Hole-drilling Method
Gary Schajer, University of British Columbia, Canada.
The hole-drilling method is a widely used technique for measuring surface in-plane
residual stresses. It involves drilling a small hole in the test material and
measuring the resulting deformations around the hole, typically using strain gauges
or optical devices. The ring-core method is similar in concept, but with an annular
ring used instead of a hole, and measurements made within the ring. In both methods,
similar mathematical techniques are used to evaluate the residual stresses from the
measured deformations. This presentation describes practical measurement equipment
and procedures, typical mathematical methods, and some example applications.
Deep Hole Drilling Method
VEQTER Ltd., UK
The Deep Hole Drilling (DHD) method measures the distortion of a reference hole
introduced into a component. The distortion is created by mechanically relaxation
of the stresses. The origins of the method are explained together with its
development for engineering components. A description of the theory for converting
the distortions is provided along with a summary of the experimental technique.
The validity of the method is illustrated using samples containing known stresses.
Case studies illustrate residual stress measurements using the method including
welded nuclear components, bimetallic sleeves for the steel rolling industry and
thick section carbon fibre-epoxy composite laminates.
Slitting Method
Michael R. Hill, University of California, Davis.
The slitting method is a technique for measuring through thickness residual stress
normal to a plane cut through a part. It involves cutting a slit (i.e., a thin slot)
in increments of depth through the thickness of the work piece and measuring the
resulting deformations as a function of slit depth. Residual stress as a function
of through thickness position is determined by solving an inverse problem using
measured deformations. The chapter describes practical measurement procedures,
provides a number of example applications, and summarizes efforts to determine
the quality of the residual stress information obtained with the method.
Contour Method
Adrian T. DeWald, Hill Engineering, LLC, McClellan, CA.
The contour method determines residual stress by cutting a specimen into two
pieces and measuring surface height maps, or contours, on the free surfaces
created by the cut. The average contour determines the deformations caused by
residual stress redistribution and is used to compute residual stresses
through an elastic finite element model of the specimen. The result is a 2-D
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 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 alternative approaches.
Application of Optical Methods
to Residual Stress Measurement
Drew Nelson, Stanford University, CA.
Basic principles of holographic and electronic (digital) speckle pattern interferometry,
Moiré interferometry and Digital Image Correlation are reviewed. Measurements of
residual stresses by hole drilling utilizing each of those methods are described and
examples given, ranging from "in the field" to within the chamber of a scanning electron
microscope. Examples of recent applications of photoelasticity to residual stress
measurement are also presented.
X-Ray Diffraction
I. Cevdet Noyan, Columbia University, New York.
This presentation details the procedures associated with quantifying the stress
state within crystalline materials through the use of x-ray diffraction.
Beginning with a description of the methods used to measure lattice strain,
the steps required to transform this data into the full stress tensor, f
rom uniaxial to triaxial stress states, are explained along with the assumptions
associated with the governing mechanical models. The effects of sample
microstructure and experimental considerations are discussed in the context of
practical examples that employ both conventional and synchrotron-based, microbeam
x-ray techniques to analyze both polycrystalline and single-crystal samples.
Synchrotron Diffraction
Philip Withers, Manchester University, UK.
Synchrotron X-ray sources are capable of providing very brilliant hard x-ray beams.
These can penetrate millimetres and even centimetres into engineering materials
providing a probe of elastic strain down to the tens of microns lengthscale and
millsecond timescales. Here the basic experimental issues associated with successful
application of the technique are introduced througfh a series of experimental
examples. Whereas laboratory X-ray and neutron diffraction are suited to measuring
the stress along a line, synchrotron diffraction can provide area maps of residual
stress or follow changes in residual stress over time, for example as a function
of phase transformation on cooling from elevated temparature. Finally future
avenues for the method are discussed.
Residual Stress Determination by
Neutron Diffraction:
How, When and When Not to Use It (Where There Be Demons)
Ron Rogge, National Research Council, Canada
Having its beginnings in the 1980s, residual stress determination by neutron diffraction
is relatively mature. The promise of neutron diffraction is that the high penetration
in most industrial materials means the method can be completely non-destructive.
In practice, it often means non-destructive in the region of interest giving it a unique
place among complementary methods. Maturity simply means, most of the mistakes been made
by now; those with the greatest experience in the field have made the most mistakes.
Common problems (mistakes) and how to avoid them will be discussed.
Overview and Comparison
Michael B. Prime, Los Alamos National Laboratory, NM.
This talk will conclude the session on measurement methods and start a round table
discussion. The various residual stress measurement methods will be compared from
the point of view of measurements of industrial parts rather than academic research.
Comparisons will include such factors as the depth of measurements into parts,
maximum and minimum part size, destructivity, resolution, accuracy and cost.
Further comparisons and discussions will focus on choosing measurements for different
purposes such as model validation, part or process certification, quality control,
and coupon testing to predict structural performance.
Forging Residual Stress
and ICME
Mark James, Alcoa Technical Center.
