company news about Residual stress: From generation to elimination

Introduction

Are you curious about why metal parts tend to deform easily after processing? Why do the welded parts of Bridges suddenly crack? Behind all these problems, there might be an "invisible killer" - residual stress! Today, let's lift the veil of mystery surrounding it. From its causes to actual impacts, and then to detection and elimination methods, we'll provide a comprehensive analysis in one article!

01 What is residual stress?

In simple terms, residual stress refers to the stress that remains within a material after external forces, temperature changes, or the completion of the processing procedure. Just like crumpling a piece of paper into a ball and then unfolding it, wrinkles will be left on the paper surface. Even if no external force is applied by hand, the pulling and deformation of the internal fibers of the paper still exist. This kind of "permanent scar" is residual stress, similar to how the surface of metal after processing seems smooth but is actually full of "scars" inside.

Macroscopic and microscopic: Macroscopically, it is manifested as tensile or compressive stress; At the microscopic level, it is closely related to lattice deformation, phase transformation, etc.

Schematic diagram understanding: Imagine a bent metal rod. After the external force is removed, although its shape is restored, there is still a stress field inside that "resists deformation"

02 Where does residual stress come from?

Its generation mainly stems from uneven physical changes:

Machining: Processes such as cutting, forging, and welding can cause local plastic deformation of materials, resulting in uneven force distribution in various parts.

Temperature gradient: For instance, the difference in expansion and contraction between the high-temperature zone and the low-temperature zone during welding.

Phase transformation and composition differences: When metals cool, their microstructure changes (such as from austenite to martensite), and the volume changes vary in different regions.

In a nutshell: Where there is "imbalance", there is residual stress!

03 The "double-edged sword" effect of residual stress

It can both destroy the heavens and the earth and benefit humanity. The key lies in how it is utilized

Negative impact

Reducing fatigue life: Tensile residual stress can accelerate the propagation of fatigue cracks, leading to premature failure of parts.

Induced brittle failure: Under low temperatures or impact loads, the residual tensile stress superimposed with external stress may cause the material to fracture "without warning".

Intensifying corrosion: Tensile stress can accelerate stress corrosion cracking, which is particularly harmful in chemical equipment.

Positive application

Surface strengthening: Processes such as shot peening and nitriding treatment introduce compressive residual stress, which can significantly enhance the fatigue strength of parts (such as engine crankshafts and aircraft landing gears).

04 How to detect residual stress?

Detection methods are divided into two major categories: destructive and non-destructive

Destructive testing

Drilling method: Drill holes on the surface and measure the released stress through strain gauges (high precision but damaging the workpiece).

Delamination method: Remove the material layer by layer and infer the stress distribution based on the deformation (suitable for flat or cylindrical specimens).

Non-destructive testing

X-ray diffraction method: Measuring stress by the variation of crystal plane spacing (the most commonly used method with high precision).

Ultrasonic method: Assess internal stress through changes in sound velocity (suitable for large-volume workpieces, such as rails and welds).

Magnetic measurement method: Applicable to ferromagnetic materials, it determines stress through changes in magnetic permeability.

05 Three Ultimate Tricks to Eliminate Residual Stress

Want the materials to "relax both body and mind"? Try these methods

Industry trend: Fully automatic vibration stress relief equipment (such as Haokeng HK3012) is becoming mainstream. It can be completed in one hour, which is environmentally friendly and highly efficient!

06 Practical Advice from Engineers

Design stage: Optimize the processing technology and reduce uneven deformation (such as symmetrical welding and controlling the cooling rate).

Inspection selection: X-ray method is preferred for precision parts, while ultrasonic method can be used for large structures.

Elimination decision: For mass production, choose vibration aging; for high-precision parts, choose thermal aging.

Conclusion

Residual stress is both a hidden danger and an opportunity. By grasping its rules, we can turn "crisis" into "opportunity" and take the performance of materials to a higher level!