3.8. RESIDUAL STRESS COMPUTATIONS 61
imposed by dependence on experimental calibrations. During the 1970s and 1980s, advances
were made in three important areas:
1. accuracy improvement of hole-drilling calibration data,
2. formulation of calibration data not measurable experimentally, and
3. creation of calibration data for additional applications.
e early works of Bijak-Zochowski (1978), Beaney and Procter (1974), Schajer (1981)
were aimed at improving calibration accuracy and consistency and established the finite element
method as a practical method for evaluating hole-drilling calibration data. An important devel-
opment was the introduction of the Integral Method for calculating the residual stress profile
through the depth of the drilled hole. Several researchers contributed to this initial development,
notably Bijak-Zochowski, Flavenot and Lu, and Schajer (1988). e significant feature of the
Integral Method is that it correctly accounts for the contributions of all stresses within the hole
depth to the measured strain response, thereby avoiding the limitations of the Differential Strain
and Average Stress methods. e use of finite element calculations was an essential prerequisite
to the development and use of the Integral Method because the needed calibration data are not
measureable experimentally. Since 1999, the ASTM Standard Test Method E837 has specified
the use of the Integral Method for residual stress profile evaluations.
e flexibility of the finite element method has enabled substantial computational de-
velopments to be made in many further areas, notably for corrections for various experimental
artifacts that can occur during the course of practical measurements. One such artifact occurs
when the drilled hole is not exactly at the geometric center of the strain gauge rosette. e
resulting eccentricity causes a systematic shift in the measured strains, thereby distorting the
corresponding computed residual stresses. In the late 1970s, Sandifer and Bowie (1978) and
Ajovalasit (1979) introduced computational approaches for correcting the effect providing that
the size and direction of the hole eccentricity are accurately known. However, the opportunity
to correct for hole eccentricity should not be allowed to grant a tolerance of such errors. Cer-
tainly it is always the best strategy is to seek to refine the experimental technique used so as to
minimize the occurrence and size of all preventable errors.
Another significant artifact occurs when the Hole-Drilling Method is used to measure
large residual stresses close to the material yield stress. e drilling of the hole creates a stress
concentration in the adjacent material, which causes local yielding. e resulting material plas-
ticity adds to the relieved strains, causing them to be larger than they would be if only elastic
deformations had occurred. Consequently, the residual stresses evaluated from the measured
strain reliefs are overestimated, often suggesting residual stresses larger than the material yield
stress. is artifact can also be ameliorated using finite-element based compensation methods.
Starting in the 1990s, Beghini and coworkers have led the initiative to develop approaches to
compensate for material plasticity and to allow hole-drilling measurements to be made for resid-
ual stresses close to yield stress. Without such corrections, the Hole-Drilling Method can be