Residual stress continues provide challenges for the aerospace community both for design/sustainment
as well as for manufacturing/distortion. However progress is being made in both of these key areas
thanks to significant focus and funding by the USAF Metals Affordability Initiative. In this talk
I will summarize one of the ongoing MAI programs (BA-11) which was introduced to the RS Summit
community at the 2010 Summit. The BA-11 program is a highly ambitious effort to make inroads
towards demonstrating value and implementing residual stress technologies for both of the key
areas mentioned above. The talk will briefly review the program objectives, summarize some key
results to date, and outline work to come in the next two years.
History of Residual Stresses in
Shipbuilding and Mitigation Strategies at Newport News Shipbuilding
Garrett
Sonnenberg, Newport News Shipbuilding.
A discussion on the history of residual stress in shipbuilding and its effect on
current products being manufactured at Newport News Shipbuilding. Since residual
stresses are predominately visualized in shipbuilding as product warping, the
presentation will discuss past Newport News Shipbuilding’s efforts to identify and
avoid the effects of residual stresses through the use of analysis. This will include
past R&D efforts to connect multiple tools via the use of a common input/output
(residual stress) and their uses in heavy manufacturing. Once this current state
of residual stress determination in heavy manufacturing has been presented, the
discussion will conclude with Newport News Shipbuilding’s vision of future efforts to
improve residual stress determination such as new recently released American Welding
Society standards and efforts to develop Integrated Computational Materials Engineering
as a design method.
Solving Residual Stress Induced
Distortion Problems in Ship Structures
T. D. Huang, Ingalls Shipbuilding.
In recent times, shipboard applications of lightweight structures have increased in both military
and commercial vessels to reduce weight and improve performance. As ship owners enforce tighter
design requirements for strength and stiffness, significant distortion problems have emerged as
shipyards work to meet these new requirements. Residual stresses, imparted to the plate as early
as production in steel mills and exacerbated by shipyard processes such as cutting, fitting, and
welding, are the primary driving force for unstable buckling distortions in lightweight steel hull
construction. Distortion may critically compromise the performance of the ship. In many extreme cases,
distorted shells, decks and bulkheads not only reduce the overall structural rigidity of the hulls,
but also increase the visibility to radar, and consequently make the ship more vulnerable to attack.
Distortion mitigation processes, such as strong-back fitting and flame straightening of distorted hull
can further induce high residual stresses into structures. In many ship construction contracts,
primary hull structural members, including longitudinal and transverse bulkheads and stiffeners,
were buckled during construction due to the high residual stresses. In numerous cases, flame
straightening alone may not be adequate to meet fairness requirements; necessitating additional
cutting and welding operations to correct severely buckled hull structures. Production strategies,
such as the use of clamping restraint, improving fitting practice and optimized cutting and welding
sequences, have been proven to significantly reduce the residual stresses formed during construction
of lightweight structures. Examples of residual stress effects and mitigation strategies developed
by Ingalls Shipbuilding will be presented, as well as a discussion of future plans for further
improvement in ship design and construction.
Distortion and Residual Stress Control in Ocean Based Structures
with Application to Oil Rig Platforms
Bud Brust, Engineering Mechanics Corporation of Columbus.
Construction of large structures which must operate in an ocean environment consists of mainly welded fabrication.
The residual stresses caused by the welds must be managed so that fatigue and stress corrosion cracking is properly
addressed. In addition, fabrication of large structures can be costly because the weld residual stresses induce
distortions which must be managed. Balancing distortion control with life considerations can be aided by the use
of computational weld modeling. This paper first discusses the weld modeling tool used and then provides several
simple examples illustrating the modeling approach to control weld residual stresses and distortions. Finally, a
detailed example of distortion control of a large oil rig platform that must be fabricated on shore and floated to
the ocean site and sunk is provided. This required the development of a novel distortion control strategy using a
pre-camber approach designed using the computational weld model.
Advanced Peening Processes for Mitigation of
Stress Corrosion Cracking in Aluminum Ship Structures: Understanding and Controlling Residual Stresses
Luke Brewer, Naval Postgraduate School.
This work examines the application and influence of compressive residual stresses on the mitigation
of stress corrosion cracking in aluminum ship structures. Stress corrosion cracking of sensitized
aluminum-magnesium alloys is of great concern in both naval and civilian ship structures. Peening processes,
such as ultrasonic impact treatment and laser peening, can help to mitigate stress corrosion cracking.
We need more understanding about how these approaches affect the residual stress distributions and deformation
microstructures of the treated material. Plates of field-sensitized aluminum alloy 5456, from naval vessels,
were metal inert gas welded to simulate weld repairs. These repair welds were then subjected to ultrasonic
impact treatment under a variety of conditions. X-ray diffraction is being used to map the resultant
residual stresses on the surface of the treated welds. These measurements, coupled with electron microscopy,
are developing the knowledge base that enables more effective implementation of ultrasonic impact treatment.
Residual Stress Analysis of Canadian
Naval Platforms
Shannon Farrell, Defence Research and Development Canada.
