Dynamic Mechanical Properties of MetalsMADISON MINSK, ANANYA GARG, RACHEL NGAI, IAN CULHANE, ERIC SPEAR

Introduction•Internal Friction: the force that resists the motion of the elements in a solid while it undergoes deformation

Introduction •Shear Modulus: the ratio of shear stress to the shear strain; describes the material's response to shear stress

Higher shear modulus results in less deformation from force

Introduction•Torsion Pendulum: torsion wire is free to twist about its axis, causing the disk to rotate, associated with mechanical deformation

Setup

Experiment1. Twist wire to initiate torsional oscillation

2. Measure frequency of oscillation

3. Measure amount of damping of oscillation

Calculations

Internal Friction

1/20 [ln(T0/T20)]

T0

T20

Calculations Shear Modulus

f = frequency in Hzp = Period in secondsG = Shear ModulusI = Moment of Inertia

=L

=r

Crystal Structure

•Steel is Body Centered Cubic (BCC)

•Carbon atoms occupy interstitial sites

Dynamic Mechanical Analysis (DMA)

•Oscillating stress is applied, strain is measured •Frequency of oscillation or temp is altered•Output: Frequency (hz) vs Probe position (mm) graph

Comparison of Shear Modulus and Internal Friction in Five Metals

Frequency (hz)

Internal Friction(milliN) x10^-3

Shear Modulus(Mpa) x10^5

Steel .842 8.73 5.25

Copper .631 8.46 3.01

Bronze .603 2.98 2.79

Titanium .601 2.73 2.66

Aluminum .449 25.0 1.59

0.064”

30.0625”

Dimensions

Conclusion/Application•The shear modulus- important when materials will be subjected to shear stress

•The internal friction- important in applications like airplane engines (subjected to vibrations)

Special Thanks

•Roy Baggerly•David Starkebaum•Davis Tran•Boeing•Tuesday Kuykendall