5 Material Failure and Reliability Free Online FlashCards

What counts as material failure?

Failure occurs when a material can no longer perform its required function safely. It can include fracture, excessive deformation, leakage, loss of function, or unacceptable wear.

How do ductile and brittle fracture differ?

Ductile fracture involves substantial plastic deformation; brittle fracture propagates with little visible deformation.

What does the stress-intensity relation show about a crack?

In a simple linear-elastic model, crack-tip stress intensity is $K = Y\sigma\sqrt{\pi a}$, where $\sigma$ is applied stress, $a$ is crack size, and $Y$ accounts for geometry.

What is fatigue failure?

Fatigue is progressive damage from repeated or fluctuating loads. A component can fail after many cycles even when each cycle’s stress is below its yield strength.

What does Paris’ law model?

Paris’ law models crack growth over part of the fatigue-growth regime: $\frac{da}{dN} = C(\Delta K)^m$. The constants depend on the material and conditions.

What are the typical stages of metal-alloy creep?

Creep is time-dependent deformation under sustained load. In a typical metal-alloy creep curve, primary deformation is followed by an approximately steady-rate secondary stage and an accelerating tertiary stage.

What causes fretting wear?

Fretting wear is damage to contacting surfaces caused by small-amplitude repeated motion, often when the surfaces are nominally fixed together.

When can galvanic corrosion occur?

Galvanic corrosion can occur when dissimilar metals are electrically connected in an electrolyte.

What conditions can cause stress-corrosion cracking?

Stress-corrosion cracking occurs when a susceptible material experiences tensile stress in a particular environment.

Why can impact damage in composites be hard to spot?

Impact can cause internal delamination or matrix cracking in composites even when visible surface damage is slight.

What does reliability mean in engineering?

Reliability is the probability that an item performs its required function for a stated time under stated conditions.

Why must NDE methods be selected for the inspection task?

No nondestructive evaluation method detects every flaw in every material. Choose a method suited to the expected flaw and component geometry, considering detection capability and procedure.