This presentation describes current approaches that are used to conduct accurate residual stress analysis
onboard Royal Canadian Navy platforms. The application of the portable miniature XRD system for measurement
of the strain state and the methodology for calculation of residual stress is explained. This includes
derivation and utilization of the experimental X-ray elastic constant (XREC) for conversion of measured strain
to stress values. To better understand the applicability of XRECs for use in weld/clad heat affected zones
(HAZ), a GleebleTM weld-simulator was employed to simulate the microstructure and texture of HAZ that are often
found in welded Q1N steel. The effect of simulated weld parameters on the XREC is discussed and the impact on
residual stress analysis on naval platforms is evaluated. Several practical examples of residual stress
investigations on naval platforms are discussed.
How Understanding Residual
Stress Can Help Solve Industrial and Forensic Problems: Some Case Studies
Lyndon Edwards, Australian Nuclear Sci. & Tech. Organisation.
Knowledge of the effects of residual stress on the structural integrity of components
and structures is sparse amongst many engineers and is only very rarely included in initial
design or remaining life assessment. Furthermore, residual stress is rarely specifically
accounted for in most design standards and processes. This can have challenges when
undertaking the forensic investigation of failures, especially when such investigations
are the subject of commercial dispute or legal process. This talk will describe a small
number of examples of forensic failure analysis where the role of residual stress has
been critical to illustrate how the knowledge of residual stress that forms the main
subject of the summit can be useful in practice.
X-Ray Diffraction Residual
Stress Measurement in Failure Analysis
Mike Brauss, Proto Manufacturing, Inc.
Broken Bits and Pieces:
Self Stresses and Failure Analysis
Pete McKeighan, Exponent Failure Analysis Associates.
In the forensic analysis and mechanical testing field, once the results of investigations become
apparent the analyst is often left with the pieces of a puzzle that simply do not fit together.
It is often the case that unquantified residual stresses play the key in being able to put a cogent
and logical process together to describe why failure occurred. In this presentation, a number of
case studies will be shown where residual stresses played a key, but often unquantified role,
influencing the failure and/or cracking process.
Forensic Determination of
Residual Stress from Fracture Surfaces
Michael B. Prime, Los Alamos National Laboratory, NM.
Residual stresses can be a main cause of fractures, but forensic failure analysis is difficult
because the residual stresses are relaxed post-fracture by the new free surface. In this presentation,
a method is presented for a posteriori determination of the residual stresses by measuring the
geometric mismatch between the mating fracture surfaces. Provided the fracture is not overly ductile,
so that plasticity may be neglected, a simple, elastic calculation based on Bueckner’s principle gives
the original residual stresses normal to the fracture plane. The method was demonstrated on a large 7000
series aluminum alloy forging that fractured during an attempt to cut a section into two pieces.
Neutron diffraction measurements on another section of the same forging convincingly validated the
residual stresses determined from the fracture surface mismatch. After accounting for closure, an
analysis of the residual stress intensity factor based on the measured residual stress agreed with
the material’s fracture toughness and fractographic evidence of the failure initiation site.
The practicality of this method to investigate various failures is discussed in light of the
required assumptions.
Measuring Crystal-scale Stresses in
Deforming Polycrystals using High Energy X-rays and in-situ Mechanical Loading
Matt Miller, Cornell University, NY.
The desire to understand and model the multiscale mechanical behavior of polycrystalline
materials has driven the quest for mechanical testing data to smaller and smaller size
scales. This talk describes the use of high energy synchrotron x-ray diffraction along
with in-situ mechanical loading to understand the mechanical response from individual
crystals within a deforming aggregate. Details of the experiments, which were conducted
at the Cornell High Energy Synchrotron Source (CHESS) and at the Advanced Photon Source
(APS) will be given. The focus of the research is to use diffraction data from monotonic
and cyclic loading histories in conjunction with crystal-based material models to
understand processes such as micro-plasticity in titanium alloys and fatigue crack
initiation in copper. New testing facilities, at the APS and at CHESS, which are
specifically focused on structural materials, will also be described.
Analysis of Neutron Diffraction
Data Using the EPSC Model
Bjørn Clausen, Los Alamos National Lab, NM.
Neutron diffraction measurements provide volume averaged bulk information about the internal
strain, texture and defect concentration. The information contained in each diffraction peak
originates solely from the sub-set of grains within the polycrystal that has the given
lattice plane normal parallel to the scattering vector for the detector. Hence conversion
of measured elastic lattice strain data into stress values representative of the bulk
macroscopic state is not trivial. The intergranular stresses developed during plastic forming
or other manufacturing processes are directly reflected in the measured data and in many
cases polycrystal deformation models, such as the Elastic-Plastic Self-Consistent (EPSC) model,
are needed for interpreting and understanding the diffraction data.
Residual Stress Measurements in
Integrated Circuits
Chuck Goldsmith, IBM.
Over the last several decades the microelectronics industry has achieved yearly cost reductions
on the orer of 20-30% while maintaining an almost 60% increase in the number of bits per chip
per year. The size of the Intel 4004 processor introduced in 1972 was 12 mm2 with a
2300 transistors. In 2010, the 16 core SPARC T3 processor was the first to have 1,000,000,000
processors in a chip 377 mm2 in area. The 2013 Xbox One Main SoC processor has
5,000,000,000 transistors in a chip 363 mm2 in size. These devices also have a
comparable number of passive elements and hundreds of meters of sub-micron Cu wire interconnections.
