Mechanisms of Failure

Failure mechanisms refer to the various ways in which materials, components, or systems can fail when subjected to internal or external stresses. There are several established mechanisms that are recognized based on the conditions and causes leading to the failure. Here’s an overview of some primary mechanisms of failure:

Elastic (Brittle) Failure:

• Occurs in materials that fail without undergoing significant plastic deformation. Such failures are sudden and can be catastrophic.
• Common in brittle materials like ceramics and some glasses.

Ductile Failure:

• Characterized by significant plastic deformation before failure.
• Typically involves necking, void formation, and coalescence leading to crack initiation and propagation.
• Common in metals like aluminum or mild steel under tensile loads.

Fatigue Failure:

• Caused by repeated or cyclic loading below the material’s ultimate tensile strength.
• Cumulative damage results in crack initiation and propagation until failure.
• Common in components subjected to cyclic stresses like aircraft wings or rotating machinery.

Creep Failure:

• Time-dependent, permanent deformation under sustained load, especially at high temperatures.
• Can lead to rupture if the deformation is significant.
• Common in turbine blades, boiler tubes, or any component exposed to high temperatures for extended periods.

Thermal Failure:

• Due to temperature gradients or cyclic thermal loads causing stresses.
• Includes thermal shock and thermal fatigue.
• Observed in components like IC engines or electronics subjected to frequent on-off cycles.

Corrosion and Oxidation:

• Chemical interaction of a material with its environment leading to material degradation.
• Can weaken the material and cause failure.
• Types include galvanic corrosion, stress corrosion cracking, and pitting.

Erosion or Wear Failure:

• Loss of material due to mechanical action.
• Includes abrasive wear, cavitation, and erosion by fluids.
• Common in pumps, bearings, and other machinery with moving parts.

Hydrogen Embrittlement:

• Absorption of hydrogen leading to reduced ductility and strength.
• Can cause sudden and unexpected failures.
• Seen in steels exposed to hydrogen-rich environments.

Buckling Failure:

• Compression-induced instability leading to sudden deformation.
• Common in slender columns or thin-walled structures.

Fracture from Stress Concentrations:

• Failure initiated at points of geometric irregularities, notches, or pre-existing flaws, where stress is concentrated.

Environmental Failure:

• Combined effects of stresses and environmental factors (humidity, temperature, etc.) causing material degradation.
• Includes phenomena like stress-corrosion cracking.

Understanding these mechanisms is vital for engineers, designers, and maintenance personnel to select appropriate materials, design reliable structures, and perform timely inspections. Proper knowledge of failure mechanisms can prevent accidents, extend the lifespan of components, and reduce maintenance costs.

UV Degradation:

• Prolonged exposure to ultraviolet (UV) light can cause certain materials, especially polymers, to degrade.
• This can lead to discoloration, loss of material strength, and eventual breakdown.
• Examples include the cracking or fading of plastic outdoor furniture due to sun exposure.

Radiation Damage:

• Certain materials can degrade when exposed to high-energy radiation, like gamma or neutron radiation.
• Common in nuclear applications, where radiation can cause embrittlement or swelling of reactor materials.

Diffusion-related Failures:

• Over time, atoms may move within a material, especially at high temperatures, leading to a change in properties.
• In electronics, this can cause issues like solder joint failures or migration of metal atoms, impacting the device’s functionality.

Hydrolysis:

• Some materials, particularly certain polymers, can degrade in the presence of water due to hydrolysis reactions.
• This can lead to chain scission and a reduction in material properties.
• Common in biodegradable polymers or in environments with high humidity and elevated temperatures.

Oxidative Degradation:

• Similar to corrosion, but mainly for polymers. Oxygen, combined with heat or UV light, can attack polymer chains, leading to degradation.
• This is why antioxidants are added to some plastics to prolong their life.

Microbial-induced Corrosion (MIC):

• Certain microbes can accelerate corrosion rates, leading to faster degradation of metals.
• Common in buried pipelines or in marine structures.