37. Sự nở nhiệt

Nguyên tắc con

1. Use the thermal expansion or contraction of a material
2. Combine materials with different expansion rates

Ví dụ

• A bimetal strip that bends to act as a switch
• Shrink-fit assembly by heating the outer part
• A greenhouse vent that opens with temperature

Ứng dụng theo lĩnh vực

• mechanical: Tightening a large bolt to an exact load is hard. Heating the bolt so it stretches, running the nut down and letting it cool sets the load as it shrinks.
• electronics: There is no room for a motor to move a microscopic part. Passing current through a thin silicon arm heats it, and its expansion pushes the part along.
• everyday: A metal lid stuck on a glass jar will not turn. Hot water poured over the lid expands the metal more than the glass, and it opens.
• materials: Thin glass is hard to cut cleanly along a chosen line. Heating a narrow line and cooling right behind it creates tensile stress that splits the glass along that line.