To achieve typical failure rates below one chip per thousand, the on-chip structures must be built
to very exacting dimensional and compositional specifications; a few atoms of contaminant in the
wrong place or displacements of a nm or so can cause failure. The thermal stresses induced by
changes in temperature acting on materials with dissimilar coefficients of thermal expansion can
cause failure during manufacturing and operation. The current densities carried by the fine metal
wires are so high that the electron wind can actually move atoms along, causing hydrostatic stresses
and fracture close to the anode end of the wires. In this presentation the stress issues we have
dealt with in the course of manufacturing and reliability analysis of microelectronics structures
from high end computers will be discussed with particular emphasis on diffraction-based stress
measurement methods.
Improvements Needed for Diffraction
Techniques and Pitfalls to Avoid
Clayton Ruud, Penn State University (retired).
The diffraction methods include X-Ray, Synchrotron and Neutron and are the only methods of
residual stress measurement that directly measure the elastic strain caused by stress in materials.
However, they are applicable only to crystalline materials.
The X-Ray methods are largely confined to surface stress measurements while the other two offer
the possibility of nondestructively measuring internal stresses. This paper will briefly review
the history of techniques applied for diffraction stress measurement, including the progress
attained in speed, precision, accuracy, spacial resolution, and improved instrumentation.
Developments needed to improve these qualities will be also be discussed as well as those to
make the techniques more widely applicable. Sources of error and misapplication of the
diffraction residual stress measurement techniques will be also be discussed.
Residual Stress Driven
Creep in Nuclear Power Plants
Mike Smith, Manchester University, UK.
The UK Advanced Gas Cooled Reactor fleet are unique in operating with reactor gas outlet
temperatures up to 650°C, well within the creep regime for austenitic stainless steels.
Indeed, they may be thought of as Generation IV prototype reactors from the 1970’s.
Creep deformation and damage generated by relaxation of weld residual stress has led to
in-service cracking in a number of boiler components, necessitating extended plant outages
and expensive plant modifications. This talk gives a historical overview of both the
problems experienced and our developing understanding and ability to model them.
Applying Engineered Residual
Stresses Through Coupled Finite Element Analysis and Crack Growth Software
Scott Carlson, Southwest Research Institute, San Antonio, TX.
Applications of deep Engineered Residual Stresses (ERS) in fatigue critical structure
have been implemented since the 1960s on the United States Air Force’s (USAF) T-38,
and later on the A-10 aircraft, because of the ability of compressive residual
stresses to improve fatigue performance. However, the ability to predict fatigue
crack growth in components with deep ERS has lagged far behind these applications.
To address the gap in analytical methods, the A-10 and T-38 Aircraft Structural
Integrity Program (ASIP) analysis groups have spent the last ten years investing
in research through internally and externally funded programs. These programs
have been designed to characterize the Cold Expansion (CX) process used during
manufacture and rework of T-38 and A-10 structure at critical fastener holes and
quantify its effects on fatigue crack growth rate and shape. Outcomes from the
research include characterization the residual stress field imposed by CX,
improved methods for predicting fatigue crack growth in the presence of the deep
residual stress field, and understanding the effects of CX on crack detection by
Non-Destructive Inspection (NDI) methods. These research outcomes are enabling
a better understanding of the fatigue performance benefits through ERS, which
in turn provides for improved fleet management decisions.
Residual Stresses in
the NRU Vessel Weld Repair
Brian Leitch, Chalk River Laboratories.
The National Reactor Universal (NRU) has been operating at the Chalk River Laboratories for
over 55 years. It is a pool-type research reactor with a heavy water moderator operating at
atmospheric pressure and a temperature of 50°C. The original containment vessel was replaced
in 1974. The vessel is manufactured from aluminium Al 5052 and is approximately 3500 mm in
diameter, 4500 mm in height and has a wall thickness of 8 mm. Over the course of normal
operations, corrosion of the vessel took place and some leakage of the moderator occurred.
To return NRU to full operation it was necessary to repair the vessel and a decision to repair
the vessel wall in-situ using a combination of filler-weld areas and welded patches. As these
repair welds were located close to the sealing edge of the vessel, many experimental tests and
computational analyses were performed to ensure the vessel integrity was not comprised during,
or after, the welding process. Stresses in excess of the material’s yield stress were
calculated but subsequent inspection did not indicate any structural changes although the
literature indicates that significant relaxation will occur. This presentation will provide
details of the challenging welding repair, the computational results and give an overview of the
research program set up to examine the effect of radiation on the vessel material and weld regions.
Analysis of SCC Initiation
and Propagation Based on Probabilistic Fracture Mechanics Under Residual Stresses
by Machining and Welding Processes of Pipes
Masahito Mochizuki, Osaka University, Japan.
Residual stress is an important factor for Stress-corrosion cracking (SCC). It
has been observed near the pipe welded zones made of austenitic stainless steel
type 316L in boiling water reactor of nuclear power plants. In the joining
processes of pipes, butt-welding is usually conducted after surface machining,
and residual stresses are generated by both processes. The residual stress
distribution by surface machining is varied by the subsequent butt-welding process.
