You have a stool with four legs, two are Aluminum, two are steel. All legs are identical in geometry (area/length). If you continiously heat up this stool, how will the load share change over as time goes on?

Mechanical Engineering Cantilever Beams
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You have a stool with four legs, two are Aluminum, two are steel. All legs are identical in geometry (area/length). If you continiously heat up this stool, how will the load share change over as time goes on?

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aluminum has a coeff of thermal expansion that is roughly 3x that of steel, so as it heats up it will want to expand much more than steel. thus the aluminum will take more load over time

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I feel like the answer to this question depends on whether we assume constant displacement or not. ie are the legs allowed to grow and tilt the seat, or is the seat fixed flat.

If the legs are allowed to grow, then the aluminum legs will grow more due to higher CTE, the seat will tilt, potentially placing a moment on the steel legs?

If the seat is fixed and remains flat, then we will have a compressive reaction force on the aluminum legs and a tensile load on the steel legs.

Someone check my reasoning here :slight_smile:

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This sounds right to me.

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Don’t we need to consider compression as well? If the aluminum legs expands due to heat and take more load, they will also compressed more than the steel legs.