Hello everyone, happy Monday, this is Shuige. Today I will explain two basic but easily confused concepts: stress relief and stress relaxation. For more content, please follow my official account!
I. Stress Relief
Basic Concept: Stress relief refers to the process of reducing or completely eliminating residual stress inside a material or component through specific methods.
Residual stress is probably familiar to everyone. It is generally the internal stress generated during processing, welding, casting, and heat treatment due to local deformation and uneven cooling.
The main purpose of stress relief is to avoid problems such as deformation, cracking, and reduced precision caused by the release of residual stress during subsequent use of the component.
To achieve stress relief, common methods include the following:
1. Natural Aging: Placing the component in a natural environment for months or even years, allowing internal stress to release naturally. This method is very time-consuming and is now generally only used for components with extremely high precision requirements.
2. Thermal Aging: Heating the component to a certain temperature (generally 40%~60% of the material’s melting point), holding for a period of time, then slowly cooling. This allows atoms inside the material to move freely, thereby releasing stress. It is currently a very common method in industry.
3. Vibration Stress Relief: Applying vibration at a certain frequency to the component, allowing residual stress inside the component to release under the action of vibration energy. This method has low cost and short time consumption, suitable for small and medium-sized components.
In engineering structures, such as steel box girders and steel frames, local high temperatures during welding cause the metal near the weld to rapidly expand and cool, creating stress differences with the surrounding base metal and forming residual stress. Vibration stress relief is generally used for residual stress treatment. For precast concrete structural components, thermal curing or natural aging can generally be used.
II. Stress Relaxation
Basic Concept: Stress relaxation refers to the phenomenon where the internal stress of a component gradually decreases over time while the total deformation (or strain) of the component remains constant. It is an inherent property of materials and is generally more pronounced under high temperature and long-term loading environments.
In prestressed concrete structures, stress relaxation is particularly significant. After tensioning and anchoring the prestressing reinforcement, the reinforcement is fixed in a stretched deformation state. Over time, stress relaxation occurs in the reinforcement, leading to prestress loss. In design, the amount of stress relaxation loss is typically estimated in advance, and the initial tensioning stress is appropriately increased. That is, prestress relaxation loss must be considered from the beginning of the design.
Comparing the two, you can simply consider that stress relief is an active means of addressing residual stress, while stress relaxation is a natural stress change process that occurs in materials under specific conditions.
So can the entire process be simulated using ANSYS for both?
The answer is: absolutely possible, though the process is somewhat complicated. When time permits, Shuige will prepare a case study for everyone!
Thank you for reading!
No comments yet