Numerical analysis of the residual stress distribution by butt-welding after
surface machining is performed by the finite element analyses with some experimental
validation. The probabilistic SCC initiation is predicted by the residual stress
obtained at the inner surface and the experimental data by SCC test. SCC growth
analyses based on the probabilistic fracture mechanics are then performed by using
the SCC initiation time and the residual stress distribution in the pipes. It is
found that the effect of plastic strain on the crack propagation is more dominant
than the analytical conditions concerning initial cracks, such as the SCC initiation
time.
Gun Tube Residual Stresses -
Known Knowns, Known Unknowns, Best Guesses and Outstanding Problems
Tony Parker, Cranfield University, UK and Ed Troiano, US Army WS & T
Center, Watervliet, NY.
Gun Tubes are autofrettaged to increase their safe maximum pressure and fatigue
lifetime, the latter being totally dominated by fatigue crack growth. There are
two popular autofrettage processes: hydraulic and swage autofrettage. Hydraulic
autofrettage involves the application of high internal pressure along an extended
length of tube, whilst swage autofrettage involves pushing an oversize mandrel
(which makes contact over a very short axial distance) along the length of the tube.
Hydraulic autofrettage is considered to be well modeled (numerically) whilst swage
has been much less widely modeled (numerically). There is limited consensus on
axial stress profiles within swaged tubes; available evidence is somewhat
contradictory. Furthermore, modern experimental validation is based almost
exclusively on axially-thin ring specimens in which axial residual stresses
have been released. Definitive measurements of axial stress are required to
ensure confidence in lifetime and re-yield assessments. Contour Modeling (CM)
appears to offer such an opportunity and some possible cutting sequences for
successful CM measurement are offered. Comments and suggestions from
practitioners will be most welcome.
Residual Stress Measurement
Implementation in the USAF Foundational Engineering Problem Program on Bulk
Residual Stress in Nickel Base Superalloy Aeroengine Disks
Iuliana Cernatescu, Pratt and Whitney.
A team of aerospace Original Equipment Manufacturers (OEMs) and suppliers has assembled
to execute a critical program to address the United States Air Force (USAF) Foundational
Engineering Problem (FEP) on residual stress within nickel-base superalloy components.
The program is aimed at establishing a framework to link predictive methods to component
design functions and product realization activities with industry-wide standardized protocols.
A major element of the program includes a demonstration task where a generic component
will be designed using Integrated Computational Materials Engineering (ICME) tools to
predict residual stress. Destructive and non-destructive residual stress measurements
will be performed to support verification and validation of the modeling methods. This
presentation will provide a program overview along with specific industrial challenges associated
with uncertainty in different residual stress measurements and approaches to model validation.
Residual Stress and Strain in U-Mo
Fuel Plates and Foils
Maria Okuniewski, Idaho National Laboratory.
There is currently an ongoing effort within the United States to replace highly-enriched uranium
nuclear fuels with low-enriched uranium (LEU) fuels in high performance research reactors (HPRRs).
In concert with this effort, there is an associated fuel development program to design, fabricate,
irradiate, and analyze these fuels. The fuel that will be utilized for the conversion of these HPRRs
is a LEU based U-10wt.%Mo (U10Mo) alloy foil with a Zr diffusion barrier that is encapsulated within
an Al-6061 cladding. The fuel foils are fabricated by various rolling processes and thermal
treatments, followed by hot isostatic pressing (HIPing) to bond the fuel foil and the cladding
together. During the various steps throughout the fabrication process, residual stresses are
introduced into the plates during the rolling of the U10Mo fuel foils, the foil heat treatments,
and HIPing processes. Both synchrotron x-ray diffraction and neutron diffraction were used to
measure the spatially resolved residual strains and stresses in a number of as-fabricated nuclear
fuel foils and plates. A variety of processing parameters and their impact on the residual strain
and stress of these systems will be discussed.
Importance of Surface Fitting Parameters for
Repeatability of the Contour Method
Mitch Olson, UC, Davis.
This talk describes the results of a contour method residual stress measurement repeatability
study and discusses the role of the model for surface fitting on repeatability. The study used an
aluminum bar with an artificially high residual stress state (+150 MPa) introduced by quenching.
Five contour measurements were performed at the mid-length of successively smaller pieces,
all pieces being long enough to contain the same mid-length residual stress field. Typical contour
method procedures are employed with careful clamping of the specimen, wire electric discharge
machining (EDM) for the cut, laser surface profiling of the cut faces, surface profile fitting,
and linear elastic stress analysis. The results show repeatability standard deviations less than
5% of the stress range over the interior of the cross section with a maximum under 10% of the
stress range at the cross section boundaries. However, it has become clear that the model choice
(i.e., analytical function) and number of fitting parameters used to fit the measured surface is
of paramount importance, especially at the edges, where stresses can change shape and be different
by up to 25% of the range of stress values, which is larger than the total repeatability standard
deviation found.
