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Residual Stresses and Distortion

Residual Stresses and Distortion. Residual Stresses and Distortion. Learning Activities Read Handbook pp 218-229 View Slides; Read Notes, Listen to lecture Do on-line workbook. Lesson Objectives When you finish this lesson you will understand:

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Residual Stresses and Distortion

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  1. Residual Stresses and Distortion

  2. Residual Stresses and Distortion • Learning Activities • Read Handbook pp 218-229 • View Slides; • Read Notes, • Listen to lecture • Do on-line workbook • Lesson Objectives • When you finish this lesson you will understand: • the generation of residual stress and distortion in welds • mechanisms to reduce residual stress Keywords Thermal Expansion Coefficient, Residual Stress, Distortion, Stress-Relief

  3. Welding Design Welding design involves consideration of strength requirements, cost, and service conditions • Mechanical & Physical properties • Joint Design • Welding stress and distortion Covered Earlier 0.1.1.3.0.T1.95.12

  4. Residual Stress and Distortion Residual Stress & Distortion in Welds • Heat flows from the weld area and causing the joint area to expand (See Previous Module) • Thermal expansion and contraction due to welding can leave behind permanent stress and distortion • Higher heat input welds are more prone to residual stress and distortion • Increased restraint can decrease distortion but can result in higher residual stress 0.1.1.3.3.T18.95.12

  5. Residual Stress and Distortion Residual Stress Pattern • Residual stress is present across an unrestrained butt weld after cooling • Tension near weld bead • Compression away from the weld bead • Restraint can affect this stress state Tension Compression

  6. Questions? • Turn to the person sitting next to you and discuss (1 min.): • We have seen from the metallurgy module that dislocation tangles and pile-ups occurring above the yield strength of materials cause the higher stresses. We have seen here that by a temperature cycle that varies across the plate we have regions that yield and residual stresses occur. We have seen that imposing operating stresses above yield cause changes in the residual stress distribution by movement of the dislocations. How else then might we get rid of some of these dislocations to remove these residual stresses?

  7. Residual Stress and Distortion Types of Distortion 0.1.1.3.3.T19.95.12

  8. Residual Stress and Distortion Distortion Transverse Shrinkage Longitudinal Shrinkage Angular Change Rotational Distortion Longitudinal Bending Buckling

  9. Residual Stress and Distortion Eliminating Distortion • Preset members to counteract distortion • Fixtures to clamp workpiece in place • Restraint reduces distortion but increases residual stress • Stress-relief heat treatment Angular distortion after welding Preset members before welding

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