Static Loading

A static load is applied gradually from zero to its maximum value and then remains constant. In most strength analyses of machine elements, loading is assumed to be static.

For a material element with:

  • Cross-sectional area \( A \)
  • Length \( l \)
  • Applied load \( W \)

The normal stress induced is:

$$ \sigma_{\text{st}} = \frac{W}{A} \quad \text{(Eq. 2.15)} $$

And the elongation (assuming modulus of elasticity \( E \)) is:

$$ \delta_{\text{st}} = \frac{Wl}{AE} $$

Dynamic Loading

In many real-world applications, loads are dynamic—they vary with time. When loads are applied suddenly or as impact loads, the resulting transient stresses and deformations are significantly higher than those from static loading.

Impact loads generate shock waves that propagate through the material, potentially causing serious consequences such as fatigue, fracture, or failure. Therefore, predicting the material response to dynamic loads is essential.

Types of Dynamic Loads

  • Impact Loads: Sudden application of force over a short time interval.
  • Shock Loads: High-intensity, short-duration loads often associated with collisions or abrupt stops.

Stress evaluation under dynamic loading can be performed using:

  • The principle of conservation of energy
  • Assumption that the material remains within its elastic region