Recent Advances and Applications of Residual Stress
Measurements in South America
Armando Albertazzi, Universidade Federal de Santa Catarina, Brazil
This presentation reports some work developed in South America related to residual stress measurement and
applications. Activities of three research groups are emphasized. A residual stress measurement approach,
using a local heating and optical method, has been developed at the University of Rosario in Argentina.
A local hot spot was produced by a carbon electrode connected to a programmable power supply. The specimen
was heated and then cooled dawn. The residual displacement field was analyzed using the finite element method.
A second group, working at the Catholic University of Rio de Janeiro, Brazil, has mapped residual stress
distribution in a UOE-Saw pipe using strain gauge based hole-drilling and has investigated the ability to use
this information to quantify the amount of bending stresses induced in a buried pipeline. Finally, the work
developed at Federal University of Santa Catarina in Brazil using optical methods is reported in more details.
It involves a portable and robust ESPI hole-drilling system with radial sensitivity that has been developed
for in-field residual stress measurement. Recent progresses in the device are reported as well as image
processing algorithm improvements to separate and analyze the principal stresses sum and differences in a
robust way. The tables present in the ASTM E-837 standard are used to quantify residual stress gradients
by incremental hole-drilling. Few recent applications are briefly reported. in addition, results of an attempt
to use indentation for residual stress measurement are also reported.
ASTM International: The Activities of E28.13
on Residual Stress Measurement
Joe Koury, ASTM.
ASTM International is a globally recognized leader in the development and delivery of international
voluntary consensus standards. Through a collaborative effort, the members of subcommittee E28.13
on Residual Stress Measurement develop and approve industry standards focusing on the measurement
of stress in materials. This presentation will give a brief overview of ASTM International as
well as cover the activities of Subcommittee E28.13.
Residual Stress in R6 and R5
British Structural Assessment Codes
Mike Smith, Manchester University, UK.
Weld residual stresses can impact the structural integrity of components operating both below
and within the creep regime. The UK structural integrity assessment procedures known as R5 and
R6 both include advice on the inclusion of residual stresses in integrity assessments. R6 covers
(1) the estimation of residual stresses, using simple assumptions (level 1), published upper
bound data for common weld types (level 2), and detailed estimates using finite element methods
and RS measurements on mock-ups; and (2) assessing the impact of residual stress on the integrity
of cracked structures operating below the creep regime. R5 covers the impact of weld residual
stress on creep deformation, creep damage accumulation, and creep crack growth. This talk gives
an overview of their advice.
ASME Codes - Potential for
Inclusion of Residual Stresses
John E. Broussard, III, Dominion Engineering,
Inc.
Section XI Appendix C of the ASME Code is used by the US nuclear industry to evaluate
flaws identified in piping components, including the nickel-based alloy welds joining
ferritic steel vessels to austentic piping (also known as dissimilar metal or DM welds).
The flaw growth analysis includes provisions for conditions where stress corrosion cracking
(SCC) is active. In the section defining the requirements for flaw growth calculation due
to SCC, the Code states "Sustained loads ... as well as residual stresses should be included.
Appropriate experimental data on residual stress distribution for different pipe sizes ...
should be used." No further requirement or discussion of residual stress is included in
Appendix C. Without additional requirements or discussion in the Code, it has been recognized
that different analysts could develop substantially different residual stress distributions
for the same component. In order to minimize the variation, the ASME Code Task Group on
Crack Growth Reference Curves has begun work on developing codified guidance on residual stresses.
The focus of this work is on DM welds, since these welds are the ones currently most affected by
SCC degradation. This presentation will summarize the progress to date on this task.
Residual stresses and Structural Integrity
for Oil and Gas
Philip Withers, Manchester University, UK.
The drive to recover oil and gas from increasingly hard to get reservoirs is extending the
envelope of performance expected of critical components. Current structural integrity procedures
are not well able to assure materials for increasing harsh and demanding environments. In this
talk I will examine some of the structural integrity issues associated with accessing reservoirs
at 20,000 psi in combination with higher temperatures and sour environments. Further I will
look at the challenges, dangers and opportunities presented by residual stresses.
Parametric Finite Element Model to
Ascertain the Limits of Geometrical Boundary Condition of the Component for the
Hole-drilling Method
Andreas Nau and Berthold Scholtes, Kassel University.
Reliable residual stress measurements are strongly in demand due to the fact that residual
stresses can be beneficial on the one hand, when they are adapted to external loads or detrimental
on the other hand, when they are unknown. Thus, this can result in an uneconomic
oversizing of the component or in its failure, respectively. Besides diffraction methods, mechanical
methods are in common use to determine unknown residual stress states. Depending
on the selected method, specific geometrical boundary conditions have to be taken into account.
In the case of the hole-drilling method, the geometry of the component should be
similar to an infinite and thick plate. The reason for this lies in the need of a calibration for
the strain-stress transformation due to the fact that no analytic solution exists for blind holes.
The calibration is usually carried out by numerical simulations. For the sake of simplicity the
geometry of the component is commonly an ideal thick plate and the hole is introduced in the
center of it. In this investigation an interface was designed which enables the parametric
design of Finite-Element Models. These models can represent plates variable in their geometry
and in the position of the measuring point but also other geometries e.g. a turbine blade.
