Material Fracture Under Force

Material Properties

• As the force increases, the crack grows until it reaches the other surface, causing complete fracture of the sample.

Hardness

• Measures the ease of cutting, finishing, and polishing a material
• Also indicates scratch resistance
• Various hardness tests exist, including:
  • Brinell
  • Rockwell
  • Barcrol
  • Shore A
  • Knoop
  • Vickers (most common)
• Each test uses a different indenter, a piece of diamond with a specific geometric shape (e.g., sphere, rhomboidal pyramid, square pyramid)
• Each material has its own unique hardness number, determined by the load applied

Surface Energy and Wettability

• Surface energy is the sum of all intermolecular forces on a material's surface
• Contact angle is the angle between a liquid drop and a smooth surface, indicating wettability
• Important in dentistry, as it affects the color matching of fillings under different light sources

Setting Time

• The time required for a material to set or harden from a plastic or fluid state
• Does not indicate the completion of the reaction, but rather when the material can no longer be used

Material Properties

• Toughness is the resistance of a material to fracture, indicating the amount of energy required to cause fracture or break a material.

Fracture Toughness

• Fracture Toughness (KIC) measures the energy consumed in plastic deformation.
• The Fracture Toughness test involves applying a force onto a sample with a specific morphology, such as a notch or crack, to measure the energy required to cause fracture.

Abrasive Wear

• Abrasive wear occurs through two-body wear, where direct sliding action occurs between antagonistic objects with no intermediate layer transmitting forces between the interlocking surfaces.

Rheological Properties

• Viscosity is the resistance of a fluid to flow, measured as shear stress/strain.
• The unit of viscosity is Poise (1 P = 0.1 Pa-s), or Centipoise (100 cP = 1P).
• Types of viscous fluids can be classified according to their flow behavior:
  • Newtonian fluids: viscosity is constant and independent of stress rate.

Sorption

• Sorption is a general term that describes both adsorption and absorption.
• Adsorption involves molecules being taken up by the surface, whereas absorption involves molecules being taken up by the volume.