When materials expand at different rates—usually due to temperature changes—it can cause several effects, especially where those materials are joined or in contact:
- Stress and Strain: If two materials are bonded or connected and they expand differently, internal stresses build up because one tries to expand more or less than the other. This can cause bending, warping, or even cracking.
- Delamination or Separation: In layered structures (like composite materials or coatings), different expansion rates can cause layers to separate or peel off over time.
- Joint Failure: In constructions or machinery, joints, screws, or welds can fail because of the repeated stress from differential expansion and contraction.
- Distortion of Shape: Parts made of different materials might deform or change shape unevenly, which can affect the precision of mechanical assemblies.
For example, in a bimetallic strip (two metals with different expansion rates bonded together), heating causes the strip to bend because one metal expands more than the other—this principle is used in thermostats.