I understand the basic definition for both. I found a literature to describe both of them.
In the paper, they states:
If a stress is applied to a concrete body, the body experiences an elastic deformation which is, to a first approximation, independent of time. If, however, this stress is maintained for a considerable period of time, the body suffers a further, time-dependent deformation. This additional deformation is com- monly known as creep. In a creep experiment the stress is usually kept constant. If instead of the stress, the length of a stressed specimen is kept constant, the creep leads to a gradual reduction of the stress originally present. This process is called stress relaxation.
Based on the paper’s description, creep and stress relaxation depends on which factor is maintained (I.e. stress or strain).
If strain change, it is a creep deformation
if stress change, it is a stress relaxation.
How do you know which one is change or maintained in the material or in a strcuture? Stress or strain?
Determining whether stress or strain changes or is maintained in a material or structure depends on the specific conditions and constraints of the application. Here's how to determine whether stress or strain is changing or maintained:
Understanding the Conditions
1. Applied Load or Deformation:
If a constant load (force) is applied to a material, the material is subjected to creep.
If a material is deformed to a specific shape or length and held in that position, it undergoes stress relaxation.
2.Boundary Conditions:
Structures or components that are held in a fixed position (fixed strain) will experience stress relaxation as the internal stress decreases over time.
Structures or components that support a constant load will experience creep, as the strain increases over time.
Identifying Changes in a Structure
1.Creep (Constant Stress, Changing Strain):
Example: A metal rod subjected to a constant tensile load.
Indicator: Measure the length of the rod over time. If the length increases, the material is creeping.
Maintenance: Stress remains constant (the load applied doesn't change).
Change: Strain changes (the deformation or elongation increases).
2.Stress Relaxation (Constant Strain, Changing Stress):
Example: A rubber band stretched to a fixed length and held.
Indicator: Measure the force required to hold the rubber band at that length over time. If the force decreases, stress relaxation is occurring.
Maintenance: Strain remains constant (the length of the rubber band doesn't change).
Change: Stress changes (the internal force decreases).
Examples in Practice
- Creep Example: A turbine blade in a jet engine operates at high temperatures and under constant load. Over time, the blade might elongate due to creep. Engineers monitor the elongation to predict the blade's lifespan.
- Stress Relaxation Example: A rubber seal in a pressure vessel is compressed to form a tight seal. Over time, the stress within the seal decreases, which could affect its sealing capability. Engineers measure the stress to ensure the seal remains effective.
Stress relaxation is a decrease in stress when a polymer is held at a constant strain over a period of time
From my own experience, creep happens over time, while stress relaxation often occurs immediately following the extrusion process, and does not continue over time.
I don't want to click Recommend on an answer obviously generated using AI, but Shashikumar Ss's answer is very good, this time.
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