Residual Stress: Formation, Effects, and Innovative Testing by Indentation Method

In mechanical manufacturing and remanufacturing processes,residual stress inevitably forms during machining, welding, heat treatment, and other operations. These stresses remain inside the material even when no external load is applied, significantly influencing its long-term performance.

Residual stress can be both harmful and beneficial. While tensile residual stress tends to promote crack initiation and corrosion,compressive residual stress can enhance fatigue strength and prevent crack propagation. Thus, accurate measurement and control of residual stress are crucial for ensuring component reliability and extending service life.

Methods of Residual Stress Measurement

Traditional methods are classified into destructive and non-destructive categories:

         Destructive methodssuch as hole-drilling and layer removal provide high accuracy but damage the specimen.

         Non-destructive methodslike X-ray diffraction, ultrasonic, and magnetic techniques avoid damage but often have limitations in geometry, material type, or field operation.

Innovation Through the Indentation Method

With recent advances in materials testing, the indentation method has emerged as an innovative approach to non-destructive stress evaluation. By applying a controlled indentation load and analyzing the indentation energy difference, this method allows precise estimation of mechanical properties and residual stress states near the material surface.

Wuxi Zhanghua Pharm & Chem Equipment Co., Ltd has developed the Portable In-situ Micro-Indentation Tester, an intelligent, non-destructive device based on the indentation and indentation energy difference principles. It enables on-site evaluation of residual stress and mechanical characteristics without damaging the component.

Key advantages include:
     Non-destructive and portable– suitable for on-site applications on vessels, welds, and pipelines;
     High sensitivity and repeatability– capable of detecting micro-level stress variations;
    Traceable and integrative– compatible with FEM analysis, lifespan assessment, and failure diagnostics.

This innovation provides an efficient and reliable solution for residual stress measurement across the energy, pharmaceutical, and high-end manufacturing industries.

Moving forward, Zhanghua will continue advancing non-destructive testing (NDT) technologies, expanding the application of the indentation method in mechanical manufacturing, materials engineering, and structural integrity evaluation, ensuring safer and longer-lasting equipment performance.