Services · Residual stress measurement
Residual Stress Measurement by XRD
Review the process parameters, application scope, required input data and feasibility for a specific component.
What are residual stresses?
Residual stresses remain trapped within a metallic material after mechanical processing, machining, or heat treatment, existing as either tensile or compressive stresses. Following Controlled Shot Peening, non-destructive or semi-destructive XRD (X-ray diffraction) measurement provides critical quantitative verification of deep compressive stress distribution at critical component locations.
The XRD technique utilizes precise X-ray diffraction geometry to analyze sub-surface crystal lattice strain in the near-surface layer. Measurement feasibility, penetration depth, and spatial resolution are verified by the testing laboratory prior to component inspection.
XRD measurements can be arranged as a stand-alone test or as part of a Shot Peening project, including comparison before and after the process. Testing is performed by a specialized external laboratory, while SP Center coordinates the scope, component preparation and delivery of results to the customer.
Almen intensity control measures process repeatability and kinetic energy transfer, but does not measure actual material stress. XRD measurement directly quantifies residual stress profiles in MegaPascals (MPa).
Information required to plan an XRD measurement
Measurement objective and expected output
Material and heat-treatment condition
Drawing with measurement points
Measurement directions
Surface measurement or depth profile
Before-and-after comparison
Report requirements
Depth Profiling & Compressive Residual Stress Evaluation
Evaluating surface stress alone is often insufficient for high-reliability components. Complete structural validation requires quantitative depth profiling.
Depth Profiling via Controlled Electro-Polishing
To determine stress levels below the surface without inducing new mechanical stresses, we combine XRD measurement with chemical electro-polishing layer removal:
- Surface Measurement: Baseline XRD scan at the outer surface layer.
- Material Removal: Micro-step material removal using targeted electro-polishing.
- Sequential Scan: Subsurface XRD measurement at predefined depth steps (e.g., 0.05 mm increments).
- Stress Profile Mapping: Generation of a depth profile curve showing surface stress, maximum subsurface peak compression, and total depth of the compressive layer.
Quality Assurance & Non-Destructive Testing (customer-specified inspections outside SP Center's service scope)
Residual stress analysis serves as an advanced customer-specified inspections outside SP Center's service scope and quality control methodology across critical manufacturing sectors:
- Shot Peening Process Validation: Quantitative proof that shot peening has achieved required subsurface compression limits set by OEM specifications.
- Grinding Burn & Machining Verification: Detecting harmful tensile stresses generated by aggressive grinding, turning, or milling before micro-cracks form.
- Heat Treatment Audit: Evaluating residual stress distribution and quantifying retained austenite content in hardened steel tools, bearings, and gears.
- Failure Analysis: Investigating field failures to determine whether premature fractures originated from unintended tensile stresses or material fatigue.