshop – 12th September 2000
Survey of UK IndustrySurvey of UK Industry
n 48 replies to Questionnaire - April 1999– 31 organisations performed measurements
n Hole Drilling (22)n XRD (19)n Neutron (14)n Layer removal (12)n Other (7)
BCA Structural Materials Workshop – 12th September 2000
Hole Drilling TechniqueHole Drilling Technique
Taken from: UMIST Stress & Damage Characterisation Unit Brochure
BCA Structural Materials Workshop – 12th September 2000
Hole DrillingHole Drilling
n Measure surface strains
n Calculate original RS distribution from these
n Relieved strains decay rapidly with depth
n Limited and variable strain sensitivity
n Susceptible to errors
– Hole position
– Hole diameter and eccentricity
– Hole depth
n Induced machining stresses
– Milling cutters, end mills, drills
> 40 µε in carbon steels
> 300 µε in austenitic steels
Schematic of Relieved Strains
BCA Structural Materials Workshop – 12th September 2000
Development of Hole Drilling TechniqueDevelopment of Hole Drilling Technique
n Kirsch (1898) – Developed empirical solution for through hole, uniaxial stress field
n Mathar (1934) – application of a mechanical extensometer
n Soete & Voncrambrugge – first application of strain gauges
n Kelsey (1956) – variation of RS with depth using the blind hole technique
n Rendler and Vigness (1966) - Empirical analysis for blind hole, developed standard rosette geometry
n Beaney and Procter (1974) – air abrasion machining
n Bijak-Zochowski (1978) – non uniform stress calculations
n Schajer (1981) - Used FEA, tabulated calibration coefficients
n Schajer (1988) – Coefficients for non-uniform stress fields
n ASTM E837-99 and Measurements Group TN-503-3
BCA Structural Materials Workshop – 12th September 2000
Basic Gauge DesignBasic Gauge Design
n D is diameter of gauge circle
n Do is diameter of drilled hole
BCA Structural Materials Workshop – 12th September 2000
Residual Stress GaugesResidual Stress Gauges
n Limited number of designs
n 3 and 6 element rosettes
n Typical hole diameter is 1 – 4 mm
n Surface preparation is critical
n Good quality installation
n 3 wire leadwire for temperature compensation
n Instrumentation resolution ±1ìå
BCA Structural Materials Workshop – 12th September 2000
Typical Hole Drilling Set upTypical Hole Drilling Set up
BCA Structural Materials Workshop – 12th September 2000
Features of Hole Drilling TechniqueFeatures of Hole Drilling Technique
n Basic Hole Drilling– Localised RS measurements– Strains are averaged over the area of the strain gauge– Limited application
n Assumptions– Isotropic, linear elastic material– Stresses do not vary significantly with depth– Residual stresses do not exceed 0.5 yield strength– Variations of stress within the boundaries of the hole are small
n Developments– Incremental hole drilling – Analyses for non-uniform stress fields– Analyses for steep stress gradients– Elastic – plastic behaviour
BCA Structural Materials Workshop – 12th September 2000
Key Attributes of the Hole Drilling TechniqueKey Attributes of the Hole Drilling Technique
n Merits– Large components
– Portable, in situ measurements
– Rapid and Inexpensive
– Little specialised equipment
– Semi-destructive
– Flat and curved shapes
– Wide variety of materials
– Metals, plastics, ceramicscomposites, cermets, coatingssingle crystals, surface treated,crystalline and amorphous,magnetic and non-magnetic
n Disadvantages– Limited to near surface stresses
– Modest strain sensitivity
– Strain sensitivity varies with depth
– Limited spatial resolution
– Induced machining stresses
– Interpretation of results
– More qualitative than quantitative?
– Destructive !
BCA Structural Materials Workshop – 12th September 2000
Basic Hole Drilling EquationsBasic Hole Drilling Equations
σmax, σmin = ε3 – ε1 ± √ (ε3 – ε1 )2 + (ε3 + ε1 - 2ε2)2
4A 4B
p = (ε3 + ε1)/2 q = (ε3 - ε1)/2
t = (ε3 + ε1 - 2ε2)/2
where A = -a (1 + υ) / 2E and B = -b / 2E
a and b are dimensionless calibration coefficients almost independent of the specimen properties
BCA Structural Materials Workshop – 12th September 2000
Coefficients (ASTM E837-99)Coefficients (ASTM E837-99)
n Coefficients are tabulated for the 3 main gauge types– Through hole and incremental drilling– Typical increments 0.05D– Max depth for a blind hole is ~ 0.4D– Some interpolation may be required
BCA Structural Materials Workshop – 12th September 2000
Coefficients (ASTM E837-99)Coefficients (ASTM E837-99)
BCA Structural Materials Workshop – 12th September 2000
Basic Hole Drilling EquationsBasic Hole Drilling Equations
σmax, σmin = P ± √ Q2 + T2
τmax = √ Q2 + T2
If…..…P = (σy + σx )/2 …. mean “hydrostatic stress”
Q = (σy + σx )/2 …. shear stress 45o to x-y axes”
T = τxy/2 ….. shear stress along x-y axes
BCA Structural Materials Workshop – 12th September 2000
Recent Developments and ApplicationsRecent Developments and Applications
n Strain Measurement– New rosette designs – 6 gauges– Full field measurements
– Laser speckle interferometry– Moiré interferometry– Holography
n Hole Drilling methods– Taper hole drilling– Optimised incremental drilling– Deep hole drilling
n Modelling and Data Analysis– Non uniform stress fields– Biaxial stress distributions– Steep stress gradients
n New Applications– Thermal Barrier Coatings– Thin coatings?