The interface is implemented in a development environment for calibrating, evaluating and
illustrating a complete hole drilling analysis. In a first step the parametric model was used to
ascertain the effects of geometrical boundary conditions. The thickness of the plate and the
distance of the measuring point to edges were considered. The results are validated experimentally
and application limits or calibration corrections are suggested, respectively.
Recent Improvements of the MTS3000 System for
Hole Drilling Tests
Alessio Benincasa, SINT Technology, Italy
The Restan-MTS3000 is an automatic system for measuring residual stresses by the hole-drilling
strain-gage method. It has been on the market since 1990, with many developments and improvements
over the years. The most recent improvements include new calculation algorithms with off-axis /
local plasticity correction, and upgraded electronic microscope for automatic positioning and measurement
of the hole diameter. The new multi-device control unit, with Ethernet / WiFi connection, also allows the
connection of the mechanical device for residual stress measurements by ring-core. Examples of typical test
results are also given.
Pulstec µ-X360 XRD Residual Stress Analyser
Based on the cos α Method of Analysis
Mike Woodward, Pulstec Industrial Co.
X-ray diffraction (XRD) has been used for many decades to identify crystallographic information and
measure structural properties including lattice strain. In the past, the diffraction patterns detection
was mainly achieved using photographic film, that needed to be removed from the diffractometer, processed
and then the analysis procedures applied. However, using this type of media and processing steps, could
result in measurement inaccuracies affecting, for example, the measurement of lattice strain. Pulstec has
developed an XRD analyser, the µ-X360, whose detector system is able to sample the full Debye rings
and analyse these data all within the system. Using the cos α method to analyse the full Debye rings,
the analyser is able to rapidly evaluate the lattice strain and determine the associated residual stress
value. Images of the Debye rings also reveal grain size and texturing information. Examples of typical
results are given in this poster.
Determining Residual Stress Fields using High Energy
X-ray Diffraction and a Finite Element Discretization
Matt Miller, Cornell University, NY.
By definition,residual stress is a field quantity: a second order tensor varying over an entire workpiece.
Diffraction measurements, on the other hand, interrogate lattice strains at single material points.
This talk presents a method for integrating lattice strain measurements taken from many spatial points over
a workpiece into a comprehensive description of the tensor field of residual stress. Lattice strain
pole figures are measured at various points within shrink-fit samples using high energy synchrotron
X-rays. A bi-scale formulation is used to determine the residual stress field from the measured lattice
strains. At each diffraction volume, a spherical harmonic expansion is used to describe the distribution
of each crystal stress component over orientation space. A finite element mesh over the entire sample is
used to locate the diffraction volumes and to impose macroscopic stress equilibrium and free-surface
conditions. The stress field is determined by matching the macroscopic stress with the crystal-scale
values integrated over each orientation within the diffraction volume. Examples from two and three
dimensional nickel-based superalloy samples and a two-dimensional titanium sample are presented.
Challenges in Measuring Pronounced Compressive
Residual Stress Depth Profiles Within Internally Pressurized Parts
Horst Bruennet, Saarland University
Pronounced compressive residual stress depth profiles are used as design tool to increase the fatigue
life of internally pressurized parts, such are as in modern diesel injection systems.
They have to withstand high pressures of well above 2,200 bar for 250,000 km up to
1,500,000 km depending on the engine application. Manufacturing processes such as hydraulic or
swage Autofrettage are used to introduce such pronounced compressive residual stress depth profiles
up to several millimetres below the surface of the treated bore. However, the measurement of the
residual stress depth profiles inside the internally pressurized components poses some severe challenges.
As the measurement position is normally not directly accessible, the components have to be
cut in order to apply measurement techniques like hole-drilling or XRD. This significantly alters the
residual stress distribution and the measured residual stress depth profiles cannot be directly used to
evaluate the effectiveness of the applied manufacturing processes.
This poster presents results of XRD- and optical hole-drilling
measurements after Autofrettage with different pressures and consecutive sample preparation for two
representative geometries: A thick-walled cylinder and a high pressure distributor block with T-shaped
bore intersection. The measurement results are compared to calculated residual stress depth profiles
using Huang’s analytical approach and the finite-element code Abaqus/CAE. It can be shown that
the application of suitable finite-element models is essential for the correct interpretation of residual
stress depth profiles within internally pressurized components.
Experimental Validation of the Calibration Function
of the Hole-Drilling-Method and Ring-Core-Method for Residual Stress Measurement
David von Mirbach, Universität Stuttgart
This study experimentally analyzes the calibration functions for residual stress measurements of the hole
drilling method (HDM) and ring core method (RCM). These functions are used for residual stress analyses
using the differential method. With a four-point-bending test machine, a defined stress can be triggered
between the middle bending. The strain in this area can be measured with strain gauges, so the stress is
well-known. In this defined loading area, the strains in two load cases with the HDM-configuration and
RCM-configuration were measured by strain-gauge-rosettes. With this measured strain and the well-known
stress, the specifically calibration functions will be calculated and presented together with the numerical ones.
