ASTM E837 Residual Stresses by Hole-Drilling Strain-Gage method

Get Certified ASTM E837 Testing for Reliable Residual Stress Measurement.

ASTM E837 testing provides a realistic approach to assessing residual stresses that may be produced during manufacturing, fabrication, machining, heat treatment, welding, forming, or service. A proper strain-gage rosette is installed, a small blind hole is drilled, and the relieved strains are recorded at predetermined depths. The engineer can then interpret these measurements to determine the magnitude of residual stress, the direction of principal stress, and the change in stress with depth. The technique is semi-destructive because it damages only a small area.

• Material type: Isotropic, linearly elastic materials.
• Stress type: In-plane residual stresses near the measured surface.
• Measurement method: Controlled hole drilling combined with strain-gage measurements.
• Hole configuration: Blind holes are generally used for residual stress evaluation.
• Stress distribution: The method can evaluate uniform and nonuniform residual stresses within the applicable measurement depth.
• Measurement location: The procedure focuses on localized near-surface residual stresses.
• Material behavior: The material should remain within the applicable linear-elastic measurement range.
• Specimen condition: The workpiece must tolerate the localized damage produced by hole drilling.

What are the Uses of ASTM E837 Testing?

ASTM E837 testing is used to assist the engineer in identifying residual stresses that exist in the material after manufacturing and during service. These stresses may lead to failure under alternating loading or in corrosive environments, but compressive residual stresses may have beneficial effects in applications like shot peening. The ASTM E837 standard:

• Measures near-surface residual stresses (magnitude).
• Estimates the orientation of principal residual stresses.
• Recognizes uniform residual stress distributions.
• Assesses non-uniform stress distributions at the measured depth.
• Helps assess residual stresses produced during manufacturing.
• Assists with the assessment of stresses arising from machining, forming, welding, etc.
• Supports the investigation of residual stresses that could lead to the failure of the component.
• Assists in process evaluation and quality control.
• Delivers localized information on residual stresses with relatively minor specimen damage.
• Helps engineers assess the impact of beneficial compressive residual stresses.

Which materials can be tested under ASTM E837?

ASTM E837 is for isotropic materials whose response to the conditions of residual-stress measurements is linearly elastic. Thus, the method can be used for the evaluation of residual stresses in numerous metallic materials if the geometry of the specimen, the level of the stresses, and the material response comply with the requirements of the standard.The method is used primarily to measure stresses near the surface, rather than internal stresses at great depths. Therefore, analysts must consider material thickness, residual stress distribution, local yielding, and the desired measurement depth before testing. ASTM E837 also refers to the procedure as semi-destructive since it creates a localized hole in the workpiece.

Why is ASTM E837 Important?

ASTM E837 is important because residual stresses can significantly influence the structural performance and service life of metallic components. Tensile residual stresses may cause cracking and failure, especially when alternating service loads are applied to a component or where corrosive conditions exist. On the other hand, compressive residual stresses are beneficial in certain applications, such as shot-peened components. The technique also yields local measurements and relatively little damage in comparison with many mechanical residual stress measurement techniques. The results, as such, must, however, be interpreted taking into account the near-surface sensitivity and the linear-elastic limitations of the method. The current ASTM scope includes the ability to make satisfactory measurements when the stresses are generally less than about 80% of the material yield stress for the particular blind-hole condition.

ASTM E837 Testing Process and Data Collection

ASTM E837 testing begins by choosing and preparing an appropriate measurement site on the part. Technicians then attach and wire the strain-gage rosette and take initial strain readings until they stabilize. They then drill the hole step by step and measure the strain relaxation caused by stress release. The measured strain data are then analyzed by the analysts to determine the magnitude of residual stress, the principal stress direction, and the variation of stress with depth. The method therefore yields information about the residual stress in the vicinity of the test surface.

Common Challenges and Troubleshooting

Accurate ASTM E837 results require careful strain-gage placement, stable instrumentation, precise hole positioning, and controlled drilling. For this reason, the measurement surface and/or rosette alignment must be checked and verified by the technicians before drilling to avoid the possibility of positioning error that can affect the calculated stress state. Strain can also be introduced if the surfaces are not properly prepared or electrical connections are not stable. Drilling must be kept under control, as too much mechanical disturbance may affect the measured strain relaxation. When interpreting results, analysts should also take into account the behavior of the material, the magnitude of the stress, the geometry of the specimen, and the depth of the measurement. Therefore, it is very important to set up carefully and collect data consistently to ensure the reliable evaluation of residual stress.

• Residual stress magnitudes can be given in MPa or ksi.
• Principal residual stresses can be determined from the measured strain relaxation.
• Principal stress direction can be reported in degrees relative to the strain-gage reference direction.
• Stress profiles may reveal the variation of the residual stress through the holes.
• When the stress is fairly constant over the depth sampled, uniform residual stresses can be assessed.
• When stress varies significantly with depth, you can evaluate non-uniform residual stress.
• Stress sensitivity drops off very quickly with depth, so near-surface results are generally more sensitive.

Link to ASTM E837