18.20: 残余应力

即使消除了原始应力的诱发因素，结构中仍然存在残余的应力。这种现象通常是由不同结构中的不同塑性变形所引起的。思考一根拉伸超过其屈服点的杆。由于它是永久变形的，它不会恢复到原来的长度。即使在去除负载后，由于存在不均匀的塑性变形，因此杆也不会完全失去应力，从而会导致具有残余的应力。在结构中，这些应力的计算是非常复杂的。在焊接过程中的温度变化等因素将会导致其发生塑性形变，从而导致其弹性降低并产生残余的应力。

例如，焊接到板上的塞子在此过程中会被显著加热，从而来减少其应力。当焊接后发生冷却时，其弹性则会增加，从而在恒定的应力水平下发生屈服现象。这也导致了残余的应力更接近钢的屈服强度。在铸造或热轧后的金属进入到冷却过程也会产生其残余应力。外层比内核冷却得更快，恢复刚度也更快，从而导致内核中能够产生残余的拉伸应力，外层中则会产生压缩应力。这些应力可能会很大，有时需要通过样品对其进行重新加热和缓慢冷却来使其消除。了解和管理残余应力对于工程的设计和制造过程是至关重要的，可确保用于保其结构和部件的可靠性和耐用性。

当杆被拉伸超过其屈服点时，它会永久变形并且不会恢复其原始长度。

由于塑性变形，即使在卸载后，加载过程中产生的应力也不会完全消除。这些剩余的应力称为残余应力。

考虑焊接到大板上的小塞子。在焊接过程中，塞子的温度显着升高，从而降低了弹性模量和应力。

一旦塞子在焊接后冷却下来，它会导致弹性模量增加，并在相当恒定的应力水平下发生屈服，从而在塞子和焊缝中产生残余应力。

铸造或热轧金属的冷却也会产生残余应力。在这些情况下，外层比内芯冷却得更快，导致它们更快地恢复刚度。

回到室温后，内芯的收缩比外层更大，导致内芯产生残余纵向拉应力。

外层产生残余压应力。通过再加热和缓慢冷却去除较大的残余应力。

• Residual Stress - Strains left within a structure post the removal of applied forces.
• Compressive Residual Stress - Residual stress that may lead to contraction or shortening of the material's structure.
• Tensile Residual Stress - The stress left in the material that could potentially cause it to stretch or elongate.
• Residual Strain - Deformation induced in materials due to residual stress, unaffected by external forces.
• Residual Stress in Welding - It's the consequent of temperature changes in the welding process causing deformation in the material.

• Define Residual Stress - Understand its occurrence and effects in the structural behavior (e.g., residual stress in steel).
• Contrast Compressive vs Tensile Residual Stress - Identify how these stresses affect a material’s form and limits (e.g., residual tensile stress).
• Explore Welding Examples - Show how welding introduces residual stress in structures (e.g., residual stress in welding).
• Explain Residual Strain - Briefly describe the correlation between residual stress and deformation in materials.
• Apply in Engineering Context - Discuss the significance and the management of residual stresses in engineering design and manufacturing processes.

• [Question 1] What is residual stress, and how does it relate to compressive and tensile stress?
• [Question 2] Are residual stress and strain interconnected?
• [Question 3] How is residual stress manifested in welding examples?

• Engineering Students - Understanding of residual stresses enhances their knowledge in structural behavior and design.
• Professors - A clear explanation of residual stress helps teach advanced engineering concepts.
• Structural Engineers - Value in stress analysis and optimizing design to increase the lifespan of structures.
• Metal Fabrication Enthusiasts - Insights into how welding practices can produce or counter residual stress for better product performance.