Thermal Expansion, Young's Modulus

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Homework Help Overview

The discussion revolves around a problem involving thermal expansion and Young's modulus, specifically related to a steel beam mounted between concrete supports in a bridge. The scenario presents a situation where the beam is constrained from expanding due to temperature changes, prompting questions about the necessary compressional stress to prevent expansion.

Discussion Character

  • Exploratory, Conceptual clarification, Mathematical reasoning

Approaches and Questions Raised

  • The original poster attempts to calculate the compressional stress but expresses confusion regarding the need for the original length of the beam. Some participants clarify the relationship between Young's modulus, stress, and strain, while others confirm the definitions of stress and strain.

Discussion Status

The discussion is active, with participants providing clarifications on the formulas involved and addressing the original poster's concerns about the need for the original length. There is a focus on understanding the concepts of stress and Young's modulus, with some guidance offered regarding the calculations.

Contextual Notes

Participants are navigating the constraints of the problem, particularly the implications of thermal expansion and the definitions of physical quantities involved. The original poster's mention of needing an original length highlights a potential gap in understanding the application of the formulas provided.

pat666
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Homework Statement


6. A steel beam is used in the road bed of a bridge. The beam is mounted between two concrete supports when the temperature is 23⁰C, with no room for thermal expansion. What compressional stress must the concrete supports apply to each end of the beam, if they are to keep the beam from expanding when the temperature rises to 42⁰C?
Co-efficient of linear expansion for steel = 11 x 10-6K-1
Young’s modulus for steel = 210GN.m-2

Homework Equations



deltaL/L=alpha deltaT
F/A*=delta L/L*Y

The Attempt at a Solution



Ive found delta L/L to be 2.09*10^-4 I've also done about a thousand other things but everything i try needs an original length, i feel like I've overlooked a simple step or something... can someone please give me a hand.
 
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You don't need the original length if you have ΔL/L
Young's modulus= stress / (ΔL/L)
You are given the modulus and need to calculate stress.
 
ok i have never seen this formula is stress defined as force of force/unit area??
 
pat666 said:
ok i have never seen this formula is stress defined as force of force/unit area??

Yes, stress is force per unit cross section area = F/A
strain is extension per unit length = ΔL/L
Young's modulus is stress/strain
 
ok i remember that from an early lecture thanks
 
How/where can I find Young's Modulus for paper?
 

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