723 degree centigrade
Eutectoid Reaction: It is also an invariant reaction and the degree of freedom is also zero at this point. At a eutectoid point, one solid phase changes into two solids phases at the same time, as we slowly cool down. The austenite phase transforms into the ?- ferrite and cementite. The obtained crystal structure is called pearlite.
Eutectoid Reaction occurs at 723 degree centigrade at approximately 0.76 % of carbon.
Creep
Time dependent permanent deformation is called creep.
Creep is defined as a time-dependent material deformation under continuous stress below the material’s yield strength. It is commonly observed to be quite impactful under elevated temperatures, especially with metals. Yet, it can still take place at room temperature, like with glass and lead, at a much slower rate.
Other names for creep include material creep and cold flow.
When materials are subjected to increasingly high-stress levels over a long period, creep can become severe. This especially applies to materials that are frequently exposed to high heat and can even permanently deform as temperatures reach the melting point. Without exceeding the material’s yield strength, creep can result in plastic strain, which is a unique aspect of this phenomenon, as plastic deformation generally happens when the yield strength is exceeded.
Strain
When a system of forces act on a body, it undergoes some deformation. This deformation per unit length is known as unit strain or simply a strain.
Mathematically
Strain = (Change in Length)/(Original Length)
Primary Strain or Linear Strain The deformation of the bar, per unit length in the direction of the force is known as primary or linear strain.
Secondary Strain or Lateral Strain Every direct stress is always accompanied by a strain in its own direction, and an opposite kind of strain in every direction, at right angles to it. Such strain is known as secondary or lateral strain.
Adhesion & cohesion
Capillary rise or capillarity is a phenomenon in which liquid spontaneously rises or falls in a narrow space such as a thin tube or in the voids of a porous material. Surface tension is an important factor in the phenomenon of capillarity.
Three main variables that determine whether a liquid possesses capillary action are:
Cohesive force: Cohesive force is the intermolecular bonding of a substance where its mutual attractiveness forces them to maintain a certain shape of the liquid.
Surface tension: Surface tension occurs as a result of like molecules, cohesive forces, banding together to form a somewhat impenetrable surface on the body of water. The surface tension is measured in Newton/meter.
Adhesive force: When forces of attraction between unlike molecules occur, it is called adhesive forces.
Euler number
The important dimensionless numbers in fluid mechanics are
1. Reynold’s number
2. Froude’s number
3. Weber’s number
4. Euler’s number
5. Mach’s number or Cauchy’s number
Reynold’s number: Reynold’s number is the ratio of inertia force to the viscous force.
Froude’s number: Froude’s number is the ratio of inertia force to the gravity force.
Weber’s number: Weber’s number is the ratio of inertia force to the surface tension force.
Euler’s number: Euler’s number is the ratio of inertia force to the pressure force.
Mach’s number or Cauchy’s number: Mach’s number or Cauchy’s number is the ratio of inertia force to the elastic force.