Mechanics of Materials - Solid Formulas
Problem:
Solve for Young's modulus
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| strain |
| change in length |
| original length |
| Young's modulus |
| stress |
| strain |
References - Books
Tipler, Paul A.. 1995. Physics For Scientists and Engineers. Worth Publishers. 3rd ed.
Background
Young's modulus, te modulus of elasticity, measures how stiff a solid material is. It shows the relationship between stress (force per unit area) and strain, which is the proportional deformation of the object. It is a fundamental concept in engineering and materials science.
Equation
The formula to calculate Young's modulus ( E ) is given by:
E = σ / ε
Where:
- E is Young's modulus in pascals (Pa)
- σ is the stress in pascals (Pa)
- ε is the strain (dimensionless)
How to Solve
To solve for Young's modulus, follow these steps:
- Determine the stress (σ): This is calculated by dividing the force applied (F) by the area (A) over which the force is distributed. ( σ = F / A ).
- Determine the strain (ε): Strain is calculated as the change in length (ΔL) divided by the original length (L). ( ε = ΔL / L ).
- Apply the Formula: Substitute the values of stress and strain into Young's modulus equation ( E = σ / ε ).
Example
Consider a metallic rod subjected to a tensile force of 1000 N. Assume the original length of the rod is 2 meters, and under the load, it stretches by 1 mm. The cross-sectional area of the rod is 0.01 square meters.
Calculate the stress:
σ = 1000 N / 0.01 m2 = 100000 Pa
Calculate the strain:
ε = 0.001 m / 2 m = 0.0005
Calculate Young's modulus:
E = 100000 Pa / 0.0005 = 200 x 106 Pa
Therefore, Young's modulus for the material of the rod is 200 x 106 Pa.
Fields/Degrees
- Mechanical Engineering
- Civil Engineering
- Aerospace Engineering
- Materials Science
- Biomechanics
Real Life Applications
- Construction: Determining suitable materials for beams, columns, and slabs.
- Automotive: Designing components such as springs, chassis, and engine parts.
- Aerospace: Material selection for aircraft frames and other structural elements.
- Consumer Electronics: In designing thin, robust cases and frames for smartphones and laptops.
- Medical Devices: Design of prosthetics and other supportive equipment.
Common Mistakes
- Mixing units (e.g., using mm versus meters for length).
- Not accounting for uniform cross-sectional area along the length of the material.
- Neglecting the effect of temperature and environment on material properties.
- Overlooking existing microscopic stress while measuring applied stress.
- Applying the modulus of elasticity beyond the elastic limit of the material.
Frequently Asked Questions
- Is Young's modulus the same for all materials?
No, Young's modulus varies from material to material, reflecting different stiffness levels.
- Can Young's modulus be negative?
No, Young's modulus is a measure of stiffness and cannot be negative.
- Does temperature affect Young's modulus?
Yes, with most materials, the increasing temperature tends to lower Young's modulus.
- How does Young's modulus relate to strength?
Young's modulus measures stiffness, not strength. High Young's modulus means a material is stiff but not necessarily strong.
- Is it applicable only under tensile stress?
Young's modulus is generally considered under both tensile and compressive stress as long as the material remains within the elastic limit.