--- title: "Residual stresses: causes, effects, relief" subject: "Manufacturing and Production Processes" chapter: 3 key: "semester_4/manufacturing_and_production_processes:residual-stresses-causes-effects-relief" source: https://www.bctengineer.com/q/semester_4/manufacturing_and_production_processes/residual-stresses-causes-effects-relief site: BCT Engineering --- # Residual stresses: causes, effects, relief Manufacturing and Production Processes · Chapter 3: Properties of Manufactured Products - Asked in: year not given, 5 marks - Video: [Residual Stress in Metals](https://www.youtube.com/watch?v=400aly0Ejzg) — Industrial Metallurgists, LLC - Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14 - Page: https://www.bctengineer.com/q/semester_4/manufacturing_and_production_processes/residual-stresses-causes-effects-relief - Whole chapter: https://www.bctengineer.com/md/semester_4/manufacturing_and_production_processes/chapter-3 ## Question What are residual stresses? Explain how they are produced in manufacturing processes, their effects on the product, and the methods of reducing or removing them. ## Short answer Residual stresses are self-balancing stresses remaining after all external loads are removed. They arise from non-uniform plastic deformation, thermal gradients, phase transformation, or machining. Compressive surface stress improves fatigue life; tensile stress reduces it and promotes cracking. Relief methods include stress-relief annealing, tempering, stretching, vibratory stress relief, and shot peening. ## Answer **Residual stresses** are stresses that remain in a body after all external loads and temperature gradients have been removed. They are self-balancing: tensile stress in one region is balanced by compressive stress in another. #### Origin Residual stress appears whenever different parts of a body deform plastically by different amounts, or cool at different rates. 1. **Non-uniform plastic deformation:** in bending, the outer fibres are plastically stretched and when the load is removed the elastic core pushes them back, leaving compressive stress on the surface that was in tension. Rolling, drawing and shot peening also leave surface compression. 2. **Thermal gradients:** in quenching, the surface cools first and contracts; later the core contracts against a rigid shell, leaving surface compression and core tension. In welding, the weld region shrinks against cold parent metal and is left in tension. 3. **Phase transformation:** martensite formation causes volume expansion in some regions (hardening of steel). 4. **Machining and grinding:** mechanical deformation under the tool and heat generated leave a thin surface layer in tension (grinding heat) or compression (sharp tools, low feed). #### Effects - Distortion and warping when material is machined away or heated. - **Compressive** residual stress at the surface improves fatigue life and resists crack growth. - **Tensile** residual stress at the surface reduces fatigue strength and causes stress-corrosion cracking and cold cracks in welds. - Dimensional instability of precision parts with time. #### Methods of reduction or removal | Method | Principle | |---|---| | Stress-relief annealing | Heat below the transformation temperature (about 550-650 degree C for steel), hold, cool slowly | | Tempering | After hardening, relieves quench stresses | | Stretching / light cold work | Small plastic deformation (about 1-2 percent) levels the stress | | Vibratory stress relief | Vibration at resonance redistributes stress | | Shot peening | Introduces beneficial surface compression | | Controlled cooling and proper process design | Reduces thermal gradient | ## Check yourself The answer's key points as multiple-choice questions, with the correct option and why. 1. Residual stresses are A. Stresses present only while the load acts B. Self-balancing stresses that remain after all external loads and temperature gradients are removed C. Stresses caused only by welding D. Stresses that always improve fatigue life Answer: B. They remain without external loads, with tension in one region balanced by compression in another. (Key point: Definition of residual stress) 2. After quenching, what residual stress pattern results and why? A. Surface tension, core compression, because surface cools last B. Surface compression, core tension, because the core contracts later against a rigid shell C. No stress, because cooling is uniform D. Surface compression only from martensite Answer: B. The surface cools and sets first; the later contracting core pulls against it, leaving core tension and surface compression. (Key point: Quenching residual stress) 3. Which effect of residual stress is correct? A. Surface tensile stress improves fatigue life B. Surface compressive stress improves fatigue life and resists crack growth C. Compressive stress causes stress-corrosion cracking D. Residual stress never causes distortion Answer: B. Compressive surface stress helps fatigue; tensile surface stress reduces fatigue strength and promotes SCC and cold cracks. (Key point: Effect on fatigue) 4. Stress-relief annealing of steel is done by A. Heating above the transformation temperature and quenching B. Heating below the transformation temperature (about 550-650 degree C), holding, and cooling slowly C. Shot peening the surface D. Heating to melting and recasting Answer: B. Heating below the transformation temperature relieves stress without changing structure; slow cooling avoids new stresses. 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