Non-destructive Residual Stress Determination of a
Friction Stir Welded Lap Joint
Michael Bach, Carleton University
This research uses a non-destructive method of neutron diffraction to measure the tri-axial residual stresses
in a friction stir welded aerospace fuselage component: a stringer-to-skin lap joint. Two different specimens
were examined. Fatigue testing was performed on both specimens to determine their fatigue lives. Effects of
the different components of residual stresses were examines and related to fatigue performance. A combination
of fractography, hardness testing, and residual stress measurement was used to predict areas of high probability
of structural failure in the friction stir welded lap joints.
Machining Induced Residual Stresses:
Effects of Tribological Factors
A. K. Balaji, University of Utah
Machining induced residual stresses are an important factor in determining the surface integrity of manufactured
products, their subsequent product life under service loads, and also from the perspective of sustainable
design and manufacturing. Typical process planning for machining process planning does not include optimization
of residual stresses as an active component, with the major focus being largely limited to issues such as
reduced tooling costs, reduced manufacturing time, reduced manufacturing costs, and enhanced surface finish
and geometrical and dimensional tolerances. This necessitates the use of expensive and time consuming
post-process surface treatment options such as shot peening and laser shock peening. In this poster, we present
some results that show that beneficial residual stress profiles in machined surfaces can be generated by
actively controlling manufacturing process parameters such as cutting speeds and feeds but also by controlling
the tribological factors such as cutting tool coatings and the use of coolants and lubricants. The individual
and combined effects of such tool coatings and cutting fluid usage on resulting residual stresses is
highlighted in this poster. When combined with controlling the geometry of the cutting edge, these
tribological factors can be tailored to generate improved surface integrity of machined surfaces.
Reconstruction of Residual Stress Fields from Measurements
made in an Incompatible Region
Harry Coules, University of Bristol
A method is introduced by which the complete state of residual stress in an elastic body may be extrapolated
from a limited set of experimental measurements. Two techniques for carrying out this reconstruction using
finite element analysis are compared and it is shown that for perfect reconstruction of the complete stress
field via this method, the stress field must be measured over all eigenstrain-containing regions of the object.
We have investigated the effects of error and incompleteness in the measurement of this part of the stress
field in a series of numerical experiments using synthetic measurement data based on the NET TG1 round-robin
weld specimen. It is hence demonstrated that accurate residual stress field reconstruction is possible using
measurement data of a quality achievable using current experimental techniques.
Pulstec µ-X360 XRD Residual Stress Analyser
Mike Woodward, Pulstec Industrial Co.
Pulstec has developed a lightweight portable Residual Stress analyser based on X-ray diffraction, for use
in the lab and/or on-site called the µ-X360. For this system Pulstec has developed an X-ray detector
that is able to detect and analyse the complete Debye ring, based on the cos α analysis method.
This system has the advantage of being able to measure the residual stress from a single short duration low
intensity X-ray exposure, as well as an option to measure retained austenite. There is the added advantage
of being able to view the X-ray intensity distribution around the Debye ring to reveal grain size and
texturing information.
Prism - Residual Stress Measurement Based on Hole-drilling and ESPI
Theo Rickert, American Stress Technologies, Inc.
The residual stress measurement system Prism is manufactured by Stresstech Group. Instead of strain-gages,
the instrument uses ESPI (Electronic Speckle Pattern Interferometry) to measure surface displacements around
the hole as it is being drilled incrementally. Stress depth profiles are then calculated using the Integral
Method. Completely new software was released this year. New tools improve measurement setup (and hence
measurement quality) and data analysis. p>
Recent Improvements of the MTS3000 System for Hole Drilling Tests
Alessio Benincasa, SINT Technology, Italy
A demo unit of the complete MTS3000 system will be demonstrated,
including mechanical, optical, electronic devices and software. Some typical results of residual stress measurements by
hole-drilling will also be displayed for different application fields (shot peening, stress relieving, welding, machining).
Micro-Measurements: RS-200 Display
Herb Roy, Vishay Precision Group - Micro-Measurements
A working model of the RS-200 residual stress
hole-drilling device will be available for hands-on discussion of its use for hole-drilling residual stress
measurements. Strain-gaged specimens will also be available for discussion of application methods.
POLAR – A Portable Optical Residual Stress Measurement Device using
DSPI and Incremental Hole-drilling
Armando Albertazzi, Universidade Federal de Santa Catarina, Brazil
The system POLAR uses a combination of digital speckle pattern interferometry (DSPI) and incremental hole-drilling
technique to measure residual stresses. Using a special diffractive optical element POLAR system combines a unique
in-plane radial sensitivity feature and high stability since it is not laser wavelength dependent. The mechanical
design makes it easy to be adjusted and stiffly attached to the surface to be measured reducing vibration effects
and enabling it for in-the-field applications. The test-oriented software was designed to guide the user to perform
incremental hole-drilling tests in a friendly way. Test data are organized in a structured way, making possible to
both present immediate in-field results and later deeper analysis. The POLAR prototype presented at Residual Stress
Summit 2013 is a new version currently under development at the Federal University of Santa Catarina, Brazil.