XRD vs Hole-Drilling Residual Stress: Match Depth and Direction
X-ray diffraction (XRD) and the hole-drilling strain-gage method do not measure the same volume of material or rely on the same assumptions. Two results that look contradictory, even with opposite signs, may describe different depths, directions or conditions rather than disagreeing laboratories. Before choosing or comparing residual-stress evidence, state the location, direction and depth that matter to your question, then match material, sign convention and depth representation. Neither method gives deep interior stress by default, and neither gives remaining fatigue life.
What hole drilling represents
ASTM E837-25e1, listed as active and last updated February 27, 2026, specifies a hole-drilling procedure for determining in-plane residual stresses near the surface of an isotropic, linearly elastic material. It applies where the stresses do not vary significantly across the diameter of the drilled hole. The measured stresses are those present within the depth of the hole, and the standard calls them uniform if they stay roughly constant within that depth or non-uniform if they vary significantly.
The standard is explicit about limits. Sensitivity falls rapidly with depth from the measured surface, and deep interior stresses cannot be evaluated or reliably identified. The method assumes linear-elastic behavior. When near-yield stresses are present, local yielding can occur around the hole, and the standard says satisfactory results can be achieved when residual stresses do not exceed about 80 percent of the material yield stress.
Hole drilling also alters the part. The standard describes it as relatively modest damage and often called semi-destructive, but it says the method should be applied only where the specimen is expendable or where a small shallow hole will not significantly affect the specimen's usefulness.
What XRD represents
ASTM E2860 is titled as a standard test method for residual stress measurement by X-ray diffraction for bearing steels. The public listing for the E2860-20 edition says it covers experimentally determining macroscopic residual stress tensor components of quasi-isotropic bearing steel materials, and that it guides determining stress values that play a significant role in bearing life. Its stated example uses include detecting abusive grinding, monitoring carburizing and nitriding effects, and failure analysis. Check which edition a report invokes, since the listing reviewed shows the 2020 edition.
That is a bearing-steel method. It should not be read as a scope that automatically covers every undercarriage alloy. Whether an XRD result applies to a given steel depends on the laboratory's stated basis, including the elastic constants and homogeneity assumptions it used.
XRD reads a shallow layer. A residual-stress equipment maker, Stresstech, states that for steel and aluminium the non-destructive measurement depth is a few to tens of micrometres below the surface, that residual stresses are rarely completely described by a surface measurement alone, and that electropolishing and successive measurements can build a depth profile. That is a vendor's description. It shows that a single XRD reading is a surface-layer value, and that a depth profile involves removing material and measuring again.
Compare the sampled volumes, not the headline numbers
A surface XRD value and a hole-drilling result averaged over a hole depth sample different things. A stress that is compressive at the surface and tensile a short distance below can produce an XRD sign opposite to a hole-drilling average without either being wrong. The comparison is only meaningful once the depth each result represents is stated.
This table is a recommended review aid, not a form required by either standard. Where the two results do not share a depth, direction and sign basis, record them as not comparable and request matched measurements.
Separate method choice from permission to damage the part
Two questions get mixed up in practice. One is which method answers the technical question at the needed depth. The other is whether anyone has authority to alter the part. Hole drilling and any XRD depth profiling that removes material both change the specimen, and the permission belongs to the owner and the laboratory, not to the method choice.
State the technical need first: the location, the stress direction, the depth range and whether the question concerns a surface treatment, a machined surface or a deeper layer. Then ask the laboratory which method fits, what it will remove or drill, and what limits it places on the answer. Residual-stress methods are not screening tools for grinding damage, and stress-relief operations are separate topics outside this article. Grinding burn inspection on hardened parts covers the screening question.
Write the measurement request
A usable request names the part and measurement location, the stress direction and sign convention, the depth or depth range, the material and its condition, the method and edition, the uncertainty to be reported, and what alteration is authorized. It also states what the result will not be used to claim, such as deep interior stress or fatigue life.
For a part from KTSU, provide the part reference, the location of interest and the evidence you hold when asking what documentation is available. The public excavator undercarriage parts collection identifies the product family. It does not establish a residual-stress measurement capability or a particular stress level.
The request is complete when location, direction and depth are matched to the question, the sampled volumes of any two results are stated, and permission to alter the part is recorded separately from the choice of method.