BCA Structural Materials Workshop – 12th September 2000
n ASTM E837-99 does not apply
n 4 Stress calculation methods have been developed
– Integral Method - Best for highly non uniform stress fields– Power Series - For smoothly varying non-uniform stress fields– Incremental Stress – least accurate– Average Stress – least accurate
n Meticulous Measurement Practice is Required
Analysis Methods – Non Uniform Stress FieldsAnalysis Methods – Non Uniform Stress Fields
BCA Structural Materials Workshop – 12th September 2000
Analysis Methods – Non Uniform Stress FieldsAnalysis Methods – Non Uniform Stress Fields
n Integral Method– Uses FE calibrations
– Use with highly non uniform stress fields
– RS assumed constant within each depth increment
– Individual contribution to measured strain identified at each depth increment
– Stresses then back calculated
– Max 4/5 depth increments
n Power Series– Uses FE calibrations
– Use when RS vary smoothly with depth
– Uses weighted averages of strain data to improve numerical stability
– Permits many small increments
– Limited spatial resolution
BCA Structural Materials Workshop – 12th September 2000
Analysis Methods – Non Uniform Stress FieldsAnalysis Methods – Non Uniform Stress Fields
n Incremental Strain– Approximate stress calculation
– Useful only when experimental calibration available
– Only considers strain relief due to new increment
– Ignores contributions from previous increments
– Errors increase significantly with depth from surface
– Use with care !
n Average Stress– Approximate stress calculation
– Useful only when experimental calibration available
– Uses concept of “Equivalent Uniform Stress”
n EUS …. is the uniform stress within the total hole depth that produces the same total strain relief as the actual non-uniform stress distribution
– Difficult to interpret, use with care!
BCA Structural Materials Workshop – 12th September 2000
Analysis Methods – Non uniform Stress FieldsAnalysis Methods – Non uniform Stress Fields
Taken from: SEM Handbook of Measurement of Residual Stresses, Ed. J. Lu, 1996
n Comparison
– Integral Method gives good stepped approximation
– Power Series Method gives a close straight line fit
– Incremental and Average Stress Methods significantly underestimate the stress field remote from the surface
BCA Structural Materials Workshop – 12th September 2000
Potential Errors and UncertaintiesPotential Errors and Uncertainties
n Hole dimensions – diameter, concentricity, profile– Centre of drilled hole to coincide with centre of gauge circle to ± 0.025 mm
n Hole depth (measure and control to < 1 µm !)n Surface roughness and flatnessn Specimen preparationn Induced stresses from machining the holen Material propertiesn Incorrect gauge selection
eg use small size where steep stress gradients
n Calibration coefficients and Data Analysisn Equipment and measurement resolution, systematic errors
n UNCERT Code of Practice No. 15
BCA Structural Materials Workshop – 12th September 2000
Typical Hole ProfilesTypical Hole Profiles
PCD Diamond Drill Air Abrasion
BCA Structural Materials Workshop – 12th September 2000
Hole Drilling Technique - DevelopmentsHole Drilling Technique - Developments
Taken from: UMIST Stress & Damage Characterisation Unit Brochure
Laser Speckle InterferometryHolography
Moiré Interferometry
Deep Hole DrillingTaper Hole Drilling
Optimised Incremental Drilling
BCA Structural Materials Workshop – 12th September 2000
Enhanced Strain SensitivityEnhanced Strain SensitivityTaper Hole DrillingOptimised Step Increments
BCA Structural Materials Workshop – 12th September 2000
Application – Quenching Stresses Application – Quenching Stresses
Repeatability of measurements- water quenched carbon steel
Quench Stresses in pearlitic steel
Taken from: SEM Handbook of Measurement of Residual Stresses, Ed. J. Lu, 1996
BCA Structural Materials Workshop – 12th September 2000
Application – Machining StressesApplication – Machining Stresses
Grinding and sanding Machining stresses - steep stress gradient
BCA Structural Materials Workshop – 12th September 2000
Application - WeldsApplication - Welds
Ref: Flavenot and Lu, Proc. Of Surface Eng, current trends and future prospects, Ed. S A Meguid, Elsevier, June 1990
Steep stress gradients
Ref: Lu and Flavenot, Experimental Techniques 21, Nov 1989
BCA Structural Materials Workshop – 12th September 2000
Application – Shot Peened SurfaceApplication – Shot Peened Surface
BCA Structural Materials Workshop – 12th September 2000
Application - CoatingsApplication - Coatings
Residual Stress Distribution in plasma sprayed HAp coatings
Coating thickness 80 µm Coating thickness 200 µm
Ref: Han, Nan et al, J. Mats. Sci. Letters,18 (1999) 1087-1089
BCA Structural Materials Workshop – 12th September 2000
SummarySummary
n Hole Drilling is rapid and versatile
n Basic Hole Drilling Technique has only limited application
n Incremental Hole Drilling should be used
n Interpretation of the data is very important (and often very difficult)
n Select a data analysis method appropriate to the stress field
n Significant research effort at present
BCA Structural Materials Workshop – 12th September 2000
NPL Project on Residual StressNPL Project on Residual Stress
n Focus on XRD and Hole Drilling
n Intercomparison – to compare techniques
n Input into draft standard for XRD
n Good Practice Guide for Hole Drilling
n Aluminium, shot peened steel, TiN coating
n Intercomparison - starts September 2000
Participation is still open !