2. Toughening and strengthening mechanisms (25 points) (a) A student states that

Question

2. Toughening and strengthening mechanisms (25 points)

(a) A student states that “fracture toughness of ceramics is controlled by maximum flaw size”. Is this valid? Why or why not?

(b) Explain why one should be careful to distinguish toughening mechanisms and strengthening mechanisms in ceramics. Which parameter is improved by toughening? Which parameter is improved by strengthening?

(c) Is it possible that improving KIc in a material by adjusting the microstructure and processing leads to a decrease in strength? If so, give an example.

(d) Explain why glass often has a strength limited by surface flaws.

(e) Fine grained metals, and fine grained ceramics, tend to be stronger than coarse grained ones. Explain the fundamental reasons for each. Use diagrams if you wish. Are the explanations for metals and ceramics similar?

Explanation / Answer

a) fracture toughness of ceramics is controlled by maximum flaw size that is completely valid

Clarification can be established by noting that the controlled flaw is often quite large relation to the Specimen cross section. The flaw is not exposed to a uniform stress field, but is really in a ramp which diminishes to zero axial stress at the neutral axis. Which gives direct toughness to the ceramic fracture zones.

b)

Toughening mechanisms in ceramic-based nano composite remaining stress around second-phase nano particle separate in matrix grains. The remaining thermal stresses approximately a round isolated particle within a concentric globe of a matrix granule were specifically analyze to clarify the possessions of residual stress on the toughening mechanism in the frontal procedure zone involving nano cracking.

The strengthening mechanism caused by nucleation of dislocation. The ratio of the thermal expansion coefficients of the atom and matrix has a marked effect on residual stresses and residual stresses were of enough magnitude to produce lattice defects such as dislocations approximately the particle even in ceramics, and that the nano size particle within a matrix can only create dislocation around the particle. The toughening and strengthening mechanisms for nano composites were also based on the diagnostic results

c) it possible that improving KIc in a material by adjusting the microstructure and processing leads to a decrease in strength

large grain size acting as the critical flaw fracture origin as uniformity of microstructure is important

improving kls with a minimum sacrifice in optical transmission is rather difficult. bcoz all the known stratergysuch as reinforcement via high modules will drastically decrease the strenghth.

d)

Under the part on strength of glass we discuss its strange properties. In terms of automatic strength the durability can be variable. The hypothetical strength of glass is tremendously high but we are unable to understand the full strength. From the instant that glass is made it is handled by equipment etc. That affects the surface of the glass in a way not able to be seen to the eye alone. Minor flaws on the surface allow stress to concentrate so under load the glass will break from an imperfection. The lack of resistance to a smash means the crack can grow until it is clear. In our calculations we allow for the impact of the flaws and design around the lowest strength.

The factor affecting glass strength and therefore durability is Size. The bigger the piece of glass the chances of judgment a critical flaw enhance.

Related Questions

Navigate

• Browse (All)
• Browse 2
• Subjects

Integrity-first tutoring: explanations and feedback only — we do not complete graded work. Learn more.