Lecture 8 - Hertz + Adhesion

Question 1

Hertzian Theory

Answer 1

If two bodies come into contact at a point, with the contact pressure acting perpendicular to the contact plane, they will deform producing an elliptic area if:
• Profiles of both bodies can be described as second-order polynomials (sphere, plate, cylinder)
• Such bodies are characterized by two principal planes of curvature, which are perpendicular to each other and contain the largest and smaller radii of curvature at the considered point

Question 2

Hertzian Contact Boundary Conditions

Answer 2

Size and orientation as well as pressure distribution can be calculated if:

1. Shape of both bodies in the vicinity of the contact can be described by means of a second-order polynomials
2. Materials of both bodies is homogenous and isotropic
3. Hooke’s law is valid
4. Deformation is small compared to the bodies dimensions
5. Only normal stresses are present
6. Both bodies have the same material

Question 3

Law of frictional adhesion

Answer 3

Both sticking and sliding friction are present simultaneously. The distribution of both depends on the slip

Question 4

Domains with different behaviours within the contact ellipse

Answer 4

Micro slip, stick-slip domain, slide

Question 5

Draw the Slip-Adhesion curve in the driving and braking domains (Figure 8.1)

Answer 5

Draw